JPH02304938A - Manufacture of thin-film transistor - Google Patents

Abstract

PURPOSE:To manufacture a TFT resisting light by two masks by laminating a gate metal, a gate insulating film and a semiconductor film to form a film, patterning the film by a first mask, substantially oxidizing the gate metal to shape an oxide film, film-forming source-drain layers onto the semiconductor film and the oxide film and patterning the film of the source-drain layers by a second mask. CONSTITUTION:A gate metal 2 and a gate insulating film 3 are formed onto a substrate 1, and a semiconductor film 9 composed of a channel layer 4 and a semiconductor-film ohmic contact layer 5 consisting of doped a-Si, etc., is laminated successively. The semiconductor-film ohmic contact layer 5, the channel layer 4, the gate insulating film 3 and the gate metal 2 are patterned by using a first mask. The gate metal 2 is oxidized substantially to shape an oxide film 6, and source-drain layers 8 are film-formed onto the semiconductor-film ohmic contact layer 5 and the oxide film 6 and patterned by a second mask. The semiconductor-film ohmic contact layer 5 is also patterned by the same pattern. Accordingly, a TFT resisting even light can be manufactured through a simple process such as a two-mask process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Liquid crystal display elements are widely applied as low power consumption flat panel displays. Among these, the active matrix method, in which a switching element is built into each pixel and driven, is being used as a large-capacity, high-quality display element in televisions, information terminals, and the like. A thin film transistor (hereinafter referred to as TPT) is used as the switching element.

The present invention relates to a method for manufacturing TPT.

[Conventional technology]

FIGS. 2 and 3 show a conventional TPT with the simplest structure.

Figure 2 shows TPT using the two-mask method proposed by the French CNET group. First, a source/drain layer 8 made of transparent type fflITO' (indium oxide) or the like and an ohmic contact layer 7 made of a semiconductor film are formed on a substrate 1 made of glass or the like, and patterned using a first mask. Next, the channel layer 4 of the semiconductor film and the gate insulating film 6 are formed.
, gate metal 2 is successively deposited and patterned with a second mask.

The ohmic contact layer 7 may be patterned using the same second mask.

Figure 3 shows TPT using the two-mask method proposed by the Matsushita Electric Group. First, a gate metal 2 is formed on a substrate 1 such as glass and patterned using a first mask. Subsequently, a gate insulating film 6, a semiconductor channel layer 4, and an ohmic contact layer 7 are successively formed, and a gate metal 2 is formed.
The channel layer 4 and the ohmic contact layer 7 are patterned by a back exposure method using as a mask. Finally, a source/drain layer 8 is formed and patterned using a second mask. The ohmic contact layer 7 can be patterned with the same second mask.

[Problem to be solved by the invention]

The conventional examples shown in FIGS. 2 and 3 are both excellent methods that can be manufactured using two masks. However, there are some drawbacks.

The disadvantage of the conventional example shown in FIG. 2 is that it is weak against light. Second
As is clear from the figure, the channel layer 4 of the semiconductor film is completely defenseless against light irradiation from the side of the substrate 1 made of glass, and the photocurrent reduces the switching ability of the TPT, especially the OFF state.
properties are impaired.

In order to withstand outdoor use under sunlight of up to 100,000 lux, a light shielding film (pattern) is required on the glass substrate side. As mentioned above, in the conventional example shown in FIG.
It is impossible to do this with just one mask, and at least three masks are required.

In the conventional example shown in FIG. 3, there are few problems because the gate metal 2 serves as a shield against light from the glass substrate 1 side. However, since the back exposure method is used, the photolithography process is performed three times even though the number of masks is two, and the process is not that simple.

The present invention provides a method for manufacturing TPT that is resistant to light, using a simple manufacturing method using two masks.

[Means to solve the problem]

In order to achieve the above object, TPT in the present invention is manufactured by the steps described below. Gate metal, gate insulating film,
A process of stacking and forming a semiconductor film and patterning it with a first mask, a process of substantially oxidizing this gate metal to form an oxide film, and a process of forming a source/drain layer on the semiconductor film and the oxide film. and patterning using a second mask.

〔Example〕

FIG. 1 shows an embodiment of the method for manufacturing TPT of the present invention.

First, as shown in FIG.
A gate metal 2 having a thickness of 5Qnm to 500nm is formed by sputtering or vacuum evaporation of x, Mo, MoSix, kl, etc. Thereafter, SiNx with a thickness of 1100 nm to 5 QQ nm is formed by plasma CVD or sputtering.

A gate insulating film 3 of 3iQx, TaQx, etc. is formed.

Thereafter, a semiconductor film 9 consisting of a channel layer 4 of intrinsic amorphous silicon (a-3i) or the like and a semiconductor film ohmic contact layer 5 of doped a-3i or the like is sequentially laminated by a plasma CVD method or the like. Then, using the mask of Node 1, the semiconductor film ohmic contact layer 5, channel layer 4, gate insulating film 6, and gate metal 2 are patterned.

Next, as shown in FIG. 1(B), the gate metal 2 is substantially oxidized to form an oxide film 6.

A first embodiment of the means for forming the oxide film 6 through substantial oxidation is an anodic oxidation method. Ta, MoSix as gate metal 2
After the process described with reference to FIG. 1A, the oxide film 6 is formed by anodic oxidation using citric acid or the like.

A second embodiment of the means for forming the oxide film 6 through substantial oxidation is a thermal oxidation method. Ta, A7 as gate metal 2! , M.O.
After the process described using FIG. 1 using lM o S i x or the like, the oxide film 6 is formed by thermal oxidation in an atmosphere of air, oxygen, or water vapor at a temperature of 400° C. to 500° C. In this thermal oxidation step, the semiconductor film 9 made of a-Si
Since the surface is slightly oxidized, the oxide film on the surface of the semiconductor film 9 is removed by etching. Since the thickness of the oxide film on the surface of the semiconductor film 9 is extremely thin compared to the oxide film 6 of the gate metal 2, the oxide film 6 of the gate metal 2 is etched by the above-described etching.
is only slightly etched.

Next, as shown in FIG. 1C, a source/drain layer 8 is formed on the semiconductor film ohmic contact layer 5 and the oxide film 6 and patterned using a second mask.

As the source/drain layer 8, a transparent conductive film such as ITO is used in a transmission type display.

The film formation method is a sputtering method, a vacuum evaporation method, etc., and the film thickness is 5Q nm to 400 nfT'l.

In this embodiment, after the source/drain layer 8 is patterned with the second mask, the semiconductor film ohmic contact layer 5 is also patterned with the same pattern.

〔Effect of the invention〕

As is clear from the above embodiments, the present invention makes it possible to provide a method for manufacturing TPT that is much more resistant to light than the conventional example, through an extremely simple process of a two-mask process.

[Brief explanation of drawings]

1) to (C) are cross-sectional views showing the method of manufacturing a thin film transistor according to the present invention in order of steps, and FIGS. 2 and 3 are cross-sectional views showing a conventional method of manufacturing a thin film transistor. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Gate metal, 6...Gate insulating film, 4...Channel layer, 5...Ohmic contact layer , 6...
・Oxide film, 7... Ohmic contact layer, 8...
- Source tunnel layer, 9... Semiconductor film. Figure 3

Claims (5)

[Claims] (1) A step of sequentially stacking and forming a gate metal, a gate insulating film, and a semiconductor film and patterning it with a first mask, a step of substantially oxidizing the gate metal to form an oxide film, and a step of forming an oxide film by substantially oxidizing the gate metal. A method for manufacturing a thin film transistor, comprising at least the step of forming a source/drain layer on an oxide film and patterning it using a second mask. (2) The semiconductor film has a stacked structure of a channel layer and a semiconductor film ohmic contact layer.
2. The method of manufacturing a thin film transistor according to claim 1, wherein after the drain layer is patterned, the semiconductor film ohmic contact layer is also patterned with the same pattern. (3) The method for manufacturing a thin film transistor according to claim 1, wherein the means for substantially oxidizing the gate metal to form an oxide film is an anodic oxidation method. (4) The method for manufacturing a thin film transistor according to claim 1, wherein the means for substantially oxidizing the gate metal to form an oxide film is a thermal oxidation method. (5) The method for manufacturing a thin film transistor according to claim 1, wherein the semiconductor film is amorphous Si.