U.S. patent application number 09/427897 was filed with the patent office on 2001-12-20 for diamond film depositing apparatus and method thereof.
Invention is credited to BAIK, YOUNG JOON, EUN, KWANG YONG, LEE, WOOK-SEONG.
Application Number | 20010053422 09/427897 |
Document ID | / |
Family ID | 19578792 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053422 |
Kind Code |
A1 |
LEE, WOOK-SEONG ; et
al. |
December 20, 2001 |
DIAMOND FILM DEPOSITING APPARATUS AND METHOD THEREOF
Abstract
A diamond film depositing apparatus and method are disclosed in
which a uniform and large plasma is formed on a substrate having a
diameter of larger than 100 mm without using a heated filament
cathode, without applying a magnetic field thereto, and without
using a ballast resistance. The thusly formed plasma is maintained
stably for a long time, so that a diamond thick film having a
diameter of larger than 4 inches and a thickness of over hundreds
of .mu.m can be deposited on a flat or curved substrate and also on
a Si wafer.
Inventors: |
LEE, WOOK-SEONG;
(EUIJEONGBU, KR) ; BAIK, YOUNG JOON; (SEOUL,
KR) ; EUN, KWANG YONG; (SEOUL, KR) |
Correspondence
Address: |
SCULLY SCOTT MURPHY & PRESSER
400 GARDEN CITY PLAZA
GARDEN CITY
NY
11530
|
Family ID: |
19578792 |
Appl. No.: |
09/427897 |
Filed: |
October 27, 1999 |
Current U.S.
Class: |
427/569 ;
427/249.1; 427/249.8; 427/255.28; 427/577 |
Current CPC
Class: |
H01J 37/32027 20130101;
H01J 37/32009 20130101; H01J 37/32541 20130101 |
Class at
Publication: |
427/569 ;
427/577; 427/249.1; 427/249.8; 427/255.28 |
International
Class: |
C23C 016/26; C23C
016/32; H05H 001/24 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 1999 |
KR |
11854/1999 |
Claims
What is claimed is:
1. A diamond film depositing apparatus comprising: a process
chamber having a gas inlet for injecting a reactive gas and an gas
exhaust outlet for discharging an exhaust gas; a cathode disposed
at an upper portion inside the process chamber; an anode for fixing
a substrate, the anode being disposed below the cathode; an
SMPS(switched-mode power supply) connected to the cathode and the
anode, applying a DC voltage to the cathode and anode to form a
plasma between the cathode and the anode; and a holder for fixing
the cathode to the upper inside portion of the process chamber.
2. The apparatus according to claim 1, wherein the cathode and the
anode each have a diameter of over 100 mm, respectively.
3. The apparatus according to claim 1, wherein a plurality of
vacuum holes and vacuum grooves are formed in an upper surface of
the anode.
4. The apparatus according to claim 1, wherein the holder includes
a central fixing bar disposed at a center of a upper surface of the
cathode, a handle threadedly engaged with the central fixing bar at
an upper end thereof, plural edge fixing bars disposed at an edge
of the upper surface of the cathode at regular intervals, and a
cooling line formed inside the holder.
5. The apparatus according to claim 1, wherein a spacer is inserted
between the cathode and the holder.
6. The apparatus according to claim 5, wherein the spacer is formed
to be a thin plate.
7. The apparatus according to claim 5, wherein the spacer is formed
of one of molybdenum, copper or stainless steel.
8. he apparatus according to claim 5, wherein the surface of the
spacer is roughly ground or indented in a uniform pattern.
9. The apparatus according to claim 1, wherein the temperature of
the cathode is controlled by varying contact intervals between the
cathode, the spacer and the holder fixed to the central fixing bar
by rotating the handle.
10. A diamond film depositing method comprising the steps of:
applying a DC or DC pulse voltage with SMPS to a cathode and an
anode disposed inside a vacuum chamber; generating a plasma between
the cathode and the anode by supplying a reactive gas therebetween;
and depositing a diamond film on a substrate disposed on a holder
while maintaining the temparature of cathode below 2000.degree. C.
and maintaining a constant gas pressure.
11. The method according to claim 10, wherein the cathode is
maintained at a temperature of 800.degree. C.-1400.degree. C.
12. The method according to claim 10, wherein the reactive gas is a
mixture of hydrocarbon and hydrogen.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a diamond film depositing
apparatus and a method thereof, and more particularly, to a diamond
film depositing apparatus and a method thereof which are capable of
depositing a diamond thick film having a thickness of more than
hundreds of .mu.m on a large substrate having a diameter larger
than 4 inches.
[0003] 2. Description of the Conventional Art
[0004] A DC PACVD (Direct Current Plasma Assisted Chemical Vapor
Deposition) method, one of the generally known diamond film
deposition methods, is notable for its advantages in that the
apparatus for DC PACVD is simple and its depositing speed is faster
than hot filament or microwave CVD techniques.
[0005] It is constructed that a pair of platy electrodes are
disposed, facing parallel to each other within a vacuum in a
reaction container and a DC voltage is applied between the two
electrodes to generate a plasma, and this plasma is used to ionize
a reactive gas introduced into the reaction container, so that a
diamond film is deposited on a substrate placed on an anode. In
this respect, a disk-type electrode is largely used, and the
reactive gas is a mixture of hydrogen and hydrocarbon. However,
this technique suffers problems in that a long-time deposition is
difficult due to instability or a loss of plasma caused by arc
generation, and in that it is hardly possible to enlarge the area
of a uniform deposition larger than 1 inch by using a single
cathode.
[0006] These problems prevent synthesizing a diamond thick film
having a diameter larger than 4 inches and a thickness of more than
hundreds of .mu.m using a single cathode.
[0007] That is, in the conventional art, it has been difficult to
form a large plasma by using a single cathode for a large substrate
having a diameter of larger than 4 inches, and even if such a
plasma was successfully formed, it was difficult to keep it stable
for a long time.
[0008] In the DC PACVD method, the temperature of the cathode and
that of the substrate work as critical deposition variables.
Varying the temperature of the cathode and the substrate over a
wide range is very important during depositing. To be described in
detail later in the description of the present invention, the
cathode and substrate should be maintained not to go beyond a
predetermined temperature range. The cathode is heated by the
collision of ions from the plasma and the substrate by the
collision of electrons. In a given structure for a cathode and a
holder, the temperatures of the cathode and substrate are varied in
accordance with the process conditions. In the conventional art, a
general method for varying the temperatures of the cathode and
substrate is seen in a manner that the cathode and the substrate
are mounted on a water-cooled holder and a spacer is inserted
between the holder and the cathode or the substrate, to thereby
control the heat transfer. In this respect, if the temperature of
the cathode and substrate could be varied by external operation
outside a chamber during the process, it would be very convenient
because there would be no need to discontinue the process to change
the spacer. However as to the DC PACVD method, no technique has
been reported to vary the temperatures of a cathode and a substrate
during the process of depositing.
[0009] Conventionally deposition of a diamond thick film of
hundreds of .mu.m in thickness regarding the single-cathode DC
PACVD is only obtained when the deposition area is quite small,
about 1 square cm. On the other hand, where deposition of a wide
area as large as 4 inches in diameter was achieved, it was not the
desirous diamond thick film having the thickness of hundreds of
.mu.m, nor the continuous film but merely the formation of diamond
particles, for which the plasma is rotated by applying a magnetic
field. In other disclosed cases of attaining both the enlargement
of area and the thick film deposition, employed a hot filament
method was and used a plurality of filaments as a cathode. This
method does not use a pair of facing plate-shape electrodes, and
thus has an intrinsic problem of difficulty in filament
maintenance, the basic defects in the hot filament technique.
[0010] Most of the conventional art techniques employ a ballast
resistance connected in series to the power supply which serves to
stabilize the plasma. The ballast resistance, having a similar
resistance value to a load value of the plasma, is disadvantageous
in that it unnecessarily wastes power because of its series
connection to the circuit. That is, a large of percentage of the
supply power is wasted in the ballast resistance, deteriorating the
power efficiency. Nonetheless, the reason why the ballast
resistance is in frequent use is that the plasma of the DC PACVD is
hardly maintained stably for a long time using only the power
supply.
[0011] The most conventional DC PACVD methods employ a
flat-plate-type substrate. Meanwhile, some fields such as for
radomes or diaphragms require that the diamond be deposited on a
spherical surface. In addition, in some cases, deposition is needed
on a cylindrical curved surface such as the internal and external
surfaces of a tube, or an external surface of a bar. The
conventional art of DC PACVD using a pair of electrodes does not
disclose such a diamond deposition performed on a curved
surface.
[0012] In the conventional DC PACVD methods, a thick plate of high
melting point material such as molybdenum or tungsten is widely
utilized as a substrate. If a silicon substrate in general use for
the semiconductor fabrication is applicable thereto, it may be
possible to be applied to the fields of SOD (Silicon On Diamond)
and SAW (Surface Acoustic Wave) devices. Yet, there is not known a
case where the diamond film is deposited on a silicon substrate
having a diameter of 4 inches. The reason is believed to be that
since the silicon substrate has a low thermal conductivity, being
thin and light, a thermal contact between the silicon substrate and
a substrate holder is not effectively made, resulting in that
maintaining of an even temperature is impossible during
synthesizing.
SUMMARY OF THE INVENTION
[0013] Therefore, the present invention is directed to provide a
diamond depositing apparatus which is capable of forming a uniform
and large plasma on a substrate having a diameter of over 100 mm
and keeping it stable, without using a hot filament as a cathode,
without applying an additional magnetic field, and without using a
ballast resistance, to thereby deposit a diamond thick film having
a thickness of over hundreds of .mu.m and having a diameter of
larger than 4 inches on a flat-surfaced substrate, a curve-surfaced
substrate and on a Si wafer, and to a method thereof.
[0014] To achieve these and other advantages, the diamond film
depositing apparatus in accordance with the present invention, as
embodied and broadly described herein comprises: a process chamber
having a gas inlet that injects a reactive gas and a gas exhaust
outlet that discharges an exhaust gas; a cathode disposed at an
internal upper portion of the process chamber; an anode for
absorbedly fixing a substrate, the anode being disposed at a lower
portion of the cathode; a switched-mode power supply(SMPS) for
forming a plasma between the cathode and the anode by applying a DC
voltage to the cathode and the anode, the SMPS being connected to
both the cathode and the anode; and a holder for fixing the cathode
to the upper portion of the process chamber and controlling a
temperature of the cathode, wherein the size of the cathode and the
anode is larger than 100 mm in diameter.
[0015] There is also provided a diamond film depositing method
comprising the steps of: applying a DC or DC pulse voltage to a
cathode and the anode disposed inside a vacuum chamber; generating
a plasma between the cathode and the anode by supplying a reactive
gas therebetween; and depositing a diamond film on a substrate by
constantly maintaining a gas pressure, while keeping the
temperature of the cathode below 2000.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0017] In the drawings:
[0018] FIG. 1 is a schematic view of the structure of a diamond
film depositing apparatus in accordance with the present
invention;
[0019] FIG. 2 is a cross-sectional view of a holder of the
apparatus of FIG. 1;
[0020] FIG. 3a and 3b are respectively a plan view and a
cross-sectional view of an anode of the apparatus of FIG. 1;
[0021] FIG. 4 is a cross-sectional view showing a form of a plasma
in case of maintaining the temperature of the cathode over
2000.degree. C.;
[0022] FIG. 5a and 5b are cross-sectional views showing the state
of deposition performed on a curved substrate by the depositing
method of the present invention;
[0023] FIG. 6a and 6b are cross-sectional views showing the state
of deposition on a cylindrical substrate by the depositing method
of the present invention; and
DETAILED DESCRIPTION OF THE INVENTION
[0024] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings.
[0025] FIG. 1 is a schematic view of the construction of a diamond
film deposition apparatus in accordance with the present invention,
FIG. 2 is cross-sectional view of a holder 8 in the apparatus of
FIG. 1, and FIGS. 3a and 3b are a plan view and cross-sectional
view, respectively, of an anode 5 in the apparatus of FIG. 1.
[0026] As shown in the drawings, the diamond film depositing
apparatus in accordance with the present invention is constructed
with a gas inlet for injecting a reactive gas into a chamber 12
being provided at an upper portion of one end of a process chamber
1, and a gas exhaust outlet for discharging an exhaust gas after a
process is performed in the chamber 1 is provided at a lower
portion of the other end of the process chamber 1. A cathode 4 and
an anode 5 each having a diameter of at least 100 mm are
respectively disposed at the upper and lower portions at a
predetermined spacing within the process chamber 1. The cathode 4
and the anode 5 are connected to an SMPS (Switched-Mode Power
Supply) 6 so that a DC voltage can be applied thereto. A holder 8
for fixing the cathode 4 to the chamber 1 and having a cooling
water line 7 for cooling the cathode 4 is disposed at an upper
portion of the cathode 4.
[0027] The construction and operation of the apparatus in
accordance with the present invention will now be described.
[0028] First, the holder 8 of the depositing apparatus is
distinctively advantageous in that it controls a temperature of the
cathode 4 without discontinuing the process and the supplied power,
and maintains the temperature of the cathode 4 evenly.
[0029] As shown in FIG. 2, the cathode 4 and the holder 8 are
constructed such that a central fixing bar 11 is disposed at the
upper central portion of a disk-type cathode 4 made of tantalum,
molybdenum or tungsten, and a plurality of edge fixing bars 12 are
disposed at regular intervals along the edge.
[0030] The central fixing bar 11 and the edge fixing bars 12 are
inserted in through holes 8a and 8b formed at the center and the
edge of the holder 8 in a state that a spacer 13 is inserted
between the cathode 4 and the holder 8. A handle 14 is threadedly
engaged with a bearing 15, in a state that the bearing 15 supports
the handle 14, at a threaded part 11a formed at the upper portion
of the central fixing bar 11. Nuts 17 supported by spring washers
16 are threadedly engaged with threaded parts 12a formed at an
upper portion of the edge fixing bars 12.
[0031] The holder 8, preferably formed of copper, includes a
cooling water inlet 18 for injecting cooling water formed at one
end and a cooling water outlet 19 for discharging the cooling water
formed at the other end.
[0032] The reason for disposing the edge fixing bars 12 for the
purpose of fixing the edge of the cathode 4 is to prevent the edge
part of the cathode 4 from sagging by hundreds of .mu.m due to the
weight of the cathode 4 when it is exposed to a high temperature
for a long time. If the edge part of the cathode 4 sags, it would
fail to contact with the holder 8 that is cooled by the cooling
water flowing through the cooling water line 7, causing the
temperature of the edge part to go up, resulting in that the
temperature of the cathode 4 becomes wholly uneven, definitely
producing a bad effect on the diamond film deposition.
[0033] The spacer 13 is formed by folding one or plural pieces of
plate having a thickness of 0.1 mm to 0.2 mm made of molybdenum,
copper or stainless steel. By varying the thickness and the number
of the thin spacer plates 13a and 13b, the heat transmission
between the holder 8 and the cathode 4 is controlled so that the
temperature of the cathode 4 is initially controlled.
[0034] The surfaces of the thin plates 13a and 13b of the spacer 13
are preferably abrasive-processed or have indentations formed
therein in a regular pattern.
[0035] After reaching a synthesizing condition by generating a
plasma 9, when the handle 14 is rotated to pull upward the central
portion of the cathode 4 fixed to the central fixing bar 11, the
heat contact is varied depending on the degree of the contact
between the cathode 4, the spacer 13 and the holder 8, so that the
temperature of the cathode 4 can be controlled without varying the
generating power of the plasma. For instance, in case that the
supply power is in the range of 30-60 kW, a possible temperature
variation range of the cathode is approximately 200-300.degree. C.
The variation range of the temperature is changed depending on the
material, the number of the thin plates 13a of the spacer 13, the
power supplied to the plasma, or the material and thickness of the
cathode 4.
[0036] Although not shown in the drawings, the cooling structure of
the cathode 4 can be applied to the anode 5 in the same manner so
that the temperature of the substrate 10 mounted on the upper
surface of the anode 5 can be varied during the process.
[0037] The temperature of the cathode 4 is maintained below
2000.degree. C., preferably 800-1400.degree. C.
[0038] A result of an experiment shows that when the temperature of
the cathode 4 was maintained above 2000.degree. C., it was
impossible not only to uniformly heat the cathode 4 having a
diameter of larger than 1 inch but to form a uniform formation of
the plasma.
[0039] Namely, when the cathode 4 having a diameter of larger than
1 inch was heated at the temperature above 2000.degree. C., as
shown in FIG. 4, the plasma 9' formed was contracted at a portion
adjacent the cathode 4, and its diameter became uniform smaller
than the cathode 4 and the substrate 10. In addition, the contact
portion of the cathode 4 and the substrate 10 to the plasma 9' was
intensively heated, making it impossible to maintain a constant
temperature. Resultantly, it confirmed the impossibility of
uniformly performing a deposition on a large substrate 10 having a
diameter of larger than 4 inches.
[0040] Meanwhile, in case that the cathode 4 was heated at the
temperature of 1400.degree. C.-2000.degree. C., the surface of the
cathode 4 was severely carburized. Carburization denotes a
phenomenon that the carbon constituent in a plasma gas is diffused
into the surface of the cathode material and then combined with the
cathode material so as to form a carbide phase. Since Carburization
which forms a carburized layer accompanies a volume expansion, when
the carburized layer is formed above a predetermined level in
thickness, it partly comes off the surface of the cathode 4,
causing the surface of the cathode 4 to be rough and nonuniform.
The thusly deteriorated state of the surface of the cathode 4
causes arc generation when the plasma is generated. Therefore, in
order to obtain a stable plasma, an additional process is necessary
to grind the unclean carburized layer and remove it.
[0041] However, in case that the cathode 4 is maintained at the
temperature of 800-1400.degree. C., a large plasma is possible to
be formed on a large substrate 10 having a diameter of at least 4
inches, and the cathode 4 having a diameter of at least 4 inches
can be uniformly heated. For instance, a disk-type molybdenum
cathode 4 having a diameter of 140 mm was disposed facing a
disk-type molybdenum substrate having a diameter of 100 mm, with
the space between the electrodes maintained at 20.about.40 mm.
While approximately 800.about.1000V and 40.about.50A of power was
being supplied between the two electrodes, a gas pressure was
maintained at 130.about.160 torr. And, when the substrate 10 was
maintained to be heated at a temperature 1150.degree. C. while the
cathode 4 was maintained to be heated at a temperature of
850.about.1200.degree. C., a uniform and large plasma 9 was formed
between the cathode 4 and the substrate 10 and the cathode 4 was
uniformly heated.
[0042] Meanwhile, in case that the temperature of the cathode 4
goes down below 800.degree. C., fine solid carbon granules and a
coalesced solid carbon layer therefrom are acceleratedly formed on
the surface of the cathode 4.
[0043] For instance, in case that the cathode 4 is maintained at
the range of 950 to 1050.degree. C., even if a gas composition of
3.5% CH.sub.4--H.sub.2 to CH.sub.4--H.sub.2 is maintained for 8 to
16 days, solid carbon granules are not formed. However, in case
that the cathode 4 is maintained at 750.degree. C.-800.degree. C.
with a gas composition of 3.5% CH.sub.4--H.sub.2, when only about
20 hours lapses, solid carbon granules are formed on the entire
surface of the cathode 4.
[0044] Since the deposition rate of diamond film is partially
decreased at the part just below the cathode where solid carbon
granules were generated, the deposition of diamond film will be
nonuniform. In addition, Since the solid carbon formed at
750.degree. C.-800.degree. C. adheres firmly on surface of cathode
and its hardness is very high, it is difficult and takes long time
to remove it from the surface. It is thus not desirous for the
solid carbon granules to generate on the surface of cathode.
[0045] According to the present invention, power is supplied
between the electrodes by a SMPS (Switch-Mode Power Supply).
[0046] Employing the SMPS itself is widely known, which is a power
supply that performs a high frequency and a high-speed switching by
using a switching device such as a FET (Field Effect Transistor) or
IGBT(lnsulated Gate Bipolar Transistor). In the field of plasma
deposition, it has been mainly used for a DC sputter deposition.
And, thanks to its capacity of performing a high-speed switching
operation, the SMPS is considered to have an excellent function of
preventing the arc generation at a sputter target during a sputter
deposition.
[0047] Thus, it would be very desirous to use the SMPS as a power
supply for the diamond film deposition system by DC PACVD method.
Application of the SMPS technique to the DC PACVD device for
diamond film deposition is not disclosed yet. The reason is
believed to be that the sputter deposition process, which is the
main application of the SMPS in the field of plasma deposition, has
not much to do with the DC PACVD process of the present
invention.
[0048] That is, first of all, the main ingredient of the plasma is
different. The DC PACVD process of the present invention uses
hydrogen as a main component, to which some hydrocarbon is added.
Meanwhile, a main component of the plasma in the sputter process is
an inert gas such as argon.
[0049] Secondly, the method of supplying a substance to be
deposited on the substrate is much different. In the DC PACVD
process of the present invention, the diamond source material is
supplied in a gaseous state, which is decomposed by the plasma and
the decomposed product is deposited on the substrate. The source
material is generally a mixture of hydrogen and hydrocarbon gas.
Meanwhile, in the sputter deposition process, a solid target
attached to a cathode is used as an ingredient of the source
material, and positive ions in the inert gas plasma collide with
the target, detaching the atoms comprising the target therefrom to
thereby be deposited on the substrate.
[0050] The cause of the arc generation is also different from each
other. In the DC PACVD process of the present invention, the main
cause of arc generation is reported to be the soot formed on the
cathode, while in case of the sputter deposition process, a
non-conductor material formed on the cathode is known to cause the
arc generation.
[0051] As other process condition differences between the two, the
DC PACVD process of the present invention requires a high gas
pressure as high as 100 torr and scores of amperes of current,
while the sputter deposition process requires a low gas pressure at
the level of millitorr and only a few amperes of current.
[0052] In spite of the outstanding differences between the two
processes, it was notably confirmed in the present invention that
arcing is preventable by using the SMPS as a power supply for the
DC PACVD for a diamond film deposition. Of the SMPS devices, only
such an SMPS having an output voltage of 1000V at maximum and a
high output current of scores of amperes can be applied to such a
large diamond film deposition having a diameter of 4 inches.
According to the experiment of the present invention, the reason
was that in case of a substrate having a diameter of 4 inches, if
the discharge current is as low as a few amperes, diamond was not
deposited, or even though it was deposited, its deposition speed
was very slow.
[0053] The output voltage to be 1000V at its maximum is required to
maintain the output current value at a high value of over scores of
amperes. An SMPS employing a FET is limited to a few amperes. Thus,
an SMPS employing a IGBT is suitable to the object of the present
invention, which enables the output voltage to be 1000V at its
maximum and the output current to be more than scores of
amperes.
[0054] When a voltage was applied between the cathode and the anode
by using the SMPS employing the IGBT in the synthesizing apparatus
of the present invention, it was observed that a stable plasma was
maintained for a long time, whether the waveform of an applied
voltage was pulsed DC or DC. The pulse form has an advantage in
that the applied voltage can be increased by controlling the ratio
of on-time and off-time of pulses even at the same power.
[0055] In case of using a phase-control power supply employing a
conventional SCR(Silicon-Controlled-Rectifier) device rather than
the SMPS, it is impossible to maintain a stable plasma for a long
time because of the arcing generated between the cathode and the
anode, unless it uses a ballast resistance having the same level of
resistance value as that of plasma. As mentioned above, a crucial
defect of the ballast resistance is that its power consumption is
too much, that is, reaching scores of percent of the whole input
power. Meanwhile, according to the result of our experiment,
without using a ballast resistance, the plasma was stably
maintained for a long time by using only the SMPS and the diamond
film deposition was successfully performed on the large substrate
having a diameter of as large as 4 inches.
[0056] For instance, when power of 820V and 35A was applied between
a molybdenum substrate and a molybdenum cathode having a diameter
of 140 mm by using the SMPS, the gas pressure of
3.5%CH.sub.4--H.sub.2 as used therefor was maintained at 130-140
torr, the gas flow rate was 100 sccm and the deposition time was
400 hours, a uniform plasma was formed between the cathode and the
substrate. When the cathode was maintained at the temperature of
950.degree. C. and the substrate was maintained at the temperature
of 1150-1250.degree. C., a diamond thick film having a thickness of
1.2 mm was deposited on the surface of the substrate having a
diameter of 4 inches. The Raman spectroscopy showed that the
FWHM(full width at half maximum) of diamond peak was in the range
of 4.2 to 5.5 cm.sup.-1.
[0057] Also, under the same conditions, when the content of methane
was made 4.5% and maintained for 200 hours, a diamond film of 0.9
mm in thickness was formed.
[0058] In another embodiment, when power of 870V and 42A was
applied between a molybdenum substrate and a molybdenum cathode
having a diameter of 140 mm by using the SMPS without ballast
resistance, the gas pressure of 6%CH.sub.4--H.sub.2 as used
therefor was maintained at 150 torr, the gas flow rate was 200 sccm
and the deposition time was 120 hours, a uniform plasma was formed
between the cathode and the substrate. The diamond thick film
having a thickness of 1.2 mm was uniformly deposited on the surface
of the substrate having a diameter of 4 inches in the growing rate
of 10 .mu.m/hour. The Raman spectroscopy showed that the FWHM of
diamond peak was in the range of 4.5 to 5.0 cm.sup.-1.
[0059] In other embodiment, when power of 870V and 42A was applied
between a molybdenum substrate and a molybdenum cathode having a
diameter of 140 mm by using the SMPS without ballast resistance,
the gas pressure of 4.5%CH.sub.4--H.sub.2 as used therefor was
maintained at 150 torr, the gas flow rate was 200 sccm and the
deposition time was 142 hours, a uniform plasma was formed between
the cathode and the substrate. The diamond thick film having a
thickness of 1.0 mm was uniformly deposited on the surface of the
substrate having a diameter of 4 inches in the growing rate of 7
.mu.m/hour. The Raman spectroscopy showed that the FWHM of diamond
peak was in the range of 3.5 to 4.5 cm.sup.-1.
[0060] According to the present invention, a diamond film can be
also deposited on a curved substrate by using a curved-type
electrode.
[0061] All of the known DC PACVD methods are only about the
techniques of depositing diamond film on a flat substrate. However,
it was observed in the experiment for the present invention that a
uniform diamond film can be deposited on a curved substrate as
follows. Under the same conditions, when the cathode facing the
curved substrate is formed for the distance from cathode to
substrate to be same at each point, a uniform plasma is formed
between the cathode and the substrate, thereby forming a uniform
diamond film on the curved substrate. FIGS. 5a, 5b, 6a and 6b
illustrate forms of the electrodes and the plasma in case of using
the curved substrate, in which the plasma P is observed with the
naked eye to contact with the substrate while keeping a distance
from the cathode. FIGS. 5a and 5b show convex or concave
substrates, while FIGS. 6a and 6b show examples of deposition
inside or outside a tube or outside a bar. In case of a curved
substrate, as shown in FIGS. 5a and 5b, the cathode may have a
concave-curved form while the substrate may have a convex-curved
form, or the substrate can have a concave surface while the cathode
has a convex surface. In this connection, the circular arcs of
making the sections of the cathode and the surface of the substrate
are preferably concentric.
[0062] For instance, referring to FIG. 5a, the upper surface of a
molybdenum disk-type plate having a thickness of 30 mm and having a
diameter of 70 mm is processed to be a convex-curved substrate
having a radius of curvature of 45 mm and a central part of a
molybdenum disk-type plate having a thickness of 30 mm and having a
diameter of 120 mm is processed to be a concave-curved cathode
having a radius of curvature of 70 mm. The central axes of the
substrate and the cathode are positioned to congruously face each
other, and the central point of the concave-curved surface of the
cathode and that of the convex-curved surface of the substrate are
distanced at 26 mm. A mixture of hydrogen and 3% to 5% of methane
is supplied thereto at a gas pressure of 100 torr, and power of
800-900V and 25-35A is supplied between the cathode and the
substrate, so that a uniform plasma is formed between the cathode
and the substrate. After a predetermined time lapses, a uniform
diamond film is deposited on the substrate.
[0063] Likewise, in case of using a curved-type cathode or
substrate, it is desirous to suitably modify the form of the holder
so as to make the temperature of both the cathode and the substrate
even. For example, when a cathode is concave in its center, as
shown in FIG. 5a, it is preferable for the holder to have such a
structure that the edge part of cathode can be cooled more actively
than its central part. For example, concentric grooves may be
formed at the part contacting with an upper surface of the plate of
the cathode in a manner that the intervals between the grooves are
longer in the central part so that the central part of the lower
surface of the cathode has a smaller contact area than the edge
part.
[0064] In case of coating an inner surface of a tube, as shown in
FIG. 6a, a bar-type or tube-type cathode is placed at the position
of the central axis of the tube to be coated, so as for its central
axis to be congruent. In case of coating an outer surface of the
tube, or bar as shown in FIG. 6b, a tube-type cathode, having a
diameter larger than the tube or the bar to be coated, is placed at
an outer surface of the tube or the bar to be coated, in the same
manner that the two central axes are congruent to each other. By
using such a structure, when a voltage is applied between the
electrodes, a cylindrical plasma is formed between the cathode and
the substrate, thereby depositing the diamond film on the
substrate. At this time, the cathode and the substrate are
preferably cooled by using a water-cooled holder so that the
desirous temperature range as mentioned above can be
maintained.
[0065] One of the advantages of the present invention is that it is
possible to deposit a diamond film having a diameter of larger than
4 inches uniformly on a substrate with low heat conductivity that
is light, thin and weak like a silicon wafer, by using the DC PACVD
method.
[0066] According to the experiment for the present invention, in
the method where a silicon substrate was merely laid on the upper
surface of an anode so as to be mounted by gravity force, it was
impossible to evenly maintain the temperature of the silicon
substrate. For example, since a molybdenum or tungsten substrate in
use usually has a high specific gravity and is of over a few mm in
thickness, its weight itself produces a close contact with the
anode. Also, since its heat conductivity is higher than that of the
silicon substrate, the temperature was evenly maintained. However,
in the case of a silicon substrate in use for semiconductor
fabrication, since it has a low specific gravity and is thin,
having a thickness of only a few mm, the substrate's weight itself
doesn't help to make a close contact with the anode. In addition,
due to its low heat conductivity, when it is contacted by a plasma,
the uneven heating gets worse. Moreover, owing to its thinness and
a low melting point, the substrate bows concave upward because of
an internal stress of the diamond film while the diamond film is
being deposited. Consequently its contact with the anode becomes
nonuniform, causing a severe unevenness in temperature. The degree
of bowing increases in proportion to the thickness of the diamond
film.
[0067] In order to solve the problems described above, in the
present invention, an anode of a vacuum chuck type is used to
attain an effectively close thermal contact between the silicon
substrate and the anode, so that the temperature of the substrate
can be maintained evenly during synthesizing, and the substrate can
be effectively vacuum-clamped onto the upper surface of the anode,
to thereby prevent the substrate from bowing or coming off,
resulting in that a stable and large-area deposition is obtained on
the silicon substrate by the DC PACVD.
[0068] FIG. 3a and 3b illustrate the structure of the anode, in
which a plurality of vacuum holes are formed in an upper surface of
a body 21 of the anode 5 at regular intervals, and plural vacuum
grooves 23 are radially and concentrically formed in
different-sized circles in an upper surface of the body 21 to be
connected to the vacuum holes 22.
[0069] Namely, as shown in broken lines, during the process, when
the vacuum is drawn through the vacuum holes 22 in a state that the
silicon substrate 24 is mounted on the surface of the body 21, the
silicon substrate 24 is uniformly and clampedly fixed to the upper
surface of the body 21.
[0070] As so far described, in the diamond film depositing
apparatus and its method of the present invention, a uniform and
large plasma is formed on the substrate having a diameter of larger
than 100 mm without using a heated filament cathode, without
applying a magnetic field thereto, and without using a ballast
resistance, and the thusly formed the plasma is stably maintained
for a long time, so that a diamond thick film having a diameter of
larger than 4 inches and a thickness of over hundreds of .mu.m can
be deposited on a flat or curved substrate and also on a Si
wafer.
[0071] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *