Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Reexamination Certificate
1999-01-08
2004-02-17
Norton, Nadine G. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C438S750000, C438S751000, C438S754000, C257S040000, C257S066000
Reexamination Certificate
active
06693044
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor thin formed on a substrate having an insulating surface and a semiconductor device using the semiconductor thin film as an active layer. Particularly, the present invention relates to a semiconductor thin film in which an amorphous semiconductor thin film containing silicon as its main ingredient is crystallized to obtain a thin film.
Moreover, the present invention relates to the structure of a semiconductor circuit and an electro-optical device, which are constituted by a semiconductor device such as a thin film transistor, and to the structure of an electronic apparatus incorporating those.
Incidentally, in the present specification, all of the thin film transistor, semiconductor circuit, electro-optical device, and electronic apparatus are contained in the category of “semiconductor device”. That is, any device capable of functioning by using semiconductor properties is called a semiconductor device. Thus, the term “semiconductor device” included in the present invention includes not only a single element such as a thin film transistor but also a semiconductor circuit obtained by integrating the single elements, an electro-optical device, and an electronic apparatus incorporating those as parts.
2. Description of the Related Art
In recent years, attention has been paid to a technique for constituting a thin film transistor (TFT) by using a semiconductor thin film (its thickness is several tens to several hundreds nm) formed on a substrate having an insulating surface. Particularly, development of the thin film transistor as a switching element of an image display device (for example, a liquid crystal display device) has been hastened.
For example, in a liquid crystal display device, trials have been made to apply TFTs to any electric circuit, such as a pixel matrix circuit for controlling each of pixel regions arranged in matrix, a driving circuit for controlling the pixel matrix circuit, and a logic circuit (arithmetic circuit, memory circuit, clock generator, etc.) for processing data signals from the outside.
In the present circumstances, although a TFT using a noncrystalline silicon film (amorphous silicon film ) as an active layer is put to practical use, a TFT using a crystalline silicon film (polysilicon film, etc.) is necessary for an electric circuit, such as a driving circuit or a logic circuit, required to have higher speed operation performance.
Conventionally, a crystalline silicon film is obtained in such a manner that heat treatment, irradiation of laser light, or irradiation of intense light is carried out after an amorphous silicon film is formed on a substrate having an insulating surface or an under film having an insulating surface by a plasma CVD method or a low pressure CVD method.
Among the above conventional methods of obtaining a crystalline silicon film, the quality of a film obtained by the method of irradiation of laser light is excellent as compared with other methods, and the method has a high throughput and has a merit that thermal damage is not caused to a substrate, so that the method is often used.
However, according to the method of irradiation of laser light, if the thickness of an amorphous silicon film is 100 nm or less, many ridges (asperities) are formed on the surface of the obtained crystalline silicon film so that the film quality is degraded. That is, when a silicon film is irradiated with laser light, the silicon film is instantaneously melted and is locally expanded, and ridges (asperities) are formed on the surface of the obtained crystalline silicon film to relieve the inner stress generated by this expansion. The difference in the height of the ridge is about ½ to 1 time the thickness of the film.
In an insulated gate semiconductor device, since a potential barrier or a trap level caused by a dangling bond, distortion of a lattice, or the like are formed in the ridge on the surface of the crystalline silicon film, an interfacial level between an active layer and a gate insulating film is raised. Further, since the top portion of the ridge is steep, an electric field is apt to be concentrated, so that the ridge becomes a generating source of leak current, and finally, breakdown occurs and a short circuit is brought about. In addition, the ridge on the surface of the crystalline silicon film damages the covering properties of the gate insulating film deposited by a sputtering method or a CVD method, and causes poor insulation or the like to degrade the reliability. Thus, the ridge on the surface of the crystalline silicon film influences all the characteristics of a TFT and even a yield is changed.
Moreover, the method of irradiation of laser light is apt to become unstable particularly under a condition to obtain excellent crystallinity, and if the energy density of laser light is increased to make sufficient crystallization, there is a tendency that ridges are increased and the surface of a film becomes rough.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above problems and to provide a semiconductor device which has high characteristics and uses a crystalline silicon film having high crystallinity and having a flat surface with few ridges (asperities), and a method of manufacturing the same.
According to a first aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising the steps of: forming a first amorphous silicon film on an insulating surface; obtaining a first crystalline silicon film by carrying out a heat treatment to crystallize the first amorphous silicon film; forming a second amorphous silicon film on the first crystalline silicon film; and obtaining a second crystalline silicon film by applying an energy to crystallize the second amorphous silicon film.
According to a second aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising the steps of: forming a first amorphous silicon film on an insulating surface; obtaining a first crystalline silicon film by carrying out a heat treatment to crystallize the first amorphous silicon film; etching a surface of the first crystalline silicon film; forming a second amorphous silicon film on the first crystalline silicon film; and obtaining a second crystalline silicon film by applying an energy to crystallize the second amorphous silicon film.
In the second aspect of the present invention, an etchant containing hydrofluoric acid is used as an etchant in the etching step.
According to a third aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising the steps of: forming a first amorphous silicon film on an insulating surface; introducing a metal element for facilitating crystallization of silicon into the first amorphous silicon film; obtaining a first crystalline silicon film by carrying out a heat treatment to crystallize the first amorphous silicon film; forming a second amorphous silicon film on the first crystalline silicon film; and obtaining a second crystalline silicon film by applying an energy to crystallize the second amorphous silicon film.
In the third aspect of the present invention, it is characterized in that one kind of or plural kinds of elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au are used as a metal element for facilitating crystallization of silicon.
Moreover, in the third aspect of the present invention, it is preferable to use nickel as the metal element for facilitating crystallization of silicon.
Moreover, in each of the above aspects of the present invention, crystallization of the second amorphous silicon film is carried out by using the surface of the first crystalline silicon film as nuclei of crystal growth.
Moreover, in each of the above aspects, it is characterized in that, as a method of applying the energy, a method of irradiation of laser light is used. Moreover, as a method of applyin
Hayakawa Masahiko
Yamazaki Shunpei
Norton Nadine G.
Semiconductor Energy Laboratory Co,. Ltd.
Vinh Lan
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