U.S. patent application number 11/976023 was filed with the patent office on 2008-11-20 for method and system for forming thin films.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Yoshimasa Kondo, Yukinori Nakamura, Naoto Ohtake, Takao Saito.
Application Number | 20080282981 11/976023 |
Document ID | / |
Family ID | 32995583 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080282981 |
Kind Code |
A1 |
Saito; Takao ; et
al. |
November 20, 2008 |
Method and system for forming thin films
Abstract
An object of the present invention is to form a thin film
reproducibly in a process for forming the thin film on the inner
wall surface facing a space formed in a substrate by plasma CVD. A
thin film 22 is produced on an inner wall surface 20b of a
substrate 20 facing a space 23 formed in the substrate 20. The
substrate 20 is contained in a chamber for plasma CVD process. A
gas for plasma reaction is then flown into the space 23 and a pulse
voltage is applied on the substrate 20 without substantially
applying a direct bias voltage on the substrate 20 to form the thin
film on the inner wall surface 20b.
Inventors: |
Saito; Takao; (Nagoya-city,
JP) ; Nakamura; Yukinori; (Nagoya-city, JP) ;
Kondo; Yoshimasa; (Nagoya-city, JP) ; Ohtake;
Naoto; (Yokosuka-city, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-city
JP
|
Family ID: |
32995583 |
Appl. No.: |
11/976023 |
Filed: |
October 19, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10766806 |
Jan 30, 2004 |
7303789 |
|
|
11976023 |
|
|
|
|
60457310 |
Mar 26, 2003 |
|
|
|
Current U.S.
Class: |
118/723R |
Current CPC
Class: |
C23C 16/045 20130101;
C23C 16/515 20130101 |
Class at
Publication: |
118/723.R |
International
Class: |
C23C 16/453 20060101
C23C016/453 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 2003 |
JP |
2003-038767 |
Claims
1. A system for producing a thin film by plasma CVD on an inner
wall surface of a substrate facing a space formed in said
substrate, said substrate having an inner wall, said system
comprising: a chamber for plasma CVD and for containing said
substrate; a supply hole for supplying a gas for plasma reaction
into said inner wall surface of said chamber; and a high voltage
pulse source for applying a pulse voltage on said substrate,
wherein said gas is flown into said space and said high voltage
pulse source applies a pulse voltage on said substrate without
substantially applying a DC bias voltage on said substrate to form
said thin film on said inner wall surface, said high voltage pulse
source applies an electric field in a range of 20 to 300 kV/m, the
inner wall faces an inner space of said substrate, and the inner
space has a diameter of 0.9 mm or smaller.
2. The system of claim 1, further comprising a means for generating
a difference of a pressure in the longitudinal direction of said
substrate.
3. The system of claim 1, wherein said substrate has one opening
therein communicating with said space.
4. The system of claim 1, wherein said thin film comprises diamond
or diamond like carbon.
Description
[0001] This is a Division of application Ser. No. 10/766,806 filed
Jan. 30, 2004. The disclosure of the prior application is hereby
incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention provides a method and system for
forming a thin film on an inner wall surface of a substrate facing
a space formed in the substrate by means of plasma CVD.
[0004] 2. Related Art Statement
[0005] It has been known to form a hard film such as a diamond film
or diamond like carbon film on a substrate to impart corrosion
resistance to the substrate. Recently, it has been tried to form a
hard film on an inner wall surface of a tubular body, whose
applications include various products.
[0006] Such hard film is formed by so called plasma CVD process.
According to the process, for example, a gaseous raw material such
as methane gas is introduced with a carrier gas such as hydrogen
gas into a furnace for plasma generating reaction. Such raw
material gas is then excited by microwave or high frequency wave to
generate plasma reaction gas, resulting in chemical reaction on the
substrate. The plasma CVD process, however, is useful for forming a
specific hard film uniformly on a plate shaped member or the other
member having a simple shape. It is, however, difficult to form a
hard film uniformly on a substrate having a complicated shape such
as an inner wall surface of a tubular member, because the supply of
the plasma reaction gas over the whole surface of the substrate
tends to be insufficient.
[0007] According to Japanese patent publication 62-136, 569A, an
electrode of graphite is positioned inside of a tubular member, and
it was tried to generate plasma reaction gas directly from a
gaseous raw material inside of the tubular member. According to the
process, a large amount of the plasma reaction gas can be
introduced over the inner wall surface of the tubular member. It is
thus possible to easily form a relatively thick and hard film
uniformly on the inner wall surface of the tubular member.
[0008] According to the process described in Japanese patent
publication 62-136, 569A, however, it is needed a graphite
electrode smaller than the inner diameter of the tubular member. As
the inner diameter of the tubular member is smaller, it becomes
extremely difficult to produce a graphite electrode usable in the
tubular member. Further, for producing hard films on the inner wall
surfaces of a plurality of tubular members at the same time, it is
needed to prepare a plurality of graphite electrodes each
corresponding with each tubular member. The design of a system for
plasma CVD becomes thus complicated so that the production of the
hard films is made rather complicated.
[0009] According to Japanese patent publication 2002-339, 072A, a
difference of pressure is generated between the upstream and
downstream of the tubular member so that a gas for plasma reaction
is flown into the inner space of the tubular member. A DC bias
voltage and pulse voltage are applied on the tubular member so that
a thin film is successfully formed on the inner wall surface of the
tubular member.
SUMMARY OF THE INVENTION
[0010] The technique described in Japanese patent publication
2002-339, 072A is superior in that a thin film having excellent
quality can be formed without inserting an electrode into the inner
space in the tubular member. The inventors have studied the
technique further, and found that the plasma reaction gas cannot be
passed through the space in the tubular member easily as the inner
diameter of the tubular member is smaller. The amount of supply of
the reaction gas into the space becomes thus smaller, so that the
formation of the thin film is made difficult and the quality of the
film may be deteriorated. Further, when an end of the tubular
member is sealed, the reaction gas is prevented from flowing in the
inner space of the tubular member. The amount of supply of the gas
for plasma reaction is thus made small so that the formation of the
thin film is made difficult and the quality of the film may be
deteriorated.
[0011] An object of the present invention is to form a thin film
reproducibly in a process for forming the thin film on the inner
wall surface facing a space in a substrate by plasma CVD.
[0012] The present invention provides a method of producing a thin
film on an inner wall surface of a substrate facing a space formed
in the substrate. The method has the steps of:
[0013] providing the substrate in a chamber for plasma CVD
(chemical vapor deposition) process; and
[0014] flowing a gas for plasma reaction into the space and
applying a pulse voltage on the substrate without substantially
applying a direct bias voltage on the substrate to from the thin
film on the inner wall surface.
[0015] The present invention further provides a system for
producing a thin film on an inner wall surface of a substrate
facing a space formed in the substrate. The system has a chamber
for plasma CVD and for containing the substrate, a supply hole for
supplying a gas for plasma reaction to the chamber, and a means for
applying a pulse voltage on the substrate. The gas is flown into
the space and the means applies a pulse voltage on the substrate
without substantially applying a direct bias voltage on the
substrate to from the thin film on the inner wall surface.
[0016] The inventors have found the followings. That is, even when
the diameter of the space is small, or when the space is sealed,
the thin film can be reproducibly formed by applying a pulse
voltage by the pulse voltage applying means without substantially
applying a direct bias voltage on the substrate.
[0017] It has been common to apply a direct bias voltage on a
substrate in a process for applying a pulse voltage on the
substrate to generate plasma of a reaction gas so that a CVD film
is formed. Contrary to this, a thin film can be reproducibly formed
by applying a pulse voltage by a pulse voltage applying means
without substantially applying a direct bias voltage on a
substrate, even when the diameter of the space is small or when the
space is sealed, according to the present invention. Such discovery
is beyond the expectation of those who skilled in the art.
[0018] These and other objects, features and advantages of the
invention will be appreciated upon reading the following
description of the invention when taken in conjunction with the
attached drawings, with the understanding that some modifications,
variations and changes of the same could be made by the skilled
person in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a block diagram schematically showing a system for
forming a thin film, according to one embodiment of the present
invention.
[0020] FIG. 2 (a) is a cross sectional view showing a tubular
member 20, a space 23, and a thin film 22 formed on the inner wall
surface facing the space 23.
[0021] FIG. 2 (b) is a cross sectional view showing a tubular
member 20A, a space 23A, and a thin film 22 formed on the inner
wall surface facing the space 23A.
[0022] FIG. 2 (c) is a cross sectional view showing a tubular
member 20B, a space 23B, and a thin film 22 formed on the inner
wall surface facing the space 23B.
[0023] FIG. 3 is a graph showing a Raman spectrum obtained by Raman
spectroscopic analysis of a diamond like carbon film formed on the
inner wall surface of a substrate.
PREFERRED EMBODIMENTS OF THE INVENTION
[0024] In the invention, a thin film is formed on the inner wall
surface facing a space of a substrate by plasma CVD process. The
shape and dimension of the space are not particularly limited.
Further, the substrate may preferably be tubular or cylindrical. A
tubular or cylindrical member has one elongate space formed therein
extending in the length of the member. The substrate is not,
however, limited to such tubular or cylindrical member. For
example, a plurality of spaces may be formed in one substrate.
[0025] The diameter of the space (inner diameter of the substrate)
is not particularly limited. As the diameter of the space is
larger, it becomes easier to form a thin film on the inner wall
surface facing the space. The upper limit of the space is not thus
particularly defined. On the other hand, when the diameter of the
space is 10 mm or smaller, it has been generally difficult to form
a thin film on the inner wall surface facing the space in a prior
art. The present invention is particularly useful in this case. On
the viewpoint, the present invention is most useful when the
diameter of the space is 3 mm or smaller. Although the lower limit
of the diameter of the space is not particularly defined, the
present invention is useful for forming a thin film on the inner
wall surface facing the space having a diameter of, for example,
0.001 mm or larger, and preferably 0.01 mm or larger.
[0026] The electric field in the substrate applied by the pulse
voltage is not particularly limited. The electric field may
preferably be 20 to 300 kV/m, and more preferably be 20 to 200
kV/m.
[0027] The pulse width of the pulse voltage is not particularly
limited, and may preferably be 1 .mu.s to 50 .mu.s.
[0028] the pulse period of the pulse voltage is not particularly
limited, and may preferably be 100 Hz to 10000 Hz.
[0029] According to the present invention, the pulse voltage is
applied without substantially applying a direct current bias
voltage on the substrate. In other words, an operation is not
performed for applying a direct current bias voltage on the
substrate by an electric source having a capability of applying a
direct current bias voltage. A direct current electric potential
may be induced between a cathode and the anode due to a reason
other than the direct current bias voltage. This embodiment is,
however, encompassed by the present invention, because a direct
current bias voltage is not applied by an electric source.
[0030] In a preferred embodiment, a difference of pressure is
generated in the longitudinal direction of the substrate to
facilitate the flow of the plasma reaction gas into the space of
the substrate. The pressure difference may be generated by any
method not particularly limited. In one embodiment, a means for
generating a magnetic field is provided, so that a magnetic field
is generated in the longitudinal direction, or the width of the
substrate. The plasma reaction gas is captured by means of the
magnetic field and flown into the space of the substrate.
[0031] In another embodiment of the present invention, a mechanism
for discharging gas is provided so that a difference of pressure is
generated in the longitudinal direction of the substrate. It is
thus possible to facilitate the flow of the plasma reaction gas
into the space of the substrate.
[0032] FIG. 1 is a block diagram showing a system for producing a
thin film according to one embodiment of the present invention. The
system for producing a thin film shown in FIG. 1 has a chamber 1
for forming a film, and a means for generating a pressure
difference composed of a tank 2-1 for controlling pressure and a
pump 2-2. The system further has a coil 3 as a means for generating
a magnetic field, and a means for generating an electric field
composed of an anode 4-1 and a cathode 4-2. The anode 4-1 is
ground, and the cathode 4-2 is connected with a source 6 for high
voltage pulse. An electric source for direct current voltage is not
provided.
[0033] Further, a gas supply hole 7 for introducing a gaseous raw
material and a pump 8 for maintaining a pressure in the chamber 1
at a predetermined value are provided in the chamber 1. Further, a
pressure gauge 9 and a window 10 are provided. It is thus possible
to monitor the degree of vacuum and the state of the plasma
reaction gas in the chamber 1. A substrate 20 is provided and fixed
over the cathode 4-2.
[0034] After the chamber 1 is evacuated with the pump 8 to a
predetermined degree of vacuum, the gaseous raw material is
supplied into the chamber 1 through the gas supply hole 7. The
pressure in the chamber 1 is maintained at a predetermined value by
the evacuation with the pump 8. The degree of vacuum is monitored
by means of the pressure gauge 9 provided in the chamber 1.
[0035] The source 6 for applying high voltage pulse then applies a
pulse voltage to excite the gaseous raw material to generate plasma
reaction gas.
[0036] The space around the cathode 4-2 and substrate 20 set on the
cathode is evacuated by means of the pump 2-2 through the tank 2-1
for controlling a pressure, so as to generate a difference or
gradient of pressure in the longitudinal direction "X" of the
substrate 20. The pressure at a rear part B in the longitudinal
direction X of the substrate 20 may preferably be 1/10 or lower,
and more preferably be 1/100 or lower, of a pressure at a front
part A in the longitudinal direction X. It is thus possible to
introduce the plasma reaction gas efficiently into the space of the
substrate 20.
[0037] In a preferred embodiment, the pressure in the chamber 1 is
about 10.sup.-2 Torr and the pressure at the front part A in the
longitudinal direction X of the substrate 20 is also about
10.sup.-2 Torr. In this case, the pressure at the rear part B in
the longitudinal direction X of the tubular member 20 is controlled
at a value of about 10.sup.-3 to 10.sup.-4 Torr by means of the
tank 2-1 for controlling pressure and pump 2-2.
[0038] A current is flown to the coil 3 to generate a magnetic
field in the longitudinal direction X of the substrate 20. The
magnetic field may preferably be focused so that the width of the
magnetic field is smaller than the inner diameter of the substrate
20 in the direction Y perpendicular to the longitudinal direction X
of the substrate 20. It is thus possible to improve the flow ratio
of the plasma reaction gas into the substrate 20 to facilitate the
formation of the thin film onto the inner wall surface facing the
space of the substrate 20.
[0039] FIGS. 2(a), 2(b) and 2(c) are cross sectional views each
showing a thin film 22 formed on each tubular substrate 20, 20A or
20B.
[0040] The substrate 20 shown in FIG. 2(a) has a relatively large
inner diameter (diameter of a space 23) "d", so that the plasma
reaction gas easily passes through the space 23 as arrows D and E.
23a represents an opening communicating with the space. The
substrate 20A shown in FIG. 2 (b) has a smaller inner diameter
(diameter of a space 23A) "d" compared with that in FIG. 2(a). A
pressure loss before the gas is discharged as an arrow E is larger
when the gas is flown into the space as an arrow D. It may be
difficult to form a thin film efficiently according to a prior
process. In the substrate 20B shown in FIG. 2(c), a sealing part
20c is provided in the downstream of the gas flow to prevent the
flow of the gas into the space 23B. The present invention is still
effective for forming a thin film on the inner wall surface.
[0041] Further, the kind of the thin film formed on the inner wall
surface of the substrate is not particularly limited, and includes
diamond, diamond like carbon, TiN, TiCN, WC, W.sub.2C, W.sub.3C,
SiO.sub.2, SiNx, a-Si:H, BCN, BN, CN or the like.
[0042] In a preferred embodiment, the thin film is made of diamond
or diamond like carbon. Such substrate may be used as a sliding
member.
Examples
[0043] A film 22 of diamond like carbon was formed on the inner
wall surface 20b of the substrate 20B as shown in FIG. 2(c),
according to the process described above referring to FIG. 1.
Specifically, the outer diameter of the substrate 20B was 5 mm, the
inner diameter was 0.9 mm, and the length was 20 mm.
[0044] The substrate 20B was mounted and fixed on the cathode 4-2,
and the inside of the chamber 1 was evacuated to a degree of vacuum
of 1.times.10.sup.-4 to 1.times.10.sup.-5 Torr by means of the pump
8. C.sub.2H.sub.2 gas was introduced at a flow rate of 20
cm.sup.3/min through the gas supply hole 7, and the pressure in the
chamber 1 was maintained at 3.75.times.10.sup.-2 Torr by
controlling the evacuation with the pump 8. 8.0 kV of the pulse
voltage was applied between the anode 4-1 and cathode 4-2 with the
high voltage pulse source 6 to generate C.sub.2H.sub.2 gas plasma.
A distance between the anode 4-1 and cathode 4-2 was 10 cm, so that
an electric field of 80 kV/m was generated between the anode 4-1
and cathode 4-2. The pulse width of the pulse voltage was 20
.mu.sec, and the pulse period was 5000 Hz.
[0045] The pressure at the rear part "B" in the longitudinal
direction X of the substrate 20 was adjusted at 4.5.times.10.sup.-4
Torr using the tank 2-1 for controlling pressure and pump 2-2.
Further, a current is flown into the coil 3 to generate a magnetic
field of 0.01 T in the longitudinal direction X of the substrate.
The pressure and magnetic field were maintained for 15 minutes and
C.sub.2H.sub.2 plasma gas was introduced to the space 23B of the
substrate. A diamond like carbon film was thus generated on the
inner wall surface 20b.
[0046] FIG. 3 is a graph showing a Raman spectrum obtained by Raman
spectroscopic analysis of a diamond like carbon film formed on the
inner wall surface of the substrate. As can be seen from FIG. 3,
characteristic scattering peaks near about 1360 cm.sup.-1 and 1580
cm.sup.-1 were observed due to diamond like carbon. It was thus
proved the presence of a film of diamond like carbon.
[0047] As described above, a thin film can be reproducibly formed
in a process for forming the thin film on the inner wall surface
facing a space formed in a substrate by plasma CVD.
[0048] The present invention has been explained referring to the
preferred embodiments. However, the present invention is not
limited to the illustrated embodiments which are given by way of
examples only, and may be carried out in various modes without
departing from the scope of the invention.
* * * * *