U.S. patent application number 09/815304 was filed with the patent office on 2001-12-13 for plasma processing apparatus with a dielectric plate having a thickness based on a wavelength of a microwave introduced into a process chamber through the dielectric plate.
Invention is credited to Hongo, Toshiaki, Osawa, Tetsu.
Application Number | 20010050059 09/815304 |
Document ID | / |
Family ID | 18601625 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050059 |
Kind Code |
A1 |
Hongo, Toshiaki ; et
al. |
December 13, 2001 |
Plasma processing apparatus with a dielectric plate having a
thickness based on a wavelength of a microwave introduced into a
process chamber through the dielectric plate
Abstract
A plasma processing apparatus applies a high-quality process to
an object to be processed by preventing impurities from being
generated due to a microwave transmitting through a dielectric
plate. The dielectric plate is provided between a process chamber
of a plasma processing apparatus and a slot electrode guiding a
microwave used for a plasma process. A thickness H of the
dielectric plate has a predetermined relationship with a wavelength
.lambda. of the microwave in the dielectric plate so that an amount
of isolation of the dielectric plate due to transmission of the
microwave is minimized. The wavelength .lambda. is represented by
.lambda.=.lambda..sub.0n, where .lambda..sub.0 is a wavelength of
the microwave in a vacuum and n is a wavelength reducing rate of
the dielectric plate represented by n=1/(.di-elect
cons..sub.t).sup.1/2, where .di-elect cons..sub.t is a specific
dielectric rate of the dielectric plate in a vacuum.
Inventors: |
Hongo, Toshiaki;
(Amagasaki-Shi, JP) ; Osawa, Tetsu; (Tsukui-Gun,
JP) |
Correspondence
Address: |
PILLSBURY WINTHROP LLP
1600 TYSONS BOULEVARD
MCLEAN
VA
22102
US
|
Family ID: |
18601625 |
Appl. No.: |
09/815304 |
Filed: |
March 23, 2001 |
Current U.S.
Class: |
118/723MW ;
156/345.41 |
Current CPC
Class: |
C23C 16/511 20130101;
H01J 37/32192 20130101 |
Class at
Publication: |
118/723.0MW ;
156/345 |
International
Class: |
H01L 021/3065 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2000 |
JP |
2000-085264 |
Claims
What is claimed is:
1. A dielectric plate adapted to be provided between a process
chamber of a plasma processing apparatus and a slot electrode
guiding a microwave used for a plasma process, wherein a thickness
H of said dielectric plate has a predetermined relationship with a
wavelength .lambda. of the microwave in said dielectric plate so
that an amount of isolation of said dielectric plate due to
transmission of the microwave is minimized, the wavelength .lambda.
being represented by .lambda.=.lambda..sub.0n, where .lambda..sub.0
is a wavelength of the microwave in a vacuum and n is a wavelength
reducing rate of said dielectric plate represented by
n=1/(.di-elect cons..sub.t).sup.1/2, where .di-elect cons..sub.t is
a specific dielectric rate of said dielectric plate in a
vacuum.
2. The dielectric plate as claimed in claim 1, wherein the
predetermined relationship between the thickness H and the
wavelength .lambda. of said dielectric plate is represented by
0.5.lambda.<H<0.75.lambda..
3. The dielectric plate as claimed in claim 2, wherein the
thickness H of said dielectric plate satisfies a relationship
represented by 0.6.lambda..ltoreq.H.ltoreq.0.7.lambda..
4. The dielectric plate as claimed in claim 1, wherein the
predetermined relationship between the thickness H and the
wavelength .lambda. of said dielectric plate is represented by
0.3.lambda.<H<0.4.lambda..
5. The dielectric plate as claimed in claim 1, wherein the
predetermined relationship between the thickness H and the
wavelength .lambda. of said dielectric plate is represented by one
of the relationships
(0.1+0.5N).lambda..ltoreq.H.ltoreq.(0.2+0.5N).lambda. and
(0.3+0.5N).lambda..ltoreq.H.ltoreq.(0.4+0.5N).lambda., where N is
an integer.
6. A plasma processing apparatus comprising: a process chamber in
which a plasma process is applied to an object to be processed; a
slot electrode having a plurality of slits guiding a microwave
introduced into said process chamber so as to generate plasma in
said process chamber; and a dielectric plate provided between said
slot electrode and said process chamber, wherein a thickness H of
said dielectric plate has a predetermined relationship with a
wavelength .lambda. of the microwave in said dielectric plate so
that an amount of isolation of said dielectric plate due to
transmission of the microwave is minimized, the wavelength .lambda.
being represented by .lambda.=.lambda..sub.0n, where .lambda..sub.0
is a wavelength of the microwave in a vacuum and n is a wavelength
reducing rate of said dielectric plate represented by
n=1/(.di-elect cons..sub.t).sup.1/2, where .di-elect cons..sub.t is
a specific dielectric rate of said dielectric plate in a
vacuum.
7. The plasma processing apparatus as claimed in claim 6, wherein
the predetermined relationship between the thickness H and the
wavelength .lambda. of said dielectric plate is represented by
0.5.lambda.<H<0.75.lambda..
8. The plasma processing apparatus as claimed in claim 7, wherein
the thickness H of said dielectric plate satisfies a relationship
represented by 0.6.lambda..ltoreq.H.ltoreq.0.7.lambda..
9. The plasma processing apparatus as claimed in claim 6, wherein
the predetermined relationship between the thickness H and the
wavelength .lambda. of said dielectric plate is represented by
0.3.lambda.<H<0.4.lambda..
10. The plasma processing apparatus as claimed in claim 6, wherein
the predetermined relationship between the thickness H and the
wavelength .lambda. of said dielectric plate is represented by one
of the relationships
(0.1+0.5N).lambda..ltoreq.H.ltoreq.(0.2+0.5N).lambda. and
(0.3+0.5N).lambda..ltoreq.H.ltoreq.(0.4+0.5N).lambda., where N is
an integer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to plasma processing
apparatuses and, more particularly, to a plasma processing
apparatus having a dielectric plate through which a microwave is
introduced into a process chamber so as to generate plasma in the
process chamber.
[0003] 2. Description of the Related Art
[0004] In recent years, a plasma processing apparatus is used to
perform a film deposition process, an etching process or an ashing
process in a manufacturing process of semiconductor devices since
the semiconductor devices have become more densified and a finer
structure. For example, in a typical microwave plasma processing
apparatus, a 2.45 GHz microwave is introduced into a process
chamber through a slot electrode. An object to be processed such as
a semiconductor wafer or an LCD substrate is placed inside the
process chamber, which is maintained under a negative pressure
environment by a vacuum pump. Additionally, a reactant gas is also
introduced into the process chamber so that the process gas is
converted into plasma by the microwave. Thus, active radicals and
ions are generated, and the radicals and ions react with the object
to be processed, which achieves a film deposition process or an
etching process.
[0005] Generally, the microwave is introduced into the process
chamber from a slot electrode by being passed through a dielectric
plate. The dielectric plate serves as a top plate of the process
chamber so as to hermetically seal the process chamber. The
dielectric plate must be made of a dielectric or insulating
material so as to let the microwave passes therethrough.
[0006] Since the microwave has a nature of wave propagation, a
standing wave is generated as a resultant wave of a synthesis of a
progressing wave traveling along the front surface of the
dielectric plate and a regressive wave reflected by the back
surface of the dielectric plate. Conventionally, the thickness of
the dielectric plate is determined so that a transmission rate of
the microwave with respect of the dielectric plate is
maximized.
[0007] However, the inventor of the present invention found that
the dielectric material of the dielectric plate isolates by a
plasma ion energy applied by transmission of a microwave isolates
the material of the dielectric plate. If the material of the
dielectric plate isolates, the material enters the object to be
processed as impurities. On the other hand, if the transmission
rate of the microwave with respect to the dielectric plate is
reduced so as to prevent the isolation of the material of the
dielectric plate, a plasma processing speed is reduced which
results in deterioration of a yield rate.
SUMMARY OF THE INVENTION
[0008] It is a general object of the present invention to provide
an improved and useful plasma processing apparatus in which the
above-mentioned problems are eliminated.
[0009] A more specific object of the present invention is to
provide a plasma processing apparatus which can apply a
high-quality process to an object to be processed by preventing
impurities from being generated due to a microwave transmitting
through a dielectric plate.
[0010] In order to achieve the above-mentioned objects, there is
provided according to one aspect of the present invention a
dielectric plate adapted to be provided between a process chamber
of a plasma processing apparatus and a slot electrode guiding a
microwave used for a plasma process, wherein a thickness H of the
dielectric plate has a predetermined relationship with a wavelength
.lambda. of the microwave in the dielectric plate so that an amount
of isolation of the dielectric plate due to transmission of the
microwave is minimized, the wavelength .lambda. being represented
by .lambda.=.lambda..sub.0n, where .lambda..sub.0 is a wavelength
of the microwave in a vacuum and n is a wavelength reducing rate of
the dielectric plate represented by n=1/(.di-elect
cons..sub.t).sup.1/2, where .di-elect cons..sub.t is a specific
dielectric rate of the dielectric plate in a vacuum.
[0011] According to the present invention, the thickness H of the
dielectric plate is determined based on the relationship with the
wavelength .lambda. of the microwave in the dielectric plate. When
the thickness H of the dielectric plate is 0.5 times the wavelength
.lambda. of the microwave in the dielectric plate, a standing wave
is generated as a resultant wave of a synthesis of a progressing
wave traveling along the front surface of the dielectric plate and
a regressive wave reflected by the back surface of the dielectric
plate. Thereby, the reflection is maximized and a power of the
microwave transmitted to the process chamber 102 is minimized. In
such a case, generation of plasma is insufficient, and, thereby a
desired process speed cannot be achieved.
[0012] On the other hand, when thickness of the dielectric plate is
0.75 times the wavelength .lambda. of the microwave in the
dielectric plate, the transmission power of the microwave is
maximized but ion energy in the plasma is also maximized. A plasma
ion energy applied by transmission of a microwave isolates the
material of the dielectric plate. If the material of the dielectric
plate isolates, the material enters the object to be processed as
impurities, thereby deteriorating a high-quality plasma
process.
[0013] In order to supply a microwave having a sufficient power but
prevent the dielectric plate from being isolated, the predetermined
relationship between the thickness H and the wavelength .lambda. of
the dielectric plate is preferably represented by
0.5.lambda.<H<0.75.la- mbda.. More preferably, the thickness
H of the dielectric plate satisfies a relationship represented by
0.6.lambda..ltoreq.H.ltoreq.0.7.lambda..
[0014] Alternatively, the predetermined relationship between the
thickness H and the wavelength .lambda. of the dielectric plate may
be represented by 0.3.lambda.<H<0.4.lambda..
[0015] In general, the predetermined relationship between the
thickness H and the wavelength .lambda. of the dielectric plate is
represented by one of the relationships
(0.1+0.5N).lambda..ltoreq.H.ltoreq.(0.2+0.5N).lambda- . and
(0.3+0.5N).lambda..ltoreq.H.ltoreq.(0.4+0.5N).lambda., where N is
an integer.
[0016] Additionally, there is provided according to another aspect
of the present invention a plasma processing apparatus comprising:
a process chamber in which a plasma process is applied to an object
to be processed; a slot electrode having a plurality of slits
guiding a microwave introduced into the process chamber so as to
generate plasma in the process chamber; and a dielectric plate
provided between the slot electrode and the process chamber,
wherein a thickness H of the dielectric plate has a predetermined
relationship with a wavelength .lambda. of the microwave in the
dielectric plate so that an amount of isolation of the dielectric
plate due to transmission of the microwave is minimized, the
wavelength .lambda. being represented by .lambda.=.lambda..sub.0n,
where .lambda..sub.0 is a wavelength of the microwave in a vacuum
and n is a wavelength reducing rate of the dielectric plate
represented by n=1/(.di-elect cons..sub.t).sup.1/2, where .di-elect
cons..sub.t is a specific dielectric rate of the dielectric plate
in a vacuum.
[0017] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description when read in conjunction of the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is an illustration of a structure of a microwave
plasma processing apparatus according an embodiment of the present
invention;
[0019] FIG. 2 is a block diagram of a temperature-adjusting device
shown in FIG. 1;
[0020] FIG. 3 is a graph showing a nitrogen distribution in a
direction of a depth when a multi-layered structure is formed on an
object to be processed at a high temperature;
[0021] FIG. 4 is a graph showing a nitrogen distribution in a
direction of a depth when a multi-layered structure is formed on an
object to be processed at an appropriate temperature;
[0022] FIG. 5 is a graph showing a relationship between a defect
density and a temperature of a silicon nitride film;
[0023] FIG. 6A is a plan view of a gas supply ring shown in FIG. 1;
FIG. 6B is a cross-sectional view taken along a line VI-VI of FIG.
6A;
[0024] FIG. 7 is a plan view of an example of a slot antenna shown
in FIG. 1;
[0025] FIG. 8 is a plan view of another example of the slot antenna
shown in FIG. 1;
[0026] FIG. 9 is a plan view of a further example of the slot
antenna shown in FIG. 1;
[0027] FIG. 10 is a plan view of another example of the slot
antenna shown in FIG. 1;
[0028] FIG. 11 is a graph showing a relationship between a
transmission power of a microwave and a thickness of a dielectric
plate;
[0029] FIG. 12 is a graph showing a relationship between the
thickness of the dielectric plate and an amount of isolation
(sputtering rate) of the dielectric plate;
[0030] FIG. 13 is a graph shown in FIG. 11 with indication of
ranges of the thickness of the dielectric plate;
[0031] FIG. 14 is a cross-sectional view of a showerhead having a
gas supply arrangement;
[0032] FIG. 15 is an enlarged cross-sectional view of a part of a
shower plate which part includes one of nozzles provided to the
shower plate;
[0033] FIG. 16 is an enlarged cross-sectional view of an eject
member provided with a nozzle passage having a single nozzle
opening;
[0034] FIG. 17 is an enlarged cross-sectional view of an eject
member provided with a nozzle passage having two nozzle
openings;
[0035] FIG. 18 is an enlarged cross-sectional view of an eject
member provided with a nozzle passage having three nozzle openings;
and
[0036] FIG. 19 is an illustrative plan view of a cluster tool,
which is connectable to the microwave plasma processing apparatus
shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] A description will now be given, with reference to FIG. 1,
of an embodiment of the present invention. FIG. 1 is an
illustration of a structure of a microwave plasma processing
apparatus 100 according to the embodiment of the present invention.
The present invention is specifically related to a dielectric plate
through which a microwave is introduced into a process chamber. A
feature of the dielectric plate is described with reference to
FIGS. 11 to 13.
[0038] The microwave plasma processing apparatus 100 shown in FIG.
1 comprises: a gate valve 101 connected to a cluster tool 300
(refer to FIG. 19); a process chamber 102 which can accommodate a
susceptor 104 on which an object to be processed such as a
semiconductor wafer or an LCD substrate; a high-vacuum pump 106
connected to the process chamber 102; a microwave supply source
110; an antenna member 120; and gas supply systems 130 and 160. It
should be noted that a control system of the plasma processing
apparatus 100 is not illustrated in FIG. 1 for the sake of
simplification.
[0039] The process chamber 102 is made of a conductive material
such as an aluminum alloy. In the present embodiment, the process
chamber 102 has a generally cylindrical shape. However the shape of
the process chamber 102 is not limited to the cylindrical shape,
and any shape can be adopted unless the process chamber 102 is
deformed by a vacuum formed in the process chamber 102. The
susceptor 104 is provided in the process chamber 102 so as to
support the object W to be processed. It should be noted that an
electrostatic chuck or a clamping mechanism to fix the object W on
the susceptor 104 is not illustrated in FIG. 1 for the sake of
simplification.
[0040] The susceptor 104 controls a temperature of the object W to
be processed in the process chamber 102. The temperature of the
susceptor 104 is adjusted to a value within a predetermined
temperature range by a temperature-adjusting device 190. FIG. 2 is
a block diagram of the temperature-adjusting device 190 shown in
FIG. 1. The temperature-adjusting device 190 comprises, as shown in
FIG. 2, a control unit 191, a cooling jacket 192, a sealing member
194, a temperature sensor 196 and a heater unit 198. Cooling water
is supplied to the temperature control device 190 from a water
source 199 such as a water line. The control unit 191 controls the
temperature of the object W to fall within a predetermined
temperature range. In order to achieve an easy control, it is
preferable that the temperature of the cooling water supplied by
the water source 199 is constant.
[0041] For example, in a case in which a silicon nitride film
(Si.sub.3N.sub.4) is to be formed on a silicon substrate as the
object W (single layer nitride film), the control unit 191 controls
the heater unit 198 so that the temperature of the silicon
substrate falls within a range from about 450.degree. C. to about
500.degree. C. If the silicon substrate is not maintained at a
temperature above 450.degree. C., a dangling bond may occur which
is not preferable since a threshold voltage may vary as described
later.
[0042] A consideration will be given of a case in which a silicon
nitride film is formed on a silicon oxidation film (SiO.sub.2)
after the silicon oxidation film is formed on the silicon
substrate. In this case, an upper portion of the silicon oxidation
film is converted into the silicon nitride film by a plasma process
by introducing nitrogen into the silicon oxidation film. In such a
process, the control unit 191 controls the heater unit 198 so that
the temperature of the silicon substrate falls within a range from
about 250.degree. C. to about 350.degree. C.
[0043] The reason for setting the temperature of the silicon
substrate below about 350.degree. C. is explained below with
reference to FIG. 3. FIG. 3 is a graph showing a nitrogen
distribution in a direction of a depth when a multi-layered
structure is formed on an object to be processed at a high
temperature (for example, about 500.degree. C.). As shown in FIG.
3, when the temperature of the silicon substrate is set to a value
greater than 350.degree. C. by controlling the heater 198, a large
amount of nitrogen is introduced into an inner portion of the
silicon oxidation film as well as a surface (an upper portion) of
the silicon oxidation film. It can be appreciated from FIG. 3 that
nitrogen reaches a position 20 .ANG. distant from the surface of
the silicon oxidation film.
[0044] In such a case, nitrogen reaches a boundary between the
silicon substrate and the silicon oxidation film, and a compound of
silicon, oxygen and nitrogen is formed. The formation of the
compound is not preferable since the compound may deteriorate a
performance of a semiconductor element formed on the silicon
substrate. A rate of nitrogen reaching the boundary between the
silicon oxidation film and the silicon substrate depends on the
size of the semiconductor element. If a gate length is in the range
of 0.18 .mu.m to 0.3 .mu.m as in the conventional semiconductor
element, an influence of the nitrogen may be negligible. However,
recent semiconductor element is reduced in its size and thus the
gate length is reduced to, for example, 0.13 .mu.m or 0.10 .mu.m.
Thus, the influence of the nitrogen will not be negligible.
[0045] On the other hand, if the temperature of the silicon
substrate controlled by the heater unit 198 is set to below
350.degree. C., the nitrogen is distributed to an inner portion of
the silicon oxidation film as well as the surface (an upper
portion) of the silicon oxidation film. FIG. 4 is a graph showing a
nitrogen distribution in a direction of a depth when a
multi-layered structure is formed on an object to be processed at
an appropriate temperature (for example, about 350.degree. C.). It
can be appreciated from FIG. 4 that the depth of the nitrogen is
within an allowable range (less than 10 .ANG.), and, therefore, the
above-mentioned problem can be eliminated by setting the
temperature of the silicon substrate below 350.degree. C.
[0046] The reason for setting the temperature of the susceptor 104
greater than about 250.degree. C. is explained below. A CV
characteristic which indicates a relationship between a gate
voltage V and a gate capacitance C is often used as an index
representing an operational characteristic of the object W to be
processed (semiconductor element). The CV characteristic has a
hysteresis at a time when the gate voltage V is applied and
released. If the hysteresis width is large, threshold voltages
(voltage at which a semiconductor element turns on and off) of the
gate voltage V is varied, which deteriorates a reliability.
Accordingly, the hysteresis width is preferably maintained within a
predetermined voltage range such as less than 0.02 V. This may be
applied to a layered structure. The hysteresis width becomes larger
as the number of defects (dangling bond) of the silicon nitride
film increases. FIG. 5 is a graph showing a relationship between
defect density of the silicon nitride film and the temperature of
the susceptor 104. In FIG. 5, a dotted line indicates an allowable
defect density. In order to maintain the hysteresis width, the
defect density of the silicon nitride film must be maintained as
indicated by a dotted line in FIG. 5. The inventors found that the
allowable defect density is about 250.degree. C. as interpreted
from FIG. 5.
[0047] The control unit 191 controls the temperature of the
susceptor 104 to be about 450.degree. C. for a CVD process and
about at least 80.degree. C. for an etching process. In any case,
the object W to be processed is maintained at a temperature at
which a water component does not adhere to the object W.
[0048] The cooling jacket 192 is provided for supplying a cooling
water so as to cool the object W to be processed during a plasma
process. The cooling jacket 192 is made of a selected material such
as a stainless steel which has a high heat conductivity and an easy
machinability to form a water passage 193. The water passage 193
extends in longitudinal and transverse directions of the cooling
jacket 192 having a square shape, and the sealing members 194 are
screwed into openings of the water passage 193. However, the shape
of the cooling jacket 192 is not limited to the square shape, and
the cooling jacket 192 and the water passage can be formed with any
shape. It should be noted that a coolant such as alcohol, gulden or
fluorocarbon may be used instead of the cooling water. The
temperature sensor 196 can be a known sensor such as a PTC
thermister an infrared sensor or a thermocouple. The temperature
sensor may either be connected or not connected to the water
passage 193.
[0049] The heater unit 198 is comprised of a heater wire wound on a
water pipe connected to the water passage of the cooling jacket
192. By controlling an electric current supplied to the heater
wire, the temperature of the cooling water flowing through the
water passage 193 of the cooling jacket 192 can be adjusted. Since
the cooling jacket 192 has high heat conductivity, the temperature
of the cooling jacket is substantially equal to the temperature of
the cooling water flowing through the water passage 193.
[0050] The susceptor 104 is movable in a vertical direction inside
the process chamber. A vertically moving system of the susceptor
104 comprises a vertically moving member, a bellows and a
vertically moving mechanism. The vertically moving system can be
achieved by any known structure in this art. The susceptor 104 is
moved up and down between a home position and a process position.
When the plasma processing apparatus 100 is not in operation or a
waiting state, the susceptor 104 is located at the home position.
The object W to be processed is transferred to the susceptor 104 at
the home position from the cluster tool 300 via the gate valve 101,
and vice versa. A transfer position other than the home position
may be defined so as to communicate with the gate valve 101. A
vertical travel of the susceptor 104 can be controlled by a
controller of the vertically moving mechanism or a control unit of
the plasma processing apparatus 100, and the susceptor can be
observed through a view port (not shown in the figure) provided to
the process chamber 102.
[0051] The susceptor 104 is connected to a lifter pin vertically
moving system (not shown in the figure). The lifer pin vertically
moving system comprises a vertically moving member, a bellows and a
vertically moving device. The vertically moving system can be
achieved by any known structure in this art. The vertically moving
member is made of aluminum, for example, and is connected to three
lifer pins, which vertically extend from vertices of an equilateral
triangle. The lifter pins are vertically movable by penetrating the
susceptor 104 so as to vertically move the object W to be processed
placed on the susceptor 104. The object W is moved in the vertical
direction at a time when the object W is put into the process
chamber 102 from the cluster tool 300, and at a time when the
object W after processing is taken out of the process chamber 102
and transferred to the cluster tool 300. The vertically moving
mechanism may be arranged to allow the vertical movement of the
lifter pins alone when the susceptor 104 is at a predetermined
position such as the home position. Additionally, a vertical travel
of the lifter pins can be controlled by a controller of the
vertically moving mechanism or a control unit of the plasma
processing apparatus 100, and the movement of the lifter pins can
be observed through a view port (not shown in the figure) provided
to the process chamber 102.
[0052] A baffle plate may be provided to the susceptor 104 if
necessary. The baffle plate may be vertically moveable together
with the susceptor 104, or may be brought in engagement with the
susceptor 104 at the process position. The baffle plate separates a
process space in which the object W to be processed is placed from
an exhaust space underneath the process space. The baffle plate
mainly serves to maintain a potential of the process space (that
is, maintain a microwave in the process space) and maintain a
predetermined degree of vacuum (for example, 50 mTorr). The baffle
plate is formed of pure aluminum, and has a hollow disk-like shape.
The baffle plate has a thickness of 2 mm, and has many through
holes arranged at random. Each of the through holes has a diameter
of about 2 mm so that an open area ratio of the baffle plate is
more than 50%. It should be noted that the baffle plate could have
a meshed structure. Additionally, the baffle plate may have a
function to prevent a reverse flow from the exhaust space to the
process space or a function to create a pressure difference between
the process space and the exhaust space.
[0053] The susceptor 104 is connected to a bias radio frequency
power supply 282 and a matching box (matching circuit) 284, and
constitutes an ion-plating device together with an antenna member
120. The bias radio frequency power source 282 applies a negative
direct current bias (for example, a 13.5 MHz radio frequency) to
the object W to be processed. The matching box 284 is provided to
eliminate influences of a stray capacitance and a stray inductance
of an electrode in the process chamber 102. The matching box, for
example, uses a variable condenser arranged parallel and serial to
a load. As a result, ions are accelerated by the bias voltage
toward the object W to be processed, resulting in promotion of the
process by ions. The energy of the ions is determined by the bias
voltage, and the bias voltage can be controlled by the radio
frequency power. The frequency of the radio frequency applied by
the power source 283 is adjustable in response to slits 210 of a
slot electrode 200.
[0054] The inside of the process chamber 102 is maintained at a
predetermined negative pressure by a high-vacuum pump 106. The
high-vacuum pump 106 uniformly evacuate gas from the process
chamber 102 so as to maintain the plasma density uniform so that
the plasma is prevented from being locally concentrated to prevent
a local change in a depth of a processed portion of the object W.
Although the high-vacuum pump 106 is provided at a corner of a
bottom of the process chamber 102 in FIG. 1, a plurality of
high-vacuum pumps may be provided to the process chamber 102, and
the position of the high-vacuum pump 106 is not limited to the
position indicated in FIG. 1. The high-vacuum pump 106 is
constituted, for example, by a turbo-molecular pump (TMP), and is
connected to the process chamber 102 via a pressure adjust valve
(not shown in the figure). The pressure adjust valve is a known
valve such as a so-called conductance valve, gate valve or
high-vacuum valve. The pressure adjust valve is closed when the
apparatus 100 is not in operation, and is open in operation so as
to maintain the process chamber 102 at a predetermined pressure
(for example, 0.1 to 10 mTorr) created by the high-vacuum pump
106.
[0055] It should be noted that, in the present embodiment shown in
FIG. 1, the high-vacuum pump 106 is directly connected to the
process chamber. The term "directly connected" means that the
high-vacuum pump is connected to the process chamber without a
connecting member between the high-vacuum pump 106 and the process
chamber 102. However, a pressure adjust valve can be provided
between the high-vacuum pump 106 and the process chamber 102.
[0056] Gas supply rings 140 and 170 made of quartz pipes are
provided to a sidewall of the process chamber 102. The gas supply
ring 140 is connected to a reactant gas supply system 130. The gas
supply ring 170 is connected to a discharge gas supply system 170.
The gas supply system 130 comprises a gas supply source 131, a
valve 132, a mass flow controller 134 and a gas supply line 136
interconnecting the aforementioned parts. Similarly, the gas supply
system 140 comprises a gas supply source 161, a valve 162, a mass
flow controller 164 and a gas supply line 166 interconnecting the
aforementioned parts.
[0057] For example, in order to deposit a silicon nitride film, the
gas supply source 131 supplies a reactant gas (or material gas)
such as NH.sub.3 or SiH.sub.4, and the gas supply source supplies a
discharge gas such as a mixture gas produced by adding N.sub.2 and
H.sub.2 to at least one of neon, xenon, argon, helium, radon and
krypton. However, the gas supplied to the process chamber 102 is
not limited to the above-mentioned gasses, and Cl.sub.2, HCl, HF,
BF.sub.3, SiF.sub.3, GeH.sub.3, AsH.sub.3, PH.sub.3,
C.sub.2H.sub.2, C.sub.3H.sub.8, SF.sub.6, Cl.sub.2,
CCl.sub.2F.sub.2, CF.sub.4, H.sub.2S, CCl.sub.4, BCl.sub.3,
PCl.sub.3 or SiCl.sub.4CO may be supplied.
[0058] The gas supply system 160 may be omitted by replacing the
gas supply source 131 with a gas supply source, which can supply a
mixture gases supplied by the gas supply sources 131 and 161. The
valves 132 and 162 are open during a plasma processing period of
the object W to be processed, and is closed during a period other
than the plasma processing period.
[0059] Each of the mass flow controllers 134 and 164 comprises a
bridge circuit, an amplifying circuit, a comparator circuit and a
flow control valve, and controls a gas flow. That is, each of the
mass flow controllers 134 and 164 controls the flow control valve
based on a measurement of flow by detecting a transfer of heat from
upstream to downstream due to the gas flow. However, any known
structure other than the above-mentioned structure may be used for
the mass flow controllers 134 and 164.
[0060] Each of the gas supply passages 136 and 166 is formed of a
seamless pipe and a bite type coupling or a gasket coupling is used
so that impurities are prevented from entering the system through
the gas supply passages 136 and 166. Additionally, in order to
prevent generation of particles due to dirt or corrosion inside the
pipes, the gas supply passages 136 and 166 may be coated by an
insulating material such as PTFE, PFA, polyimide or PBI.
Additionally, an electropolishing may be applied to an inner
surface of the pipes forming the gas supply lines 136 and 166.
Further, a dust particle trap filter may be provided to the gas
supply lines 136 and 166.
[0061] FIG. 6A is a plan view of a gas supply ring 140, and FIG. 6B
is a cross-sectional view taken along a line VI-VI of FIG. 6A. As
shown in FIGS. 6A and 6B, the gas supply ring 140 comprises: a
ring-like housing or main part 146 which is made of quartz and
attached to the sidewall of the process chamber 102; an inlet port
141 connected to the gas supply passage 136; an annular gas passage
142 connected to the inlet port 141; a plurality of gas supply
nozzles 143 connected to the gas passage 142; an outlet port 144
connected to the gas passage 142 and a gas exhaust passage 138; and
a nozzle part 145 which is made of quartz and fixed to the sidewall
of the process chamber 102.
[0062] The gas supply nozzles 143 arranged at an equal interval in
a circumferential direction contribute to form an even gas flow
within the process chamber 102. The gas introducing means is not
limited the gas supply ring 140, and a radial flow type or a
showerhead type may be applied as described later.
[0063] Gas inside the gas supply ring 140 can be evacuated trough
the outlet port 144 connected to the gas exhaust passage 138. Since
each of the gas supply nozzles has a diameter of about 0.1 mm, a
water component remaining inside the gas supply ring 140 cannot be
effectively removed by evacuating the gas by the high-vacuum pump
106 connected to the process chamber 102 thorough the gas supply
nozzles. Accordingly, the gas supply ring 140 according to the
present embodiment effectively remove the remainder such as a water
component within the gas passage 142 and the gas supply nozzles 143
through the outlet port 144 having an opening diameter much greater
than that of the gas supply nozzles 143.
[0064] Similar to the gas supply nozzles 143, the gas supply
nozzles 173 are provided to the gas supply ring 170, which has the
same structure as the gas supply ring 140. Accordingly, the gas
supply ring 170 comprises a main part 176; an inlet port 171, an
annular gas passage 172, a plurality of gas supply nozzles 173, an
outlet port 174 and a nozzle part 175. Similar to the gas supply
ring 140, gas inside the gas supply ring 170 can be evacuated
trough the outlet port 174 connected to the gas exhaust passage
168. Since each of the gas supply nozzles has a diameter of about
0.1 mm, a water component remaining inside the gas supply ring 170
cannot be effectively removed by evacuating the gas by the
high-vacuum pump 106 connected to the process chamber 102 thorough
the gas supply nozzles. Accordingly, the gas supply ring 170
according to the present embodiment effectively remove the
remainder such as a water component within the gas passage 172 and
the gas supply nozzles 173 through the outlet port 174 having an
opening diameter much greater than that of the gas supply nozzles
173.
[0065] In the present embodiment, a vacuum pump 152 is connected to
the gas exhaust passage 138, which is connected to the outlet port
144 of the gas supply ring 140, via a pressure adjust valve 151.
Similarly, a vacuum pump 154 is connected to the gas exhaust
passage 168, which is connected to the outlet port 164 of the gas
supply ring 170, via a pressure adjust valve 153. Each of the
vacuum pumps 152 and 154 can a turbo-molecular pump, a sputter ion
pump, a getter pump, a sorption pump or a cryopump.
[0066] The pressure adjust pumps 151 and 153 are closed when the
respective valves 132 and 162 are open, and are opened when the
respective valves 132 and 162 are closed. As a result, when a
plasma process is performed by opening the valves 132 and 162, the
vacuum pumps 152 and 154 are disconnected from the respective gas
supply system by the pressure control valve 151 and 153 being
closed so that the reactant gas and the discharge gas are
introduced into the process chamber 102. The vacuum pumps 152 and
154 are connected to the gas supply system be the pressure adjust
valves 151 and 153 being open after completion of the plasma
process. That is, the vacuum pumps 152 and 154 can evacuate gas
from the respective gas supply rings 140 and 170 during a period
other than a period when the plasma process performed.
Specifically, the vacuum pumps 152 and 154 can be operated during a
period for carrying the object W into the process chamber or taking
out of the process chamber 102 or a period for moving the susceptor
104. Accordingly, the vacuum pumps 152 and 154 can evacuate the
remaining gas from the gas supply rings 140 and 170 to an extent
that an influence of the remaining gas is negligible. Thereby, the
gas supply nozzles 143 and 173 are prevented from being closed by
impurities such as a water component remaining in the gas supply
rings, thereby preventing an uneven introduction of the gas from
the gas supply rings 140 and 170. Additionally, the object W to be
processed is prevented from being contaminated by impurities
discharged from the gas supply rings 140 and 170. Thus, the vacuum
pumps 152 and 154 enables a high-quality plasma process being
applied to the object W to be processed.
[0067] It should be noted that, instead of providing the vacuum
pumps 152 and 154, the gas supply rings 140 and 170 may be directly
connected to the high-vacuum pump 106 by bypass passages (not shown
in the figure) that bypass the process chamber 102.
[0068] In the present embodiment, a microwave is generated by a
microwave generator 110. The microwave generator 110 comprises a
magnetron, which can generate, for example, a 2.45-GHz microwave
(for example, 5 kW). The microwave generated by the microwave
generator 110 is converted into a TM mode, a TE mode or a TEM mode
by a mode converter 112. It should be noted that, in FIG. 1, an
isolator for absorbing a microwave returning to the microwave
generator 110 and a stub tuner for load matching are not shown for
the sake of simplification of the figure.
[0069] The antenna member 120 comprises a temperature control plate
122, an antenna-accommodating member 123 and a dielectric plate
230. The temperature control plate 122 is connected to a
temperature control unit 121. The antenna-accommodating member 123
accommodates a slow-wave member 124 and a slot electrode 200 which
contacts the slow-wave member 124. The dielectric plate 230 is
positioned under the slot electrode 200. The antenna-accommodating
member 123 is made of a material having a high heat conductivity
such as stainless steel. A temperature of the antenna accommodating
member 123 can be controlled nearly equal to the temperature of the
temperature control plate 122.
[0070] The slow-wave member 124 is made of a material having a
predetermined permittivity to reduce the wavelength of the
microwave transmitted therethrough. In order to make the plasma
density in the process chamber 102 uniform, many slits must be
formed in the slot electrode 200. Thus, the slow-wave member 124
has a function to enable the formation of many slits in the slot
electrode 200. Ceramics such as SiN or AlN can be used for the
slow-wave member 124. For example, the specific permittivity
.di-elect cons..sub.t of AlN is about 9 and, thus, the wavelength
reducing rate n is 0.33 (n=1/(.di-elect cons..sub.t).sup.1/2=0.33).
Accordingly, the transmission rate of the microwave after passing
through the slow-wave member 124 becomes 0.33 times the original
transmission rate, and, thus, the wavelength also becomes 0.33
times the original wavelength. Accordingly, a distance between
adjacent slits 210 of the slot electrode 200 can be reduced,
resulting in a larger number of slits 210 being provided in the
slot electrode 200. The slot electrode 200 is formed of a copper
plate having a circular shape whose diameter is, for example, about
50 cm and thickness is less than 1 mm. The slot electrode 200 is
fixed to the slow-wave member 124 by screws.
[0071] The slot electrode 200 may be referred to as a radial inline
slot antenna (RLSA) or an ultra high efficiency flat antenna. The
present invention is not limited to such an antenna, and other type
antenna such as a single layer waveguide flat antenna or a
dielectric substrate parallel slot array may be used.
[0072] FIGS. 7, 8, 9 and 10 are plan views of examples of the slot
antenna 200 shown in FIG. 1. Hereinafter, the reference numerals
such as 200 generally represent all the reference numerals having a
suffix such as 200a, 200b, 200c and 200d. Any one of the slot
electrodes 200a, 200b, 200c and 200d can be used in the plasma
processing apparatus 100 shown in FIG. 1.
[0073] The slot electrode 200 has a plurality of T-slits 210
consisting of a pairs of slits 212 and 214 arranged in a T-shape
with a predetermined distance therebetween. The T-slits 210 are
arranged in a plurality of areas or sections defined by virtually
dividing the surface of the slot electrode 200 on a one-to-one
basis. In the slot electrode 200a shown in FIG. 7, each of the
virtually divided areas has a hexagonal shape. In the slot
electrodes 200b, 200c and 200d shown in FIGS. 8, 9 and 10, each of
the virtually divided areas has a square shape. It should be noted
that each of the T-slits 210d of the slot electrode 200d shown in
FIG. 10 is a variation of the T-slit 210, and the actual shape
formed by the slits 211d and 214d is similar to V-shape.
[0074] The T-slits 210 are arranged on the surface of the slot
electrode 200 so that the density of the T-slits 210 is
substantially uniform over the entire surface of the electrode 200.
This is to prevent an isolation of the material forming the
dielectric plate 230 so as to prevent the isolated material as
impurities from being mixed to a reactant gas. Since the slot
electrode 200 can provide a substantially uniform distribution of
ion energy to the dielectric plate 230, the dielectric plate 230 is
prevented from being isolated which results in a high-quality
plasma process being achieved.
[0075] As mentioned above, each T-slit 210 comprises a pair of
slits 212 and 214 forming a T-shape with a predetermined distance
therebetween. More specifically, each of the slits 212 and 214 has
a length L1 which is in the range of about one half of the
wavelength .lambda..sub.0 of the microwave to 2.5 times a free
space wavelength. The width of each of the slits 212 and 214 is
about 1 mm. A distance L2 between two adjacent pairs of slits along
a radial direction is approximately equal to the wavelength
.lambda..sub.0. That is, the length L1 of each of the slits 212 and
214 is set to satisfy the following relationship.
(.lambda..sub.0/2.times.1/{square root}{square root over (
)}.di-elect
cons..sub.t).ltoreq.L1.ltoreq.(.lambda..sub.0.times.2.5)
[0076] By setting each of the slits 212 and 214 to the
above-mentioned structure, a uniformly distributed microwave can be
achieved in the process chamber 102.
[0077] Each of the slits 212 and 214 is slanted with respect to a
radial line connecting the center of the slot electrode 200 and an
intersecting point between longitudinal axes of the slits 214 and
214. The size of the T-slits 210 becomes larger as a distance from
the center of the slot electrode 200 increases. For example, if the
distance from the center is twice, the size of each of the slits
212 and 214 is increased to about 1.2 to 2 times.
[0078] It should be noted that the shape of the slits 210 and their
arrangement are not limited to that shown in FIGS. 7, 8, 9 and 10
as long as the density of the slits can be uniform over the surface
of the slot electrode 200. That is, the configuration of the pair
of slits 212 and 214 is not limited to the above-mentioned shape,
and, for example, L-shaped slits may be used for the slot electrode
200. Additionally, the shape of each of the virtually divided areas
is not limited to the hexagonal shape or the square shape, and an
arbitrary shape such as a triangular shape may be adopted.
Accordingly, the virtually divided areas may be different in their
shape and size. Further, the slits 210 may be arranged along a
plurality of concentric circles or a spiral although the density of
the slits may not be uniform.
[0079] A radiation element having a width of a few millimeters may
be provided on the periphery of the slot electrode 200 so as to
prevent reflection of the microwave transmitted toward the
periphery of the slot electrode 200. The radiation element provided
for increasing an antenna efficiency of the slot electrode 200.
[0080] The temperature control plate 122 serves to control the
temperature change of the antenna-accommodating member 123 and
component parts near the antenna-accommodating member 123 to fall
within a predetermined range. A temperature sensor and a heater
unit (both not shown in the figure) are connected to the
temperature control plate 122. The temperature control unit 121
controls a temperature of the temperature control plate 122 to be a
predetermined temperature by introducing a cooling water or a
coolant such as alcohol, gulden or flon into the temperature
control plate 122. The temperature control plate 122 is made of a
material such as stainless steel, which has high heat conductivity
and can be machined to form a fluid passage for the cooling water
therein.
[0081] The temperature control plate 122 contacts the
antenna-accommodating member 123, and each of the antenna
accommodating member 123 and the slow-wave member 124 has a high
heat conductivity. Accordingly, the temperature of each of the
slow-wave member 124 and the slot electrode 200 can be controlled
by merely controlling the temperature of the temperature control
plate 122. The temperature of each of the slow-wave member 124 and
the slot electrode 200 is increased due to energy absorption when
the microwave of the microwave generator 110 is supplied thereto
for a long period of time. As a result, each of the slow-wave
member 124 and the slot electrode 200 may deform due to thermal
expansion.
[0082] For example, if the slot electrode 200 thermally deforms,
the length of each slit is changed, which results in a decrease in
the plasma density or localization of the plasma in the process
chamber 102. The decrease in the plasma density may slow down a
plasma processing speed such as an etching rate or a film
deposition rate. As a result, if the plasma processing is
controlled based on a processing time, there may be a case in which
a desired result of the plasma processing (such as plasma etching
depth or plasma deposition thickness) cannot be obtained when the
plasma processing is applied for a predetermined time period (for
example, two minutes), that is, for example, if the object W is
processed for a predetermined time (for example, two minutes) and
thereafter removed from the process chamber 102. Additionally, if
the plasma density in the process chamber 102 is localized, the
magnitude of plasma processing applied to the semiconductor wafer
may vary. As mentioned above, if a deformation occurs in the slot
electrode 200, the quality of plasma processing may
deteriorate.
[0083] Further, if the temperature control plate 122 is not
provided, the slot electrode 200 may warp since the materials of
the slow-wave member 124 and the slot electrode 200 are different
from each other and both members are fixed to each other by screws.
In such a case, the quality of plasma processing may deteriorate
for a reason similar to the above-mentioned reason.
[0084] A dielectric plate 230 is provided between the slot
electrode 200 and the process chamber 102 so as to close the top
opening of the process chamber 102. The slot electrode 200 is
tightly joined to the surface of the dielectric plate 230 by
brazing. Alternatively, the slot electrode 200 can be formed by a
copper plate applied to the surface of the dielectric plate
230.
[0085] It should be noted that the function of the temperature
control plate 122 may be provided to the dielectric plate 230. That
is, the temperature of the dielectric plate 230 can be controlled
by integrally forming a temperature control plate with the
dielectric plate 230, which temperature control plate has a coolant
passage near the side of the dielectric plate 230. By controlling
the temperature of the dielectric plate 230, the temperature of the
slow-wave member 124 and the slot electrode 200 can be controlled.
The dielectric plate 230 is mounted to the process chamber 102 with
an O-ring provided therebetween. Accordingly, the temperature of
the dielectric plate 230 can be controlled by controlling a
temperature of the O-ring, and, thereby controlling the temperature
of the slow-wave member 124 and the slot electrode 200.
[0086] The dielectric plate 230 is made of a dielectric material
such as aluminum nitride (AlN). The dielectric plate 230 prevents
the slot electrode 200 from being deformed due to a negative
pressure generated in the process chamber 102. Additionally, the
dielectric plate 230 prevents the slot electrode 200 from being
exposed to the atmosphere inside the process chamber 102 so that
the environment inside the process chamber 102 is prevented from
being contaminated by copper. If necessary, the dielectric plate
230 may be formed of a dielectric material having a low heat
conductivity so as to prevent the slot electrode 200 from being
influenced by heat from the process chamber 102.
[0087] In the present embodiment, the thickness of the dielectric
plate 230 is greater than 0.5 times the wavelength of the microwave
in the dielectric plate 230 and smaller than 0.75 times the
wavelength of the microwave in the dielectric plate 230.
Preferably, the thickness is in the range of 0.6 to 0.7 times the
wavelength of the microwave in the dielectric plate 230. The 2.45
GHz microwave has a wavelength of about 122.5 mm in a vacuum. If
the dielectric plate 230 is made of aluminum nitride (AlN), the
wavelength reducing rate n is equal to 0.33 since the specific
permittivity .di-elect cons..sub.t is about 9 as mentioned above.
Accordingly, the wavelength of the microwave in the dielectric
plate 230 is about 40.8 mm. Thus, if the dielectric plate 230 is
formed of AlN, the thickness of the dielectric plate 230 is
preferably greater than about 20.4 mm and smaller than about 30.6
mm, and, more preferably within a range from about 24.5 mm to about
28.6 mm. In general, the thickness H of the dielectric plate 230
preferably satisfies a relationship
0.5.lambda.<H<0.75.lambda., and, more preferably,
0.6.lambda..ltoreq.H.ltoreq.0.7.lambda.. The wavelength .lambda. of
the microwave in the dielectric material 230 is represented by
.lambda.=.lambda..sub.0n, where .lambda..sub.0 is a wavelength of
the microwave in the vacuum and n is a wavelength reducing rate
(n=1/.di-elect cons..sub.t.sup.1/2).
[0088] When the thickness of the dielectric plate 230 is 0.5 times
the wavelength of the microwave in the dielectric plate 230, a
standing wave is generated as a resultant wave of a synthesis of a
progressing wave traveling along the front surface of the
dielectric plate 230 and a regressive wave reflected by the back
surface of the dielectric plate 230. Thereby, the reflection is
maximized and a power of the microwave transmitted to the process
chamber 102 is minimized as shown in FIG. 11, which is a graph
showing a relationship between a transmission power of the
microwave and the thickness of the dielectric plate. In such a
case, generation of plasma is insufficient, and, thereby a desired
process speed cannot be achieved.
[0089] On the other hand, when thickness of the dielectric plate
230 is 0.75 times the wavelength of the microwave in the dielectric
plate 230, the transmission power of the microwave is maximized but
ion energy in the plasma is also maximized. The inventors found
that a plasma ion energy applied by transmission of a microwave
isolates the material of the dielectric plate 230 as shown in FIG.
12. FIG. 12 is a graph showing a relationship between the thickness
of the dielectric plate 230 and an amount of isolation (sputtering
rate) of the dielectric plate 230. If the material of the
dielectric plate 230 isolates, the material enters the object W to
be processed as impurities, thereby deteriorating a high-quality
plasma process.
[0090] Accordingly in the present embodiment, the thickness H of
the dielectric plate 230 is set to a value ranging from 0.3.lambda.
to 0.4.lambda. (0.3.lambda..ltoreq.H.ltoreq.0.4.lambda.) or a value
ranging from 0.6.lambda. to 0.7.lambda.
(0.6.ltoreq.H.ltoreq.0.7.lambda.) as shown in FIG. 13. The
thickness H of the dielectric plates 230 may be set to a value
ranging from 0.8.lambda. to 0.9.lambda.
(0.8.lambda..ltoreq.H.ltoreq.0.9.lambda.) or a value ranging from
1.1.lambda. to 1.2.lambda.
(1.1.lambda..ltoreq.H.ltoreq.1.2.lambda.) although the thickness H
of the dielectric plates 230 is increased. In general form, the
thickness H of the dielectric plate 230 is set to a value ranging
from (0.1+0.5N).lambda. to (0.2+0.5N).lambda. or a value ranging
from (0.3+0.5N).lambda. to (0.4+0.5N).lambda., where N is an
integer. In other words, the thickness H of the dielectric plate
230 satisfies a relationship
(0.1+0.5N).lambda..ltoreq.H.ltoreq.(0.2+0.5N).la- mbda. or
(0.3+0.5N).lambda..ltoreq.H.ltoreq.(0.4+0.5N).lambda.. Considering
a mechanical strength of the dielectric plate 230, the thickness H
of the dielectric plate 230 is preferably set to a value ranging
from 0.6.lambda. to 0.7.lambda.. However, for example, if the
dielectric plate 230 is made of quartz having a specific
permittivity of 3.8, a value ranging from 0.3.lambda. to
0.4.lambda. or a value ranging from 0.1.lambda. to 0.2.lambda. may
be used. Additionally, the above-mentioned relationship in general
form is applicable to a wave used for generating plasma other than
a microwave.
[0091] Since the gas supply systems 130 and 160 are arranged to
supply a reactant gas and a discharge gas from the nozzles 143 and
173, respectively, the gasses may traverse the surface of the
object W to be processed. Accordingly, a uniform the plasma density
cannot be achieved even if the nozzles 143 and 173 are arranged in
symmetric positions with respect to the center of the susceptor
104. In order to solve such a problem, it is considered to provide
a showerhead structure made of glass above the susceptor 104. A
description will be given, with reference to FIG. 14, of such a
showerhead structure. FIG. 14 is an illustrative cross-sectional
view of a showerhead having a gas supply arrangement.
[0092] The showerhead shown in FIG. 14 comprises a dielectric plate
240 and a shower plate 250. It should be noted that the dielectric
plate 240 and the shower plate 250 may be integrally formed with
each other by a dielectric material. The dielectric plate 240 is
formed of an aluminum nitride (AlN) plate having a thickness of 30
mm. The shower plate 250 is attached to a bottom surface of the
dielectric plate 240. The dielectric plate 240 has an inlet port
241, a gas passage 242 and an outlet port 244.
[0093] The gas supply passage 136 of the gas supply system 130 is
connected to the inlet port of the dielectric plate 240. The gas
exhaust passage 138 is connected to the outlet port 144 of the
dielectric plate 240. Although the dielectric plate 240 shown in
FIG. 14 is applied to the gas supply system 130, a mixture of the
gasses supplied by the gas supply systems 130 and 160 may be
supplied to the inlet port 141 of the dielectric plate 240. A
plurality of the inlet ports 141 may be provided to the dielectric
plate 241 so that a gas supplied through the inlet ports 241 is
uniformly introduced into the process chamber through the
showerhead. Additionally, a part of the inlet ports 241 may be
connected to the gas supply passage 136, and the rest of the inlet
ports 241 may be connected to the gas supply passage 166.
[0094] Alternatively, the gas supply system 160 may be provided to
the sidewall of the process chamber as shown in FIG. 1. This is
because the discharge gas such as argon is not easily decomposed as
compared to silane or methane, and, thus, the uniformity of the
plasma density is not so deteriorated if the discharge gas is
introduced into the process chamber 102 from the side.
[0095] A shown in FIG. 14, the outlet port 144 of the dielectric
plate 240 is connected to the gas exhaust passage 138, which is
connected to the vacuum pump 152 via the pressure adjust valve 151.
The function of the vacuum pump 151 is the same as that described
above, and a description thereof will be omitted.
[0096] A description will now be give, with reference to FIG. 15,
of a structure of the shower plate 250 shown in FIG. 14. FIG. 15 is
an enlarged cross-sectional view of a part of the shower plate 250
which part includes one of nozzles 253 provided to the shower plate
250. As shown in FIG. 15, the dielectric plate 240 has recessed
portions 246 at positions corresponding to the nozzles 253 of the
shower plate 250.
[0097] The shower plate 250 is made of an aluminum nitride (AlN)
plate having a thickness of about 6 mm. The shower plate 250 has a
plurality of nozzles 253 positioned in a predetermined uniform
arrangement. As shown in FIG. 15, each of the nozzles 253 is
provided with an eject member 260. The eject member 260 is
constituted by a screw (262 and 264) and a nut 266.
[0098] The screw head 262 has a height of about 2 mm. A pair of
eject passages 269 are formed in the screw head 262. Each of the
eject passages 269 extends from the center of the screw head 262 in
a direction inclined 45 degrees with respect to the bottom surface
256 of the shower plate 250. An end of each of the eject passages
269 is connected to a nozzle passage 268 formed in the screw part
254. Each of the eject passages 269 has a diameter of about 0.1 mm.
The eject passages 269 are inclined so as to achieve a uniform
introduction of the reaction gas. Accordingly, the number of the
eject passages 269 and their angle with respect to the shower plate
250 may be changed so as to achieve uniform distribution of the
reaction gas. It should be noted that, according to experiments
conducted by the inventors, uniform distribution of the reaction
gas was not achieved by a single ejecting passage extending in a
direction perpendicular to the surface 256 of the shower plate 250.
It was found that the eject passage 269 is preferably inclined so
as to achieve uniform distribution of the reaction gas.
[0099] The nozzle passage 268 formed in the screw part 264 has a
diameter of about 1 mm, and extends in a longitudinal direction of
the screw part 264. An end of the nozzle passage 268 is open to a
gap space 242 formed between the dielectric plate 240 and the
shower plate 250. The screw part 264 is inserted into a through
hole formed in the shower plate 250, and the screw is fastened to
the shower plate 250 by the nut 266 being engaged with the end of
the screw part 264. The nut 266 is accommodated in the recessed
portion 246 formed on the surface of the dielectric plate 240
facing the shower plate 250.
[0100] The gap space 242 is provided for preventing generation of
plasma. The thickness of the gap space 242 required for preventing
generation of plasma varies according to a pressure of the reactant
gas. That is, for example, the thickness of the gap space 242 is
set to about 0.5 mm when the pressure is 10 Torr. In this case, the
process space under the shower plate 250 in the process chamber 102
is set to a pressure of about 50 mTorr. The reactant gas is
introduced into the process chamber 102 at a predetermined speed by
controlling the pressure difference between the reactant gas and
the atmosphere in the process chamber 102.
[0101] According to the shower plate 250 provided in the present
embodiment, the reactant gas can be uniformly introduced and
distributed in the process space in the process chamber 102 without
generation of plasma before reaching the process space. An amount
of flow of the reaction gas can be controlled according to the
pressure difference between the gap space 242 and the process space
in the process chamber 102, the number of eject passages 269, the
inclination angle of the eject passages 269 and the size of each of
the eject passages 269.
[0102] The eject member 260 may be integrally formed with a part or
a whole of the shower plate 250, and can be any shape. For example,
the eject member 260 may be replaced by eject members shown in
FIGS. 16, 17 and 18. FIG. 16 is an enlarged cross-sectional view of
the eject member 350a provided with a nozzle passage 352a having a
single nozzle opening 354a. FIG. 17 is an enlarged cross-sectional
view of the eject member 350b provided with a nozzle passage 352b
having two nozzle openings 354b. FIG. 18 is an enlarged
cross-sectional view of the eject member 350c provided with a
nozzle passage 352c having three nozzle openings 354c.
[0103] A description will now be given, with reference to FIG. 19,
of a cluster tool that can be connected to the plasma processing
apparatus 100 shown in FIG. 1. FIG. 19 is an illustrative plan view
of the cluster tool 300 that is connectable to the microwave plasma
processing apparatus 100 shown in FIG. 1. As mentioned above, the
temperature of the object W can be controlled by the susceptor 104.
However, in a CVD process, it takes a considerable time to raise
the temperature of the object W from a room temperature to about
250.degree. C. to 350.degree. C. by the susceptor 104. In order to
eliminate such a problem, the cluster tool 300 heats the object W
prior to providing the object W to the process chamber 102 of the
microwave plasma processing apparatus 100. Similarly, it takes a
considerable time to decrease the temperature of the object W from
250.degree. C. to 350.degree. C. to a room temperature by the
susceptor 104 after the plasma processing is completed. In order to
eliminate such a problem, the cluster tool 300 cools the object W
prior to starting another process after the object W is taken out
of the process chamber 102 of the microwave plasma processing
apparatus 100.
[0104] As illustratively shown in FIG. 19, the cluster tool 300
comprises: a conveyor section 320 including a conveyor arm which
holds and conveys the object W to be processed; a preheating
section 340 for heating the object W; a cooling section 360 for
cooling the object W; and load-lock (L/L) chambers 380. In FIG. 19,
two process chambers 102A and 102B are shown. Each of the process
chambers 102A and 102B can be the process chamber 102 of the
microwave plasma processing apparatus 100 shown in FIG. 1. The
number of process chambers provided in the cluster tool 300 is not
limited to two.
[0105] The conveyor section 320 is provided with the conveyor arm
which holds the object W and a rotating mechanism for rotating the
conveyor arm. The preheating section 340 is provided with a heater
so as to heat the object W to a temperature close to a process
temperature before the object W is placed in the process chamber
102A or 102B. The cooling section 340 is provided with a cooling
chamber, which is cooled by a coolant so as to cool the object W
taken out of the process chamber 102A or 102B to a room temperature
before the object W is conveyed to a subsequent apparatus such as
an ion implantation apparatus or an etching apparatus. Preferably,
the cluster tool 300 comprises a rotational angle sensor, a
temperature sensor, at least one control unit and a memory for
storing control programs so as to control the rotation of the
conveyor arm of the conveyor section 320 and control a temperature
of each of the preheating section 340 and cooling section 360. Such
a sensor, a control unit and a control program are known in the
art, and descriptions thereof will be omitted. Additionally, the
conveyor arm of the conveyor section 320 places the object W in the
process chamber 102A or 102B through the gate valve 101.
[0106] A description will now be given of an operation of the
microwave plasma processing apparatus 100 shown in FIG. 1. First,
the conveyor arm of the conveyor section 320 shown in FIG. 19 holds
the object W to be processed so as to place the object W in the
process chamber 102 (in FIG. 19, one of the process chambers 102A
and 102B corresponds to the process chamber 102). It is assumed
that the object W is subjected to a CVD process in the process
chamber 102. In such as case, the control unit (not shown in the
figure) of the cluster tool 300 sends an instruction to the
conveyor section 320 to convey the object W to the preheating
section 340 so as to heat the object W to a temperature of about
300.degree. C. before placing the object W in the process chamber
102.
[0107] For example, the cluster tool 300 forms a silicon oxidation
film on a silicon substrate in the process chamber 102A by applying
a plasma process. Thereafter the cluster tool 300 transfers the
silicon substrate to the process chamber B so as to form a silicon
nitride film by plasma processing the silicon oxidation film by
introducing nitrogen into the process chamber 102B. A reactant gas
introduced into the process chamber 102A so as to form the silicon
oxidation film is typically SiH.sub.4--N.sub.2O. However, instead
of SiH.sub.4, TEOS (tetraethylorthosilicate), TMCTS
(tetramethylcyclotetrasiloxane) or DADBS
(diacetoxyditertiarybutoxysilane) may be used. The reactant gas
introduced into the process chamber 102B is typically
SiH.sub.4--NH.sub.3. However, instead of SiH.sub.4, SiF.sub.6,
NF.sub.3 or SiF.sub.4 may be used.
[0108] Upon receiving the instruction, the conveyor section 320
moves the object W to the preheating section 340 so as to heat the
object W. When the temperature sensor (not shown in the figure) of
the cluster tool 300 detects that the object W to be processed is
heated to a temperature of about 300.degree. C., the control unit
of the cluster tool 300 sends an instruction to the conveyor
section 320 to move the object W to be processed from the
preheating section 340 to the process chamber 102 through the gate
valve 101. Accordingly, the conveyor arm of the conveyor section
320 conveys the heated object W to the process chamber 102 through
the gate valve 101. When the heated object W reaches a position
above the susceptor 104 in the process chamber 102, the lifter pin
vertically moving system moves the lifter pins (not shown in the
figure) so as to support the object W by the three lifter pins (not
shown in the figure) protruding from the upper surface of the
susceptor 104. After the object W is transferred from the conveyor
arm to the lifter pins, the conveyor arm returns through the gate
vale 101. Thereafter, the conveyor arm may be moved to a home
position (not shown in the figure).
[0109] After the object W is transferred to the lifter pins, the
vertical moving unit 146 moves the vertical moving member 142
downward so as to return the lifter pins inside the susceptor 104
and place the object W on the susceptor 104. At this time, a
susceptor moving member can be moved while maintaining the hermetic
seal of the process chamber 102 by a bellows (not shown in the
figure). The susceptor 104 heats the object W placed thereon to a
temperature of 300.degree. C. At this time, since the object W is
preheated, it takes a short time to completely the process
preparation. More specifically, the heater control unit 191
controls the heater unit 198 so as to raise the temperature of the
susceptor 104 to 300.degree. C.
[0110] Thereafter, the high-vacuum pump 106 maintains the pressure
in the process chamber 102 at 50 mTorr by being controlled by the
pressure adjust valve. Additionally, the valves 151 and 153 are
opened, and the vacuum pumps 152 and 154 evacuate gas form the gas
supply rings 140 and 170. As a result, a water component remaining
in the gas supply rings 140 and 170 is sufficiently removed
therefrom.
[0111] Additionally, the susceptor vertically moving system moves
the susceptor 104 and the object W to a predetermined process
position from a home position. The bellows (not shown in the
figure) maintains the negative pressure environment in the process
chamber 102 during the vertically moving operation, and prevents an
atmosphere from exiting outside the process chamber 102.
Thereafter, the valves 151 and 153 are closed.
[0112] Thereafter, the valves 132 and 162 are opened so as to
introduce a mixture of NH3, helium, nitrogen and hydrogen into the
process chamber 102 from the gas supply rings 140 and 170 via the
mass flow controllers 134 and 164. Since the valves 151 and 153 are
closed, the vacuum pump 152 and 154 do not evacuate the gases in
the gas supply systems 130 and 160 from being introduced into the
process chamber 102.
[0113] When the shower plate 250 shown in FIG. 14 is used, the
process chamber 102 is maintained, for example, at 50 mTorr, and a
mixture of helium, nitrogen, hydrogen and NH.sub.3, for example, is
supplied to the dielectric plate 240. Thereafter, the mixture gas
is introduced into the process chamber by being passed through the
gap space 242, the recessed portions 246 and the nozzle passages
268 and 269 of the eject members 260. The mixture gas is not
converted into plasma, and is introduced into the process chamber
102 with a high controllability of flow and a uniform density.
[0114] The temperature of the process space of the process chamber
102 is adjusted to be 300.degree. C. A microwave is generated by
the microwave generator 110, and is supplied to the
wavelength-reducing member 124 of the antenna member 120 in a TEM
mode via a square waveguide or a coaxial waveguide. The microwave
passing through the wavelength-reducing member 124 is reduced in
its wavelength, and enters the slot electrode 200. The microwave is
then introduced into the process chamber 102 via the slits 210 and
the dielectric material plate 230. Since a temperature of the
wavelength reducing member 124 and the slot electrode 200 is
controlled, there is no deformation due to thermal expansion.
Accordingly, an optimum length of the slits 210 can be maintained.
Thus, the microwave can be introduced into the process chamber 102
at a desired density without local concentration.
[0115] Thereafter, the reactant gas in the process chamber 102 is
converted into plasma by the microwave, and a plasma CVD process is
performed on the object W placed on the susceptor 104. If the
baffle plate 194 is used, the baffle plate maintains the potential
in the process space so as to prevent the microwave from exiting
the process space. Thus, a desired process speed can be
maintained.
[0116] If a temperature of the susceptor 104 is raised higher than
a predetermined upper limit temperature due to continuous use, the
susceptor 104 is cooled by the temperature control unit 191. On the
other hand, if the temperature of the susceptor 104 is below a
predetermined lower limit temperature at an initial stage of the
operation of the apparatus or when the susceptor 104 is over
cooled, the temperature control unit 191 heats the susceptor
104.
[0117] The plasma CVD process is continued for a predetermined
period of time (for example, about 2 minutes). Thereafter, the
object W is taken out of the process chamber 102 through the gate
valve 101 by the conveyor section 320 of the cluster tool 300 in a
reversed way of the above-mentioned procedure. When the susceptor
104 is taken out, the vertically moving mechanism (not shown in the
figure) returns the susceptor 104 and the object W to the home
position. The predetermined process time of 2 minutes is determined
by a CVD processing time generally required for forming the layered
nitride film. That is, even if the temperature control unit 190
sets the temperature to about 250.degree. C. to 350.degree. C., a
long time deposition process may cause a problem similar to when
the temperature is set higher than 350.degree. C. Additionally, if
the process time is too short, there may be a case in which a
semiconductor element produced from the object W cannot effectively
prevent a leak current.
[0118] Since the microwave is uniformly supplied to the process
chamber 102 with a predetermined density, a silicon oxidation film
and a silicon nitride film having a desired thickness are formed on
the object W to be processed. Additionally, since the temperature
of the process chamber 102 is maintained in the predetermined range
so that a water component (impurities) does not enter the object W,
the deposited film can be maintained at a desired quality. The
object W taken out of the process chamber 102 is transferred to the
cooling section 360 and the object W is cooled to a room
temperature in a short time. Then, if necessary, the object W is
conveyed by the conveyor section 320 to a next stage apparatus such
as an ion implantation apparatus.
[0119] In the present embodiment, the gas supply system 130 or 160
may be arranged to use the dielectric plate 240 and the shower
plate 250 as shown in FIG. 14. In such a case, the outlet port 244
of the dielectric pate is connected to the bypass passage 182 or
184 so that the gas passage 242 is connected to the vacuum pump 6
by bypassing the process chamber 102.
[0120] It should be noted that the microwave plasma processing
apparatuses 100 can utilize an electron cyclotron resonance, and
therefore, an electromagnetic coil may be provided so as to
generate a magnetic field in the process chamber 102. Additionally,
although the microwave plasma processing apparatus 100 according to
the present embodiment performs the plasma CVD process as plasma
processing, the plasma processing is not limited to the plasma CVD
process. That is, for example, a plasma etching process or a plasma
cleaning process may be performed by the microwave plasma
processing apparatus 100. Additionally, the present invention is
not limited to the RLSA type plasma processing apparatus, and may
be applied to a parallel plate plasma processing apparatus
utilizing a grow discharge. Further, the object W to be processed
by the microwave plasma processing apparatus 100 is not limited to
the wafer for producing a semiconductor device, and the microwave
plasma processing apparatus 100 may be used to process an LCD
substrate or a glass substrate.
[0121] The present invention is not limited to the specifically
disclosed embodiments, and variations and modifications may be made
without departing from the scope of the present invention.
[0122] The present application is based on Japanese priority
application No. 2000-085264 filed on Mar. 24, 2000, the entire
contents of which are hereby incorporated by reference.
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