Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reissue Patent
2001-04-20
2003-10-07
Lebentritt, Michael S. (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S156000, C438S162000, C438S166000
Reissue Patent
active
RE038266
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a silicon semiconductor thin film which has a crystallinity and is formed on a substrate having an insulation surface of a glass substrate or the like.
2. Description of the Related Art
In recent years, attention is paid on a technology for constructing a thin film transistor by using a silicon thin film which is formed on a glass substrate. This thin film transistor is primarily used in an active matrix type liquid crystal electro-optical device and other thin film integrated circuits. The liquid crystal electro-optical device changes optical characteristics of a liquid crystal thereby displaying an image by charging a liquid crystal into a pair of glass substrates and applying an electric field.
In particular, the active matrix type liquid crystal display device using a thin film transistor is characterized in that the thin film transistor is arranged in each pixel, an electric charge held in a pixel electrode is controlled by using the thin film transistor as a switch. Since the active matrix type liquid crystal display device is capable of displaying a fine image at a high speed, the device can be used in displays for various electronic apparatuses (for example, a portable word processor, and a portable computer or the like).
As a thin film transistor used in the active matrix type liquid crystal display device, an amorphous silicon thin film is commonly used. However, the thin film transistor using the amorphous silicon thin film has the following problems.
(1) The liquid crystal thin film transistor has low characteristics and cannot display a higher quality image.
(2) The liquid crystal thin film transistor cannot constitute a peripheral circuit for driving a thin film transistor arranged on a pixel.
The aforementioned second problem can be considered by dividing the problem into the following two aspects. One aspect of the problem is that since a P-channel type thin film transistor cannot be used for practical purposes with the thin film transistor using an amorphous silicon thin film, a CMOS circuit cannot be constituted. Another aspect of the problem is that since the thin film transistor using an amorphous silicon thin film cannot be operated at a high speed, and a large current cannot flow in the thin film transistor, a peripheral driving circuit cannot be assembled.
Means for solving the aforementioned problems include a technology for forming a thin film transistor by using a crystalline silicon thin film. The methods for obtaining a crystalline thin film include a method for heat treating an amorphous silicon film and a method for irradiating the amorphous silicon thin film with laser light.
SUMMARY OF THE INVENTION
However, a method for crystallizing am amorphous silicon film by heat treatment in the prior art has the following problem.
In the case where a thin film transistor is constituted which is used in a liquid crystal electro-optical apparatus, it is demanded that the thin film transistor is formed on a translucent substrate. Examples of the translucent substrate include a quartz substrate and a glass substrate. However, the quartz substrate is expensive and cannot be used in the liquid crystal electro-optical device which has a large technological problem of a cost reduction. Consequently, the glass substrate is commonly used. However, it has a problem of a low heat resistance.
Generally, as the glass substrate used in the liquid crystal electro-optical device, Corning 7059 glass substrate is used. The strain point of this glass substrate is 593° C. When the substrate is heat treated at this temperature or more, the shrinkage or the deformation of the substrate becomes conspicuous. In recent years, the liquid crystal electro-optical device tends to have a larger area and the shrinkage and the deformation of the substrate must be suppressed as much as possible.
However, it has been proved in the experiment that a temperature of 600° C. or more is required to crystallize the amorphous silicon film by heating. It is also made clear that tens of hours are required for heating. A large area glass substrate cannot be subjected to such high temperature and long hour heating at all.
Further, a technology of crystallizing the amorphous silicon film by laser light irradiation is also known. However, it is difficult as a practical problem to irradiate uniformly a large area with laser light and to irradiate the area while keeping a definite level of irradiation power.
An object of the present invention is to solve the aforementioned problems and to provide a technology of transforming the amorphous silicon film into a crystalline silicon film by heat treatment at an extremely low temperature.
In particular, an object of the invention is to provide a crystalline silicon thin film which is capable of constituting a thin film transistor with a high performance characteristics.
In accordance with a major aspect of the present invention, there is provided a method for fabricating a semiconductor thin film comprising the steps of:
introducing into an amorphous silicon film a metal element which promotes the crystallization of silicon;
obtaining a crystalline silicon film by crystallizing the aforementioned amorphous silicon film by heat treatment;
forming a metal element diffusion film on said crystalline silicon film;
diffusing the aforementioned metal element into the aforementioned metal element diffusion film; and
removing the metal element diffusion film into which the metal element has been diffused.
In the aforementioned structure, examples of the amorphous silicon film include a film which is formed by the plasma CVD or by the low pressure thermal CVD on a glass substrate or on a glass substrate on which an insulating film is formed.
Further, examples of the metal element which promotes the crystallization of the aforementioned silicon include one or more kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au. Among these metal elements, the most effective metal element is nickel (Ni).
Methods for introducing the metal element which promotes the crystallization of the aforementioned silicon include a method for providing these metal layers or a layer including the metal on the surface of the amorphous silicon film. Specifically, the methods include a method for forming a metal element layer or a layer including a metal element by the CVD, the sputtering process, vapor deposition or the like, and a method for coating a solution containing a metal element on the amorphous silicon film. In particular, since the latter method using the latter solution enables easily controlling a density of the metal element, the latter method is more favorable than the former method. In addition, since the metal element can be held uniformly in contact with the surface of the amorphous silicon film in the latter method, the latter method is very favorable in this respect, too. For reference, when the aforementioned CVD and the sputtering process, vapor deposition or the like is used, it is difficult to form an extremely thin uniform film. Consequently, there is a problem in that the metal element is non-uniformly present on the amorphous silicon film, and the metal element is liable to be deviated at the time of the crystal growth.
To crystallize by heating the silicon film to which the metal element promoting the crystallization of silicon is introduced, the silicon film may be heated at a temperature of 450° C. or more. The upper limit of this heating temperature is limited by the heat-resistant temperature of the glass substrate used as the substrate. In the case of the glass substrate, the heat resistant temperature can be regarded as the strain point of glass. When materials such as quartz substrate or the like which can endure a temperature of 1000° C. or more, the heating temperature in heating can be heightened in accordance with the heat insulating temperature.
As one example of heat treatment, it is appropriate to set the temperature to about
Miyanaga Akiharu
Ohtani Hisashi
Teramoto Satoshi
Yamazaki Shunpei
Lebentritt Michael S.
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Method for fabricating semiconductor thin film 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 for fabricating semiconductor thin film, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for fabricating semiconductor thin film will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3163594