U.S. patent application number 13/193011 was filed with the patent office on 2011-12-01 for determining physical property of substrate.
Invention is credited to Dominic J. Benvegnu, Ingemar Carlsson, Jeffrey Drue David, Lakshmanan Karuppiah, Harry Q. Lee, Jun Qian, Abraham Ravid, Boguslaw A. Swedek.
Application Number | 20110294400 13/193011 |
Document ID | / |
Family ID | 39316405 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110294400 |
Kind Code |
A1 |
Ravid; Abraham ; et
al. |
December 1, 2011 |
Determining Physical Property of Substrate
Abstract
A method of determining a physical property of a substrate
includes recording a first spectrum obtained from a substrate, the
first spectrum being obtained during a polishing process that
alters a physical property of the substrate. The method includes
identifying, in a database, at least one of several previously
recorded spectra that is similar to the recorded first spectrum.
Each of the spectra in the database has a physical property value
associated therewith. The method includes generating a signal
indicating that a first value of the physical property is
associated with the first spectrum, the first value being
determined using the physical property value associated with the
identified previously recorded spectrum in the database. A system
for determining a physical property of a substrate includes a
polishing machine, an endpoint determining module, and a
database.
Inventors: |
Ravid; Abraham; (Cupertino,
CA) ; Swedek; Boguslaw A.; (Cupertino, CA) ;
David; Jeffrey Drue; (San Jose, CA) ; Qian; Jun;
(Sunnyvale, CA) ; Carlsson; Ingemar; (Milpitas,
CA) ; Benvegnu; Dominic J.; (La Honda, CA) ;
Lee; Harry Q.; (Los Altos, CA) ; Karuppiah;
Lakshmanan; (San Jose, CA) |
Family ID: |
39316405 |
Appl. No.: |
13/193011 |
Filed: |
July 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12822096 |
Jun 23, 2010 |
8014004 |
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13193011 |
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12253160 |
Oct 16, 2008 |
7746485 |
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12822096 |
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11611640 |
Dec 15, 2006 |
7444198 |
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12253160 |
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Current U.S.
Class: |
451/5 |
Current CPC
Class: |
Y10S 707/99936 20130101;
G01B 11/0683 20130101; G01B 11/0625 20130101 |
Class at
Publication: |
451/5 |
International
Class: |
B24B 51/00 20060101
B24B051/00 |
Claims
1. A method of determining a polishing endpoint of a substrate, the
method comprising: polishing a surface of a substrate; storing in a
database a plurality of previously recorded spectra, each of the
previously recorded spectra having a value associated therewith
stored in the database; during polishing, directing a beam of white
light to impinge the surface of the substrate and generate a
reflected light beam and measuring a sequence of first spectra of
the reflected light beam; for each first spectrum from the first
spectra, determining a second spectrum from the plurality of
previously recorded spectra stored in the database that matches the
first spectrum to generate a sequence of second spectra, wherein
the second spectrum matches the first spectrum when the second
spectrum is similar to the first spectrum; for each second spectrum
in the sequence of second spectra, identifying from the database
the value stored in the database associated with the second
spectrum to generate a sequence of values; and determining a
polishing endpoint from the sequence of physical property
values.
2. The method of claim 1, wherein the value is a value of a
physical property selected from the group consisting of: a layer
thickness on the substrate and a step height on the substrate.
3. The method of claim 2, wherein the physical property is a layer
thickness on the substrate.
4. The method of claim 2, wherein the physical property is a step
height on the substrate.
5. The method of claim 1, further comprising determining a linear
function for the sequence of physical property values.
6. The method of claim 5, wherein determining a linear function
comprising fitting a linear function to the sequence of values.
7. The method of claim 5, further comprising calculating a
resulting value of the physical property from the linear
function.
8. The method of claim 7, wherein calculating includes
extrapolation of the resulting value from the linear function.
9. The method of claim 6, further comprising determining the
polishing endpoint from the linear function.
10. The method of claim 9, wherein determining the polishing
endpoint from the linear function comprises calculating when the
linear function reaches a target value.
11. A computer program product tangibly embodied in a
computer-readable storage device, the computer program product
including instructions that, when executed, cause a processor to
perform operations comprising: polishing a surface of a substrate;
storing in a database a plurality of previously recorded spectra,
each of the previously recorded spectra having a value associated
therewith stored in the database; during polishing, directing a
beam of white light to impinge the surface of the substrate and
generate a reflected light beam and measuring a sequence of first
spectra of the reflected light beam; for each first spectrum from
the first spectra, determining a second spectrum from the plurality
of previously recorded spectra stored in the database that matches
the first spectrum to generate a sequence of second spectra,
wherein the second spectrum matches the first spectrum when the
second spectrum is similar to the first spectrum; for each second
spectrum in the sequence of second spectra, identifying from the
database the value stored in the database associated with the
second spectrum to generate a sequence of values; and determining a
polishing endpoint from the sequence of values.
12. The computer program product of claim 11, wherein the value is
a value of a physical property selected from the group consisting
of: a layer thickness on the substrate and a step height on the
substrate.
13. The computer program product of claim 12, wherein the physical
property is a layer thickness on the substrate.
14. The computer program product of claim 12, wherein the physical
property is a step height on the substrate.
15. The computer program product of claim 11, further comprising
determining a linear function for the sequence of physical property
values.
16. The computer program product of claim 15, wherein determining a
linear function comprising fitting a linear function to the
sequence of values.
17. The computer program product of claim 15, further comprising
calculating a resulting value of the physical property from the
linear function.
18. The computer program product of claim 17, wherein calculating
includes extrapolation of the resulting value from the linear
function.
19. The computer program product of claim 16, further comprising
determining the polishing endpoint from the linear function.
20. The computer program product of claim 19, wherein determining
the polishing endpoint from the linear function comprises
calculating when the linear function reaches a target value.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 12/822,096, filed Jun. 23, 2010, which is a continuation of
U.S. application Ser. No. 12/253,160, filed Oct. 16, 2008, now U.S.
Pat. No. 7,746,485, which is a continuation of U.S. application
Ser. No. 11/611,640, filed Dec. 15, 2006, now U.S. Pat. No.
7,444,198. The disclosure of the prior applications is considered
part of (and is incorporated by reference in) the disclosure of
this application.
TECHNICAL FIELD
[0002] This description relates to determining a physical property
of a substrate during a polishing process.
BACKGROUND
[0003] There are many situations in which light rays can be used
for determining a physical characteristic of a material. For
example, it is sometimes desirable to measure the thickness of a
layer that is deposited on top of a substrate. That is, when a
layer on top of a substrate is being planarized or otherwise
partially removed in a polishing process, one may want to determine
(directly or indirectly) the remaining thickness so that too much
material is not removed. As another example, when a layer is being
deposited on a substrate, one may want to determine (directly or
indirectly) the deposited thickness so that too much or too little
of the layer material is not deposited. It can also be important to
determine uniformity of the layer thickness. Thus, the purpose of
determining the thickness in some situations may be to determine a
desired end point of a manufacturing process or what pressure
profile to use across the wafer, and/or a polish time to use for
the wafer. In other examples, a physical characteristic such as
thickness may be determined for quality control, classification,
calibration, compatibility testing, or other purposes.
[0004] Chemical mechanical polishing (CMP) is one example of a
manufacturing process in which end point determination or real-time
thickness monitoring is performed. For example, CMP is sometimes
performed on a wafer or other substrate that includes integrated
circuits. An integrated circuit is typically formed on a substrate
by the sequential deposition of conductive, semiconductive or
isolative layers on a silicon wafer. After each layer is deposited,
the layer is etched to create circuitry features. As a series of
layers are sequentially deposited and etched, the outer or
uppermost surface of the substrate, i.e., the exposed surface of
the substrate, becomes increasingly non-planar. This non-planar
surface presents problems in the photolithographic steps of the
integrated circuit fabrication process or the electrical properties
of the contact lines or the devices. The deposited layers must be
planarized and then polished down to a specified thickness.
[0005] CMP is one accepted method of planarization. This
planarization method typically requires that the substrate be
mounted on a carrier or polishing head. The exposed surface of the
substrate is placed against a rotating polishing pad, or a pad that
is an axially moving sheet. The polishing pad may be either a
"standard" pad or a fixed-abrasive pad. A standard pad has a
durable roughened surface, whereas a fixed-abrasive pad has
abrasive particles held in a containment media. The carrier head
provides a controllable load profile, i.e., pressure, on the
substrate to push it against the polishing pad. A polishing slurry,
including at least one chemically-reactive agent, and abrasive
particles if a standard pad is used, is supplied to the surface of
the polishing pad.
[0006] The effectiveness of a CMP process may be measured by its
polishing rate, and by the resulting finish (absence of small-scale
roughness) and flatness (absence of large-scale topography) of the
substrate surface. The polishing rate, finish and flatness are
determined by many factors, including the pad and slurry
combination, the carrier head configuration, the relative speed
between the substrate and pad, and the force pressing the substrate
against the pad.
[0007] In order to determine the effectiveness of different
polishing tools and processes, a so-called "blank" wafer, i.e., a
wafer with multiple layers but no pattern, may be polished in a
tool/process qualification step. After polishing, the remaining
layer thickness may be measured at several points on the substrate
surface. The variation in layer thickness provides a measure of the
wafer surface uniformity, and a measure of the relative polishing
rates in different regions of the substrate. One approach to
determining the substrate layer thickness and polishing uniformity
is to remove the substrate from the polishing apparatus and examine
it. For example, the substrate may be transferred to a metrology
station where the thickness of the substrate layer is measured,
e.g., with an ellipsometer. This process can be time-consuming and
thus costly, and the metrology equipment is costly.
[0008] One challenge in CMP is determining whether the polishing
process is complete or uniform, i.e., whether a substrate layer has
been uniformly planarized to a desired flatness or thickness. Many
different factors can cause variations in the material removal
rate, including variations in the initial thickness of the
substrate layer and its properties, the slurry composition, the
polishing pad condition, the relative speed between the polishing
pad and the substrate, and the load on the substrate. These
variations in turn cause variations in the time needed to reach the
desired thickness and uniformity. Therefore, these and other
properties cannot be determined merely as a function of polishing
time.
SUMMARY
[0009] The invention relates to determining a physical property of
a substrate. For example, it is described that a database can be
created from spectra measured from substrates, the spectra having
been associated with corresponding values for one or more physical
properties. By comparing a currently measured spectrum with the
database, a value for the physical property can be determined.
[0010] In a first general aspect, a method of determining a
physical property of a substrate includes recording a first
spectrum obtained from a substrate, the first spectrum being
obtained during a polishing process that alters a physical property
of the substrate. The method includes identifying, in a database,
at least one of several previously recorded spectra that is similar
to the recorded first spectrum. Each of the spectra in the database
has a physical property value associated therewith. The method
includes generating a signal indicating that a first value of the
physical property is associated with the first spectrum, the first
value being determined using the physical property value associated
with the identified previously recorded spectrum in the
database.
[0011] Implementations can include any or all of the following
features. Multiple spectra can be identified in the database as
being similar to the recorded first spectrum. The method can
further include processing the physical property values associated
with the multiple identified spectra to determine the first
value.
[0012] The physical property can be one selected from the group
consisting of: a layer thickness on the substrate and a step height
on the substrate. The physical property can be one that is
determined using a non-optical method. The method can further
include establishing the database before the steps of recording,
identifying and assigning are performed. Establishing the database
can include performing a first measurement of a physical property
of the substrate specimen before it is polished, the physical
property being measured in several predefined zones on the
substrate specimen. Establishing the database can include:
polishing the substrate specimen after measuring the thickness, the
polishing being done in several rotations; and collecting spectra
from the substrate specimen while it is being polished.
Establishing the database can include performing a second
measurement of the physical property of the substrate specimen in
the several predefined zones after it is polished. The method can
further include assigning, in the database, the first measured
physical property to a spectrum that was the first one to be
collected during polishing, and assigning the second measured
physical property to a spectrum that was the last one collected.
The method can further include determining interpolation values for
the physical property using the first and second measured
thicknesses and assigning the interpolation values to intermediate
spectra. The interpolation values can be determined by adapting a
mathematical curve to correlated measurements of the physical
property.
[0013] In a second general aspect, a system for determining a
physical property of a substrate includes a polishing machine for
performing a polishing process that alters a physical property of
the substrate of a substrate. The system further includes a module
for recording at least a first spectrum obtained from the substrate
during the polishing process. The system further includes a
database having stored therein multiple spectra, each associated
with a value of the physical property, wherein at least one
spectrum in the database that is similar to the first spectrum is
identified, and the endpoint determining module receives a value
determined using the physical property value associated with the
identified spectrum.
[0014] Implementations can include any or all of the following
features. A database management module can perform the
identification and forward the associated value to the endpoint
determining module. The database management module can further be
used in establishing the database by collecting the spectra and
associating them with the respective physical-property values. An
automated process control module can control the polishing machine
using a preselected value obtained from the database before the
polishing process, the preselected value obtained through a
pre-polish measurement of the substrate. A metrology tool can
determine the physical property values before they are associated
with the respective spectra in the database.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a block diagram of an example system for
determining a physical property of a substrate.
[0016] FIG. 2 is a schematic diagram of an example system for
establishing a database of measured spectra associated with
physical property values of a substrate.
[0017] FIG. 3 is an example graph of two physical properties versus
wafer diameter.
[0018] FIG. 4 is a flow chart of an example process for polishing a
substrate to a particular thickness.
[0019] FIG. 5 is an example graph of thickness versus number of
polishing rotations.
[0020] FIG. 6 is a block diagram of an example system that measures
a physical characteristic of a patterned wafer.
[0021] FIG. 7 is a schematic diagram of an example generic computer
system.
[0022] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0023] FIG. 1 is a block diagram of an example system for
determining a physical property of a patterned substrate before,
during, and/or after polishing. For example, the substrate may be a
wafer that includes integrated circuitry. Particularly, the
patterned substrate may include active regions and trench regions,
which are well-known in the area of semiconductor manufacturing. As
is also well-known, the substrate may be covered by an oxide layer
or another dielectric layer that covers both the active regions and
the trench regions. The apparatus can be used for determining a
thickness of a layer on a substrate, for example an oxide layer, by
recording a spectrum from the substrate being polished and finding
one or more matching spectra in a database of previously measured
spectra.
[0024] A polishing machine 102 polishes the substrate using
conventional polishing techniques. An automated process control
module 104 controls the polishing machine 102 to start the
polishing and may define parameters for the process. Alternatively,
a process other than polishing may be performed, such as deposition
(e.g., chemical vapor deposition), removal processes (e.g., wet and
dry etching), or patterning (e.g., lithography).
[0025] The system includes a module using physical property 106
that will use a physical property determined for the substrate. In
one implementation, the module 106 records a spectrum reflected
from the substrate and matches that spectrum with previously
recorded spectra in a database. The module using physical property
106 may include, for example, a light source and a spectrum
recorder. In one implementation, the module using physical property
106 can be configured to interrupt or otherwise alter the polishing
process (or other process) when the substrate reaches a certain
value of a physical property. In another implementation, the
spectrum can be obtained from the substrate in another way, for
example by being transmitted through the substrate.
[0026] A database management module 108 receives a spectrum
recorded by the module using physical property 106. If the spectrum
is recorded during a setup process for a database 110, the module
108 can record the spectrum in the database 110, where it can then
be used for determining one or more physical properties for a
substrate. In one implementation, and particularly after receiving
a spectrum as part of a property-determining operation, the module
108 compares that spectrum with previously recorded spectra that
have physical property values associated with them, selects a
matching one of the spectra, and generates a signal indicating the
identified physical property value. The database management module
108 retrieves the identified physical property value from the
database 110.
[0027] The database 110 stores previously recorded spectra
reflected from one or more substrates in connection with one or
more previous processes. In addition, the database 110 stores
measured physical property values associated with the recorded
spectra. A reference metrology tool 112 measures the physical
property values to be associated with the previously recorded
spectra. For example, a spectrum recorded before (or at the
beginning of) polishing is associated with a physical property
measurement made before polishing and a spectrum recorded after (or
at the end of) polishing is associated with a physical property
measurement made after polishing. Physical property values
corresponding to spectra with characteristics between those of the
beginning spectrum and the end spectrum may be extrapolated between
the beginning physical property value and the end physical property
value.
[0028] The database management module 108 identifies one or more
previously recorded spectra that are similar to the spectrum
recorded by the module using physical property 106 and generates a
signal that indicates the physical property value associated with
the similar spectra. Alternatively, a physical property value may
be extrapolated based on the similar spectrum, the recorded
spectra, and the physical property value associated with the
similar spectra. The signal including the physical property value
may be forwarded to the module using physical property 106 or the
automated process control module 104 and used to control the
polishing machine 102.
[0029] In another implementation, the signal is generated by a
separate signal generating module 114. This module can receive an
instruction from the database management module as to what value is
to be output. In response to receiving that communication, the
module 114 can generate a signal that identifies the value and
indicates that it is associated with the obtained spectrum. For
example, the module 114 can generate such a signal for receipt by
the module using physical property 106 or by the automated process
control module 104.
[0030] For example, the measured physical property may be a step
height of structures on the surface of the substrate and may be
provided by a profilometer, such as a high resolution profiler
(HRP). In addition, the recorded spectra may indicate by optical
interferometry a thickness of a borophosphosilicate glass (BPSG)
layer of the substrate. The spectrum reflected by the BPSG during
the polishing process is matched with a similar spectrum previously
recorded to determine a previously measured HRP step height.
Reflected spectra may be repeatedly matched to various ones of
previously recorded spectra until a desired HRP step height is
achieved from the polishing process. After the database 110 of
spectra and physical property values is established, profilometer
measurements may be provided without the presence of a profilometer
during the polishing process. In addition, multiple spectra may be
recorded that correspond to multiple zones of the substrate. The
recorded spectra may be used to determine multiple physical
property values associated with the multiple zones. The multiple
values may be of a common property or of two or more different
properties. For example, any physical property that is manifested
in a spectrum generated from a substrate can be determined.
[0031] When multiple spectra are identified in the database as
being similar to the spectrum obtained from the substrate, their
corresponding physical-property values can be processed to generate
the sought value. For example, the system can calculate the average
of the values associated with the identified spectra. As another
example, the values can be statistically processed to determine a
representative value, such as with a least squares method or by
eliminating extreme maxima or minima among the values.
[0032] FIG. 2 shows a schematic diagram of an example system 200
for generating the database by identifying one or more physical
property values associated with multiple zones 204a-d of a
substrate 202. A physical property measurement is made for each of
the zones 204a-d, such as step heights of the zones 204a-d before a
polishing begins. In certain implementations, another physical
property may be measured. Moreover, multiple measurements can be
made for a single zones, and these measurements can then be used in
determining the property value. For example, the value can be
determined as an average of all the taken measurements for the
zone. As another example, this processing can take into account a
distribution of the values and the average can be skewed
accordingly. In each of the implementations, a large number of
values may be taken in an attempt to pick up a variance in the
measured variable on the wafer.
[0033] A polishing apparatus 206 polishes the substrate 202. The
apparatus 206 includes a light source 208 for producing a light
beam to impinge on the substrate 202, and a detector 210 for
receiving light that is reflected off the substrate 202. For
example, the light source 208 may be a light bulb that produces
white light, such as light that is essentially within the
ultraviolet (UV) to infrared (IR) wavelength range. In selected
embodiments, a wavelength range of 2000-15000 Angstrom (A) may be
used. In some implementations, the light source 208 is a Tungsten,
Xenon, or Mercury lamp. Optionally, light source 208 includes fiber
optics for guiding the produced light beam onto the substrate 202.
The detector 210 may be a spectro-photometer that measures
reflectance from the patterned substrate 202. The detector can have
several elements, and each such element can be dedicated to a
different wavelength range. In some implementations, the detector
210 includes an array of silicon diodes as is well-known. The
detector 210 is capable of measuring reflectance over a range of
wavelengths.
[0034] A reflected light beam emerges from the substrate 202 as a
result of the incident light beam. The reflected light is
preferably detected separately for the various zones 204a-d. The
reflected light beam, as is well-known, consists of light that is
reflected from several different layers in the substrate 202. That
is, when the substrate 202 consists of several layers with
different refractions indices, each boundary between layers may
give rise to a light reflection that contributes to the overall
reflected light beam.
[0035] The detector 210 detects the reflected light beam and
transmits the detected spectrum to a computer that may also control
the light source 208. The detector 210 may detect reflectances from
the substrate 202 over a wavelength interval, for example,
2500-8000 A. For example, the detector 210 transmits information to
the computer that can be graphically displayed as a reflectance
spectrum over the registered wavelength range.
[0036] The reflected light beam for each of the regions 204a-d is
detected by detector 210 and corresponding spectra are transmitted
to the computer. These measured reflectances can be used to build a
database of measured spectra and associated physical
characteristics for the patterned substrate 202.
[0037] The substrate 202 is measured again after the polishing
process to obtain new step heights (or another physical property)
of the zones 204a-d. These pre-polishing and post-polishing
measurements will be used in generating the database. Spectra 214
taken during a first rotation of the polishing apparatus 206 and
spectra 216 taken during a last rotation of the polishing apparatus
206 are associated with physical property values 218 measured
before and after the polishing, respectively. In certain
implementations, this establishes a database of spectra and
associated physical property values that may be used to identify
physical property values of subsequent similar substrates during
polishing processes.
[0038] FIG. 3 shows an example graph 300 of step height and
thickness versus wafer diameter. Here, wafer diameter, shown on the
horizontal axis, is measured in millimeters from the center of the
substrate in a positive and a negative direction. The step height
physical property is measured in Angstroms and is shown on the left
vertical axis. The thickness is measured in nanometers and is shown
on the right vertical axis. Line 302 in the graph represents a
height physical property of a substrate as measured by an HRP
metrology tool. For example, this tool can be included in the
reference metrology tool 112 (FIG. 1). Particularly, each of the
discrete data points shown in the line 302 here corresponds to a
measurement done with the tool, and the remainder of the line
represents an interpolation between these points. Line 304, in
turn, is a height as determined by matching spectra recorded from
the substrate with previously recorded spectra having associated
height measurements. These previously recorded spectra and their
associated physical characteristic values (here, thicknesses) can
be stored in the database 110 (FIG. 1). The matching of spectra
from the current substrate with previously recorded spectra allow
height measurements to be determined for the recorded spectra as
shown by the line 304.
[0039] More than one physical property of the substrate can be
determined using the spectra recorded from the substrate. For
example, a layer thickness can be determined in addition to, or in
lieu of, the step height as will now be described. Line 306 is a
thickness physical property as determined by an optical thickness
metrology tool. Similarly to the above description, the data points
can be determined by the optical thickness metrology tool and this
tool can be included in the metrology tool 112 (FIG. 1). Line 308
is a thickness as determined by matching spectra recorded from the
substrate with previously recorded spectra having associated
thickness measurements. The matching of spectra from the current
substrate with previously recorded spectra allow thickness values
to be determined for the recorded spectra as shown by the line 308.
Particularly, the spectra used in determining the line 304 can be
used for determining the line 308. Also, each of the previously
recorded spectra can have property values for multiple types of
properties associated therewith. For example, assume that each of
the individual step height values that makes up the line 304 is
identified by a match with a separate spectrum in the database 110
(FIG. 1). Each of these separate spectra in the database can also
have thickness values associated with it, and these thickness
values are in this example used to obtain the respective thickness
values that make up the line 308. For example, when a match is
found in the database, one or more of the corresponding property
values associated therewith can be retrieved.
[0040] FIG. 4 shows an example process 400 for polishing a
substrate using a database of spectra and physical property values.
Process 400 measures (402) a wafer during polishing. In addition,
process 400 extracts pre and post polish thickness profiles. For
example, the thickness profiles may be derived from spectra
recorded at the beginning and end of the polishing. A process
control engine presets (404) polish parameters for a next wafer
based on the pre and post polish profiles of the first wafer. The
process control engine may preset (404) the polish parameters again
for one or more wafers based on the pre and post thickness profiles
of the first wafer. Thus, polishing parameters for a next wafer to
be polished can be set using profiles for a previously polished
wafer.
[0041] FIG. 5 shows an example graph 500 of thickness versus
polishing rotations. The horizontal axis ranges from 0 to 60
rotations of a polishing machine that is operating on a substrate.
Alternatively, the horizontal axis could be measured in units of
time for the polishing process. The vertical axis represents the
thickness of the substrate in Angstroms. Data points 502 represent
measurements of the thickness taken at each rotation of the
polishing machine for a particular location on the substrate, a
middle-center zone. Particularly, there are several measurements in
this zone for each rotation. An equation of a line 504 is
determined based on the data points 502, such as a line determined
by linear regression. In addition, a correlation factor or goodness
of fit calculation is made to determine how well the determined
line 504 represents the data points 502. The line 504 may be used,
for example, to calculate thickness values for rotation values
where spectra were not recorded.
[0042] The line 504 is of the form:
y=kx+c,
where y is the thickness, x is the number if rotations, k is a
removal rate per rotation, and c is the initial thickness of the
substrate. Thicknesses in the regions outside of the measured
thicknesses may be interpolated using the equation above. For
example, a thickness less than the smallest measured thickness,
such as 2500, may be achieved with a number of polishing rotations
greater than the largest measured rotation, such as 60.25. The
number of rotations (i.e., 60.25) needed to reach a thickness of
2500 is determined using the equation of the line 504.
[0043] Each data point 502 corresponds to a measured spectrum. Thus
data points 502 near the left side of the graph 500 correspond to a
spectrum measured at the beginning of the polishing process, such
as the spectrum 214, and data points 502 near the right side of the
graph 500 correspond to a spectrum measured at the end of the
polishing process, such as the spectrum 216. Thicknesses associated
with previously recorded spectra stored in a database are
retrieved. The thicknesses and their associated number of polishing
rotations are shown here in the graph 500.
[0044] The equation above may also be used to determine the amount
of wear on a polishing device (e.g., a polishing pad). As the
polishing device begins to wear, the thickness determined begins to
stray from the line 504 determined by the equation. Less material
is removed as the polishing device wears down and the thickness
determined by, for example, optical thickness metrology is greater
than the thickness as calculated by the equation. This causes the
slope of the line 504 (i.e., the polishing rate) to be reduced and
the line 504 flattens out. Accordingly, monitoring this property
during the process can give an indication of whether the process is
progressing normally.
[0045] Implementations described herein can be used with any type
of procedure where one or more physical properties of a substrate
are determined, and not only in connection with a polishing
process, which has been mentioned above as an example.
Nevertheless, as an illustration of a polishing process there will
now be described how a polishing system can be configured and
operated. FIG. 6 shows a chemical mechanical polishing (CMP)
apparatus 20 in which one or more substrates 10 can be polished.
For example, a Shallow Trench Isolation (STI) process could produce
the substrate 10. The CMP apparatus includes a rotatable platen 24
on which is placed a polishing pad 30. This may be a two-layer
polishing pad with a hard durable outer surface or a relatively
soft pad. If substrate 10 is an "eight-inch" (200 millimeter) or
"twelve-inch" (300 millimeter) diameter disk, then the platen and
polishing pads will be about twenty inches or thirty inches in
diameter, respectively. The platen 24 may be connected to a platen
drive motor (not shown). For most polishing processes, the platen
drive motor rotates platen 24 at thirty to two hundred revolutions
per minute, although lower or higher rotational speeds may be
used.
[0046] Polishing pad 30 typically has a backing layer 32 which
abuts the surface of platen 24 and a covering layer 34 which is
used to polish substrate 10. Covering layer 34 is typically harder
than backing layer 32. However, some pads have only a covering
layer and no backing layer. Covering layer 34 may be composed of an
open cell foamed polyurethane or a sheet of polyurethane with a
grooved surface. Backing layer 32 may be composed of compressed
felt fibers leached with urethane. A two-layer polishing pad, with
the covering layer composed of IC-1000 and the backing layer
composed of SUBA-4, is available from Rodel, Inc., of Newark, Del.
(IC-1000 and SUBA-4 are product names of Rodel, Inc.).
[0047] The CMP apparatus 20 may include one or more carrier head
systems 70, optionally mounted on a rotatable multi-head carousel
(not shown). The carrier head system is supported by a support
plate 66. The carrier head system includes a carrier or carrier
head 80. A carrier drive shaft 74 connects a carrier head rotation
motor 76 to each carrier head 80 so that each carrier head can
independently rotate about it own axis. In addition, each carrier
head 80 independently laterally oscillates. For example, a slider
(not shown) may support each drive shaft in its associated radial
slot, and a radial drive motor (not shown) may move the slider to
laterally oscillate the carrier head.
[0048] The carrier head 80 performs several mechanical functions.
Generally, the carrier head holds the substrate against the
polishing pad, evenly distributes a downward pressure across the
back surface of the substrate, transfers torque from the drive
shaft to the substrate, and ensures that the substrate does not
slip out from beneath the carrier head during polishing
operations.
[0049] Carrier head 80 may include a flexible membrane 82 that
provides a mounting surface for substrate 10, and a retaining ring
84 to retain the substrate beneath the mounting surface.
[0050] Pressurization of a chamber 86 defined by flexible membrane
82 forces the substrate against the polishing pad. Retaining ring
84 has a lower surface 88 which may reflect light.
[0051] A slurry 38 containing a reactive agent and a
chemically-reactive catalyzer (e.g., potassium hydroxide for oxide
polishing) may be supplied to the surface of polishing pad 30 by a
slurry supply port or combined slurry/rinse arm 39. If polishing
pad 30 is a standard pad, slurry 38 may also include abrasive
particles (e.g., silicon dioxide for oxide polishing).
[0052] In operation, the platen is rotated about its central axis
25, and the carrier head is rotated about its central axis 81 and
translated laterally across the surface of the polishing pad. A
hole 26 is formed in platen 24 and a transparent window 36 is
formed in a portion of polishing pad 30 overlying the hole. Hole 26
and transparent window 36 are positioned such that they have a view
of substrate 10 during a portion of the platen's rotation,
regardless of the translational position of the carrier head.
[0053] An optical system 40 is secured to platen 24 generally
beneath hole 26 and rotates with the platen. The system includes
the light source 44 and the detector 46. The light source generates
a light beam 42 which propagates through transparent window 36 and
slurry 38 to impinge upon the exposed surface of substrate 10. The
light beam 42 is projected from light source 44 at an angle a from
an axis normal to the surface of substrate 10, i.e., at an angle a
from axes 25 and 81. In addition, if the hole 26 and window 36 are
elongated, a beam expander (not illustrated) may be positioned in
the path of the light beam to expand the light beam along the
elongated axis of the window.
[0054] Light source 44 may operate continuously. Alternately, it
may be activated to generate light beam 42 during a time when hole
26 is generally adjacent substrate 10. CMP apparatus 20 may include
a position sensor 160, such as an optical interrupter, to sense
when window 36 is near the substrate. For example, the optical
interrupter could be mounted at a fixed point opposite carrier head
80. A flag 162 is attached to the periphery of the platen. The
point of attachment and length of flag 162 is selected so that it
interrupts the optical signal of sensor 160 from a time shortly
before window 36 sweeps beneath carrier head 80 to a time shortly
thereafter. The output signal from detector 46 may be measured and
stored while the optical signal of sensor 160 is interrupted.
[0055] In operation, light source 44 may generate the light beam 42
to impinge on the substrate 10. The detector 46, in turn, receives
a light beam 56 that is reflected off the substrate 10. The
detector 46 may transmit corresponding information about the
reflected light beam 56 to the computer 48. Information received or
processed by the computer 48 may be output on the display device
49. For example, the computer determines an endpoint as described
above. When the computer 48 determines that the endpoint of the CMP
process has been reached, it can terminate the CMP by deactivating
the CMP apparatus 20.
[0056] FIG. 7 is a schematic diagram of an example of a generic
computer system 700. The system 700 can be used for the operations
described in association with the methods described herein. For
example, the system 700 may be included in either or all of the
system 100 and the apparatus 200.
[0057] The system 700 includes a processor 710, a memory 720, a
storage device 730, and an input/output device 740. Each of the
components 710, 720, 730, and 740 are interconnected using a system
bus 750. The processor 710 is capable of processing instructions
for execution within the system 700. In one implementation, the
processor 710 is a single-threaded processor. In another
implementation, the processor 710 is a multi-threaded processor.
The processor 710 is capable of processing instructions stored in
the memory 720 or on the storage device 730 to display graphical
information for a user interface on the input/output device
740.
[0058] The memory 720 stores information within the system 700. In
one implementation, the memory 720 is a computer-readable medium.
In one implementation, the memory 720 is a volatile memory unit. In
another implementation, the memory 720 is a non-volatile memory
unit.
[0059] The storage device 730 is capable of providing mass storage
for the system 700. In one implementation, the storage device 730
is a computer-readable medium. In various different
implementations, the storage device 730 may be a floppy disk
device, a hard disk device, an optical disk device, or a tape
device.
[0060] The input/output device 740 provides input/output operations
for the system 700. In one implementation, the input/output device
740 includes a keyboard and/or pointing device. In another
implementation, the input/output device 740 includes a display unit
for displaying graphical user interfaces.
[0061] The features described can be implemented in digital
electronic circuitry, or in computer hardware, firmware, software,
or in combinations of them. The apparatus can be implemented in a
computer program product tangibly embodied in an information
carrier, e.g., in a machine-readable storage device or in a
propagated signal, for execution by a programmable processor; and
method steps can be performed by a programmable processor executing
a program of instructions to perform functions of the described
implementations by operating on input data and generating output.
The described features can be implemented advantageously in one or
more computer programs that are executable on a programmable system
including at least one programmable processor coupled to receive
data and instructions from, and to transmit data and instructions
to, a data storage system, at least one input device, and at least
one output device. A computer program is a set of instructions that
can be used, directly or indirectly, in a computer to perform a
certain activity or bring about a certain result. A computer
program can be written in any form of programming language,
including compiled or interpreted languages, and it can be deployed
in any form, including as a stand-alone program or as a module,
component, subroutine, or other unit suitable for use in a
computing environment.
[0062] Suitable processors for the execution of a program of
instructions include, by way of example, both general and special
purpose microprocessors, and the sole processor or one of multiple
processors of any kind of computer. Generally, a processor will
receive instructions and data from a read-only memory or a random
access memory or both. The essential elements of a computer are a
processor for executing instructions and one or more memories for
storing instructions and data. Generally, a computer will also
include, or be operatively coupled to communicate with, one or more
mass storage devices for storing data files; such devices include
magnetic disks, such as internal hard disks and removable disks;
magneto-optical disks; and optical disks. Storage devices suitable
for tangibly embodying computer program instructions and data
include all forms of non-volatile memory, including by way of
example semiconductor memory devices, such as EPROM, EEPROM, and
flash memory devices; magnetic disks such as internal hard disks
and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM
disks. The processor and the memory can be supplemented by, or
incorporated in, ASICs (application-specific integrated
circuits).
[0063] To provide for interaction with a user, the features can be
implemented on a computer having a display device such as a CRT
(cathode ray tube) or LCD (liquid crystal display) monitor for
displaying information to the user and a keyboard and a pointing
device such as a mouse or a trackball by which the user can provide
input to the computer.
[0064] The features can be implemented in a computer system that
includes a back-end component, such as a data server, or that
includes a middleware component, such as an application server or
an Internet server, or that includes a front-end component, such as
a client computer having a graphical user interface or an Internet
browser, or any combination of them. The components of the system
can be connected by any form or medium of digital data
communication such as a communication network. Examples of
communication networks include, e.g., a LAN, a WAN, and the
computers and networks forming the Internet.
[0065] The computer system can include clients and servers. A
client and server are generally remote from each other and
typically interact through a network, such as the described one.
The relationship of client and server arises by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other.
[0066] Although a few implementations have been described in detail
above, other modifications are possible. In addition, the logic
flows depicted in the figures do not require the particular order
shown, or sequential order, to achieve desirable results. In
addition, other steps may be provided, or steps may be eliminated,
from the described flows, and other components may be added to, or
removed from, the described systems. Accordingly, other
implementations are within the scope of the following claims.
[0067] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
* * * * *