Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-02-13
2003-03-25
Cao, Phat X. (Department: 2814)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S770000
Reexamination Certificate
active
06537911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Chemical Vapor Deposition (hereinafter referred to as CVD) method. More particularly, the present invention relates to a CVD method suited to mass production of oxide films having favorable characteristics, especially suited to mass production of oxide films for gate and having favorable characteristics.
2. Description of the Related Art
As a manufacturing method of liquid crystal display, a method of using high temperature polysilicon TFT (thin film transistor) and a method of using low temperature polysilicon TFT have been known. In the manufacturing method of using high temperature polysilicon TFT, in order to obtain a silicon oxide film of high quality, a quartz substrate which can be fit for a high temperature exceeding 1000° C. is used. By contrast, in manufacture of low temperature polysilicon TFT, an ordinary glass substrate for TFT is used, so that it is necessary to form a film at low temperature (for example, 400° C.). The manufacturing method of liquid crystal display by using low temperature polysilicon TFT has an advantage that its manufacturing cost is small, since it dose not require any special substrate. So that, it is hence widely employed recently, and its production is expanding.
In manufacturing of liquid crystal display by using low temperature polysilicon TFT, and forming a silicon oxide film appropriate as gate insulating film at low temperature, plasma enhanced CVD is used.
When forming a silicon oxide film by the plasma enhanced CVD, silane or tetraethoxy silane (TEOS), etc. are used as representative material gas. The material gas is generally used in a state of adding carrier gas such as helium (He), etc., and hereinafter it is merely referred to as the material gas.
When forming a silicon oxide film by plasma enhanced CVD, using silane or the like as material gas, in a conventional plasma enhanced CVD system, the material gas and oxygen are introduced in the front space of the substrate, and then, plasma is produced by mixed gas of material gas and oxygen, and the substrate is exposed to the plasma, thereby a silicon oxide film is formed on the surface of the substrate. In such a conventional plasma enhanced CVD system, the material gas is directly supplied into the plasma produced in the plasma enhanced CVD system. Accordingly, in the conventional plasma enhanced CVD system, ions of high energy are injected from the plasma exiting in the front space of the substrate to the film forming surface of the substrate, and the silicon oxide film is damaged, so that, film propertied are impaired. Further, since the material gas is directly introduced into the plasma, the material gas and plasma react violently with each other to generate particles, thereby lowering the yield.
To solve the problems, in the previous Japanese Patent Application (unexamined Japanese Patent Publication No. JP P2000-345349A), it has been attempted to improve the conventional plasma enhanced CVD system, and a new CVAD system was proposed.
The CVD system proposed in JP P2000-345349A is a system for producing plasma in vacuum container to generate neutral exciting radicals, that is to say to generate exciting radicals, and forming a film on the substrate by the said exciting radicals and materials gas. A conductive partition wall is disposed in the inside of the vacuum container of the said CVD system. Thereby, the inside of the vacuum container is separated by the conductive partition wall into two compartments. One of these two compartments is formed as a plasma generating space containing high frequency electrode, and the other is formed as a film forming space with a substrate holding mechanism for mounting substrate. The conductive partition wall has plural penetration holes for communicating between the plasma generating space and film forming space, and also has an inner space separated from the plasma generating space and communicating with the film forming space through plural diffusion holes.
In a CVD method conducted by a CVD system proposed in JP P2000-345349A, the material gas is supplied from outside into the inner space of the conductive partition wall, and is introduced into the film forming space through the plural diffusion holes. On the other hand, exciting radicals formed in the plasma generating space are introduced into the film forming space only through the plural penetration holes opened in the conductive partition wall. And, in the film forming space, a film is formed on the substrate by the exciting radicals and materials gas introduced into the film forming space as the before described.
In the CVD system proposed in this JP P2000-345349A, concerning the size (length and diameter) and structure of the penetration holes and diffusion holes, the penetration holes are defined in the size length and diameter) and structure so that the material gas introduced in the film forming space may not diffuse reversely into the plasma generating space, and the diffusion holes are defined in the size (length and diameter) and structure so that the exciting radicals introduced in the film forming space may not diffuse reversely into the inner space of the conductive partition wall.
That is, in the CVD system proposed in JP P2000-345349A, the condition of uL/D>1 is satisfied, where u is the gas flow velocity in penetration holes, L is the substantial length of penetration holes (see
FIG. 3
, in this case, L is the length of the portion of the minimum diameter), and D is the binary diffusivity (mutual gas diffusion coefficient of two types of gases of material gas and process gas, for example, silane gas and oxygen gas). Concerning with the diffusion holes, too, the same condition as in the penetration holes is applied.
By the CVD system proposed in JP P2000-345349A, worsening of film properties of silicon oxide film formed on the glass substrate can be prevented, and the product yield can be improved.
Generally, silicon oxide film formed on a substrate by using exciting radicals, which are produced by generating plasma in a vacuum container, and material gas contains OH, hydrogen atom, or excessive silicon in the thin film (silicon oxide film) or in the lower interface of the thin film (silicon oxide film). The said OH, hydrogen atom, etc. may deteriorate the characteristics of silicon oxide film, which are required as insulating film. For example, the said deterioration of characteristics may include any increase of leak current, and hysteresis in capacitance-voltage curve.
SUMMARY OF THE INVENTION
It is hence an object of the present invention in manufacture of large-sized liquid crystal display using low temperature polysilicon TFT, to provide a CVD method capable of improving the film properties by using the CVD system newly proposed in JP P2000-345349A, which has successively prevented reverse diffusion of material gas into the plasma forming region, in the case of forming silicon oxide film on a substrate of a large area by using material gas such as silane, on the basis of the CVD making use of plasma.
To achieve the object, the present invention provides the following CVD method.
That is, the CVD method according to an aspect of the present invention is a CVD method for generating plasma in a vacuum container to produce exciting radicals, and forming a film on a substrate by the said exciting radicals and material gas. The CVD system to which this method is applied is composed as follows. That is, the inside of the vacuum container of the CVD system is separated into two compartments by a conductive partition wall, and one of the two separated compartments is formed as a plasma generating space containing a high frequency electrode, and the other compartment is formed as a film forming space containing a substrate holding mechanism for mounting substrates. The conductive partition wall has plural penetration holes for communicating between the plasma generating space and film forming space. And the conductive partition wall also has an inner space separated from the pla
Ko Sang-Tae
Yuda Katsuhisa
Anelva Corporation
Cao Phat X.
Le Thao X.
Wenderoth , Lind & Ponack, L.L.P.
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