U.S. patent application number 10/276721 was filed with the patent office on 2003-09-11 for plasma processing device.
Invention is credited to Goto, Tetsuya, Hirayama, Masaki, Ohmi, Tadahiro, Sugawa, Shigetoshi.
Application Number | 20030168008 10/276721 |
Document ID | / |
Family ID | 18948496 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030168008 |
Kind Code |
A1 |
Ohmi, Tadahiro ; et
al. |
September 11, 2003 |
Plasma processing device
Abstract
In a microwave plasma processing apparatus, the reflection of
microwave by the joint unit between the microwave supplying
waveguide and the microwave antenna is reduced by providing a taper
surface or a member having a medium permittivity between the
microwave supplying waveguide and the microwave antenna so as to
moderate an impedance change. Accordingly, the efficiency of power
supplying is improved, and reduced discharge ensures stable
formation of plasma.
Inventors: |
Ohmi, Tadahiro; (Miyagi,
JP) ; Hirayama, Masaki; (Miyagi, JP) ; Sugawa,
Shigetoshi; (Miyagi, JP) ; Goto, Tetsuya;
(Miyagi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Family ID: |
18948496 |
Appl. No.: |
10/276721 |
Filed: |
November 18, 2002 |
PCT Filed: |
March 28, 2002 |
PCT NO: |
PCT/JP02/03109 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
H01J 37/3244 20130101;
H01J 37/3222 20130101; H01J 37/32229 20130101; H01J 37/32192
20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2001 |
JP |
2001-094271 |
Claims
What is claimed is:
1. A plasma processing apparatus, comprising: a processing vessel
defined by an outer wall and having a stage for holding a substrate
to be processed; an evacuation system coupled to said processing
vessel; a microwave transparent window provided on said processing
vessel as a part of said outer wall, and opposite said substrate
held on said stage; a plasma gas supplying part for supplying
plasma gas to said processing vessel; a microwave antenna provided
on said processing vessel in correspondence to said microwave; and
a microwave power source electrically coupled to said microwave
antenna, wherein said microwave antenna comprising a coaxial
waveguide connected to said microwave power source, said coaxial
waveguide having an inner conductor core and an outer conductor
tube surrounding said inner conductor core, and an antenna body
provided to a point of said coaxial waveguide; said antenna body
further comprising a first conductor surface forming a microwave
radiation surface coupled with said microwave transparent window,
and a second conductor surface opposite said first conductor
surface via a dielectric plate, said second conductor surface being
connected to said first conductor surface at a peripheral part of
said dielectric plate; said inner conductor core is connected to
said first conductor surface by a first joint unit; said outer
conductor tube is connected to said second conductor surface by a
second joint unit; said first joint unit forms a first taper unit
in which an outer diameter of said inner conductor core increases
toward said first conductor surface; and said second joint unit
forms a second taper unit in which an inner diameter of said outer
conductor tube increases toward said first conductor surface.
2. The microwave plasma processing apparatus as claimed in claim 1,
wherein the distance between an outer surface of said inner
conductor core and an inner surface of said outer conductor tube
increases toward said first conductor surface.
3. The microwave plasma processing apparatus as claimed in claim 1,
wherein said first taper unit is defined by a first curved surface;
and said second taper unit is defined by a second curved
surface.
4. The microwave plasma processing apparatus as claimed in claim 1,
further comprising a dielectric member provided in a space between
said inner conductor core and said outer conductor tube, defined by
a first edge face and a second edge face opposing said first edge
face, said first edge face being adjacent to said dielectric plate,
a permittivity of said dielectric member being lower than a
permittivity of said dielectric plate and higher than a
permittivity of air.
5. The microwave plasma processing apparatus as claimed in claim 4,
wherein composition of said dielectric member is changed from said
first edge face to said second edge face.
6. The microwave plasma processing apparatus as claimed in claim 4,
wherein said dielectric plate is made of either alumina, silicon
oxide, silicon oxynitrided, or silicon nitrided; and said
dielectric member is made of silicon oxide.
7. The microwave plasma processing apparatus as claimed in claim 4,
further comprising another dielectric member in a space between
said inner conductor core and said outer conductor tube, adjacent
to said second edge face of said dielectric member, a permittivity
of said other dielectric member being lower than a permittivity of
said dielectric member and higher than a permittivity of air.
8. The microwave plasma processing apparatus as claimed in claim 7,
wherein said dielectric member is made of silicon oxide, and said
other dielectric member is made of Teflon.
9. The microwave plasma processing apparatus as claimed in claim 4,
wherein said second edge face of said dielectric member forms a
taper surface; and an outer diameter of said dielectric member
decreases as a distance from said first edge face increases.
10. The microwave plasma processing apparatus as claimed in claim
9, wherein an outer diameter of said dielectric member linearly
decreases as a distance from said first edge face increases.
11. The microwave plasma processing apparatus as claimed in claim
9, wherein an outer diameter of said dielectric member
exponentially decreases as a distance from said first edge face
increases.
12. The microwave plasma processing apparatus as claimed in claim
1, wherein said plasma gas supplying part further comprises a
plasma gas passage connectable to a plasma gas source, said plasma
gas passage being made of a microwave-transparent material, and a
shower plate having a plurality of openings in communication with
said plasma gas passage, provided in an interior of said microwave
transparent window in intimate contact.
13. The microwave plasma processing apparatus as claimed in claim
12, wherein said shower plate is made of alumina.
14. The microwave plasma processing apparatus as claimed in claim
1, wherein said plasma gas supplying part is provided in an outer
wall of said processing vessel.
15. The microwave plasma processing apparatus as claimed in claim
14, wherein said plasma gas supplying part is tubes provided in
said outer wall of said processing vessel.
16. The plasma processing apparatus as claimed in claim 1, wherein
said microwave antenna is provided so that said first conductor
surface touches said microwave transparent window.
17. The plasma processing apparatus as claimed in claim 1, wherein
said microwave antenna is provided so that said first conductor
surface is spaced from said microwave transparent window.
18. The plasma processing apparatus as claimed in claim 1, wherein
a processing gas source is provided between said substrate and said
plasma gas supplying part, in said processing vessel, said
processing gas supplying part opposing to said substrate; a first
opening through which plasma formed in said processing vessel
passes and a second opening through which processing gas is
provided; and said second opening is in communication with a
processing gas passage connected to a processing gas source, formed
in said processing gas supplying source.
19. A plasma processing apparatus, comprising: a processing vessel
defined by an outer wall and having a stage for holding a substrate
to be processed; an evacuation system coupled to said processing
vessel; a microwave transparent window provided on said processing
vessel as a part of said outer wall, opposite said substrate held
on said stage; a plasma gas supplying part for supplying plasma gas
to said processing vessel; a microwave antenna provided on said
processing vessel in correspondence to said microwave; and a
microwave power source electrically coupled to said microwave
antenna, wherein said microwave antenna comprising a coaxial
waveguide connected to said microwave power source, said coaxial
waveguide having an inner conductor core and an outer conductor
tube surrounding said inner conductor core, and an antenna body
provided to a point of said coaxial waveguide; said antenna body
further comprising a first conductor surface forming a microwave
radiation surface coupled with said microwave transparent window,
and a second conductor surface opposite said first conductor
surface via a dielectric plate, said second conductor surface being
connected to said first conductor surface at a peripheral part of
said dielectric plate; said inner conductor core is connected to
said first conductor surface by a first joint unit; said outer
conductor tube is connected to said second conductor surface by a
second joint unit; a dielectric member is provided in a space
between said inner conductor core and said outer conductor tube,
defined by a first edge face and a second edge face opposing said
first edge face, said first edge face being adjacent to said
dielectric plate, a permittivity of said dielectric member being
lower than a permittivity of said dielectric plate and higher than
a permittivity of air.
20. The plasma processing apparatus as claimed in claim 19, wherein
said inner conductor core is connected substantially
perpendicularly to said first conductor surface in said first joint
unit.
21. The plasma processing apparatus as claimed in claim 19,
wherein, in said second joint unit, said outer conductor core is
connected substantially perpendicularly to said second conductor
surface.
22. The plasma processing apparatus as claimed in claim 19, wherein
composition of said dielectric member changes from said first edge
face to said second edge face.
23. The plasma processing apparatus as claimed in claim 19, wherein
said dielectric plate is made of either alumina, silicon oxide,
silicon oxynitridated, or silicon nitridated; and said dielectric
member is made of silicon oxide.
24. The plasma processing apparatus as claimed in claim 21,
wherein, in a space between said inner conductor core and said
outer waveguide, another dielectric member having a permittivity
lower than a permittivity of said dielectric member and higher than
a permittivity of air is provided adjacent to said second edge face
of said dielectric member.
25. The plasma processing apparatus as claimed in claim 24, wherein
said dielectric member is made of silicon oxide, and said other
dielectric member is made of Teflon.
26. The plasma processing apparatus as claimed in claim 21, wherein
said second edge face of said dielectric member forms a taper
surface, and an outer diameter of said dielectric member decreases
as a distance from said first edge face increases.
27. The plasma processing apparatus as claimed in claim 26, wherein
an outer diameter of said dielectric member decreases linearly as a
distance from said first edge face increases.
28. The plasma processing apparatus as claimed in claim 26, wherein
an outer diameter of said dielectric member decreases exponentially
as a distance from said first edge face increases.
29. The plasma processing apparatus as claimed in claim 19, wherein
said plasma gas supplying part is provided with a plasma gas
passage connectible to a plasma gas source, made of a microwave
transparent material, and a shower plate having a plurality of
openings in communication with said plasma gas passage.
30. The plasma processing apparatus as claimed in claim 29, wherein
said microwave transparent window and said shower plate are made of
alumina.
31. The plasma processing apparatus as claimed in claim 19, wherein
said plasma gas supplying part is provided in an outer wall of said
processing vessel.
32. The plasma processing apparatus as claimed in claim 31, wherein
said plasma gas supplying part is tubes provided in said processing
vessel.
33. The plasma processing apparatus as claimed in claim 19, wherein
said microwave antenna is provided so that said first conductor
surface touches said microwave transparent window.
34. The plasma processing apparatus as claimed in claim 19, wherein
said microwave antenna is provided so that said first conductor
surface separates from said microwave transparent window.
35. The plasma processing apparatus as claimed in claim 19, wherein
a process gas supplying part is provided between said substrate and
said plasma gas supplying part in said processing vessel, said
process gas supplying part opposing to said substrate; a first
opening through which plasma gas formed in said processing vessel
passes and a second opening through which process gas is supplied
are formed in said process gas supplying part; and said second
opening is connected to a process gas passage formed in said
process gas supplying part and connected to a process gas source.
Description
TECHNICAL FIELD
[0001] The present invention is generally related to a plasma
processing apparatus, and more particularly, to a microwave plasma
processing apparatus.
[0002] Plasma processing and plasma processing apparatuses are an
indispensable technology for fabricating ultrafine semiconductor
devices these days called deep submicron devices or deep subquarter
micron devices characterized by a gate length of near 0.1 .mu.m or
less, and for fabricating ultra high-resolution flat-panel display
devices including liquid crystal display devices.
[0003] Conventionally, various plasma excitation methods have been
used in plasma processing apparatuses used for fabrication of
semiconductor devices and liquid crystal display devices.
Particularly, a parallel-plate type high-frequency excitation
plasma processing apparatus or an induction-coupled plasma
processing apparatus are commonly used. However, such conventional
plasma processing apparatuses have a drawback of non-uniform plasma
formation in that the region of high electron density is limited,
and it has been difficult to conduct a uniform process over the
entire substrate surface with a high processing rate, and hence
with high throughput. This problem becomes particularly acute when
processing a large diameter substrate. Further, such a conventional
plasma processing device has several inherent problems associated
with its high electron temperature, in that the semiconductor
devices formed on the substrate sustain damage and that significant
metal contamination is caused as a result of sputtering of a
chamber wall. Thus, there are increasing difficulties for such
conventional plasma processing apparatuses to meet the stringent
demand of further device miniaturization and further improvement of
productivity in manufacturing semiconductor devices and liquid
crystal display devices.
[0004] Meanwhile, there are proposals of a microwave plasma
processing apparatus that uses high-density plasma excited by a
microwave electric field, in place of a direct-current magnetic
field. For example, there is a proposal of a plasma processing
apparatus that causes excitation of plasma by radiating a microwave
into a processing vessel from a planar antenna (radial line slot
antenna) having a number of slots disposed so as to form a uniform
microwave, such that the microwave electric field causes ionization
of a gas in a vacuum vessel. (See for example Japanese Laid-Open
Patent Application 9-63793). In the microwave plasma thus excited,
it is possible to realize a high plasma density over a wide area
right underneath the antenna, and it becomes possible to conduct
uniform plasma processing in a short duration. The microwave plasma
thus formed is characterized by low electron temperature, and
damaging or metal contamination of the substrate is avoided.
Further, it is possible to form uniform plasma over a large surface
area, and it can be easily applied to the fabrication process of a
semiconductor device using a large diameter semiconductor substrate
and a large size liquid crystal display device.
BACKGROUND ART
[0005] FIGS. 1A and 1B show the construction of a conventional
microwave plasma processing apparatus 100 having such a radial line
slot antenna, wherein FIG. 1A shows the microwave plasma processing
apparatus in a cross-sectional view while FIG. 1B shows the
construction of the radial line slot antenna.
[0006] Referring to FIG. 1A, the microwave plasma processing
apparatus 100 has a processing chamber 101 evacuated from plural
evacuation ports 116, and a stage 115 is formed for holding a
substrate 114 to be processed. In order to realize uniform
evacuation in the processing chamber 101, a ring-shaped space 101A
is formed around the stage 115, and the plural evacuation ports 116
are formed in communication with the foregoing space 101A at a
uniform interval, and hence in axial symmetry with regard to the
substrate. Thereby, it becomes possible to evacuate the processing
chamber 101 uniformly through the space 101A and the evacuation
ports 116.
[0007] On the processing chamber 101, there is formed a shower
plate 103 of plate-like form at the location corresponding to the
substrate 114 on the stage 115 as a part of the outer wall of the
processing chamber 101, and the shower plate 103 is sealed with
respect to the processing chamber 101 via a seal ring 109, wherein
the shower plate 103 is formed of a dielectric material of small
loss and includes a large number of apertures 107. Further, a cover
plate 102 also of a dielectric material of small loss is provided
on the outer side of the shower plate 103, and the cover plate 102
is sealed with respect to the shower plate 103 via another seal
ring 108.
[0008] The shower plate 103 is formed with a passage 104 for a
plasma gas on the top surface thereof, and each of the plural
apertures 107 are formed in communication with the foregoing plasma
gas passage 104. Further, there is formed a plasma gas supply
passage 108 in the interior of the shower plate 103 in
communication with a plasma gas supply port 105 provided on the
outer wall of the processing vessel 101. Thus, the plasma gas of
Ar, Kr or the like supplied to the foregoing plasma gas supply port
105 is supplied to the foregoing apertures 107 from the supply
passage 108 via the passage 104 and is released into a space 101B
underneath the shower plate 103 in the processing vessel 101 from
the apertures 107 with substantially uniform concentration.
[0009] On the processing vessel 101, there is provided a radial
line slot antenna 110 having a radiation surface shown in FIG. 1B
on the outer side of the cover plate 102 with a separation of 4-5
mm from the cover plate 102. The radial line slot antenna 110 is
connected to an external microwave source (not shown) via a coaxial
waveguide 110A and causes excitation of the plasma gas released
into the space 101B by the microwave from the microwave source. It
should be noted that the gap between the cover plate 102 and the
radiation surface of the radial line slot antenna 110 is filled
with air.
[0010] The radial line slot antenna 110 is formed of a flat
disk-like antenna body 110B connected to an outer waveguide of the
coaxial waveguide 110A and a radiation plate 110C is provided on
the mouth of the antenna body 110B, wherein the radiation plate
110C is formed with a number of slots 110a and slots 110b wherein
slots 110b are formed in a direction crossing the slots 110a
perpendicularly as represented in FIG. 1B. Further, a retardation
plate 110D of a dielectric film of uniform thickness is inserted
between the antenna body 110B and the radiation plate 110C.
[0011] In the radial line slot antenna 110 of such a construction,
the microwave supplied from the coaxial waveguide 110 spreads
between the disk-like antenna body 110B and the radiation plate
110C as it is propagated in the outward radial directions, wherein
there occurs a compression of wavelength as a result of the action
of the retardation plate 110D. Thus, by forming the slots 110a and
110b in concentric relationship in correspondence to the wavelength
of the radially propagating microwave so as to cross
perpendicularly with each other, it becomes possible to emit a
plane wave having a circular polarization state in a direction
substantially perpendicular to the radiation plate 110C.
[0012] By using such a radial line slot antenna 110, uniform plasma
is formed in the space 101B underneath the shower plate 103. The
high-density plasma thus formed is characterized by a low electron
temperature and thus no damage is caused to the substrate 114 and
no metal contamination occurs due to sputtering of the vessel wall
of the processing vessel 101.
[0013] In the plasma processing apparatus of FIG. 1, it should
further be noted that there is provided a conductor structure 111
in the processing vessel 101 between the shower plate 103 and the
substrate 114, wherein the conductor structure 111 is formed with a
number of nozzles 113 supplied with a processing gas from an
external processing gas source (not shown) via a processing gas
passage 112 formed in the processing vessel 101, and each of the
nozzles 113 releases the processing gas supplied thereto into a
space 101C between the conductive structure 111 and the substrate
114. It should be noted that the conductive structure 111 is formed
with openings between adjacent nozzles 113 with a size such that
the plasma formed in the space 101B passes efficiently from the
space 101B to the space 101C by way of diffusion.
[0014] Thus, in the case wherein a processing gas is released into
the space 101C from the conductive structure 111 via the nozzles
113, the processing gas is excited by the high-density plasma
formed in the space 101B and uniform plasma processing is conducted
on the substrate 114 efficiently and at a high rate, without
damaging the substrate or the devices on the substrate, and without
contaminating the substrate. Further, it should be noted that the
microwaves emitted from the radial line slot antenna 110 are
blocked by the conductive structure 111 and there is no possibility
of such microwaves causing damage to the substrate 114.
[0015] By the way, it is necessary in the case of the plasma
processing apparatus 100 to efficiently supply high-power
microwaves formed by a microwave source (not shown) to the radial
line slot antenna 110.
[0016] An impedance matching structure is generally provided
between a microwave antenna and a waveguide connected to the
microwave antenna to inject a weak microwave signal received by the
microwave antenna into the waveguide without loss. Meanwhile, in
the case of the plasma processing apparatus 100 of FIG. 1,
high-power microwaves are provided to the radial line slot antenna
110 through the waveguide, and additionally, reflective microwaves
reflected by the plasma formed in the processing vessel 101 are
also superimposed on the high-power microwaves in the antenna 110
and the waveguide. There is a possibility of abnormal discharge
being caused in the radial line slot antenna 110 and the coaxial
waveguide due to inappropriate impedance matching between the
antenna body 110 and the waveguide. Accordingly, the impedance
matching of the power supply unit connecting the waveguide and the
antenna body 110 is much more important than usual.
DISCLOSURE OF THE INVENTION
[0017] Accordingly, it is an object of the present invention to
provide a novel and useful plasma processing apparatus wherein the
foregoing problems are eliminated.
[0018] Another and more specific object of the present invention is
to provide a plasma processing apparatus having a microwave
antenna, forming plasma in the processing vessel by providing
microwaves from the microwave antenna to the processing vessel
through the microwave transparent window, and processing the
substrate in the plasma, in which the efficiency of supplying
microwaves from the microwave waveguide to the microwave antenna is
increased, and the abnormal discharge problem due to the
mismatching of impedance at the joint unit between the microwave
waveguide and the microwave antenna is eliminated.
[0019] Yet another object of the present invention is to provide a
plasma processing apparatus, comprising, a processing vessel
defined by an outer wall and having a stage for holding a substrate
to be processed, an evacuation system coupled to said processing
vessel, a microwave transparent window provided on said processing
vessel as a part of said outer wall, and opposite said substrate
held on said stage, a plasma gas supplying part for supplying
plasma gas to said processing vessel, a microwave antenna provided
on said processing vessel in correspondence to said microwave, and
a microwave power source electrically coupled to said microwave
antenna, wherein said microwave antenna comprising a coaxial
waveguide connected to said microwave power source, said coaxial
waveguide having an inner conductor core and an outer conductor
tube surrounding said inner conductor core, and an antenna body
provided to a point of said coaxial waveguide, said antenna body
further comprising a first conductor surface forming a microwave
radiation surface coupled with said microwave transparent window,
and a second conductor surface opposite said first conductor
surface via a dielectric plate, said second conductor surface being
connected to said first conductor surface at a peripheral part of
said dielectric plate, said inner conductor core is connected to
said first conductor surface by a first joint unit, said outer
conductor tube is connected to said second conductor surface by a
second joint unit, said first joint unit forms a first taper unit
in which an outer diameter of said inner conductor core increases
toward said first conductor surface, and said second joint unit
forms a second taper unit in which an inner diameter of said outer
conductor tube increases toward said first conductor surface.
[0020] Another object of the present invention is to provide a
plasma processing apparatus, comprising, a processing vessel
defined by an outer wall and having a stage for holding a substrate
to be processed, an evacuation system coupled to said processing
vessel, a microwave transparent window provided on said processing
vessel as a part of said outer wall, opposite said substrate held
on said stage, a plasma gas supplying part for supplying plasma gas
to said processing vessel, a microwave antenna provided on said
processing vessel in correspondence to said microwave, and a
microwave power source electrically coupled to said microwave
antenna, wherein said microwave antenna comprising a coaxial
waveguide connected to said microwave power source, said coaxial
waveguide having an inner conductor core and an outer conductor
tube surrounding said inner conductor core, and an antenna body
provided to a point of said coaxial waveguide, said antenna body
further comprising a first conductor surface forming microwave a
radiation surface coupled with said microwave transparent window
and a second conductor surface opposite said first conductor
surface via a dielectric plate, said second conductor surface being
connected to said first conductor surface at a peripheral part of
said dielectric plate, said inner conductor core is connected to
said first conductor surface by a first joint unit, said outer
conductor tube is connected to said second conductor surface by a
second joint unit, a dielectric member is provided in a space
between said inner conductor core and said outer conductor tube,
defined by a first edge face and a second edge face opposing said
first edge face, said first edge face being adjacent to said
dielectric plate, a permittivity of said dielectric member being
lower than a permittivity of said dielectric plate and higher than
a permittivity of air.
[0021] According to the present invention, the rapid change in
impedance by the joint unit between the microwave waveguide and the
microwave antenna is avoided. As a result, microwaves reflected by
the joint unit are efficiently reduced. As the reflective waves are
reduced, abnormal discharge at the joint unit and consequent damage
on the antenna caused by the abnormal discharge is avoided.
Additionally, the reduction in the reflective waves stabilizes the
supply of microwaves to the processing vessel through the microwave
transparent window, and makes it possible to form stable plasma in
the processing vessel as desired.
[0022] Other features and advantages of the present invention will
become more apparent from the following best mode for implementing
the invention when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIGS. 1A and 1B are diagrams showing the construction of a
conventional microwave plasma processing apparatus that uses a
radial line slot antenna;
[0024] FIGS. 2A and 2B are diagrams showing the construction of a
microwave plasma processing apparatus according to a first
embodiment of the present invention;
[0025] FIGS. 3A and 3B are diagrams showing the construction of the
joint between a coaxial waveguide and a radial line slot antenna of
the apparatus of FIG. 2;
[0026] FIG. 4 is a graph showing the effect of eliminating
reflection by the construction of FIG. 3;
[0027] FIG. 5 is a graph showing the reflection coefficient
measured for the microwave plasma formed in the plasma processing
apparatus of FIGS. 2A and 2B using the power supplying structure of
FIG. 3;
[0028] FIG. 6 is a diagram showing the construction of the process
gas supplying structure of the microwave plasma processing
apparatus shown in FIG. 2A;
[0029] FIG. 7 is a diagram showing the construction of the
microwave power source coupled to the microwave plasma processing
apparatus of FIG. 2A;
[0030] FIG. 8 is a diagram showing the construction of a microwave
supplying structure according to a variation of the present
embodiment;
[0031] FIG. 9 is a diagram showing the construction of a microwave
supplying structure according to a second embodiment of the present
invention;
[0032] FIG. 10 is a diagram showing a variation of the microwave
supplying structure of FIG. 9;
[0033] FIG. 11 is a diagram showing another variation of the
microwave supplying structure of FIG. 9;
[0034] FIG. 12 is a diagram showing another variation of the
microwave supplying structure of FIG. 9;
[0035] FIG. 13 is a diagram showing yet another variation of the
microwave supplying structure of FIG. 9;
[0036] FIG. 14 is a diagram showing yet another variation of the
microwave supplying structure of FIG. 9;
[0037] FIG. 15 is a diagram showing the construction of microwave
plasma processing apparatus according to a third embodiment of the
present invention;
[0038] FIG. 16 is a diagram showing the construction of microwave
plasma processing apparatus according to a fourth embodiment of the
present invention;
[0039] FIG. 17 is a diagram showing the construction of microwave
plasma processing apparatus according to a fifth embodiment of the
present invention;
[0040] FIG. 18 is a diagram showing the construction of a
semiconductor fabrication apparatus according to a sixth embodiment
of the present invention, using the microwave plasma processing
apparatus of FIGS. 2A and 2B;
[0041] FIG. 19 is a diagram showing the construction of an
exhaustion system of the semiconductor fabrication apparatus of
FIGS. 18A and 18B;
[0042] FIG. 20 is a diagram showing the construction of a screw
molecular pump used for the exhaustion system of FIG. 19;
[0043] FIG. 21 is a diagram showing the construction of a
gradational lead screw pump used for the exhaustion system of FIG.
19;
[0044] FIG. 22 is a diagram showing the construction of a gas
supplying system used for the processing unit of FIG. 19; and
[0045] FIG. 23 is a diagram showing the construction of a current
control apparatus used for the gas supplying system of FIG. 22.
BEST MODE FOR IMPLEMENTING THE INVENTION
[0046] Preferred embodiments of the present invention will be
described below.
[0047] [First Embodiment]
[0048] FIGS. 2A and 2B are diagrams showing the construction of a
microwave plasma processing apparatus 10 according to a first
embodiment of the present invention.
[0049] Referring to FIG. 2A, the microwave plasma processing
apparatus 10 includes a processing vessel 11 and a stage 13
provided in the processing vessel 11 for holding a substrate 12 to
be processed by an electrostatic chuck, wherein the stage 13 is
preferably formed of AlN or Al.sub.2O.sub.3 by a hot isostatic
pressing (HIP) process. In the processing vessel 11, there are
formed two or three evacuation ports 11a in a space 11A surrounding
the stage 13 with an equal distance, and hence with an axial
symmetry with respect to the substrate 12 on the stage 13. The
processing vessel 11 is evacuated to a low pressure via the
evacuation ports 11a by a gradational lead screw pump.
[0050] The processing vessel 11 is preferably formed of an
austenite stainless steel containing Al, and there is formed a
protective film of aluminum oxide on the inner wall surface by an
oxidizing process. Further, there is formed a disk-shaped shower
plate 14 of dense Al.sub.2O.sub.3, formed by a HIP process, in the
part of the outer wall of the processing vessel 11 corresponding to
the substrate 12 as a part of the outer wall, wherein the shower
plate 14 includes a large number of nozzle apertures 14A. The
Al.sub.2O.sub.3 shower plate 14 thus formed by the HIP process is
formed by using an Y.sub.2O.sub.3 additive and has porosity of
0.03% or less. This means that the Al.sub.2O.sub.3 shower plate is
substantially free from pores or pinholes and has a very large,
while not so large as that of AlN, thermal conductivity for a
ceramic of 30W/m.multidot.K.
[0051] The shower plate 14 is mounted on the processing vessel 11
and sealed thereto via a seal ring 11s, and a cover plate 15 of
dense Al.sub.2O.sub.3 formed also by an HIP process is provided on
the shower plate 14 and sealed thereto via a seal ring lit. The
shower plate 14 is formed with a depression 14B communicating with
each of the nozzle apertures 14A and serving as a plasma gas
passage, a side thereof formed by the cover plate 15. The
depression 14B also communicates with another plasma gas passage
14C formed in the interior of the shower plate 14 in communication
with a plasma gas inlet 11p formed on the outer wall of the
processing vessel 11.
[0052] The shower plate 14 is held by an extending part 11b formed
on the inner wall of the processing vessel 11, wherein the
extending part 11b is formed with a round surface,at the part
holding the shower plate 14 so as to suppress electric
discharge.
[0053] Thus, plasma gas such as Ar or Kr supplied to the plasma gas
inlet 11p is supplied to a space 11B underneath the shower plate 14
uniformly via the apertures 14A after being passed through the
passage 14C and the depression 14B in the shower plate 14.
[0054] On the cover plate 15, there is provided a radial line slot
antenna 20 formed,of a disk-shaped slot plate 16 formed with a
number of slots 16a and 16b shown in FIG. 3B in intimate contact
with the cover plate 15, a disk-shaped antenna body 17 holding the
slot plate 16, and a retardation plate 18 of a dielectric material
of low loss such as Al.sub.2O.sub.3, SiO.sub.2 or Si.sub.3N.sub.4
sandwiched between the slot plate 16 and the antenna body 17. The
radial line slot antenna 20 is mounted on the processing vessel 11
and sealed thereto by way of a seal ring 11u, and a microwave of
2.45 GHz or 8.3 GHz frequency is fed to the radial line slot
antenna 20 from an external microwave source (not shown) via a
coaxial waveguide 21. The microwave thus supplied is radiated into
the interior of the processing vessel from the slots 16a and 16b in
the slot plate 16 via the cover plate 15 and the shower plate 14.
Thereby, the microwaves cause excitation of plasma in the plasma
gas supplied from the apertures 14A in the space 11B underneath the
shower plate 14. It should be noted that the cover plate 15 and the
shower plate 14 are formed of Al.sub.2O.sub.3 and function as an
efficient microwave-transmitting window. In order to avoid plasma
excitation in the plasma gas passages 14A-14C, the plasma gas is
held at a pressure of about 6666 Pa-13332 Pa (about 50-100 Torr) in
the foregoing passages 14A-14C.
[0055] In order to improve intimate contact between the radial line
slot antenna 20 and the cover plate 15, the microwave plasma
processing apparatus 10 of the present embodiment has a ring-shaped
groove 11g in a part of the processing vessel 11 so as to be
adjacent to the slot plate 16. By evacuating the groove 11g via an
evacuation port 11G communicating therewith, the pressure in the
gap formed between the slot plate 16 and the cover plate 15 is
reduced and the radial line slot antenna 20 is urged firmly upon
the cover plate 15 by the atmospheric pressure. It is noted that
such a gap includes not only the slots 16a and 16b formed in the
slot plate 16 but also a gap formed for various other reasons. It
should be noted further that such a gap is sealed by the seal ring
11u provided between the radial line slot antenna 20 and the
processing vessel 11.
[0056] By filling the gap between the slot plate 16 and the cover
plate 15 with an inert gas of small molecular weight via the
evacuation port 11G and the groove 11g, heat transfer from the
cover plate 15 to the slot plate 16 is facilitated. It is
preferable to use He for such an inert gas in view of large thermal
conductivity and large ionization energy. In the case wherein the
gap is filled with He, it is preferable to set the pressure to
about 0.8 a tm. In the construction of FIG. 3, there is provided a
valve 11V on the evacuation port 11G for the evacuation of the
groove 15g and filling of the inert gas into the groove 15g.
[0057] It is noted that an outer waveguide 21A of the coaxial
waveguide 21A is connected to the disk-shaped antenna body 17 while
a center conductor 21B is connected to the slot plate 16 via an
opening formed in the retardation plate 18. Thus, the microwave fed
to the coaxial waveguide 21A is propagated in the outer radial
directions between the antenna body 17 and the slot plate 16 and is
emitted from the slots 16a and 16b.
[0058] FIG. 2B shows the slots 16a and 16b formed in the slot plate
16.
[0059] Referring to FIG. 2B, the slots 16a are arranged
concentrically, and the slots 16b, each corresponding to a slot 16a
and being perpendicular to the corresponding slot 16a, are also
arranged concentrically. The slots 16a and 16b are formed with an
interval corresponding to the wavelength of the microwave
compressed by the retardation plate 18 in the radial direction of
the slot plate 16, and as a result, the microwave is radiated from
the slot plate 16 in the form of a near plane wave. Because the
slots 16a and the slots 16b are formed in a mutually perpendicular
relationship, the microwave thus radiated forms a circularly
polarized wave including two perpendicular polarization
components.
[0060] In the plasma processing apparatus 10 of FIG. 2A, there is
provided a cooling block 19 formed with a cooling water passage 19A
on the antenna body 17, and the heat accumulated in the shower
plate 14 is absorbed via the radial line slot antenna 20 by cooling
the cooling block 19 with cooling water in the cooling water
passage 19A. The cooling water passage 19A is formed on the cooling
block 19 in a spiral form, and cooling water having a controlled
oxidation-reduction potential is supplied thereto, wherein the
control of the oxidation reduction potential is achieved by
eliminating oxygen dissolved in the cooling water by way of
bubbling of an H.sub.2 gas.
[0061] In the microwave plasma processing apparatus 10 of FIG. 2A,
there is further provided a process gas supply structure 31 in the
processing vessel 11 between the shower plate 14 and the substrate
12 on the stage 13, wherein the process gas supply structure 31 has
gas passages 31A arranged in a lattice shape and releases a process
gas supplied from a process gas inlet port 11r provided in the
outer wall of the processing vessel 11 through a large number of
process gas nozzle apertures 31B (see FIG. 4). Thereby, desired
uniform substrate processing is achieved in a space 11C between the
process gas supply structure 31 and the substrate 12. Such
substrate processing includes plasma oxidation processing, plasma
nitridation processing, plasma oxynitridation processing, and
plasma CVD processing. Further, it is possible to conduct a
reactive ion etching of the substrate 12 by supplying a readily
decomposing fluorocarbon gas such as C.sub.4F.sub.8, C.sub.5F.sub.8
or C.sub.4F.sub.6 or an etching-gas containing F or Cl from the
process gas supply structure 31 to the space 11C and further by
applying a high-frequency voltage to the stage 13 from a
high-frequency power source 13A.
[0062] In the microwave plasma processing apparatus 10 of the
present embodiment, it is possible to avoid deposition of reaction
byproducts on the inner wall of the processing vessel by heating
the outer wall of the processing vessel 11 to a temperature of
about 150.degree. C. Thereby, the microwave plasma processing
apparatus 10 can be operated constantly and with reliability, by
merely conducting a dry cleaning process once a day or so.
[0063] In the case of the plasma processing apparatus 10 of FIG.
2A, a taper unit 21Bt of the center conductor 21B is formed at the
joint/power supplying unit that connects the coaxial waveguide 21
to the radial line slot antenna 20, so that the radius or the cross
sectional area of the center conductor 21B gradually increases
towards the slot plate 16. Thus, the rapid change in impedance
caused by the joint/power supply unit is smoothed by forming such a
taper structure, which results in a great reduction of reflective
waves caused by the rapid change in impedance.
[0064] FIG. 3A is an expanded diagram showing in detail the
construction of the joint/microwave supplying unit between the
coaxial waveguide 21 and the radial line slot antenna 20 of the
plasma processing apparatus 10 of FIG. 2A. The slots 16a and 16b
formed on the slot plate 16 are not shown to simplify the
drawing.
[0065] Referring to FIG. 3A, the inner conductor 21B has a circular
cross section having a diameter of 16.9 mm. A 4 mm-thick alumina
plate having a relative permittivity of 10.1 is formed between the
slot plate 16 and the antenna body 17 as the retardation plate 18.
The outer waveguide 21A defines a cylindrical space having a
circular cross section having an inner diameter of 38.8 mm in which
the inner conductor 21B is provided.
[0066] As shown in FIG. 3A, the cross sectional area of the inner
conductor 21B is gradually increased from 7 mm above the joint
between the inner conductor 21B and the slot plate 16 to the joint.
As a result, the inner conductor 21B has a circular cross section
of a diameter of 23 mm at the joint. Additionally, the antenna body
17 is provided with a taper surface 21At corresponding to the taper
surface 21Bt thus formed, the taper surface 21At starting from the
position 10 mm (the thickness of the retardation plate 18 4 mm+the
thickness of the antenna body 17 6 mm=10 mm) above the joint of the
inner conductor 21B and the slot plate 16.
[0067] FIG. 4 shows the reflective ratio of microwave provided to
the antenna 20 through the waveguide 21 in the case where the
radial line slot antenna 20 and the waveguide 21 are used as shown
in FIG. 3A, and the parameter "a" shown in FIG. 3A is set at 6.4
mm. In FIG. 4, the reflective ratio is indicated by ".cndot.". In
addition, "*" shown in FIG. 4 indicates a reflective ratio of the
construction shown in FIG. 3B to which the taper units 21At and
21Bt are not provided.
[0068] Referring to FIG. 4, the reflective microwave includes not
only the microwave reflected by the joint/supplying unit between
the waveguide 21 the radial line antenna 20, but also the microwave
reflected by the plasma. In the case of the construction of FIG.
3B, the reflective ratio is about -2 dB regardless of a frequency,
which means about 80% of the microwave is reflectively returned to
the waveguide 21 and the microwave source connected to the
waveguide 21.
[0069] To the contrary, in the case of the construction of FIG. 3A
to which the taper surfaces 21At and 21Bt are provided, the
reflective ratio depends on the frequency of the microwave. The
reflective ratio becomes the minimum -23 dB (about 14%) in the
neighborhood of 2.4 GHz at which the plasma is excited.
[0070] FIG. 5 shows a microwave reflection factor measured by a
power monitor provided between the waveguide 21 and the microwave
source in the case of the antenna construction shown in FIG. 3A
under the following condition: the inner pressure in the processing
vessel being set at 133 Pa (about 1 Torr), Ar and 0.sub.2 being
supplied from the shower plate 14 at a flux of 690 SCCM and 23
SCCM, respectively, and microwaves of a frequency 2.45 GHz and a
power of 1.6 kW is supplied from the waveguide 21 to the radial
line slot antenna 20. Accordingly, the reflective factor includes
not only the reflection of microwave by the joint between the
waveguide 21 and the antenna 20, but also the reflection by the
plasma formed under the shower plate 14 in the processing vessel
11.
[0071] Referring to FIG. 5, it is noted that in the case of the
joint construction of FIG. 3B, the reflective ratio is about 80%
(the factor of reflection .apprxeq.0.8), but in the case of the
joint construction of FIG. 3A, the reflective ratio is reduced to
about 30% (the factor of reflection .apprxeq.0.3) and substantially
constant. Since the reflection ratio at the joint unit between the
coaxial waveguide 21 and the radial line antenna 20 is about 14% as
shown in FIG. 4, the reflective ratio of about 30% as shown in FIG.
5 includes the reflection by the plasma.
[0072] FIG. 6 is a bottom view showing the construction of the
process gas supply structure 31 of FIG. 2A.
[0073] Referring to FIG. 6, the process gas supply structure 31 is
formed by a conductive body such as an Al alloy containing Mg or a
stainless steel added with Al. The lattice shaped gas passage 31A
is connected to the process gas inlet port 11r at a process gas
supply port 31R and releases the process gas uniformly into the
foregoing space 11C from the process gas nozzle apertures 31B
formed at the bottom surface. Further, openings 31C are formed in
the process gas supply structure 31 between the adjacent process
gas passages 31A for passing the plasma or the process gas
contained in the plasma therethrough. In the case wherein the
process gas supply structure 31 is formed of an Al alloy containing
Mg, it is preferable to form a fluoride film on the surface
thereof. In the case wherein the process gas supplying structure 31
is formed of a stainless steel added with Al, it is preferable to
form a passivation film of aluminum oxide on the surface thereof.
In the plasma processing apparatus 10 of the present invention, the
energy of incident plasma is low because of the low electron
temperature of the excited plasma, and the problem of metal
contamination of the substrate 12 by the sputtering of the process
gas supply structure 31 is avoided. Further, it is possible to form
the process gas supply structure 31 by a ceramic such as
alumina.
[0074] The lattice shaped process gas passages 31A and the process
gas nozzle apertures 31B are formed so as to encompass an area
slightly larger than the substrate 12 represented in FIG. 4 by a
broken line. By providing the process gas supply structure 31
between the shower plate 14 and the substrate 12, the process gas
is excited by the plasma and uniform processing becomes possible by
using such plasma excited process gas.
[0075] In the case of forming the process gas supply structure 31
by a conductor such as a metal, the process gas supply structure 31
can form a shunting plane of the microwaves by setting the interval
between the lattice shaped process gas passages 31A shorter than
the microwave wavelength. In such a case, the microwave
excitation.of plasma takes place only in the space 11B, and there
occurs excitation of the process gas in the space 11C including the
surface of the substrate 12 by the plasma that has caused diffusion
from the excitation space 11B. Further, such a construction can
prevent the substrate from being exposed directly to the microwave
at the time of ignition of the plasma, and thus, damaging of the
substrate by the microwave is avoided.
[0076] In the microwave plasma processing apparatus 10 of the
present embodiment, the supply of the process gas is controlled
uniformly by the process gas supply structure 31, and the problem
of excessive dissociation of the process gas on the surface of the
substrate 12 is eliminated. Thus, it becomes possible to conduct
the desired substrate processing even in the case wherein there is
formed a structure of large aspect ratio on the surface of the
substrate 12 up to the very bottom of the high aspect ratio
structure. This means that the microwave plasma processing
apparatus 10 is effective for fabricating various semiconductor
devices of different generations characterized by different design
rules.
[0077] FIG. 7 shows the schematic construction of the microwave
source connected to the coaxial waveguide 21 of FIG. 2A.
[0078] Referring to FIG. 7, the coaxial waveguide is connected to
an edge of the waveguide extending from an oscillation part 25
including therein a magnetron 25A oscillating at the frequency of
2.45 GHz or 8.3 GHz via an isolator 24, a power monitor 23 and a
tuner 22 in this order. Thus, the microwave formed by the
oscillator 25 is supplied to the radial line slot antenna 20, and
the microwave reflected back from the high-density plasma formed in
the plasma processing apparatus 10 is returned again to the radial
line slot antenna 20 after conducting an impedance adjustment by
the tuner 22. Further, the isolator 24 is an element having
directivity and functions so as to protect the magnetron 25A in the
oscillation part 25 from the reflection wave.
[0079] In the microwave plasma processing apparatus 10 of the
present embodiment, the rapid change in impedance caused by the
joint is reduced by forming the taper units 21At and 21Bt at the
joint, or the power supplying unit, between the coaxial waveguide
21 and the radial line slot antenna 20. As a result, the reflection
of microwaves caused by the rapid change in impedance is
suppressed, which makes the supplying of microwaves from the
coaxial waveguide 21 to the antenna 20 stable.
[0080] In addition, in the microwave plasma processing apparatus 10
according to the present embodiment, as shown in a variation shown
in FIG. 8, it is possible to replace the taper faces 21At and 21Bt
with round faces 21Ar and 21Br, respectively. The change in
impedance caused by the joint is further reduced by forming the
round faces, which results in further efficient suppressing of the
reflective wave.
[0081] In the microwave plasma processing apparatus 10 of the
present embodiment, the distance between the shower plate 14
exposed to the heat caused by the plasma and the cooling unit is
reduced substantially, compared with the conventional microwave
plasma processing apparatus of FIGS. 1A and 1B. As a result, it
becomes possible to use a material such as Al.sub.2O.sub.3 having a
small dielectric loss and also a small thermal conductivity for the
microwave transmission window in place of AlN, which is
characterized by large dielectric loss. Thereby, the efficiency of
plasma processing and hence the processing rate are improved while
simultaneously suppressing the temperature rise of the shower
plate.
[0082] In the microwave plasma processing apparatus 10 of the
present embodiment, it is further noted that the gas including the
reaction byproduct formed in the space 11C as a result of the
substrate processing forms a stable gas flow to the space 11A at
the outer surrounding area because of the reduced distance between
the shower plate 14 and the substrate 12 facing the shower plate
14, and the byproduct is removed from the space 11C quickly. By
maintaining the temperature of the outer wall of the processing
vessel 11 to be about 150.degree. C., it becomes possible to
substantially eliminate the deposition of the reaction byproduct on
the inner wall of the processing vessel 11, and the processing
apparatus 10 quickly becomes ready for the next process.
[0083] By the way, in the above description of the present
embodiment, specific dimensions are mentioned, but the present
invention is not limited to such dimensions.
[0084] [Second Embodiment]
[0085] FIG. 9 shows the construction of the joint/supplying unit
between the coaxial waveguide 21 and the radial line antenna 20
according to a second embodiment of the present invention. In FIG.
9, portions previously described are referred to by the same
reference numerals, and their description will be omitted.
[0086] Referring to FIG. 9, the outer waveguide 21A constructing
the coaxial waveguide 21 and the body 17 of the radial line antenna
20 are connected perpendicularly to each other forming the
joint/supplying unit that is perpendicularly bent. The inner
conductor 21B is also connected to the slot plate 16
perpendicularly.
[0087] Meanwhile, in the construction of FIG. 9, the retardation
plate 18 is made of Al.sub.2O.sub.3 having a high relative
permittivity, and a ring-shaped member 18A made of SiO.sub.2, for
example, is formed between the outer waveguide 21A and the inner
conductor 21B so that an end of the member 18A contacts the
retardation plate 18.
[0088] Because of this construction, the impedance changes
stepwise, and the reflective waves are reduced. The length of the
member 18A can be optimized based on the property of the antenna
structure of the coaxial waveguide 21 and the antenna 20.
[0089] In the embodiment of FIG. 9, the second edge face opposing
the first edge face in contact with the retardation plate 18 is
exposed to air. As is shown in FIG. 10, it is possible, however, to
provide another ring-shaped member 18B made of Teflon, for example,
having smaller relative permittivity on the second face of the
ring-shaped member 18A and to increase the number of steps in the
impedance change at the joint unit.
[0090] Further, as is shown in FIG. 11, the ring-shaped member 18A
may be made of sintered mixture of SiO.sub.2 and Si.sub.3N.sub.4
having different permittivity, and the mixture ratio of SiO.sub.2
and Si.sub.3N.sub.4 in the ring-shaped member 18A may be controlled
so that the permittivity continuously increases from the first edge
face to the second edge face.
[0091] FIG. 12 shows the construction of the joint unit between the
coaxial waveguide 21 and the radial line antenna 20 according to
another variation of the present embodiment. In FIG. 12, portions
previously described are referred to by the same reference numeral,
and their description will be omitted.
[0092] Referring to FIG. 12, in this variation, the second edge
face of the ring-shaped member 18A is considered to be a taper
surface, and the thickness of the ring-shaped member 18A is
linearly increased toward the retardation plate 18.
[0093] Using this construction, in the case where the ring-shaped
member 18A is made of the same material as the retardation plate 18
such as Al.sub.2O.sub.3, the impedance of the joint/supplying unit
increases continuously toward the retardation plate 18, and
reflection caused by the rapid change in impedance is reduced,
which results in an efficient and stable supply of microwaves.
[0094] In addition, as is shown in FIG. 13, in a variation it is
also possible to make the taper face of the ring-shaped member 18A
a curved surface so that the thickness of the ring-shaped member
18A changes non-linearly to the property of the joint/supplying
unit. For example, it is possible to increase the thickness of the
ring-shaped member 18A exponentially.
[0095] Further, as is shown in FIG. 14, the ring-shaped member 18A
may be coupled with the construction of FIG. 3A having taper
surfaces 21At and 21Bt. In this case, the ring-shaped member 18A is
not limited to that of FIG. 9, but may be any construction of FIGS.
9 through 13.
[0096] [Third Embodiment]
[0097] FIG. 15 is a diagram showing the construction of a plasma
processing apparatus 10A according to a third embodiment of the
present invention. In FIG. 15, the parts described earlier are
referred to by the same reference numerals, and their description
is omitted.
[0098] Referring to FIG. 15, in the plasma processing apparatus
10A, the shower plate 14 is removed, and a plurality of plasma gas
inlets 11P are formed, preferably in symmetry, in communication
with the gas passage lip in the processing vessel 11. In the plasma
processing apparatus 10A according to the present embodiment, the
construction is simplified, and the fabrication cost can be reduced
substantially.
[0099] In the plasma processing apparatus 10A thus constructed, the
reflection of microwaves is reduced by forming the taper surfaces
21At and 21Bt in the joint/supplying unit between the radial line
slot antenna 20 and the coaxial waveguide 21, which results in an
increase in the power supplying efficiency, a reduction in abnormal
discharge caused by the reflective waves, and an increased
stability of the plasma formation. In the present embodiment, the
construction of the joint unit is not limited to that shown in FIG.
3A, and any construction of FIGS. 8 through 14 can be used.
[0100] [Fourth Embodiment]
[0101] FIG. 16 is a diagram showing the construction of a microwave
plasma processing apparatus 10B according to a fourth embodiment of
the present invention. In FIG. 16, parts that have been previously
described are referred to by the same numerals, and their
description will be omitted.
[0102] Referring to FIG. 16, in the construction of the microwave
plasma processing apparatus 10B, the process gas supply structure
31 is removed. Additionally, the entire face of the extending part
11b holding the shower plate 14 is rounded out.
[0103] The plasma processing apparatus 10B thus constructed cannot
perform film-forming or etching by supplying a process gas besides
the plasma gas since the lower shower plate 31 is removed. The
plasma processing apparatus 10B, however, can form an oxidized
layer, a nitrified layer, or an oxidized-nitrified layer by
supplying an oxidizing gas or a nitrifying gas from the shower
plate 14 together with the plasma gas.
[0104] In the plasma processing apparatus 10B thus constructed, the
reflection of microwaves is reduced by forming the taper surfaces
21At and 21Bt in the joint/supplying unit between the radial line
slot antenna 20 and the coaxial waveguide 21, which results in an
increase in the power supplying efficiency, a reduction in abnormal
discharge caused by the reflective waves, and an increased
stability of the plasma formation. In the present embodiment, the
construction of the joint unit is not limited to that shown in FIG.
3A, and any construction of FIGS. 8 through 14 can be used.
[0105] [Fifth Embodiment]
[0106] The joint/supplying structure according to the present
invention is not limited to the plasma processing apparatus 10 of
FIG. 2A or its variation, and is applicable to the plasma
processing apparatus 100 using a conventional radial line slot
antenna previously described by referring to FIGS. 1A and 1B.
[0107] FIG. 17 shows the construction of a plasma processing
apparatus 100A according to a fifth embodiment of the present
invention using the joint/supplying structure of the present
invention. In FIG. 17, the parts previously described are referred
to by the same numerals, and their description will be omitted.
[0108] Referring to FIG. 17, the plasma processing apparatus 100A
has substantially the same construction as the conventional plasma
processing apparatus 100, but is different in that the plasma
processing apparatus 100A includes taper surfaces similar to the
taper surfaces 21At and 21Bt in the joint unit between the coaxial
waveguide 110A and the radial slot antenna body 110B or the slot
plate 110D.
[0109] In the present embodiment, the reflection of microwaves is
reduced by forming the taper surfaces in the joint/supplying unit
between the coaxial waveguide 110A and the radial line slot
antenna, which results in an increase in the power supplying
efficiency, a reduction in abnormal discharge caused by the
reflective waves, and an increased stability of the plasma
formation. In the present embodiment, the construction of the joint
unit is not limited to that shown in FIG. 3A, and any construction
of FIGS. 8 through 14 can be used.
[0110] [Sixth Embodiment]
[0111] FIG. 18 is a cross sectional view showing the entire
construction of a semiconductor fabrication apparatus 40 according
to a sixth embodiment,of the present invention including the
microwave plasma processing apparatus 10 of FIGS. 2A and 2B.
[0112] Referring to FIG. 18, the semiconductor fabrication
apparatus 40 includes a vacuum transfer room 401 provided with a
robot 405 having a transportation arm 415, and the microwave plasma
processing apparatus 10 is formed on the top face of the vacuum
transfer room 401. In this case, the stage 13 can be moved up and
down by a cylinder 406 covered by a bellows 410. When the stage 13
descends to the end, the substrate 12 is set or taken out by the
transportation arm 415. When the stage 13 ascends to the end, the
substrate 12 is shut off from the vacuum transfer room 401 by a
seal 410A and processed as desired.
[0113] A load lock room 402 having a stage 418 to hold a stack of
substrates, is provided at another position on the upper side of
the vacuum transfer room 401. When the stage 418 ascends to the
end, the load rock room 402 is shut off from the vacuum transfer
room 401 by a seal 417. Meanwhile, when the stage 418 descends to
the end, the substrate stack 404 descends to the vacuum transfer
room 401, and the transportation arm 415 picks up a substrate from
the substrate stack 404 or returns a processed substrate
thereto.
[0114] In the case of semiconductor fabrication apparatus 40 thus
constructed, since a substrate is loaded and unloaded vertically,
and not through a side wall, an axially symmetry plasma is formed
in the processing vessel 11, and a gas in the processing vessel is
exhausted through a plurality of exhaustion ports provided in an
axial symmetry by a plurality of pumps. Accordingly, the
semiconductor fabrication apparatus 40 can guarantee uniform plasma
processing.
[0115] FIG. 19 shows the construction of an exhaustion system of
the process unit A.
[0116] Referring to FIG. 19, in the process unit A, each exhaustion
port 11a of the processing vessel 11 is connected to a duct D1, and
a gas in the processing vessel 11 is exhausted by screw molecular
pumps P1 and P2, each having a construction as shown in FIGS. 14A
and 14B, provided in the duct D1. The screw molecular pumps P1 and
P2 are connected, at their exhaustion side, to an exhaustion line
D2 commonly provided to the other processing units B and C of the
semiconductor fabrication apparatus 40. The exhaustion line D2 is
connected to an exhaustion line D3 commonly provided to the other
semiconductor fabrication apparatuses via an intermediate booster
pump P3.
[0117] FIG. 20A shows the construction of the screw molecular pumps
P1 and P2.
[0118] Referring to FIG. 20A, the screw molecular pump has a
cylindrical body 51 and a pump inlet at an end part of the body 51
and a pump outlet on the sidewall of the body 51 near the bottom
part. In the body 51, there is provided a rotor 52 shown in FIG.
20B, and a gradational lead screw 52A is formed on the rotor 52. It
should be noted that the gradational lead screw 52A has a
construction in which there is a large pitch formed at the pump
inlet part and the pitch is decreased toward the outlet. Associated
with this, the lead angle of the screw is decreased gradually from
the inlet side toward the outlet side. Further, the volume of the
pump chamber is decreased gradually from the inlet side toward the
outlet side.
[0119] Further, the screw molecular pump of FIG. 20A includes a
motor 53 provided in the rotor 52, an angle detector 54 detecting
the angular position of the rotor 52 and a magnet 55 cooperating
with the angle detector 54, wherein the rotor 52 is urged toward
the outlet side by an electromagnet mechanism 56.
[0120] Such a screw molecular pump has a simple construction and is
operable over a wide pressure range from the atmospheric pressure
to several millitorrs with small electric power consumption.
Further, the screw pump can obtain a pumping speed reaching 320
mL/min, which is larger than the pumping speed of conventional
turbo molecular pumps.
[0121] FIG. 21 shows the construction of a gradational lead screw
pump (GLSP) 60 used for the intermediate booster pump P3 for
evacuating the screw pumps P1 and P2 in the construction of FIG.
19.
[0122] Referring to FIG. 21, the gradational lead screw pump
includes, in a pump body 61 having an inlet 61A at an end and
outlets 63A and 63B at another end, a pair of screw rotors 62A and
62B each changing a screw pitch thereof gradually from an inlet
side to an outlet side as shown in FIG. 20B, in a meshing
relationship of the screws, wherein the rotors 62A and 62B are
driven by a motor 64 via gears 63A and 63B.
[0123] The gradational lead screw pump 60 of such a construction is
operable over a wide pressure range from ordinary pressure to a low
pressure of as much as 10.sup.-4 Torr, and can achieve a flow rate
reaching 2,500 L/min.
[0124] In the construction of FIG. 19, in which the semiconductor
fabrication apparatus is evacuated by the common back pump P4 via
the intermediate booster pump P3, the back pump P4 is operated in
the most efficient pressure range, and the electric power
consumption is reduced substantially.
[0125] In the construction of FIG. 19, the back pump P4 can operate
at the most efficient pressure range by exhausting the exhausted
gas from the other semiconductor fabrication apparatus, which
results in a substantially reduced power consumption.
[0126] FIG. 22 shows the construction of the gas supplying system
cooperating with each of the processing units A-C in the
semiconductor fabrication apparatus 40 of FIG. 18.
[0127] As explained before, the semiconductor fabrication apparatus
40 avoids deposition of reaction byproduct formed associated with
the substrate processing on the processing vessel 11 of the
microwave plasma processing apparatus 10 by maintaining the
processing vessel 11 at a temperature of about 150.degree. C. Thus,
the processing unit of FIG. 19 has a feature that the memory or
hysteresis of the preceding processing can be erased completely
without conducting a specific cleaning process.
[0128] Thus, by using the processing unit of FIG. 19, it becomes
possible to conduct different substrate processing one after
another by switching the plasma gas and/or process gas. For this,
however, it is necessary to provide a gas supply system that can
switch the process gas quickly.
[0129] Referring to FIG. 22, one or two gases selected fro N.sub.2,
Kr, Ar, H.sub.2, NF.sub.3, C.sub.4F.sub.8, CHF.sub.3, O.sub.2, CO,
HBr, SiCl.sub.4 and the like, are supplied to the plasma gas inlet
port lip provided on the processing vessel 11 in communication with
the shower plate 14 through the first and/or second flow rate
control apparatuses FCS1 and FCS2, and one or more gases selected
from N.sub.2, Kr, Ar, H.sub.2, NF.sub.3, C.sub.4F.sub.8, CHF.sub.3,
O.sub.2, CO, HBr, SiCl.sub.4 and the like, are supplied to the
process gas inlet port 11r communicating with the process gas
supply structure 30 via the third through seventh flow rate control
apparatuses FCS3-FCS7.
[0130] By using a flow rate control apparatus as shown in FIG. 23,
having a construction-in which a control valve 71, a manometer 72,
a stop valve 73 and an orifice 74 are formed consecutively on a
straight tube 70 and by controlling the pressure P.sub.2 at the
downstream side of the orifice 74 to be equal to or smaller than
one-half the pressure P.sub.1 at the upstream side of the stop
valve 73 (P.sub.1.gtoreq.2P.sub.2), it becomes possible to supply
the process gas instantaneously with a predetermined flow rate.
This is because there is no dead space in the flow rate control
apparatus in which flow rate control is not possible.
[0131] Thus, by using the flow control apparatus of FIG. 23 in the
gas supply system of FIG. 22, it becomes possible to switch the
plasma gas or process gas instantaneously depending on the type of
the substrate processing to be conducted in the processing
unit.
[0132] In the semiconductor fabrication apparatus 40, it is noted
that not only the plasma processing apparatus 10 but also the
plasma processing apparatuses according to the modifications
thereof, or the plasma processing apparatuses 10A and 10B according
to other embodiments can also be used.
[0133] Further, the present invention is not limited to the
specific embodiments noted above but various variations and
modifications may be made within the scope of the invention set
forth in claims.
[0134] Industrial Applicability
[0135] According to the present invention, in the microwave plasma
processing apparatus, the rapid change in impedance caused by the
joint between the coaxial waveguide providing microwaves and the
microwave antenna radiating the microwaves in the processing vessel
of the plasma processing apparatus is reduced. As a result, the
reflection of microwaves caused by the rapid change in impedance is
suppressed, which results in forming stable microwave plasma in the
processing vessel.
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