U.S. patent application number 11/850722 was filed with the patent office on 2008-09-11 for plasma processing apparatus.
Invention is credited to Takashi Fujii, Kazuhiro Joo, SHIGERU NAKAMOTO, Hiroshige Uchida, Tatehito Usui.
Application Number | 20080216956 11/850722 |
Document ID | / |
Family ID | 39740459 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080216956 |
Kind Code |
A1 |
NAKAMOTO; SHIGERU ; et
al. |
September 11, 2008 |
PLASMA PROCESSING APPARATUS
Abstract
To provide a plasma processing apparatus using a measuring
method of a film thickness of a material to be processed, which
method is capable of accurately measuring an actual residual film
amount and an etching depth of the layer to be processed. The
plasma processing apparatus includes: a detector 11 adapted to
detect interference light of a plurality of wavelengths from the
surface of a sample in a vacuum container; pattern comparing means
15 adapted to compare actual deviation pattern data relating to the
interference light obtained at an arbitrary time point during the
processing of the sample, with a plurality of standard deviation
patterns which are data of interference light of a plurality of
wavelengths relating to processing of another sample obtained
before the processing of the sample, and which correspond to a
plurality of thicknesses of the film, and adapted to calculate a
deviation between the actual deviation pattern data and the
standard deviation patterns; deviation comparing means 115 adapted
to compare the deviation between the actual deviation pattern data
and the standard deviation patterns, with a deviation set
beforehand, and to output data relating to the film thickness of
the sample at the time; residual film thickness time series data
recording means 18 adapted to record the data relating to the film
thickness as time series data; and an end point determining device
230 adapted to determine that etching of a predetermined amount is
ended, by using the data of the film thickness.
Inventors: |
NAKAMOTO; SHIGERU;
(Kudamatsu-shi, JP) ; Usui; Tatehito;
(Kasumigaura-shi, JP) ; Joo; Kazuhiro;
(Kudamatsu-shi, JP) ; Fujii; Takashi;
(Kudamatsu-shi, JP) ; Uchida; Hiroshige;
(Kudamatsu-shi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
39740459 |
Appl. No.: |
11/850722 |
Filed: |
September 6, 2007 |
Current U.S.
Class: |
156/345.25 |
Current CPC
Class: |
H01J 37/32935 20130101;
G01B 11/0625 20130101; G01B 11/0683 20130101; H01J 37/32972
20130101; H01J 2237/334 20130101 |
Class at
Publication: |
156/345.25 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2007 |
JP |
2007-057426 |
Claims
1. A plasma processing apparatus adapted to perform etching
processing of a film on the surface of a sample in a vacuum
container by using plasma formed in the vacuum container,
comprising: a detector adapted to detect interference light of a
plurality of wavelengths from the sample surface during the
processing; pattern comparing means adapted to compare actual
deviation pattern data relating to the interference light obtained
at an arbitrary time point during the processing of the sample,
with a plurality of standard deviation patterns which are data of
interference light of the plurality of wavelengths, relating to
processing of another sample obtained before the processing of the
sample, and which correspond to a plurality of thicknesses of the
film, and adapted to calculate a deviation between the actual
deviation pattern data and the plurality of standard deviation
patterns; deviation comparing means adapted to compare the
deviation between the actual deviation pattern data and the
plurality of standard deviation patterns with a deviation set
beforehand, and to output data relating to a film thickness of the
sample at the arbitrary time point; residual film thickness time
series data recording means adapted to record the data relating to
the film thickness from the deviation comparison means as time
series data; and an end point determining device adapted to
determine that an etching of a predetermined amount is ended, by
using the data on the film thickness from the deviation comparison
means.
2. The plasma processing apparatus according to claim 1, wherein
when a minimum value of the deviation is larger than a
predetermined value, the determining device determines the reaching
of the film thickness estimated from the value of the film
thickness determined before the arbitrary time point.
3. The plasma processing apparatus according to claim 1, wherein
the determining device is means adapted, when a minimum value of
the deviation is larger than a predetermined value, to determine
the reaching of the film thickness estimated from the value of the
film thickness determined before the arbitrary time point, and to
determine a value obtained by interpolation using film thickness
values at each time point within a predetermined time period before
the arbitrary time point, as a film thickness at the arbitrary time
point.
4. The plasma processing apparatus according to claim 1, wherein
the determining device is means adapted, when a minimum value of
the deviation is larger than a predetermined value, to determine
the reaching of the film thickness estimated from the value of the
film thickness determined before the arbitrary time point, and to
use a value obtained by performing interpolation using film
thickness values at respective time points within a predetermined
time period before the arbitrary time point, for determining the
film thickness at a time point after the arbitrary time point.
5. The plasma processing apparatus according to claim 1, wherein
the determining device is means adapted, when a minimum value of
the deviation is larger than a predetermined value, to determine
the reaching of the film thickness estimated from the value of the
film thickness determined before the arbitrary time point, and to
determine a value obtained by performing extrapolation using film
thickness values at respective time points within a predetermined
time period before the arbitrary time point, as the film thickness
at a time point after the arbitrary time point.
6. A plasma processing apparatus adapted to perform etching
processing of a film on the surface of a sample in a vacuum
container by using plasma formed in the vacuum container,
comprising: a detector adapted to detect interference light of a
plurality of wavelengths from the sample surface during the
processing; a differentiator adapted to obtain an actual
differential pattern constituted by a time series of actual
differential waveforms by differentiating changes in intensity of
the detected interference light; a differential waveform pattern
database which is a differential waveform obtained by
differentiating a change in intensity of interference light of the
plurality of wavelengths relating to processing of another sample
obtained before the processing of the sample, and which is
constituted by a plurality of standard differential waveforms
respectively corresponding to a plurality of thicknesses of the
film; a differential waveform comparator adapted to compare a real
time differential waveform formed by differentiating a change in
intensity of interference light obtained at an arbitrary time point
from the start of the processing of the sample, with a pattern of
standard differential waveforms stored in the differential waveform
pattern database, and to output a pattern matching deviation value
between the real time differential waveform and the pattern of
standard differential waveforms; a deviation value setting device
in which a minimum value of the pattern matching deviation value is
set; and a determining device adapted to determine reaching of a
film thickness corresponding to a pattern of the data for which the
pattern matching deviation value is minimized, wherein when a
difference between the determined film thickness value and a film
thickness value determined at a time point just before the
arbitrary time point is larger than a predetermined value, the
determining device determines reaching of a film thickness
estimated from the film thickness determined before the arbitrary
time point.
7. The plasma processing apparatus according to claim 6, comprising
the determining device which determines a value obtained by
performing interpolation using film thickness values at respective
time points within a predetermined time period before the arbitrary
time point, as a film thickness at the arbitrary time point.
8. The plasma processing apparatus according to claim 6, further
comprising the value obtained by performing interpolation as the
determination value used for the film thickness determination at
the arbitrary time point and at a time point subsequent to the
arbitrary time point.
9. The plasma processing apparatus according to claim 6 or claim 7,
further comprising a determining device adapted to use a value
obtained by performing extrapolation.
10. A plasma processing apparatus adapted to perform etching
processing of a film on the surface of a sample in a vacuum
container by using plasma formed in the vacuum container,
comprising: a detector adapted to detect interference light from
the sample surface in the vacuum container; and a determining
device adapted to compare data relating to the interference light
obtained by differentiating an output obtained from the detector at
an arbitrary time point during the processing, with a plurality of
patterns of data which are interference light data of a plurality
of wavelengths obtained by differentiating the outputs from the
detector in processing of another sample obtained before the
processing of the sample, and which respectively correspond to a
plurality of thicknesses of the film, and to determine reaching of
a film thickness at which the difference between the data and the
plurality of patterns is minimized, wherein when a ratio
(difference) between the output value of the detector at the
arbitrary time point and an output value of the detector at a time
point just before the arbitrary time point is larger than a
predetermined value, the output value at the arbitrary time point
is corrected to make the ratio at the arbitrary time point equal to
the ratio at the time point just before the arbitrary time point
(to eliminate the difference therebetween).
11. A plasma processing apparatus adapted to perform etching
processing of a film on the surface of a sample in a vacuum
container by using plasma formed in the vacuum container,
comprising: a first detector adapted to detect light emission of
plasma in the vacuum container; a second detector adapted to detect
interference light from the sample surface in the vacuum container;
and a determining device adapted to compare data relating to the
interference light obtained by differentiating an output obtained
from the second detector at an arbitrary time point during the
processing, with a plurality of patterns of data which are
interference light data of a plurality of wavelengths obtained by
differentiating outputs obtained from the second detector in
processing of another sample obtained before the processing of the
sample, and which respectively correspond to a plurality of
thicknesses of the film, and to determine reaching of a film
thickness at which the difference between the data and the
plurality of patterns is minimized, wherein when a ratio
(difference) between an output value of the first detector at the
arbitrary time point and an output value of the first detector at a
time point just before the arbitrary time point is larger than a
predetermined value, a coefficient obtained to make the output
value at the arbitrary time point equal to the output value at the
time point just before the arbitrary time point (to eliminate the
difference therebetween) is multiplied to the output of the second
detector at the arbitrary time point.
12. A plasma processing apparatus adapted to perform etching
processing of a film on the surface of a sample in a vacuum
container by using plasma formed in the vacuum container,
comprising: a detector adapted to detect interference light of a
plurality of wavelengths from the sample surface during the
processing; a differentiator adapted to obtain an actual
differential pattern constituted by a time series of actual
differential waveforms obtained by differentiating changes in
intensity of the detected interference light; a differential
waveform pattern database which is a differential waveform obtained
by differentiating a change in intensity of interference light of
the plurality of wavelengths relating to processing of another
sample obtained before the processing of the sample, and which is
constituted by a plurality of standard differential waveforms
respectively corresponding to a plurality of thicknesses of the
film; a differential waveform comparator adapted to compare a real
time differential waveform at an arbitrary time point formed by
differentiating a change in intensity of the interference light
obtained at the arbitrary time point from the start of the
processing of the sample, with a pattern of a standard differential
waveform stored in the differential waveform pattern database, and
to output a pattern matching deviation value between the real time
differential waveform and the pattern of the standard differential
waveform; an etching rate comparator adapted to compare a current
etching rate calculated on the basis of an instantaneous film
thickness value obtained by the differential waveform comparator,
with an etching rate of the differential waveform pattern database;
a film thickness corrector adapted, when the current etching rate
is abnormal, to correct the current etching rate to the etching
rate of the differential waveform pattern database; and an end
point determining device adapted to determine that the etching of a
predetermined amount is ended, by using film thickness data from
the film thickness corrector.
Description
[0001] The present application is based on and claims priority of
Japanese patent application No. 2007-057426 filed on Mar. 7, 2007,
the entire contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a film thickness and
etching depth measuring method for detecting an etching amount of a
material to be processed by an emission spectroscopy method in the
manufacture of a semiconductor integrated circuit or the like, and
to a processing method of the material to be processed by using the
measuring method. More particularly, the present invention relates
to a measuring method and device of a depth and a film thickness of
a material to be processed, suitable for accurately measuring
etching amounts of respective layers provided on a substrate in an
etching processing using plasma discharge, and for obtaining a
desired film thickness and an etching depth of the layers, and
relates to a processing method and device of the material to be
processed, using the measuring method.
[0004] 2. Description of the Related Art
[0005] In the manufacture of a semiconductor wafer, dry etching is
widely used for removing a layer of various materials formed on the
surface of a wafer, and particularly for removing a layer of a
dielectric material or forming a pattern of the dielectric
material. For the control of process parameters, it is most
important to accurately determine an etching end point to stop the
etching at a desired film thickness and etching depth during the
processing of the layers.
[0006] During the dry etching processing of the semiconductor
wafer, the emission intensity of a specific wavelength in plasma
light is changed in accordance with the progress of etching of a
specific film. Thus, conventionally, as one of the methods for
detecting the etching end point of the semiconductor wafer, there
is a method for detecting the change in the emission intensity of
the specific wavelength from plasma during the dry etching
processing, and detecting the etching end point of the specific
film on the basis of the detection result. In this case, it is
necessary to prevent an erroneous detection based on fluctuation of
a detected waveform due to a noise. As a method for accurately
detecting the change in the emission intensity, there are known a
detecting method based on a moving average method (see, for
example, Japanese Patent Laid-Open Publication No. 61-53728 (Patent
Document 1)), a method for reducing a noise by an approximate
processing based on a primary least-squares method (see, for
example, Japanese Patent Laid-Open Publication No. 63-200533
(Patent Document 2)), and the like.
[0007] In accordance with the miniaturization and high integration
of a semiconductor in recent years, an opening ratio (area to be
etched in a semiconductor wafer) is reduced, whereby the emission
intensity of the specific wavelength taken into a photodetector
from a photosensor is made weak. As a result, the level of a
sampling signal from the photodetector is lowered to make it
difficult for an end point determining device to surely detect the
etching end point on the basis of the sampling signal from the
photodetector.
[0008] Further, in the case of detecting the etching end point and
stopping the etching processing, it is actually important that the
remaining thickness of the dielectric layer is equal to a
predetermined value. In the conventional process, the whole process
is monitored by using a time and thickness control technique based
on a premise that the etching rate of each layer is constant. The
values of the etching rate are obtained by, for example, processing
a sample wafer in advance. In this method, the etching process is
stopped once time period corresponding to a predetermined etching
film thickness has lapsed, on the basis of a time monitoring
method.
[0009] However, it is known that an actual film, for example, an
SiO2 layer formed by a LPCVD (low pressure chemical vapor
deposition) technique has a low reproducibility of thickness. The
allowable thickness error due to the process fluctuation during the
LPCVD processing corresponds to about 10% of the initial thickness
of the SiO2 layer. Therefore, the actual final thickness of the
SiO2 layer remaining on a silicon substrate cannot be accurately
measured by the method based on the time monitoring. Thus, the
actual thickness of the remaining layer is finally measured by a
technique using a standard spectroscopic interferometer. When it is
found that the layer is excessively etched, the wafer is judged as
unacceptable and discarded.
[0010] Further, in an insulating film etching device, there are
known time-based changes such as a decrease in the etching rate in
accordance with repetition of etching. This may result in a case
where the etching is stopped in the midway, and hence is a problem
which must be solved. In addition, for the stable process
operation, it is important to monitor the time-based fluctuation of
the etching rate. In the conventional method, however, only the
time for determining the etching end point is monitored, and any
suitable method is not used to cope with the time-based change and
fluctuation of the etching rate. Further, for determining the
etching end point in the case where the etching time is as short as
about ten seconds, it is necessary to adapt the end point
determining method to shorten the determination preparation time
period, and also to sufficiently shorten the interval of
determination time. However, these measures are not always enough.
Further, in an insulating film, the area to be etched is 1% or less
in many cases, and the change in the plasma emission intensity from
a reaction product generated in accordance with the etching is
small. Therefore, an end point determining system capable of
detecting even a slight change is necessary, but there is no such
system that is practical and inexpensive.
[0011] On the other hand, there is also known various methods using
an interferometer as the other methods for detecting the etching
end point of the semiconductor wafer. That is, a first method is a
method in which the etching end point detection is performed by
detecting interference light (plasma light) by the use of three
kinds of color filters of red, green and blue (see, for example,
Japanese Patent Laid-Open Publication No. 5-179467 (Patent Document
3)). A second method is a method in which extreme values of an
interference waveform (maximum and minimum values: zero-crossing
points of a differential waveform) are counted by using the time
change of an interference waveform of two wavelengths and the
differential waveform of the interference waveform, and in which an
etching rate is calculated by measuring the time until the counted
value reaches a predetermined value, and the remaining etching time
until reaching a predetermined film thickness is obtained on the
basis of the calculated etching rate, to stop the etching
processing on the basis of the remaining etching time (see, for
example, Japanese Patent Laid-Open Publication No. 8-274082 (U.S.
Pat. No. 5,658,418 Specification) (Patent Document 4)). A third
method is a method in which a waveform (with the wavelength taken
as a parameter) of difference between a light intensity pattern
(with the wavelength taken as a parameter) of interference light
before processing and a light intensity pattern after the
processing or during the processing is obtained, and in which a
level difference (film thickness) is measured by the comparison
between the obtained difference waveform and difference waveforms
stored in a database (see, for example, Japanese Patent Laid-Open
Publication No. 2000-97648 (Patent Document 5)). A fourth method is
a method which relates to a rotary coating device, and in which a
film thickness is obtained by measuring the time change in
interference light over multiple wavelengths (see, for example,
Japanese Patent Laid-Open Publication No. 2000-106356 (Patent
Document 6)). A fifth method is a method in which a characteristic
behavior of the time change of interference light is obtained by
measurement and stored in a database, and the etching end
determination is performed by the comparison between the database
and a measured interference waveform, and prompts to change etching
process conditions on the basis of the determination (see, for
example, U.S. Pat. No. 6,081,334 Specification (Patent Document
7)).
[0012] In the method using the interferometer, monochromatic
radiation emitted from a laser is made incident on a wafer
including a laminated structure of different kinds of materials, at
the vertical incident angle. For example, in a wafer in which an
SiO2 layer is laminated on a Si3N4 layer, an interference fringe is
formed by the emitted light reflected by the upper surface of the
SiO2 layer, and the emitted light reflected by the interface formed
between the SiO2 layer and the Si3N4 layer. The reflected emitted
light is irradiated on a suitable detector, to generate a signal
whose intensity is changed with the thickness of the SiO2 layer
during the etching process. As soon as the upper surface of the
SiO2 layer is exposed during the etching process, the etching rate
and the current etching thickness can be continuously and
accurately monitored. There is also known a method for measuring a
predetermined emitted light emitted from plasma instead of the
laser by a spectrometer.
[0013] The above described known techniques cause the following
problems.
[0014] A. In the case of film thickness determination in a thick
film processing process (resist etch-back with film thickness of
several .mu.m and the like), the interference light changes with
time in a complicated manner for several tens periods or more,
which causes the film thickness determination to be influenced by a
slight disturbance.
[0015] B. In the case of film thickness determination in a thin
film processing process (etch-back of a gate oxide film, an oxide
film or the like), a weak change in interference light needs to be
measured, which causes the film thickness determination to be
influenced by a slight disturbance. That is, the time change in the
interference light during the thin film processing is not more than
1/2 to 1/4 periods, and the interference fringe is slightly
changed, so that it is necessary to eliminate the effect of a noise
in the film thickness determination.
[0016] C. In a wafer for processing in the mass production process,
peripheral circuits or the like are mixedly provided, and various
kinds of materials (a mask material, a material to be etched, the
other materials in the peripheral circuits) are simultaneously
subjected to etching processing, and hence interference lights from
different materials are superimposed with each other in a
complicated manner. In addition, there is a variation in the film
thickness of various materials of the wafer for processing in a lot
or between the lots, and hence the time change of the interference
light during etching processing is changed in a lot or between the
lots.
[0017] D. In the mass production processing of small amount and
many kinds, since various etching processes are mixedly performed,
the etching device is liable to change with time, so that an
abnormal discharge or the like is caused to make the plasma
fluctuate. Thereby, plasma light emission is changed and a
disturbance is superimposed on the interference light, to influence
the determination.
[0018] For the above described reasons, it has been difficult to
accurately measure and control, in a required precision, a residual
amount of film and an etching depth of a processed layer, and
especially of a processed layer in the plasma etching
processing.
[0019] An object of the present invention is to provide an etching
end point determining method using a measuring method of a film
thickness or an etching depth of a material to be processed, which
is capable of accurately measuring online an actual residual amount
of film and an etching depth of a layer to be processed in a plasma
etching process in a semiconductor element manufacturing process,
and to provide a plasma processing apparatus adapted to perform the
etching end point determining method, a plasma processing method of
a material to be processed, using the plasma processing apparatus,
and a plasma processing apparatus using the plasma processing
method.
[0020] Further object of the present invention is to provide an
etching processing method which is capable of performing highly
precise online control to make each layer of a semiconductor
element processed into a predetermined film thickness and etching
depth in a semiconductor element manufacturing process.
[0021] Further object of the present invention is to provide a
measuring device of a film thickness and an etching depth of a
material to be processed, which is capable of accurately measuring
online an actual film thickness and etching depth of a material to
be processed in a semiconductor element manufacturing process.
SUMMARY OF THE INVENTION
[0022] In order to solve the above described problems of the prior
art, and to attain the above described objects of the present
invention, the present inventors have obtained a time differential
waveform of interference waveform for each of a plurality of wave
lengths, and obtained a pattern showing a wavelength dependence of
a differential value of the interference waveform (that is, a
pattern of the differential value of the interference waveform,
with the wavelength taken as a parameter), thereby effecting
following malfunction operation prevention measures at the time of
measuring a film thickness by using the pattern.
[0023] 1) In a standard pattern database of an interference
waveform corresponding to an etching amount (film thickness and
depth) of a material to be etched, a comparison with a standard
pattern whose etching amount is not more than a target etching
amount, is not performed.
[0024] 2) In the pattern matching between an interference waveform
pattern measured at the time of etching and the standard pattern, a
standard deviation value is monitored, and when the standard
deviation value is large, the etching amount at the time point is
estimated on the basis of the past etching amount transition.
[0025] 3) When the etching amount obtained from the pattern
matching with the standard pattern is greatly different from the
amount estimated from the past etching amount transition, the
etching amount at the time point is estimated on the basis of the
past etching amount transition.
[0026] 4) When the etching rate obtained from the past etching
amount transition is compared with the etching rate of the standard
pattern database and the obtained etching rate is greatly different
from the standard pattern, the etching amount at the time point is
estimated on the basis of the past etching amount transition.
[0027] 5) When the etching rate obtained from the past etching
amount transition is compared with the etching rate of the standard
pattern database and the obtained etching rate is greatly different
from the standard pattern, the etching amount which can be obtained
by the pattern matching with the standard pattern is replaced by
the etching amount which can be obtained from the etching rate of
the standard pattern at the time point, and the etching amount at
the time point is estimated on the basis of the replaced etching
amount and the past etching amount transition.
[0028] The reason for using the pattern showing the wavelength
dependence of a time differential value of an interference waveform
in the present invention is that the measurement is based on the
in-situ (real time) measurement during etching, and hence the film
thickness of a processed film is changed every moment. Therefore,
it is possible to perform time differential processing of the
interference waveform, in order to reduce the influences of
contamination and scraping of a measuring window which cause a
problem in the interference light intensity measurement, but the
time differential processing of the interference waveform need not
always be performed.
[0029] Further, when plasma light emission is abruptly changed by
abnormal discharge associated with the time-based change of a
device, or the like, the etching amount measurement based on the
interference light and the etching end point determination based on
plasma light emission are performed in such a manner that a change
quantity (ratio: correction coefficient) of the light emission is
obtained by comparing a current light emission waveform with past
light emission waveforms, and a current and future light emission
waveforms are corrected on the basis of the correction
coefficient.
[0030] In order to solve the above described problems of the prior
art and further to achieve the above described objects of the
present invention, the present inventors have devised a method
wherein a waveform is obtained by arranging in time series time
differentials of interference waveforms for each of a plurality of
wavelengths of a reflection wave from a sample (semiconductor
element) during plasma processing, wherein on the basis of the
obtained waveform, a pattern showing a wavelength dependence of a
differential value of the interference waveform, that is, a pattern
in which the differential values of the interference waveforms,
with the wavelength taken as a parameter, are arranged in time
series, is obtained, and wherein a film thickness measurement is
performed by using a pattern which is obtained by arranging in time
series differential values of changes in the intensity of
interference light of a plurality of wavelengths relating to the
processing of another sample, and obtained before the processing of
the sample currently processed, and which is formed by a plurality
of standard differential waveforms respectively corresponding to a
plurality of thicknesses of the film to be processed of the
sample.
[0031] The reasons for using the pattern showing the wavelength
dependence of a time differential value of an interference waveform
in the present invention are as follows.
[0032] A. In the present invention, since the measurement is based
on the in-situ (real time) measurement during etching, a residual
film thickness of a processed film which is changed every moment,
can be subjected to a time differential processing by using an
interference waveform, and further a noise of the interference
waveform can be removed by the differential processing.
[0033] B. Due to the fact that refractive indices of materials to
be etched (for example, silicon and a nitride film of a mask
material) are different from each other with respect to the
wavelength, a characteristic change (film thickness dependence) of
the each material can be measured by the interference light
measurement over multiple wavelengths.
[0034] According to an aspect of the present invention, a residual
film thickness measuring method and an etching depth measuring
method which are an etching amount measuring method of a material
to be processed, includes:
[0035] A. a step of setting, with the wavelength taken as a
parameter, a standard differential pattern PS of a differential
value of interference light with respect to a predetermined etching
amount of a first (sample) material to be processed;
[0036] B. a step of setting, with the wavelength taken as a
parameter, a standard differential pattern PM of a differential
value of interference light with respect to a predetermined etching
amount of a mask material which prevents the first material to be
processed from being scraped;
[0037] C. a step of measuring, respectively for a plurality of
wavelengths, the interference light intensity of a second material
to be processed, which has the same constitution as that of the
first material to be processed and is to be actually subjected to
etching processing, and of obtaining an actual differential pattern
(Pr) of a differential value of the measured interference light
intensity, with the wavelength taken as a parameter; and
[0038] D. a step of obtaining an etching amount of the second
material to be processed on the basis of the standard differential
patterns (PS and PM) and the actual differential pattern (Pr) of
the differential value.
[0039] According to the present invention, in the plasma
processing, especially in the plasma etching processing, it is
possible to provide a measuring method of a residual film thickness
or an etching depth of a material to be processed, which is capable
of accurately measuring online an actual etching amount of the
material to be processed, and to provide a processing method of a
sample of the material to be processed by using the measuring
method.
[0040] Further, it is possible to provide an etching process
capable of performing highly precise online control to make each
layer of a semiconductor element (semiconductor device) processed
to a predetermined etching amount. Further, it is possible to
provide a measuring device of a residual thickness or a measuring
device of an etching-depth of a material to be processed, which is
capable of accurately measuring online an actual etching amount of
a layer to be processed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a block diagram showing a whole constitution of an
etching device of a semiconductor wafer, provided with an etching
amount measuring device according to a first embodiment of the
present invention;
[0042] FIG. 2 is a flow chart showing a procedure for obtaining a
residual film thickness of a material to be processed, when an
etching processing is performed by using the etching amount
measuring device shown in FIG. 1;
[0043] FIG. 3 is a figure showing time changes in interference
light and reference light, and a result of film thickness
transition during a normal etching processing according to the
first embodiment of the present invention;
[0044] FIG. 4 is a figure showing changes in interference light and
reference light, and a result of film thickness transition, when
there is discharge fluctuation in the first embodiment of the
present invention;
[0045] FIG. 5 is a figure showing time changes in interference
light and reference light, and a result of film thickness
transition, when a minimum film thickness setting processing
according to the first embodiment of the present invention is
performed;
[0046] FIG. 6 is a figure showing time changes in interference
light and reference light, and a result of film thickness
transition when a pattern matching deviation processing according
to a second embodiment of the present invention is performed;
[0047] FIG. 7 is a figure showing time changes in interference
light and reference light, and a result of film thickness
transition when an allowable film thickness range processing
according to a third embodiment of the present invention is
performed;
[0048] FIG. 8 is a block diagram showing a whole constitution of an
etching device of a semiconductor wafer, provided with an etching
amount measuring device which performs a film thickness comparison
and an etching rate comparison, according to a fourth embodiment of
the present invention;
[0049] FIG. 9 is a flow chart showing a procedure for obtaining a
residual film thickness of a material to be processed, when an
etching processing is performed by using the etching amount
measuring device shown in FIG. 8;
[0050] FIG. 10 is a figure showing time changes in interference
light and reference light, and a result of film thickness
transition when an etching rate allowable range processing
according to a fourth embodiment of the present invention is
performed;
[0051] FIG. 11 is a block diagram showing a whole constitution of
an etching device of a semiconductor wafer, provided with an
etching amount measuring device according to a fifth embodiment of
the present invention;
[0052] FIG. 12 is a block diagram showing a whole constitution of
an etching device of a semiconductor wafer, provided with a
reference light measuring device according to a modification of the
fifth embodiment of the present invention;
[0053] FIG. 13 is a block diagram showing a whole constitution of
an etching device of a semiconductor wafer, provided with the
reference light measuring device according to the modification of
the fifth embodiment of the present invention;
[0054] FIG. 14 is a flow chart showing a procedure for obtaining a
residual film thickness of a material to be processed, when an
etching processing is performed by using the etching amount
measuring device shown in FIG. 11;
[0055] FIG. 15 is a figure showing time changes in interference
light and reference light, and a result of film thickness
transition in the fifth embodiment of the present invention;
[0056] FIG. 16 is a block diagram showing a whole constitution of a
semiconductor wafer etching device provided with an etching amount
measuring device according to a sixth embodiment of the present
invention;
[0057] FIG. 17 is a flow chart showing a procedure for obtaining a
residual film thickness of a material to be processed, when an
etching processing is performed by using the etching amount
measuring device shown in FIG. 16; and
[0058] FIG. 18 is a figure showing a concept for performing an
instantaneous film thickness correction according to the sixth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0059] In the following, respective embodiments according to the
present invention will be described. Note that in the following
respective embodiments, an element having the same function as that
in the first embodiment is denoted by the same reference numeral as
that in the first embodiment, and the detailed explanation thereof
is omitted.
Embodiment 1
[0060] In the following, a first embodiment according to the
present invention will be described with reference to FIG. 1 to
FIG. 5. The first embodiment is adapted, when subjecting a material
to be processed, such as a semiconductor wafer, to a plasma etching
processing, to set a standard differential pattern PS showing a
wavelength dependence (with the wavelength taken as a parameter) of
a differential value of interference light with respect to an
etching amount of each layer of the sample material to be processed
(first material to be processed), then to respectively measure the
intensity of interference light of a plurality of wavelengths at
arbitrary time from the start of the plasma etching processing in
an actual processing of a material to be processed (second material
to be processed) having the same constitution as that of the sample
material, to obtain an actual differential pattern (Pr) (with the
wavelength taken as a parameter) showing a wavelength dependence of
differential values of the measured interference light intensity,
and to obtain an etching amount of the material to be processed by
comparing the standard differential pattern (Ps) with the actual
differential pattern (Pr) of the differential values.
[0061] First, with reference to FIG. 1, there is explained a whole
constitution of a plasma processing apparatus which is provided
with a measuring device of an etching amount (a residual film
thickness of a mask material or an etching depth of silicon)
according to the present invention, and which is an etching device
of a semiconductor wafer for forming a semiconductor element. An
etching device (plasma processing apparatus) 1 is provided with a
vacuum container 2. An etching gas is introduced into the inside of
the vacuum container 2 from gas introducing means (not shown) and
is decomposed by microwave power or the like into a state of plasma
3, so that a material to be processed 4 such as a semiconductor
wafer on a sample stage 5, are etched by the plasma 3. An emitted
light of multiple wavelengths from a measuring light source (for
example, halogen light source) provided in a spectroscope 11 of an
etching amount measuring device 10 (a residual film thickness of a
mask material or an etching depth of silicon) is introduced into
the vacuum container 2 by an optical fibre 8 and made incident at
the vertical incident angle onto the material to be processed 4. An
interference light from the material to be processed 4 is
introduced to the spectroscope 11 of the etching amount measuring
device 10 via the optical fibre 8. On the basis of the state of the
interference light, measurements of an etching depth of silicon or
a residual thickness of a mask material, and a processing for
determining an end point of etching processing are performed.
[0062] The etching amount measuring device 10 includes a
spectroscope 11, a first digital filter circuit 12, a
differentiator 13, a second digital filter circuit 14, a
differential waveform comparator 15, a differential waveform
pattern database 16, a pattern matching deviation comparator 115, a
deviation value setting device 116, a residual film thickness time
series data recorder 18, a regression analyzer 19, an end point
determining device 230, and an indicator 17 which displays a result
from the end point determining device. Note that FIG. 1 shows a
functional constitution of the etching amount measuring device 10,
an actual constitution of the etching amount measuring device 10
excluding the indicator 17 and the spectroscope 11, can be
constituted by a CPU, storage devices constituted by a ROM for
storing a mask material residual film thickness measuring
processing program or a silicon etching depth measuring processing
program, and various data such as a differential waveform pattern
database of interference light, a RAM for storing measurement data
and an external storage device and the like, a data input/output
device, and a communication control device.
[0063] In the spectroscope 11, an emitted light of multiple
wavelengths from a measuring light source (for example, halogen
light source) is introduced into the inside of the vacuum container
2 by the optical fibre 8, and made incident at the vertical
incident angle onto the material to be processed 4. An interference
light from the material to be processed 4 is introduced into the
spectroscope 11 of the etching amount measuring device 10 via the
optical fibre 8, and on the basis of the state of the interference
light, an etching depth measurement of silicon or a residual film
thickness measurement of a mask material, and an end point
determination processing of etching processing are performed.
[0064] The emission intensity of the interference light of multiple
wavelengths received by the spectroscope 11 are made into current
detecting signals, each of which corresponds to emission intensity
for each specific wavelength, and converted to voltage signals. The
signals of a plurality of specific wavelengths (j denotes the
number of wavelength) outputted as sampling signals by the
spectroscope 11 are stored as time series data yi,j in a storage
device such as a RAM (not shown). Next, the time series data yi,j
at time i is subjected to a smoothing processing by the first
digital filter circuit 12, and stored as smoothed time series data
Yi,j in a storage device such as a RAM (not shown). On the basis of
the smoothed time series data Yi,j, time series data di,j of
differential coefficient values (first-order differential values or
second-order differential values) is calculated by the
differentiator 13, and stored in a storage device such as a RAM
(not shown). The time series data di,j of the differential
coefficient values is subjected to a smoothing processing by the
second digital filter circuit 14, and stored as smoothed
differential coefficient time series data Di,j in a storage device
such as a RAM (not shown). Then, an actual differential pattern
(Prj)=.SIGMA.j (Di,j) (wavelength j taken as a parameter) which
shows the wavelength dependence of the differential value of the
interference light intensity can be obtained from the smoothed
differential coefficient time series data Di,j.
[0065] On the other hand, in the differential waveform pattern
database 16, there are set differential waveform pattern data
values PSj of the interference light intensity with respect to the
each wavelength corresponding to an etching depth which is obtained
beforehand by using the first (sample) material to be processed,
and expressed by a residual film thickness s of the material to be
processed, so as to serve as a target of the etching amount
measurement. In the differential waveform comparator 15, the actual
differential pattern (Prj)=.SIGMA.(Di,j) and the differential
waveform pattern data value PSj of the film thickness s are
compared with each other. In the pattern matching deviation
comparator 115, a pattern matching (minimum) deviation value
.sigma.s at which a pattern matching deviation (.sigma.s=
(.SIGMA.j(Di,j-PSj).times.(Di,j-PSj)/j)) is minimized, is obtained
and compared with a pattern matching (set) deviation value .sigma.0
set beforehand in the deviation value setting device 116. When the
pattern matching (minimum) deviation value .sigma.s is not more
than the pattern matching (set) deviation value .sigma.0, the film
thickness value s is stored as an instantaneous film thickness Zi
at time i in the film thickness time series data recorder 18. When
the pattern matching (minimum) deviation value .sigma.s is not less
than the pattern matching (set) deviation value .sigma.0, the
instantaneous film thickness Zi at time i is not stored.
[0066] In the regression analyzer 19, a calculated film thickness F
at time i is obtained on the basis of the regression straight line
approximation using the instantaneous film thickness data before
the time i. Whether or not the calculated film thickness F is not
more than the target film thickness set beforehand is determined by
the end point determining device 230. The result of etching amount
of the material to be processed which is obtained by the above
described processing is displayed by the result indicator 17.
[0067] Note that there is shown a case where only one spectroscope
11 is provided in the first embodiment, but when it is desired that
the inside of the surface of a material to be processed is measured
in an expanded state and controlled, a plurality of spectroscopes
11 may be provided.
[0068] Next, by using a flow chart shown in FIG. 2, there is
explained a procedure for obtaining an etching amount of a material
to be processed, when performing etching processing by the etching
amount measuring device 10 shown in FIG. 1.
[0069] First, there are performed a setting of a target etching
amount (target residual film thickness value), and a setting of
differential patterns (residual film thickness standard
differential patterns) PSj of wavelength regions (at least three
wavelength regions) extracted from the differential waveform
pattern database 16, and a setting of a pattern matching (set)
deviation value .sigma.0 (step 600). That is, a standard
differential pattern PSj corresponding to an etching amount
(residual film thickness) s which is needed in accordance with
processing conditions of a material to be processed is set
beforehand in the differential waveform pattern database 16.
[0070] In the subsequent step, a sampling (at every 0.25 to 0.5
seconds) of interference light from an object to be processed is
started (step 601). That is, a sampling start instruction is issued
in accordance with the start of etching processing. The emission
intensity of multiple wavelengths which changes in accordance with
the progress of etching is detected by a photodetector
(spectroscope 11) as a photodetection signal of a voltage
corresponding to the emission intensity. The photodetection signal
of each wavelength j from the spectroscope 11 is digitally
converted so that a sampling signals yi,j are obtained.
[0071] Next, multiple wavelength output signals yi,j from the
spectroscope 11 are smoothed by the first stage digital filter 12,
so that smoothed time series data Yi,j are calculated (step 602).
That is, a noise is reduced by the first stage digital filter, so
that smoothed time series data Yi,j are obtained.
[0072] Next, differential coefficients di,j for each wavelength are
calculated by differentiating the smoothed time series data Yi,j by
the S-G method in the differentiator 13 (step 603). That is,
(first-order or second-order) differential coefficients di,j of
signal waveforms for the respective wavelengths are obtained by the
differential processing (the S-G method). Further, the smoothed
differential coefficient time series data Di,j are calculated by
the second stage digital filter 14 (step 604). Then, in the
differential waveform comparator 15, a matching pattern (minimum)
deviation value .sigma.s= (.SIGMA.(Di,j-PSj)2/j) is calculated to
obtain a minimum value .sigma. of the matching pattern (minimum)
deviation value .sigma.s with respect to the residual film
thickness s (step 605).
[0073] Next, in the pattern matching deviation comparator 115, the
determination whether .sigma..ltoreq..sigma.0 is performed by
comparing the calculated matching pattern (minimum) deviation value
.sigma. with the matching pattern (set) deviation value .sigma.0
(step 606). When .sigma..ltoreq..sigma.0, it is determined that the
film thickness of the material to be processed is made into a
residual film thickness s, and an instantaneous film thickness Zi
at a time point i is stored in the residual film thickness time
series data recorder 18 (step 607). Except when
.sigma..ltoreq..sigma.0, the instantaneous film thickness Zi at the
time point i cannot be obtained from the standard differential
pattern database, and the instantaneous film thickness is not
stored in the residual film thickness time series data recorder 18
(step 608). These smoothed differential coefficient time series
data Di,j and the differential patterns PSj set beforehand in the
differential waveform comparator 15 are compared with each other,
so that a residual film thickness value Zi at the time point is
calculated (step 615).
[0074] Next, by the use of the stored past time series data Zi, a
first-order regression straight line Y=Xa.times.t+Xb (Y: residual
film amount, t: etching time, absolute value of Xa: etching rate,
and Xb: initial film thickness) is obtained by the regression
analyzer 19, so that a calculated residual film amount F at time
point i (present time) is calculated on the basis of the regression
straight line (step 609). Next, in the end point determining device
230, the calculated residual film amount F and the target residual
film thickness value are compared with each other to determine the
etching amount (residual film thickness value). When the calculated
residual film amount F is not more than the target residual film
thickness value, it is determined that the etching amount of the
material to be processed is made into a predetermined value, and
the comparison result is displayed in the indicator 17 (step 610).
When the calculated residual film amount F is not less than the
target residual film thickness value, the process returns to step
602 and these steps are repeated. Finally, when the calculated
residual film amount F is not more than the target residual film
thickness value in step 610, the setting of the end of the sampling
is performed (step 611).
[0075] Here, the calculation of the smoothed differential
coefficient time series data Di relating to a certain wavelength j
at time point i is explained. As the first digital filter circuit
12, for example, a second-order Butterworth type low pass filter is
used. The smoothed time series data Yi can be obtained by the
second-order Butterworth type low pass filter on the basis of the
following formula (1).
Yi=b1yi+b2yi-1+b3yi-2-[a2Yi-1+a3Yi-2] (1)
[0076] Here, numerical values of the coefficients b and a are
different in dependence upon a sampling frequency and a cut-off
frequency. For example, there are used a2=-1.143, a3=0.4128,
b1=0.067455, b2=0.13491, b3=0.067455 (sampling frequency: 10 Hz,
cut-off frequency: 2.5 Hz), or a2=-0.00073612, a3=0.17157,
b1=0.29271, b2=0.58542, b3=0.29271 (cut-off frequency: 2.5 Hz), or
the like.
[0077] The time series data di of second-order differential
coefficient values are calculated as follows on the basis of the
following formula (2) using the polynomial fitting smoothing
differential method of the time series data Yi of five points by
the differentiator (differential coefficient operation circuit)
13.
di = j = 2 j = 2 wjYi + j ( 2 ) ##EQU00001##
Here, w-2=2, w-1=-1, w0=-2, w1=-1, and w2=2.
[0078] By the use of the time series data di of the differential
coefficient values, the smoothed differential coefficient time
series data Di can be obtained by the second digital filter circuit
(second-order Butterworth type low pass filter, but the
coefficients a and b of the digital filter circuit may be
different) 14 based on the following formula (3).
Di=b1di+b2di-1+b3di-2-[a2-Di-1+a3Di-2] (3)
[0079] FIG. 3 shows a relation between the interference intensity
and the etching time when poly-silicon is subjected to an etching
processing and the determination is made at a poly-silicon film
thickness of 45 nm. An initial film thickness of poly-silicon as a
material subjected to the etching processing is about 170 nm. In
the figure, there are shown an interference light waveform of a
wavelength of 500 nm observed from the wafer surface, a first-order
differential waveform of the interference light waveform, a plasma
light (reference light) of a wavelength of 500 nm obtained by not
observing the wafer surface, and a time change (instantaneous film
thickness transition) of the film thickness of poly-silicon during
the etching processing, obtained by a matching comparison between
the first-order differential waveform and a standard differential
pattern. Here, the instantaneous film thickness transition is
obtained in such a manner that the first-order differential pattern
at each time point is compared with the standard differential
pattern corresponding to each film thickness, to select a film
thickness with a smallest pattern matching deviation, and the
change of the selected film thickness is plotted.
[0080] FIG. 4 shows a change in the instantaneous film thickness
transition generated when the above described etching processing of
poly-silicon is continuously performed. In the figure, the
instantaneous film thickness is abruptly reduced during the etching
processing time period from about 25 seconds to about 31 seconds,
so that the film thickness reaches about 10 nm. This phenomenon is
considered to be caused by a slight change in etching plasma due to
reaction products accumulated in a part inside the chamber or by a
slight change in electric power generating the plasma. However,
after the instantaneous film thickness is abruptly reduced only
during the etching processing time period from about 25 seconds to
about 30 seconds, the transition of the instantaneous film
thickness returned to the state before the abrupt change and the
etching processing is normally ended. When such change in the
instantaneous film thickness is caused, for example, the film
thickness becomes below the determination film thickness of 45 nm
at the time point of 25 seconds. Thus, the etching processing is
ended at the film thickness of about 100 nm, and a defective
element is manufactured. Therefore, the film thickness determining
system needs to perform an accurate film thickness determination in
correspondence with such abrupt change.
[0081] Here, in order to prevent the abrupt lowering of the
instantaneous film thickness, the behavior of the interference
waveform was analyzed. Generally, in the interference waveform
change, when a material is made into a thin film, the interference
light ceases to change in many wavelength regions, and hence
first-order differential changes at these wavelengths
simultaneously approach zero. Further, even when plasma fluctuation
is caused, the corresponding changes are simultaneously caused in
many wavelength regions, and the first-order differentials at the
wavelengths are simultaneously changed. As the change in plasma is
reduced, the first-order differential at the wavelengths approaches
zero. Such behavior of the first-order differential is similar to
that of the change in the interference light of a thin film.
Therefore, in order to prevent such abrupt change, it is necessary
to avoid the use of data for thin film thickness as much as
possible among the data of standard differential patterns used for
the thickness measurement. That is, it is necessary to perform the
pattern matching processing with the standard differential pattern,
in such a manner that a standard differential pattern of a film
thickness less than a target determination film thickness is not
used for obtaining an instantaneous film thickness during the
etching processing.
[0082] FIG. 5 shows a result in the case where a minimum film
thickness of the standard differential pattern used for the pattern
matching processing is set to 20 nm. From the figure, it can be
seen that the abrupt film thickness reduction can be avoided in the
etching processing time period from about 25 to about 30 seconds in
which plasma fluctuation is caused. Further, as a result of the
pattern matching processing at the time when plasma fluctuation is
caused, the pattern matching deviation is 0.05 or more, and there
is no film thickness at which the standard differential pattern and
the actual differential pattern match with each other. Thus, the
film thickness at the time is set to the initial film thickness
when the standard differential pattern is created. As for the
setting of the standard differential pattern with respect to the
film thickness used for the film thickness measurement, when a
target residual film thickness value is set in step 600 in the flow
chart shown in FIG. 2, a minimum film thickness of the standard
differential pattern is defined on the basis of this value, and the
standard differential pattern not less than the minimum film
thickness is adopted.
[0083] Next, there is shown a further embodiment for avoiding
plasma fluctuation. Here, there is utilized the fact that when
plasma fluctuation is caused, the pattern matching deviation is
increased. Generally, during a period of several seconds from the
start of the differential processing for film thickness
determination after the start of the etching processing, the
interference waveform is slightly disturbed due to the influence of
plasma ignition, so that the pattern matching deviation value
.sigma. deteriorates. On the basis of the pattern matching (set)
deviation value .sigma.0 at this time point, the pattern matching
deviation value .sigma. after the time point is calculated. When
the pattern matching deviation value .sigma. is larger than the
pattern matching (set) deviation value .sigma.0, it is determined
that the pattern matching with the standard differential pattern is
not enough. Then, the instantaneous film thickness Zi is not
obtained from the standard differential pattern, but set, for
example, to the initial film thickness of the database (standard
differential patterns). Thus, the instantaneous film thickness data
set as the initial film thickness at this time point is not used
for the regression straight line approximate analysis for obtaining
the calculated film thickness F.
Embodiment 2
[0084] As a second embodiment, FIG. 6 shows a result obtained in
such a manner that an instantaneous film thickness Zi at a time
point i during etching processing is obtained by using a pattern
matching deviation value .sigma.0=0.04 during a period of 2 seconds
after the start of the differential processing, and that a
calculated film thickness F at the time point i is calculated by
the regression straight line approximation on the basis of the time
series data of the instantaneous film thickness Zi before the time
point i. From the figure, it can be seen that the obtained film
thickness transition can be stabilized without being influenced by
plasma fluctuation, and the film thickness determination can be
sufficiently performed. Here, the pattern matching deviation value
.sigma.0 is obtained in a period of several seconds after the start
of the time differential processing for each wafer processing, and
the pattern matching determination is performed. However, it may
also be adapted such that a plurality of wafers are processed and
an average value of respective pattern matching deviation values
.sigma.0 is set in step 600 in the flow chart shown in FIG. 2.
[0085] In the process of mass production adapted to process a
semiconductor wafer by using plasma in order to produce a
semiconductor device from the semiconductor wafer, a plasma
processing apparatus such as the device according to the present
invention is continuously operated, to cause fluctuation in
conditions in the processing chamber, due to adherence and
deposition of products onto the surface of member inside the
processing chamber in accordance with the increase in the number of
pieces of materials to be processed, and the like. This causes the
state of plasma generated in the processing chamber to fluctuate,
and causes the surface shape obtained as a result of the processing
to be changed. Therefore, it is necessary to manage the process so
as to control the fluctuation in the result of processing of the
material to be processed in the above described mass production. In
the case where such mass production management is performed in the
present embodiment, the number of times when the pattern matching
deviation value exceeds a predetermined value is monitored in the
processing for each wafer as a material to be processed, and the
number of times is counted by a recorder, a counter (both not
shown), or the like. Such counting may also be performed by the
pattern matching deviation comparator 115.
[0086] Further, it is possible to grasp a device status and a wafer
etching status by comparing transition of the number of times with
a predetermined value (for example, a predetermined value about a
value of the number of times and an increasing rate). That is, when
the number of times is gradually increased, a predetermined value
of the number of times is used as a measure to start maintenance
work, such as the wet cleaning, in the plasma processing apparatus.
When the number of times is abruptly increased and the increasing
rate becomes larger than a predetermined value, the need for
measures, such as conveying the wafer to be processed to the wafer
inspection step, is informed to a user, or a warning is issued to
the user. Such notification and warning are displayed, for example,
in the indicator 17 shown in FIG. 1 and the like, in accordance
with a command from the pattern matching deviation comparator
115.
Embodiment 3
[0087] Next, a third embodiment for avoiding plasma fluctuation is
explained. Here, instead of stabilizing the instantaneous film
thickness transition by the above described pattern matching
deviation comparison, the instantaneous film thickness Zi at a time
point i during etching processing is obtained. In the case where a
calculated film thickness F at the time point i is calculated by
the regression straight line approximation on the basis of the time
series data of the instantaneous film thickness Zi before the time
point i, and where the difference (absolute value) between the
calculated film thickness F and the instantaneous film thickness Zi
is not less than a film thickness allowable value set beforehand,
it is determined that the instantaneous film thickness Zi at the
time point i is not an accurate film thickness. FIG. 7 shows a
result obtained by a method in which the instantaneous film
thickness Zi is determined to be not accurate in this manner is not
used for the calculation of the calculated film thickness based on
the regression straight line approximation after the time point i.
From FIG. 7, it can be seen that even with this method, it is also
possible to similarly avoid the abrupt change during the etching
processing period from about 25 seconds to about 30 seconds in
which plasma fluctuation is caused as shown in FIG. 4. Here, a
value of 20 nm is used as the film thickness allowable value. The
setting of the film thickness allowable value can be determined on
the basis of the change in the interference waveform appearing
during the etching processing. For example, when poly-silicon of
the initial film thickness of 200 nm is etched as a material to be
etched, since the interference waveform at the wavelength of 500 nm
continues for about 7/2 periods, the interference waveform within
1/4 periods (in which the sign of differential value is changed)
may be accurately determined, and the film thickness is set to
about 20 nm.
Embodiment 4
[0088] Next, there is explained a fourth embodiment which relates
to avoiding erroneous determination in the film thickness
measurement, and which utilizes the fact that the etching rate
during the mass production processing is almost constant and the
fluctuation of the etching rate is in a range of at most .+-.10%.
From the instantaneous film thickness transition shown in FIG. 3,
it can be seen that the inclination of the change of the
instantaneous film thickness Zi during the normal etching
processing (from 32 to 60 seconds) is constant, and the etching
rate obtained from the inclination is about 123 nm/min. On the
other hand, it can be seen that the inclination of the change of
the instantaneous film thickness during the period (from 25 to 31
seconds) in which plasma fluctuation is caused as shown in FIG. 4
is smaller than the inclination during the normal etching
processing. When the etching rate becomes twice or half in the mass
production processing, the etching processing is abnormal, and
hence it is necessary to return the etching device to the normal
state by performing processing such as the wet cleaning of the
etching device. FIG. 8 shows a constitution of a plasma processing
apparatus provided with a film thickness determining device
according to a fourth embodiment. Further, FIG. 9 shows a flow
chart of the film thickness determination.
[0089] As shown in FIG. 8, the fourth embodiment has a feature that
an residual film thickness comparator 20 and an etching rate
comparator 21 are added between the regression analyzer 19 and the
end point determining device 230 of the etching amount measuring
device 10 in the plasma processing apparatus shown in FIG. 1.
[0090] First, as shown in FIG. 9, there are set a target etching
amount (target residual film thickness value), differential
patterns (residual film thickness standard differential patterns)
PSj whose wavelength regions (at least three wavelength regions)
are extracted from the differential waveform pattern database, a
pattern matching (set) deviation value .sigma.0, a film thickness
allowable value Z0, and an etching rate allowable value R0 (step
1600).
[0091] In the subsequent step, the sampling of interference light
(for example, every 0.25 to 0.5 seconds) is started (step 1601).
That is, a sampling start instruction is issued in correspondence
with the start of etching processing. The emission intensity of
multiple wavelengths which is changed in accordance with the
progress of etching is detected by the photodetector as a
photodetection signal of a voltage corresponding to the emission
intensity. The photodetection signal of the spectroscope 11 is
digitally converted, so that the sampling signals yi,j are
acquired.
[0092] Next, the multiple wavelength output signals yi,j from the
spectroscope 11 are smoothed by the first stage digital filter 12,
and the smoothed time series data Yi,j are calculated (step 1602).
That is, a noise is reduced by the first stage digital filter, so
that the smoothed time series data Yi,j are obtained.
[0093] Next, the differential coefficients di,j are calculated by
the S-G method in the differentiator 13 (step 1603). That is,
(first-order or second-order) differential coefficients di of the
signal waveforms are obtained by the differential processing (the
S-G method). Further, the smoothed differential coefficient time
series data Di,j are calculated by the second stage digital filter
14 (step 1604). Then, in the differential waveform comparator 15,
the pattern matching (minimum) deviation value .sigma.s=
(.SIGMA.(Di,j-PSj)2/j) is calculated to obtain a minimum value
.sigma. which is the smallest pattern matching (minimum) deviation
value .sigma.s with respect to a film thickness s (step 1605).
[0094] Next, in the pattern matching deviation comparator 115, the
determination whether .sigma..ltoreq..sigma.0 is performed for
comparing the calculated matching pattern deviation value (minimum
value) .sigma. and the matching pattern (set) deviation value
.sigma.0 with each other (step 1606). When .sigma..ltoreq..sigma.0,
it is determined that the film thickness of the material to be
processed is made into the film thickness s, and an instantaneous
film thickness Zi at a time point is stored in the residual film
thickness time series data recorder 18 (step 1607). Except when
.sigma..ltoreq..sigma.0, the instantaneous film thickness Zi at the
time point i cannot be obtained from the standard differential
pattern database, and the instantaneous film thickness is not
stored in the residual film thickness time series data recorder 18
(step 1608).
[0095] As for the etching rate during the processing, the
calculated film thickness F and the inclination Xa thereof are
obtained by the first-order regression straight line approximation
in the regression analyzer 19 on the basis of the data in the
residual film thickness time series data recorder 18 (1609). Next,
in the residual film thickness comparator 20, it is determined
whether or not the instantaneous film thickness Zi is a film
thickness limited by the calculated film thickness F and the film
thickness allowable value z0 (F-z0.ltoreq.Zi.ltoreq.F+z0), or in
the etching rate comparator 21, it is determined whether or not the
inclination of the straight line Xa obtained by the regression
approximation is an etching rate limited by the etching rate R at
the time of creating the standard differential pattern and the
etching rate allowable value R0 (R-R0.ltoreq.Xa.ltoreq.R+R0). In
the case where (F-z0.ltoreq.Zi.ltoreq.F+z0) or where
(R-R0.ltoreq.Xa.ltoreq.R+R0), the instantaneous film thickness Zi
is stored in the residual film thickness time series data recorder
18 (step 1612). In the other cases, the instantaneous film
thickness Zi is not stored in the residual film thickness time
series data recorder 18 (step 1611).
[0096] Subsequently, the film thickness determination is performed
on the basis of the calculated film thickness F. When the
calculated film thickness F is not more than the target residual
film thickness value, it is determined that the etching amount of
the material to be processed has reached the predetermined value,
and the result is displayed in the indicator 17 (step 1613). The
state of the film thickness change during etching can be displayed
by displaying the calculated film thickness F. When the calculated
film thickness F is not less than the target residual film
thickness value, the process returns to step 1602 and these steps
are repeated. Finally, the setting of the end of the sampling is
performed (step 1614).
[0097] FIG. 10 shows a result of the calculated film thickness
transition in the fourth embodiment, when the allowable film
thickness range value is set to 20 nm, the etching rate allowable
value is set to 50% (etching rate: 117 nm/min), and the minimum
film thickness is set to 1 nm (target residual film thickness
value: 50 nm). From the figure, it can be seen that the transition
of the calculated film thickness F is stabilized without being
influenced by plasma fluctuation, so that the target film thickness
of 50 nm can be accurately determined. Here, the target film
thickness is a film thickness set as a target to be obtained by the
etching processing, and the minimum film thickness is a minimum
value of the film thickness which can be determined when the
minimum value is determined. In the present embodiment, since the
film thickness allowable range value is 20 nm, the remaining film
thickness may be in the range of the target film thickness 50
nm.+-.20 nm. In the case where the minimum film thickness value of
30 nm can be detected, even when a film thickness not more than the
minimum film thickness value is suddenly detected, the detected
value can be ignored.
[0098] When the etching processing is normally performed, the
number of data of the instantaneous film thickness which have not
been stored in the residual film thickness time series data
recorder 18, is almost zero. When the etching characteristic of the
etching device is changed due to the time-based change of the
device, the matching of the interference differential pattern
deteriorates so as to increase the number of data which are not
stored. Further, when the specification of the wafer to be
processed is changed, the pattern matching deteriorates so as to
increase the number of data. Therefore, in the mass production
process, it is possible to perform the device management of the
etching device and the production management of processed wafers,
by displaying in the indicator 17 the number of data of the
instantaneous film thickness which have not been stored in the
residual film thickness time series data recorder 18.
Embodiment 5
[0099] Next, there is explained a fifth embodiment in which the
film thickness determination is performed by correcting the
interference light and reference light, which are observed when
plasma fluctuation is caused. The interference light is changed by
a steep change in plasma emission caused by plasma fluctuation
(abnormality), which may make it difficult to obtain an accurate
film thickness, as shown, for example, in FIG. 4 and FIG. 5.
Further, since the digital filter processing and the polynomial
fitting smoothing differential processing are used to improve the
S/N ratio of observed optical signals, the steep change in the
light emission is moderated by these processings to cause the
effect of the steep change to appear for a long period of time. As
a method for avoiding this effect, there is a method adapted such
that when there is a steep change in plasma emission, the digital
filter processing and the polynomial fitting smoothing differential
processing are temporarily interrupted. However, when these
processings are interrupted, the instantaneous film thickness
cannot be obtained to make it impossible to perform the film
thickness determination.
[0100] Thus, there is explained a method for obtaining a film
thickness in a manner of detecting a steep change in plasma,
obtaining a change quantity for each wavelength used for
measurement, correcting an optical signal of each wavelength in
accordance with the change quantity of each wavelength, and
performing processings such as the digital filter processing and
the polynomial fitting smoothing differential processing to the
corrected optical signals.
[0101] When collecting the standard pattern data as a database for
film thickness determination, a change quantity (difference during
a period between time points i and i-1) at a sampling point of the
time point i, of the emission data obtained by measuring the time
change of the interference light and the reference light, is
checked for each wavelength, so that maximum change amounts during
etching processing are obtained for the interference light and the
reference light. A noise threshold value is set on the basis of the
maximum changes per one sampling, so that a steep change in plasma
is detected by using the noise threshold value.
[0102] Next, when there is a change quantity exceeding the noise
threshold value, each correction coefficient for each wavelength
(intensity ratio: Si,j=yi-1,j/yi,j) is obtained, to correct the
optical signals yi,j on the basis of a formula: y'i,j=Si,j*yi,j.
The instantaneous film thickness Zi is obtained by performing
processings such as the digital filter processing and the
polynomial fitting smoothing differential processing for the
corrected optical signals y'i, j, and the determination is
performed.
[0103] With reference to FIG. 11, there is explained a constitution
of a plasma processing apparatus which is capable of avoiding the
plasma fluctuation in this manner and is provided with a film
thickness determining device according to a sixth embodiment, in
which the film thickness determination was performed. An etching
device (plasma processing apparatus) 1 is provided with a vacuum
container 2. An etching gas introduced into the inside of the
vacuum container 2 is decomposed by microwave power or the like
into a state of plasma, so that a material to be processed 4 such
as a semiconductor wafer on a sample stage 5, is etched by the
plasma 3. An emitted light of multiple wavelengths from a measuring
light source (for example, halogen light source) provided in a
spectroscope 11 of an etching amount measuring device 10 (a
residual film thickness or an etching depth) is introduced into the
vacuum container 2 by an optical fibre 8 and made incident at the
vertical incident angle onto the material to be processed 4. An
interference light from the material to be processed is introduced
to the spectroscope 11 of the etching amount measuring device 10
via the optical fibre 8. On the basis of the state of the
interference light, a measurement of an etching film thickness of
silicon and a processing for determining an end point of etching
are performed.
[0104] The etching amount measuring device 10 includes the
spectroscope 11, a sampling data comparator 110, a noise value
setting device 111 for setting a noise threshold value, a
correction coefficient recorder and indicator 113, a sampling data
corrector 112, a first digital filter circuit 12, a differentiator
13, a second digital filter circuit 14, a differential waveform
comparator 15, a differential waveform pattern database 16, a
pattern matching deviation comparator 115, a deviation value
setting device 116, a residual film thickness time series data
recorder 18, a regression analyzer 19, an end point determining
device 230, and an indicator 17 for displaying a result from the
end point determining device 230.
[0105] The emission intensities of multiple wavelengths received by
the spectroscope 11 are made into current detecting signals, each
of which corresponds to emission intensity for each specific
wavelength, and converted to voltage signals. The signals of a
plurality of specific wavelengths (j pieces) outputted as sampling
signals by the spectroscope 11 are compared, in the sampling data
comparator 110, with values set beforehand in the noise value
setting device 111. When the change value of the signals exceeds
the noise value, the time series data yi,j are corrected in the
sampling data corrector 112, so as to prevent the signals from
being changed. The correction coefficients at this time are stored
in the correction coefficient recorder and indicator 113. In this
way, the time series data y'i,j obtained by being corrected on the
basis of the instantaneously changed signals are stored in a
storage devices such as a RAM. Next, the time series data y'i,j at
a time point i are smoothed by the first digital filter circuit 12,
and stored in a storage device such as a RAM, as a smoothed time
series data Yi,j. On the basis of the smoothed time series data
Yi,j, time series data di,j of differential coefficient values
(first-order differential values or second-order differential
values) are calculated by the differentiator 13, and stored in a
storage devices such as a RAM. The time series data di,j of the
differential coefficient value are subjected to a smoothing
processing by the second digital filter circuit 14, and stored as
smoothed differential coefficient time series data Di,j in a
storage device such as a RAM. Thus, an actual pattern (with
wavelength taken as a parameter) which shows the wavelength
dependence of the differential value of interference light
intensity can be obtained from the smoothed differential
coefficient time series data Di,j.
[0106] On the other hand, in the differential waveform pattern
database 16, there are set beforehand differential waveform pattern
data values PSj of the interference light intensity with respect to
respective wavelengths, each of which value corresponds to a film
thickness s of the material to be processed, as an object of the
etching amount measurement. In the differential waveform comparator
15, an actual pattern and the differential waveform pattern data
value PSj of the film thickness s are compared with each other. In
the pattern matching deviation comparator 115, a pattern matching
(minimum) deviation value .sigma.s at which a pattern matching
deviation (.sigma.s= (.SIGMA.j(Di,j-PSj).times.(Di,j-PSj)/j)) is
minimized, is obtained and compared with a deviation value .sigma.0
set beforehand in the deviation value setting device 116. When the
pattern matching (minimum) deviation value .sigma.s is not more
than the pattern matching (set) deviation value .sigma.0, the film
thickness value s is stored as an instantaneous film thickness at
the time point i in the film thickness time series data recorder
18. When the pattern matching (minimum) deviation value as is not
less than the pattern matching (set) deviation value .sigma.0, the
instantaneous film thickness at the time point i is not stored. In
the regression analyzer 19, a calculated film thickness F at the
time point i is obtained on the basis of the regression straight
line approximation using the instantaneous film thickness data Zi
before the time point i. Whether or not the calculated film
thickness F is not more than the target film thickness set
beforehand is determined by the end point determining device 230.
The resultant etching amount of the material to be processed, which
is obtained by the above described processing, is displayed by the
result indicator 17.
(Modification)
[0107] In the block diagram shown in FIG. 11, there is described
the processing means of the interference light. However, in a
modification of the fifth embodiment as shown in FIG. 12, plasma
light measuring means 1001 provided in the side wall of the etching
processing container 2, a spectroscope 1003, a sampling data
comparator 1110, and a noise value setting device 1111 are provided
not for the interference light measurement based on the light from
the external light source, but as the processing means of the
interference light measurement utilizing plasma light. Further, as
plasma light measuring means, plasma light measuring means 1002
provided in the bottom of the etching processing container 2, the
spectroscope 1003, the sampling data comparator 1110, and the noise
value setting device 1111 may also be provided as shown in FIG. 13.
These devices operate similarly to the spectroscope 103, the
sampling data comparator 110, and the noise value setting device
111 which are shown in FIG. 11. The output of the sampling data
comparator 1110 is outputted to the first digital filter 12 via the
sampling data corrector 112, similarly to the output of the
sampling data comparator 110 in FIG. 11.
[0108] Next, with reference to a flow chart shown in FIG. 14, there
is explained a procedure for obtaining an etching amount of a
material to be processed, when the etching processing is performed
by the etching amount measuring device 10 shown in FIG. 11.
[0109] First, there are set a target etching amount (target
residual film thickness value), differential patterns PSj whose
wavelength regions (at least three wavelength regions) are
extracted from the standard differential pattern database, a
deviation value .sigma.0, and a noise value N (step 2600). That is,
a standard differential pattern corresponding to an etching amount
s needed in accordance with processing conditions of a material to
be processed, is set beforehand in the differential waveform
pattern databases 15 and 25.
[0110] In the subsequent step, the sampling of the interference
light (for example, every 0.25 to 0.5 seconds) is started (step
2601). That is, a sampling start instruction is issued in
correspondence with the start of the etching processing. The
emission intensity of multiple wavelengths which is changed in
accordance with the progress of etching is detected by a
photodetector as a photodetection signal of a voltage corresponding
to the emission intensity. The photodetection signals of the
spectroscope 11 are digitally converted, so that the sampling
signal yi,j are acquired.
[0111] Next, differences between the multiple wavelength output
signals yi,j and signals yi-1,j at a time point i-1 are obtained
(step 2604). It is determined whether or not the differences
(yi,j-yi-1,j) are larger than the value N set beforehand in the
noise value setting device 111, by using the sampling data
comparator 110 (step 2620). In the cases of the embodiments shown
in FIG. 12 and FIG. 13, whether or not output signals relating to
plasma emission at the time point i-1 and the time point are larger
than a value set beforehand in the noise value setting device 1111
is determined by using the sampling data comparator 1110. When the
output signals are larger than the preset value, change rates, that
is, correction coefficients are obtained by a formula: Si,j
yi-1,j/yi,j (step 2621). When the output signals are smaller than
the preset value, the correction coefficients are set as Si,j=1
(step 2622). The multiple wavelength output signals yi,j from the
spectroscope are corrected by these correction coefficients in a
manner that y'i,j=Si,j.times.yi,j (step 2623). Note that these
correction coefficient values are stored or displayed in the
correction coefficient recorder and indicator 113, and are used for
the mass production management of the etching process. The signals
y'i,j corrected in this way are transmitted to and smoothed by the
first stage digital filter 12, so that the time series data Yi,j
are calculated (step 2602). That is, the noise is reduced by the
first stage digital filter, so that the smoothed time series data
Yi,j are obtained.
[0112] Next, the differential coefficients di,j are calculated by
the S-G method in the differentiator 13 (step 2603). That is, the
(first-order or second-order) differential coefficients di of the
signal waveforms are obtained by the differential processing (the
S-G method). Further, the smoothed differential coefficient time
series data Di,j are calculated by the second stage digital filter
14 (step 2604). Then, in the differential waveform comparator 15,
the value .sigma.s= (.SIGMA.(Di,j-PSj)2/j) is calculated, to obtain
a minimum value .sigma. of the pattern matching (minimum) deviation
value .sigma.s with respect to the film thickness s (step 2605).
Next, in the pattern matching deviation comparator 115, the
determination (.sigma.s: matching pattern (minimum) deviation value
.sigma., and .sigma.0: matching pattern (set) deviation value) is
performed (step 2606). When .sigma.s.ltoreq..sigma.0, it is
determined that the film thickness of the material to be processed
is made into the film thickness s, and an instantaneous film
thickness at the time point i is stored in the residual film
thickness time series data recorder 18 (step 2607). Except when
.sigma.s.ltoreq..sigma.0, the instantaneous film thickness at the
time point i cannot be obtained from the standard differential
pattern database, and the instantaneous film thickness is not
stored in the residual film thickness time series data recorder 18
(step 2608). The smoothed differential coefficient time series data
Di,j and differential patterns PZj set beforehand in the
differential waveform comparator 15 are compared with each other,
so that a residual film value Zi at that time point is calculated
(step 2615). Next, by the use of the stored past time series data
Zi, a first-order regression straight line Y=Xa.times.t+Xb (Y:
residual film amount, t: etching time, absolute value of Xa:
etching rate, Xb: initial film thickness) is obtained by the
regression analyzer 19, so that a calculated residual film amount F
at the time point i (present time) is calculated on the basis of
the regression straight line (step 2609). Next, in the end point
determining device 230, the calculated residual film amount F and
the target residual film thickness value are compared with each
other. When the calculated residual film amount F is not more than
the target residual film thickness value, it is determined that the
etching amount of the material to be processed is made into the
predetermined value, and the comparison result is displayed in the
indicator 17 (step 2609). When the calculated residual film amount
F is not less than the target residual film thickness value, the
process returns to step 2604 and these steps are repeated. Finally,
the setting of the end of the sampling is performed (step
2611).
[0113] Next, there is explained the interference light measurement
when discharge fluctuation is caused as shown in FIG. 4, in
relation to specific embodiment according to the present invention.
The maximum change quantities per one sampling of the time changes
in the interference light and the reference light of the standard
pattern data for film thickness determination, which are used here,
are determined as follows. In the above described etching
processing of poly-silicon (during a period between time points 5
seconds and 55 seconds from the start of etching), the maximum
change quantity of the interference light of the standard pattern
data is 50 counts and the maximum change quantity of the reference
light of the standard pattern data is 20 counts. Therefore, the
noise threshold values for detecting a steep change in plasma are
set to 100 counts and 50 counts which are predetermined values
defined in accordance with the specification that the noise
threshold value be set to a value between two and three times of
the maximum change quantity.
[0114] FIG. 15 shows a result obtained by correcting a steep change
in plasma by performing the above described processing. As shown in
FIG. 15, it can be seen that the fluctuation of the light emission
generated at the time point of about 25 seconds after the start of
etching as shown in FIG. 4 is corrected, and abnormal changes in
the interference light waveform and the reference light waveform
are reduced. In this example, since the noise (abnormal light
emission) of the interference waveform is small, any change larger
than the noise threshold value is not caused. However, since the
noise (abnormal light emission) of the reference light is large,
the change in plasma can be sufficiently detected, and the
correction is performed to the reference light and the interference
light at the time point when the change in plasma is detected. This
makes it possible to correct a slight change in the interference
light. It can be seen that it is possible to stabilize the
transition of the instantaneous film thickness which can be
obtained during etching, by the above described processings.
[0115] In this example, the reference light is used as means for
detecting a steep change in plasma, but it may be adapted such that
values of reflection power and a matching point of electric power
for generating plasma, or values of reflection power and a matching
point of bias applied to the wafer are monitored, and a change in
the values are used as means for detecting the steep change in
plasma.
[0116] Further, here, the correction coefficients are obtained by
Si,j=yi-1,j/yi,j, but an average value of a plurality of waveform
data before the time point i-1 may also be used as the correction
coefficient. Further, the approximate value at the time point i-1
based on a smooth curve obtained from the past time series data by
using an interpolation method, such as the Lagrange interpolation
method and a spline interpolation method, may also be used as the
correction coefficient. In addition, the emission data at the time
point i may be further modified by applying the Lagrange
interpolation method and the spline interpolation method to the
emission data at the time point i which are modified by the
correction coefficient. Further, in the embodiments shown in FIG.
12 and FIG. 13, similarly to the case where the interference light
from the sample surface is used, the sampling data of the
interference light may be corrected by using the correction
coefficient obtained on the basis of the result of comparison
relating to plasma light emission performed by the sampling data
comparator 1110. Further, when it is detected at an arbitrary time
point that the noise threshold value is exceeded, it may be adapted
such that the film thickness is detected by an arithmetic operation
using the above described regression analysis at least at one time
point corresponding to a predetermined number of times when the
noise threshold value is exceeded, and that when it is detected
that the noise threshold value is exceeded at a time point after
the one time point, the film thickness is detected by using the
correction coefficient.
[0117] When the etching processing is normally performed, the
number of times when the noise threshold value is exceeded is zero.
However, when the etching characteristic of the etching device is
changed due to the time-based change of the device and the plasma
state deteriorates, the number of times when the noise threshold
value is exceeded is increased. Therefore, in the mass production
process, it is possible to perform the device management of the
etching device by displaying in the indicator 17 the number of
times when the noise threshold value is exceeded.
Embodiment 6
[0118] Next, with reference to FIG. 16 to FIG. 18, there is
explained a sixth embodiment in which the film thickness
measurement is performed by correcting a result of matching with
the differential waveform pattern database when there is plasma
fluctuation at an initial period from the start of etching. FIG. 16
shows a device constitution of the sixth embodiment. The sixth
embodiment has a feature that an etching rate comparator 21, a film
thickness corrector 201, and a noise determining device 202 are
added between the residual film thickness time series data recorder
18 and the regression analyzer 19 of the etching amount measuring
device 10 in the plasma processing apparatus shown in FIG. 1.
[0119] First, as shown in FIG. 17, there are set a target etching
amount, differential patterns (residual film thickness standard
differential patterns) PSj whose wavelength regions (at least three
wavelength regions) are extracted from the differential waveform
pattern database, an etching rate allowable value R0, a film
thickness value at the start of etching, and an etching rate R at
the time of creating the standard differential pattern (step
3600).
[0120] In the subsequent step, the sampling of the interference
light (for example, every 0.25 to 0.5 seconds) is started (step
3601). That is, a sampling start instruction is issued in
correspondence with the start of the etching processing. The
emission intensity of multiple wavelengths which is changed in
accordance with the progress of etching is detected as a
photodetection signal of a voltage corresponding to the emission
intensity by the photodetector. The photodetection signal of the
spectroscope 11 is digitally converted, so that the sampling
signals yi,j are acquired.
[0121] Next, the multiple wavelength output signals yi,j from the
spectroscope 11 are smoothed by the first stage digital filter 12,
and the smoothed time series data Yi,j are calculated (step 3602).
That is, a noise is reduced by the first stage digital filter, so
that the smoothed time series data Yi,j are obtained.
[0122] Next, the differential coefficients di,j are calculated by
the S-G method in the differentiator 13 (step 3603). That is, the
(first-order or second-order) differential coefficients di of the
signal waveforms are obtained by the differential processing (the
S-G method). Further, the smoothed differential coefficient time
series data Di,j are calculated by the second stage digital filter
14 (step 3604). Then, in the differential waveform comparator 15,
the pattern matching (minimum) deviation value .sigma.s=
(.SIGMA.(Di,j-PSj)2/j) is calculated to obtain the instantaneous
film thickness data Zi from a minimum value .sigma. of the pattern
matching (minimum) deviation value .sigma.s with respect to the
film thickness s (step 3605). The instantaneous film thickness data
Zi is stored in the residual film thickness time series data
recorder 18.
[0123] As for the etching rate during the processing, an
inclination Xa is obtained by the etching rate comparator 21 from a
regression straight line 1 on the basis of the instantaneous
residual film time series data Zi (step 3606). Next, it is
determined whether or not the current inclination Xa is an etching
rate limited by the etching rate R at the creation time of the
standard differential pattern, and the etching rate allowable value
R0 (R-R0.ltoreq.Xa.ltoreq.R+R0) (step 3607). In the case where
(R-R0.ltoreq.Xa.ltoreq.R+R0), the instantaneous film thickness Zi
is stored in the residual film thickness time series data recorder
18 (step 3608). In other cases, the instantaneous film thickness Zi
is not stored in the residual film thickness time series data
recorder 18 (step 3609). When the instantaneous film thickness Zi
is not stored, correction instantaneous film thickness data Fei and
correction instantaneous film thickness auxiliary data Fepi and
Femi which are respectively values of Fei .+-.10%, are obtained
from the etching rate R at the creation time of the standard
differential pattern, and stored in the residual film thickness
time series data recorder 18 instead of the current instantaneous
film thickness data Zi (step 3610). Here, the reason for using the
values of Fei .+-.10% is based on the fact that the fluctuation of
the etching rate is at most about .+-.10%, but other values may
also be set depending upon the kind of wafer and the state of
etching.
[0124] Next, in the noise determining device 202, the instantaneous
film thickness time series data Zi, the correction instantaneous
film thickness data Fei, the correction instantaneous film
thickness auxiliary data Fepi and Femi which are respectively the
values of Fei .+-.10%, are compared with the regression straight
line 1 calculated in step 3606, so that the instantaneous film
thickness data Zi having a difference not less than a fixed value
(for example, not less than 10 nm) from the regression straight
line 1 is set as noise data (step 3611). FIG. 18 shows an
instantaneous film thickness correcting function based on the
correction instantaneous film thickness data Fei, the correction
instantaneous film thickness auxiliary data Fepi and Femi. When the
etching rate Xa is outside the allowable range, the instantaneous
film thickness data Zi is not adopted. Instead, the correction
instantaneous film thickness data Fei and the correction
instantaneous film thickness auxiliary data Fepi and Femi are
adopted. Thereby, the film thickness transition in the early stage
of etching is stabilized. At the initial timing from the start of
etching, plasma is not stable in many cases, and hence a mismatch
easily occurs in the matching operation with the database. Further,
the amount of the past residual film thickness time series data Zi
for obtaining the regression straight line is small, so that the
calculated film thickness value obtained by the regression straight
line 2 is liable to have low reliability and to be abnormal. Thus,
the correction instantaneous film thickness data Fei and the
correction instantaneous film thickness auxiliary data Fepi and
Femi are adopted instead of Zi determined as the noise data. The
adoption of the correction instantaneous film thickness auxiliary
data Fepi and Femi is to increase the number of data at the time of
obtaining the calculated film thickness value by the regression
straight line 2, and to improve the reliability of the calculated
film thickness value. Further, when the correction instantaneous
film thickness data Fei and the correction instantaneous film
thickness auxiliary data Fepi and Femi are determined as the noise
by the noise determining device 202, the data are excluded from the
object data of the regression straight line 2 for calculating the
calculated film thickness value.
[0125] The calculated film thickness F at the time point i is
obtained by the regression straight line 2 in the regression
analyzer 19 by using the data of the instantaneous film thickness
time series data Zi, the correction instantaneous film thickness
data Fei and the correction instantaneous film thickness auxiliary
data Fepi and Femi, which data are not determined as the noise by
the noise determining device 202 (step 3612). It is determined in
the end point determining device 230 whether or not the calculated
film thickness F is not more than the target residual film
thickness value set beforehand (step 3613). Finally, when the
calculated residual film amount F is not more than the target
residual film thickness value in step 3613, the setting of the end
of the sampling is performed (step 3614). The result of etching
amount of the material to be processed obtained by the above
processing is displayed in the result indicator 17.
[0126] In the sixth embodiment, the transition of the calculated
film thickness value in the unstable region of plasma during the
early stage of etching is stabilized by the film thickness
correcting function. In a thin film wafer, the etching time period
is short, and the calculated film thickness value stabilized from
the early stage of etching is important. When the calculated film
thickness value is unstable, the etching processing is ended at a
film thickness not less than the target film thickness, which
results in a production failure.
[0127] In the case where the mass production management is
performed in the present embodiment, the totals of the number of
data determined as the noise and the data deviation amount (noise
amount) are monitored by the processing for each wafer, and the
totals of the number of data determined as the noise and the data
deviation amount are counted by a recorder, a counter or the like
(not shown). Such counting operation may also be performed by the
film thickness corrector 201. Further, it is possible to grasp the
state of the device and the etching state of the wafer, by
comparing the transition of the totals of the number of data
determined as the noise and the data deviation amount with
predetermined values (for example, predetermined values relating to
a value of the number of data and the increasing rate). That is, in
the case where the above described number of data is gradually
increased, the predetermined values for the totals of the number of
data and the data deviation amount are used as measures for
starting the maintenance work, such as the wet cleaning, in the
plasma processing apparatus. When the totals of the number of data
and the data deviation amount are abruptly increased and the
increasing rate of the totals exceeds the predetermined value, the
need for a measure such as that of conveying the wafer to the
inspection process of the wafer to be processed, is informed to a
user, and a warning is issued. Such information and warning are
displayed, for example, in the indicator 17 shown in FIG. 16 and
the like, in response to a command from the film thickness
corrector 201.
[0128] According to the present invention, it is possible to
provide a film thickness measuring method in which an etching
amount of a material to be processed can be accurately measured
online in plasma processing, especially in plasma etching
processing, and to provide a process end point determining method
using the film thickness measuring method.
[0129] Further, it is possible to provide an etching process in
which a layer to be etched of a semiconductor device can be highly
precisely controlled online, so as to be etched by a predetermined
etching amount. Further, it is possible to provide an etching
amount measuring device of a material to be processed, in which an
actual etching amount of a layer to be processed accurately
measured online.
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