Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2000-12-21
2003-04-29
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S150000, C438S158000, C438S160000
Reexamination Certificate
active
06555419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film transistor suitable as a switching element for a display picture element of an active matrix type display panel or the like.
2. Description of the Related Art
FIG. 1
is a cross sectional view showing the arrangement of a bottom gate type thin film transistor.
Such a thin film transistor is formed as follows:
On the surface of an insulating transparent substrate
1
, a gate electrode
2
made of a metal with a high melting point i.e. a refractory metal such as tungsten or chromium is disposed. This gate electrode
2
is tapered so that both end portions are wider on the transparent substrate
1
side. On the transparent substrate
1
to which the gate electrode
2
is arranged, a silicon oxide film
4
is deposited through a silicon nitride film
3
. The silicon nitride film
3
prevents the impurities included in the transparent substrate
1
from entering the active region to be described later, and the silicon oxide film
4
functions as a gate insulating film. On the silicon oxide film
4
, a polycrystalline silicon film
5
is deposited so as to cross the gate electrode
2
. This polycrystalline silicon film
5
is the active region of a thin film transistor.
On the polycrystalline silicon film
5
, a stopper
6
made of an insulating material such as silicon oxide is disposed. The region covered by the stopper
6
of the polycrystalline silicon film
5
is a channel region
5
c
, while the remaining region of the polycrystalline silicon film
5
is a source region
5
s
and a drain region
5
d
. On the polycrystalline silicon film
5
to which the stopper
6
is formed, a silicon oxide film
7
and a silicon nitride film
8
are deposited. These silicon oxide film
7
and silicon nitride film
8
are layer to layer insulating films for protecting the polycrystalline silicon film
5
including the source region
5
s
and the drain region
5
d.
In specified places of the silicon oxide film
7
and the silicon nitride film
8
on the source region
5
s
and the drain region
5
d
, contact holes
9
are formed. At the portions of these contact holes
9
, a source electrode
10
s
and a drain electrode
10
d
are arranged, which are connected to the source region
5
s
and the drain region
5
d
. On the silicon nitride film
8
to which the source electrode
10
s
and the drain electrode
10
d
are disposed, an acrylic resin layer
11
transparent to visible light is deposited. This acrylic resin layer
11
fills up the irregularity produced by the gate electrode
2
or the stopper
6
, so that the planarization of the surface may be performed.
In the acrylic resin layer
11
on the source electrode
10
s
, a contact hole
12
is formed. Then, a transparent electrode
13
made of ITO (Indium Tin Oxide) or the like to be connected to an aluminum electrode
10
through this contact hole
12
is arranged so as to spread over the acrylic resin layer
11
. This transparent electrode
13
forms a pixel electrode of a liquid crystal display panel.
A plurality of such thin film transistors are arranged by the matrix layout on the transparent substrate
1
together with the pixel electrode
13
, and respectively applies, to the pixel electrode, the image data supplied to the drain electrode
10
d
, responding to the scanning control signal applied to the gate electrode
2
.
In the polycrystalline silicon film
5
, it is preferable that the crystal grain diameter thereof be formed of a sufficient size so that the polycrystalline silicon film
5
may function as the active region of a thin film transistor. As a method to form polycrystalline silicon film
5
crystals of sufficiently large grain diameter, laser annealing methods using an excimer laser is well known. In laser annealing, silicon in an amorphous state is deposited on a silicon oxide film
4
to be the gate insulating film, and the silicon is irradiated with the excimer laser so that at one point it melts to consequently crystallize the silicon. When such a laser annealing method is used, it is unnecessary to raise the temperature of the transparent substrate
1
, so that a glass substrate with a low melting point can be adopted as the transparent substrate
1
.
Polycrystalline silicon films
5
crystallized by laser annealing typically include many crystal defects. As electrons moving in the film may then easily be captured, it is not preferable that such a polycrystalline silicon film
5
be made to be the active region of a transistor. Therefore, on the once formed polycrystalline silicon film
5
, an insulating film including many of hydrogen ions (hydrogen atoms) is formed, and, by performing the annealing together with that insulating film in the atmosphere of nitrogen, the crystal defects are filled with hydrogen ions (hydrogen atoms).
Silicon nitride film is a well known insulating film including many hydrogen ions and a source of hydrogen ions for the polycrystalline silicon film
5
. As shown in
FIG. 1
, it is often disposed that an interlayer insulating film comprises a silicon nitride film
8
. However, as the stopper
6
used as a mask during the doping of ions is disposed on the channel region
5
c
of the polycrystalline silicon film
5
, a problem is created that it is difficult for the hydrogen ions supplied from the silicon nitride film
8
to reach the channel region
5
c
. As for this stopper
6
, if the film thickness is made thinner so that the hydrogen ions may be permeable, the stopper
6
does not function as a mask during the doping of ions in some cases, and film thickness is, to some extent, necessary.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to optimize the film thickness of a stopper so that hydrogen ions may effectively be supplied to a semiconductor film from an interlayer insulating film, and so that the stopper may function as a mask during ion doping.
A thin film transistor of the present invention comprises a substrate; a gate electrode disposed on one main surface of said substrate; a gate insulating film deposited on said substrate so as to cover said gate electrode; a semiconductor film deposited on said gate insulating film so as to lie across said gate electrode; a stopper disposed on said semiconductor film so as to overlap with said gate electrode; and an interlayer insulating film deposited on said semiconductor film, wherein said stopper is made of a silicon oxide film with a film thickness of 800 angstroms to 1200 angstroms.
Furthermore, in said thin film transistor, said interlayer insulating film may comprise a silicon oxide film contacting said semiconductor film, and a silicon nitride film formed on the silicon oxide film.
Moreover, the total film thickness of said stopper and said silicon oxide film may be set so as to be a value equal or less than the square root of the value determined by multiplying the film thickness of said silicon nitride by 8000 angstroms.
More preferably, the total film thickness of said stopper and said silicon oxide film may be set so as to be a value equal or less than the square root of the value determined by multiplying the film thickness of said silicon nitride by 4000 angstroms.
Furthermore, another aspect of the present invention is a manufacturing method of a thin film transistor, comprising a first step of forming a refractory metal film on one main surface of a substrate and of forming gate electrode by etching this refractory metal film into a specified pattern; a second step of depositing a gate insulating film on said substrate so as to cover said gate electrode and of depositing a semiconductor film on this gate insulating film; a third step of forming an insulating layer with a predetermined film thickness on said semiconductor film and of forming a stopper by this insulating layer into a pattern corresponding to said gate electrode; a fourth step of depositing an interlayer insulating film on said semiconductor film so as to cover said stopper; and a fifth step of heating said semiconductor film and
Nakanishi Shiro
Oda Nobuhiko
Yamada Tsutomu
Yuda Shinji
Cantor & Colburn LLP
Sanyo Electric Co,. Ltd.
Toledo Fernando
LandOfFree
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