U.S. patent application number 12/351159 was filed with the patent office on 2009-05-14 for disturbance-free, recipe-controlled plasma processing system and method.
Invention is credited to Shoji Ikuhara, Akira Kagoshima, Hiroyuki Kitsunai, Toshio Masuda, Natsuyo Morioka, Kenji Tamaki, Junichi Tanaka, Hideyuki Yamamoto.
Application Number | 20090120580 12/351159 |
Document ID | / |
Family ID | 19036210 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090120580 |
Kind Code |
A1 |
Kagoshima; Akira ; et
al. |
May 14, 2009 |
Disturbance-Free, Recipe-Controlled Plasma Processing System And
Method
Abstract
A plasma processing apparatus includes a vacuum processing
apparatus for performing a multi-step processing operation for a
sample, a sensor for monitoring process parameters during at least
a first step of the processing operation, a signal compression unit
for compressing a signal from the sensor to generate an apparatus
state signal, a worked result estimate model unit which estimates a
processed result on the basis of the apparatus state signal and a
set processed-result estimation equation, an optimum recipe
calculation model unit which calculates corrections to processing
conditions so that the processed result becomes a target value, a
usable recipe selecting unit which judges validity of an optimum
recipe. At a next step of the processing operation, sample
processing is performed under optimum conditions on the basis of
the usable recipe selected by the selected usable recipe.
Inventors: |
Kagoshima; Akira;
(Kudamatsu, JP) ; Yamamoto; Hideyuki; (Kudamatsu,
JP) ; Ikuhara; Shoji; (Hikari, JP) ; Masuda;
Toshio; (Toride, JP) ; Kitsunai; Hiroyuki;
(Chiyoda, JP) ; Tanaka; Junichi; (Tsuchiura,
JP) ; Morioka; Natsuyo; (Tokyo, JP) ; Tamaki;
Kenji; (Yokohama, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
19036210 |
Appl. No.: |
12/351159 |
Filed: |
January 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10933413 |
Sep 3, 2004 |
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12351159 |
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10350061 |
Jan 24, 2003 |
6881352 |
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10933413 |
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09946503 |
Sep 6, 2001 |
6733618 |
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10350061 |
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Current U.S.
Class: |
156/345.24 |
Current CPC
Class: |
H01L 22/26 20130101;
H01J 37/32935 20130101; Y02P 90/02 20151101; G05B 2219/45031
20130101; Y02P 90/20 20151101; G05B 19/41875 20130101; Y02P 90/22
20151101; H01L 22/20 20130101 |
Class at
Publication: |
156/345.24 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2001 |
JP |
2001-198830 |
Claims
1. A plasma processing apparatus comprising: a vacuum processing
apparatus for performing a multi-step processing operation for a
sample accommodated within a vacuum processing chamber of the
plasma processing apparatus; a sensor for monitoring process
parameters during at least a first step of the processing operation
of the vacuum processing apparatus; a signal compression unit for
compressing a signal from said sensor to generate an apparatus
state signal; a worked result estimate model unit which estimates a
processed result on the basis of the apparatus state signal from
the signal compression unit and a set processed-result estimation
equation; an optimum recipe calculation model unit which calculates
corrections to processing conditions so that the processed result
becomes a target value on the basis of the estimated processed
result of the worked result estimate model unit; and a usable
recipe selecting unit which judges validity of an optimum recipe
which is calculated by the optimum recipe calculation model unit
and selects a usable recipe; wherein at a next step of the
processing operation for the sample within the vacuum processing
chamber, sample processing is performed under optimum conditions on
the basis of the usable recipe selected by the usable recipe
selecting unit during the processing of the sample within the
vacuum processing chamber.
2. A plasma processing apparatus according to claim 1, wherein the
worked result estimate model unit corrects the processed-result
estimation model on the basis of the measured result of a shape of
the sample obtained as a result of the processing.
3. A plasma processing apparatus according to claim 1, wherein the
usable recipe selecting means selects one of previously-stored
recipes which is the closest to the optimum recipe calculated by
the optimum recipe calculation model unit.
4. A plasma processing apparatus according to claim 1, wherein
feed-forward control is applied to the optimum recipe calculating
model unit on the basis of the measured result of a shape of the
sample before the processing, to calculate processing conditions
such that the processed result becomes the target value.
5. A plasma processing apparatus according to claim 2, wherein
feed-forward control is applied to the optimum recipe calculating
model unit on the basis of the measured result of a shape of the
sample before the processing, to calculate processing conditions
such that the processed result becomes the target value.
6. A plasma processing apparatus according to claim 1, wherein the
optimum recipe calculating model unit corrects the processed-result
estimation model on the basis of the measured result of a shape of
the sample obtained as a result of the processing.
7. A plasma processing apparatus according to claim 1, wherein the
vacuum processing apparatus is a plasma etcher.
8. A plasma processing apparatus according to claim 2, wherein the
vacuum processing apparatus is a plasma etcher.
9. A plasma processing apparatus according to claim 6, wherein the
vacuum processing apparatus is a plasma etcher.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. application Ser. No.
10/933,413, filed Sep. 3, 2004, which is a continuation of U.S.
application Ser. No. 10/350,061, filed Jan. 24, 2003, now U.S. Pat.
No. 6,881,352, which is a division of U.S. application Ser. No.
09/946,503, filed Sep. 6, 2001, now U.S. Pat. No. 6,733,618, the
subject matter of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to plasma processing systems
and methods and more particularly, to a plasma processing system
and method which can suppress influences caused by a
disturbance.
[0003] As a plasma processing system, there is known, for example,
a system wherein an etching gas is introduced into a vacuum
processing chamber so that plasma is generated under a vacuum
pressure, and radicals or ions generated in the plasma react with a
surface of a wafer to be processed for etching. In the dry etching
system for performing such processing, the etching is carried out
under manufacturing conditions (gas flow rate, gas pressure, input
power, etching time, etc.) called recipe. The recipe is always kept
constant in a specific manufacturing step (in the same process) of
a semiconductor device. In this connection, the single process may
sometimes be divided into several steps and the manufacturing
conditions may be changed for each of the steps.
SUMMARY OF THE INVENTION
[0004] When a process using a dry etching system is executed in a
semiconductor manufacturing step, wafer processing is carried out
with manufacturing conditions called the recipe set constant for
each wafer processing.
[0005] In a recent dry etching process which demands finer
processing, however, a product generated by a reaction between a
wafer and an etching gas is deposited on an inner wall of a
processing chamber, an unnecessary gas called outgas is produced
from the deposit, which results in a change with time in an
environment within the processing chamber. Further, the environment
within the chamber is also changed even by the temperature change
of parts associated with the chamber and by the wear of the parts.
Such a dry etching system is susceptible to various disturbance
factors.
[0006] In addition, even variations in the shape dimensions of a
mask formed in a lithography step as a pretreatment of the above
etching processing have also a great effect on its etched
result.
[0007] That is, even when etching processing is carried out with a
constant recipe, it is difficult to obtain a constant performance
due to various disturbances.
[0008] In view of the problems in the prior art, it is therefore an
object of the present invention to provide a plasma processing
control system and method which can suppress influences caused, in
particular, by disturbances.
[0009] In order to solve the above problems, in accordance with an
aspect of the present invention, there is provided a plasma
processing control system which includes a plasma processor for
performing plasma processing operation over a sample accommodated
within a vacuum processing chamber, a sensor for monitoring process
parameters during processing operation of the processor, means for
providing a processed-result estimation model to estimate a
processed result on the basis of a monitored output from the sensor
and a preset processed-result prediction equation, means for
providing an optimum recipe calculation model to calculate optimum
processing conditions in such a manner that the processed result
becomes a target value on the basis of the estimated result of the
processed-result estimation model, and a controller for controlling
the plasma processing system on the basis of the recipe generated
using the optimum recipe calculation model.
[0010] In accordance with another aspect of the present invention,
there is provided a method for performing plasma processing
operation over a sample accommodated within a vacuum processing
chamber, which includes the steps of monitoring process parameters
during the processing operation, estimating a processed result on
the basis of the monitored result, calculating correction values of
processing conditions in such a manner that the processed result
becomes a target value on the basis of an estimated result of the
processed result to thereby generate an optimum recipe, and
controlling a plasma processor on the basis of the generated
optimum recipe.
[0011] Other objects, features and advantages of the present
invention will become apparent from the following description of
the embodiments of the invention taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram of a dry etching system in
accordance with an embodiment of the present invention;
[0013] FIG. 2 shows an arrangement of the entire dry etching
system;
[0014] FIG. 3 is a flowchart for explaining feedback control of the
dry etching system;
[0015] FIG. 4 is a diagram for explaining how to correct an optimum
recipe calculation model;
[0016] FIG. 5 is a diagram for explaining how to calculate an
optimum recipe;
[0017] FIG. 6 shows another embodiment of the dry etching
system;
[0018] FIG. 7 shows a further embodiment of the dry etching
system;
[0019] FIG. 8 shows processed result estimation and processing
control effect using an in-situ sensor;
[0020] FIG. 9 is a flowchart for explaining etching control of the
dry etching system;
[0021] FIG. 10 shows a stabilized effect caused by feedback control
or feedforward control;
[0022] FIG. 11 is a diagram for explaining operations of generating
a processed-result prediction equation;
[0023] FIG. 12 shows yet another embodiment of the dry etching
system;
[0024] FIG. 13 is a flowchart for explaining how to construct an
optimum recipe calculation model;
[0025] FIG. 14 is a diagram for explaining how to select a usable
recipe with use of a usable recipe selecting means;
[0026] FIG. 15 is a still further embodiment of the dry etching
system; and
[0027] FIG. 16 is an additional embodiment of the dry etching
system.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0028] FIG. 1 shows a block diagram of a dry etching system in
accordance with an embodiment of the present invention. In FIG. 1,
reference numeral 1 denotes a plasma processor for generating a
plasma 1c, and reference symbol 1b denotes a wafer as an object to
be processed which is mounted in a wafer stage 1a within a
processing chamber. Reference numeral 2 denotes sensors for
monitoring in-process parameters including a flow rate, pressure of
a gas supplied to the dry etching system and an input power
thereof. These sensors are usually incorporated as standard
components in the dry etching system. Reference numeral 3 denotes
an additional sensor such as an optical emission spectroscopy (OES)
for analyzing a spectrum of plasma light or a quadrupole mass
spectrometer (QMS) for analyzing the mass of a plasma particle.
Reference numeral 4 denotes an actuator for controlling the dry
etching system according to data indicative of a recipe 6, numeral
5 denotes a database for saving therein in-process parameters
linked to the recipe or production management information such as a
lot number or wafer ID. In this connection, the recipe may be
changed during processing operation of the wafer or for each wafer
processing operation.
[0029] FIG. 2 is an arrangement of an entire dry etching system in
accordance with a first embodiment of the present invention. The
system includes a feedback (FB) control system and a feedforward
(FF) system.
[0030] In FIG. 2, reference numeral 21 denotes a
photolithographical processor which coats a resist on, e.g.,
semiconductor substrate and etches the resist in such a manner
that, for example, a gate electrode having a desired electrode
width can be obtained at a gate part of a field-effect transistor
(FET) as a target. The target value of the electrode width or the
value of a processed result will be referred to as the critical
dimension (CD) value, hereinafter. Reference numeral 22 denotes a
measuring instrument such as a CD-scanning electron microscope
(SEM) for measuring the CD value of the resist after the etching
process, numeral 23 denotes a plasma etcher, and 24 denotes sensors
(which will be referred to as in-situ sensors, hereinafter) for
monitoring a flow rate and pressure of a gas supplied to the plasma
etcher, an input power thereof, and in-process parameters of the
OES and QMS. Reference numeral 25 denotes information indicative of
a processed-result estimation model which is used to estimate a
processed result (e.g., the aforementioned CD value of the
processed result) with use of monitored outputs of the in-situ
sensors or a processed-result prediction equation. In this
conjunction, since the in-situ sensors can monitor each wafer
during the wafer processing operation, the estimation model can be
used to estimate a processed result for each wafer. Further, the
estimation model can be corrected based on an output of an
instrument for measuring a processed result (which will be
explained later).
[0031] Reference numeral 26 denotes information indicative of an
optimum recipe calculation model, which can be corrected on the
basis of the estimated result of the processed-result estimation
model and a target value 27, e.g., as shown by Example 1 or 2 in
the drawings to generates an optimum recipe. Further, in the
calculation model, the output of the measuring instrument 22 such
as the CD-SEM can be used as a feedforward control input as shown
in Example 3.
[0032] Reference numeral 28 denotes a usable recipe selecting means
which acts to select one of recipes stored in a recipe server 29
which is the closest to the optimum recipe generated by the optimum
recipe calculation model and set it as a usable recipe.
[0033] Reference numeral 30 denotes a critical dimension scanning
electron microscope (CD-SEM) for measuring the CD value of a
processed result, and numeral 31 denotes a processed result
measuring instrument such as a cross section scanning electron
microscope (X-SEM) which outputs a processed result as the CD value
or gate shape signal 32. In this connection, the CD-SEM 30 and
measuring instrument such as the X-SEM 31 sample wafers for each
processing unit of the plasma etcher, that is, on a lot basis, for
measurement. For this reason, the CD value or gate shape can be
obtained for each lot.
[0034] FIG. 3 is a flowchart for explaining feedback control of the
dry etching system of the present embodiment. In a step 1, first,
the system set a processing target value (CD value). In a step 2,
the system calculates an optimum recipe for attaining the target
value from the processing target value on the basis of the optimum
recipe calculation model. The system selects in a step 3 one of
recipes which is the closest to the optimum recipe and sets in a
step 4 the selected recipe for the plasma etcher 23. In a step 5,
the system starts its etching operation. In a step 6, the system
monitors a state of the system during the etching operation with
use of the in-situ sensors. When completing etching operation
corresponding to a single wafer in a step 7, the system estimates a
processed result of the wafer on the basis of the measured values
of the in-situ sensors and with use of the processed-result
estimation model in a step 8. In a step 9, the system corrects the
optimum recipe calculation model on the basis of the estimated
processed result and target value as shown in FIG. 4, and sets the
corrected optimum recipe for the plasma etcher 23. The system then
proceeds to the step 2 for processing of the next wafer.
[0035] As mentioned above, further, wafers in each lot may be
sequentially sampled one after another, actual dimensions of each
wafer may be measured by the CD-SEM 30 or the processed result
measuring instrument such as the X-SEM 31, and a processed-result
estimation model can be accurately corrected based on the measured
results. The correction of the estimation model enables realization
of highly accurate inspection comparable to the wafer total-number
inspection by the above sampling inspection alone.
[0036] With such a control system, the processed result can be
estimated with use of the measured values of the in-situ sensors
and feedback control can be correspondingly carried out. Further,
since the measured values of the in-situ sensors are used, when
compared to a method (not using the in-situ sensors) of measuring
actual dimensions of wafers with use of the CD-SEM 30 or the
processed result measuring instrument such as the X-SEM 31 alone,
the method of the present invention can form a high-speed feedback
loop (feedback control loop for each wafer) and thus mass
production of defective wafers can be suppressed.
[0037] Explanation will next be made as to feedforward control of
the dry etching system of the present embodiment by referring to
FIGS. 2 and 5. A resist processing dimension (e.g., CD value) of
the wafer processed by the photolithographical processor 21 is
measured by the measuring instrument 22 such as the CD-SEM. The
optimum recipe calculation model 26 compares the measured value
with the target value 27 to obtain a difference or shift
therebetween, estimates (Y in FIG. 5) a processing amount (CD shift
value) for cancellation of the shift from the target value of the
resist processing dimension in the photolithography step, and
calculates an optimum recipe on the basis of the estimated value.
The usable recipe selecting means 28 next selects one of recipes
stored in the recipe server which is the closest to the optimum
recipe generated by the optimum recipe calculation model, and sets
the selected recipe as a usable recipe.
[0038] Shown in FIG. 4 is an example when the processed result in
the photolithography step is larger than the target CD value. In
such a case, resist is made thinner (slimming process) through
etching operation so as to reach the target CD value, or the resist
is adjusted through the etching operation of BARC/HLD (bottom
anti-reflection coating/high temperature, low pressure dielectric)
so as to reach the target CD value. Next etching operation is
carried out with use of the resist having the target CD value or
BARC/HLD as a mask. In this case, the system estimates a CD shift
value generated by side-etching of the target resist, and
calculates an optimum recipe on the basis of the estimated CD shift
value with use of the optimum recipe calculation model as shown in
FIG. 5. Thereafter the system selects usable one of the recipes
which is the closest to the calculated optimum recipe and performs
its etching operation over the resist using the selected
recipe.
[0039] Similarly, the system, on the basis of the CD value of the
resist, then calculates an optimum recipe with use of the optimum
recipe calculation model, selects usable one of the recipes which
is the closest to the calculated optimum recipe, performs its
etching operation over the wafer based on the selected recipe, and
completes its etching step.
[0040] FIG. 6 shows a block diagram of a dry etching system in
accordance with another embodiment of the present invention. In
FIG. 6, parts having the same functions as those in FIG. 2 are
denoted by the same reference numerals, and explanation thereof is
omitted. In this embodiment, such a processed-result estimation
model as shown in FIG. 2 is not used. With no use of the model, the
feedback loop speed becomes slow, but feedback using
actually-measured data from the processed result measuring
instrument 30 or 31 can be realized. For this reason, the optimum
recipe calculation model can be more accurately corrected.
[0041] FIG. 16 shows a dry etching system in accordance with a
further embodiment of the present invention. In the drawing, parts
having the same functions as those in FIG. 2 are denoted by the
same reference numerals, and explanation thereof is omitted. In
this embodiment, as opposed to the embodiment of FIG. 6, the CD-SEM
30, X-SEM 31 and processed result 32 shown in FIG. 2 are not used.
This is because, when the in-situ sensors 24 and processed-result
estimation model 25 can be kept highly accurate as in the present
embodiment, the need for model correction from the CD-SEM or the
like can be eliminated. In this manner, a processing method which
can eliminate the need for an inspection instrument such as the
CD-SEM or X-SEM can be realized, and thus the number of inspection
steps in manufacturing a semiconductor can be reduced.
[0042] FIG. 7 shows a dry etching system in accordance with yet
another embodiment of the present invention. In FIG. 7, parts
having the same functions as those in FIG. 2 are denoted by the
same reference numerals, and explanation thereof is omitted. In
this embodiment, the in-situ sensors 24 shown in FIG. 2 are
replaced by a scattered-light shape estimating means
(scatterometry). The scatterometry radiates light on a plurality of
lattice marks provided on a wafer with a wavelength or incident
angle as a parameter to measure a reflectivity. The system then
compares the measured reflectivity with a feature library
previously made through theoretical computation, searches the
library for a library waveform having a good matching therewith,
and adjusts shape parameters to estimate shape and dimensions of
the wafer formed by the plurality of grating marks.
[0043] When the scatterometry 24A is used to measure a processed
shape of the grating marks of the wafer sampled for each lot and to
correct the processed-result estimation model 25 as in a
modification example of FIG. 15, the shape estimation accuracy can
be corrected without implementation of destructive inspection by
the X-SEM.
[0044] The scatterometry 24A is built in the plasma etcher 23 as a
measuring instrument (integrated metrology) for monitoring process
parameters to measure the wafer immediately after etched within the
etcher and to estimate dimensions and shape thereof. How to correct
the optimum recipe calculation model based on the estimated result
is substantially the same as in FIG. 2.
[0045] FIG. 8 shows processed result estimation and the effect of
processing control using the in-situ sensor. FIG. 8 shows an
example where the in-situ sensor measures, as an example, plasma
luminescence during the processing operation. The plasma
luminescence includes information about etchants or ions which
dominate the process, and thus a change in the processed result can
be estimated on the basis of a change in the peak intensity of the
plasma luminescence or in the spectrum shape.
[0046] In this connection, since a change in the plasma
luminescence is slight, it is desirable to apply some numerical
data processing operation to the plasma luminescence to extract a
changed component in the luminescence spectrum with a high
sensitivity. The arithmetic processing includes, for example,
finding of a ratio or difference with respect to a standard
spectrum. Alternatively, when a statistical analysis technique,
e.g., main component analysis is employed, only changed one of many
luminescence peak components can be filtered and extracted.
[0047] Shown in a left column of FIG. 8 is a result of plasma
luminescence after subjected to the numerical data processing. Mark
* in the drawing indicates a change in the luminescence peak which
influences the deposit of a side wall. On the basis of an analysis
result of the luminescence peak, a processed result can be
estimated based on the processed-result estimation model. The model
is illustrated in a central column in FIG. 8, from which it can be
estimated that, when compared to a predetermined processing shape
(shown in the uppermost row), the side wall deposit is increased
and a taper angle is increased as the luminescence peak varies.
[0048] On the basis of these results, the system calculates an
optimum recipe for processing control. The calculation of the
optimum recipe is realized by correcting a processing recipe. The
correction is carried out according to a deviation from the
processing target value. For example, when the taper angle
coincides with a target value, no correction is applied; whereas,
when the taper angle is large, the correction is set to be large.
As a result, the taper angle can be kept constant as shown in a
right column of FIG. 8. How to calculate the optimum recipe will be
explained later. Although the in-situ sensor has been used to
detect the plasma luminescence here, it is also possible, in
addition to the above, to use, for example, discharge voltage
(Vpp), bias voltage (Vdc) or impedance monitor.
[0049] FIG. 9 shows a block diagram of etching control of the dry
etching system according to the present embodiment.
[0050] A sensor 91 for monitoring process parameters and also a
processed result can include a sensor such as an emission
spectroscope for outputting many pieces of data, a sensor such as a
plasma impedance monitor highly sensitive to a plasma state, and
various sensors for detecting a pressure, temperature, voltage,
power incidence and reflection. Further, a single sensor such as an
emission spectroscope, which can acquire many pieces of data at the
same time, can be provided. The sensor outputs a signal indicative
of a state of the dry etching system at intervals of a constant
time, e.g., one second. The number of sensor data pieces per one
output of the above sensor is several tens to several thousands of
pieces.
[0051] A signal compressor 92 compresses such many pieces of data
into a system state signal. The number of such system state signals
varies from situation to situation and sometimes is several to
several thousands of signals. The signal compression may employ a
statistical analysis such as a main component analysis.
[0052] A processed result estimator 93 generates a processing state
signal for each wafer through average or differentiation operation
from time changes of the system state signals.
[0053] In this connection, an processed-result prediction equation
94 in FIG. 9 is an equation for predicting a processed result of
the wafer after processed on the basis of the generated processing
state signal of each wafer, and is previously stored in a database.
The processed result estimator 93 further predicts a processed
shape of the wafer with use of the processing state signal and
prediction equation. In this connection, when there is a range of
variance in the processed shape among the wafers, the estimator
also calculates the variance range.
[0054] An optimum recipe calculation model 95 inputs the above
predicted result and a processing target value 96 and calculates
correction values of the processing conditions so that the
processed result becomes the target value. The model 95 passes the
corrected processing conditions (optimum recipe) to a system
controller 97 to control an etcher 98 for processing of a next
wafer. In this case, the accuracy certification of the
processed-result prediction equation can be made by comparing a
processed-result prediction value with an actually-measured result
of the instrument such as a CD-SEM for measuring a processed
shape.
[0055] FIG. 10 shows an effect of stabilization caused by feedback
control or feedforward control. In the drawing, a vertical axis or
ordinate indicates CD gain and an increase caused by processing of
the CD value. For the purpose of production management, it is ideal
that the CD gain is kept constant at a slightly positive value.
However, due to deposition of a reaction product on the inner wall
of a reactor, the state of the plasma or chemistry varies though it
is slight, which results in a long-term fluctuation in the
processing. The fluctuation is identified as inter-lot fluctuation
in the drawing. The fluctuation takes place, in particular, during
a time from full cleaning of the reactor after the reactor is
opened to the atmosphere and the deposit on the inner wall of the
reactor is removed to stabilization of the state on the inner wall
surface of the reactor. Further, even in a lot, the deposition of a
reaction product or a temperature change on the inner wall surface
causes a short-term fluctuation (in-lot fluctuation). Furthermore,
the processing of the photolithography or etching step also causes
a fluctuation in the processing.
[0056] In the prior art, such a fluctuation was accommodated in a
device processing margin by hardware improvement of temperature
adjustment on the inner wall surface, etc. or by cleaning the wall
at intervals of a suitable time (e.g., for each lot or wafer) to
remove the deposit to thereby stabilize the state of the reactor.
However, as the device is required to be finer and the processing
margin is required to be correspondingly smaller, the prior art
method had its stabilization limit. Meanwhile, when feedback
control or feedforward control is applied as in the present
embodiment, it is possible to suppress the inter-lot fluctuation,
in-lot fluctuation and processing fluctuation and to accommodate it
in the device processing margin, as shown in a lower stage in FIG.
10.
[0057] FIG. 11 is a flowchart for explaining how to generate the
processed-result prediction equation shown in FIG. 9. In a step S1,
first, the system performs etching operation over a sample (wafer)
with use of the etcher. The system compresses data about sensors
for monitoring process parameters in the data compressor in a step
S2, and stores the compressed data in a processing state signal
database in a step S3. The system measures the processed shape of
the wafer after the above processing, e.g., with use of a CD-SEM in
a step S4, and saves it in a processed result database in a step
S5. In a step S6, the system finds a correlative relationship
between the actually-measured processed shape and processing state
signal by multiple regression and generates a processed-result
prediction equation.
[0058] FIG. 12 shows another control example of the dry etching
system of the present invention. In this example, a response
surface model generally used for statistical processing was used as
a method for modeling an optimum recipe calculation model. FIG. 13
also shows how to construct the optimum recipe calculation model in
the example of FIG. 12.
[0059] Assume first that A, B and C indicate etching performance
items as targets and a, b, c, d, e and f denote 6 recipe parameters
to be set for the etching system. A, B and C refer to, e.g.,
selectivity, side-etching amount, taper angle, etc.; whereas a, b,
c, d, e and f refer to, e.g., gas flow rate, pressure, voltage,
power, temperature and time respectively. First of all, the system
performs an evaluation test by a Taguchi method in a step 1, and
selects one or ones of recipe parameters which affect(s) a
uniformity and removes it or them from controllable parameters in a
step 2. When these parameters (d, e and f in the drawing) are made
always stationary as fixed recipe parameters, feedback control
(Run-to-Run control) for each wafer prevents the deterioration of
the uniformity.
[0060] The system acquires data necessary for the modeling by an
experimental design method in a step 3, and creates an optimum
recipe calculation model in a step 4. In FIG. 11, a
three-dimensional model wherein only etch performances A, B, etch
performances A, C, and etch performances B, C contribute to the
recipe parameters a, b and c respectively, was assumed for easy
understanding of a basic idea of the optimum recipe calculation
model. In actuality, the optimum recipe calculation model generated
by a response surface methodology is a multi-dimensional model
which has the etch performances A, B and C as its inputs and has
the recipe parameters a, b and c as its outputs. In the
construction example, in order to change the etch performance, a
method of changing the slope of the model was employed. The recipe
parameters a', b' and c' and the fixed recipe parameters d, e and f
derived and updated using such a corrected model in this manner are
given as processing conditions of a next wafer. The system performs
its etching operation according to the etching conditions in a step
5.
[0061] FIG. 14 is a diagram for explaining how a usable recipe
selection means selects a usable recipe. When it is desired in a
process to process a first wafer, the system first calculates a
recipe No. 20 shown by {circle around (1)} in the drawing using the
optimum recipe calculation model on the basis of the target values
of the CD shift value and CD taper and performs the recipe
processing operation. Although the target values were used as two
variables for simplicity of the explanation, two or more variable
may be used similarly.
[0062] After completing the etching operation over the first wafer,
the system measures its processed result by the processed-result
estimation model or a measuring instrument such as a CD-SEM. The
measured result is assumed to have been shifted from the target as
shown by {circle around (2)}. Then, the system judges that the
initial calculation mode is fluctuated by a variation with time,
moves or tilts the model in such a manner that the initial recipe
(corresponding to No. 20 in this case) coincides with the processed
result for model correction as shown by {circle around (3)} (that
is, moves the initial optimum recipe calculation model to obtain an
optimum recipe calculation model (1) after the correction).
[0063] Upon etching operation of a second wafer, the system selects
an optimum recipe (corresponding to a recipe No. 10 of the second
wafer shown by {circle around (4)}) from the target value with use
of the corrected optimum recipe calculation model (1).
[0064] However, when the model after its correction became "optimum
recipe calculation model (2) after its correction" given in the
drawing, there exists no optimum recipe as the target value. In
this case, accordingly, the system issues an alarm and performs no
etching operation. Thus, when the system became abnormal, the
system can beforehand prevent production of many defective
products. Further, the alarm can be used also as an execution
judgement for the maintenance operation called `full cleaning`.
Although the plasma etching system has been used as a typical
example for the plasma processing system in the foregoing
explanation, the present invention can be applied even to another
plasma processing system such as a plasma CVD system.
[0065] As has been explained above, in accordance with the present
embodiment, since the feedback control or feedforward control is
applied on the basis of the outputs of the sensors for monitoring
process parameters or on the basis of the measured result of the
processed result measuring instrument, the system can suppress
inter-lot fluctuation, in-lot fluctuation and variance and can
realize accurate device processing.
* * * * *