JPH07176749A - Thin-film transistor - Google Patents

Abstract

PURPOSE:To prevent a glass substrate from being etched and damaged when an etching stopper is patterned by a method wherein the etching stopper is formed of a thin film in which an etchant has a large selection ratio to a lower- layer film. CONSTITUTION:A conductive thin film which is to be used as a gate electrode 2 is formed on an insulating substrate 1, and the surface of TaNx is anodically oxidized, so that an anodic oxide film 3 is formed. Then, a gate insulating film 4 is formed of SiNx and a semiconductor layer 5 is formed of amorphous silicon. An ITO film which is to be used as an etching stopper is sputtered and formed on the surface. Then, a resist pattern for the etching stopper 9 is formed in a self-aligned manner by using a rear exposure operation, and the ITO film is etched and patterned by using an iron chloride-based solution. Then, an n<+> amorphous Si film which is to be used as a contact layer 6 is formed, a resist pattern is formed, and the semiconductor layer 5 and the contact layer 6 are patterned simultaneously, so that a gap 10 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The thin film transistor according to the present invention relates to an inverted stagger type field effect thin film transistor (FET) which is often used for a switching element of a picture element electrode for liquid crystal display.

[0002]

2. Description of the Related Art FIG. 7 is a plan view of a thin film transistor disclosed in Japanese Patent Laid-Open No. 1-217422, and FIG.
A sectional view is shown. As shown in FIGS. 7 and 8, the gate electrode 2 is provided on the insulating substrate 1, and the semiconductor layer 5 is formed via the gate insulating films 3 and 4. Contact layers 6 are formed on both sides of the etching stopper 9 as shown in FIG. At this time, as shown in FIG. 9, the contact layer 6 may be formed without forming the etching stopper.
A source electrode 7 and a drain electrode 8 are formed so as to overlap the contact layer 6.

[0003]

The thin film transistor is formed by patterning an electrode thin film, an insulating thin film, and a semiconductor thin film formed by a sputtering method, a plasma CVD method or the like by a photolithography technique. Small holes are present in this thin film due to the inclusion of dust, foreign matter, etc. during formation. When the thin film transistor is formed using a substrate having a small selection ratio with respect to a hydrofluoric acid-based solution such as a glass substrate, when the hole is present in the gate insulating film,
In the process of etching the upper layer amorphous Si, SiNx, SiO2, etc. using a hydrofluoric acid-based solution,
The glass may be deeply etched. If a source and a drain are formed on this, there is a high possibility of disconnection. Further, damage (holes) in the glass substrate often causes etching residue of the upper layer film, which often causes a leak. Further, in the case of a liquid crystal display device substrate using these thin film transistors, there is a possibility of pixel defects. Thus, it is a factor that reduces the yield and reliability of the device.

In order to solve this problem, a base coat film of a hydrofluoric acid resistant solution may be formed on a glass substrate. However, there are holes in this base coat film, and it cannot be said to be a fundamental solution. For this reason, there is a method of dry-etching a thin film that may damage the glass substrate. However, in a structure in which an etching stopper such as SiNx or SiO2 is formed on amorphous Si, the etching stopper is patterned by dry etching using amorphous Si and SiN.
x, SiO2, etc. cannot be selected. For this reason, the present situation is that wet etching is performed using a hydrofluoric acid-based solution with a high selection ratio. Therefore, in the conventional structure in which the etching stopper is formed, damage to the glass due to the etchant of the etching stopper is unavoidable.

[0005]

According to the present invention, the etching stopper is formed by using a thin film such as an ITO film having a large selection ratio with an underlying film such as amorphous Si or glass having an etchant, and a contact layer (n + -Si) is formed. By removing the etching stopper on the channel after the patterning of 1), it is possible to form a thin film transistor that solves the above problems.

[0006]

As described above, according to the present invention, since the etching stopper is formed by using a thin film such as an ITO film whose etchant has a large selection ratio with the lower layer film such as amorphous Si or glass, it is possible to form a gate at the time of patterning the etching stopper. The glass substrate is not damaged by being etched through the holes in the insulating film. Therefore, it is possible to reduce disconnection and leakage of the source electrode and the drain electrode formed thereon, which greatly contributes to the improvement in the manufacturing yield of the thin film transistor.

[0007]

【Example】

Example 1 An example of a method of manufacturing a thin film transistor structure according to the present invention will be described below. FIG. 1 shows a plan view of a thin film transistor according to the present invention. FIG. 2 shows a sectional view taken along the line AA ′ in FIG. Further, FIGS. 3 to 5 are sectional views taken along the line AA ′ in each step for explaining the manufacturing method of the present invention.

A conductive thin film to be the gate electrode 2 is formed on the insulating substrate 1. In this example, a glass substrate was used as the insulating substrate 1, and TaNx formed by sputtering a conductive thin film was used. After forming the resist pattern, patterning was performed by dry etching. Next, the TaNx surface was anodized to form an anodized film 3. However, TaN
A structure in which the x surface is not anodized may be adopted. Next, the gate insulating film 4 and the semiconductor layer 5 were continuously formed. In this embodiment, SiNx is used for the gate insulating film 4 and amorphous Si is used for the semiconductor layer 5. Then, an ITO film to serve as an etching stopper 9 was formed on the surface by sputtering. Next, the resist pattern of the etching stopper 9 was formed by self-alignment using backside exposure, and the ITO film was etched and patterned using an iron chloride-based solution. Next, n + amorphous Si that becomes the contact layer 6
After forming a resist pattern and forming a resist pattern, the semiconductor layer 5 and the contact layer 6 were simultaneously patterned to form the gap portion 10. As a result, the structure shown in FIG. 3 is formed.

Next, a conductive thin film 12 to be the source electrode 7 and the drain electrode 8 is formed. (FIG. 4) In this embodiment, T
aNx was used. After forming the resist pattern, the source electrode 7 and the drain electrode 8 were patterned by dry etching. Next, the etching stopper 9 of ITO in the gap portion 10 between the source electrode 7 and the drain electrode 8 was removed using an iron chloride-based solution. As described above, as shown in FIG. 5, a thin film transistor having a structure in which the ITO film 11 remains in a part in the vicinity of the gap 10 between the semiconductor layer 5 and the contact layer 6 can be manufactured.

Example 2 In this example, the semiconductor layer 5 and the contact layer 6 were formed in the same manner as in Example 1 as shown in FIG. Then, an ITO film was used for the conductive thin film 12 to be the source electrode 7 and the drain electrode 8. Then, after forming the resist pattern, the source electrode 7 and the drain electrode 8 were patterned using an iron chloride-based solution. Alternatively, by over-etching, the ITO etching stopper 9 in the gap portion 10 was simultaneously etched and removed. At this time, the source / drain electrodes and the etching stopper may be separately etched. As described above, as shown in FIG. 5, a thin film transistor having a structure in which the ITO film 11 remains in a part in the vicinity of the gap 10 between the semiconductor layer 5 and the contact layer 6 can be manufactured.

Example 3 When the thin film transistor of the present invention is used as a switching element of a liquid crystal display device,
As shown in FIG. 6, when the ITO etching stopper 9 is formed, the pixel electrode 13 is simultaneously formed. However,
The pixel electrode 13 may be formed as a film in a process different from that of the ITO of the etching stopper 9.

[0012]

In the manufacturing process of the thin film transistor having the structure of the present invention, it is not necessary to use the etching stopper such as SiNx or SiO2 which has been forced to use the hydrofluoric acid type solution in the conventional manufacturing process. For this reason,
During patterning, the glass substrate, which is easily etched by the hydrofluoric acid-based solution, is not etched and damaged from the hole of the gate insulating film. Therefore, disconnection and leakage of the source electrode and the drain electrode formed thereover can be reduced. In addition, in the liquid crystal display element using the same thin film transistor, in addition to the reduction of the disconnection and leakage of the source electrode and the drain electrode, the occurrence of point defects due to the defective pixel electrode can be reduced. As described above, the manufacturing yield of the thin film transistor and the element including the thin film transistor such as the liquid crystal display element is greatly improved, and the manufacturing cost can be reduced. In addition, it can also contribute to improving reliability.

[Brief description of drawings]

FIG. 1 is a plan view of a thin film transistor of the present invention.

FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 3 is a cross-sectional view taken along the line AA ′ of FIG. 1 in the manufacturing process of the embodiment.

FIG. 4 is a cross-sectional view taken along the line AA ′ of FIG. 1 in the manufacturing process of the embodiment.

FIG. 5 is a cross-sectional view taken along the line AA ′ of FIG. 1 in the manufacturing process of the embodiment.

FIG. 6 is a sectional view of a transistor portion of a liquid crystal display substrate according to a third embodiment.

FIG. 7 is a plan view of a conventional thin film transistor.

FIG. 8 is a cross-sectional view (with an etching stopper) taken along the line BB ′ of FIG. 7.

9 is a sectional view taken along line BB ′ in FIG. 7 (without an etching stopper).

[Explanation of symbols]

 1 Glass Substrate 2 Gate Electrode 3 Gate Insulating Film (Anodic Oxide) 4 Gate Insulating Film 5 Semiconductor Layer 6 Contact Layer 7 Source Electrode 8 Drain Electrode 9 Etching Stopper 10 Gap Part 11 Thin Film 12 Conductivity to be Source Electrode 7 and Drain Electrode 8 Thin film 13 Pixel electrode

Claims (4)

[Claims] 1. An insulating substrate (1), a gate electrode (2) formed on the insulating substrate (1), and an insulating film (4) formed on the gate electrode (2). A semiconductor layer (5) and a source electrode (7) and a drain electrode (8) formed on both sides of the semiconductor layer (5) via a contact layer (6), the semiconductor layer (5) A thin film transistor, wherein a thin film (11) is formed at a position near the source-drain gap portion at the interface between the contact layer (6) and the contact layer (6). 2. A thin film (11) formed in a part of the interface between the semiconductor layer (5) and the contact layer (6) in the vicinity of the source-drain gap part is formed of amorphous Si and glass, Si-based materials such as SiNx and SiO2. The thin film transistor according to claim 1, which is a thin film that can be etched using an etchant having a large selection ratio with a compound. 3. The thin film (11) formed in a part of the interface between the semiconductor layer (5) and the contact layer (6) near the source-drain gap portion is a conductive thin film. 2. The thin film transistor according to 2. 4. An insulating substrate (1), a gate electrode (2) formed on the insulating substrate (1), and an insulating film (4) formed on the gate electrode (2). A thin film transistor having a semiconductor layer (5), and a source electrode (7) and a drain electrode (8) formed on both sides of the semiconductor layer (5) via a contact layer (6). ) And the contact layer (6) at a portion near the source-drain gap portion, an ITO film is formed.