Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-03-25
2004-11-02
Dang, Phuc T. (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S149000
Reexamination Certificate
active
06812081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a circuit comprising a thin film transistor (hereinafter referred to as a TFT), for example, an electro-optical device represented by a liquid crystal display panel and an electronic device in which such an electro-optical device is mounted as parts.
Note that in this specification, a semiconductor device indicates a general device functioning by utilizing semiconductor characteristics, that is, an electro-optical device, a semiconductor device, and an electronic device each are a semiconductor device.
2. Description of the Related Art
In recent years, a technique of structuring a thin film transistor (TFT) using a semiconductor thin film (about several to several hundred nm in thickness) formed on a substrate having an insulating surface is drawing attention. The thin film transistor is widely applied to an electronic device such as an IC or an electro-optical device. In particular, the development for a switching element of an image display device is being advanced.
A material of a crystalline semiconductor film suitably used for the TFT is silicon. A silicon film having a crystalline structure (hereinafter referred to as a crystalline silicon film) is generally formed through the following process. That is, an amorphous silicon film is deposited on a substrate made of glass. quartz. or the like by a plasma CVD method or a low pressure CVD method and then crystallized by heating treatment or laser light irradiation (hereinafter referred to as laser processing in this specification) to obtain the crystalline silicon film.
However, in the case of the crystalline silicon film produced by the above conventional method. the crystal orientation planes are present randomly and an orientation ratio with respect to a specific crystal orientation is low. When the orientation ratio is low, it is almost impossible to keep continuity of lattices because of a grain boundary produced by collision of crystals with different orientations. Thus, it can be estimated that a large number of dangling bonds are produced. Dangling bonds which can be produced in the grain boundary become trapping centers of carriers (electron and hole) to reduce transporting characteristics. That is, since the carriers are scattered or trapped, even when a TFT is manufactured using such a crystalline semiconductor film, a TFT having high field effect mobility cannot be expected.
Also, a large number of distortions, defects and the like are present in a silicon film having a crystalline structure, that is, in a polysilicon film. They function as traps of carriers to deteriorate electrical characteristics. Thus, even in the channel forming region of the TFT, an existence configuration of a distortion, a volume of a lattice defect, and the like become large factors for causing a variation in characteristic.
SUMMARY OF THE INVENTION
An object of the present invention is to provide means for solving such problems. That is, an object of the present invention is to increase an orientation ratio of a crystalline semiconductor film obtained by crystallizing an amorphous semiconductor film and to suppress a distortion thereof so that a TFT using such a crystalline semiconductor film is provided.
The present invention is characterized in that at the time of formation of the amorphous semiconductor film or after the formation thereof, a noble gas, typically, argon is included in the semiconductor film and crystallization is performed therefor, and thus an orientation ratio of the film can be increased and a distortion present in the semiconductor film after the crystallization is suppressed as compared with that present in the semiconductor film before the crystallization.
Also, the crystallization of the present invention is characterized in that a metallic element for promoting crystallization of silicon is introduced, a crystalline silicon film is formed by heating treatment at a lower temperature than a conventional one, and a noble gas element is removed or reduced by laser light irradiation performed later.
A distribution of crystal orientation is preferably obtained from an electron backscatter diffraction pattern (EBSP). In the case of the EBSP method, a dedicated purpose detector is provided in a scanning electron microscopy (SEM) and a crystal orientation is analyzed from back scattering of a primary electron. When an electron beam is incident into a sample having a crystalline structure, inelastic scattering is also caused in the rear. Of the inelastic scattering, a linear pattern inherent to a crystal orientation due to Bragg diffraction in the sample (generally called a Kikuchi pattern) is also observed. In the case of EBSP, a Kikuchi pattern displayed on the screen of the detector is analyzed to obtain a crystal orientation of the sample. When an orientation analysis is repeated while a position of the sample into which an electron beam is irradiated is shifted (a mapping measurement is performed), information of crystal orientation or alignment can be obtained with respect to a sheet sample. When all crystal orientations of respective crystal grains are obtained by the mapping measurement, a state of crystal orientations in a film can be statistically displayed.
The present inventor(s) et al. performed the following experiment.
(Experiment)
First, a sample in which a base insulating film (silicon oxynitride film: 150 nm in thickness) is formed on a glass substrate and an amorphous silicon film having a thickness of 54 nm is formed thereon by a plasma CVD method is prepared. Next. argon is added to the amorphous silicon film by an ion doping method. An ion doping condition at this time is set such that an accelerating voltage is 30 kV, a dose is 2×10
15
/cm
2
, and a concentration of argon included in the film is about 3×10
20
/cm
3
. Next, a solution including nickel at 100 ppm in weight conversion is applied to the amorphous silicon film and then thermal treatment is performed at 500° C. for 1 hour. After that, thermal treatment is performed at 600° C. for 8 hours to crystallize the amorphous silicon film. Thus, a silicon film having a crystalline structure is formed. A distribution of crystal orientation in the thus obtained silicon film having the crystalline structure is examined by an EBSP.
FIG. 14
is an inverse pole figure obtained from the EBSP. The inverse pole figure is often used in the case where a preferred orientation of polycrystal is displayed and collectively indicates which lattice plane is coincided with a specific surface (here, the surface of the film) of the sample. Note that an object having a fan shape in
FIG. 14
is generally called a standard triangle and all indexes with respect to a cubic system are included therein. Also, a length in this drawing corresponds to an angle with respect to a crystal orientation. For example, an angle between {001} and {101} is 45 degrees, an angle between {101} and {111} is 35.26 degrees. and an angle between {111} and {001} is 54.74 degrees.
Also,
FIG. 14
is obtained by plotting all measurement points by mapping on the standard triangle. Since a density of points becomes high near {101} and {111}, it can be read that a preferred orientation is made for specific indexes (here, {111} and {111}.
Thus, when it is clear that a preferred orientation is made for specific indexes, a ratio as to what degree of crystal grains is gathered near the indexes is digitized and thus the degree of the preferred orientation is easy to image. In the inverse pole figure as shown in
FIG. 14
, a ratio of the number of points present within an area produced by a deviation angle of 10 degrees from {111} to the whole can be indicated as an orientation ratio.
With respect to the thus obtained orientation ratio, a ratio in the case where an angle produced by a {101} plane detected by a reflection electron d
Mitsuki Toru
Yamazaki Shunpei
Costellia Jeffrey L.
Dang Phuc T.
Peabody LLP Nixon
Semiconductor Energy Laboratory Co.,.Ltd.
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