Coating processes – Direct application of electrical – magnetic – wave – or... – Electrical discharge
Reexamination Certificate
2000-07-14
2002-02-26
Mills, Gregory (Department: 1763)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrical discharge
C118S7230ER, C118S729000
Reexamination Certificate
active
06350497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma processing apparatus that can be used as a deposited film forming apparatus for forming a deposited film on a substrate and to a plasma processing method that can be applied to a deposited film forming method. More particularly, the invention relates to a plasma processing apparatus used in forming a functional film, particularly a deposited film suitably used in semiconductor devices, photosensitive members for electrophotography, sensors for input of image, photographing devices, photovoltaic devices, and so on, and to a plasma processing method that can be applied to the formation of such a deposited film.
2. Related Background Art
There are many conventional methods including vacuum evaporation, sputtering, ion plating, thermal CVD, photo CVD, plasma CVD, and so on as methods for forming deposited films used in the semiconductor devices, photosensitive members for electrophotography, line sensors for input of image, photographing devices, photovoltaic devices, other various electronic devices, and optical elements, and apparatus therefor are also in practical use.
Among them the plasma CVD, which is a method for decomposing a source gas by a dc or high frequency or microwave glow discharge to form a thin deposited film on a substrate. Plasma CVD is now in practical use as a favorable method for forming a deposited film of hydrogenated amorphous silicon (hereinafter referred to as “a-Si:H”) used in photosensitive members for electrophotography or the like, and a variety of apparatuses therefor have been proposed heretofore.
The outline of the deposited film forming apparatus and forming method of this type will be described below.
FIG. 1
is a schematic, structural view to show an example of the deposited film forming apparatus by the RF plasma CVD process (hereinafter abbreviated as “RFPCVD”) using the frequency in the RF band as a power source. Specifically, it is an example of an apparatus for forming a light receiving member for electrophotography. The structure of the forming apparatus shown in
FIG. 1
is as follows.
This apparatus is principally composed of a deposition device
2100
, a source gas supply device
2200
, and an evacuation device (not illustrated) for depressurizing the inside of a reaction vessel
2101
. Inside the reaction vessel
2101
in the deposition device
2100
there are a cylindrical substrate
2112
, a substrate support
2113
internally provided with a heater for heating the substrate, and source gas inlet pipes
2114
. A high frequency matching box
2115
is connected to a cathode electrode
2111
composing a part of the reaction vessel
2101
. The cathode electrode
2111
is insulated from the ground potential by insulators
2120
and a high frequency voltage can be applied between the cathode electrode
2111
and the cylindrical substrate
2112
also serving as an anode electrode while being maintained at the ground potential through the substrate support
2113
.
The source gas supply device
2200
is composed of cylinders
2221
to
2226
of source gases such as SiH
4
, GeH
4
, H
2
, CH
4
, B
2
H
6
, PH
3
, etc., valves
2231
to
2236
,
2241
to
2246
,
2251
to
2256
, and mass flow controllers
2211
to
2216
, each source gas cylinder being connected through a valve
2260
to the gas inlet pipes
2114
in the reaction vessel
2101
.
Formation of a deposited film using this apparatus can be carried out as follows using a cylindrical substrate such as a photosensitive member for electrophotography.
First, the cylindrical substrate
2112
is set in the reaction vessel
2101
and the inside of the reaction vessel
2101
is evacuated by an unrepresented evacuation device (for example, a vacuum pump). In the subsequent step, the temperature of the cylindrical substrate
2112
is controlled to a predetermined temperature of 200° C. to 350° C. by the heater for heating the substrate provided in the substrate support
2113
.
For allowing the source gas for formation of a deposited film to flow into the reaction vessel
2101
, the following operations are carried out; after checking that the valves
2231
to
2236
of the gas cylinders and a leak valve
2117
of the reaction vessel are closed and further that the inflow valves
2241
to
2246
, outflow valves
2251
to
2256
, and auxiliary valve
2260
are opened, a main valve
2118
is first opened to evacuate the inside of the reaction vessel
2111
and a gas pipe
2116
.
When the reading of a vacuum gage
2119
reaches about 7×10
−4
Pa, the auxiliary valve
2260
and outflow valves
2251
to
2256
are closed.
Then the valves
2231
to
2236
are opened to introduce the gases from the gas cylinders
2221
to
2226
and the pressure of each gas is adjusted to 2 kg/cm
2
by pressure adjuster
2261
to
2266
. Then the inflow valves
2241
to
2246
are gradually opened to introduce each gas into the associated mass flow controller
2211
to
2216
.
After completion of the preparation for film formation as described above, formation of each layer is carried out according to the following procedures.
When the cylindrical substrate
2112
reaches a desired temperature, necessary valves out of the outflow valves
2251
to
2256
, and the auxiliary valve
2260
are gradually opened to introduce desired gases from the gas cylinders
2221
to
2226
through the gas inlet pipes
2114
into the reaction vessel
2101
. Then the flow rate of each source gas is adjusted to a predetermined value by the mass flow controller
2211
to
2216
. On that occasion the aperture of the main valve
2118
is controlled while checking the vacuum gauge
2119
so that the pressure in the vacuum vessel
2101
becomes a predetermined value. After the internal pressure becomes stable, an RF power source (not illustrated) of the frequency 13.56 MHz is set to a desired power and the RF power is guided through the high frequency matching box
2115
and cathode
2111
into the reaction vessel
2101
, thus inducing a glow discharge with the cylindrical substrate
2112
acting as an anode. This discharge energy decomposes the source gases introduced into the reaction vessel and a desired deposited film comprising silicon as a main component is formed on the cylindrical substrate
2112
. After the deposited film is formed in a desired thickness, the supply of RF power is stopped and the outflow valves are closed to stop the flow of the gases into the reaction vessel, thus terminating the formation of the deposited film.
By repetitively carrying out the operation similar to the above several times, a light receiving layer can be formed in a desired multilayer structure.
It is a matter of course that all the other outflow valves than those for necessary gases are closed during formation of each layer. In order to avoid the gas from remaining in the reaction vessel
2101
and in the pipes from the outflow valves
2251
to
2256
to the reaction vessel
2101
, the operation to close the outflow valves
2251
to
2256
, to open the auxiliary valve
2260
, and to fully open the main valve
2118
to evacuate the inside of the system once to a high vacuum is carried out as occasion may demand.
In order to make the film formation uniform, it is also effective to rotate the cylindrical substrate
2112
at a desired rate by a driving device (not illustrated) during the layer formation.
Further, the gas species and valve operations described above are modified according to production conditions of each layer.
In addition to the deposited film forming apparatus and forming method by the RF plasma CVD process using the frequency in the above RF band as described above, the VHF plasma CVD (hereinafter abbreviated as “VHF-PCVD”) process using the high frequency power in the VHF band is also drawing attention in recent years. Development of various deposited film forming apparatuses using VHF-PCVD is also active. This is because the VHF-PCVD process is expected to be able to achieve reduction of cost and enhancement of quality of prod
Akiyama Kazuyoshi
Hosoi Kazuto
Murayama Hitoshi
Ohtsuka Takashi
Okamura Ryuji
Hassanzadeh P.
Mills Gregory
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