E 5 215
US005963314A
Ulllted States Patent [19]
[11] Patent Number:
Worster et al.
[45]
[54]
Date of Patent:
5,127,726
INSPECTION AND ANALYSIS OF SUB-
5,129,010
7/1992 Higuchi et a1.
MICRON PARTICLES
5,243,406
9/1993
5,280,542
1/1994 OZeki et a1. .......................... .. 356/375
5,448,364
9/1995
.
.
’
_
'_
’
_
5,583,632
5,621,532
5,627,646
Cahf-
5,671,056
5,680,207
[73] Assignee: Ultrapointe Corporation, San Jose,
Calif
_
_
_
Nonce'
_
_
. 356/376
Ando'et a1. . . . . .
. . . ..
12/1996
356/394
Moran ................................... .. 356/430
356/237
Haga ............. ..
356/237
4/1997 Ooki et a1.
5/1997 Stewart et a1. ..
356/444
356/237
9/1997
Sato
.......... ..
.. 356/394
10/1997 Hagiwara .............................. .. 356/237
OTHER PUBLICATIONS
_
_
Gerd Hausler and Eva Korner, “Imaging With Expanded
Tlhl_s Patent 15 Sublect to a termmal dls'
Depth Of Focus”, Zeiss Information, Oberkochen, 29, 9—13
C almer'
(1986/87), No. 98E.
[21] APPI NO_; 08/730,254
Primary Examiner—David B. Hardy
_
Attorney, Agent, or Firm—Skjerven, Morrill, MacPherson,
Flled:
Oct‘ 15’ 1996
Franklin & Friel; Alan H. MacPherson; Gary J. Edwards
Related US. Application Data
[60]
7/1992 Moran ................................... .. 356/237
5,465,145 11/1995 Nakashige et al
Pleasantom Chnstopher R- Falrley’
52191056; Ken K- Lee> L05 A1t°$> all of
[22]
*Oct. 5, 1999
LASER IMAGING SYSTEM FOR
[75] Inventors‘ 23f;_vfiafl°gstgéliifiiifgle E‘
[*]
5,963,314
[57]
Continuation of application No. 08/518,284, Aug. 23, 1995,
ABSTRACT
A laser imaging System is used to analyze defects on
abandoned, which is a division of application No, 08/080,
semiconductor Wafers that have been detected by patterned
[51]
014, J11I1~ 17, 1993, Pat NO- 5,479,252
Int. Cl.6 ................................................... .. G01N 21/88
Wafer defect detecting systems (Wafer scanners). The laser
imagmgsystffm replacés Optical miCYOSCOPe review Stations
[52]
U S C]
noW utilized in the semiconductor fab environment to exam
.-
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3 5 6B37 2_ 250/559 39
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[58] Fleld of searczhs
536726’
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[56]
H1530
Re 34 214
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.
References Cited
U.S. PATENT DOCUMENTS
copy techniques, and operates under class 1 cleanroom
5 1996 L
’
defects. In addition to analyzing defects, the laser imaging
system can perform a variety of microscopic inspection
functions includin defect detection and metrolo . The
.
.
g
.
gy.
41993
’
ine detected optical anomalies that may represent Wafer
laser 1mag1ng system uses confocal laser scanning micros
395 124
""""""""""""" " 3543/93
conditions and Without exposure of the Wafers to operator
contamination or air?ow. Unlike scanning electron micro
4’111’557
9/1978 Rottenkolber et a1‘
356/168
472477203
1/1981 Levy et aL __________ __
356/398
scopes~ (SEMs) that have previously been used for defect
analysis, the laser 1mag1ng system Wlll not damage samples
473477001
4,448,532
8/1982 Levy et a1_
5/1984 Joseph et a1. .
356598
356/394
or sloW processing, costs signi?cantly less to implement
than an SEM, can produce a three dimensional image Which
4,579,455
4/1986 Levy et a1. ...... ..
356/394
provides quantitative dimensional information, and alloWs
4,618,938 10/1986 Sandland et a1
364/552
sub-surface vieWing of defects lying beneath dielectric lay
4786470
356/318
ers. The laser imaging system is adaptable to cluster or
11/1988 Groebler ~~~~~~~~~ ~~
478057123
2/1989 spejcht et a1‘ '
364/559
in-situ applications, Where examination of defects or struc
4,845,558
7/1989 Tsai et a1. ....... ..
358/106
mes durin
4,957,367
9/1990
356/394
5,030,008
7/1991 Scott et a1. ............................ .. 356/394
4,877,326 10/1989 Chadwick et a1.
Dulman ........... ..
356/394
g
ondine
p
rocessin
g
can be
p
“formed
51 Claims, 6 Drawing Sheets
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U.S. Patent
0a. 5, 1999
Sheet 1 of6
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5,963,314
U.S. Patent
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Sheet 2 of6
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0a. 5, 1999
Sheet 3 of6
5,963,314
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5,963,314
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U.S. Patent
Oct. 5, 1999
Sheet 5 0f 6
5,963,314
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POSITION
SENSOR
5,963,314
1
2
LASER IMAGING SYSTEM FOR
INSPECTION AND ANALYSIS OF SUB
MICRON PARTICLES
acceptable difference, an anomalous optical site is identi?ed.
KLA of San Jose, Calif. makes a Wafer scanner of this type
as, for example, Model 2131.
The video systems generally cost about three times as
much as the laser scanning systems, i.e., the laser scanning
This application is a continuation of application Ser. No.
08/518,284, ?led Aug. 23, 1995, noW abandoned, Which is
a divisional of Ser. No. 08/080,014 ?led Jun. 17, 1993, now
systems typically cost approximately $350,000 While the
video systems typically cost approximately $1,000,000.
US. Pat. No. 5,479,252.
HoWever, While the laser scanning systems are more effec
tive in detecting bumps than in detecting pits, the video
CROSS-REFERENCE TO RELATED
APPLICATIONS
10
systems Work Well in detecting either bumps or pits, and can
also sense subsurface defects.
As these Wafer scanners Were developed, the need to
This application is related to the commonly oWned,
co-pending US. Patent Application entitled “Surface
identify positively the nature, e.g., type of material, type of
Extraction from a Three-Dimensional Data Set,” by Ken K.
Lee, application Ser. No. 08/079,193, ?led on the same date
defect (defects are classi?ed broadly as particulate or pro
cess ?oW defects; there are many sub-types Within each of
15
as the present application and incorporated by reference
these classi?cations), and the precise location and siZe of the
herein.
defects Was not appreciated. This information is important
BACKGROUND OF THE INVENTION
20
1. Field of the Invention
This invention relates to lasers and, in particular, to a laser
imaging system for use in analyZing defects on semicon
ductor Wafers.
2. Related Art
calculate the density of defects in general, and, along With
25
Semiconductor chip manufacturers have increasingly
sought to improve yields in their production processes. Key
to this effort is the reduction of particulate contamination
during Wafer processing. As the line Widths of features on
the chip have shrunk from 10 microns several years ago to
one micron and beloW today (With line Widths approaching
0.3 micron or less expected in the next feW years), the ability
to detect and control smaller and smaller particles to achieve
higher degrees of cleanliness has become paramount.
Additionally, production of acceptable chips requires accu
35
evaluate the previously detected defects. Revisiting of the
defects by the revieW stations is done off-line from the defect
detection process so as not to limit the throughput of the
Wafer scanners. Little engineering Was done in the design of
increased dramatically, due to the increasing complexity of
these revieW stations: in particular With respect to the optics
and cleanliness (e.g., the revieW stations typically use off
the-shelf, visible light, research-style microscopes).
As noted above, the decreasing line Widths of features on
current and future semiconductor chips increase the impor
tance of detection of contaminants and other defects having
45
microscopes currently being used in defect revieW stations
lack suf?cient resolution to resolve defects of such small
siZe, or to resolve this siZe structure on larger defects to aid
50
in identi?cation. Visible light scanning microscopes (both
White light and laser-based) that are built by modifying
off-the-shelf microscopes can improve the resolution
signi?cantly, but they are currently in limited use, mostly as
scanning system), anomalous optical sites are identi?ed by
comparing the light scatter from locations on knoWn good
chips to the light scatter from the corresponding locations on
the chips being tested. If the tWo light scatters are different,
than an anomalous optical site has been detected. Wafer
a diameter, Width, or other characteristic dimension on the
order of 0.1 to 0.3 microns. The visible light, off-the-shelf
optical sites that are characteristic of particulate contamina
tion (but may represent other ?aWs as Well). Defects can be
either a pit or a bump in the surface of the Wafer.
In one type of Wafer scanner, in Which a laser beam is
focussed on and scanned over the surface of the chip (laser
in the chip production process.
30
semiconductor devices (many more layers and process
steps) and the development of larger Wafers (up to 200 mm
diameter), further accentuating the need for defect detection
and control.
Instrument suppliers have addressed a portion of this
Wafers (Wafer scanners) during production for anomalous
identi?cation of the nature of the defects, the density of
particular types of defects. This information can then be
used to more closely monitor and/or to modify process steps
As the need for more precise defect analysis has become
apparent, semiconductor manufacturers’ demand for the
ability to “revisit” defects (or a subset of them) found by the
above-described Wafer scanners, for purposes of positive
identi?cation of the nature, location and siZe of the defects,
has led to the hasty design and production of revieW stations
based on laboratory microscopes With precision Wafer han
dling stages that alloW an operator to close in on and
rate performance of each of the process steps carried out on
the Wafer. The value of product on each Wafer has also
problem by developing defect detecting systems Which scan
for several reasons. Identi?cation of the nature of the defect
can be used to determine the origin of the defect. The
number, location and siZe of the defects can be used to
part of complex and expensive research setups. Additionally,
55
the use of conventional microscopes increases the risk of
contamination of the semiconductor chips during the revieW
process, since a (relatively dirty) human is in close proxim
scanners of this type are made by Tencor Instruments of
Mountain VieW, Calif. as Model 7500, and by Inspex of
ity to the Wafer surface and because the presence of the
Billerica, Mass. as Model TPC 8500.
In another type of Wafer scanner, a video picture is taken
microscope causes turbulent ?oW near the Wafer Which tends
60
With a conventional video camera of the surface of a knoWn
good chip and compared to a corresponding video picture
taken of a chip to be tested. Typically, these video systems
use White light imaging. The video pictures are analyZed by
comparing them on a pixel by pixel basis, i.e., numerical
data representing the video image at each pixel is compared
and, if the difference falls outside of a pre-established
65
to pull in nearby contaminants to the Wafer.
Consequently, the semiconductor processing industry has
attempted to use scanning electron microscopes (SEMs) that
Will provide increased resolution and perform energy dis
persive (EDX) analysis. In EDX analysis, X-rays are
directed toWard the surface of the semiconductor chip. By
measuring the Wavelength spectrum of the re?ected light,
information can be gleaned regarding the types of material
5,963,314
3
4
present on the Wafer surface. Unfortunately, EDX analysis
The laser imaging system presents a real time video image
With resolution superior to a conventional microscope. An
requires high voltage (up to approximately 40,000 volts)
SEMs; bombardment of the Wafer surface With electrons
from high voltage SEMs causes damage to the Wafer,
operator can vieW the image on a conventional computer
rendering the Wafers unusable for further processing.
Recently, loW voltage SEMs (100—1000 volts) have seen
the Wafers to operator contamination or air?oW.
limited use in Wafer fabs for “critical dimension” measure
microscopy techniques, including multiline visible light
ments of line Widths, but loW voltage SEMs are too sloW to
use except on a sample basis, and, in addition, provide no
lasers, and can be optionally ?tted With an ultraviolet laser,
analytical (i.e., EDX) capability. Further, in both high and
display, With comfortable ergonomics, and Without exposing
The laser imaging system utiliZes confocal laser scanning
improving resolution even further due to the shorter Wave
10
loW voltage SEMs, the time to load samples into the SEM
and pump doWn the load-lock chamber containing the SEM
resolution on the order of 0.1 to 0.2 microns. The laser
imaging system can also be used for metrology.
Additional capabilities of the instrument include ?uores
cence of contaminants (for assistance both in locating them
is relatively long, undesirably sloWing doWn processing of
the Wafers. As a result, defect revisiting With SEMs is
usually done off-line in a quality control or analysis labo
15
ratory.
20
analysis on-line or off-line, and capacity for image storage.
For future product line expansion, the laser imaging
system is adaptable to cluster or in-situ applications, Where
SUMMARY OF THE INVENTION
According to the invention, a laser imaging system that
alloWs hands-off operation and operates under class 1 clean
against the complex background of patterned Wafers, and in
identifying their origins), a variety of softWare to assist the
operator in evaluating and classifying the defect, commu
nications and data storage capabilities for providing trend
In an attempt to overcome the limitations of SEMs, some
major semiconductor producers have begun to use systems
Which include both loW and high voltage SEMS. HoWever,
such systems are expensive, selling in the $1,000,000 to
$1,500,000 range.
lengths of the ultraviolet light. The laser imaging system has
examination of defects or structures during on-line process
ing can be performed.
25
BRIEF DESCRIPTION OF THE DRAWINGS
room conditions, has several distinct advantages over con
ventional systems for sub-micron particle structure evalua
tion. In one embodiment, the laser imaging system “revisits”
defects on production semiconductor Wafers, Where the
defects are ?rst detected (but not analyZed or evaluated) by
30
conventional Wafer scanners such as are available from
laser imaging system.
vendors as Inspex, KLA, or Tencor Instruments, among
FIG. 3 is a schematic diagram of the electronics associ
others. The laser imaging system replaces and outperforms
ated With the laser imaging system according to the inven
conventional microscopes noW used to analyZe defects on
production semiconductor Wafers.
Signi?cantly, the laser imaging system according to the
35
tion.
FIG. 4 is a vieW of a display screen resulting from analysis
of an area of the surface of a semiconductor chip by a laser
invention is the ?rst defect revieW tool Whose optics and
functionality have been designed explicitly for ef?cient
performance of the dedicated revisit task. Unlike scanning
electron microscopes (SEMs) that have previously been
FIG. 1 is a perspective vieW of a laser imaging system
according to the invention.
FIG. 2 is a schematic diagram of a laser imaging system
according to the invention illustrating the operation of the
imaging system according to the invention.
40
DETAILED DESCRIPTION OF EMBODIMENTS
OF THE INVENTION
used for defect analysis, the laser imaging system Will not
damage samples or sloW processing, and costs signi?cantly
A laser imaging system according to the invention is used
less to implement than an SEM. Further, While SEMs can
to analyZe defects on semiconductor Wafers that have been
produce images With resolution on the nanometer scale, they
have certain limitations. For example, the SEM image has an
extended depth of ?eld, like a photograph taken through a
high f-stop aperture, but this image contains no quantitative
depth information. Some methods of dealing With this
de?ciency are sample tilting or coating to produce a “shad
oWing” effect or perspective change, but these methods
require additional process steps and cost, may damage the
Wafer, and do not completely resolve the problem.
Unlike the SEM, the laser imaging system according to
45
scope revieW stations noW utiliZed in the semiconductor fab
environment to examine detected optical anomalies that may
represent Wafer defects. In addition to analyZing defects, the
50
laser imaging system can perform a variety of microscopic
inspection functions including defect detection and metrol
ogy.
FIG. 1 is a perspective vieW of laser imaging system 100
according to the invention. Laser imaging system 100
includes housing 102 made of stainless steel. Laser imaging
the invention operates in air With class 1 cleanroom com
patibility. Also unlike the SEM, the laser imaging system
can produce a three dimensional image, using simple image
detected by patterned Wafer defect detecting systems (Wafer
scanners). The laser imaging system replaces optical micro
55
rendering techniques, Which provides quantitative dimen
system 100 occupies a footprint Which ?ts inside a 48“
standard clean hood. Laser imaging system 100 has con
trolled internal air?oW (clean air from the cleanroom is
system has an ability the SEM cannot match: sub-surface
draWn in through the top of laser imaging system 100 and
exhausted from laser imaging system 100 outside of the
cleanroom), maintaining class 1 conditions in the Wafer area,
Which is isolated from the operator console.
A cassette of Wafers (not shoWn) of a given siZe, e.g.,
vieWing of defects lying beneath dielectric layers. Combined
Wafers ranging from 3 inches (75 mm) to 8 inches (200 mm)
sional information. The image can be stored and recalled for
later vieWing. The image can be rotated or tilted or shaded,
With correct perspective maintained, Without necessity for
sample tilting or coating. Additionally, the laser imaging
With three-dimensional analysis softWare, the user is able to
examine cross sections of the defect and surrounding
material, and to assess the impact on circuit layers of the
Wafer.
60
in diameter, is positioned on cassette platform 101. One of
65
a set of interchangeable mounting plates (not shoWn), there
being a different mounting plate for each cassette siZe (i.e.,
Wafers of different siZes are held by different cassettes), is
5,963,314
5
6
attached to cassette platform 101. Typically, defects have
previously been identi?ed on the Wafers by a defect detect
as described beloW. The operator accomplishes ?ne align
ment of the Wafer (de-skeW point) by lining up the visible
ing system, as described above. Wafers from the cassette are
light microscope ?eld of vieW With etched ?ducial marks or
other pre-speci?ed structures on the Wafer surface. After this
loaded through Wafer door 103 formed in housing 102 into
a Wafer processing area housed by optics housing section
107 of housing 102. The Wafers are either loaded by the
precise de-skeW alignments the system can accurately trans
late any speci?ed location on the Wafer into the ?eld of vieW
of the microscope With an accuracy of a feW microns.
The heart of laser imaging system 100 is the laser scan
operator or by a robot 104 that is part of a standard machine
interface (SHIF) i.e., micro-environmentally controlled,
interface. The SHIF interface, Which is a “box” for trans
ferring Wafers in Which clean room conditions are
maintained, is conventional and is available from Asyst
Technologies in Milpitas, Calif. (various models are avail
able and can be used With the invention) After inspection,
10
211, 212, 219, 220, 221, 222, and 223 shoWn in FIG. 2
beloW. The optics head includes a laser, confocal beam
scanning optics, and ultraviolet and visible photo detection
electronics, together With commercial microscope compo
the Wafers are unloaded by either the operator or the robot
104. An optional 3-cassette carousel (not shoWn) may be
mounted on laser imaging system 100 alloWing sorting of
Wafers after inspection.
Robot 104 is a conventional precision, high reliability
(less than one Wafer drop per million transfers) robotic Wafer
ning microscopic optics module (“optics head”) Which
includes elements 201, 202, 203, 204, 205, 207, 208, 210,
15
nents to achieve high quality real time confocal images.
Laser imaging system 100 Will produce a complete
XY-scanned laser image, in a single plane of focus, at video
rates. The resulting image is displayed on a high resolution
monitor, also in real time. Thus, the operator can scan
through different levels of focus in real time, as With a
handler, such as is available from MECS in Japan as part no.
UTX-1000. Robot 104 Will reliably sense, load, and unload
Wafers from cassettes, interchangeably handling 75 mm to
conventional microscope.
FIG. 2 is a schematic diagram of laser imaging system
200 mm Wafers. Robot 104 senses missing or skeWed Wafers
100 according to the invention illustrating the operation of
in the cassette(s), as Well as the presence or absence of a
Wafer on the robot arm or vacuum chuck 224 (see FIG. 2). 25 laser imaging system 100. Laser imaging system 100 uses
the basic principles of confocal microscopy, in Which illu
Robot 104 (and other components of laser imaging system
minating light passes through a pinhole, and the image of
this pinhole is then cast by the system optics on the sample
to be vieWed. The light scattering from the sample returns
100) is designed to eliminate any Wafer contamination (laser
imaging system 100 maintains Class 1 compatible cleanli
ness While handling Wafers). Robot 104 has suf?cient utility
backup (poWer, air, vacuum) to protect any Wafer in transit
through the system optics to the pinhole, but only light from
the focal plane of the imaging (objective) lens returns
through the pinhole, i.e., light from the plane through the
on robot 104 from damage. Upon restart after a poWer
failure, all Wafer locations (cassette slots, robot arms,
vacuum chuck 224 (FIG. 2), plus missing cassettes, are
sampled for the presence or absence of Wafers and/or
cassettes, and appropriate responses made.
When loading Wafers, robot 104 removes Wafers from
cassette platform 101 and performs a pre-alignment step,
35
sample at Which it is desired to obtain imaging data.
Laser imaging system 100 includes an air cooled, multi
line argon ion laser 201 Which provides up to siX different
Wavelengths of light for imaging surfaces and structures in
semiconductors. An eXample of a laser that can be used With
the invention is the Model 2204-25ML air-cooled argon ion
using pre-aligner 105 Which senses a notch and/or ?at(s) on
the Wafer. Optionally, any bar code (identifying the particu
laser produced by Uniphase Corporation, San Jose, Calif. It
lar Wafer) Which may be present on the Wafer may also be
read at this time.
While the Wafer is being loaded, a ?le of data from the
is important to perform imaging With a selection of Wave
defect detecting system, specifying the Wafer coordinates of
the detected defects, is transferred to the laser imaging
system computer Within housing 102 (not visible in FIG. 1),
lengths of laser light to overcome absorption, re?ection, and
interference problems that can occur for a speci?c Wave
length for a given material. That is, one Wavelength Will not
give good results for all materials, ?lm thicknesses, and
45
either by diskette or other media, or by communication via
a link or netWork such as Ethernet, RS232, etc. A computer
(such as Helium-Neon or Helium Cadmium) could also be
used to supply light at other Wavelengths.
Laser 201 produces polariZed light at several discrete
Wavelengths The light passes through a “notch” ?lter 202
Maynard (Archive) 21501S, are attached Within disk drive
bay 106 of housing 102.
mounted on a conventional computer controlled ?lter Wheel
55
the invention is available from Edmund Scienti?c of
Barrington, N]. as part no 43120. Other ?lters are available
from the same source for other Wavelengths.
conventional vacuum chuck 224 (FIG. 2). (In this
The light having the selected Wavelength(s) passes from
notch ?lter 202 to polariZing beam splitter 203. PolariZing
beam splitter 203 is attached to selectable notch ?lter 202
using conventional optical mounts. PolariZing beam splitter
203 preferentially re?ects light only of the proper polariZa
?rst “de-skeW” point (i.e., pre-determined orientation of the
placement error), and automatically focuses using the laser
(not shoWn) Within optics housing section 107. Notch ?lter
202 isolates a laser line or lines. A notch ?lter for use With
description, a Cartesian coordinate system is used in
description of various aspects of the system. The X and Y
aXes de?ne a plane parallel to the patterned surface of the
Wafer and the Z-aXis is perpendicular to the patterned
surface of the Wafer.) The system translates the Wafer to the
Wafer that accounts for the mis-orientation of the patterns on
the Wafer With respect to the Wafer ?at and the robot 104
able to observe through one or more top layers of material
(typically dielectric) Which Will re?ect or absorb some
Wavelengths strongly, but Will alloW transmission of others
to perform the imaging desired. Other Wavelength lasers
for use With laser imaging system 100 is available from
Silicon Graphics in Mountain VieW, Calif. as part no. SGI
XS24Z. A disk drive, available from Silicon Graphics in
Mountain VieW, Calif. as part no. P3-F252, and tape drive,
available from Hamilton/Avnet in Mountain VieW, Calif. as
After pre-alignment, the Wafer is loaded into the Wafer
processing area through Wafer door 103 onto the optical
unit’s XYZ-stage (translational motion) and is secured on a
surface properties. Additionally, in many cases, it is desir
65
tion and directs the light to spatial ?lter 204. The polariZa
tion of the light emitted from laser 201 is oriented so that
most of the light is re?ected by polariZing beam splitter 203
5,963,314
7
8
at 90 degrees into the focusing optics of spatial ?lter 204. A
small portion of the light passes through polariZing beam
available from Olympus of Japan by specifying 100><BF
splitter 203 to a conventional poWer monitor diode (not
Objective lenses 205 are mounted on a computer controlled
shoWn) mounted behind polariZing beam splitter 203, Where
motoriZed turret 223 that enables automatic changing of
objective lenses 205 and autofocus (one lens is focused and
1-LM590. Many interchangeable lenses are available.
the light is absorbed. ApolariZing beam splitter for use With
the invention is available from belles Griot of Irvine, Calif.
focus offsets stored in the computer are used to automati
cally focus the other lenses) of each objective lens 205. A
as part no. 03PBB003.
Spatial ?lter 204 consists of optics Which expand the
beam and then focus it on a pinhole aperture. The diameter
of the pinhole aperture is selected according to Well-knoWn
10
techniques to re-image the light through the doWnstream
optics and a selected one of a plurality of objective lenses
205 to produce a diffraction-limited spot on Wafer 206. The
diameter of the pinhole aperture is also selected to alloW
easy alignment of the beam of light and a signi?cant amount
15
?lter for use With the invention is available from Melles
Griot of Irvine, Calif. as Compact Spatial Filter NeWport/
910. Spatial ?lter 204 is attached to polariZing beam splitter
203 by conventional optics mounts.
Subsequent optics Within spatial ?lter 204 and betWeen
the pinhole assembly and the scanner mirrors collimate the
tube lens 211 as a standard component are mounted together
illuminator assembly bolts to the optics baseplate.
According to the principles of confocal imaging, the light
striking Wafer 206 is scattered and a portion of the light
scanner 207. An X-Y beam scanner for use With the inven
25
Mass. as part no. 000-3011003. X-Y beam scanner 207 is
attached to spatial ?lter 204 by conventional optics mounts.
The mirrors in X-Y beam scanner 207 can oscillate their
angle With respect to the beam of light passing through X-Y
re?ected back into objective lens 205, returning through the
optical path described above. As the returning light passes
through quarter Wave plate 210, the returning light is con
verted to light linearly polariZed and 90° out of phase With
respect to the polariZation of the light originally emitted by
laser 201. The light continues back along the path through
the ?eld lens, scan lens 208, and mirrors of X-Y scanner 207
beam scanner 207. X-Y beam scanner 207 includes tWo
until the light reaches the pinhole aperture of spatial ?lter
oscillating galvanometers, one a high speed resonant unit
204. If the light spot Was in focus on the sample, the image
is imposed on the aperture. If the light spot Was out of focus
on the sample, very little light returns through the aperture.
operating at 8 kHZ, the other a servo controlled unit,
operating at 13 or 26 HZ (but capable of other speeds). The
servo steps in small increments, so that the X-Y beam
property of an objective lens in Which higher numbers
indicate a broader cone of gathered light) objective lenses
205 (magni?cations of 100 and 150 times actual siZe and
0.95 NA). Turret 223 and a vertical illuminator containing
With a ?ange and held by a locking screW. The turret/
light, and direct the light to mirrors mounted on X-Y beam
scanner 207 traces out a raster pattern in space. Araster scan
handle loW poWer (magni?cations of 5, 10 and 20 times
actual siZe) as Well as medium poWer (magni?cation of 50
times actual siZe) and high poWer, high N.A. (numerical
aperture, a conventional designation for the light gathering
of high poWer light to pass through the aperture. A spatial
tion is available from General Scanning of WatertoWn,
turret for use With the invention is available from Olympus
of Japan as part no. BL0920. Turret 223 is designed to
accommodate three to six objective lenses 205, and can
35
Consequently, signals in the confocal optics get darker, not
merely blurred, as occurs With conventional optics, When the
of 256 or 512 lines is produced at approximately 26 or 13
sample is out of focus. Light Which passes through the
frames per second, and is imaged at the back focal plane of
aperture reaches the polariZing beam splitter 203, Which,
being oppositely polariZed, passes through polariZing beam
the tube lens 211.
This raster pattern is imaged in space by the scan lens 208
splitter 203 undeviated and is imaged on the photodetector
in the plane of the ?eld lens (not shoWn, but betWeen beam
212.
splitter 209 and quarter Wave plate 210). A scan lens for use
By measuring the light intensity at each XY location of
With the invention is available from Applied Optics of
Pleasanton, Calif. as part no. 000424. Scan lens 208 is
attached to X-Y beam scanner 207 by conventional optical 45
the raster scan, a map of light intensity in the focal plane of
the objective lens 205 is constructed. This map can either be
stored in the memory of system computer 214, or analyZed
providing a more uniform brightness across the raster pat
by surface data processor 213, Which stores the readings,
and makes a comparison of the intensity With previously
tern and alloWing more light to reach the tube lens 211,
stored maps from other scans, as described beloW. The light
described beloW, Without distorting the image. The tube lens
intensity map is also Written directly into the video memory
of the system computer 214 and may be displayed live on the
computer display 215 in an appropriate WindoW, as
described beloW.
To obtain a three dimensional image, the optics head
Works With the ?ne Z-stage control 216 to develop an
mounts The ?eld lens serves to collect high angle light,
211 and objective lenses 205, described in more detail
beloW, are standard in?nity corrected optics.
Quarter Wave plate 210 is attached to scan lens 208 and
is positioned to convert the linearly polariZed laser light to
circularly polariZed laser light. A quarter Wave plate for use
With the invention is available from Melles Griot of Irvine,
Calif. as part no. 02WRM005. Beam splitter 209 is attached
to quarter Wave plate 210 by a conventional optical mount,
and is explained in more detail beloW. Tube lens 211 is
attached to beam splitter 209 by a conventional optical
mount and Works With objective lens 205 to de-magnify the
raster scanned pinhole image and project it on the Wafer 206.
55
expanded depth-of-?eld image. The sample height is
stepped over a pre-selected vertical interval (typically 12 nm
or some multiple thereof) using the ?ne Z-stage control 216.
After each complete raster scan at a particular sample height,
the height of the sample is changed using ?ne Z-stage control
216, and a neW raster scan performed, as described above,
to obtain a map of light intensity in the focal plane of
A tube lens for use With the invention is available from
objective lens 205 (at the neW sample height) by measuring
Olympus of Japan as part of their vertical illuminator model
the light intensity at each XY location of the raster scan.
X-Y stage control 218 is used to position the defect or
region of interest in the ?eld of vieW. The X-Y stage control
is then held still While the ?ne Z-stage control 216 is used as
described above.
SLK220.
The image of the light spot is focused and demagni?ed by
the objective lens 205 in the focal plane of the objective lens
205. Objective lenses 205 for use With the invention are
65
5,963,314
10
imaging system 100. As noted above, beam splitter 209 is
A three-dimensional image can be obtained from the
multiple XY light intensity maps in one of tWo Ways. First,
attached betWeen quarter Wave plate 210 and tube lens 211.
as noted above, the XY data from each raster scan can be
By imposing beam splitter 209 in the path of light from laser
201 just prior to tube lens 211, and using suitable ?ltering
analyZed by surface data processor 213 by comparing the
light intensity at each point of the XY scan With correspond
ing points of a “master map.” This “master map” stores the
maximum light intensity values found at each XY point,
these values resulting from previous comparisons of XY
light intensity maps. The Z-axis location of the maximum
light intensity at each XY location is also stored. After all of
the XY light intensity maps have been obtained and com
pared to the “master map,” the data representing the light
intensity maximum at each XY location and the Z-axis
location of each light intensity maximum are used to con
struct the three-dimensional image of the Wafer surface.
With this method, it takes about 5 seconds to acquire all of
the light intensity data and extract the surface.
Alternatively, especially if the Wafer is multilayered, i.e.,
producing multiple peaks at each X-Y location along the
Z-axis (Which might occur, for instance, Where transparent
layers are formed), each light intensity map can be stored in
that blocks the re?ected laser light but lets other Wave
lengths pass to the video camera, a conventional microscope
image can be obtained, in addition to the laser image, by
using a conventional microscope illuminator 220 and video
camera 219, charge coupled device (CCD). The White light
10
15
detail beloW, or on a separate video monitor display (not
shoWn).
20
8215-1000 Which vieWs the sample in White light emitted by
microscope illuminator 220, and inserted into the optical
path by beam splitter 221. A microscope illuminator for use
map. If it is desired to create a three-dimensional image of
the surface of the Wafer, the XY light intensity maps are
intensity at each XY location. The Z-axis location of the
25
maximum light intensity at each XY location is stored and,
at the conclusion of the series of comparisons of the XY light
intensity maps, is used With the maximum light intensity
data to construct the three-dimensional image of the Wafer
surface. With this method, it takes about 35 seconds to
using a processor in system computer 214.
A process for constructing a three-dimensional image of
a surface from a three-dimensional data set is described in 35
more detail in commonly oWned, co-pending US. Patent
Application entitled “Surface Extraction from a Three
Dimensional Data Set,” by Ken K. Lee, application Ser. No.
light from laser 201 is prevented from saturating the image
at video camera 219 With re?ected light. A ?lter for use With
the invention is available from Edmund Scienti?c of
Barrington, NJ. as part no. 22754 Video camera 219 and
?lter Wheel 222 are mounted on brackets Which position
video camera 219 and ?lter 222 in line With beam splitter
221. Beam splitter 221 is mounted on the turret assembly
With conventional optical mounts.
To get a White light image alone, laser imaging system
08/079,193, ?led on the same date as the present application,
100 can remove beam-splitter 221 and substitute a mirror
40
reference.
The raster scan is repeated 13 times per second for a 512
by 512 pixel image, or faster for smaller (i.e., feWer pixels
such as 256 by 256) images. (Note that raster scan siZes
other than 512 by 512 or 256 by 256 can be used.) A
complete three-dimensional volume data set Will typically
With the invention is available from Olympus of Japan as
part no. 5LK220. A beam splitter for use With the invention
is available from Melles Griot of Irvine, Calif. as part no.
03BSC007. Filter 222 blocks the laser line in use, but passes
broad bands of light having other Wavelengths, so that laser
30
acquire all of the light intensity data, then extract the surface
the pertinent disclosure of Which is hereby incorporated by
The White light microscope image is produced alone or
simultaneously With the live laser image by video camera
219 available from COHV of Danville, Calif. as part no.
system computer 214, along With the Z-axis height of each
successively compared to determine the maximum light
imaging is accomplished Without the use of microscope
eyepieces that Would result in undesirable proximity of the
operator to the Wafer being analyZed that may result in
contamination of the Wafer. Rather, the microscope image is
displayed on a computer display (simultaneously With the
laser image, if desired), either in a separate WindoW on
computer display 215, using softWare described in more
45
(not shoWn) so that only the video camera light path is
active. Then, the blocking ?lter (mounted on a ?lter Wheel)
can be removed and the full spectrum White light image
vieWed.
FIG. 3 is a schematic diagram of the electronics associ
ated With laser imaging system 100. FIG. 3 shoWs all analog
include 64 raster scans (other numbers can be used), for a
and digital electronics, plus poWer supplies, for complete
total data array of siZe 512 by 512 by 64. For a 512 by 512
pixel image, the total time to accumulate the data to con
operation of laser imaging system 100. Laser imaging sys
struct the three-dimensional image of the surface (assuming
64 raster scans, i.e., vertical height steps) is approximately
tem 100 operates on 220 volts (200—240 volt nominal),
50
?ve seconds.
The light intensity at each data point is stored in system
computer 214 as an 8-bit quantity. A simple map of a
three-dimensional surface is created using the three
dimensional graphics (such as the Silicon Graphics Inc.
Graphics Library, available as part of the XS24Z computer
55
Japanese equivalents).
The SDP Frame Grabber 301 interfaces With photo detec
tor 212 (FIG. 2) and is synchroniZed With the scanner
electronics 309, and ?ne Z-stage control 310, to digitiZe the
photodetector data and produce a three-dimensional map of
light intensity Which can either be stored directly in the
computer memory, or processed to immediately extract a
package) of system computer 214 by plotting the X, Y, and
Z position of each maximum intensity point, and displaying
the map as a continuous surface. The brightness of each
50/60 HZ single phase electric poWer (or the European and
60
surface image. The SDP Frame Grabber 301 interfaces
through the SDP interface 302 to the system computer 303
(also shoWn as 214 in FIG. 2). Frame Grabber 301 is fast and
point on the surface is determined by the light intensity
enables surface data to be extracted from the volume data.
measured at that point. The map display may be done in gray
scale, in false color converted from the gray scale, in a mode
Workstation, such as a Silicon Graphics Iris Indigo XS24Z
The system computer 303 is a high speed RISC graphical
shoWing shape (position) only, or shape With height repre
sented in gray scale.
The capacity for White light imaging, in addition to the
laser imaging described above, is another feature of laser
manufactured by Silicon Graphics of Mountain VieW, Calif.,
65
or equivalent, capable of handling concurrent tasks of robot
functions, stage motion, operator interface, and optics
control, While also performing image processing functions.
5,963,314
11
12
In addition, system computer 303 must Work With a Win
the re?ectivity of the Wafer) may also be employed to
automate most of the operator’s tasks in acquiring the
three-dimensional image. The three-dimensional image may
doWing user interface and high resolution color graphics.
The X, Y, and coarse Z stage controllers 304 communicate
With system computer 303 via an RS-232C interface 305, as
be examined in pseudocolor, pro?led, shadoWed, rotated,
do the robot and pre-aligner controllers 306.
etc.
The user can utiliZe laser imaging system 100 as a White
The balance of the system electronic functions commu
light microscope. The microscope vieW is presented in a
different WindoW than the laser vieW. In White light mode,
nicate through Local Operating Network (LON) interface
307 built on the same interface slot as RS-232C interface
305. The LON 308 itself is a pair of Wires that plug into each
node serially around the system. Each node contains a local
processor and ?rmware for LON communications, self
the user can select vieWs (e.g., tWo-dimensional), translate
10
The overall system softWare is designed for operation of
laser imaging system 100 in both operator and engineering
diagnosis, and local operation of certain functions.
All user interface is via an operator console that is part of
system computer 303 and Which includes computer display
215, a mouse/trackball, a joystick controller, and a keyboard.
(X-Y movement) and focus on details (Z-direction
movement), change objective lens magni?cation.
mode, optionally using defect ?les supplied by various
15
Wafer scanners in a variety of formats. Both operator and
The operator console may optionally be remotely mounted
engineering mode are passWord protected separately, as
(i.e., outside the cleanroom). Image processing and analysis
eXplained in more detail beloW.
In engineering mode, the user can use a recipe develop
functions may be controlled from the console. Through these
controls and the WindoWing softWare, the operator can set
up, program and operate any part of laser imaging system
ment editor to develop recipes for routine inspection of
speci?ed types of Wafers at speci?c process steps for that
Wafer, i.e., to pre-specify operating parameters for use by
operators Working on a speci?c process level and product.
100 including Wafer selection and handling, defect editing
and selection, automatic and/or manual Wafer loading,
defect classi?cation, etc. For example, the joystick control
The recipes can specify Which screen and WindoWs are to be
used, enable the laser Wavelength and poWer to be used to
be selected, speci?cation of the number of slices of data and
ler alloWs the user to move the coarse Z-stage control 217 in
small increments, to bring an object or region of interest on
the Wafer into vieW. Alternatively, for enhanced ease in
making very small lateral movements, the operator can use
the mouse to point and click to cause the X-Y stage control
218 to change position.
their spacing (in nanometers), autofocus to be speci?ed, and
the offset in the Z-direction (vertical direction) from the
autofocus position to the ideal vieWing position to be preset.
3O
Engineering mode also alloWs access to system mainte
The operator has three modes from Which to select
nance functions such as utiliZing the LON access to run
vieWing: White-light conventional microscope optics
(“White light mode”), real time laser scanning optics (“laser
diagnostic checks on the electronics or recalibrate XY and Z
mode”), or both laser and White light optics simultaneously
(“combination mode”). In White light mode, the operator can
select from one of several objective lenses, varying effective
magni?cation of the image. (The laser image scales simul
35
taneously With the White-light image.)
Utilities are available in pop-up menus to enable manual
control of the ?ne Z-stage control 216, coarse Z-stage
control 217 and X-Y stage control 218, polling of stage
variables, and robot manual control (e.g., to alloW move
Laser or White light imaging of a region of the Wafer
produces data regarding the Wafer characteristics in the
imaged region. The data is stored on system computer 214.
After imaging of a region of the Wafer, the operator eXam
ines each defect image as laser imaging system 100 presents
it to him. If the defect is not in vieW (if, for instance, the
defect location data from the Wafer scanner is slightly
erroneous), or the operator Wishes to eXamine a larger or
different area, the joystick controller alloWs him to “cruise”
the Wafer. After the operator eXamines the defect, the opera
stage motion
In operator mode, the operator loads, inspects and clas
si?es lots of Wafers per the predetermined recipe associated
With the particular lot number and Wafer ID. The operator
has limited options to alter the inspection sequence.
ment of a Wafer from the ?at ?nder or stage after a poWer
failure). Diagnostics can also be called up via a pop-up
WindoW displaying all LON nodes and system variables. The
45
status of LON nodes can be checked and revised. From the
display of LON nodes, direct control of system functions,
e.g., open and close the laser shutter, can be accomplished.
As an aid to Workers revieWing defects (especially during
tor classi?es the defect, optionally records the image, and
proceeds to eXamine the neXt defect. Upon completion of
revieW of all desired defects, or other inspection tasks, the
production), laser imaging system 100 has the capability to
Wafer is returned to its cassette, and the neXt Wafer loaded,
be used to represent typical defects for comparison by the
operator With the defect currently being classi?ed. Laser
imaging system 100 can be con?gured to bring up such
store Wafer images and to bring them up in Library Win
doWs. These images are usually stored as bit maps and can
repeating the process above.
In the live laser image, presented in a particular WindoW
of the screen of computer display 215, as eXplained in more
detail beloW, the operator sees a real-time narroW depth of
?eld laser image, Which may be Zoomed to higher effective
55
for comparison betWeen inspection systems, thus enabling
the operator to compare the image produced by laser imag
magni?cations The operator can translate the sample in the
Z-direction (vertical direction) to cover an entire vertical
region of interest. The operator can also select a range of
vertical motion, and have laser imaging system 100 con
ing system 100 With familiar images. The bit maps can be
displayed in special WindoWs to help operators classify
defects.
struct a 3-dimensional image of the region speci?ed. Auto
matic ranging (automatic selection of vertical distance to
traverse in obtaining imaging data), automatic focus
(automatic focusing of objective lens at desired vertical
location) and automatic gain control (automatic adjustment
of the photodetector gain to compensate for differences in
images automatically as different defect classi?cations are
selected. Bit map images from other devices, such as White
light microscopes or SEMs can also be stored and recalled,
The system softWare includes different levels of passWord
protection. At one level, engineering personnel can access
65
laser imaging system 100 to set up predetermined recipes for
screen con?guration, laser scan parameters, and defect
codes. At a different level, operators can access laser imag
5,963,314
13
14
ing system 100 to call up the recipe for the particular Wafer
vieWed simultaneously With the laser image or can be vieW
level and product being used in order to examine defects on
Wafers to be inspected. This feature, combined With auto
White-light image.
in White-light only mode for optimum vieWing of the
matic focus, ranging, and gain control, alloWs competent
operation of laser imaging system 100 With a minimum of
5
operator training.
The Laser WindoW directly displays the live laser image
produced by the scanning laser beam. Controls for changing
the focus of the laser through its range are available.
Laser imaging system 100 uses an Ethernet interface that
Additional controls include autofocus, laser intensity, Zoom,
supports standard ?le transfer and management (data and
number of slices to utiliZe for a three-dimensional image,
recipe upload/doWnload, etc.). Laser imaging system 100
and the step siZe of three-dimensional image slices, plus
other imaging control features.
The 2-D WindoW utiliZes the acquired three-dimensional
includes softWare for generating output report ?les for use
by data analysis (trending, statistical analysis, etc.) softWare
as Well as printed reports. A number of confocal images may
be stored in ?les for subsequent revieW on or off line from
surface image, and presents a tWo-dimensional image of a
slice through the three-dimensional data. In “XY” mode, the
2-D WindoW displays a top vieW in false color of the Wafer
laser imaging system 100.
As noted above, laser imaging system 100 includes com
15
puter display 215. Computer display 215 displays pictorial
and numerical results of the analysis of the defects on the
semiconductor chips, and lists menu selections for control of
laser imaging system 100. Laser imaging system 100 pro
vides the capacity for displaying any number of different
display screens on computer display 215. Each display
screen is de?ned by the number, type, siZe and location of
the WindoWs included Within the display screen. The number
of WindoWs that can be displayed on a display screen is
limited only by the siZe of the WindoWs to be displayed.
25
Generally, the types of WindoWs that can be displayed on
each screen are icon WindoWs, picture WindoWs and infor
mation WindoWs.
FIG. 4 is a vieW of display screen 400 resulting from
analysis of an area of the surface of a semiconductor chip by
laser imaging system 100. Display screen 400 includes a
multilayer semi-transparent samples.
The 3-D WindoW projects a perspective vieW of the
surface image. The 3-D WindoW may be rotated, tilted,
Zoomed, shaded, etc. by the operator to obtain a desired
401a, 401b, 401C, 401d, 4016, 401f and 401g are icon
and WindoW 403 is an information WindoW.
35
duced by a Wafer scanner that is not part of laser imaging
system 100. Defects are shoWn as a color-to-siZe coded dot
on the screen. The operator can select a defect to revisit by,
pro?le seen in WindoW 402b or the planar surface vieW seen
in FIG. 402a. Icon Window 4016 commands display of a
for instance, using a mouse to “point and click” on the
defect. Arubber band metrology box may be used to display
a portion of the defect map to higher precision in an enlarged
three-dimensional image in one of the pictorial WindoWs,
45
vieW Alternatively, a list of defects can be brought up in a
pop-up text WindoW (the defect locations are given as
coordinates of a Cartesian coordinate system), scrolled
through and selected directly by highlighting items on the
doW 403 gives tabular information regarding the siZe and
location of particular defects on the chip and is describe in
list.
The Cassette Map WindoW diagrammatically represents a
loaded cassette. The operator can select and load any Wafer
from the cassette by, for instance, using a mouse to “point
and click” on the Wafer. The operator can also unload the
more detail beloW.
Laser imaging system 100 includes a number of pre
de?ned screens (in one embodiment, on the order of 4—5
screens), i.e., screens having WindoWs of a pre-determined
type and siZe located at pre-determined locations. HoWever,
laser imaging system 100 includes the capability for a user
image for analysis.
The Wafer Map WindoW displays the defect map of the
Wafer under inspection, the defect map having been pro
In FIG. 4, the icon WindoWs list choices for pictorial
display in the picture WindoWs. For instance, icon WindoWs
401a and 401d command display of a tWo-dimensional
image in one of the pictorial WindoWs, e.g., the surface
e.g., the three-dimensional surface image seen in WindoW
402C. The pictorial WindoWs 402a, 402b and 4026 show tWo
or three-dimensional images of the semiconductor chip
being analyZed, as discussed above. The information Win
defect. In “cut” mode, the “XY” mode vieW includes cursor
lines Which can be controlled by, for instance, a mouse to
select “XZ” mode or “YZ” mode slices. If the 2-D WindoW
is used With a volume data set rather than a surface data set,
the “XY” mode display shoWs a single slice scan of data,
rather than a surface outline. The “XZ” mode and “YZ”
mode shoW vertical cuts through the data set. Special options
alloW pro?les of volume data sets to shoW multiple layer
structures. This occurs by analyZing volume data from
plurality of WindoWs of various types. In FIG. 4, WindoWs
WindoWs; WindoWs 402a, 402b, 4026 are picture WindoWs;
surface, i.e., a projection of an effectively in?nite depth of
?eld image of the Wafer surface. In “XZ” and “YZ” modes,
the surface image is represented as surface pro?les of
selected vertical slices. In the tWo-dimensional images, a
rubber band metrology box (i.e., a variable siZe cursor box)
can be used to determine the siZe (in the plane chosen) of the
Wafer to a cassette on the cassette platform 101 of laser
imaging system 100.
to de?ne an unlimited number of screens, each screen having
There is a major advantage to using a laser With multiple
lines to image surfaces, to account for different re?ectivities
any desired combination of WindoWs according to WindoW
type, WindoW siZe and WindoW location.
The screen (WindoW and arrangement of WindoWs) to be
displayed is selected by the operator. For each screen, each
automatically. Confocal optics are a natural Way to perform
an autofocus due to the extremely narroW depth of ?eld.
HoWever, a single spot autofocus may not Work Well if a
55
and absorption. It is alWays a problem to focus microscopes
pictorial WindoW is stored as an icon WindoW When not in
use. WindoWs in different regions of the screen may be
very dark spot on the sample is being imaged. By scanning
interchanged by “clicking and dragging” the WindoW to the
signal, a much more reliable autofocus is obtained. If a
the laser spot in real-time, and averaging over the return
particular material is strongly absorbing, different Wave
neW location.
The Microscope WindoW contains a live video presenta
tion of the White-light image taken from the Wafer surface
through the microscope objective lens. This image may be
65
lengths may be selected. Alternatively, a laser ?lter may be
used Which transmits each Wavelength of the laser inversely
proportionally to the intensity of the Wavelength and so
5,963,314
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16
illuminates the sample With multiline laser light Which is
the computer can adjust laser poWer and photodetector gain
determination of the vertical site of defects, or to provide
some specialiZed inspection. For example, stress voids in
metal layers beloW dielectric layers can be vieWed. The
depth of metal plugs in glass insulators can also be seen.
to achieve a good autofocus.
False color can be used to see small defects, either on the
opaque, diffusely scattering surfaces.
sure to select at least one Wavelength Which re?ects strongly.
In a simpler mode, the laser can be used With no ?lter, and
surface or under the surface. By converting images to false
color from black and White, very small objects may be
detected that Would otherWise go unnoticed, because the
human eye can discern thousands of separate hues, While
In its simplest mode, laser imaging system 100 Works on
The laser imaging system according to the invention is
unique in its capability for combining live video, live laser
scan, three-dimensional imaging, Wafer maps, and Wafer
10
surface pro?les all on one screen. By selecting screens With
different siZe and composition of WindoWs the operator may
vieW all the relative data needed for completion of his task.
The system according to the invention can be easily
small differences in brightness are hard for the eye to detect.
This is one Way in Which laser imaging system 100 exceeds
the “Rayleigh Criterion” (a common measure of resolution)
adapted for use in other materials science industries such as
in its ability to see structures on the order of 0.1 to 0.2
micron siZe Other aids in small feature detection are the 15
production of magnetic media, thin ?lm heads, ?at panel
improvement in resolution obtained With confocal optics,
system 100 Would include some softWare changes and some
and the oversampling (overlapping images) performed by
changes in the material handling system.
laser imaging system 100 that enables detection of features
Appendix A accompanying this speci?cation is a draft
User’s Manual for laser imaging system 100 and is herein
as small as 0.1 to 0.2 microns.
As an option, the laser optics can be used to obtain a
incorporated by reference.
?uorescence image of the Wafer, detecting visible light in
preselected Wavelength bands. Fluorescence using White
light or laser light in the same system is possible. Illumi
nating light of selected Wavelengths Will ?uoresce certain
materials, such as skin ?akes or photoresist, the material
displays, etc. The necessary adaptations to laser imaging
25
Various embodiments of the invention have been
described. The descriptions are intended to be illustrative,
not limitative. Thus, it Will be apparent to one skilled in the
art that certain modi?cations may be made to the invention
as described Without departing from the scope of the claims
emitting light at a longer Wavelength. Suitable ?lters in front
set out beloW.
of the video camera block the illuminating radiation
We claim:
Wavelength, but pass the longer Wavelength, thus enabling
1. An imaging system comprising:
identi?cation of the material. This may also be done With the
means for supporting a semiconductor Wafer to be imaged
laser, ?uorescing With a short Wavelength, and placing a
by the imaging system;
?lter passing the longer Wavelengths in front of the photo
means for inspecting the Wafer to determine the ef?cacy
of a process previously performed on the Wafer, the
detector 212.
Polarized light images of objects or structures on the
sample may be taken by illuminating the objects or struc
tures With polariZed White light and vieWing the sample
through a cross polariZed ?lter. Optically active materials
such as quartZ Will appear bright against the dark polariZa
inspecting means including:
35
objective lenses and illumination may be used to help locate
particles and other defects on the Wafer surface.
The same technique may be used With the confocal optics,
re?ected from a plurality of points on a surface of the
Wafer to de?ne a plurality of test values, each of the
test values representing the intensity of light
by using linearly polariZed light Inserting a second quarter
detector, but light further rotated by passing through the
re?ected from one of the plurality of points on the
45
optically active medium is alloWed to pass and shoWs as a
bright spot on the live laser scan.
A second major use of conventional microscope stations,
Wafer surface; and
means for storing the plurality of test values;
means for comparing the stored plurality of test values to
a plurality of reference values to identify differences
betWeen the test values and the reference values,
Wherein the differences betWeen the test and reference
values indicate the presence of an optical anomaly; and
means for analyZing the differences to determine the
different from the revieW or “revisit” function, is the more
general defect detection function, Where preselected sites on
a Wafer are inspected for ef?cacy of a previous process step.
Laser imaging system 100 according to the invention is
directly usable for this application, Which faces exactly the
same problems as defect imaging: decreasing siZe of objects
lengths;
means for directing the laser light toWard the support
ing means;
means for measuring a ?rst intensity of laser light
tion extinction background. Optional bright-?eld/dark ?eld
Wave plate in the beam adds another 90 degree rotation, so
that re?ected light from the sample no longer passes to the
means for emitting laser light of a plurality of Wave
nature and origin of the anomaly.
2. The imaging system of claim 1, Wherein the analyZing
55
of interest, a lack of resolution, and the need for three
means is capable of determining Whether the anomaly Was
caused by a contaminant.
3. The imaging system of claim 2, Wherein the analyZing
dimensional imaging. The hardWare required is exactly the
means further comprises means for determining at least one
same, as is the system control softWare. Only a variation in
material of Which the contaminant is constituted.
the application softWare is needed, so that predetermined
inspection sites may be speci?ed instead of defect map sites.
Overlay registration is another possible use of laser imag
ing system 100. Laser imaging system 100 can vieW pho
toresist layers on top of underlying structures to ascertain
accuracy of placement of the photoresist layer With respect
to features of the underlying structures.
Laser imaging system 100 can also be used to vieW
through transparent (e.g., dielectric or glass) layers to allow
4. The imaging system of claim 1, Wherein the analyZing
means is capable of determining Whether the anomaly Was
caused by a deformation of the Wafer.
5. The imaging system of claim 1, Wherein the analyZing
means further comprises means for determining at least one
65
dimension of the anomaly.
6. The imaging system of claim 1, Wherein the analyZing
means further comprises means for determining a location of
the anomaly on the Wafer.
5,963,314
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18
7. The imaging system of claim 1, further comprising
the measured intensity of laser light re?ected from
means for isolating the Wafer Within a region of the system,
Wherein air Within the region conforms to Class 1 cleanroom
conditions.
the surface is at a maXimum intensity When the
surface lies in the focal plane of the lens; and
a White-light imaging system for imaging the surface
simultaneous With the laser imaging system, the White
8. The imaging system of claim 7, further comprising
means for remotely loading and unloading the Wafer onto
and off of the supporting means such that the air Within the
region conforms to Class 1 cleanroom conditions.
light imaging system including:
a White light source for emitting White light toWard the
stage; and
a second photodetector for measuring the intensity of
White light re?ected from the surface;
9. The imaging system of claim 1, Wherein the imaging
system can resolve features on the Wafer as small as approXi
mately 0.1 microns.
10. The imaging system of claim 1, Wherein the means for
emitting laser light includes an ultraviolet laser.
11. The imaging system of claim 1, Wherein the imaging
system renders images of the Wafer in false color.
12. A microscope for imaging a surface of an object, the
15
microscope comprising:
Wherein the microscope further comprises a ?lter for
alloWing light of the second Wavelength to pass through
the ?lter and for preventing light of the ?rst Wavelength
from passing through the ?lter.
18. An imaging system for detection or analysis of defects
a stage for supporting the object;
a laser imaging system con?gured to provide a three
dimensional image of the surface, the laser imaging
system including:
in or on an object to be imaged, the system comprising:
a laser light source for emitting a beam of laser light;
a lens arranged to be betWeen the laser light source and
a stage for supporting the object;
the stage, the lens having a focal plane;
a beam scanner for scanning the beam and for directing
a source of polariZed light of a ?rst polarity, the source for
25
the scanned beam toWard the stage through the lens;
and
a ?rst photodetector for measuring the intensity of laser
light re?ected from the surface of the object, Wherein
the measured intensity of laser light re?ected from
polarity travels through the pinhole aperture toWard the
stage;
surface lies in the focal plane of the lens; and
a lens, mounted betWeen the source of polariZed light and
a White-light imaging system for imaging the surface
simultaneous With the laser imaging system, the White
the stage, for focusing the portion of the light of the ?rst
35
a White light source for emitting White light toWard the
stage; and
a second photodetector for measuring the intensity of
White light re?ected from the surface.
13. The microscope of claim 12, further comprising a
?lter for preventing laser light from impinging upon the
second photodetector and for alloWing White light to
impinge upon the second photodetector.
14. The microscope of claim 12, Wherein the laser imag
ing system further comprises a ?rst display for displaying
the laser light image of the surface, and the White-light
imaging system further comprises a second display for
photodetector, for changing the polariZation of
45
?rst polarity.
performed, the system comprising:
a stage for supporting the Wafer to be inspected;
a light source for emitting a beam of light;
a beam scanner for scanning the beam and directing the
scanned beam toWard the stage, Wherein the stage is
arranged such that a portion of the scanned beam Will
55
be re?ected from a plurality of points on a surface of
the Wafer to be inspected;
a photodetector for measuring the intensity of the
re?ected portion of the scanned beam from the plurality
a stage for supporting the object;
a laser imaging system for imaging the surface, the laser
imaging system including:
of points on the Wafer surface to de?ne a plurality of
test values, each of the test values representing the
a laser light source for emitting a beam of laser light;
a lens arranged to be betWeen the laser light source and
intensity of light re?ected from one of the plurality of
points on the Wafer surface;
a ?rst region of memory for storing the plurality of test
the stage, the lens having a focal plane;
a beam scanner for scanning the beam and for directing
the scanned beam toWard the stage through the lens;
and
re?ected light so that the polariZation of light re?ected
by the surface is of a second polarity different from the
19. A system for inspecting a semiconductor Wafer to
determine the ef?cacy of a Wafer process previously
16. The microscope of claim 12, Wherein the laser imag
ing system further comprises a polariZer for polariZing the
a ?rst photodetector for measuring the intensity of laser
light re?ected from the surface of the object, Wherein
a photodetector for measuring the intensity of light
re?ected from the object When the object is supported
by the stage, Wherein the intensity of light re?ected
from the object is at a maXimum intensity When a
image of the surface can be displayed as a three-dimensional
vieW.
microscope comprising:
polarity to a focal point of the lens;
surface of the object and the focal point are coincident;
and
a ?lter, positioned betWeen the stage and the
displaying the White-light image of the surface.
15. The microscope of claim 14, Wherein the laser light
laser light and a cross polariZed ?lter.
17. A microscope for imaging a surface of an object, the
directing polariZed light toWard the stage, Whereby the
polariZed light impinges upon the object When the
object is supported by the stage;
a pinhole aperture positioned betWeen the light source and
the stage such that a portion of the light of a ?rst
the surface is at a maXimum intensity When the
light imaging system including:
Wherein one of the laser light or the White light is to be
emitted at a ?rst Wavelength for causing ?uorescence of
a particular material in or on the surface such that the
one of the laser light or White light is re?ected from the
material at a second Wavelength, and
65
values;
a second region of memory for storing a plurality of
reference values, each of the reference values repre
5,963,314
19
20
senting the intensity of light re?ected from one of a
plurality of points on a reference surface; and
means for comparing ones of the plurality of test values
With corresponding ones of the plurality of reference
Wherein the differences betWeen corresponding ones of
the test and reference values indicate the presence of an
optical anomaly, and
Wherein the optical anomaly provides an indication of the
efficacy of the process,
said system further comprising a third region of memory
for storing a group of difference values, the group of
difference values representing the differences betWeen
corresponding test and reference values, and
values to identify differences betWeen corresponding
ones of the test and reference values,
Wherein the differences betWeen corresponding ones of
the test and reference values diagnose Whether an
optical anomaly is present on the Wafer and
Wherein the optical anomaly provides an indication of the
ef?cacy of the process.
20. The system of claim 19, further comprising a proces
sor capable of processing the test values to provide display
data to a ?rst display, thereby enabling the ?rst display to
produce an image of the Wafer surface.
21. The system of claim 20, further comprising a White
10
Wherein the means for comparing may be used to analyZe
the group of difference values to determine a location
of the anomaly on the Wafer, the location being de?ned
by X, Y, and Z coordinates.
30. A system for inspecting a semiconductor Wafer to
determine the ef?cacy of a Wafer process previously
performed, the system comprising:
light imaging system for simultaneously providing a White
light image of the Wafer surface.
a stage for supporting the Wafer to be inspected;
a laser light source for emitting a beam of light, Wherein
the laser light source is capable of emitting light of a
22. The system of claim 19, further comprising a third
region of memory for storing a group of difference values,
the group of difference values representing the differences
betWeen corresponding test and reference values.
23. The system of claim 22, Wherein the means for
comparing may be used to analyZe the group of difference
plurality of Wavelengths;
values to determine at least one material that caused the 25
anomaly.
a beam scanner for scanning the beam and directing the
scanned beam toWard the stage, Wherein the stage is
arranged such that a portion of the scanned beam Will
be re?ected from a plurality of points on a surface of
the Wafer to be inspected;
24. The system of claim 22, Wherein the means for
comparing may be used to analyZe the group of difference
a photodetector for measuring the intensity of the
re?ected portion of the scanned beam from the plurality
values to determine at least one dimension of the anomaly.
of points on the Wafer surface to de?ne a plurality of
test values, each of the test values representing the
25. The system of claim 22, further comprising a hood for
encapsulating the stage and the Wafer, Wherein air Within the
intensity of light re?ected from one of the plurality of
points on the Wafer surface;
a ?rst region of memory for storing the plurality of test
hood conforms to Class 1 cleanroom conditions.
26. The system of claim 25, further comprising a robot for
remotely loading and unloading the Wafer onto and off of the
stage such that air Within the hood conforms to Class 1
cleanroom conditions.
values;
35
27. The system of claim 19, further comprising collimat
ing optics betWeen the light source and the beam scanner.
28. The system of claim 19, Wherein the light source is a
laser.
29. A system for inspecting a semiconductor Wafer to
determine the ef?cacy of a Wafer process previously
values to identify differences betWeen corresponding
performed, the system comprising:
a stage for supporting the Wafer to be inspected;
a light source for emitting a beam of light;
a beam scanner for scanning the beam and directing the
scanned beam toWard the stage, Wherein the stage is
arranged such that a portion of the scanned beam Will
be re?ected from a plurality of points on a surface of
the Wafer to be inspected;
45
X, y, and Z aXes describing a set of unique X-y-Z coordinates,
the method comprising the steps of:
55
ones of the test and reference values,
scanning the test surface in the test volume With a
focussed beam so that the focal point of the focussed
beam coincides, in turn, With each unique X-y-Z coor
dinate Within the test volume;
determining, for each unique X-y-Z coordinate in the test
volume, a re?ected intensity of the focussed beam to
create a set of re?ected intensity values; and
comparing the set of re?ected intensity values to a set of
values;
values to identify differences betWeen corresponding
an optical anomaly, and
Wherein the optical anomaly provides an indication of
the ef?cacy of the process.
volume represented by a Cartesian coordinate system having
intensity of light re?ected from one of the plurality of
points on the Wafer surface;
a ?rst region of memory for storing the plurality of test
a second region of memory for storing a plurality of
reference values, each of the reference values repre
senting the intensity of light re?ected from one of a
plurality of points on a reference surface; and
means for comparing ones of the plurality of test values
With corresponding ones of the plurality of reference
ones of the test and reference values,
Wherein the differences betWeen corresponding ones of
the test and reference values indicate the presence of
31. A method of locating an optical anomaly on a test
surface, Wherein the test surface is contained Within a test
a photodetector for measuring the intensity of the
re?ected portion of the scanned beam from the plurality
of points on the Wafer surface to de?ne a plurality of
test values, each of the test values representing the
a second region of memory for storing a plurality of
reference values, each of the reference values repre
senting the intensity of light re?ected from one of a
plurality of points on a reference surface; and
means for comparing ones of the plurality of test values
With corresponding ones of the plurality of reference
reference values to determine Whether the set of
re?ected intensity values is different from the set of
reference values;
65
Wherein differences betWeen the set of re?ected intensity
values and the set of reference values indicate the
presence of an optical anomaly.
5,963,314
21
22
32. The method of claim 31, wherein the focussed beam
41. The system of claim 38, further comprising a third
comprises White light.
memory means for storing a group of difference values, the
33. The method of claim 31, Wherein the focussed beam
comprises at least one beam of laser light.
34. The method of claim 31 further comprising the steps
of:
group of difference values representing the differences
betWeen corresponding test and reference values.
42. The system of claim 41, Wherein the means for
comparing may be used to analyZe the group of difference
determining, for each column of points speci?ed by a
values to determine at least one material that caused the
anomaly.
unique X-y coordinate of the test volume, the Z coor
dinate resulting in a maXimum re?ected intensity of the
focussed beam;
10
43. The system of claim 41, Wherein the means for
comparing may be used to analyZe the group of difference
values to determine at least one dimension of the anomaly.
44. The system of claim 41, further comprising a means
storing all the locations along the Z aXes of all unique X-y
coordinates to form a set of Z test data representing a
for encapsulating the stage and the Wafer, Wherein air Within
three-dimensional image of the test surface; and
the encapsulating means conforms to Class 1 cleanroom
conditions.
45. The system of claim 44, further comprising a means
comparing the set of Z test data With a set of Z reference
15
data to determine Whether the set of Z test data is
different from the set of Z reference data.
for remotely loading and unloading the Wafer onto and off of
35. The method of claim 34, Wherein the light source
provides White light.
the stage such that air Within the hood conforms to Class 1
cleanroom conditions.
36. The method of claim 34, Wherein the light source
provides at least one beam of laser light.
37. A method comprising the steps of:
means is a laser.
46. The system of claim 38, Wherein the light-emitting
47. A system for inspecting a semiconductor Wafer to
determine the ef?cacy of a Wafer process previously
generating three-dimensional microscope image data rep
resenting a semiconductor Wafer;
comparing the three-dimensional microscope image data
performed, the system comprising:
25
to reference three-dimensional image data; and
characteriZing structures on the semiconductor Wafer
based on the step of comparing.
38. A system for inspecting a semiconductor Wafer to
determine the ef?cacy of a Wafer process previously
beam toWard the stage, Wherein the stage is arranged
such that a portion of the scanned beam Will be
re?ected from a plurality of points on a surface of the
Wafer to be inspected;
performed, the system comprising:
means for supporting the Wafer to be inspected;
means for emitting a beam of light;
means for scanning the beam and directing the scanned
beam toWard the stage, Wherein the stage is arranged
such that a portion of the scanned beam Will be
means for supporting the Wafer to be inspected;
means for emitting a beam of light;
means for scanning the beam and directing the scanned
means for measuring the intensity of the re?ected portion
of the scanned beam from the plurality of points on the
Wafer surface to de?ne a plurality of test values, each
35
of the test values representing the intensity of light
re?ected from one of the plurality of points on the
Wafer surface;
re?ected from a plurality of points on a surface of the
Wafer to be inspected;
means for measuring the intensity of the re?ected portion
of the scanned beam from the plurality of points on the
a ?rst memory means for storing the plurality of test
Wafer surface to de?ne a plurality of test values, each
ence values, each of the reference values representing
the intensity of light re?ected from one of a plurality of
points on the Wafer surface; and
means for comparing ones of the plurality of test values
With corresponding ones of the plurality of reference
values;
a second memory means for storing a plurality of refer
of the test values representing the intensity of light
re?ected from one of the plurality of points on the
Wafer surface;
a ?rst memory means for storing the plurality of test
45
values to identify differences betWeen corresponding
values;
ones of the test and reference values,
Wherein the differences betWeen corresponding ones of
the test and reference values indicate the presence of an
a second memory means for storing a plurality of refer
ence values, each of the reference values representing
the intensity of light re?ected from one of a plurality of
points on the Wafer surface; and
means for comparing ones of the plurality of test values
With corresponding ones of the plurality of reference
optical anomaly, and
Wherein the optical anomaly provides an indication of the
efficacy of the process,
values to identify differences betWeen corresponding
ones of the test and reference values,
55
Wherein the differences betWeen corresponding ones of
the test and reference values diagnose Whether an
optical anomaly is present on the Wafer, and
Wherein the optical anomaly provides an indication of the
ef?cacy of the process.
the group of difference values to determine a location
by X, Y, and Z coordinates.
48. A system for inspecting a semiconductor Wafer to
determine the ef?cacy of a Wafer process previously
display means, thereby enabling the display means to pro
for simultaneously providing a White-light image of the
Wafer surface.
difference values representing the differences betWeen
corresponding test and reference values; and
Wherein the means for comparing may be used to analyZe
of the anomaly on the Wafer, the location being de?ned
39. The system of claim 38, further comprising a means
for processing the test values to provide display data to a
duce an image of the Wafer surface.
40. The system of claim 39, further comprising a means
said system further comprising a third memory means for
storing a group of difference values, the group of
performed, the system comprising:
65
means for supporting the Wafer to be inspected;
a laser capable of emitting light of a plurality of Wave
lengths;
5,963,314
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23
means for scanning the beam and directing the scanned
beam toward the stage, Wherein the stage is arranged
such that a portion of the scanned beam Will be
Wherein the differences betWeen corresponding ones of
the test and reference values indicate the presence of
an optical anomaly, and
Wherein the optical anomaly provides an indication of
the e?icacy of the process.
re?ected from a plurality of points on a surface of the
Wafer to be inspected;
means for measuring the intensity of the re?ected portion
of the scanned beam from the plurality of points on the
Wafer surface to de?ne a plurality of test values, each
of the test values representing the intensity of light
re?ected from one of the plurality of points on the
10
Wafer surface;
51. A method comprising the steps of:
a ?rst memory means for storing the plurality of test
generating three-dimensional microscope image data rep
values;
a second memory means for storing a plurality of refer
ence values, each of the reference values representing
the intensity of light re?ected from one of a plurality of
points on a reference surface; and
means for comparing ones of the plurality of test values
With corresponding ones of the plurality of reference
values to identify differences betWeen corresponding
ones of the test and reference values,
49. The system of claim 19 Wherein the reference values
are not generated from the Wafer.
50. The system of claim 38 Wherein the reference values
are not generated from the Wafer.
resenting a Workpiece bearing an integrated circuit
15
pattern;
comparing the three-dimensional microscope image data
to reference three-dimensional image data; and
characteriZing structures on the Workpiece based on the
step of comparing.
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