JPH03200338A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To reduce a process wherein a gate electrode is insulated from the other electrodes and prevent a defect from being generated by selectively oxidizing the end portions of the gate electrode to make them insulating films and filling pin holes generated in a gate insulating film so as not to affect characteristics, respectively. CONSTITUTION:A region corresponding to the gate of a transistor is selectively formed by sequentially etching a gate insulating film 3 and a gate electrode film 2. Anode oxide films 7 are formed on the end portions of the gate electrode film 2 by an anodic oxidation method. In a process wherein anodic oxidation is performed, when a pin hole is present in the gate insulating film 3 on the gate electrode film 2, the anode oxide film 7 is formed on one end of the gate electrode film 2 and, at the same time, the portion of the pin hole is covered by the anode oxide film 7, enabling an insulation to be kept between the anode oxide film 7 and a film formed thereof. Thus, the detect of a thin film transistor caused by the pin hole can perfectly be prevented from being generated and a manufacture yield is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing thin film transistors used as switching devices in active matrix liquid crystal display devices, sensor devices, and the like.

[Summary of the invention]

The present invention relates to a thin film transistor and a method for manufacturing the same.
The present invention applies a method of anodic oxidation of the end portion of a gate electrode to provide a thin film transistor that requires fewer photomask steps, can be manufactured in a compact manner, and has fewer defects, and a method for manufacturing the same.

[Conventional technology]

Figures 2 (Ta) to (fl) show a conventional manufacturing method for thin film transistors used in active matrix liquid crystal display devices.Manufacture of thin film transistors can be accomplished with fewer photomask steps than the conventional method, with only three steps. The method includes (Step fb of selectively forming a gate electrode 11 made of a metal film such as chromium on an insulating substrate IO such as Al glass) A gate insulating film 12 made of silicon nitride, silicon oxide, etc. is formed thereon. Step of successively depositing a first semiconductor film 13 made of amorphous silicon or polycrystalline silicon, a second semiconductor film 14 doped with N-type impurities, and a metal electrode film 15 made of chromium or the like (C1 above). Metal electrode film 15
．． Second semiconductor film 14 doped with impurities. Step of selectively etching the first semiconductor film 13 into substantially the same planar shape to form a channel region of a thin film transistor (dl transparent conductive film 16 made of indium tin oxide, etc.)
(step of forming the shape of the source and drain electrodes of the thin film transistor with photoresist 17 using EL photolithography (")") step of depositing the transparent conductive film 16, the metal electrode film 15, and the second semiconductor film 14 doped with impurities. Selectively etching the source 16' and drain electrodes 16' of the transistor.
It consists of the process of forming.

This conventional manufacturing method consists of three photolithography steps, which is extremely small for a transistor manufacturing method, but when applied to active matrix liquid crystal display devices and sensors, a large number of transistors are formed in one element. That is, in the case of a liquid crystal display device, tens of thousands to millions of transistors are formed within a vertical and horizontal size of several centimeters to several tens of centimeters. If even one transistor becomes defective, the display device becomes defective.

The main causes of this defect are: ■ Adjacent conductive film patterns are short-circuited due to dust etc. during the photolithography process, ■ Electrodes that should have been connected due to dust etc. during the photolithography process Wiring may become disconnected; ■ Pinholes in the insulating film caused by dust generated during the insulating film formation process may cause short circuits between the conductive films above and below the insulating film.

Among these, the short circuit (■) is corrected by cutting off the pattern connected by the laser. It is possible to prevent the disconnection (2) by performing the photolithography process twice. However, the pinholes shown in (1) have a thickness of 50 to 1000 nanometers, which is about the same size as the thickness of the insulation, and are extremely difficult to prevent or correct. For this reason, it is extremely difficult to manufacture an active matrix display device with a high yield, and it has not been possible to manufacture an active matrix display device with a high yield for practical use.

(Problems to be Solved by the Invention) Therefore, the present invention has been made to solve these conventional drawbacks. be.

[Means to solve the problem]

In order to solve the above problems, the present invention converts the end portion of the gate electrode film into an insulating film using an anodic oxidation method.

[Effect]

By selectively oxidizing the end of the gate electrode using anodization to form an insulating film, it is possible to reduce the process of insulating the gate electrode from other electrodes (source, drain), and at the same time reduce the process of insulating the gate electrode from other electrodes (source, drain). To prevent the occurrence of defects by blocking pinholes in a manner that hardly affects the characteristics of a transistor.

〔Example〕

1a) to 1(a) are cross-sectional views of one embodiment showing the order of manufacturing steps of a thin film transistor according to the present invention, in which a gate electrode film made of tantalum or a tantalum alloy is formed on an insulating substrate 1 made of fat glass or the like. 2 by a sputtering method or vapor deposition method, and a gate insulating film 3 made of silicon oxide, silicon nitride, etc. by a sputtering method, a CVD method, a plasma CVD method, or the like. A second step (fc) in which the gate electrode film 2 is sequentially etched to selectively form a region corresponding to the gate of the transistor; and a third step (fc) in which the anodic oxide film 7 is formed at the end of the gate electrode 2 by an anodic oxidation method. (However, anodizing may be performed while leaving the resist used for patterning the gate insulating film and gate electrode film.) (d) CVD the first semiconductor film 4 made of amorphous silicon, polycrystalline silicon, etc.
The second semiconductor film 5 doped with N or P type using a similar method is chromium, sputtering, plasma CVD, etc.
The fourth step (e) is to form a three-layer fl film using a metal electrode film 6 made of aluminum, tantalum, tungsten steel, etc. or a multilayer film of these materials by sputtering or vapor deposition. Electrode film 6, N or P
Second semiconductor film 5 doped in the mold; Fifth step of selectively etching the first semiconductor film 4 (di i3 Fourth step of forming a bright conductive film 8ffl)
The sixth step (step 6) of forming the shape of the source and drain electrodes of the thin film transistor using photoresist 9 in the photolithography step (step 1) selectively etching the transparent conductive film 8, metal electrode film 6, and doped second semiconductor film 5. W4) A seventh step of forming a source electrode 8" and a drain electrode 8" of the transistor.

In this example, a thin film transistor can be formed by performing the photomask process three times.

As described in the conventional example, among the defects that occur during the manufacturing process of thin film transistors, those caused by pinholes in the gate insulating film occur most frequently, and measures such as laser repair are required. In the manufacturing method of the thin film transistor of the present invention, in the third step of anodic oxidation, if there is a pinhole in the gate insulating film 3 on the gate electrode 2, one end of the gate electrode may be damaged. At the same time as the anodic oxide film is formed, the pinhole portion is also covered with the anodic oxide film, and insulation between the pinhole and the film formed thereon can be maintained. As a result, defects in transistors caused by pinholes can be completely prevented, and manufacturing yields can be greatly improved.

In the embodiments of the present invention, the metal electrodes serving as the source/drain electrodes are for obtaining good electrical contact between the semiconductor film and the transparent conductive film, and are not essential. Furthermore, although the transparent conductive film is described in this embodiment in the case where the thin film transistor of the present invention is used as a switch of a pixel of an active matrix liquid crystal display device, it is not necessarily necessary to be a transparent film in applications such as sensors. Further, according to the present invention, FIG.
Figure +al ~ (As shown by the shu, a capacitance can be formed between the gate electrode 2 and the drain electrode 8'', and it can be used as a signal holding capacitor used in active matrix liquid crystal display devices, etc.) .

〔Effect of the invention〕

As described above, according to the present invention, thin film transistors can be produced with a high yield through as few steps as three mask steps. In addition, the anodized end of the gate electrode can greatly reduce the probability of a sit between the gate and drain or source at the stepped portion, and even if there is a pinhole in the gate insulating film, the anodized Can eliminate pinholes.

[Brief explanation of drawings]

FIGS. 1(al) to (g) are cross-sectional views showing an embodiment of the method for manufacturing a thin film transistor according to the present invention, and FIGS.
fl is a cross-sectional view showing a conventional method for manufacturing a thin film transistor. 1, 11, 4.13, 6.15, 8.16, 8', 16', 8'', 16'', 9...Gate electrode...A-3i film...Electrode film...Transparent conductive Film: Source electrode, Drain electrode: More than photoresist

Claims (1)

[Claims] In the manufacturing process of a thin film transistor, at least (a) a first step of forming a gate electrode film and a gate insulating film on an insulating substrate; (b) etching the gate insulating film and the gate electrode film in order; (c) a third step of forming an insulating film at the end of the gate electrode by an anodic oxidation method; (d) a first semiconductor film; a second semiconductor film doped with N or P type; Fourth step of forming a metal electrode film (e) Fifth step of selectively etching the metal electrode film and the doped second semiconductor film (f) Sixth step of forming a transparent conductive film (g) Applicable A method for manufacturing a thin film transistor, comprising a seventh step of selectively etching a transparent conductive film, the metal electrode film, and the second semiconductor.