Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2001-03-22
2004-08-24
Hassanzadeh, Parviz (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230AN, C156S345430
Reexamination Certificate
active
06779482
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a plasma deposition device for forming a thin film, especially a plasma deposition device for forming a film functioning as a semiconductor. More specifically, the present invention relates to a plasma deposition device for forming a thin film preferably utilizing a plasma-excited chemical vapor deposition method utilized for manufacturing an insulation film or a semiconductor film such as amorphous silicon (hereinafter referred to as a-Si) utilized in the electronic industry.
DESCRIPTION OF THE RELATED ART
The method for manufacturing an electronic device such as an integrated circuit, a liquid crystal display, an amorphous solar battery and the like by depositing a semiconductor film and the like using plasma is called a plasma-excited chemical vapor deposition (CVD) method, which is advantageous in its simplicity and its maneuverability and is applied to manufacture various electronic devices.
The general CVD method will now be explained, with reference to
FIGS. 8 and 9
showing the structure of a plasma deposition device (plasma CVD device) utilizing this general CVD method.
FIG. 8
is a cross-sectional view explaining the concept of the structure of the plasma CVD device, and
FIG. 9
is a perspective view showing the structure of the main portion of the device.
A prior-art plasma CVD device comprises a first electrode
13
-
1
mounted on the first surface of an electrode substrate
11
, a gas supply space
15
formed to the back side of the electrode substrate
11
, a deposition substrate
30
arranged to oppose to the first electrode
13
-
1
with a predetermined distance d in between, a second electrode
13
-
2
mounted to the back surface of the deposition substrate
30
, a vacuum container
50
, an induction terminal
51
, a deposition substrate holder
52
, a power source
60
, and a gas supply unit
70
. A plurality of gas introducing holes
12
are provided to the electrode substrate
11
and the first electrode
13
-
1
mounted thereto, supplying material gas G to plasma generation space
10
. High-frequency output from the power source provides electric energy to the first electrode
13
-
1
and the second electrode
13
-
2
. The gas supply unit
70
is connected via a gas supply tube
16
to the gas supply space
15
, through which material gas for forming the thin film is supplied during deposition.
The plasma CVD device generates plasma by causing discharge DC to be performed between the first electrode
13
-
1
and the second electrode
13
-
2
, which are two conducting plates mutually insulated and opposed to each other in parallel, and provides material gas G thereto so as to dissociate the gas and to generate radicals R. Thereby, a semiconductor film and the like is deposited on the deposition substrate
30
made of silicon or glass and mounted to the second electrode
13
-
2
.
The means for generating plasma that resolves the material gas to be deposited utilizes a high-frequency power generally having a frequency of 13.56 MHz. That is, one conductor plate electrode
13
-
2
is set to ground potential, and high-frequency voltage is applied between the electrode
13
-
1
opposed thereto, thereby generating a high-frequency electric field between both conductor plates. This state of breakdown generates plasma as a glow discharge phenomenon. The electrode
13
-
1
to which high-frequency voltage is impressed is called the cathode electrode, and a large electric field is formed near the electrode, which accelerates the electron in the plasma and encourages dissociation of material gas, thereby generating radicals R.
Accompanied by the recent advancement in plasma engineering and semiconductor engineering, a new proposal has been made to the plasma CVD method. One example involves improving the deposition speed of the semiconductor film by increasing the frequency of the utilized high frequency output from 13.56 MHz to a VHF band (J. Vac. Sci. Technol. A10 (1992) 1080, A. A. Howling).
Electronic devices such as the liquid crystal display or the amorphous solar battery are especially large-sized electronic devices, and there is strong demand for a larger product formed by utilizing a deposition substrate
30
having a size ranging from the order of 10 cm square to 1 m square.
However, there is a limit to the prior art method related to forming a thin film by deposition to a deposition substrate
30
having a small size. A large-sized electronic device such as a liquid crystal display or an amorphous solar battery was difficult to manufacture according to the prior art method, since it was difficult to deposit a high-quality film having a uniform film thickness to a deposition substrate
30
having a large area.
One reason causing difficulty in securing a uniform film thickness is that when high frequency is used, the inductance of the material constituting electrodes
13
-
1
and
13
-
2
or the partial difference in electrical connection of the parts constituting the electrodes
13
-
1
and
13
-
2
causes high-frequency power that generates uneven plasma on the deposition substrate
30
, resulting in uneven density distribution of the plasma particles and radical particles. As a result, the thickness of the film formed on the deposition substrate
30
varies locally.
In the case of a TFT (thin film transistor) liquid crystal display utilizing an a-Si film, if the thickness of the a-Si film functioning as the switching layer varies within one deposition substrate
30
, the switching property is partially varied, and thus, the display becomes uneven. There is a demand for a method that reduces the uneven distribution of the plasma density, and enables to grow a film having a uniform thickness on the deposition substrate
30
.
One reason causing difficulty in obtaining a high-quality deposition is that the deposition substrate
30
is mounted on ground electrode during deposition. When plasma is generated, a potential difference called a sheath voltage occurs on the surface of the deposition substrate
30
positioned above the ground electrode, and basically such potential difference cannot be avoided as long as plasma exists. Sheath voltage accelerates the ion within the plasma towards the deposition substrate, which results in ions providing impact to the surface of the deposited film, deteriorating the quality of the film.
A method is proposed in Japanese Patent Laid-Open Publication No. 11-144892 that improves the film-thickness distribution to the deposition substrate
30
and deposits a high-quality film. The disclosed method for manufacturing the film includes providing a plurality of electrodes having a wavy uneven surface, and providing the deposition substrate
30
away from the electrodes so as to form a horizontal electric field, thereby enabling to manufacture a uniform and high-quality film having a large size. However, according to this deposition method, if discharge electrodes are formed to have a width of a couple of millimeters, the cross-section of the electrodes can be shaped as a triangle, a trapezoid, a semicircle, or a T-shape and the like, which causes the height of the electrodes to be varied for a couple of millimeters. Thereby, the surfaces of the electrodes are not positioned at fixed distances from the deposition substrate. If a uniform deposition is to be formed under such condition, the deposition substrate
30
must be separated by a considerably long distance away from the surfaces of the electrode surfaces so as to reduce the ratio of dispersion of the distance between each electrode for deposition. According further to this method, during formation of discharge electrodes, the step for forming a wavy form to the electrode formation surface having a large area ranging from the order of 10 cm square to over 1 m square requires high mechanical accuracy. Moreover, since the distance between electrodes is fixed according to the structure, the Paschen property for plasma generation (the value of plasma-discharge-starting voltage×inter-electrode distance relativity) li
Akai Toshio
Okamoto Satoshi
Sakai Osamu
Conlin, Esq. David G.
Edwards & Angell LLP
Hassanzadeh Parviz
Roos, Esq. Richard J.
Sharp Kabushiki Kaisha
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