Plasma CVD apparatus and plasma processing method

Details Plasma CVD apparatus and plasma processing method Plasma CVD apparatus and plasma processing method

1997-08-22

2002-08-20

Mills, Gregory (Department: 1763)

Coating apparatus

Gas or vapor deposition

With treating means

C118S7230AN, C204S192120, C204S298050, C204S298280, C216S068000

Reexamination Certificate

active

06435130

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma CVD apparatus and a plasma processing method. More particularly, the present invention relates to a plasma CVD apparatus and a plasma processing method which are suited for the production of various electronic devices such as semiconductor devices, electrophotographic photosensitive devices (or electrophographic light receiving members), image input line sensors, flat panel displays, image pickup devices, photovoltaic devices, and the like.
2. Related Background Art
Recently, in the production of an electronic device such as semiconductor device and the like, a plasma CVD apparatus has been often used. Particularly, a plasma CVD apparatus in which a high frequency with 13.56 HMz or a microwave with 2.45 GHz is used has been widely used, since various substrates and depositing materials regardless of their properties being electrically conductive or electrically insulating can be optionally plasma-processed by the plasma CVD apparatus.
As an example of such plasma CVD apparatus, there can be mentioned a parallel plane plate type plasma CVD apparatus in which a high frequency energy is used, as shown in FIG.
1
.
Description will be made of the plasma CVD apparatus shown in FIG.
1
.
The plasma CVD apparatus shown in
FIG. 1
comprises a reaction chamber
1
in which a cathode electrode
3
is arranged through a cathode electrode support
2
. Around the cathode electrode
3
, an earth shield
4
is arranged so as to prevent discharge from being generated between a side portion of the cathode electrode
3
and the reaction chamber
1
. The cathode electrode
3
is electrically connected to a high frequency power source
10
through a matching circuit
9
.
Reference numeral
5
indicates a counter electrode which is arranged in parallel to the cathode electrode
3
.
Reference numeral
6
indicates a plate-like shaped substrate as an object to be plasma-processed which is positioned on the counter electrode
5
. Reference numeral
7
indicates an exhausting means (such as vacuuming pump) which is communicated with the inside of the reaction chamber
1
through an exhaust pipe. Reference numeral
8
indicates a raw material gas supply source which is communicated with the inside of the reaction chamber
1
through a gas feed pipe.
The substrate
6
can be maintained at a desired temperature by means of a substrate temperature control means (not shown).
Plasma CVD (plasma chemical vapor deposition) using the plasma CVD apparatus shown in
FIG. 1
is conducted, for example, in the following manner.
The reaction chamber
1
is evacuated to bring the inside to a desired high vacuum by operating the exhausting means
7
, followed by introducing a given raw material gas from the raw material gas supply source
8
into the reaction chamber
1
, and the gas pressure in the reaction chamber is maintained at a predetermined pressure. Thereafter, a high frequency power from the high frequency power source
10
is supplied to the cathode electrode
3
, whereby plasma is generated between the cathode electrode
3
and the counter electrode
5
, where the raw material gas introduced into the reaction chamber
1
is decomposed and excited to cause the formation of a deposited film on the substrate
6
.
In this case, as the high frequency power, there is generally used an RF power with 13.56 MHz. In the case of using a discharging frequency of 13.56 MHz, although there are advantages such that the discharging conditions can be relatively easily controlled and a deposited film having excellent film quality can be obtained, there are drawbacks such that the raw material gas utilization efficiency is insufficient and the deposition rate for a film deposited is relatively small.
In view of such situation as above described, various studies have been made of a plasma CVD method using a high frequency with 25 to 150 MHz.
For instance,
Plasma Chemistry and Plasma Processing,
Vol. 7. No. 3. pp. 267-273 (1987) (hereinafter, referred to as Document 1) discloses a manner in which using a parallel plane plate type glow discharge decomposition apparatus, a raw material gas (silane gas) is decomposed with a high frequency energy having a frequency with 25 MHz to 150 MHz to form an amorphous silicon (hereinafter referred to as a-Si) deposited film on a substrate. Specifically, Document 1 describes that a-Si deposited films were formed while changing the frequency in the range of 25 MHz to 150 MHz; and the deposition rate in the case of using 75 MHz was 2.1 nm/sec which is the largest among others and which is greater by about five to eight times over that in the case of the plasma CVD using a frequency with 13.56 MHz. Document 1 also describes that the defect density, optical bandgap and conductivity of an a-Si film obtained are less influenced by an excitation frequency employed.
However, the film formation described in the Document 1 is of a laboratory scale. Document 1 does not even suggest anything of whether or not such effect as above described can be expected in the case of forming an a-Si deposited film having a large area. Further, Document 1 is absolutely silent about a manner of simultaneously forming an a-Si deposited film on a plurality of large area substrates to efficiently produce a plurality of large area semiconductor devices which can be desirably used in practice. In fact, Document 1 merely mentions a possibility that the use of higher frequencies (13.56 up to ~200 MHz) opens interesting perspectives for fast processing of low cost, large area a-Si thin film devices in which thicknesses of several &mgr;m are required.
The above example is of the case where the plasma CVD apparatus which is appropriate for plasma-processing a plate-shaped substrate.
Besides, an example of a plasma CVD apparatus which is appropriate for forming a deposited film on a plurality of cylindrical substrates is disclosed in European Patent Publication No. 154160 A (hereinafter referred to as Document 2). Particularly, Document 2 discloses a plasma CVD apparatus using a microwave power source having a frequency with 2.45 GHz (this apparatus will be hereinafter referred to as microwave plasma CVD apparatus) and a plasma CVD apparatus using a radio frequency (RF) power source (this apparatus will be hereinafter referred to as RF plasma CVD apparatus).
In the microwave plasma CVD apparatus disclosed in Document 2, since a microwave energy is used, the density of plasma generated upon film formation is extremely high. Because of this, a film-forming raw material gas is rapidly is decomposed, whereby the deposition of a film is conducted at a high speed. However, there is a problem such that it is difficult to stably and continuously form a high quality dense film.
Next, description will be made of the RF plasma CVD apparatus described in Document 2 while referring to FIGS.
2
(A) and
2
(B).
FIG.
2
(A) is a schematic diagram illustrating an RF plasma CVD apparatus based on the RF plasma CVD apparatus described in Document 2. FIG.
2
(B) is a schematic cross-sectional view, taken along the line X—X in FIG.
2
(A).
The RF plasma CVD apparatus shown in FIGS.
2
(A) and
2
(B) comprises a reaction chamber
100
in which six cylindrical substrate holders
105
A each having a cylindrical substrate
106
for film formation positioned thereon are concentrically and spacedly arranged at a predetermined interval. The reaction chamber
100
has a plasma generation region A circumscribed by the substrate holders
105
A. Reference numeral
105
B indicates a dummy holder which serves to cap an end portion of the cylindrical substrate
106
positioned on the substrate holder
105
A.
Each substrate holder
105
A is provided with a heater
104
in the inside thereof so that the cylindrical substrate
106
can be heated from the inner side thereof. Each substrate holder
105
A is held on a shaft
131
coupled to a driving motor
132
so that the substrate holder
105
A can be rotated.
Reference numeral
103
indicates a cathode electrode arran

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