JPH05291294A - Manufacture of thin film transistor - Google Patents

Abstract

(57) [Summary] [Objective] In the method of converting an amorphous silicon film into a polysilicon film by heat treatment and solid phase growth, the surface of the converted polysilicon film is made flat. [Structure] A crystal grain movement suppressing film 13 made of silicon oxide or silicon nitride on the amorphous silicon film 12.
Are formed, and heat treatment is performed in that state to convert the amorphous silicon film 12 into a polysilicon film by solid phase growth. During the solid phase growth, the movement of the crystal grains of the amorphous silicon film 12 is suppressed by the crystal grain movement suppressing film 13, so that the surface of the converted polysilicon film can be kept flat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor.

[0002]

2. Description of the Related Art In a method of manufacturing a thin film transistor, an amorphous silicon film is deposited on an insulating substrate such as glass and the amorphous silicon film is subjected to Xe flash lamp annealing or CW laser annealing or the like.
A heat treatment is performed at about 0 ° C. to convert into a polysilicon film by solid phase growth, and this polysilicon film is used as a semiconductor layer for forming source / drain regions.

[0003]

However, in the above-mentioned conventional manufacturing method, since the crystal grains of the amorphous silicon film move during solid phase growth, the surface of the converted polysilicon film becomes uneven. Therefore, for example, in FIG.
As shown in, when the gate insulating film 2 is formed on the surface of the polysilicon film 1, the interface between the gate insulating film 2 and the polysilicon film 1 becomes uneven, and the gate breakdown voltage becomes poor. That is, the electric field strength E of the gate has a relationship as shown in the following equation with the radius of curvature r of the irregularities on the interface. E = Eo / (1 + tox / r) Here, Eo is the electric field strength when the interface is flat, tox is the film thickness of the gate insulating film 2, and r is the radius of curvature of the interface. Therefore, if the interface is uneven, the radius of curvature r becomes small and the electric field strength E becomes small, so that the gate breakdown voltage deteriorates. And when the gate breakdown voltage deteriorates,
There is a problem that a thin film transistor with excellent reliability and switching characteristics cannot be obtained.

An object of the present invention is to provide a method of manufacturing a thin film transistor capable of flattening the surface of a polysilicon film as a semiconductor layer for forming source / drain regions which is converted from an amorphous silicon film by solid phase growth.

[0005]

According to the present invention, after depositing an amorphous silicon film, a crystal particle movement suppressing film for suppressing the movement of crystal particles is formed on the amorphous silicon film, and heat treatment is performed in that state to perform solid phase. The amorphous silicon film is converted into a polysilicon film by growth.

[0006]

According to the present invention, since the crystal grain movement suppressing film is formed on the amorphous silicon film, the movement of the crystal grains of the amorphous silicon film is suppressed during the solid phase growth, and thus the converted polysilicon film is formed. The surface of can be made flat.

[0007]

1 to 4 are sectional views showing an embodiment of the present invention in the order of manufacturing steps. An embodiment of the present invention will be described below with reference to these drawings. First, as shown in FIG. 1, low temperature plasma C is placed on an insulating substrate 11 such as glass.
The amorphous silicon film 12 is formed by the VD method or the like. Next, the crystal grain movement suppression film 13 is formed on the amorphous silicon film 12. The crystal grain movement suppression film 13 is specifically a film of silicon oxide, silicon nitride or the like, and is formed by the CVD method.

Next, the amorphous silicon film 12 is heat-treated at about 600 ° C. by Xe flash lamp annealing or CW laser annealing, etc., so that the amorphous silicon film 12 is converted into a polysilicon film 14 by solid phase growth as shown in FIG. Convert. At this time, since the crystal particle movement suppressing film 13 is formed on the amorphous silicon film 12, the movement of the crystal particles of the amorphous silicon film 12 is suppressed, and thus the surface of the converted polysilicon film 14 is held flat. It After that, the crystal grain movement suppression film 1
3 and the polysilicon film 14 are patterned to leave only in the device region, and then the crystal grain movement suppressing film 13 is removed from the polysilicon film 14. This state is shown in FIG.

Next, as shown in FIG. 4, a gate insulating film 15 is formed on the entire surface, and the gate insulating film 15 covers the polysilicon film 14. After that, the gate electrode 16 is formed on the gate insulating film 15 so as to correspond to the channel region of the polysilicon film 14.
Then, ion implantation of impurities is performed using the gate electrode 16 as a mask to form the source / drain regions 17 in the polysilicon film 14 portions on both sides of the gate electrode 16. After that, an interlayer insulating film 18 is formed on the entire surface, and the interlayer insulating film 18 and the gate insulating film 15 are formed of a source
Contact hole 1 so as to reach drain region 17
Open 9 Then, source / drain electrodes 20 are formed so as to be connected to the source / drain regions 17 through the contact holes 19. Thus, the thin film transistor is completed.

[0010]

As described above, according to the present invention, the heat treatment is carried out in the state where the crystal grain movement suppressing film is formed on the amorphous silicon film to carry out the solid phase growth. The movement of the crystal particles of the amorphous silicon film is suppressed, and the surface of the converted polysilicon film can be kept flat. Therefore, the interface can be made flat when the polysilicon film is covered with the gate insulating film, and as a result, the gate breakdown voltage can be improved and the reliability and switching characteristics of the thin film transistor can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the steps of forming a crystal grain movement suppression film in one embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a step that follows FIG. 1 in one embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a step that follows FIG. 2 in one embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a step that follows FIG. 3 in one embodiment of the present invention.

FIG. 5 is a cross-sectional view showing an interface state between a polysilicon film and a gate insulating film by a conventional method.

[Explanation of symbols]

 12 Amorphous silicon film 13 Crystal particle movement suppression film 14 Polysilicon film

Claims (1)

[Claims] 1. After the amorphous silicon film is deposited, a crystal particle movement suppressing film for suppressing the movement of crystal particles is formed on the amorphous silicon film, and heat treatment is performed in that state to perform solid phase growth on the amorphous silicon film to form a polycrystal film. A method of manufacturing a thin film transistor, characterized in that the thin film transistor is converted into a silicon film.