Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2002-10-08
2004-08-17
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S077000, C257S347000
Reexamination Certificate
active
06777713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having a circuit composed of thin film transistors (hereinafter, referred to as TFTs) and a method of manufacturing the semiconductor device. For example, the present invention relates to an electro-optical device typified by a liquid crystal display panel and an electronic equipment mounted with the electro-optical device as a component.
Note that the term semiconductor device in this specification indicates devices in general capable of functioning with the use of semiconductor characteristics, and electro-optical devices, semiconductor circuits and electronic equipment are all included in the category of the semiconductor device.
2. Description of the Related Art
In recent years, a technology of constituting a thin film transistor (TFT) by using a semiconductor thin film (with a thickness of approximately several to several hundred of nm) formed on a substrate having an insulating surface has attracted attention. The thin film transistor is widely applied to an electronic device such as an IC or an electro-optical device, and needs to be developed promptly as, in particular, a switching element of an image display device.
An active matrix liquid crystal module is known as a typical example of the thin film transistors. Particularly, a TFT having a silicon film having a crystalline structure (typically, polysilicon film) as an active layer (hereafter, referred to as polysilicon TFT) has high filed-effect mobility compare to a TFT having a silicon film having a amorphous structure (typically, amorphous silicon film), and thus such TFTs are multiused recently.
Although there are various technologies of obtaining the silicon film having crystalline structure, especially, a technology given in Japanese Unexamined Patent Publication No. Hei. 8-78329 official report, in which the metallic elements (typically nickel) promoting crystallization to an amorphous silicon film are added alternatively, thereby performing a heat treatment to form the crystalline silicon film which spreads with an addition region as the starting point. Since the size of the crystal grain obtained thereof is very large compared with other technologies, and the field effect mobility is high, various circuits equipped with various functions can be formed thereby. For example, in case of using the technology of the above-mentioned official report, to a liquid crystal module carried in a liquid crystal display device, drive circuits for controlling pixel portions, such as pixel portions which perform an image display for every functional block, a shift register circuit based on a CMOS circuit, a level shifter circuit, a buffer circuit, and a sampling circuit, and the like can form on one substrate.
Moreover, the above-mentioned official report technology can lower approximately 50-100° C. crystallization temperature of an amorphous silicon film by the action of metallic elements compared to a method without using metallic elements, thereby a glass substrate can be used without any problems occurring in process. Moreover, required time in the crystallization of the above-mentioned official report technology can be reduced to ⅕-{fraction (1/10)} compared to the method without using metallic elements, thereby the above-mentioned official report technology is also excellent in productivity.
SUMMARY OF THE INVENTION
A new further improvement is added to the technology of the above-mentioned official report, the manufacturing method of improving the film characteristic of a semiconductor film having a crystalline structure, and TFTs in which such a semiconductor film used as an active layer, excellent in the TFTs characteristics, such as the field effect mobility, are offered.
Considering the results of many experiments performed from a wide variety of fields in order to resolve the aforementioned various problems has lead to the present invention. When heat treatment is performed for crystallization, it is preferable to reduce the concentration of oxygen, which impedes crystallization, within a semiconductor film having an amorphous structure to which a metallic element is added for promoting crystallization, to a value as small as possible, specifically to less than 5×10
18
/cm
3
. It was discovered that the above problems can be resolved, in particular field effect mobility can be increased, by performing the introduction of oxygen into the film after performing heat treatment.
The oxygen concentration within the film may be set from 5×10
18
/cm
3
to 1×10
21
/cm
3
by irradiating laser light under an inert gas atmosphere, or in a vacuum, after oxidizing a surface of the semiconductor having a crystalline structure by using ozone water as a processing of introducing oxygen into the semiconductor film having a crystalline structure.
Alternatively, the oxygen concentration within the film may be set from 5×10
18
/cm
3
to 1×10
21
/cm
3
by irradiating laser light under an atmosphere containing oxygen or water molecules as another process of introducing oxygen into the semiconductor film having a crystalline structure.
In addition, the oxygen concentration within the film may be set from 5×10
18
/cm
3
to 1×10
21
/cm
3
by irradiating laser light under an inert gas atmosphere, or in a vacuum, after performing oxidation under an atmosphere containing oxygen or water molecules by using an electric furnace or the like. Further, the oxygen concentration within the film may be set from 5×10
18
/cm
3
to 1×10
21
/cm
3
by irradiating laser light under an inert gas atmosphere, or in a vacuum, after adding oxygen by ion doping or ion implantation so that the oxygen concentration within the semiconductor film becomes 5×10
18
/cm
3
to 1×10
21
/cm
3
. Furthermore, the semiconductor film is melted instantaneously from the surface, after which the melted semiconductor film is cooled and solidified from the substrate side because of thermal conduction to the substrate, for cases in which laser light is irradiated to the semiconductor film. Recrystallization takes place during the solidification process, and the semiconductor film becomes the one having a crystalline structure with a large grain size, but volumetric expansion develops due to the temporary melting, and unevenness referred to as ridges forms in the semiconductor surface. In particular, the surface on which the ridges form becomes an interface with a gate insulating film for top gate TFTs, and therefore the element characteristics vary greatly. In addition to the above processes, the oxide film on the semiconductor film surface is removed after laser light irradiation according to the present invention, and in addition, laser light is then irradiated under an inert gas atmosphere, or in a vacuum to level the surface of the semiconductor film having a crystalline structure.
Note that, differing from a technique for performing crystallization of the film having an amorphous structure by a first laser light and leveling by using a second laser light (JP 2001-60551 A), the present invention concerns irradiating the first laser light to the semiconductor film having a crystalline structure. Further, the present invention is the one in which a metallic element for promoting crystallization is added, a semiconductor film having a crystalline structure is formed, and levelness is additionally increased by the addition of the metallic element.
A first aspect of the present invention disclosed by this specification relates to a method of manufacturing a semiconductor device, including:
a first step of forming a semiconductor film having an amorphous structure on an insulating surface;
a second step of adding a metallic element to the semiconductor film having an amorphous structure;
a third step of heat-treating the semiconductor film having an amorphous structure to form a semiconductor film having a crystalline structure, and then removing an oxide film from the crystalline semiconductor film surf
Makita Naoki
Matsuo Takuya
Miyairi Hidekazu
Nomura Katsumi
Shiga Aiko
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