Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Amorphous semiconductor
Reexamination Certificate
2001-02-08
2002-07-09
Ghyka, Alexander G. (Department: 2812)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Amorphous semiconductor
C438S478000, C438S680000, C438S788000, C427S569000, C427S574000
Reexamination Certificate
active
06417079
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a discharge electrode, a high frequency plasma generator, a method of power feeding to a discharge electrode, and a method of manufacturing semiconductor device. More particularly, the present invention relates to a high frequency plasma generator used for forming a film of a semiconductor, such as amorphous silicon, microcrystal silicon, polycrystal thin silicon, silicon nitride and the like, used in a solar cell, a thin film transistor and the like, and etching a film of a semiconductor, and its discharge electrode, a method of power feeding to the discharge electrode, and a method of manufacturing semiconductor device using it.
BACKGROUND ART
As an example of a configuration of the high frequency plasma generator and a method of manufacturing semiconductor device using it, two typical examples of: {circle around (1)} a case of a usage of parallel plate electrodes; and {circle around (2)} a case of a usage of ladder electrodes are described in a case when amorphous silicon semiconductor thin film (hereafter, referred to as a-Si) is manufactured by using a plasma chemical vapor deposition apparatus (hereafter, referred to as a PCVD apparatus).
FIG. 11
shows one configuration example of an apparatus using the {circle around (1)} parallel plate electrodes usually used for the a-Si film formation. A substrate heater
2
is mounted within a reactor
1
, and electrically grounded. A flat plate electrode
3
is mounted at a position opposite to the substrate heater
2
, and it is placed, for example, 20 mm away from the substrate heater
2
. An external high frequency power supply
4
is connected through an impedance matching device
5
and a coaxial cable
6
to the flat plate electrode
3
. An earth shield
8
is mounted near the flat plate electrode
3
so that unnecessary plasma is not generated on a side opposite to a plane opposite to the substrate heater
2
of the flat plate electrode
3
.
The a-Si film is formed in the following procedure.
At first, a substrate
16
on which the a-Si thin film is formed is placed on the substrate heater
2
whose temperature is set, for example, to 200° C. SiH
4
gas is introduced from a gas supply tube
17
, for example, at a velocity of flow of 50 sccm. Then, a pressure within the reactor
1
is adjusted, for example, to 100 mTorr by adjusting an exhaust speed in a vacuum pump system (not shown) connected to a vacuum exhaust pipe
18
.
The supply of high frequency electric power causes the plasma to be generated between the substrate
16
and the flat plate electrode
3
. The impedance matching device
5
is adjusted such that the high frequency electric power is effectively fed to a plasma generator. The SiH
4
is decomposed in a plasma
19
. The a-Si film is formed on a surface of the substrate
16
. The a-Si film having a necessary thickness is formed, for example, by carrying out the film formation under the above-mentioned condition for about ten minutes.
FIG. 12
shows one configuration example of the apparatus using the {circle around (2)} ladder electrode
303
. The ladder electrode is reported in detail, for example, in Japanese Laid Open Patent Application (JP-A-Heisei, 4-236781).
FIG. 13
is a view illustrating the structure of the ladder electrode
303
drawn from an A-direction of
FIG. 12
so that it can be sufficiently understood.
The substrate heater
2
(not shown in
FIG. 13
) is mounted within the reactor
1
, and electrically grounded. The ladder electrode
303
is mounted at the position opposite to the substrate heater
2
, and it is placed, for example, 20 mm away from the substrate heater
2
. The external high frequency power supply
4
is connected through the impedance matching device
5
and the coaxial cable
6
to the ladder electrode
303
. An earth shield
308
is mounted near the ladder electrode
303
so that the unnecessary plasma is not generated on the side opposite to the plane opposite to the substrate heater
2
of the ladder electrode
303
.
The a-Si film is formed in the following procedure.
At first, the substrate
16
on which the a-Si thin film is formed is placed on the substrate heater
2
whose temperature is set, for example, to 200° C. The SiH
4
gas is introduced from the gas supply tube
17
, for example, at the velocity of flow of 50 sccm. Then, the pressure within the reactor
1
is adjusted, for example, to 100 mTorr by adjusting the exhaust speed in the vacuum pump system (not shown) connected to the vacuum exhaust pipe
18
.
The supply of the high frequency electric power causes the plasma to be generated between the substrate
16
and the ladder electrode
303
. The impedance matching device
5
is adjusted such that the high frequency electric power is effectively fed to a region where a plasma
319
is generated. The SiH
4
is decomposed in the plasma
319
. The a-Si film is formed on the substrate
16
. The a-Si film having the necessary thickness is formed, for example, by carrying out the film formation under the above-mentioned condition for about ten minutes.
The configuration examples shown in
FIGS. 12 and 13
have the following two features, as compared with the configuration example of FIG.
11
.
The first feature lies in the usage of the electrode referred to as the ladder type in which electrode bars of circular cross sections are assembled in the form of ladders without using the flat plate electrode as the electrode. This electrode has the feature that raw material can be uniformly supplied since the SiH
4
gas of the raw material freely flows between the electrode bars.
The second feature lies in the fact that the power feeding operation is not carried out at only one point and it is carried out at a plurality of points (in this case, four points).
Presently, the low cost resulting from a film formation at the high speed and the high qualities such as a low defect density, a high crystallinity and the like are required of a thin film transistor for a flat panel display and a thin film semiconductor for a solar cell which are manufactured by using the above-mentioned technique and the like. As a new method of generating a plasma, which satisfies those requirements, there is a method of making a frequency of a high frequency power supply higher (30 MHz to 300 MHz). The fact that the higher qualities and the higher speed of the film formation are both attained by making the frequency higher is disclosed, for example, in “Document Mat. Res. Soc. Symp. Proc. Vol. 424, pp9, 1997”. Especially, it has been recently known that this high frequency is suitable for a film formation at a high speed and at a high quality in a microcrystal Si thin film remarked as a new thin film instead of the a-Si.
By the way, the film formation through the high frequency operation has the defect that it is difficult to form a consistent wide area film. This reason is as follows. That is, a wavelength of a high frequency is at an order similar to a size of an electrode. Thus, a voltage distribution resulting from a standing wave mainly caused by a reflected wave occurring in an end of an electrode and the like is induced within the surface of the electrode, which makes the plasma nonuniform. This results in a nonuniform film formation.
In the configuration example exemplified as the {circle around (1)} usage of the parallel plate electrode, if the size of the electrode exceeds 30 cm or if the frequency exceeds 30 MHz, the influence of the standing wave becomes strong, which disables the attainment of a film formation uniformity of 10% that is at least necessary for the film formation of the semiconductor.
FIG. 14
is an example of a voltage distribution resulting from a standing wave at 100 MHz.
FIG. 14
simultaneously shows an ion saturation current distribution. The ion saturation current distribution is substantially equal to an electron density distribution. Its measurement is easy. Thus, it is typically used as an index of a plasma distribution. From the voltage distribution, it is understood that the standing wave is induced on the elec
Danno Minoru
Satake Koji
Yamakoshi Hideo
Armstrong Westerman & Hattori, LLP
Ghyka Alexander G.
Mitsubishi Heavy Industries Ltd.
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