U.S. patent application number 17/010183 was filed with the patent office on 2021-01-28 for polishing-amount simulation method for buffing, and buffing apparatus.
The applicant listed for this patent is EBARA CORPORATION. Invention is credited to Itsuki Kobata, Toshio Mizuno, Kuniaki Yamaguchi.
Application Number | 20210023672 17/010183 |
Document ID | / |
Family ID | 1000005146903 |
Filed Date | 2021-01-28 |
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United States Patent
Application |
20210023672 |
Kind Code |
A1 |
Yamaguchi; Kuniaki ; et
al. |
January 28, 2021 |
POLISHING-AMOUNT SIMULATION METHOD FOR BUFFING, AND BUFFING
APPARATUS
Abstract
The invention simulates polishing amount taking into account
pressure concentration that occurs in the vicinity of the edge of a
substrate when a small-diameter buffing pad overhangs the substrate
to be buffed. One embodiment of the invention provides a method for
simulating polishing amount in a case where a polishing pad of a
smaller size than a substrate is used to buff the substrate. The
method includes measuring distributions of pressure that is applied
from the polishing pad to the substrate according to each overhang
amount of the polishing pad relative to the substrate by using a
pressure sensor, and correcting the pressure that is used in the
polishing amount simulation in accordance with the overhang amounts
and the measured pressure distributions.
Inventors: |
Yamaguchi; Kuniaki; (Tokyo,
JP) ; Kobata; Itsuki; (Tokyo, JP) ; Mizuno;
Toshio; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EBARA CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
1000005146903 |
Appl. No.: |
17/010183 |
Filed: |
September 2, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15514785 |
Mar 27, 2017 |
10792782 |
|
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PCT/JP2016/051206 |
Jan 18, 2016 |
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17010183 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/10 20130101;
H01L 22/20 20130101; H01L 21/30625 20130101; B24B 37/005 20130101;
B24B 49/16 20130101; B24B 37/34 20130101 |
International
Class: |
B24B 37/005 20060101
B24B037/005; B24B 49/16 20060101 B24B049/16; B24B 37/10 20060101
B24B037/10; B24B 37/34 20060101 B24B037/34; H01L 21/306 20060101
H01L021/306; H01L 21/66 20060101 H01L021/66 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 2015 |
JP |
2015-007699 |
Claims
1-8. (canceled)
9. A buffing apparatus for buffing a substrate by using a polishing
pad of a smaller size than the substrate, wherein: the buffing
apparatus is configured so that a part of the polishing pad
oscillates over the substrate during buffing, and the buffing
apparatus includes a simulation section configured to simulate
polishing amount of the substrate on a given buffing condition.
10. The buffing apparatus of claim 9, wherein the simulation
section performs pressure correction for correcting an effect of
pressure concentration that occurs when the polishing pad
oscillates over the substrate.
11. The buffing apparatus of claim 9, wherein the simulation
section calculates a buffing condition that is required to achieve
a given target polishing amount.
12. The buffing apparatus of claim 11, wherein the buffing
condition to be calculated is oscillation velocity of the polishing
pad.
13. The buffing apparatus of claim 11, including a sensor for
measuring the polishing amount of the substrate, wherein the
simulation section compares the measured polishing amount of the
substrate that is buffed on the calculated buffing condition with
the target polishing amount and, if the target polishing amount is
not achieved, calculates a required buffing condition based on the
measured polishing amount and the target polishing amount.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing-amount
simulation method for buffing, and more specifically, to a method
for calculating a pressure correction value for the
polishing-amount simulation for buffing.
BACKGROUND ART
[0002] Semiconductor devices become more and more highly integrated
in late years, and circuit wiring and integrated devices are
accordingly miniaturized. This trend has generated a need for
planarization of semiconductor wafer surfaces by polishing the
surfaces coated with, for example, metal films. Planarization
methods include polishing by a chemical mechanical polishing (CMP)
apparatus. The chemical mechanical polishing apparatus has
polishing members (polishing cloth, a polishing pad, etc.) and
holding member (a top ring, a polishing head, a chuck, etc.) for
holding a substrate such as a semiconductor wafer. The apparatus
presses the surface (surface to be polished) of the substrate
against the surface of the polishing member, and brings the
polishing member and the substrate into relative movement while
supplying a polishing liquid (abrasive solution, chemical solution,
slurry, deionized water or the like) into between the polishing
member and the substrate. In this manner, the apparatus polishes
and planarizes the surface of the substrate. It is known that the
chemical mechanical polishing apparatus achieves excellent
polishing performance as a result of the combination of chemical
and mechanical polishing actions.
[0003] In common chemical mechanical polishing, the to-be-polished
surface of a substrate held by a top ring is pressed against a
polishing surface having a larger diameter than the substrate. A
polishing table and the top ring are then rotated while slurry as a
polishing solution is supplied onto the polishing surface. The
polishing surface and the to-be-polished surface thus come into
relative sliding movement, which polishes the to-be-polished
surface of the substrate.
[0004] In late years, the planarizing technology including CMP
deals with a wide variety of materials to be polished and is
required to satisfy growing demands for high polishing performance
(for example, planarity, less polishing damage, and also
productivity). Besides, the miniaturization of semiconductor
devices creates demands for higher polishing performance and
purity. In such a situation, buffing is occasionally performed in
the CMP apparatus to buff a substrate by means of a buffing pad of
a smaller size than the substrate to be processed. In general, a
buffing pad of a smaller size than a substrate to be processed is
excellent in controllability in that such a pad makes it possible
to planarize the unevenness that is locally generated in the
substrate, polish only a particular area of the substrate, and
adjust the polishing amount according to the position of the
substrate.
[0005] To enhance process efficiency and accuracy of planarity in
the CMP process, it is important to accurately estimate polishing
amount and efficiently optimize polishing conditions (such as
control parameters of the polishing apparatus) based on the
estimation. Under the situation, several simulation methods related
to CMP have been proposed.
[0006] With regard to simulation for the polishing, the estimation
of polishing amount is fundamental. In the conventional
polishing-related simulations of various kinds, the polishing
amount is estimated by Preston's formula h.varies.pvt, where h
represents polishing rate or polishing amount for polishing a
substrate (to-be-polished object); p represents load or pressure
applied to the substrate; v represents contact relative velocity
between a polishing member and the substrate or contact relative
velocity at an area, the polishing amount in which is calculated;
and t represents polishing time. In other words, the polishing
amount is proportional to the product of the pressure p, the
contact relative velocity v, and the polishing time t. In this
specification, the term "polishing amount" also means polishing
amount at each position of the substrate and is referred to also as
a polishing profile.
SUMMARY OF INVENTION
Technical Problem
[0007] In the buffing is carried out using a buffing pad with a
smaller diameter than a substrate, such as a semiconductor wafer,
when the entire surface of the buffing pad is within a periphery of
the substrate, the pressure applied from the buffing pad to the
substrate is substantially even. As is known, however, when the
buffing pad overhangs the substrate, that is, when the buffing pad
partially protrudes over the substrate, pressure concentration
occurs in the vicinity of an edge of the substrate. For this
reason, the simulation of polishing amount based on Preston's
formula requires consideration of effects of the pressure
concentration that occurs in the vicinity of the substrate edge
when the buffing pad overhangs the substrate.
[0008] In this light, an object of the present invention is to
simulate polishing amount, taking into account pressure
concentration that occurs in vicinity of a substrate edge when a
small-diameter buffing pad overhangs the substrate to be buffed.
Another object of the invention is to determine optimal buffing
conditions based on the polishing amount simulation.
Solution to Problem
[0009] A first embodiment provides a method for simulating
polishing amount in a case where a polishing pad of a smaller size
than a substrate is used to buff the substrate. The method includes
the steps of measuring distributions of pressure that is applied
from the polishing pad to the substrate according to each overhang
amount of the polishing pad relative to the substrate by using a
pressure sensor, and correcting the pressure that is used in the
polishing amount simulation in accordance with the overhang amount
and the measured pressure distributions.
[0010] A second embodiment provides the method according to the
first embodiment, the method including quantifying the measured
distributions of the pressure applied to the substrate with respect
to each overhang amount of the polishing pad relative to the
substrate; one-dimensionalizing the quantified pressure
distributions with respect to the each overhang amount along a
radial direction of the substrate; summing the one-dimensionalized
pressure distributions of the each overhang amount in the radial
direction of the substrate; and determining a pressure correction
value by dividing the total of the pressure distributions of the
polishing pad in the each radial position of the substrate by
distance of the polishing pad on the substrate.
[0011] A third embodiment provides a method for simulating
polishing amount in a case where a polishing pad of a smaller size
than a substrate is used to buff the substrate. The method
simulates polishing amount in a case where a part of the polishing
pad oscillates over the substrate during buffing.
[0012] A fourth embodiment provides the method according to the
third embodiment, wherein the polishing amount is calculated using
a pressure correction value for correcting an effect of pressure
concentration that occurs when the polishing pad oscillates over
the substrate.
[0013] A fifth embodiment provides the method according to the
third or fourth embodiment, wherein a buffing condition that is
required to achieve a given target polishing amount is
calculated.
[0014] A sixth embodiment provides the method according to the
fifth embodiment, wherein the buffing condition to be calculated is
oscillation velocity of the polishing pad.
[0015] A seventh embodiment provides a computer program including a
command for carrying out the simulation according to any one of the
third to sixth embodiments.
[0016] An eighth embodiment provides a storage medium that stores
the computer program of the seventh embodiment.
[0017] A ninth embodiment provides a buffing apparatus for buffing
a substrate by using a polishing pad of a smaller size than the
substrate, wherein the buffing apparatus is configured so that a
part of the polishing pad oscillates over the substrate during
buffing, and the buffing apparatus includes a simulation section
configured to simulate polishing amount of the substrate on a given
buffing condition.
[0018] A tenth embodiment provides the buffing apparatus according
to the ninth embodiment, wherein the simulation section performs
pressure correction for correcting an effect of pressure
concentration that occurs when the polishing pad oscillates over
the substrate.
[0019] An eleventh embodiment provides the buffing apparatus
according to the ninth or tenth embodiment, wherein the simulation
section calculates a buffing condition that is required to achieve
a given target polishing amount.
[0020] A twelfth embodiment provides the buffing apparatus
according to the eleventh embodiment, wherein the buffing condition
to be calculated is oscillation velocity of the polishing pad.
[0021] A thirteenth embodiment provides the buffing apparatus
according to the eleventh or twelfth embodiment, the buffing
apparatus including a sensor for measuring the polishing amount of
the substrate, wherein the simulation section compares the measured
polishing amount of the substrate that is buffed on the calculated
buffing condition with the target polishing amount and, if the
target polishing amount is not achieved, calculates a required
buffing condition based on the measured polishing amount and the
target polishing amount.
[0022] A fourteenth embodiment provides a method for determining a
correction value of pressure that is applied from a polishing pad
to a substrate, the correction value being used to simulate
polishing amount in a case where the polishing pad of a smaller
size than the substrate is used to buff the substrate, wherein the
method includes the steps of: measuring distributions of pressure
that is applied from the polishing pad to the substrate according
to each overhang amount of the polishing pad relative to the
substrate by using a pressure sensor; and determining the pressure
correction value based on the overhang amount and the measured
pressure distribution.
[0023] A fifteenth embodiment provides the method according to the
fourteenth embodiment, the method including the steps of:
quantifying the measured distributions of the pressure applied to
the substrate with respect to each overhang amount of the polishing
pad relative to the substrate; one-dimensionalizing the quantified
pressure distributions with respect to the each overhang amount
along a radial direction of the substrate; summing the
one-dimensionalized pressure distributions of the each overhang
amount in the radial direction of the substrate; and determining a
pressure correction value by dividing the total of the pressure
distributions of the polishing pad in the each radial position of
the substrate by distance of the polishing pad on the
substrate.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a side view of a wafer W being buffed with a
buffing pad and also illustrates a graph showing a wiping distance
on a wafer position.
[0025] FIG. 2 shows pressure concentration that occurs in a wafer
edge when the wafer W is buffed with the buffing pad.
[0026] FIG. 3 shows layout during measurement of amount of pressure
applied from the buffing pad to the wafer W.
[0027] FIG. 4 schematically show results of the pressure
measurements illustrated in FIG. 3.
[0028] FIG. 5 shows a result of quantification of the amount of
pressure applied from the buffing pad to the wafer W.
[0029] FIG. 6 shows a result of quantification of the amount of
pressure applied from the buffing pad to the wafer W.
[0030] FIG. 7 is a graph showing a pressure ratio on the wafer
position with respect to each overhang amount.
[0031] FIG. 8 is a graph showing a pressure ratio on the wafer
position with respect to each working pressure.
[0032] FIG. 9 shows a map of a pressure ratio, in which a
horizontal axis represents a center position of the buffing pad on
the wafer, and a vertical axis represents the wafer position.
[0033] FIG. 10 is a graph showing a pressure ratio on the center
position of the buffing pad on the wafer with respect to each wafer
position.
[0034] FIG. 11 is a graph showing a pressure ratio to the wafer
position.
[0035] FIG. 12 is a graph showing an example of a polishing profile
in which pressure correction applied during overhang is made.
[0036] FIG. 13 is a graph showing polishing amount in a case where
buffing is actually carried out on the same conditions except that
different pressures A, B and C are applied.
[0037] FIG. 14 is a graph showing pressure coefficients obtained
under the pressures A, B and C illustrated in FIG. 13.
[0038] FIG. 15 shows examples of target polishing profiles of the
wafer.
[0039] FIG. 16 shows a state in which an oscillation zone where the
buffing pad oscillates from the center of the wafer toward the edge
of the wafer is evenly divided into eight, and also shows a
pressure correction zone and an oscillation velocity correction
zone.
[0040] FIG. 17 is a schematic view showing a method for calculating
the oscillation-velocity correction value according to one
embodiment.
[0041] FIG. 18 is a schematic view showing a method for calculating
the oscillation-velocity correction value according to one
embodiment.
[0042] FIG. 19 is a schematic view showing a buffing apparatus
according to one embodiment.
[0043] FIG. 20 is a flowchart showing the steps of buffing
simulation according to one embodiment.
[0044] FIG. 21 is a flowchart showing the steps of buffing using
the buffing simulation according to one embodiment.
DESCRIPTION OF EMBODIMENTS
[0045] Embodiments of a method for simulating polishing amount
according to the present invention will be explained below with
reference to the attached drawings. In the attached drawings,
identical or similar components are provided with identical or
similar reference marks, and overlapping descriptions will be
omitted in the detailed description. Features described in each
embodiment can be applied to another embodiment as long as there is
no contradiction therebetween.
[0046] When buffing is carried out by oscillating a buffing pad 502
relative to a wafer W (substrate) at a constant rate while the
wafer W and the buffing pad 502 are being rotated at respective
constant rotational speeds, a wiping distance between the buffing
pad 502 and the wafer W is just as shown in FIG. 1.
[0047] FIG. 1 is a schematic side view of the buffing pad 502
buffing the wafer W while oscillating on the wafer W. Illustrated
under the side view is a graph showing the wiping distance between
the buffing pad 502 and the wafer W relative to a position of the
wafer W. As illustrated in FIG. 1, when the buffing pad 502
overhangs the wafer W, the wiping distance is decreased toward an
edge of the wafer W.
[0048] The wiping distance is a product of a contact relative
velocity between the buffing pad 502 and the wafer W, and a
processing time. Polishing amount therefore can be calculated from
Preston's formula by multiplying the wiping distance by pressure
that is applied from the buffing pad 502 to the wafer W.
[0049] When the buffing pad 502 is completely within a periphery of
the wafer W, the pressure of the buffing pad 502 is considered to
be substantially even. When the buffing pad 502 overhangs the wafer
W, however, pressure concentration occurs in the vicinity of the
edge of the wafer W as illustrated in FIG. 2.
[0050] FIG. 2 is a schematic side view of the buffing pad 502
buffing the wafer W while oscillating on the wafer W. Arrows in
FIG. 2 denote pressures. The longer arrows represent higher
pressures. In FIG. 2, if the buffing pad 502 is located at a
position indicated by solid lines, the buffing pad 502 is
completely within the periphery of the wafer W, so that the
pressure is substantially even as shown by solid arrows. When the
buffing pad 502 oscillates to a position indicated by broken lines,
however, the buffing pad 502 overhangs the wafer W, which causes
the pressure concentration as shown by broken-line arrows in FIG.
2.
[0051] To achieve accurate simulation of the polishing amount using
Preston's formula, therefore, the pressure concentration needs to
be taken into account.
[0052] One embodiment of the present invention measures pressure
distributions when the buffing pad 502 overhangs the wafer W and
calculates a pressure correction value as below.
[0053] First, the wafer W is set on a buffing table 400. A
sheet-type pressure sensor 1000 (tactile sensor) is placed between
the wafer W and the buffing pad 502. The buffing pad 502 presses
against the wafer W with predetermined force F. The pressure
applied to the wafer W is then measured. FIG. 3 is a side view
showing layout of the buffing table 400, the buffing pad 502, the
sheet-type pressure sensor 1000, and the buffing pad when the
pressure applied to the wafer W is measured. The pressure
distributions are measured with respect to each overhang amount
while the overhang amount is altered by changing the position of
the buffing pad 502 relative to the wafer W.
[0054] FIG. 4 schematically show the pressure distributions
measured by the sheet-type pressure sensor. FIG. 4 schematically
respectively show, as an example, the pressure distributions
measured when the overhang amounts are zero percent, 20 percent,
and 40 percent. The percentage of the overhang amount here means
the ratio of overhang amount of the buffing pad 502 against the
diameter of the wafer W. For example, a 20 percent overhang amount
means that 20 percent of the diameter of the buffing pad 502 is in
the outer side of the wafer W. If the buffing pad has a diameter of
100 mm, the diameter of the buffing pad protrudes over the wafer W
by 20 mm. In each of FIG. 4, a solid-line circle represents a
periphery of the buffing pad. Broken-line arcs each represent a
part of the edge of the wafer W.
[0055] When the overhang amount is zero percent as illustrated
(FIG. 4A), the pressure applied from the buffing pad 402 to the
wafer W is substantially even. When the overhang amount is 20
percent (FIG. 4B), the pressure is increased in the vicinity of the
edge of the wafer W and decreased toward an inner side of the wafer
W. Likewise, when the overhang amount is 40 percent (FIG. 4C), the
pressure is increased in the vicinity of the edge of the wafer W
and decreased toward the inner side of the wafer W. In FIG. 4,
"HIGH", "MEDIUM" AND "LOW" indicate relative pressure magnitudes.
The pressure changes in a greater way when the overhang amount is
40 percent as compared to when the overhang amount is 20
percent.
[0056] After the measurement of two-dimensional distribution of the
pressure applied from the buffing pad 502 to the wafer W, the
measured area is divided into plural divisions, and the measured
pressure is quantified with respect to each division.
[0057] FIGS. 5 and 6 show, as examples, results of quantification
of pressure distributions measured when the overhang amount in FIG.
4 are zero percent and 40 percent, respectively. The magnitude of
numerical values is shown in grayscale. In the drawings, darker
grays indicate greater numerical values. A broken-line arc in each
of the drawings represents a periphery of the wafer W.
[0058] As illustrated in FIG. 5, when the overhang amount is zero
percent, pressure distributions are substantially even. The
divisions lying under the buffing pad 502 have a constant value,
for example, 1.0, and are shown in a uniform gray tone as
illustrated.
[0059] FIG. 6 shows a result of quantification of the pressure
distributions measured when the overhang amount is 40 percent. It
is evident from the drawing that, due to the pressure concentration
that occurs in the circumference of the wafer W, the pressure
applied to the circumference of the wafer W is high, and the
pressure is decreased toward the inner side of the wafer W.
[0060] Secondly, the two-dimensional distribution of pressure,
which has been quantified as illustrated in FIGS. 5 and 6, is
one-dimensionalized along a radial direction of the wafer W. More
specifically, an average of numerical values in a direction of rows
(horizontal direction) of FIGS. 5 and 6, or on a so-called wafer
circumference, is calculated. The pressure distributions are then
one-dimensionalized in the radial direction of the wafer W (arrow
directions in FIGS. 5 and 6). In this way, a pressure ratio to the
radial direction of the wafer W is calculated.
[0061] FIG. 7 is a graph showing a pressure ratio to the radial
direction of the wafer W in the case where the overhang (OH) amount
ranges from zero percent to 40 percent, inclusive. A horizontal
axis represents a radial position of the wafer W. The wafer W has a
diameter of 300 mm. That is, 150 mm on the wafer W-position axis
indicates the edge of the wafer W. As illustrated in FIG. 7, the
pressure ratio increases toward the edge of the wafer W in
proportion to the overhang amount.
[0062] The above-described process is repeated, changing the
pressure that is applied from the buffing pad 502 to the wafer W
within an actual working pressure range. As the result, the
pressure ratio to the wafer W position at each working pressure is
obtained.
[0063] FIG. 8 is a graph showing the pressure ratio to the wafer W
position at three working pressures as an example. The graph shows
a case in which the overhang (OH) amount is 20 percent. As is
apparent from FIG. 8, even if the working pressure is changed,
there is no significant change in the pressure ratio to the wafer W
position with respect to each overhang amount. Therefore, the same
pressure ratio can be applied, regardless of the working
pressure.
[0064] In the next, an approximate expression is made from the
pressure ratio to the wafer W position with respect to each working
pressure. Any expressions, such as a polynomial function, an
exponential function, etc., can be used for making the approximate
expression.
[0065] A pressure ratio map relating to the wafer W position and
the buffing pad position on the wafer W is then created from the
approximate expression. FIG. 9 shows a pressure ratio map relating
to the wafer W position and the center position of the buffing pad
on the wafer W. A horizontal axis represents the buffing pad
position on the wafer W. The buffing pad gets closer to the edge of
the wafer W toward the right side of the horizontal axis. A
vertical axis represents the position of the wafer W. An upper end
of the vertical axis denotes the center of the wafer W, whereas a
lower end represents the edge of the wafer W. In FIG. 9, the
pressure ratio is shown in grayscale. The darker the gray is, the
higher the pressure ratio. The pressure ratio is zero in a region
of the wafer W, where the buffing pad 502 does not exist. When the
entire surface of the buffing pad 502 lies completely within the
periphery of the wafer W (when the overhang amount is zero
percent), the pressure ratio is 1.0.
[0066] Pressure ratios at the center position of the buffing pad on
the wafer W are summed up with respect to each corresponding wafer
W position. In other words, the pressure ratios shown in FIG. 9 are
summed up along the horizontal axis. The total of the pressure
ratios with respect to each wafer W position is divided by the
buffing pad diameter (except for the position where the pressure
ratio is zero). A result of the division is a pressure correction
value at each wafer W position.
[0067] FIG. 10 is a graph showing as an example the pressure ratio
to the center position of the buffing pad on the wafer W when wafer
positions are 100 mm, 120 mm, 141 mm, and 148 mm. The pressure
correction value at each wafer position can be calculated by
calculating area on the graph, which is shown in FIG. 10 with
respect to each wafer position, and dividing the area by the
buffing pad diameter (except for the position where the pressure
ratio is zero). As an example, FIG. 10 includes a shaded area that
is the area in the case where the wafer position is 100 mm, and
shows the buffing pad diameter by an arrow.
[0068] FIG. 11 is a graph showing a pressure correction value at
each wafer position, which is calculated as explained in the
description of FIG. 10. As illustrated in FIG. 11, the pressure
correction value becomes larger toward the edge of the wafer.
[0069] Once the pressure correction value at each wafer W position
is determined as described, the pressure correction value can be
applied to the pressure p in Preston's formula h.varies.pvt. The
wiping distance shown in FIG. 1 is a product of oscillation
velocity and polishing time. Polishing amount can be calculated by
multiplying the wiping distance by the pressure p. The
substantially constant pressure p obtained when the buffing pad 502
does not overhang the wafer W is multiplied by the pressure
correction value at each wafer position, to thereby obtain the
polishing amount taking into account the overhang of the buffing
pad 502. To be more precise, the wiping distance shown in FIG. 1 is
multiplied by the substantially constant pressure p and the
pressure correction value shown in FIG. 11, which makes it possible
to simulate the wafer polishing amount, namely, a wafer polishing
profile. FIG. 12 is a graph showing an example of the polishing
profile that is obtained using constant oscillation velocity and
constant pressure, taking into account the pressure correction
applied during overhang.
[0070] According to the present invention, since it is possible to
simulate the wafer polishing amount taking into account the
overhang of the buffing pad, a variety of design parameters of the
buffing apparatus can be estimated and optimized by performing the
simulation. For example, the simulation can be performed for
optimization of the buffing pad diameter, optimization of
rotational speed and rotational speed ratio of the wafer and the
buffing pad, optimization of the area where the buffing pad
oscillates on the wafer, optimization of the buffing pad
oscillation velocity distribution, etc. Technology relating to
pressure measurement, which is disclosed here, is not limited to
the above-described embodiments and can be also applied to a case
in which a pad of a smaller size than a substrate is pressed
against the substrate.
[0071] The following description explains the polishing amount
simulation using the pressure correction value applied during the
buffing pad overhang, and also describes creation of buffing
conditions.
[0072] First, the polishing amount simulation using the pressure
correction value applied during the buffing pad overhang will be
explained. As already discussed, the polishing amount can be
basically calculated in accordance with Preston's formula
h.varies.pvt. In Preston's formula, h is the polishing rate or
polishing amount of a substrate (object to be polished); p is load
or pressure applied to the substrate); v is contact relative
velocity or contact relative velocity of an area, the polishing
amount of which is calculated between a polishing member and the
substrate; and t is polishing time. vt represents a wiping distance
between the substrate (wafer) and the polishing pad (buffing pad).
The polishing amount is basically proportional to the wiping
distance and the pressure. However, the actual polishing amount
varies with conditions. For this reason, empirical values obtained
by actually performing the buffing on various conditions are used
as parameter coefficients to improve accuracy in the polishing
amount simulation. The polishing amount is calculated from a
formula, wiping distance.times.pressure.times.pressure correction
value.times.parameter coefficient.
[0073] In the present embodiment, the buffing pad is rotated and
simultaneously pressed against the wafer in rotation to polish the
wafer. In this process, the buffing pad is oscillated on the wafer
to polish the entire surface of the wafer. The wiping distance can
be calculated by a simulator based on software that is separately
commercially available. The graph of FIG. 1 shows the wiping
distance in the case where the buffing pad rotating at constant
speed is oscillated on the wafer rotating at constant speed.
[0074] The parameter coefficient is calculated from buffing
conditions, features of a dresser, slurry, and a buffing pad that
are used for the buffing, and the like. For example, the parameter
coefficient can be determined by a polishing amount/pressure ratio
as a pressure coefficient that can be one of the parameter
coefficients. FIG. 13 is a graph showing the polishing amount in a
case where the buffing is actually carried out on the same
conditions except that different pressures A, B and C are applied.
The polishing amount shown in FIG. 13 is divided by the pressure to
calculate the pressure coefficient. FIG. 14 shows pressure
coefficients at the pressures A, B and C. In the same manner,
various parameter coefficients can be determined from a slurry flow
rate and dilution rate, the features of the dresser and the buffing
pad, which are used for the buffing, etc. Actual parameter
coefficients can be acquired as below. The coefficient is assumed
as "1" under predetermined baseline conditions (for example, the
pressure is 1 psi; the slurry flow rate is 0.3 L/min; and the
buffing pad is provided with horizontal and vertical grooves in a
contact face with the wafer). Change amounts of the polishing
amount under conditions other than the predetermined baseline
conditions can be used as various parameter coefficients. The
parameter coefficients are previously obtained from a test and
stored in a database.
[0075] If the pressure correction value applied during the buffing
pad overhang is used, the polishing amount can be calculated from
the formula, wiping distance.times.pressure.times.pressure
correction value.times.parameter coefficient. FIG. 12 shows an
example of the polishing amount (also referred to as polishing
profile) that is calculated by the foregoing method.
[0076] The following description explains a method for determining
buffing conditions for acquiring a desired polishing profile by
using the polishing amount simulation. Consideration is given to a
case in which the oscillation velocity of the buffing pad is
determined as a buffing condition for acquiring the desired
polishing profile on the condition that the rotational speed of the
buffing pad, the rotational speed of the wafer, and the pressure
applied from the buffing pad to the wafer are given values that are
set by user.
[0077] FIG. 15 shows examples of target polishing profiles of the
wafer. FIG. 15 illustrates a polishing profile in which the entire
surface of the wafer is planarized, a polishing profile in which
the polishing amount is decreased toward the wafer edge, and a
polishing profile in which the polishing amount is increased toward
the wafer edge. The buffing pad oscillation velocity that is
determined in the following description is for achieving the
polishing profile in which the entire surface of the wafer is
planarized as a target wafer profile.
[0078] First, the polishing profile obtained at constant
oscillation velocity is calculated by the foregoing method on the
buffing conditions (the rotational speed of the buffing pad, the
rotational speed of the wafer, the pressure applied from the
buffing pad to the wafer, etc.) that are set by user. If the
polishing profile is calculated in this way, a planarized polishing
profile cannot be acquired in the vicinity of the wafer edge as
seen in FIG. 12 due to the pressure concentration that occurs
during the overhang and the wiping distance distribution. To solve
this, time duration in which the buffing pad stays on the wafer is
adjusted to obtain such oscillation velocity distributions that the
entire surface of the wafer is planarized.
[0079] To obtain the oscillation velocity distributions of the
buffing pad, the wafer position is divided in a direction from the
center of the wafer toward the edge of the wafer. In the present
embodiment, the oscillation velocity is determined with respect to
each division so that the entire surface of the wafer is
planarized. FIG. 16 shows as an example a state in which an
oscillation zone where the buffing pad oscillates from the center
of the wafer toward the edge of the wafer is evenly divided into
eight. As other embodiments, the number of divisions may be more or
less than eight. The oscillation zone does not have to be evenly
divided and, for example, may be divided so that the divisions are
smaller in the vicinity of the wafer edge.
[0080] Since the buffing pad has constant area, a zone in which the
oscillation velocity is corrected differs from the pressure
correction zone in which the pressure is corrected taking into
account the overhang. In concrete terms, as illustrated in FIG. 16,
the oscillation velocity correction zone begins from where the
buffing pad oscillates from the center toward the edge and enters
the pressure correction zone.
[0081] A method for calculating a correction value of the
oscillation velocity correction zone will be explained below with
reference to FIGS. 17 and 18. FIG. 17 shows, in a lower half of the
drawing, pressure-corrected polishing profiles at positions I, II
and III of the buffing pad oscillating from the center of the wafer
toward the edge of the wafer. Curved lines between I and II and
those between II and III in FIG. 17 correspond to the
pressure-corrected polishing profiles at positions between I and II
and those II and III of the buffing pad. As discussed below, the
correction value of the oscillation zone can be calculated by
synthesizing these polishing profiles.
[0082] To calculate the oscillation-velocity correction value,
oscillation starting points of the pressure-corrected polishing
profiles at the respective positions of the buffing pad are aligned
with one another as shown in FIG. 18. An average of the
pressure-corrected polishing profiles at the respective positions
of the buffing pad with the oscillation starting points aligned is
the correction value of the oscillation velocity. If the buffing
pad oscillates on the wafer so that the velocity distributions are
achieved in accordance with the oscillation-velocity correction
value, a planarized polishing profile can be obtained. The
oscillation velocity of the buffing pad may be successively
controlled so that the oscillation velocity corresponds with the
oscillation-velocity correction value. In the present embodiment,
an oscillation range is divided into eight as described above, and
the oscillation velocity is controlled to be constant within each
division. To that purpose, velocity in each division is calculated
from the obtained oscillation-velocity correction value. In the
embodiment illustrated in FIG. 18, the oscillation velocity in each
division is an average value of the oscillation-velocity correction
values within the corresponding division.
[0083] It is thus possible to calculate the oscillation velocity of
the buffing pad for achieving the target polishing profile (in the
foregoing example, polishing profile for planarizing entire
surface) from the user-set buffing conditions. FIG. 18 shows that
the planarized polishing profile can be obtained if the polishing
amount is simulated based on the user-set buffing conditions and
the user-created buffing pad oscillation velocity.
[0084] A buffing apparatus with the above-described simulation
function will be described below. FIG. 19 shows a schematic
configuration of a buffing apparatus 300A according to one
embodiment. As illustrated in FIG. 19, the buffing apparatus 300A
comprises the table 400 on which the wafer W is set, a head 500
fitted with the buffing pad 502 for processing a to-be-processed
surface of the wafer W, and an arm 600 adapted to the head 500. The
buffing apparatus 300A may further comprise a process liquid supply
system for supplying a process liquid and a conditioning section
for conditioning (dressing) the buffing pad 502. For clear
illustration, the process liquid supply system and the conditioning
section are omitted in FIG. 19. The buffing pad 502 illustrated in
FIG. 19 has a smaller diameter than the wafer W. As an example, if
the wafer W has a diameter of 300 mm, the diameter of the buffing
pad 502 is preferably 100 mm or smaller, and more preferably, falls
in a range between 60 mm and 100 mm. The process liquid may be at
least one of DIW (deionized water), a cleansing liquid, and a
polishing liquid such as slurry. The buffing pad 502 is made of,
for example, a foamed polyurethane-type hard pad, a suede-type soft
pad or sponge. When controlling or reworking is carried out to
reduce dispersion within the wafer surface, a smaller contact area
between the buffing pad 502 and the wafer W makes it possible to
deal with a wider variety of dispersions. In this view, it is
desirable that the buffing pad diameter is small. To be more
precise, the buffing pad diameter is 70 mm or smaller and
preferably 50 mm or smaller. The kind of the buffing pad 502 may be
selected as necessary in consideration of the material of the
substrate and the condition of contamination to be removed. For
example, when the contamination is varied under the surface of the
substrate, the hard pad that makes it easy to apply a physical
force to the contamination, that is, a pad with high hardness or
rigidity, may be used as a pad. When the substrate is a material
having a small mechanical strength, such as a low-k film, the soft
pad may be used to reduce damage to the to-be-processed surface.
When the process liquid is a polishing liquid such as slurry, a
substrate removal rate, contamination removal efficiency, and
whether or not damage occurs are not determined solely by the
hardness or rigidity of the pad. The pad thereby may be selected as
appropriate. The above-listed pads may have surfaces provided with
grooves, such as concentric grooves, X-Y grooves, convoluted
grooves, and radiate grooves. It is also possible to provide the
pad with at least one hole formed through the pad to supply the
process liquid through the hole. The pad may be made of sponge-type
material, such as PVA sponge, into which the process liquid can
penetrate. It is then possible to achieve uniform distributions of
a process liquid flow within the pad surface and quick discharge of
the contamination removed by the processing.
[0085] The table 400 has a mechanism for vacuum-chucking the wafer
W and thus holds the wafer W. The table 400 can be rotated around a
rotation axis A by means of a drive mechanism 410. The table 400
may also be configured to bring the wafer W into angle rotation or
scroll motion by means of the drive mechanism 410. The buffing pad
502 is fitted to a surface of the head 500, which faces the wafer
W. The head 500 is rotatable around a rotation axis B by means of a
drive mechanism, not shown. The head 500 is capable of pressing the
pad 502 against the to-be-processed surface of the wafer W by means
of a drive mechanism, not shown. The arm 600 is capable of
oscillating the head 500 as shown by arrows C within the radius or
diameter of the wafer W. The arm 600 is further capable of
oscillating the head 500 to such a position that the buffing pad
502 faces the conditioning section, not shown.
[0086] As illustrated in FIG. 19, the buffing apparatus 300A
includes a Wet-ITM (In-line Thickness Monitor) 912. The Wet-ITM 912
includes a detection head that is located above the wafer W without
making contact with the wafer W and moves over the entire surface
of the wafer. The Wet-ITM 912 thus can detect (measure) film
thickness distributions (or distributions of information about film
thickness) of the wafer W. The Wet-ITM is useful as an ITM for
taking measurement during the processing. However, the ITM may be
designed to take measurement after the buffing.
[0087] A controller 920 is capable of controlling various
operations of the buffing apparatus. The controller 920 controls
the pressure applied from the buffing pad 502 to the wafer,
rotational number of the buffing head 500, rotational number of the
buffing table 400, oscillation velocity of the buffing head 500,
etc. The controller 920 receives the film thickness of the
to-be-processed surface of the wafer, which has been detected by
the ITM 912, or a signal corresponding to the film thickness. The
controller 920 includes a user interface and receives buffing
conditions entered and/or selected by user. The controller 920 has
a function of calculating the pressure correction of the buffing
pad, a function of simulating the polishing amount, and a function
of calculating optimum oscillation velocity distributions of the
buffing pad to achieve the desired polishing profile. The
controller 920 may comprise a dedicated or all-purpose computer.
For example, the controller 920 can be configured by installing
computer programs including commands for implementing the
above-mentioned various control functions, calculations, and
simulations in an all-purpose computer. The computer programs can
be stored in an all-purpose storage medium, such as a hard disc, a
CD, and a DVD. A common user interface, such as a monitor, a mouse,
a keyboard, and a tablet, may be used as the user interface of the
controller 920.
[0088] The buffing apparatus 300A further includes a database
(storage section) 930 that previously stores the polishing amount
corresponding to a plurality of buffing conditions (the pressure of
the buffing pad 502 against the wafer W, the rotational number of
the head 500, and a time duration in which the buffing pad 502 is
in contact with the wafer W). The database 930 also stores preset
target film thickness distributions of the to-be-processed face of
the wafer W. The database 930 further stores after-mentioned data
of various kinds, which are required for the polishing amount
simulation.
[0089] FIG. 20 is a flowchart for explaining the steps of the
polishing amount simulation and the optimization of the oscillation
velocity in the buffing apparatus 300A. The polishing amount
simulation and the optimization of the oscillation velocity are
carried out by the controller 920.
[0090] As illustrated in FIG. 20, the buffing simulation is first
started (Step S100). In this step, software required for the
simulation is activated in the controller 920.
[0091] Polishing conditions for the simulation is then entered
(Step S102). The buffing conditions include, for example, the size
of the wafer as a substrate, the size of the buffing pad 502, the
pressure at which the buffing pad 502 is pressed against the wafer,
the oscillation range of the buffing head 500, the rotational
number of the buffing table 400, the rotational number of the
buffing head 500, and the oscillation velocity of the buffing head
500. These conditions can be entered through the user interface
provided to the controller 920.
[0092] In the next step, the pressure correction value is
calculated from the entered buffing conditions (Step S104). The
pressure correction value is a value that is required when the
buffing pad 502 overhangs the wafer. The pressure correction value
can be calculated by the above-described method and is as shown in
FIG. 11, for example. The pressure correction value is previously
determined according to the sizes of the buffing pad and the wafer
used for the buffing through a test by the steps described above,
and is stored in the database 930. It is then possible to use the
pressure correction value that is required to meet the buffing
conditions entered in Step S102.
[0093] The polishing amount is then calculated from the buffing
conditions entered in Step S102 and the pressure correction value
calculated in Step S104 (Step S106). The polishing amount can be
calculated from a formula, wiping
distance.times.pressure.times.parameter coefficient, using
Preston's formula. As mentioned above, the parameter coefficient is
previously determined by a test or the like and stored in the
database 930, which makes it possible to use the parameter
coefficient that is required to meet the buffing conditions entered
in Step S102. The polishing amount results in, for example, the
polishing profile shown in FIG. 12.
[0094] The next step calculates difference between the target
polishing profile and the polishing profile calculated in Step S106
(Step S108). The difference is a polishing-amount correction value.
The target polishing profile may be entered in either Step S102 or
Step S108. For example, the polishing profile shown in FIG. 15 may
be selected as the target polishing profile.
[0095] The next step calculates an oscillation correction zone and
an oscillation-velocity correction value, which are required to
achieve the target polishing profile (Step S110). The
oscillation-velocity correction value can be calculated by the
method explained with reference to FIGS. 15 to 18.
[0096] In the next step, the buffing conditions entered in Step
S102 are updated based on the oscillation-velocity correction value
calculated in Step S110 (Step S112). To be specific, the
oscillation velocity is replaced with the oscillation velocity
calculated in Step S110.
[0097] The polishing amount is calculated again on the buffing
conditions updated in Step S112 (Step S114). Since the oscillation
velocity has been optimized, the target polishing profile is
calculated.
[0098] The buffing simulation is then ended (Step S116).
[0099] The buffing method using the above-discussed buffing
simulation will be now explained. FIG. 21 is a flowchart showing
the buffing method using the buffing simulation according to one
embodiment. The buffing can be carried out using, for example, the
buffing apparatus 300A illustrated in FIG. 19.
[0100] Once the buffing is started (Step S200), the buffing
conditions are first set (Step S202). The buffing conditions used
here are the buffing conditions created using the polishing amount
simulation explained with reference to FIG. 20.
[0101] The buffing is started on the buffing conditions set in Step
S202 (Step S204).
[0102] When the buffing carried out on the set buffing conditions
is finished, the film thickness of the wafer that has been buffed
is measured by the film thickness monitor (ITM 912) (Step
S206).
[0103] The next step determines whether the polishing profile
obtained from the film thickness distributions measured by the film
thickness monitor conforms to the target polishing profile (Step
S208). The determination can be made by, for example, comparing the
obtained polishing profile with the target polishing profile in the
buffing simulation to check if the obtained polishing profile
satisfies given conditions.
[0104] If Step S208 determines that the target polishing profile is
not achieved, buffing oscillation conditions are optimized (S210),
and the buffing is carried out again. The buffing oscillation
conditions can be implemented by the buffing simulation. More
specifically, in Step S108 associated with the buffing simulation,
the polishing-amount correction value is calculated from the
difference between the target polishing profile and the polishing
profile measured in Step S206, and the oscillation correction zone
and the oscillation-velocity correction value are calculated again.
The buffing is carried out again on the buffing conditions thus
obtained.
[0105] If Step S208 determines that the target polishing profile is
achieved, the buffing is ended (Step S208).
[0106] According to another embodiment, closed-loop control in
which the determination by Step S208 and the optimization by Step
S210 take place does not necessarily have to be implemented.
[0107] According to the present invention, it is possible to
simulate the wafer polishing amount taking into account the buffing
pad overhang as discussed above. Therefore, the estimation and
optimization of various design parameters of the buffing apparatus
can be made by carrying out the foregoing simulation.
REFERENCE SIGNS LIST
[0108] 400 buffing table [0109] 410 drive mechanism [0110] 500
buffing head [0111] 502 buffing pad [0112] 600 buffing arm [0113]
912 ITM (film thickness monitor) [0114] 920 controller [0115] 930
database [0116] 1000 sheet-type pressure sensor [0117] W wafer
* * * * *