Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1999-11-15
2003-06-17
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S150000, C438S151000
Reexamination Certificate
active
06579749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fabrication method for fabricating a semiconductor device such as a thin film transistor and a fabrication apparatus therefor. Particularly, the present invention relates to a fabrication method for fabricating a thin film transistor for use in an active matrix type liquid crystal display and an apparatus for realizing the same method.
2. Description of the Related Art
Recently, the research and development of the thin film transistor used as a driving device for each of pixels of a liquid crystal flat panel display has been promoted remarkably. With the popularization of the note type personal computer, the demand of liquid crystal display is increased rapidly and, further, with the increased demand of the same for a large size monitor display, the improvement of productivity thereof and the improvement of performance thereof have been required.
The productivity of liquid crystal display depends upon the fabrication step of a thin film transistor substrate and one of important factors which determine the performance of high precision liquid crystal display is the performance of thin film transistor element. Therefore, it will become very important to fabricate a high performance thin film transistor with high productivity.
In the reverse-staggered type thin film transistor, a non-doped amorphous silicon is used as an active layer. An n-type amorphous silicon film is formed on the amorphous silicon film as an ohmic contact layer, and source and drain electrodes are provided thereon. In the conventional fabrication method of reverse-staggered type thin film transistor, the n-type amorphous silicon film is formed by using plasma CVD, mainly. For example, Japanese Patent Application Laid-open Nos. Hei 5-304171, Hei 9-223800 and Hei 10-12882 disclose method for fabricating the n-type amorphous silicon film by using plasma CVD.
The method disclosed in Japanese Patent Application Laid-open No. Hei 5-304171 will be described briefly as a general method of reverse-staggered type thin film transistor.
First, a metal film is formed on a transparent insulating substrate
1
and a gate electrode is formed by patterning the metal film to a desired shape. Thereafter, a silicon nitride film as a gate insulating film, an amorphous silicon film and an n-type amorphous silicon film are formed on the gate electrode in the order by plasma CVD, etc.
Then, the n-type amorphous silicon film and the amorphous silicon film are patterned to an island configuration. Further, after a metal film is formed on a whole surface of the wafer, the source and drain electrodes are formed by patterning the metal film.
Finally, unnecessary portion of the n-type amorphous silicon film on a channel is removed by etching, resulting in a reverse-staggered type thin film transistor.
In order to fabricate the thin film transistor with high yield, it is preferable to make the number of film forming steps as small as possible. If it is possible to fabricate a thin film transistor without separately forming the n-type amorphous silicon film, it becomes possible to improve the yield and reduce the fabrication cost.
A method for fabricating a reverse-staggered thin film transistor without separately forming an n-type amorphous silicon film is disclosed in Japanese Patent Application Laid-open No. Hei 2-163971. According to the disclosed method, the formation of the n-type amorphous silicon film becomes unnecessary by using a metal containing nickel phosphide for source and drain electrodes. Furthermore, the metal for the source and drain electrodes are formed by sputtering with using nickel phosphide and another metal or a mixture of them as a target material. It is described in the specification of Japanese Patent Application Laid-open No. Hei 2-163971 that measurements of characteristics of a thin film transistor fabricated according to the disclosed method is substantially the same as those of a thin film transistor having an n-type amorphous silicon film formed separately.
A method for continuously forming an amorphous silicon film, a gate insulating film and an aluminum film for forming a gate wiring on a substrate in vacuum is disclosed in Japanese Patent Application Laid-open No. Hei 9-331067.
However, according to the method disclosed in Japanese Patent Application Laid-open No. Hei 2-163971, a new problem that a resistance value of the source and drain electrodes is increased since phosphor is contained in the source and drain electrodes as an impurity.
Particularly, this problem becomes a source of signal delay in realizing a large size liquid crystal display and influences a displayed image adversely.
Further, according to the method disclosed in Japanese Patent Application Laid-open No. Hei 9-331067, in which the amorphous silicon film is formed as the lowest layer, it is necessary, in order to make the amorphous silicon film n type, to inject phosphor ions into the amorphous silicon film first. Therefore, it is very difficult to avoid the necessity of separately forming the n-type amorphous silicon film.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for fabricating a thin film transistor having the source and drain electrodes free from phosphor impurity, without necessity of separately forming an n-type amorphous silicon film, and an apparatus for performing the same method.
According to the first aspect of the present invention, the object can be achieved by a method for fabricating a semiconductor device such as a thin film transistor, which comprises the first step of forming an amorphous silicon film on a substrate, the second step of performing a plasma processing with respect to a substrate having the amorphous silicon film formed thereon and the third step of forming a metal film on the amorphous silicon film while keeping the reduced pressure condition. The plasma processing contains an n-type impurity element selected from a group V of a periodic table to provide an n-type region in the top surface of the amorphous silicon film. For example, a phosphine plasma processing is performed under a reduced pressure condition.
According to this method, an impurity element of the group V such as a phosphor is either deposited on a surface of the amorphous silicon film or diffused into the surface thereof in the second step. Thereafter, when the metal film is formed in the third step, the phosphor further diffuses into a surface portion of the amorphous silicon film, so that an n-type amorphous silicon film is automatically formed between the metal film and the amorphous silicon film. That is, according to the present method, the metal film for forming the source and drain electrodes is free from the above mentioned impurity such as the phosphor impurity and it is unnecessary to form an n-type amorphous silicon film separately.
According to the second aspect of the present invention, the object can be achieved by a method for fabricating a semiconductor device, which comprises the first step of forming an amorphous silicon film on a substrate under a reduced pressure condition, the second step of performing a phosphine plasma processing with respect to the substrate without exposing the substrate to an oxidizing atmosphere and the third step of forming a metal film on the amorphous silicon film. Preferably, at least two adjacent steps are successively performed without exposing the substrate to the oxidizing atmosphere.
According to this semiconductor fabricating method, it is possible to obtain a similar effect to that obtained by the thin film transistor fabrication method mentioned previously. Especially, a cleaner interface can be achieved by performing each process without exposing the substrate to the oxidizing atmosphere.
According to the third aspect of the present invention, the object can be achieved by a method for fabricating a semiconductor device, which comprises the first step of forming an insulating film and an amorphous silicon film covering a gate electrode formed on a s
Jr. Carl Whitehead
NEC Corporation
Schillinger Laura M
Scully Scott Murphy & Presser
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