Plasma CVD process

Details Plasma CVD process Plasma CVD process

2001-06-06

2001-12-25

Beck, Shrive P. (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Plasma

C427S248100, C427S255500, C118S7230ER, C118S7230AN, C156S345420

Reexamination Certificate

active

06333079

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plasma CVD (chemical vapor deposition) process and a plasma CVD system which make use of high-frequency power and are usable in the manufacture of semiconductor devices, electrophotographic photosensitive member devices, image-inputting line sensors, flat-panel display devices, image pickup devices, photovoltaic devices and so forth.
2. Related Background Art
In recent years, in the process of producing semiconductor devices and the like, plasma CVD systems and plasma CVD processes have been put into practical use in an industrial scale. In particular, plasma CVD systems making use of a high-frequency power of 13.56 MHz are in wide use because processing can be carried out regardless of whether substrate materials and deposited-film materials are conductors or insulators.
As an example of conventional plasma-producing high-frequency electrodes and plasma CVD systems and processes making use of such electrodes, a parallel-plate type system will be described with reference to FIG.
1
. In a reactor
101
, a high-frequency electrode
103
is provided via an insulating high-frequency electrode support base
102
.
The high-frequency electrode
103
is a flat plate provided in parallel to an opposing electrode
105
, and plasma is caused to take place by the aid of an electric field determined by electrostatic capacitance exhibited between the electrodes. Once plasma has taken place, a plasma region which is substantially a conductor and a sheath which acts chiefly as a capacitor in an equivalent manner between the plasma and the both electrodes or reactor wall are formed between the electrodes to provide an impedance greatly different from that before the plasma takes place.
Around the high-frequency electrode
103
, an earth shield
104
is provided so that any discharge may not occur between the side of the high-frequency electrode
103
and the wall of the reactor
101
. To the high-frequency electrode
103
, a high-frequency power source
111
is connected through a high-frequency power supply wire
110
.
A flat-plate film-forming substrate
106
on which plasma CVD is carried out is attached to the opposing electrode
105
provided in parallel to the high-frequency electrode
103
, and the substrate
106
to be processed is kept at a desired temperature by a substrate temperature control means (not shown).
Plasma CVD using this system is carried out in the following way. After the inside of the reactor
101
is evacuated to a high vacuum by an evacuation means
107
, reaction gases are fed into the reactor
101
through a gas feed means
108
, and its inside is kept at a predetermined pressure. A high-frequency power is supplied from the high-frequency power source
111
to the high-frequency electrode
103
to cause a plasma to take place across the high-frequency electrode and the opposing electrode.
Thus, the reaction gases are decomposed and excited by plasma to form a deposited film on the film-forming substrate
106
. As the high-frequency power, it is common to use a high-frequency power of 13.56 MHz. Use of such a discharge frequency of 13.56 MHz makes it relatively easy to control discharge conditions and brings about an advantage that the film formed can have a good film quality, but may result in a low gas utilization efficiency and a relatively small deposited-film formation rate.
Taking account of these points, studies are made on plasma CVD carried out at a high-frequency power having a frequency of about 25 to 150 MHz. For example, Plasma Chemistry and Plasma Processing, Vol. 7, No. 3, 1987, pp.267-273 (hereinafter “publication 1”) discloses that a material gas (silane gas) is decomposed by a high-frequency power having a frequency of about 25 to 150 MHz, using a parallel-plate type glow discharge decomposition system.
Stated specifically, the publication 1 discloses that, in the formation of a-Si films at frequencies changed within the range of from 25 MHz to 150 MHz, film deposition rate reaches a maximum of 2.1 nm/sec when 70 MHz is used, and this is a formation rate about 5 to 8 times that in the plasma CVD carried out at 13.56 MHz, and that a-Si film defect density, optical band gap and conductivity are not so much affected by excitation frequencies.
The publication 1 shows an example of a plasma CVD system suited for the processing of flat substrates of a laboratory scale. As for an example of a plasma CVD system suited for the formation of deposited films on film-forming substrates of a large industrial scale (e.g., cylindrical substrates), it is disclosed in, e.g., U.S. Pat. No. 5,540,781 (hereinafter “publication 2”).
This publication 2 discloses a plasma CVD process and a plasma CVD system which make use of a high-frequency power of what is called VHF band, having a frequency of from 60 MHz to 300 MHz. The plasma CVD system as disclosed in the publication 2 will be described with reference to FIG.
2
.
The plasma CVD system shown in
FIG. 2
is the VHF plasma CVD system disclosed in the publication 2.
In
FIG. 2
, reference numeral
200
denotes a reactor. The reactor
200
has a base plate
201
, insulating members
202
A, cathode electrodes
203
C, insulating members
221
B, cathode electrodes
203
B, insulating members
221
A, cathode electrodes
203
A, insulating members
202
B and a top cover
215
.
Reference numeral
205
A denotes a substrate holder, which has a heater column
205
A′ inside. Reference numeral
205
A″ denotes a substrate heater attached to the heater column
205
A′. Reference numeral
206
denotes a cylindrical film-forming substrate provided on the substrate holder
205
A. Reference numeral
205
B denotes an auxiliary holding member for the cylindrical film-forming substrate
206
. The substrate holder
205
A has at its bottom a rotating mechanism (not shown) connected to a motor and is so designed as to be optionally rotatable. Reference numeral
207
denotes an exhaust pipe having an exhaust valve, and the exhaust pipe communicates with an exhaust mechanism
207
′ having a vacuum pump. Reference numeral
208
denotes a material gas feed assemblage constituted of gas cylinders, mass-flow controllers, valves and so forth. The material gas feed assemblage
208
is connected to gas release pipes
216
having a plurality of gas release holes, through a gas feed pipe
217
. Material gases are fed into the reactor through the plurality of gas release holes of the gas release pipes
216
. Reference numeral
211
denotes a high-frequency power source, and a high-frequency power generated here is supplied to the cathode electrodes
203
(
203
A to
203
C) through a high-frequency power supply wire
218
and matching circuits
209
(
209
A to
209
C). In the plasma CVD system shown in
FIG. 2
, the cathode electrodes are so constituted as to be divided electrically into three electrodes
203
A,
203
B and
203
C in the axial direction of the cylindrical film-forming substrate. The high-frequency power generated in the high-frequency power source
211
is divided into three parts by a high-frequency power dividing means (distributor)
220
, and then supplied to the cathode electrodes
203
A,
203
B and
203
C through matching circuits
209
A,
209
B and
209
C, respectively.
The publication 2 also describes a plasma CVD process carried out using the plasma CVD system shown in FIG.
2
.
That is, in the system shown in
FIG. 2
, the cylindrical film-forming substrate
206
is set to the substrate holder
205
, and thereafter the inside of the reactor
200
is evacuated by the operation of the exhaust mechanism
207
′ to evacuate the inside of the reactor to have a predetermined pressure. Then, the heater
205
A″ is electrified to heat the substrate
206
so as to be kept at a desired temperature.
Next, material gases are fed into the reactor
200
from the material gas feed assemblage
208
through the gas feed pipe
217
and gas release pipes
216
, and the inside of the reactor is adjusted to a desired pressure. In this st

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