U.S. patent application number 12/354994 was filed with the patent office on 2009-06-25 for plasma etching method and plasma etching apparatus.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Keiichi Matsunaga, Mitsuhiro OHKUNI.
Application Number | 20090159209 12/354994 |
Document ID | / |
Family ID | 37573958 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090159209 |
Kind Code |
A1 |
OHKUNI; Mitsuhiro ; et
al. |
June 25, 2009 |
PLASMA ETCHING METHOD AND PLASMA ETCHING APPARATUS
Abstract
The plasma etching method first forms a coating film on the
inner surface of the chamber. Next, an etching process is performed
on a wafer under a condition in which the coating film is formed,
and thereafter a reaction product adhered onto the coating film in
the etching process is removed together with the coating film. Each
of these processes is implemented at a frequency in which the
condition of the chamber inner surface is nearly always the same at
the time of initiating the etching process.
Inventors: |
OHKUNI; Mitsuhiro;
(Nara-shi, JP) ; Matsunaga; Keiichi; (Toyama-shi,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Assignee: |
PANASONIC CORPORATION
|
Family ID: |
37573958 |
Appl. No.: |
12/354994 |
Filed: |
January 16, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11471700 |
Jun 21, 2006 |
7494827 |
|
|
12354994 |
|
|
|
|
Current U.S.
Class: |
156/345.1 |
Current CPC
Class: |
H01L 21/31116
20130101 |
Class at
Publication: |
156/345.1 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2005 |
JP |
2005-180739 |
Claims
1-14. (canceled)
15. A plasma etching apparatus for performing an etching process on
an object to be processed by plasma maintained in a chamber,
comprising: a coating film formation unit configured to form a
coating film on the chamber inner surface; a first gas supply unit
configured to supply into the chamber a process gas used for the
etching process of an object to be processed; a second gas supply
unit configured to supply into the chamber a process gas used for
removal of the coating film; and wherein, a reaction product
adhered on the coating film during the etching process is removed
together with the coating film by supplying a process gas by the
second gas supply unit after the etching process by using a process
gas supplied by the first gas supply unit is completed under the
condition where the coating film is formed.
16. The plasma etching apparatus according to claim 15, further
comprising, the chamber comprising a dielectric wall which
transmits an electromagnetic wave at the opposing position to an
object to be processed; a flat coil configured to create the
induction magnetic field to maintain the plasma provided at the
exterior of the chamber in response to the dielectric wall; and, a
Faraday shield electrode provided between the flat coil and the
dielectric wall.
Description
RELATED APPLICATION
[0001] This present application claims the benefit of patent
application number 2005-180739, filed in Japan on Jun. 21, 2005,
the subject matter of which is hereby incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a plasma etching method and
plasma etching apparatus, and more particularly relates to a plasma
etching method and plasma etching apparatus that performs an
etching process for transferring a fine pattern.
[0004] 2. Description of the Related Art
[0005] In recent years, the shrinking of dimensions for transistors
comprising a semiconductor integrated circuit device has made
advances in response to demand for high integration, high
functionality, and high speed operation in a semiconductor
integrated circuit device. In conjunction with this shrinkage,
transistors have been developed that provide a metal gate electrode
(hereafter referred to as a metal gate) composed of metallic
material such as TiN, TaN, TaSiN, or the like; and a gate insulator
(hereafter referred to as high-k film) composed of a high dialectic
film including a hafnium-based oxide such as HfO.sub.x and
HfSiO.sub.x, or the like. To manufacture a stable fine transistor
that provides this type of metal gate and high-k film, a
microfabrication technology is necessary that enables the gate
material to be processed stably and with high precision.
[0006] The fabrication process of this type of metal gate material
uses a dry etching apparatus such as a plasma etching apparatus in
the same manner as the fabrication process of a gate electrode
consisting of conventional polysilicon film. The etching gas used
with such dry etching apparatus is a halogen-based gas such as
chlorine, and etching can proceed because the metallic material
reacts with the plasma of the halogen-based gas to create a metal
halide.
[0007] In order to be able to process a metal gate stably and with
favorable yield rate using this type of dry etching apparatus,
particles which are major source of pattern defects must be
reduced. In the fabrication process of the metal gate described
above, the metal halide is generated at etching process and adheres
to the inner surface of the chamber. An adhesiveness of the metal
halide is low against the chamber inner surface and easily
exfoliates from the chamber inside surface. For this reason, in
order to stably fabrication of the metal gate, exfoliation of
reaction product adhered to the chamber inner surface that includes
the metal halide must be suppressed.
[0008] As a technology for preventing the exfoliation of the
reaction product having a low adhesiveness with the chamber inner
surface, Japanese unexamined patent publication No. 2003-257946
(hereafter referred to as JP2003-257946) discloses the technology
in which an adhesive layer is formed on the chamber inner surface
in the condition that the chamber inner surface is clean without a
reaction product adhered thereon, and etching is performed on a
film to be etched in the condition that the adhesive layer has been
formed.
[0009] For example, with a parallel plate type plasma etching
apparatus on which is mounted a wafer for etching at a lower
electrode, an adhesive layer is formed at the upper electrode
opposing the wafer in a clean chamber condition. Next, the etching
process is performed by generating plasma of etching gas supplied
passing through the upper electrode within the chamber in
conjunction with the wafer being placed at the lower electrode. At
this time, the reaction product reached on the upper electrode
during the etching process is solidified onto the adhesive layer.
In other words, the reaction product deposits in the condition
having a high degree of adhesiveness onto the adhesive layer formed
on the surface of the upper electrode. Therefore, the exfoliation
of the reaction product becomes more difficult and the generation
of particles can be suppressed.
[0010] Further, an adhesive layer is formed on the upper electrode
on which the reaction product is adhered. By so doing, the
exfoliation of reaction product from the upper electrode can be
prevented because the reaction product already adhered to the upper
electrode is interposed between the adhesive layers and the
reaction product generated by the subsequent etching process is
adhered onto the newly formed adhesive layer. As the result, the
generation of particles can be suppressed. In other words, a
lamination layer structure is formed in which an adhesive layer and
a reaction product are formed (adhered) alternatively on the
surface of the upper electrode opposing the wafer to be etched. In
this way, the generation of the particles can be suppressed in the
etching process.
SUMMARY OF THE INVENTION
[0011] The metal gate formation process, as shown for instance in
FIG. 4A, first forms films on a silicon wafer 21 in order from the
bottom layer of a HfSiO.sub.x film 22 and TiN film 23. On the TiN
film 23, the antireflection film 24 and photoresist film are formed
in that order, and the photoresist pattern 25 covered the formation
area of the metal gate is formed by using photolithography.
[0012] Next, as shown in FIG. 4B, the antireflection film 24, TiN
film 23, and HfSiO.sub.x film 22 are etched by the plasma etching
process with resist pattern 25 as the etching mask, then. At this
time, although the resist pattern 25 functions as the etching mask,
the resist pattern 25 is side-etched during the etching process.
Then, the gate length W2 of the metal gate 26 formed after etching
is smaller in comparison to the width W1 of the gate length
direction of the resist pattern 25 before etching. In addition, the
resist pattern 25 and the antireflection film pattern 27 remaining
on the metal gate 26 are removed by ashing process, and the
formation of the metal gate is completed as shown in FIG. 4C.
[0013] In a gate length with a short gate length transistor of 50
nm or below, the difference between the resist pattern measurement
W1 and the metal gate measurement W2, W1-W2 (hereafter referred to
as the dimension shift) is in the same order as the gate length of
the metal gate. In this case, the dimension shift must be managed
to be always constant in order to realize stable transistor
properties.
[0014] However, with the method disclosed in JP2003-257946 in which
a reaction product generated at the time of plasma etching for a
film to be etched and a new adhesive layer are adhered
alternatively on the adhesive layer adhered to the chamber inner
surface, the total thickness of the films adhered to the chamber
inner surface increase gradually. In this case, since the condition
of the plasma (plasma potential, plasma density, and the like)
gradually changes over time in conjunction with the repetition of
the etching process on the object to be processed, the dimension
shift also changes.
[0015] FIGS. 5A and 5B show the dependence of the gate shape on the
number of etching wafers under the metal gate is formed by the
method disclosed in JP2003-257946. FIG. 5A shows the dependence of
the dimension shift on the total number of wafers and FIG. 5B shows
the dependence of the interior angle a at the bottom part of the
metal gate cross-section (see FIG. 4C). From FIG. 5A, it can be
understood that the dimension shift is reduced while increasing the
total number of wafers and the gate length is larger with the
method disclosed in JP2003-257946. Further, in FIG. 5B, it is
understood that the cross-section shape of the metal gate has a
width at the upper end that is a narrower shape than the width of
the bottom end (a so-called over-cut shape) as a result of the
interior angle a reducing while the total number of wafers
increases. In other words, even though a reduction in the number of
particles generated at the time of etching processing of the metal
gate is possible with the method disclosed in JP2003-257946, it is
insufficient technology from the perspective of stably forming a
fine metal gate.
[0016] The present invention has been proposed considering the
conventional situation, and its objective is to provide a plasma
etching method and a plasma etching apparatus that has the ability
to perform stable etching even on a fine metal gate electrode.
[0017] The present invention employs the following means in order
to accomplish the aforementioned object. The plasma etching method
that relates to the present invention, first forms a coating film
on the inner surface of the chamber in which plasma used in an
etching process is maintained. Next, an etching process is
performed on an object to be processed under the condition in which
the coating film is formed, and a reaction product adhered onto the
coating film in the etching process is etched and removed together
with the coating film. Further, each of these processes is
implemented at a frequency in which the condition of the chamber
inner surface is nearly always the same at the time of initiating
the etching process. The fact that the condition of the chamber
inner surface is nearly the same indicates that the change in the
plasma condition that accompanies the change in the total thickness
of the coating film and the reaction product adhered onto the
coating film is in a range in which the difference in the shape
after the etching process of the object to be processed is not
obvious.
[0018] According to this composition, the removal of the coating
film is, for instance, performed every time in the etching process
of an object to be processed, enabling the etching process to be
performed with the internal chamber always in the same condition.
Therefore, stable processing can be performed with favorable
fabrication even with an etching process that forms a fine
pattern.
[0019] The coating film preferably contains, for instance, a
constituent element of the object to be processed on which etching
is performed immediately after the formation of the coating film.
Especially, in the case that the object to be processed contains a
metal element, the coating film preferably contains such metal
element. Therefore, the reaction product generated during the
etching process adheres to the coating film in the condition of
high adhesiveness, and the generation of particles can be
suppressed in.
[0020] Further, the formation of the coating film is preferably
performed by using a sputtering method and chemical vapor
deposition method that can be executed as a series of processes
with the etching process in order to avoid a significant reduction
in the throughput of the etching process.
[0021] Meanwhile, from another perspective, the present invention
can provide a plasma etching apparatus favorable for implementation
with aforementioned plasma etching method. In other words, the
plasma etching apparatus that relates to the present invention
comprises a coating film formation unit for forming a coating film
on the chamber inner surface, a first gas supply unit for supplying
into the chamber process gas used in the etching process of an
object to be processed, and a second gas supply unit for supplying
the chamber process gas used in the removal of the coating film.
Further, After the etching process that used the process gas
supplied by the first gas supply unit is completed under the
coating film is formed, the second gas supply unit supplies the
process gas and the reaction product adhered onto the coating film
is removed together with the coating film in the etching
process.
[0022] With the present invention, a coating film is formed to the
chamber inner surface prior to the etching process on the object to
be processed, and the reaction product adhered by arriving onto the
inner surface of the chamber in the etching process is removed
together with the coating film after the etching process. In other
words, when the etching process is initiated, a coating film formed
as a film under the same conditions exists on the inner surface of
the chamber, and the condition of the chamber inner surface can
always be reproduced to the same. Therefore, the plasma potential
and plasma density of the plasma used in the etching process for
the object to be processed is in the same condition, and it is
possible to perform a stable process with high reproducibility even
for the etching process for forming a fine pattern.
[0023] In addition, by adopting a film which is superior in
adhesion for the reaction product generated during the etching
process, the reaction product is not only easily adhered onto the
chamber inner surface, but the exfoliation of the reaction product
adhered onto the coating film is also suppressed. Consequently, the
generation of particles, caused by tiny suspended particles in the
chamber and the exfoliation of the reaction product that is adhered
onto the inner surface of the chamber, can be suppressed.
[0024] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic diagram showing a plasma etching
apparatus that relates to an embodiment of the present
invention.
[0026] FIG. 2 is a flow diagram showing the process of a plasma
etching method that relates to an embodiment of the present
invention.
[0027] FIGS. 3A and 3B are drawings showing the dependence of the
pattern shape on the total number of wafer being processed in a
plasma etching method that relates to an embodiment of the present
invention.
[0028] FIGS. 4A to 4C are cross sectional views showing a laminated
structure of the metal gate.
[0029] FIGS. 5A and 5B are drawings showing the dependence of the
pattern shape on the total number of wafer being processed in a
conventional plasma etching method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] A detailed description is provided hereafter of an
embodiment of the present invention with reference to drawings.
FIG. 1 is a schematic cross-sectional view of a plasma etching
apparatus that relates to the present embodiment. FIG. 2 is a flow
diagram of the process of the plasma etching method that relates to
the present embodiment.
[0031] As shown in FIG. 1, a plasma etching apparatus 10 of the
present embodiment comprises a chamber 1 of nearly cylindrical
shape having an axis in the vertical direction. The upper wall of
the chamber 1 is constructed from, for instance, a plate-shaped
dielectric wall 2 consisting of a dielectric material such as
quarts, and a flat coil 3 is provided at the upper surface of the
dielectric wall 2. A high-frequency power source 5 to output
high-frequency power, for instance, at the frequency of 13.56 MHz,
is connected to the flat coil 3 via an impedance matching network
4.
[0032] The flat coil 3 is an electrically unified coil which is
constructed in, for instance, a whorl-shape or nearly concentric
circle shape. When the RF power is applied from the high-frequency
power source 5, the flat coil 3 generates a magnetic field where
electrons have a nearly circular motion by making the axis of the
chamber 1 to be the center of axis within the face perpendicular to
the axial direction of the chamber 1. In addition, the side wall
and lower wall of the chamber 1 are constructed from aluminum in
the present embodiment, and a film having a corrosion resistance is
formed by anodization on at least the inner surface of the
aluminum.
[0033] Meanwhile, a stage 6 where a wafer 7 is placed to be the
object of etching, is provided at the opposing position to the
dielectric wall 2 in the chamber 1. A high-frequency power source 9
to output high-frequency power, for instance, at the frequency of
13.56 MHz is connected to the stage 6 via an impedance matching
network 8.
[0034] Further, a plate-shaped Faraday shield electrode 13 is
provided between the flat coil 3 and the dielectric wall 2. A
high-frequency power source 15 to output high-frequency power, for
instance, at the frequency of 13.56 MHz is connected to the Faraday
shield electrode 13 via an impedance matching network 14. The
Faraday shield electrode 13 has a feature to regulate the quantity
of injected ion which enters the dielectric wall 2 after being
created in plasma by shifting the relative electrical potential of
the dielectric wall 2 in relation to plasma created in the chamber
1.
[0035] In addition, the impedance matching networks 4, 8, and 14
are adjusted to a matching state in which the loss of the
high-frequency power applied by each of the high-frequency power
sources 5, 9, and 15 is minimized in accordance with the impedance
object to the high-frequency power application which fluctuates
with the creation of plasma by the electrical power supplied from
each of the high-frequency power sources 5, 9, and 15.
[0036] Furthermore, a gas feed port 11, where the process gas
supplied from a gas supply unit 30 is introduced, is provided to
the upper sidewall of the chamber 1; and a gas exhaust port 12,
where the vacuum pump to keep the inside of the chamber 1 in the
prescribed pressure is connected, is provided to the lower part of
the chamber 1. In addition, the wafer 7 placed on the stage 6 is
loaded and unloaded from the chamber 1 via an inlet/outlet port,
which is not illustrated, provided at the sidewall of the chamber 1
with the ability to open and close.
[0037] When an etching process is performed with the plasma etching
apparatus 10, a coating film is formed first at the inner surface
of the chamber 1 (FIG. 2 S1). Preferably, this coating film
contains a constituent element of an etching film in which the
etching process is performed later on. For instance, in the case
teat a HfSiO.sub.x film 22, TiN film 23, and antireflection film 24
are formed in order from the bottom illustrated by the examples in
FIGS. 4A to 4C, and the etching process is performed to a resist
pattern 25 as an etching mask, a film containing titanium such as
titanium film and titanium nitride film, and a film containing
tantalum such as tantalum film and tantalum nitride film can be
adopted as the coating film.
[0038] In the etching process of a multilayer film having the
laminated structure shown in FIG. 4A, the metal halide (TiCl.sub.4)
which is the reaction product generated at the time of the etching
process of TiN film 23 has the lowest adhesion to the inner surface
of the chamber 1. Consequently, the adhesion of the metal halide
can be improved by forming a film containing titanium as the
coating film. By so doing, the reaction product becomes easier to
adhere to the inner surface of the chamber 1, and the reaction
product that has adhered on the coating film is suppressed from
exfoliating. As a result, the generation of particles, caused by
tiny suspended particles in the chamber, and the exfoliation of the
reaction product that is adhered onto the inner surface of the
chamber, can be suppressed.
[0039] Such film formation containing titanium can be achieved by
placing a substrate composed of, for instance, Ti or TiN at the
stage 6, and performing sputter etching onto the substrate. Such
sputter etching is possible to be implemented by introducing argon
gas at a flow rate of 10 sccm into chamber 1 by the coating film
formation gas supply unit 31 (coating film formation unit), and at
the same time, maintaining the pressure inside chamber 1 at about
10 Pa, and applying the electrical power to the stage 6 by the
high-frequency power source 9. At that time, the high-frequency
power (at the frequency of 13.56 MHz) applied by the high-frequency
power source 9 is 500 W. Further, the temperature of the stage 6 in
this process is maintained at about 70.degree. C. by a
non-illustrated heater housed in the stage 6.
[0040] In addition, because the coating film is removed after the
etching process as described hereafter, the thickness of the
coating film is preferably as thin as possible in the range that
the inner surface of the chamber 1 can be coated so as to be easily
removed. For instance, if the irregularities of the inner surface
of the chamber 1 are a few micrometers, the thickness of the
coating film may be about 10 nm. Furthermore, the titanium
contained film may be formed by performing the plasma enhanced
chemical vapor deposition in the chamber 1 to, for example,
TiCl.sub.4 gas supplied from the coating film formation gas supply
unit 31 without limiting the film formation method.
[0041] When the formation of the coating film on the inner surface
of the chamber 1 is completed as described above, the wafer used
for the formation of the coating film is unloaded from the chamber
1. Subsequently, the wafer 7 that is the object to be processed is
loaded into the chamber 1, and the etching process (FIG. 2 S2 to
S3) is performed by using the gas supplied from the etching gas
supply unit 32 (first gas supply unit). In the case of the
construction illustrated by the example in FIG. 4A, etching is
performed first to the antireflection film 24 by using the resist
pattern 25 as an etching mask.
[0042] For instance, in the case teat the antireflection film 24 is
composed of organic material, the etching can be performed by
introducing a flow rate of 90 sccm of SO.sub.2 gas, and 10 scam of
O.sub.2 gas into the chamber 1, and at the same time, maintaining
the pressure inside the chamber 1 at about 0.5 Pa, and applying the
electrical power to the flat coil 3 by the high-frequency power
source 5 and to the stage 6 by the high-frequency power source 9.
At the time, the high-frequency power (at the frequency of 13.56
MHz) applied by the high-frequency power source 5 is 1000 W, and
the high-frequency power (at the frequency of 13.56 MHz) applied by
the high-frequency power source 9 is 100 W. Further, the
temperature of the stage 6 is maintained at about 20.degree. C.
[0043] When the etching of the antireflection film 24 is completed,
the application of the high-frequency power from the high-frequency
power sources 5 and 9 is stopped and gas is exhausted once from the
interior of the chamber 1. Subsequently, the TiN film 23 comprising
the material of the metal gate is etched by using the resist
pattern 25 as an etching mask.
[0044] In the etching, for instance, the flow rate of 90 sccm of
the BCl.sub.3 gas and 10 sccm of the Cl.sub.2 gas are introduced
into the chamber 1, the pressure inside the chamber 1 is maintained
at about 0.5 Pa, and the high-frequency power source 5 applies the
electrical power to the flat coil 3 and the high-frequency power
source 9 applies the electrical power to the stage 6. At that time,
the high-frequency power source 5 applies the high-frequency power
(at the frequency of 13.56 MHz) of 1500 W to the flat coil 3, and
the high-frequency power source 9 applies the high-frequency power
(at the frequency of 13.56 MHz) of 150 W to the stage 6. In
addition, the temperature of the stage 6 is maintained at about
50.degree. C.
[0045] The reaction product that is generated in the etching
process as described above adheres and accumulates on the coating
film at the time that reaction product has reached the inner
surface of the chamber 1. In the case that the coating film is the
film containing titanium as described above, the metal halide (in
this case, titanium chloride) that is generated in the process of
the etching process of the TiN film is easily accumulated on the
coating film in the condition having the higher adhesion compared
to when having no coating film.
[0046] When the etching process is completed as described above,
the application of the electrical power from the high-frequency
power resources 5 and 9 is stopped, and the wafer 7 in which the
etching process is completed is unloaded from the chamber 1 via the
inlet/outlet port which is not illustrated (FIG. 2 S4).
[0047] After the wafer 7 is unloaded, if there is a wafer to be
processed next, the process to remove the coating film of the inner
surface of the chamber 1 is performed (FIG. 2 S5Yes to S6Yes to
S7). Here, an explanation is given in regards to a case in which
the coating film is removed each time a piece of the wafer 7 is
etched. However, in the case that there are fewer reaction products
generated in the etching process, and the condition of the inner
surface of the chamber 1 does not show much change after a piece of
the wafer 7 is etched, the etching process may be performed to the
next wafer without removing the coating film (FIG. 2 S6No to
S1).
[0048] The removal of coating film can be achieved by plasma
etching which uses the gas supplied from a coating film removal gas
supply unit 33 (second gas supply unit). The etching to remove the
coating film in the above case can be achieved by introducing the
Cl.sub.2 gas at a flow rate of 300 sccm, O.sub.2 gas at a flow rate
of 20 sccm into the chamber 1, and applying the electrical power to
the flat coil 3 by the high-frequency power source 5, and to the
Faraday shield electrode 13 by the high-frequency power source 15.
At the time, the high-frequency power source 5 applies the
high-frequency power of 100 W (at the frequency of 13.56 MHz) to
the flat coil 3 and the high-frequency power source 15 applies the
high-frequency power of 500 W (at the frequency of 13.56 MHz) to
the Faraday shield electrode 13. In addition, the temperature of
the stage 6 is maintained at about 70.degree. C. at the time.
[0049] According to the etching condition, the electrical potential
difference between the plasma and the dielectric wall 2 increases
by the high-frequency power applied to the Faraday shield electrode
13. Consequently, the quantity of injected ion into the plasma to
the dielectric wall 2 increases, and the reaction product
accumulated on the coating film and the coating film on the
dielectric wall 2 can be removed effectively.
[0050] Further, when the removal of reaction product accumulated on
the coating film and the coating film on the inner surface of the
chamber 1 is completed, the coating film is formed again, and the
wafer 7 can be etched (FIG. 2 S1 to S2).
[0051] When the etching process is completed on all wafers as
described above, the process completes after removing the coating
film (FIG. 2 S5No to S8).
[0052] FIGS. 3A and 3B show the dependence of the metal gate shape
on the number of wafers in the case of accumulation processing of
when the etching process is performed as shown in the examples of
FIGS. 4A to 4C. The lateral axis corresponds to the total number of
wafers in FIGS. 3A and 3B. Further, the vertical axis corresponds
to the dimension shift value as described above in FIG. 3A.
Furthermore, the vertical axis corresponds to the interior angle a
(refer to FIG. 4C) of the bottom section of the metal gate
cross-section profile in FIG. 3B. Moreover, the data shown by the
examples in FIGS. 5A and 5B is indicated by a dashed line as a
comparative example.
[0053] As can be understood from FIG. 3A, even when the total
number of wafers being processed reaches 1000, the dimension shift
value is suppressed below 1 nm, and a stable etching process with
high reproducibly is realized according to the method of the
present embodiment. Further, it also can be understood that even
when the total number of wafers being processed reaches to 1000,
the shape of the cross-section of the metal gate becomes the
favorable shape of nearly rectangular and not becoming as the over
cut shape as in conventional method.
[0054] For that matter, a favorable result also is obtained even
when the total number of wafers being processed reaches to 7000,
the dimension shift value is constantly suppressed below 1 nm, and
the interior angle a also maintained constantly at 89.0
degrees.
[0055] As described above, according to the present embodiment,
when the etching process (FIG. 2 S2 to S4) is initiated, the
identical coating film is formed on the inner surface of the
chamber 1. In other word, the inner surface of the chamber 1 is
constantly in the same condition when the etching process is
initiated. Consequently, the condition of plasma used for the
etching process is also the same. Accordingly, the dependence of
the dimension shift on the total number of wafers described above
can be eliminated, and an extremely stable etching process with
high reproducibility can be realized.
[0056] In addition, the present invention is not limited to the
embodiment described above, and various modifications and
applications are possible in the range which can prove the effect
of the present invention. The embodiment having the function so as
to improve the adhesion of the reaction product to the coating film
is described above as the preferred embodiment. However, if a
quality of material can adhere to the reaction product, a coating
film composed of any material, for instance silicon dioxide film
and the like, can be used.
[0057] Further, Cl.sub.2 gas is used in the above as the etching
gas to remove the coating film with the adhered reaction product.
However, any gas which can remove the coating film may be used as
the etching gas. For instance, a similar effect can be obtained by
using SF.sub.6 gas.
[0058] Furthermore, the case example in which the material of the
metal gate is TiN film is explained in the above description.
However, a similar effect can be obtained by using other materials
such as TaN film and the like.
[0059] Moreover, the inductively coupled plasma etching apparatus
comprising the Faraday shield electrode is explained as the plasma
etching apparatus in the above description. However, it is needless
to say that the present invention can be applied to any type of
plasma etching apparatuses.
[0060] The present invention is capable of performing stable
etching process with high accuracy for forming a fine pattern such
as the metal gate, so it is very useful for dry etching
process.
[0061] While the invention has been described in detail, the
foregoing description is in all aspects illustrative and not
restrictive. It is understood that numerous other modifications and
variations can be devised without departing from the scope of the
invention.
* * * * *