Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
1999-12-07
2001-08-28
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S485000, C438S787000, C438S789000, C427S569000, C427S579000
Reexamination Certificate
active
06281147
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma CVD method used for manufacturing a semiconductor integrated circuit such as a thin-film transistor.
2. Description of the Related Art
At the present time, as the semiconductor integrated circuit is made high in integration as well as density, there is advanced that the structure of a semiconductor element is made finer. Under this condition, there is such a demand that an interlayer insulating film not only has an insulating characteristic, but also can be filled closely between wires which are complicated and have high aspects. Up to now, since a silicon oxide film which is made of TEOS as raw material and formed through the CVD method is excellent in coating shape, it has been widely used as an interlayer insulating film. In particular, the plasma CVD method is applied since it enables the silicon oxide film to be manufactured at a low temperature of 400° C. or lower and also enables a large area to be processed, in a process of manufacturing a TFT which is to be formed on a glass substrate.
However, as the semiconductor integrated circuit is made high in integration as well as density, the influence of charge-up of electrons caused during a plasma process becomes remarkable. For example, it is presumed that the failure of U-shaped display and the defect of points are caused by electric damages during the process. In the active matrix type liquid-crystal display unit, the failure of one TFT means the failure of an entire panel, thereby leading to the deterioration of a yield.
SUMMARY OF THE INVENTION
In order to eliminate the above problem, an object of the present invention is to provide a plasma CVD method that is capable of suppressing the deterioration of a device which is caused by charge particles.
The process by which the present invention has been achieved will be described.
In the plasma CVD device, in a state before plasma is developed, a voltage applied from an RF electrode acts as an electric field for a substrate. It is presumed from the viewpoints of an interval between an electrode and a wire, the thickness of a substrate, etc., that in this state, the intensity of an electric field is not so much as a device formed on the substrate is destroyed.
On the other hand, due to charge particles (electrons and positive ions) are produced in the process of generating plasma, a space between the RF electrodes becomes conductive. A substrate surface starts to be negatively charged with respect to plasma due to a difference in mobility between electrons and positive ions (the generation of ion sheath). Thereafter, the amount of generation of charge particles is balanced with the amount of disappearance of charge particles, that is, the amount of charge-up of charge particles is saturated, resulting in a stationary plasma state.
Hence, it is presumed that because the ion sheath produced on the substrate surface is not considered to become an excessively value, the intensity of electric field and ion irradiation energy are not so much as they destroy the device.
However, there is the possibility of allowing current to flow in a portion where little current flows in the stationary state until the amount of charge-up is saturated in a moment when plasma is generated, and if a large current flows in that portion transitionally, the device is then destroyed instantly.
Up to now, in order to form a silicon oxide film which is made of TEOS as raw material through plasma CVD, two processes consisting of a pre-process for generating plasma and a process of supplying TEOS to form the film are continuously conducted (in a state where O
2
plasma is being generated).
To elucidate the transitional phenomenon in the plasma CVD, the present inventors, et al. have observed the waveform of voltage applied between the RF electrodes with the connection of an oscilloscope to an RF power supply.
FIG. 5
shows the waveform of voltage applied between the RF electrodes in a conventional film forming process, and the unit of a vertical axis is 200 V/div whereas the unit of a horizontal axis is 500 msec/div. In both of the plasma generating process and the film forming process, an RF output is 250 W.
FIGS. 6A
to
6
C show the waveforms of voltage applied between the RF electrodes in an O
2
plasma generating process where the RF output is 250 W.
FIG. 6A
shows the waveform at the time of starting oscillation, and
FIGS. 6B and 6C
show the waveforms at the time of starting discharge, respectively. The instant that the discharge starts can be recognized as the shift of waveforms. It should be noted that the unit of the vertical axis of
FIGS. 6A
to
6
C is 200 V/div, respectively, whereas the unit of the horizontal axis is 100 msec/div in
FIG. 6A
, 20 msec/div in
FIG. 6B
, and 2 msec/div in FIG.
6
C.
Although the RF power supply oscillates at a predetermined voltage immediately after starting oscillation, a period of several tens msec is required from the oscillation start to the discharge start. However, a large voltage waveform (hereinafter referred to “beard pulse”) was transitionally observed in the moment that discharge is started as shown in
FIG. 6C
although it cannot be recognized in
FIGS. 5
,
6
A and
6
B.
For example, consideration is made about the plasma CVD process of a TFT disposed on a pixel panel of the active matrix type display unit. In order to surely hold image data, there is required that the TFT of the pixel panel is excellent in off-state current characteristic. For that reason, the TFT comprises, for example, the LDD structure, as shown in FIG.
1
E. Because the LDD region functions as a high resistant region, the off-state current can be reduced. It should be noted that
FIG. 1
will be described in detail with reference to a first embodiment.
In the process of manufacturing the TFT with the LDD structure, source/drain regions
112
and
113
of an active layer
103
which is made of silicon are exposed as shown in
FIG. 1E
before forming a first interlayer insulating film
116
(refer to FIG.
1
F). Also, because a gate electrode
105
is not cut into respective devices, its length is substantially identical with the width of a substrate as it is, and about several hundreds of gate electrodes
105
with the above structure are disposed in parallel.
In the above state, in the case where the first interlayer insulating film
116
is formed through plasma CVD, unless the plasma density and the plasma potential are not uniform even in the stationary plasma state, gate potential is distributed so that a current flows in the gate electrode
105
, with the result that the device is deteriorated. However, in the moment that plasma is generated, a transitional beard pulse is generated as shown in FIG.
6
C. Further, if plasma is unevenly generated, then a current which is remarkably larger than that in the stationary state is allowed to flow in the gate electrode.
Moreover, in an initial stage of forming the first interlayer
116
, because electrons are irradiated directly onto silicon (source/drain regions
112
and
113
), silicon is negatively charged. As a result, because electric field is developed in the gate insulating film
110
, the gate insulating film
110
is deteriorated. However, if silicon (source/drain regions
112
and
113
) is covered with the first interlayer insulating film
116
, silicon is prevented from being directly charged up.
Therefore, in order to form the first interlayer insulating film through plasma CVD, there arises such a problem that a transitional change in voltage such as the beard pulse must be eliminated or suppressed between the RF electrodes until silicon finishes being charged up.
In order to solve the above problem, according to a first aspect of the present invention, there is provided a plasma CVD method that increases gradually or continuously an output of an RF power supply up to a value which is at the time of forming a film.
According to a second aspect of the present invention, there is provided a plasma CVD method that con
Hiroki Masaaki
Sakama Mitsunori
Yamazaki Shunpei
Fish & Richardson P.C.
Ghyka Alexander G.
Niebling John F.
Semiconductor Energy Laboratory Co,. Ltd.
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