Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – By reaction with substrate
Reexamination Certificate
2002-08-15
2004-04-06
Nhu, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
By reaction with substrate
C438S197000, C438S510000
Reexamination Certificate
active
06716768
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a thin-film transistor and a liquid crystal display.
BACKGROUND ART
A thin-film transistor (TFT) in a liquid crystal display is composed of a silicon film and other films that are formed on an insulating substrate such as a glass substrate, and used as a switching element provided for a pixel of the liquid crystal display or a driver element in a peripheral circuit. As a silicon film for a TFT, an amorphous silicon film is used in many cases. In recent years, however, a polycrystalline silicon (hereinafter also referred to as simply “polysilicon”) film that has higher characteristics has been used, and now is being developed increasingly.
Hereinafter, as an example of a conventional method of manufacturing a thin-film transistor, a method of manufacturing a top gate polysilicon TFT will be explained with reference to FIG.
6
. The below mentioned method includes steps up to a step of depositing a gate insulating film.
First, an amorphous silicon film is deposited on the entire surface of a substrate
31
, followed by crystallization to make the amorphous silicon film into a polysilicon film
32
(FIG.
6
(
a
)). Then, the polysilicon film
32
is subjected to patterning into a predetermined island pattern so as to be formed into a semiconductor layer of a transistor. This patterning generally is carried out as follows. First, a photoresist is coated on the polysilicon film
32
and dried, followed by exposure and development to form a predetermined resist pattern
34
(FIG.
6
(
b
)). Next, the polysilicon film
32
is etched partially away by using the resist pattern
34
as a mask (FIG.
6
(
c
)). Thereafter, the resist pattern
34
is removed by, for example, immersing it in a peeling solution (FIG.
6
(
d
)). A SiO
2
film
35
as a gate insulating film is deposited so that it covers the thus obtained polysilicon film
32
with a predetermined pattern (FIG.
6
(
e
)).
Furthermore, in the method of manufacturing the polysilicon TFT, a process in which impurities directly are implanted into the polysilicon film may be used. A conventional example of this process will be explained with reference to FIG.
7
.
As in the above-mentioned conventional example, a polysilicon film
32
is formed in an island form on a substrate
31
(FIG.
7
(
a
)). Impurities such as phosphorus (P) are implanted selectively into predetermined regions on the polysilicon film. First, a photoresist is coated on the polysilicon film
32
and dried, followed by exposure and development to form a resist pattern
34
on a region into which impurities are not implanted (a region to be formed into a channel) (FIG.
7
(
b
)). Next, impurity ions
38
, for example, P ions etc. are implanted into the polysilicon film
32
by using the resist pattern
34
as a mask so as to form a region into which impurities are implanted (regions to be formed in source and drain regions)
37
(FIG.
7
(
c
)). Thereafter, the resist pattern
34
is removed, by, for example, immersing it in a peeling solution (FIG.
7
(
d
)). A SiO
2
film
35
as a gate insulating film is deposited so that it covers the thus obtained polysilicon film
32
(FIG.
7
(
e
)).
When a polysilicon TFT is formed in the method shown in
FIGS. 6 and 7
, polysilicon inevitably is exposed to the peeling solution in a step of peeling off the resist, and the surface of polysilicon may be chemically deteriorated or may be etched slightly due to alkaline components in the peeling solution. Furthermore, a subsequent step may proceed with the peeling solution or components of the resist remaining on the surface of the polysilicon. As a result, there arises a problem in that deterioration of the TFT properties, for example, a shortage of ON-state current, variation of threshold voltage, may be caused. In particular, it is desired that a thin-film transistor used for a liquid crystal display secures the reliability of products by suppressing the above-mentioned deterioration of a TFT over the entire region of a large-sized substrate.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide a method of manufacturing a thin-film transistor excellent in characteristics and reliability and also to provide a liquid crystal display manufactured by using this method.
The method of manufacturing a thin-film transistor of the present invention includes: bringing a surface of a semiconductor film formed on a substrate into contact with ozone-containing water to form a surface-oxidized layer on the surface, forming a predetermined pattern mask on the semiconductor film directly or via another film, carrying out either of processes selected from etching and impurity ion implantation by using the mask, and removing the mask with the surface-oxidized layer being formed at least on an exposed portion of the surface of the semiconductor film.
With the manufacturing method of the present invention, since the surface-oxidized layer is formed, the semiconductor film is not exposed directly to the peeling solution. Therefore, it is possible to suppress the deterioration or erosion of the semiconductor film. It also is possible to suppress the components of the mask or the peeling solution from remaining on the semiconductor film. Furthermore, since the manufacturing method of the present invention uses the ozone-containing water, it is possible to oxidize the surface of the semiconductor film rapidly and uniformly. Therefore, the manufacturing method using ozone-containing water of the present invention is particularly suitable for manufacturing a liquid crystal display including a large-sized substrate.
In the above-mentioned manufacturing method, the surface-oxidized layer may remain. However, it is preferable that the above-mentioned method further includes removing the surface-oxidized layer after the mask is removed. This is because even if contaminants such as the above-mentioned components remain on the surface-oxidized layer, the contaminants can be removed together with the surface-oxidized layer.
The above-mentioned manufacturing method further may include removing a surface layer of the semiconductor film before the surface-oxidized layer is formed. If contaminants are removed in advance, the surface of the semiconductor film further can be kept clean.
The thickness of the surface-oxidized layer is suitably in the range from 0.5 nm to 5 nm, and particularly suitably in the range from 1 nm to 5 nm. When this thickness is too thin, the effect of protecting the surface cannot be obtained sufficiently. On the other hand, when the film thickness of the surface-oxidized layer is too thick, although the effect of protecting the surface of the semiconductor film can still be obtained, there may arise a problem in that the other exposed surface such as a glass surface, may be etched in the step of removing the surface-oxidized layer.
As a pattern mask, a photoresist is used in many cases. In this case, for removing the photoresist, an alkaline peeling solution may be used.
As the semiconductor film, in general, at least one selected from a polycrystalline silicon film and an amorphous silicon film is used. However, when the present invention is used particularly for a polysilicon film, a greater effect can be obtained. This is because the polysilicon film is more excellent in the electric property than an amorphous silicon film, but it is susceptible to the surface contamination.
The typical step in which the present invention preferably is used is a process (etching or impurity ions implantation) of a semiconductor film with a mask. However, the present invention is not necessarily limited to these and similarly can be used for any other step when the step requires removing a mask with the surface of a semiconductor film exposed. For example, in the step in which a mask with a predetermined pattern is formed on a semiconductor film via at least one insulating film and the insulating film is etched by the use of this mask, the surface of the semiconductor film is exposed by
Merchant & Gould P. C.
Nhu David
LandOfFree
Method of manufacturing thin-film transistor, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing thin-film transistor, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing thin-film transistor, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3257811