Thin film transistor, display device having thin film transistor, and method for manufacturing the same

Abstract

A thin film transistor with excellent electric characteristics, a display device having the thin film transistor, and methods for manufacturing the thin film transistor and the display device are proposed. The thin film transistor includes a gate insulating film formed over a gate electrode, a microcrystalline semiconductor film formed over the gate insulating film, a pair of buffer layers formed over the microcrystalline semiconductor film, a pair of semiconductor films to which an impurity element imparting one conductivity type is added and which are formed over the pair of buffer layers, and wirings formed over the pair of semiconductor films to which the impurity element imparting one conductivity type is added. A part of the gate insulating film or the entire gate insulating film, and / or a part of the microcrystalline semiconductor or the entire microcrystalline semiconductor includes the impurity element which serves as a donor.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a thin film transistor, a display device having the thin film transistor at least in a pixel portion, and a method for manufacturing the thin film transistor and the display device.[0003]2. Description of the Related Art[0004]In recent years, technology for forming thin film transistors using a thin semiconductor film (with a thicknesses of from several tens of nanometers to several hundreds of nanometers, approximately) formed over a substrate having an insulating surface has been attracting attention. Thin film transistors are applied to a wide range of electronic devices such as ICs or electro-optical devices, and prompt development of thin film transistors that are to be used as switching elements in display devices, in particular, is being pushed.[0005]As a switching element in a display device, a thin film transistor including an amorphous semiconductor film, a thin film transistor...

AI Technical Summary

Benefits of technology

[0007]A thin film transistor including a polycrystalline semiconductor film has advantages that the field effect mobility thereof is two or more orders of magnitude higher than that of a thin film transistor including an amorphous semiconductor film, and that a pixel portion and a peripheral driver circuit of a display device can be formed over one substrate. However, the thin film transistor including a polycrystalline semiconductor film requires a more complicated process than the thin film transistor including an amorphous semiconductor film because of crystallization of the semiconductor film. Thus, there are problems such as a reduction in yield and an increase in cost.

[0009]In view of the above problems, it is an object of the present invention to provide a thin film transistor having excellent electric characteristics, a display device having the thin film transistor, and a method for manufacturing the thin film transistor and the display device.

[0026]Further, with regard to a microcrystalline semiconductor film in contact with a gate insulating film, forming a microcrystalline semiconductor film including an impurity element which serves as a donor can increase the speed of carrier travel in the microcrystalline semiconductor film, so that a thin film transistor with high field effect mobility and high on-current can be manufactured.

[0030]Further, thin film transistors (TFTs) are manufactured using the microcrystalline semiconductor film of the present invention, and a display device is manufactured using the thin film transistors for a pixel portion and further for a driver circuit. Since the microcrystalline semiconductor film of the present invention has high crystallinity at the interface with the gate insulating film, a thin film transistor including the microcrystalline semiconductor film has a field effect mobility of from 2.5 to 10 cm2 / V·sec, which is 5 to 20 times as high as that of a thin film transistor including an amorphous semiconductor film; thus, a part of the driver circuit or the entire driver circuit can be formed over the same substrate as that of the pixel portion, so that a system-on-panel can be manufactured.

[0034]According to the present invention, a microcrystalline semiconductor film which has high crystallinity from an interface with an insulating film can be formed, and a thin film transistor with excellent electric characteristics can be manufactured using the microcrystalline semiconductor film for a channel formation region. Further, a display device having the thin film transistor can be manufactured.

Problems solved by technology

However, the thin film transistor including a polycrystalline semiconductor film requires a more complicated process than the thin film transistor including an amorphous semiconductor film because of crystallization of the semiconductor film.

Thus, there are problems such as a reduction in yield and an increase in cost.

Further, an inverted-staggered thin film transistor including a microcrystalline semiconductor film has problems in that the crystallinity of an interface region between a gate insulating film and a microcrystalline semiconductor film is low and electric characteristics are poor.

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