Electric heating – Metal heating – By arc
Reexamination Certificate
1999-02-26
2001-11-06
Walberg, Teresa (Department: 3742)
Electric heating
Metal heating
By arc
C219S121360, C204S192130, C324S644000
Reexamination Certificate
active
06313430
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a processing apparatus and a processing method using plasma and, more particularly, it relates to a plasma processing apparatus and a plasma processing method that can suitably be used for forming on a substrate a deposition film of a non-single crystal, silicon-based semiconductor such as amorphous silicon, amorphous silicon germanium, amorphous silicon carbide or fine crystal silicon that can be used for thin film solar batteries, or for conducting a processing operation using plasma such as etching, annealing or ashing.
2. Related Background Art
Among non-single crystal semiconductors, amorphous silicon provides a particular advantage, as a semiconductor film can be formed of it with a large area by means of plasma CVD so that it is more adapted to produce a semiconductor device having a large area than crystal silicon or polycrystal silicon.
Therefore, amorphous silicon film is used for semiconductor devices that need to show a large area such as solar batteries, photosensitive drums of copying machines, image sensors of facsimile equipment and thin film transistors of liquid crystal displays.
Thus, these devices using amorphous silicon film occupy a large area as compared with a device made of a crystal semiconductor such as LSI or CCD. In the case of a solar battery showing a conversion efficiency of 10%, an area of about 30 m
2
may be required for it to produce the power output rate of about 3 kW that is required to feed an ordinary family; each solar battery element will be required to have a considerably large area. Therefore, there is a need for techniques which quickly form a deposition film having a large area.
A plasma CVD method typically used for forming an amorphous silicon film consists in producing plasma of a source gas containing silicon in the form of SiH
4
or Si
2
H
6
by decomposing it by means of high frequency electric discharge to form a film on a substrate placed in the plasma.
A high frequency wave with an RF (of about 13.56 MHz) has been popularly used for forming an amorphous silicon film by means of plasma CVD.
However, in recent years, a plasma CVD technique using a VHF has been attracting attention. For example, Amorphous Silicon Technology, 1992, p.15-p.26 (Materials Research Society Symposium Proceedings, Volume 258) reports the use of a discharge frequency in the VHF zone in place of 13.56 MHz in the RF zone to remarkably raise the film forming rate and produce excellent deposition film at an enhanced rate.
On the other hand, as a result of a series of experiments conducted by the inventors of the present invention in an attempt to produce a deposition film having a large area by means of plasma CVD using such a VHF, it has been found that the following points should be considered.
When the discharge electrode of a diode parallel plate plasma CVD system that is normally used with an RF to produce a deposition film having a large area is utilized with a VHF, a desired electric discharge occurs as in the case of using an RF when the discharge electrode has a relatively small area but the discharge electrode comes to show a large impedance to make it impossible to drive the matching circuit properly so that power cannot be used effectively when the discharge electrode is made to have a large area in order to produce evenly distributed plasma.
This problem may conveniently be avoided by using a discharge electrode not in the form of a plate but a straight rod or a rod with radial fins or comb-like teeth having a relatively small surface area for producing plasma evenly over a large area. However, the use of such a discharge electrode considerably reduces its impedance so that the electric discharge is significantly affected by the stray capacitance found between the discharge electrode and the matching circuit, and the waveform of the high frequency wave can easily become distorted beyond the matching circuit to give rise to harmonics. As the waveform of the high frequency wave is distorted and harmonics are generated, problems arise including that the applied power cannot be determined correctly, that a correct matching cannot be realized and that the reproducibility of the application of high frequency power can become very low.
FIG. 1
of the accompanying drawings illustrates a deposition film forming apparatus utilizing plasma CVD as a type of plasma processing apparatus.
The deposition film forming apparatus of
FIG. 1
comprises as major components thereof a plasma processing section (depositing section)
101
and a high frequency power source section
102
. The plasma processing section
101
has a vacuum vessel
103
containing therein a discharge chamber
104
, which has gas inlet pipe
106
for introducing desired gas into the discharge chamber
104
and an exhaust pipe
105
for evacuating the inside of the discharge chamber
104
. The substrate
107
to be processed by means of plasma (on which a deposition film is formed) is placed on a substrate mount section arranged in the discharge chamber
104
. An appropriate heater
108
is provided in the vacuum vessel
103
to heat the substrate
107
to a desired temperature level or maintain the temperature of the substrate
107
to a desired level.
An antenna
109
is arranged in the discharge chamber
104
by way of a high frequency power introducing section
122
arranged in the vacuum vessel
103
. The antenna
109
is electrically connected to the high frequency power source
102
.
The high frequency power source
102
includes as major components a high frequency power supply circuit section
110
adapted to oscillate at a high frequency and absorb reflected waves, a power detection circuit section
111
for detecting incident and reflected high frequency power and a matching circuit
112
.
The high frequency power supply circuit section
110
has a high frequency oscillation circuit
113
, a circulator
114
and a reflected wave absorbing load
115
, whereas the power detection circuit section
111
has a directional coupler
116
as well as a pair of detectors
117
, a pair of amplifiers
118
and a pair of meters
119
connected to the directional coupler
116
for incident power and reflected power respectively.
The high frequency power (traveling wave) from the directional coupler
116
is regulated for impedance by way of the matching circuit
112
after passing through a high frequency cable
121
and before reaching the antenna
109
. The reflected wave from the antenna
109
reversely follows the route of the traveling wave until it reaches the directional coupler
116
.
Thus, in a deposition film forming apparatus adapted to use plasma CVD as shown in
FIG. 1
, the applied high frequency power is read by a power detection circuit
111
typically provided in the high frequency power source
102
for both incident power and reflected power. If the power detection circuit
111
is of the transmission type employing a directional coupler
116
for constantly monitor the power, the power detection circuit
111
is so calibrated as to indicate the right value only for the fundamental oscillation frequency. Therefore, if the high frequency wave shows a distorted waveform beyond the matching circuit
112
to produce harmonics, the reflected waves of a number of harmonics reach the power detection circuit
111
of the high frequency power source
102
. In this way, both the incident power and the reflected power cannot be read correctly, thereby rendering the matching operation inaccurate.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a plasma processing apparatus and a plasma processing method that can suitably be used for carrying out a processing operation, using plasma, uniformly over a large area with an enhanced degree of reproducibility. The present invention solves the problem that the introduced high frequency power is distorted to become apt to generate harmonics and make it impossible to accurately read both the incident power and the ref
Fujioka Yasushi
Kanai Masahiro
Kohda Yuzo
Okabe Shotaro
Sakai Akira
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Van Quang
Walberg Teresa
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