U.S. patent application number 10/875213 was filed with the patent office on 2005-09-01 for plasma processing apparatus and processing method.
Invention is credited to Ikuhara, Shoji, Kagoshima, Akira, Kitsunai, Hiroyuki, Tanaka, Junichi, Yamamoto, Hideyuki.
Application Number | 20050189070 10/875213 |
Document ID | / |
Family ID | 34879734 |
Filed Date | 2005-09-01 |
United States Patent
Application |
20050189070 |
Kind Code |
A1 |
Tanaka, Junichi ; et
al. |
September 1, 2005 |
PLASMA PROCESSING APPARATUS AND PROCESSING METHOD
Abstract
The present invention provides a plasma processing apparatus and
processing method capable of maintaining a constant processing
profile. The plasma processing apparatus for providing a plasma
processing to a wafer placed in a processing chamber comprises a
processing vessel 1a constituting the processing chamber 1, process
gas supply devices 3, 4 for supplying processing gas to the
processing chamber 1, and a plasma generating means 2 for
generating plasma by supplying electromagnetic energy to the
processing chamber and dissociating the process gas supplied to the
processing chamber, wherein the apparatus further comprises a
processing chamber surface temperature control unit 15 for
controlling the inner surface temperature of the processing
chamber, the control unit controlling the temperature by heating
the inner surface of the processing chamber by generating plasma in
the chamber for a predetermined processing time based on a
processing history after terminating a cleaning process and prior
to performing the wafer processing.
Inventors: |
Tanaka, Junichi; (Tokyo,
JP) ; Kitsunai, Hiroyuki; (Ibaraki-ken, JP) ;
Yamamoto, Hideyuki; (Kudamatsu-shi, JP) ; Ikuhara,
Shoji; (Hikari-shi, JP) ; Kagoshima, Akira;
(Kadamatsu-shi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
34879734 |
Appl. No.: |
10/875213 |
Filed: |
June 25, 2004 |
Current U.S.
Class: |
156/345.27 ;
156/345.37 |
Current CPC
Class: |
H01L 21/67248 20130101;
H01J 37/32522 20130101; H01L 21/67103 20130101 |
Class at
Publication: |
156/345.27 ;
156/345.37 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2004 |
JP |
2004-054229 |
Claims
1. A plasma processing apparatus for providing a plasma processing
to a wafer transferred into a vacuum processing vessel, the
apparatus comprising: a vacuum processing vessel constituting a
vacuum processing chamber; a processing gas supply unit for
supplying a processing gas to the vacuum processing vessel; a
plasma generating means for generating plasma by supplying
electromagnetic energy to the vacuum processing vessel and
dissociating the processing gas supplied to the processing chamber;
and a processing chamber surface temperature control unit for
controlling the inner surface temperature of the vacuum processing
chamber, wherein the control unit controls the inner surface
temperature by generating plasma in the processing chamber under
processing conditions set in advance according to a processing
history and heating the inner surface of the processing chamber
prior to performing the wafer processing.
2. The plasma processing apparatus according to claim 1, wherein
the heating process for heating the inner surface of the processing
chamber is carried out for every lot of wafers to be processed.
3. The plasma processing apparatus according to claim 1, wherein
the heating process for heating the inner surface of the processing
chamber is carried out for every wafer to be processed.
4. The plasma processing apparatus according to claim 1, wherein
heating time is estimated based on processing conditions of a lot
processing of wafers carried out immediately prior to the
processing to be performed.
5. The plasma processing apparatus according to claim 4, wherein
the processing conditions include at least one of the following: an
idle time from the termination of an immediately previous lot
processing, a processing time, a processing power, a processing
pressure, a number of wafers being processed or a state of magnetic
field distribution of the immediately previous lot processing.
6. The plasma processing apparatus according to claim 1, wherein
termination of a cleaning process is detected based on a spectral
intensity of plasma emission.
7. The plasma processing apparatus according to any one of claims 1
through 6, wherein the plasma processing apparatus comprises plural
processing chambers, and the wafers stored in a cassette are
subjected to continuous processing in the plural processing
chambers.
8. The plasma processing apparatus according to claim 1, wherein
the apparatus is equipped with a mechanism for cooling the vacuum
processing vessel.
9. A plasma processing method comprising: supplying electromagnetic
energy to a vacuum processing vessel; dissociating a processing gas
supplied to a processing chamber so as to generate plasma; and
providing using the generated plasma a plasma processing to a wafer
transferred into the vacuum processing vessel; wherein prior to the
wafer processing, plasma is generated in the processing chamber
during a processing time set in advance according to a processing
history so as to heat an inner surface of the processing chamber
and control the inner surface temperature of the processing
chamber.
10. The plasma processing method according to claim 9, wherein the
heating of the inner surface of the processing chamber by plasma is
carried out for every lot of wafers to be processed.
11. The plasma processing method according to claim 9, wherein the
heating of the inner surface of the processing chamber by plasma is
carried out for every wafer to be processed.
12. The plasma processing method according to claim 9, wherein
processing time for heating the inner surface of the processing
chamber by plasma is estimated based on processing conditions of a
lot processing of wafers carried out immediately prior to the
processing to be performed.
13. The plasma processing method according to any one of claims 9
through 12, further comprising cooling the vacuum processing
vessel.
14. The plasma processing method according to claim 9, wherein a
chamber cleaning process is run after the heating process and the
termination of the cleaning process is detected based on a spectral
intensity of plasma emission.
15. The plasma processing apparatus according to claim 1, wherein
the control unit controls the inner surface temperature of at least
a sidewall of the vacuum processing chamber by at least generating
plasma in the processing chamber prior to performing the wafer
processing so as to heat the inner surface of at least the sidewall
of the processing chamber prior to performing the wafer
processing.
16. The plasma processing method according to claim 9, wherein
plasma is generated in the processing chamber prior to the wafer
processing so as to heat the inner surface of at least a sidewall
of the processing chamber and control the inner surface temperature
of at least the sidewall of the processing chamber prior to the
wafer processing.
Description
[0001] The present application claims priority from Japanese patent
application No. 2004-54229 filed on Feb. 27, 2004, the content of
which is hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0002] The present invention relates to a plasma processing
apparatus and processing method, and more specifically, to a plasma
processing apparatus and processing method preferably applied to
the micromachining of semiconductor devices.
DESCRIPTION OF THE RELATED ART
[0003] A plasma processing apparatus is a device for forming fine
patterns on a surface of a wafer to be fabricated into a
semiconductor device or the like. One typical example of the plasma
processing apparatus is a plasma etching apparatus. The plasma
etching apparatus is equipped with a processing chamber for
processing the wafer, a sample stage for placing the wafer disposed
in the processing chamber, and a gas supply system including, for
example, a shower plate for introducing the gas used for etching
reaction into the processing chamber. The apparatus is further
equipped with a gas exhaust system including, for example, a
discharge pump and a pressure regulating valve for keeping the
interior of the processing chamber to reduced pressure and
maintaining a stable plasma discharge.
[0004] Further, the plasma processing apparatus is equipped with a
plasma generating mechanism for supplying electromagnetic energy
such as microwaves and RF waves to the processing chamber so as to
generate plasma from the etching gas supplied to the processing
chamber, and a bias voltage application mechanism for applying bias
voltage to the sample stage so as to accelerate the ions in the
plasma toward the wafer placed on the sample stage.
[0005] The ions accelerated toward the wafer bombard the wafer from
a direction perpendicular to the wafer, and thus, the direction of
ion irradiation is regulated. The surface of the wafer that is not
covered with a mask is etched perpendicularly, and thus,
anisotropic etching is carried out in which microscopic patterns
having perpendicular side walls are formed on the wafer surface.
Further, the etching reaction is not only carried out by ions. For
example, the electrons in the plasma activate the etching gas and
generate reactive species called radicals, and this reaction
species cause chemical reaction to occur at the wafer surface that
has been energized by ions, thereby accelerating the etching
reaction.
[0006] The dimensions of semiconductor devices have become refined
year after year, along with which the processing accuracy required
when processing wafers in the plasma processing apparatuses have
become more demanding. On the other hand, the processing profile
achieved by processing wafers in a plasma processing apparatus
fluctuates by the state of plasma and radicals in the processing
chamber. Therefore, in order to continuously carry out uniform
processing with an accuracy in the order of a few nanometers during
repeated processing of wafers, it is necessary to maintain the
states of plasma and radicals as constant as possible.
[0007] The reaction products and radicals generated during etching
of the wafers can be discharged through the exhaust system.
However, the reaction products will gradually deposit in the
processing chamber during repeated wafer processing, and cause the
state of the inner surface of the processing chamber (the surface
of the processing chamber exposed to plasma and radicals, and the
surface of components disposed in the processing chamber) to
change.
[0008] The states of the plasma and radicals contained in the
processing chamber are easily affected by the surface state of the
processing chamber, and therefore, the processing profiles of the
semiconductor devices gradually vary during repeated etching even
under the same processing conditions, causing the performance of
the semiconductor devices to deteriorate. Not only the change of
surface state of the processing chamber body but also the change of
surface state of the components in the chamber such as the sample
stage or the shower plate exposed to plasma and radicals may cause
the state of plasma and radicals to fluctuate.
[0009] If the deposits in the processing chamber are left
unremoved, the thickness of the deposits increases gradually, and
the repeated thermal stress of plasma heating causes the thick
deposits to crack and create fine contaminants. If the contaminants
fall on the wafers, they obstruct the etching process and cause
process defects that lead to malfunction of the processed
devices.
[0010] The changes of surface conditions of the processing chamber
etc. are not only caused by deposits. If oxygen gas is used as one
of the etching gases, it causes the processing chamber surface to
oxidize, and if halogen gas is used, it causes the surface to be
halogenated. Further, if the inner surface of the processing
chamber is exposed to vacuum without being used for a long period
of time, the surface state may change, for example, by the
vaporization of a portion of the chemical substances that
constitute the inner surface of the chamber.
[0011] In the prior art, plasma cleaning was carried out in an
attempt to solve the above-mentioned problems by removing the
deposits in the processing chamber using plasma. Another
conventional countermeasure was to increase the temperature of the
inner wall of the processing chamber so as to suppress the
deposition of reaction products to the inner surface of the
chamber. However, most of these measures were not sufficient, and
the processing profiles of the semiconductor devices were still
gradually varied. Therefore, it was necessary to replace or to
clean the components of the processing apparatus before the
fluctuation of the processing profiles caused problems.
[0012] Patent document 1 discloses one example of plasma cleaning
in which rapid cleaning is performed by reversing the current flow
direction of at least one of a plural solenoid coils constituting a
plasma processing apparatus. Patent document 2 discloses a method
for cleaning a plasma processing apparatus that is used for
processing nonvolatile members, capable of suppressing the
deposition of reaction products to the inner wall of the vacuum
vessel and removing the deposited reaction products efficiently.
Further, patent document 3 discloses performing plasma cleaning for
a plasma generating chamber using O2 gas etc. whenever a sample is
processed using plasma. Patent document 4 discloses a method for
suppressing the deposition of reaction products on a shower plate
having many bores that allow gas to be supplied into the processing
chamber, by controlling the temperature of the shower plate via a
temperature controller disposed outside the processing chamber.
Patent document 5 discloses carrying out plasma cleaning via
in-situ cleaning, and thereafter, redepositing a polymer coating to
the surface of the processing chamber to stabilize the etching
process.
[0013] Patent document 1:
[0014] Japanese Patent Application Laid-Open 2003-173976
[0015] Patent document 2:
[0016] Japanese Patent Application Laid-Open 2003-243362
[0017] Patent document 3:
[0018] Japanese Patent No. 3404434
[0019] Patent document 4:
[0020] Japanese Patent Application Laid-Open 2003-309106
[0021] Patent document 5:
[0022] Published Japanese Translation of PCT Patent Application No.
2003-518328
[0023] The apparatuses disclosed in patent documents 1, 2 and 3 are
capable of removing the deposits in the processing chamber.
However, they are not capable of suppressing the fluctuation of
processing profiles of the wafers. This is because the composition
of the processing gas used for removing the deposits differ from
the composition of the gas used for etching the wafers. Thus, it is
difficult to maintain a constant plasma and radical state and to
maintain a fixed processing profile just by removing the deposits
in the processing chamber.
[0024] According to the apparatus disclosed in patent document 5,
the etching process is stabilized by providing a polymer coating to
the inner surface of the processing chamber after carrying out
plasma cleaning. However, the state of radicals cannot be made
constant simply by coating the inner surface of the processing
chamber with polymer. This is because the state of surface reaction
may change according to the temperature of the inner walls of the
processing chamber.
[0025] Patent document 4 provides means for adjusting the
temperature of the shower plate by heating the same. However, when
the temperature of the shower plate is controlled from outside, the
surface of the shower plate being exposed to plasma is heated by
the ions in the plasma. Therefore, the temperature of the surface
exposed to plasma rises compared to the other portions. Thus, it is
difficult to uniformly control the surface temperature thereof
which has the greatest influence on surface reaction.
[0026] Especially when quarts or other material having low thermal
conductivity is used to form components, the temperature of the
inner surface of the quarts-made component exposed to plasma and
that of the outer surface exposed to the heating means may differ
greatly. In other words, the inner surface temperature of the
processing chamber may be left substantially uncontrolled, and this
may cause the fluctuation of the radical state.
SUMMARY OF THE INVENTION
[0027] In view of the above-mentioned problems, the present
invention offers a plasma processing apparatus and processing
method capable of maintaining a constant processing profile.
[0028] In order to solve the problems, the present invention
provides the following solution.
[0029] A plasma processing apparatus for providing a plasma
processing to a wafer transferred in to a vacuum processing vessel
comprses: a vacuum processing vessel constituting a vacuum
processing chamber; a processing gas supply unit for supplying a
processing gas to the vacuum processing vessel; a plasma generating
means for generating plasma by supplying electromagnetic energy to
the vacuum processing vessel and dissociating the processing gas
supplied to the processing chamber; a means for heating or cooling
the vacuum processing vessel; and a processing chamber surface
temperature control unit for controlling the inner surface
temperature of the vacuum processing chamber, wherein the control
unit controls the inner surface temperature by generating plasma in
the processing chamber based on processing conditions set in
advance according to a processing history so as to heat the inner
surface of the processing chamber, after terminating a cleaning
process and prior to performing the wafer processing.
[0030] The present invention provides a plasma processing apparatus
and processing method having the above-mentioned structure that is
capable of maintaining a constant processing profile.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is an explanatory view illustrating a plasma
processing apparatus according to a preferred embodiment of the
present invention;
[0032] FIG. 2 is a diagram showing the continuous lot
processing;
[0033] FIG. 3 is a chart illustrating the change of surface
temperature of the processing chamber during lot processing;
[0034] FIG. 4 is a diagram showing the continuous lot processing
according to the present invention;
[0035] FIG. 5 is a chart showing an example of the change of inner
surface temperature of the processing chamber;
[0036] FIG. 6 is an explanatory view of the method for determining
the processing conditions for a pre-lot temperature control
step;
[0037] FIG. 7 is a diagram showing another example of the
continuous lot processing according to the present invention;
[0038] FIG. 8 is an explanatory view of the method for determining
the processing conditions for the pre-lot temperature control step
of FIG. 7;
[0039] FIG. 9 is a chart showing an example of the change of inner
surface temperature of the processing chamber;
[0040] FIG. 10 is an explanatory view of the endpoint determination
of the cleaning process or seasoning process;
[0041] FIG. 11 is a chart showing the end point determination of a
per-wafer cleaning process performed based one mission spectral
intensity;
[0042] FIG. 12 is a chart showing an example of how the end point
of seasoning is determined based on principal component analysis;
and
[0043] FIG. 13 is an explanatory view showing an example of how the
present invention is applied to a plasma processing apparatus
having plural processing chambers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0044] Now, the preferred embodiments of the present invention will
be explained with reference to the accompanying drawings. FIG. 1
illustrates a plasma processing apparatus according to a first
embodiment of the present invention. As shown in the drawing, the
plasma processing apparatus comprises a processing vessel 1, a
sample stage 6 disposed in the processing vessel 1 for placing a
wafer 7, and a gas supply system for introducing the gas required
for carrying out etching reaction into the processing chamber. The
gas supply system includes, for example, a shower plate 5 through
which gas is introduced into the processing chamber, a gas supply
pipe 3 for supplying gas to the shower plate 5, and a flow
controller 4 for controlling the gas flow. Further, the plasma
processing apparatus includes a gas exhaust system 9 and a pressure
regulating valve 8, through which the pressure chamber is
maintained at a low pressure condition enabling plasma discharge to
be stably maintained.
[0045] Furthermore, the plasma processing apparatus comprises an
electromagnetic energy supply means 2 for supplying microwaves or
RF waves into the processing chamber in order to generate plasma
from the etching gas maintained at low pressure in the processing
chamber. The apparatus further comprises a bias power supply 10 and
a bias power transmission line 11 through which bias voltage is
applied to the sample stage 6 to attract and accelerate the ions in
the plasma toward the wafer 7 placed on the sample stage 6.
[0046] The plasma processing apparatus further comprises a
temperature regulator (such as a heater) 12 and a temperature
regulating power supply 13 for regulating the wall temperature of
the processing chamber by heating or cooling. It further comprises
a system control unit 14 for controlling each of the
above-mentioned means. The system control unit 14 is equipped with
a processing chamber surface temperature control unit 15 for
controlling the surface temperature of the processing chamber.
Furthermore, the apparatus is equipped with a wafer transfer unit
17 for transferring the wafer into the processing vessel 1 from a
cassette 16 capable of housing plural wafers.
[0047] FIG. 2 is a view explaining the continuous processing of a
single lot of wafers (a group of plural wafers to be fabricated
into a semiconductor device of the same type is called a "lot", and
the process for continuously processing a lot of wafers housed in a
cassette when carrying out wafer processing is called continuous
lot processing. This process enables the amount of processing per
unit time to be increased.).
[0048] Lot processing is started in step S1, a pre-lot cleaning is
carried out in step S2 for cleaning the processing chamber, and
when the pre-lot cleaning step S2 is terminated, a pre-lot
seasoning is carried out in step S3 for allowing the processing
chamber wall to adapt to the gas used for wafer processing.
[0049] Thereafter, a wafer processing step S4 for continuously
processing the wafers in the lot is carried out repeatedly until
the termination of the processing of wafers in the lot is detected
in step S5.
[0050] FIG. 3 illustrates the change in surface temperature of the
processing chamber during lot processing. The processing vessel 1
is constantly heated by a temperature regulator 12. When plasma is
turned on (that is, when plasma is generated in the processing
chamber), the ions become incident on the inner surface of the
processing chamber and heat the inner surface, so the inner surface
temperature of the processing chamber is not constant. For example,
the processing of a single wafer comprises plural processing steps
in which the processing conditions such as gas species or pressure
differ, and plasma may be turned off during the plural processing
steps.
[0051] In such case, despite the temperature regulation performed
via the heater 12, the inner surface temperature of the processing
chamber rises when plasma is turned on, and falls when plasma is
turned off. As described, the temperature repeatedly rises and
falls during processing of a single wafer, and fluctuates within a
certain range shown by .DELTA.T in FIG. 3.
[0052] The fluctuation range of the temperature during a single
wafer processing should preferably be the same for all the wafers
so as to suppress the change in processed profile. However, if
there is a long idle time between the processing of a previous lot
and the starting of processing of a current lot (idle time between
lots) in the processing chamber 1, the processing chamber 1 is
cooled even by the heating performed by the temperature regulator
12 since plasma heating is not performed. Therefore, as shown in
FIG. 3, the temperature of the inner surface of the processing
chamber rises along with the repeated wafer processing, and
drifting of temperature shown by D1 in FIG. 3 occurs between
wafers.
[0053] Such temperature drift D1 is not preferable since it causes
variation of processing profile. The drop of processing chamber
temperature due to the idle time between lots occurs even when the
idle time is as short as approximately ten minutes. Further, the
processing chamber is cooled even when plural lots are processed
continuously without any idle time. For example, the cooling occurs
when processing a lot requiring a large processing power directly
after processing a lot requiring a very small processing power.
This is because when a lot requiring a small processing power is
processed, the surface of the processing chamber is not heated
much. As described, if the processing of a lot requiring a small
processing power is performed prior to the processing of a lot with
a processing condition that heats the inner surface of the chamber
greatly, it is preferable to heat the processing chamber in advance
via a processing chamber surface temperature control step. Other
than the fluctuation of processing power, the same phenomenon is
sometimes caused by the fluctuation of magnetic field conditions or
the like.
[0054] FIG. 4 explains the continuous lot processing according to
the present invention, and FIG. 5 illustrates an example of the
change in inner surface temperature of the processing chamber when
thirteen wafers are continuously processed according to the
processing steps shown in FIG. 4 after allowing the processing
chamber 1 to cool by leaving the chamber unused for approximately
two hours. In FIG. 4, the same steps as those shown in FIG. 2 are
denoted by the same reference numbers, and detailed descriptions
thereof are omitted.
[0055] In the drawing, a pre-lot temperature control step S7 is for
controlling the temperature of the inner surface of the processing
chamber prior to wafer processing (step S4). By heating the inner
surface of the pressure chamber as shown in FIG. 5, the range of
the temperature drift during the processing of thirteen wafers can
be reduced as shown by D2 of FIG. 5. The pre-lot temperature
control step S7 in the example of FIG. 5 is performed continuously
under the same processing conditions as the pre-lot cleaning
performed directly prior to step S7. According to this example, the
processing chamber is heated for a processing time of approximately
180 seconds.
[0056] FIG. 6 is a view explaining the method for determining the
processing conditions for pre-lot temperature control step S7. In
the present invention, the processing conditions are determined
based on the processing sequence as shown in FIG. 6, without
detecting the surface temperature of the processing chamber by
sensors etc. during wafer processing. It is difficult to measure
the surface temperature of the processing chamber from outside, and
if a temperature sensor etc. is installed inside the processing
chamber, the sensor may be damaged by plasma and subjected to aging
deterioration, or the sensor installed in the processing chamber
may cause metal contamination of the wafers.
[0057] The important parameters for determining the processing
conditions of the pre-lot temperature control step S7 are the
processing time, the processing power, the processing pressure and
the number of wafers being processed in the lot processed directly
prior to the present lot, and based on these parameters, it is
possible to estimate the rise of surface temperature of the
processing chamber at the time the processing of the previous lot
had been terminated. Based on this estimation, it is possible to
estimate the surface temperature T0 at the time the previous lot
processing had been terminated. If effective magnetic field plasma
is performed, the magnetic field distribution is also an important
parameter.
[0058] Next, it is possible to estimate a surface temperature T1 of
the processing chamber at the time the current lot processing is to
be started based on the idle time of the processing chamber from
the time of termination of the previous lot processing. Thereafter,
a surface temperature T2 of the processing chamber when starting
the pre-lot temperature control step S7 (when terminating the
pre-lot cleaning step S2) can be estimated based on the processing
power, the processing pressure, the processing time and so on of
the pre-lot cleaning step S2. If it is estimated that the surface
temperature of the processing chamber is higher than the set value
at the time the pre-lot cleaning S2 is terminated, the pre-lot
temperature control step S7 carries out a cooling process of the
processing chamber surface by allowing the processing chamber to
rest with the plasma turned off. If the temperature drift as
illustrated in FIG. 5 becomes a problem, a mechanism for cooling
the processing chamber may be adopted so as to cool the processing
chamber gradually when a number of wafers have been processed
continuously.
[0059] The processing conditions of the pre-lot temperature control
step S7 can be determined based on a database 22 storing pre-lot
temperature control processing conditions using the past processing
conditions as search key 21 as shown in FIG. 6. The database 22
storing the pre-lot temperature control processing conditions can
be created by inputting actual measurement values measured via
sensors etc. disposed in the processing chamber by experiments
carried out in advance. The database 22 can also be created by
inputting the surface temperature of the processing chamber
calculated in advance via numerical simulation.
[0060] Instead of using a database, it is also possible to use a
formula, such as an experimental formula calculated via experiments
or a model formula calculated via numerical simulation. The
variables of these formulas are preferably the physical quantity
values listed as the search key 21 of FIG. 6. The temperature
control in the pre-lot temperature control step S7 can be carried
out either by controlling the processing time while using a
constant processing power or by controlling the processing power
during a fixed processing time. When effective magnetic field
plasma is used, the temperature control can also be carried out by
controlling the magnetic field conditions.
[0061] It is further preferable to adjust the inner surface
temperature of the processing chamber by combining the plural
processing conditions so as to control the distribution of wall
heating. Especially in the case of effective magnetic field plasma,
the plasma distribution can be easily changed by varying the
magnetic field conditions, so it is preferable to combine plural
magnetic field conditions.
[0062] In the example of FIG. 5, during lot processing, the
temperature fluctuation while processing the second through fifth
wafers is greater than that of the sixth and subsequent wafers, and
a drop in inner surface temperature of the processing chamber
during the initial stage is observed. This is due to the heat
capacity of the entire processing chamber. Even when the inner
surface of the processing chamber is heated by plasma, the average
temperature of the entire processing chamber heated by the heater
is low, so initially, the surface temperature of the processing
chamber drops by the heat applied to the surface of the chamber
being conducted to the entire processing chamber.
[0063] FIG. 7 is a view explaining another example of continuous
lot processing according to the present invention. Following step
S11 for starting lot processing, a pre-lot cleaning step S12 for
cleaning the processing chamber is carried out. The pre-lot
cleaning step S12 can be omitted if the processing chamber is
sufficiently cleaned via a per-wafer cleaning step S14 described
later. However, the pre-lot cleaning step S12 is usually carried
out while placing a dummy wafer on the sample stage, so it can be
performed advantageously for a long period of time, for a few
minutes to tens of minutes, without damaging the sample stage
surface by plasma. Therefore, it is capable of performing cleaning
more thoroughly than the per-wafer cleaning step S14 where cleaning
is performed without placing the dummy wafer. Thus, even if step
S12 can be omitted, it is preferable to perform step S12 once per
several lots.
[0064] After terminating the pre-lot cleaning step S12, the pre-lot
temperature control step S13 is executed, wherein the inner surface
temperature of the processing chamber is adjusted for example by
heating the chamber if it is cooled. If the currently processed lot
is continuously processed after processing the previous lot, the
pre-lot temperature control step S13 can be omitted to enhance the
throughput of the apparatus.
[0065] Next, a per-wafer cleaning step S14 is performed. This step
is for removing the deposits adhered to the chamber and electrodes
during previous wafer processing, so it does not have to be
performed before processing the first wafer. However, if the
pre-lot cleaning step S12 is omitted as described earlier, it must
be performed for processing the first wafer.
[0066] Next, the surface temperature of the processing chamber is
adjusted again through a per-wafer temperature control step S15.
This step is for correcting the inner surface temperature of the
processing chamber to within a predetermined range for wafer
processing if the temperature could not be controlled to fall
within a predetermined fluctuation range in the pre-lot temperature
control step S13 due to the thermal capacity of the processing
chamber as shown in FIG. 5.
[0067] Thereafter, a per-wafer seasoning step S16 is carried out.
This step aims at adapting the surface of the processing chamber to
the etching gas and plasma used in the subsequent wafer processing
step S17. Adapting the surface means modifying the surface of the
processing chamber by what is called ion mixing in which ions are
implanted on the surface having radicals from the plasma adhered
thereto, whether the surface material of the processing chamber is
quartz, alumina, ceramic or metal. For example, when halogenation
gases such as Br or Cl gases are used as etching gas, the surface
of the processing chamber is halogenated, and if hydrogen exists in
the chamber, hydrogen is occluded on the chamber surface and the
surface is adapted to the etching gas plasma. This per-wafer
seasoning step S16 enables to suppress the radical fluctuation just
after starting the subsequent wafer processing step S17, according
to which stable processing profile is achieved. From the viewpoint
of better throughput of the apparatus, the per-wafer seasoning step
S16 is preferably performed without placing a wafer on the sample
stage. However, sometimes the seasoning process is stabilized by
the existence of silicon, so in that case, a dummy wafer can be
placed on the sample stage.
[0068] Next, the wafer processing step S17 for continuously
processing the wafers in a lot is carried out. The processes of
steps S14 through S17 are repeated until the termination of wafer
processing in a lot is detected in step S18.
[0069] FIG. 8 is a diagram explaining the method for determining
the processing conditions for the pre-lot temperature control step
S15 (per-wafer temperature control) in FIG. 7. The processing
chamber surface temperature controlling unit 15 uses the past
processing conditions as search key 24 as shown in FIG. 8 to make
an inquiry with a database 25 storing per-wafer temperature control
processing conditions, and retrieves a standard correction
processing time per wafer. The database 25 storing per-wafer
temperature control processing conditions can be created by actual
measurement values measured via sensors etc. disposed in the
processing chamber by an experiment carried out in advance. In
stead of using a database, it is also possible to use a formula,
such as an experimental formula obtained via experiments or a model
formula obtained via numerical simulation.
[0070] When the lots are continuously processed and the processing
chamber is not cooled, the standard correction processing time can
be set to zero for all the wafers. Furthermore, when this standard
correction processing time is either measured in advance via
experiments or calculated via numerical simulation, it is desirable
to determine the standard processing conditions for per-wafer
cleaning, and if the processing time of the per-wafer cleaning step
S14 becomes longer than the standard processing condition, the
processing time of the per-wafer temperature control step S15 can
be shortened accordingly.
[0071] FIG. 9 is a view showing an example of the change of inner
surface temperature of the processing chamber that was observed
when thirteen wafers were continuously processed according to the
processing steps of FIG. 7 after allowing the processing chamber 1
to rest for approximately two hours to cool. According to the
example shown in FIG. 9, the fluctuation of surface temperature of
the processing chamber due to continuous lot processing can be
substantially completely suppressed compared to the example shown
in FIG. 5. Therefore, the variation of processing profile between
wafers can be suppressed to a very small level.
[0072] FIG. 10 illustrates the end point determination of the
cleaning process or the seasoning process. According to the example
of FIG. 10, a spectroscope 31 for monitoring the plasma emission is
used as the sensor for monitoring the state of plasma or radicals
in the processing chamber. The plasma emission observed through an
observation window 33 disposed to the processing chamber 1 is
transmitted to the spectroscope 31 via an optical fiber 32, and is
subjected to spectral decomposition in the spectroscope 31. Signals
of spectral decomposition are transmitted to an end point
determination unit 34 within the system control unit 14, where the
end point of cleaning or seasoning is determined. In the plasma
emission, the emission with a wavelength in the range of 200 nm to
400 nm is especially important to determine the end point of
cleaning or seasoning. Thus, it is preferable to create the
observation window 33 or the optical fiber 32 with quartz. If the
window and fiber are made of glass or plastic, the light having a
wavelength of 300 nm or smaller will be absorbed in glass etc. and
cannot be observed. Further, other than observing the plasma
emission, the state of plasma can also be observed through use of a
sensor for detecting the electrical properties such as for
measuring the bias voltage applied to the plasma.
[0073] The end point of cleaning such as pre-lot cleaning or
per-wafer cleaning can be determined by monitoring the time change
of emission spectral intensity of the products generated via
etching reaction for removing the deposits on the inner wall of the
processing chamber. For example, if a silicon wafer is used as the
sample, the deposits include silicon. Therefore, it is preferable
to monitor the peak of emission spectrum of silicon. Further, if
the deposits are removed using chlorine-based gas such as Cl.sub.2,
it is preferable to monitor the time change of the peak of emission
spectrum of silicon chlorides such as SiCl. Furthermore, if the
deposits are removed using fluorine-based gas such as SF.sub.6 or
CF.sub.4, it is preferable to monitor the time change of the peak
of emission spectrum of silicon fluorides such as SiF.
[0074] Moreover, it is possible to monitor the emission spectral
intensity of a radical so-called an etchant for removing the
deposits on the inner wall of the processing chamber. The etchant
is generated by the etching gas being activated by plasma. The
density of the etchant is decreased during cleaning since it is
consumed by the reaction with the deposits. However, when the
cleaning is terminated, the deposits are removed and the etchant is
no longer consumed. Therefore, the density of etchant in the
processing chamber rises and saturates. The density and the
emission intensity of etchant are closely related. Therefore, the
end point of cleaning can be determined by monitoring the emission
intensity of the etchant.
[0075] FIG. 11 is an explanatory chart of the endpoint
determination of the per-wafer cleaning process performed based on
the emission spectral intensity. This chart illustrates an example
recording the change of emission spectral intensity of fluorine
radicals when silicon-based deposits are cleaned with
fluorine-based gas. The change of emission spectral intensity of
fluorine radicals stops after approximately 20 seconds from the
start of the cleaning process step S14, and so it is possible to
determine that the cleaning process has terminated at this point.
The per-wafer temperature control step S15 is carried out for 15
seconds starting from this point, under the same conditions as the
per-wafer processing. The end point of the seasoning process can
also be determined in a similar manner. In order to determine the
termination of the seasoning process, it is necessary to determine
that the states of many radicals have become equal. Therefore, it
is preferable to extract the change of emission spectrum via
principal component analysis or other multivariate analysis and to
determine the end point from the variation of the signals being
extracted.
[0076] FIG. 12 is a chart showing an example of how the end point
of seasoning is determined using principal component analysis.
Principal component analysis is a statistical method for binding
the fluctuation of a large number of variables based on
correlations in order to compress the variables into a small number
of variables called principal component scores. The principal
component scores obtained by compressing the emission spectrum via
principal component analysis can be used as parameters representing
the radical variation of plasma. FIG. 12 is a graph showing the
result of the principal component analysis of emission spectral
fluctuation performed during the seasoning step, wherein the
horizontal axis represents the primary principal component score
and the vertical axis represents the secondary principal component
score. As shown in the graph of FIG. 12, the state of the emission
spectrum is gradually varied from a seasoning start point 35 toward
the direction of evolution (direction shown by arrow 38), and
finally, when it enters a seasoning termination determination zone
37, that point is determined as the seasoning end point 36 and the
seasoning is terminated. By controlling the process so that the
pair of principal component scores obtained from the emission
spectrum enters the seasoning termination determination zone 37,
the state of the plasma or the radicals in the processing chamber
can be maintained constant. It is desirable to adjust the range of
the seasoning termination determination zone 37 according to the
process accuracy required for the processed semiconductor device.
Generally, if a high level of process accuracy is required, the
termination determination zone is set narrower. According to the
present example, the determination was performed in a
two-dimensional plane using the primary and secondary principal
component scores, but it is also possible to determine the
termination of the seasoning step in multidimensional space using
more principal components.
[0077] FIG. 13 illustrates an example of how the present invention
is applied to a plasma processing apparatus having plural
processing chambers.
[0078] In a plasma processing apparatus having plural processing
chambers, each of the plural processing chambers is usually used to
process a separate lot. In this case, the processing history of
each processing chamber differs, and the inner surface temperature
of each chamber also differs. Thus, the processing profile will
vary among the processing chambers. Therefore, even if the plasma
processing apparatus having plural processing chambers is equipped
with a function to enhance throughput by carrying out distributed
processing of a single lot of wafers in plural processing chambers,
it is not possible to perform distributed processing if the
processing profile differs per processing chamber.
[0079] According to the example shown in FIG. 13, upon starting lot
processing, the pre-lot processing 41 including the pre-lot
cleaning step S12 and the pre-lot temperature control step S13 is
applied. As shown in FIG. 12, the wafer processing is performed
sequentially in the plural processing chambers, in the order
starting from the chamber having completed the pre-lot processing
41 and ready to perform processing. Thus, the plural processing
chambers can be used simultaneously for processing a single lot of
wafers without deteriorating the quality of the processing profile,
and the throughput of the apparatus can thereby be improved.
[0080] The embodiments of the present invention have been described
taking a semiconductor device as an example of the object to be
processed, but other samples, such as LCD devices, can also be the
object to be processed.
[0081] As have been described, each embodiment of the present
invention is equipped with a processing chamber surface temperature
control unit, and through use of this control unit, enables to
maintain the inner surface temperature of the processing chamber
within a predetermined range based on past processing conditions.
Thus, the present invention enables to suppress the fluctuation of
the processing profile of the processed objects. Moreover, by
adopting a sensor and an end point determination unit for
determining the end point of the cleaning process or seasoning
process, the present invention enables to remove the deposits in
the processing chamber and adjust the inner surface temperature of
the chamber by determining the end point of the cleaning process,
and the present invention enables to appropriately adapt the inner
surface of the processing chamber to the plasma of the etching gas
by determining the end point of the seasoning process. According
further to the present invention, the state of radicals can be made
constant during wafer processing so as to suppress the fluctuation
of processing profile of the processed objects.
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