U.S. patent application number 10/893275 was filed with the patent office on 2005-01-27 for method of setting etching parameters and system therefor.
Invention is credited to Nagatomo, Wataru, Nakagaki, Ryo, Shishido, Chie, Takagi, Yuji, Tanaka, Maki.
Application Number | 20050016682 10/893275 |
Document ID | / |
Family ID | 34074392 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050016682 |
Kind Code |
A1 |
Nagatomo, Wataru ; et
al. |
January 27, 2005 |
Method of setting etching parameters and system therefor
Abstract
The present invention relates to a system that automatically
calculates optimal etching parameters in order to perform desired
etching in an etching process in semiconductor manufacturing. A
model representing etching parameters and an etching performance
quantitative value at the time when etching is performed with the
etching parameters is prepared in advance, and when desired etching
is performed, optimal etching parameters are calculated from the
model.
Inventors: |
Nagatomo, Wataru; (Yokohama,
JP) ; Nakagaki, Ryo; (Kawasaki, JP) ; Tanaka,
Maki; (Yokohama, JP) ; Shishido, Chie;
(Yokohama, JP) ; Takagi, Yuji; (Kamakura,
JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
34074392 |
Appl. No.: |
10/893275 |
Filed: |
July 19, 2004 |
Current U.S.
Class: |
156/345.24 ;
257/E21.252; 257/E21.311; 257/E21.525 |
Current CPC
Class: |
H01L 21/32136 20130101;
H01L 22/20 20130101; H01L 2924/0002 20130101; H01L 21/31116
20130101; H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
156/345.24 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2003 |
JP |
2003-198844 |
Claims
What is claimed is:
1. A system for setting parameters for etching, comprising: an
electron beam image acquiring unit that acquires an electron beam
image of a pattern formed on a surface of a wafer treated by an
etching apparatus; a unit that processes the electron beam image of
the pattern formed on the surface of the wafer, which is obtained
by the electron beam image acquiring unit, and judges workmanship
of the pattern; a unit that presents a result of judgment by the
workmanship judging unit to a user; a unit that calculates
corrected values of etching parameters for the etching apparatus on
the basis of the result of judgment by the workmanship judging
unit; and a transmitting unit that transmits the corrected values
calculated by the calculating unit to the etching apparatus.
2. A system for setting parameters for etching according to claim
1, wherein the electron beam image acquiring unit includes: an
electron beam irradiating unit that irradiates a converged electron
beam on the surface of the wafer and scans the surface; and a
detecting unit that detects secondary charged particles that are
generated from the surface of the wafer as the electron beam
irradiating unit irradiates an electron beam on the surface and
scans the surface, and the electron beam irradiating unit can
change an incident angle of the converged electron beam with
respect to the pattern on the surface of the wafer in a range from
0.degree. to 15.degree. with respect to a normal direction of the
surface of the wafer.
3. A system for setting parameters for etching according to claim
1, wherein the unit that judges workmanship of the pattern
includes: a dimension extracting unit that processes the image of
the pattern to calculate dimensions of plural portions of the
pattern as workmanship of the pattern; and a comparing unit that
compares the dimensions of the plural portions of the pattern
calculated in the dimension extracting unit with target values set
in advance.
4. A system for setting parameters for etching according to claim
1, wherein the unit that calculates corrected values of etching
parameters for the etching apparatus includes; a storing unit that
stores a model representing a relation between information on
workmanship of a pattern and etching parameters; and a corrected
value calculating unit that compares the information on workmanship
of the pattern judged by the workmanship judging unit and the model
stored in the storing unit to calculate corrected values of the
etching parameters.
5. A system for setting parameters for etching according to claim
1, wherein, in the case in which the pattern is a contact hole, the
unit that judges workmanship of a pattern processes an image of the
pattern to calculate any one of a hole diameter, hole roundness, a
white band portion width, roughness of a white band portion
contour, roughness of a hole bottom pattern, a hole depth, and an
inclination angle of a hole wall portion as a characteristic amount
of the pattern, and judges workmanship of the pattern on the basis
of the calculated characteristic amount.
6. A system for setting parameters for etching according to claim
1, wherein, in the case in which the pattern is a line pattern, the
unit that judges workmanship of a pattern calculates any one of a
line width, a white band portion width in an image photographed by
a scanning electron microscope, roughness of a white band portion
contour, and an inclination angle of a wall portion as a
characteristic amount of the pattern and judges workmanship of the
pattern on the basis of the calculated characteristic amount.
7. A system for setting parameters for etching, comprising: an
electron beam image acquiring unit that acquires an electron beam
image of a pattern formed on a surface of a wafer treated by an
etching apparatus; a characteristic amount extracting unit that
processing the electron beam image of the pattern formed on the
surface of the wafer, which is obtained by the electron beam image
acquiring unit, and extracts a characteristic amount of the
pattern; a unit that judges performance of acquiring information on
a three-dimensional structure with the characteristic amount
extracting unit; a unit that presents a result of judgment by the
performance judging unit to a user; and a unit that calculates
corrected values for etching parameters for the etching apparatus
on the basis of a result of judgment by the performance judging
unit.
8. A system for setting parameters for etching according to claim
7, wherein the electron beam image acquiring unit includes: an
electron beam irradiating unit that irradiates a converged electron
beam on the surface of the wafer and scans the surface; and a
detecting unit that detects secondary charged particles that are
generated from the surface of the wafer as the electron beam
irradiating unit irradiates an electron beam on the surface and
scans the surface, the electron beam irradiating unit can change an
incident angle of the converged electron beam with respect to the
pattern on the surface of the wafer in a range from 0.degree. to
15.degree. with respect to a normal direction of the surface of the
wafer.
9. A system for setting parameters for etching according to claim
7, wherein, in the case in which the pattern is a contact hole, the
characteristic amount extracting unit calculates any one of a hole
diameter, hole roundness, a white band portion width, roughness of
a white band portion contour, roughness of a hole bottom pattern, a
hole depth, and an inclination angle of a hole wall portion as a
characteristic amount of the pattern.
10. A system for setting parameters for etching according to claim
7, wherein, in the case in which the pattern is a line pattern, the
characteristic amount extracting unit calculates any one of a line
width, a white band portion width in an image photographed by a
scanning electron microscope, roughness of a white band portion
contour, and an inclination angle of a wall portion as a
characteristic amount of the pattern and judges workmanship of the
pattern on the basis of the calculated characteristic amount.
11. A system for setting parameters for etching according to claim
7, wherein the unit that calculates corrected values of etching
parameters for the etching apparatus includes; a storing unit that
stores a model representing a relation between information on
workmanship of a pattern and etching parameters; and a corrected
value calculating unit that compares the information on workmanship
of the pattern judged by the performance judging unit and the model
stored in the storing unit to calculate corrected values of the
etching parameters.
12. A system for setting parameters for etching according to claim
7, further,comprising a transmitting unit that transmits the
corrected values calculated by the corrected value calculating unit
to the etching apparatus.
13. A method of setting parameters for etching, comprising the
steps of: acquiring an electron beam image of a pattern formed on a
surface of a wafer treated by an etching apparatus; processing the
acquired electron beam image of the pattern formed on the surface
of the wafer and judging workmanship of the pattern; presenting a
result of judging the workmanship to a user; calculating corrected
values of etching parameters for the etching apparatus on the basis
of the result of judging the workmanship; and transmitting the
calculated corrected values to the etching apparatus.
14. A method of setting parameters for etching according to claim
13, wherein, in the step of acquiring an electron beam image, a
converged electron beam is irradiated on the surface of the wafer
at an incident angle of a range between 0.degree. to 15.degree.
with respect to a normal direction of the surface of the wafer to
scan the surface of the wafer.
15. A method of setting parameters for etching according to claim
13, wherein, in the step of judging workmanship of the pattern, in
the case in which the pattern is a contact hole, an image of the
pattern is processed, any one of a hole diameter, hole roundness, a
white band portion width, roughness of a white band portion
contour, roughness of a hole bottom pattern, a hole depth, and an
inclination angle of a hole wall portion is calculated as a
characteristic amount of the pattern, and workmanship of the
pattern is judged on the basis of the calculated characteristic
amount.
16. A method of setting parameters for etching according to claim
13, wherein, in the step of judging workmanship of the pattern, in
the case in which the pattern is a line pattern, any one of a line
width, a white band portion width in an image photographed by a
scanning electron microscope, roughness of a white band portion
contour, and an inclination angle of a wall portion is calculated
as a characteristic amount of the pattern and workmanship of the
pattern is judged on the basis of the calculated characteristic
amount.
17. A method of setting parameters for etching, comprising the
steps of: acquiring an electron beam image of a pattern formed on a
surface of a wafer treated by an etching apparatus; processing the
acquired electron image of the pattern formed on the surface of the
wafer and extracting a characteristic amount of the pattern;
comparing the extracted characteristic amount of the pattern with
data set in advance and judging workmanship of the pattern;
presenting a result of judging the workmanship to a user, and
calculating corrected values of etching parameters of the etching
apparatus on the basis of the result of judging the
workmanship.
18. A method of setting parameters for etching according to claim
17, wherein, in the step of acquiring an electron beam image, a
converged electron beam is irradiated on the surface of the wafer
at an incident angle of a range between 0.degree. to 15.degree.
with respect to a normal direction of the surface of the wafer to
scan the surface of the wafer.
19. A method of setting parameters for etching according to claim
17, wherein, in the step of extracting the characteristic amount,
in the case in which the pattern is a contact hole, an image of the
pattern is processed, and any one of a hole diameter, hole
roundness, a white band portion width, roughness of a white band
portion contour, roughness of a hole bottom pattern, a hole depth,
and an inclination angle of a hole wall portion is calculated as a
characteristic amount of the pattern.
20. A method of setting parameters for etching according to claim
17, wherein, in the step of extracting the characteristic amount,
in the case in which the pattern is a line pattern, any one of a
line width, a white band portion width in an image photographed by
a scanning electron microscope, roughness of a white band portion
contour, and an inclination angle of a wall portion is calculated
as a characteristic amount of the pattern and workmanship of the
pattern is judged on the basis of the calculated characteristic
amount.
21. A method of setting parameters for etching according to claim
17, wherein, in the step of calculating corrected values of etching
parameters for the etching apparatus, information on workmanship of
the pattern judged in the step of judging workmanship is compared
with a model representing a relation between information on
workmanship of a pattern stored in advance and etching parameters,
and corrected values of the etching parameters are calculated.
22. A method of setting parameters for etching according to claim
17, further comprising the step of sending the calculated corrected
values of the etching parameters to the etching apparatus.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application relates to and claims priority from
Japanese Patent Application No. 2003-198844, filed on Jul. 18,
2003, the entire disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of setting optimal
etching parameters in a semiconductor manufacturing process and a
system therefor. More specifically, the present invention relates
to a system that picks up an image of a pattern formed on a wafer,
represents workmanship of the pattern quantitatively, performs
etching parameter correction for reducing an amount of deviation
between a quantitative value of the workmanship and a target
etching pattern, and realizes setting for optimal etching
parameters, and a performance evaluation system that evaluates
performance of etching.
[0004] 2. Description of the Related Art
[0005] A conventional method of setting etching parameters (a gas
flowrate, a pressure, a voltage, electric power, temperature, time,
etc.) for an etching process in semiconductor manufacturing will be
explained with reference to FIG. 2. In the etching process, in
order to obtain desired etching performance, it is necessary to set
plural etching parameters to optimal values.
[0006] Instep 201, in order to perform desired etching, a person
determines initial values of etching parameters, which are suitable
for a quality of material of an etching object and an etching
shape, with a help of experiences in the past and intuition on the
basis of characteristics, which have been obtained through
experiments, concerning the quality of material of the etching
object and characteristics of an etching apparatus being used.
[0007] In step 202, the person performs etching with the etching
parameters determined in step 201. In step 203, the person observes
a pattern on a wafer, which is formed by the etching, with a
scanning electron microscope (SEM) or the like to measure the
etching pattern. In step 204, the person judges manually whether
desired etching performance is obtained on the basis of a
measurement value obtained in step 203. If it can be judged that a
result of the etching is satisfactory, the person determines
etching parameters.
[0008] If it is judged that the result of the etching is
unsatisfactory, in step 205, the person performs correction for the
etching parameters, which brings etching performance close to the
desired etching performance, on the basis of experiences in the
past. Then, the person returns to step 202 and performs etching
again with etching parameters set anew.
[0009] According the method described above, the person determines
etching parameters most suitable for obtaining the desired etching
performance.
[0010] In the above-mentioned conventional technique, the person
determines initial values and corrected values of etching
parameters according to experiences and intuition to derive optimal
etching parameters. However, such manual setting for etching
parameters is inefficient because the manual setting takes time
until optimal setting for etching parameters is obtained. In
addition, it is possible that set values contain individual
differences.
SUMMARY OF THE INVENTION
[0011] Thus, the present invention has been devised in view of
these problems, and it is an object of the present invention to
provide a method of setting optimal etching parameters for
performing desired etching and a system therefor.
[0012] The present invention provides a method of setting
parameters for etching, which includes: acquiring an electron beam
image of a pattern formed on a surface of a wafer treated by an
etching apparatus; processing the acquired electron beam image of
the pattern formed on the surface of the wafer to judge workmanship
of the pattern; presenting a result of judging the workmanship to a
user; calculating corrected values of etching parameters for the
etching apparatus on the basis of the result of judging the
workmanship; and sending the calculated corrected value to the
etching apparatus, and a system for the method.
[0013] In addition, the present invention provides a method of
setting parameters for etching, which includes: acquiring an
electron beam image of a pattern formed on a surface of a wafer
treated by an etching apparatus; processing the acquired electron
beam image of the pattern formed on the surface of the wafer to
extract a characteristic amount of the pattern; comparing the
extracted characteristic amount of the pattern with data set in
advance to judge workmanship of the pattern; presenting a result of
judging the workmanship to a user; and calculating corrected values
of etching parameters for the etching apparatus on the basis of the
result of judging the workmanship, and a system for the method.
[0014] These and other objects, features and advantages of the
invention will be apparent from the following more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the accompanying drawings:
[0016] FIG. 1 is a diagram showing a system for setting optimal
etching parameters according to the present invention;
[0017] FIG. 2 is a diagram showing a conventional method;
[0018] FIG. 3 is a conceptual diagram showing the system for
setting optimal etching parameters;
[0019] FIGS. 4A and 4B are diagrams showing examples of
characteristics of etching performance;
[0020] FIG. 5 is a flow diagram of processing for deriving an
etching performance quantitative value;
[0021] FIG. 6 is a conceptual diagram showing a system for setting
optimal etching parameters in a mass production process;
[0022] FIG. 7 is a diagram showing a structure of a scanning
electron microscope (SEM);
[0023] FIG. 8 is a diagram showing an example of GUI display of an
etching performance quantitative value;
[0024] FIG. 9 is a flow diagram of processing for creating an
optimal parameter calculation model;
[0025] FIG. 10 is a conceptual diagram showing a method of changing
parameters;
[0026] FIG. 11 is a flow diagram of processing for setting optimal
etching parameters;
[0027] FIG. 12 is a flow diagram of correction for the optimal
parameter calculation model in a mass production process; and
[0028] FIG. 13 is a diagram showing a structure of a scanning
electron microscope (SEM) that is capable of acquiring a tilt
image.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Embodiments of the present invention will be hereinafter
explained with reference to the accompanying drawings.
First Embodiment
[0030] Outline
[0031] FIG. 1 shows a system configuration for automating parameter
setting at the time of an etching process in semiconductor
manufacturing in accordance with an embodiment of the present
invention. This system includes an etching apparatus 1, a scanning
electron microscope (SEM) 2 that picks up images of an etching
pattern, and a computer 3 including a processing unit 4, which
performs image processing and optimal etching parameter derivation
processing, and a storage 5, which saves etching pattern images,
etching parameters, and the like. The respective components are
connected by a bus 6.
[0032] FIG. 3 shows a flow of processing of this system. First, in
step 301, a modeled relation between various image characteristic
amounts, which are derived from electron beam images of etching
patterns that are formed when etching is performed by changing
etching parameters (a gas flow rate, a pressure, wafer temperature,
a coil magnetic field, etc.) in various ways, and the etching
parameters are prepared in a preliminary experiment (hereinafter
referred to as an optimal parameter calculation model). In step
302, an etching target value for an etching pattern to be formed by
etching is set. In step 303, initial etching parameters are set
using the optimal parameter calculation model prepared in advance.
In step 304, etching is performed on the basis of the etching
parameters set in step 303. In step 305, an image of an etching
pattern on a wafer formed by the etching is picked up by a scanning
electron microscope (SEM) or the like. In step 306, a performance
value of the etching is calculated by image processing with respect
to the image obtained in step 305. In step 307, it is judged
whether the obtained etching performance value satisfies the
etching target value. If the etching performance value satisfies
the etching target value, an etching recipe at that point is set as
optimal etching parameters for the etching target value. If the
etching performance value does not satisfy the etching target
value, in step 308, an etching parameter corrected value for
bringing an etching result close to the target etching value is
calculated on the basis of the optimal parameter calculation model.
In step 309, optimal etching parameters are set on the basis of the
calculated corrected value. Then, etching is performed again with
an etching recipe set anew (the processing is returned to step
304).
[0033] Details of the respective steps will be hereinafter
explained.
[0034] (1) Derivation of an Optimal Parameter Calculation Model
(Step 301 in FIG. 3).
[0035] A method of deriving an optimal parameter calculation model
will be explained. In this embodiment, a response surface model,
which is generally used for statistical processing, is used as a
modeling method for an optimal parameter calculation model. FIG. 9
is a diagram showing processing to establishing an optimal
parameter calculation model. First, it is assumed that items of a
target etching performance quantitative value are A, B, and C, and
items of etching parameters to be set in an etching apparatus are
a, b, c, d, e, and f. A, B, and C are, for example, line edge
roughness, a line width, a contact hole diameter, a hole roundness,
and a characteristic amount of a contact hole bottom pattern, and
a, b, c, d, e, and f are, for example, a gas flow rate, a pressure,
a voltage, electric power, temperature, and time.
[0036] First, in step 901, an evaluation experiment using, for
example, a Taguchi method is performed to find parameters, which
affect in-plane evenness in an etching process, among the etching
parameters. In step 902, the etching parameters affecting in-plane
evenness are excluded from controllable parameters (e.g., d, e, and
f). These parameters are always fixed as fixed etching parameters,
whereby evenness on a wafer is prevented from being ruined. In step
903, experiment data necessary for the derivation of an optimal
parameter calculation model (experiment data with the etching
parameters a, b, and c as inputs and the etching performance
quantitative values A, B, and C as outputs) is acquired using, for
example, an experimental design method. In step 904, an optimal
parameter calculation model using a response curve is created. An
optimal parameter calculation model to be generated by the response
surface method is a multidimensional model with the items of the
target etching performance quantitative value A, B, C as inputs and
the etching parameters a, b, and c as outputs.
[0037] (2) Setting for an Etching Target Value (Step 302 in FIG.
3)
[0038] A desired etching target value is set. For example, in the
case in which an etching pattern is a contact hole, a hole
diameter, hole roundness, a white band portion width in an image
photographed by a scanning electron microscope, roughness of a
white band portion contour, roughness of a hole bottom pattern, a
hole depth, an inclination angle of a hole wall, and the like are
target values.
[0039] (3) Etching Parameter Setting Using the Optimal Parameter
Calculation Model
[0040] The etching target value is inputted to the optimal
parameter calculation model prepared in advance in step 301 to
calculate initial etching parameters.
[0041] (4) Acquisition of an SEM Image (step 305 in FIG. 3)
[0042] An image of an etching pattern is picked up by a scanning
electron microscope (SEM). FIG. 7 is a block diagram showing a
structure of the scanning electron microscope (SEM) that observes
an object formed by etching on a wafer (contact hole, etc.). In
FIG. 7, a primary electron beam 702 emitted from an electron gun
701 of an electro-optic system 700 is focused and irradiated on a
wafer 710 placed on a stage 711 through a condensing lens 703, a
beam deflector 704, an E.times.B deflector 705, and an object lens
706. When the electron beam is irradiated, a secondary electron is
generated from the wafer 710.
[0043] The secondary electron generated from the wafer 710 is
deflected by the E.times.B deflector 705 and detected by a
secondary electron detector 707. A two-dimensional electron beam
image is obtained by two-dimensional scanning of the electron beam
by the beam deflector 704 or repeated scanning in an X direction of
the electron beam by the beam deflector and detection of electrons
that are generated from the wafer 710 in synchronization with
continuous movement in a Y direction of the wafer 710 by a stage
711.
[0044] A signal detected by the secondary electron detector 707 is
converted into a digital signal by an A/D converter 708 and sent to
an image processing unit 720. The image processing unit 720 has an
image memory for temporarily storing a digital image and a CPU that
performs calculation for a line profile and a characteristic amount
from an image on the image memory. In addition, the image
processing unit 720 has a storage medium 721 for saving the
characteristic amount calculated from a result of image processing
as a database and a display 722 that displays the image and the
processing result.
[0045] In this embodiment, prior to carrying in a product wafer, a
correspondence model of etching parameters, which are adjusted to
obtain a desired etching pattern, and a characteristic amount,
which is desired from an electron image of an etching pattern that
is formed when the etching parameters are changed, (hereinafter
referred to as an optimal parameter calculation model) is derived
by a preliminary experiment and saved in a storage 5b shown in FIG.
1.
[0046] As the scanning electron microscope to be used, a scanning
electron microscope that picks up a tilt image may be used in
addition to the one that picks up a top-down view image. As means
for picking up a tilt image, a system for inclining a table 711 on
which the wafer 710 is mounted or a system for controlling a
trajectory of a primary electron beam with an electro-optic system
of the scanning electron microscope (SEM) to make the primary
electron beam incident on a wafer surface from an inclined
direction maybe adopted. In both the systems, a tilt angle (an
inclination angle of a primary electron beam with respect to a
normal direction of the wafer surface) is set between 0.degree. to
about 15.degree. to obtain a tilt image.
[0047] FIG. 13 shows an example of an SEM structure for obtaining a
tilt image by inclining a table (tilt stage). The SEM structure
shown in FIG. 13 is substantially the same as that shown in FIG. 7.
A primary electron beam 1302 emitted from an electron gun 1301 of
an electro-optic system 1300 is focused and irradiated on a wafer
1301 placed on a stage 1311 through a condensing lens 1303, a beam
deflector 1304, an E.times.B deflector 1305, and an object lens
1306. A secondary electron generated from the wafer 1310 is
deflected by the E.times.B deflector 1305, detected by a secondary
electron detector 1307, converted into a digital signal by an A/D
converter 1308, and sent to an image processing unit 1320. The
image processing unit 1320 has an image memory for temporarily
storing a digital image and a CPU that performs calculation for a
line profile and a characteristic amount from an image on the image
memory. In addition, the image processing unit 1320 has a storage
medium 1321 for saving the characteristic amount calculated from a
result of image processing as a database and a display 1322 that
displays the image and the processing result.
[0048] Here, the structure show in FIG. 13 is different from the
structure shown in FIG. 7 in that the table 1311 has a tilt
function and it is possible to set an inclination angle of a
primary electron beam with respect to a normal direction of a
surface of the wafer 1311 to obtain a tilt image. The image
processing unit 1320 calculates a height of a pattern according to
a principle of stereo graphic view from a tilt image and a top-down
view image obtained by the SEM with such a structure, and
information on a three-dimensional structure (a pattern height, a
taper angle, etc.) is used as a characteristic amount of an etching
pattern. Consequently, more detailed setting for an etching target
is performed.
[0049] (5) Performance Quantization (Step 306 in FIG. 3)
[0050] As an example of a characteristic amount derived from an
electron beam image of an etching pattern (a line patter, a hole
pattern, etc.), an etching performance quantitative value is
proposed. The etching performance quantitative value is obtained by
picking up an image of an object generated by etching with an SEM
and applying image processing to the picked-up image. For example,
in the case in which an object of formation on a wafer to be
observed is a line pattern, characteristic amounts (a line width
401, line edge roughness 402, a white band width 403, etc.) are
represented quantitatively by image processing as shown in FIG.
4A.
[0051] In addition, in the case in which an object of formation on
a wafer is a hole pattern, characteristic amounts (a hole diameter
410, hole roundness 411, a white band portion width 412, roughness
of a white portion contour line 413, roughness of a contact hole
bottom pattern 414, etc.) are represented quantitatively by image
processing as shown in FIG. 4B. FIG. 5 shows a method of deriving a
workmanship quantitative value of a contact hole.
[0052] (6) Judgment (Step 307 in FIG. 3)
[0053] It is judged using threshold processing or the like whether
or not the performance quantitative value calculated in step 306 is
within a fixed allowable range with respect to the etching target
value set in step 302. In addition, an amount of deviation of an
optimal etching parameter from a target value is calculated.
[0054] (7) Etching Parameter Correction Using a Minimum Parameter
Calculation Model
[0055] FIG. 10 a conceptual diagram showing how optimal etching
parameters are calculated from an amount of deviation of an etching
performance quantitative value from a target value. In the figure,
in order to facilitate explanation, a three-dimensional model, in
which only etching parameter elements a and b relate to an etching
performance quantitative value A, is assumed. In the case in which
the etching performance value A does not satisfy a target value, it
is assumed from a shape of a model surface how the etching
parameters (the parameters a and b) should be change from etching
parameter positions on the model at that point to bring a result of
etching close to a target etching performance value. The etching
parameters are changed finely in a direction of the change and use
them as next etching parameters.
[0056] In FIG. 11, an optimal etching parameter determination
method is shown which uses an optimal parameter calculation model
at the time when the etching performance quantitative values are A,
B, and C in the case in which etching parameters are a, b, c, d, e,
and f. In this figure, a three-dimensional model, in which only the
etching parameters a and b, the etching parameters b and c, and the
etching parameters c and a relate to the etching performance
quantitative values (which is indicated as "etching performance" in
the figure) A, B, and C, respectively, is assumed. Actually, as
described before, an optimal parameter calculation model, which is
generated according to the response surface method, is a
multidimensional model with the items of the target etching
performance quantitative value A, B, and C as inputs and the
etching parameters a, b, and c as outputs.
[0057] As described above, etching parameters most suitable for
realizing desired etching are derived on the basis of the optimal
parameter calculation model. In the above-mentioned method, etching
parameters are changed finely. However, etching parameters leading
to an optimal etching performance value, which are calculated from
the model, may be used as the next etching parameters directly.
[0058] (8) GUI (Step 306 and Step 307 in FIG. 3)
[0059] An etching performance quantitative value after etching
calculated in step 306 is displayed on a GUI shown in FIG. 8. An
inputted image 801 and a result of performance quantization area
extraction 802 are displayed in an upper part of the screen and a
result of judgment on quality of etching and performance
quantitative values (hole diameter, white band portion thickness,
white band portion contour roughness, hole bottom pattern
roughness, etc.) are displayed in a lower part of the screen (803)
such that a user can easily understand a state of etching
performance.
[0060] In addition, if a result of the quality judgment for etching
calculated in step 307 indicates defectiveness, a result of judging
a cause of the defectiveness (etching stop, occurrence of
deposition, etc.) is also displayed (804).
[0061] This embodiment is a system that automatically derives
etching parameters most suitable for realizing target etching as in
the above-mentioned method.
Second Embodiment
[0062] System for Calculating Optimal Etching Parameters at the
Time of Mass Production
[0063] This embodiment is an example concerning optimization for
etching parameters in an etching process at the time of mass
production in semiconductor manufacturing. FIG. 6 shows a
constitution of this embodiment. When an etching apparatus is
continuously operated at the time of mass production in
semiconductor manufacturing, with the method of deriving etching
parameters described above (first embodiment), desired etching
cannot be calculated in some cases due to disturbance such as dirt
in the apparatus. Such a situation may be caused because effective
values of etching parameters deviate from set values thereof due to
dirt in the apparatus. This is equivalent to deviation of axes of
etching parameters in an optimal etching parameter calculation
model. Thus, in order to control between-lot variation, within-lot
variation, and dispersion variation based on variation with time
and to carry out accurate device processing, in the case in which a
result of measurement of the etching parameters deviates from a
target value, axes of etching parameters at the time of creation of
an initial calculation model are corrected.
[0064] The optimal parameter calculation model is used again after
the correction to calculate an optimal recipe from the target
value. However, in the case in which values of etching parameters
calculated from the corrected model are outside a range of values
that can be set by the etching apparatus, an alarm is notified for
etching treatment for a second wafer to prevent the etching
treatment from being performed. Consequently, when abnormality has
occurred in the apparatus, a large number of defects can be
prevented from being caused. In addition, this alarm can also be
used for judgment on execution of maintenance processing called
total cleaning. According to the above-mentioned method, optimal
etching parameters are set in an etching process at the time of
mass production.
[0065] A processing flow shown in FIG. 6 will be explained. First,
in step 601, an etching target value for an etching pattern to be
formed by etching is set. In step 602, initial etching parameters
are set. In step 603, etching is performed on the basis of the
etching parameters set in step 602. In step 604, an image of an
etching pattern on a wafer formed by the etching is picked up by a
scanning electron microscope (SEM) or the like. In step 605, a
performance value of the etching is calculated by image processing
with respect to the image obtained in step 604. In step 606, it is
judged whether the obtained etching performance value satisfies the
etching target value set in step 601. Here, if the etching
performance value satisfies the etching target value, wafers are
subjected to etching treatment one after another without changing
the etching parameters at that point.
[0066] If it is judged in step 606 that the etching performance
value does not satisfy the etching target value, in step 608, an
etching parameter corrected value for bringing an etching result
close to the target etching value is calculated, and a result of
the calculation is fed back to step 602 for setting optimal etching
parameters to set optimal etching parameters. Then, etching is
performed again with an etching recipe based on the etching
parameters set anew.
[0067] The present invention makes it possible to calculate optimal
etching parameters for obtaining desired etching performance in an
etching process in semiconductor manufacturing. In addition, the
present invention makes it possible to control influence of
disturbance due to continuous operation of an apparatus to continue
etching with optimal parameters at the time of mass production in
an etching process.
[0068] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiment is therefor to be considered in all
respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and range of equivalency of the claims are therefore intended to be
embraced therein.
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