JPH05182984A - Manufacture of thin-film transistor - Google Patents

Abstract

PURPOSE:To obtain a thin-film transistor whose electric characteristic is excellent by a method wherein the deterioration of the film quality of a semiconductor active layer due to an etching operation is avoided. CONSTITUTION:A gate electrode 2, a gate insulating film 3, a semiconductor active layer 4 and an interlayer insulating film 5 are formed sequentially on a transparent insulating substrate 1. After that, a pair of contact holes 6a, 6b are formed in prescribed regions of the interlayer insulating film 5; a highly conductive semiconductor substance is filled into the contact hole; ohmic electrodes 7a, 7b as source-drain electrodes are formed.

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 which has excellent electric characteristics and can be used as an optical device.

[0002]

2. Description of the Related Art FIG. 8A is a sectional view showing a conventional thin film transistor, and FIG. 8B is a plan view thereof. Note that FIG. 8A is a sectional view taken along the line AA of FIG.

A gate electrode 12 having a predetermined shape is formed on a transparent insulating substrate 11. The gate insulating film 13 is formed on the substrate 11 so as to cover the gate electrode 12.
Are formed. Further, the semiconductor active layer 14 is formed on the gate insulating film 13 so as to cover the gate electrode 12.
Are formed.

On the semiconductor active layer 14, a pair of ohmic electrodes 17a and 17b which are source / drain electrodes.
Are formed. Then, on the substrate 11, the wiring layers 18a connected to the ohmic electrodes 17a, 17b,
18b is formed in a predetermined pattern. The ohmic electrodes 17a and 17b are arranged such that a part thereof overlaps the gate electrode 12 in a plan view.

In the conventional thin film transistor thus configured, when a predetermined voltage is applied to the gate electrode 12 and the source / drain electrodes (ohmic electrodes 17a and 17b), the semiconductor active layer 1 above the gate electrode 12 is applied.
An electric field is applied to 4 to generate an inversion layer at the interface between the gate insulating film 13 and the semiconductor active layer 14. This enables a predetermined operation as a thin film transistor.

Next, a method of manufacturing the above-mentioned thin film transistor will be described with reference to FIGS. 8 (a) and 8 (b).

First, the gate electrode 1 is formed on the transparent insulating substrate 11.
2 is selectively formed. After that, the gate insulating film 13 is formed in the region on the substrate 11 including the gate electrode 12.

Next, a semiconductor active layer 14 and an ohmic layer made of a semiconductor material having high conductivity are sequentially formed in a predetermined region on the gate insulating film 13.

Next, an etching method is used to form a groove 19 which reaches the semiconductor active layer 14 from the surface of the ohmic layer.
To form the ohmic layer on the gate electrode 1
2 is electrically divided into two above the ohmic electrode 17a,
You get 17b. In this case, part of the ohmic electrodes 17a and 17b overlaps the gate electrode 12 in plan view.

Next, the wiring layers 18a and 18b contacting the ohmic electrodes 17a and 17b are formed in a predetermined pattern. Thereby, the thin film transistor is completed.

[0011]

However, the above-described conventional method of manufacturing a thin film transistor has the following problems. That is, conventionally, after forming a thin film (that is, an ohmic layer) made of a semiconductor material having high conductivity on the semiconductor active layer 14, the ohmic electrode 17 is formed by forming a groove 19 in this thin film by, for example, a dry etching method.
a and 17b are formed. In this case, the ohmic electrodes 17a and 17b are prevented from electrically shorting each other,
The surface of the semiconductor active layer 14 needs to be slightly etched so that the bottom surface of the groove 19 is located slightly below the lower surface of the ohmic layer. Therefore, the active region above the gate electrode 12 (that is, the gate insulating film 13 and the semiconductor active layer 14 is formed).
The region near the interface with) and the portion of the semiconductor active layer 14 exposed by etching are significantly damaged by the application of the etching gas and the electric field, and the film quality deteriorates. Therefore, the electrical characteristics of the thin film transistor are also deteriorated. In particular, when the semiconductor active layer 14 is thin, the influence of damage in etching is great and the electrical characteristics are significantly deteriorated.

The present invention has been made in view of the above problems, and provides a method of manufacturing a thin film transistor which can reduce damage to a semiconductor active layer due to etching and can manufacture a thin film transistor having excellent electrical characteristics. The purpose is to

[0013]

A method of manufacturing a thin film transistor according to the present invention comprises a step of selectively forming a gate electrode on a surface of a substrate having at least the surface made of an insulator, and the step of including the gate electrode. A step of forming a gate insulating film in a region on the substrate; a step of selectively forming a semiconductor active layer on the gate insulating film; a step of forming an interlayer insulating film on the semiconductor active layer; A step of forming a pair of contact holes reaching the surface of the semiconductor active layer in regions on both sides of the gate electrode in a plan view of the film; and a step of filling these contact holes with a semiconductor material to form an ohmic electrode. , Are included.

[0014]

In the present invention, an interlayer insulating film is formed on a semiconductor active layer, a pair of contact holes are provided in a predetermined region of the interlayer insulating film, and these contact holes are filled with a semiconductor material to form an ohmic electrode. .. Therefore, in the present invention, the ohmic electrode can be formed without etching the semiconductor active layer. Further, since the semiconductor active layer is covered with the interlayer insulating film at the time of forming the contact hole, damage to the semiconductor active layer due to etching at the time of forming the contact hole can be avoided. Accordingly, a thin film transistor having excellent electric characteristics can be obtained.

[0015]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

1 to 6 are sectional views showing a method of manufacturing a thin film transistor according to an embodiment of the present invention step by step.
7A is a sectional view showing a thin film transistor manufactured by the method of this embodiment, and FIG. 7B is a plan view thereof.
7A is a sectional view taken along the line AA of FIG. 7B.

First, as shown in FIG. 1, the transparent insulating substrate 1
The gate electrode 2 is selectively formed on the upper surface by a metal such as Mo, Cr, or Al or a semiconductor conductive film.

Next, as shown in FIG. 2, the gate insulating film 3 is formed in a region on the substrate 1 including the gate electrode 2 by using silicon nitride (SiN _x ) or silicon oxide (SiO ₂ ).
To form.

Next, as shown in FIG. 3, a semiconductor active layer 4 made of a semiconductor film such as a single crystal silicon thin film or a polycrystalline silicon thin film is selectively formed on the gate insulating film 3.

Next, as shown in FIG. 4, the semiconductor active layer 4
Silicon nitride (SiN _x ) or silicon oxide (S
The interlayer insulating film 5 is formed of iO ₂ ) or the like. After that, by dry etching or wet etching, a pair of contact holes 6 that reach the surface of the semiconductor active layer 4 in regions on both sides of the gate electrode 2 in plan view in the interlayer insulating film 5.
a and 6b are formed. In addition, these contact holes 6
The a and 6b are arranged so as to slightly overlap the gate electrode 2 in plan view.

Next, as shown in FIG. 5, ohmic electrodes 7a and 7b are formed by filling the contact holes 6a and 6b with a semiconductor material having high conductivity. In this case, the ohmic electrodes 7a and 7b are made to extend slightly above the interlayer insulating film 5.

Next, as shown in FIG. 6, the wiring layers 8a and 8b connected to the ohmic electrodes 7a and 7b are connected to, for example, C
It is selectively formed on the substrate 1 with a conductor such as r, Mo, or Al. As a result, the thin film transistor shown in FIGS. 7A and 7B is completed.

In this embodiment, the contact holes 6a,
Since the ohmic electrodes 7a and 7b are formed by embedding a semiconductor material having high conductivity in 6b, it is not necessary to etch the semiconductor active layer 4 which becomes the active region of the thin film transistor. Further, since the surface of the semiconductor active layer 4 is covered with the interlayer insulating film 5 when the contact holes 6a and 6b are formed, it is possible to prevent the deterioration of the film quality of the semiconductor active layer 4 due to the etching when forming the contact holes 6a and 6b. You can Therefore, according to the method of this embodiment, a thin film transistor having excellent electrical characteristics can be obtained.

Further, in the thin film transistor manufactured by the method of this embodiment, since the film quality of the semiconductor active layer 4 is stable, even if light or the like enters the active layer region from the outside, for example,
Carriers do not behave uniquely on the surface of the semiconductor active layer. Therefore, according to the method of this embodiment, a thin film transistor that can be used as an optical device can be manufactured.

[0025]

As described above, according to the present invention, an interlayer insulating film is formed on a semiconductor active layer, a pair of contact holes are formed in the interlayer insulating film, and these contact holes are filled with a semiconductor material. Since an ohmic electrode is formed,
The deterioration of the film quality of the semiconductor active layer due to etching can be avoided, and a thin film transistor having excellent electrical characteristics can be manufactured. Further, the thin film transistor manufactured by the method of the present invention, the film quality of the semiconductor active layer is stable,
It can be used as an optical device.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a step in a method of manufacturing a thin film transistor according to an embodiment of the present invention.

FIG. 2 is a sectional view showing another step of the method according to the embodiment.

FIG. 3 is a sectional view showing another step of the method of the embodiment.

FIG. 4 is a sectional view showing another process of the method of the embodiment.

FIG. 5 is a sectional view showing another step of the method according to the embodiment.

FIG. 6 is a sectional view showing another step of the method of the example.

7A is a cross-sectional view showing a thin film transistor manufactured by a method according to an embodiment of the present invention, and FIG. 7B is a plan view thereof.

8A is a sectional view showing a conventional thin film transistor, and FIG. 8B is a plan view of the same.

[Explanation of symbols]

 1, 11; Substrate 2, 12; Gate electrode 3, 13; Gate insulating film 4, 14; Semiconductor active layer 5; Interlayer insulating film 6a, 6b; Contact hole 7a, 7b, 17a, 17b; Ohmic electrode 8a, 8b, 18a, 18b; wiring layer

Claims (1)

[Claims] 1. A step of selectively forming a gate electrode on a surface of a substrate having at least a surface made of an insulator, and a step of forming a gate insulating film in a region on the substrate including the gate electrode. A step of selectively forming a semiconductor active layer on the gate insulating film, a step of forming an interlayer insulating film on the semiconductor active layer, and a step of forming an interlayer insulating film on the regions on both sides of the gate electrode in plan view of the interlayer insulating film. A method of manufacturing a thin film transistor, comprising: a step of forming a pair of contact holes reaching the surface of the semiconductor active layer; and a step of filling the contact holes with a semiconductor material to form an ohmic electrode.