JPH047876A - Thin film transistor - Google Patents

Abstract

PURPOSE:To improve the breakdown strength of a gate insulating film, and prevent the disconnection of source/drain electrodes, by pattern forming a gate electrode and a tantalum oxide film by selectively oxidizing a tantalum film. CONSTITUTION:A gate electrode 2 is patterned and formed by selectively oxidizing a tantalum film 3 stuck on an insulative substrate 1. Hence, differently from the case that the gate electrode is formed by eliminating an unnecessary Ta film, the Ta film 3 in the part except the gate electrode 2 is left as a Ta2O3 film. Hence a step-difference part is not formed between the gate electrode and the Ta2O3 film in the part except the gate electrode, so that the step coverage of a gate insulating film 4 and source/drain electrodes 7, 8, which are formed in order on the gate electrode and the Ta2O3 film, can be improved. Thereby the breakdown strength of the gate insulating film can be improved, and the disconnection of the source drain electrodes can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thin film transistor with an inverted staggered structure using amorphous silicon, and particularly to a highly reliable thin film transistor.

[Prior Art] FIG. 3 is a cross-sectional view showing an example of a conventional N-channel thin film transistor having an inverted staggered structure.

As shown in FIG. 3, the glass substrate 11'' is made of Cr.
A gate electrode 12 made of , Ta, NiCr, or the like is patterned by etching.

A gate insulating film 14 made of a silicon oxide film, a silicon nitride film, etc. is provided on the gate electrode 12 and the glass substrate 11.
is covered. An amorphous silicon film 15, which is an intrinsic semiconductor, is deposited on the gate insulating film 14, and a recessed portion is formed in the amorphous silicon film 15 directly above the gate electrode 12.

N3-type amorphous silicon regions 16 are selectively formed in two regions on the surface of the amorphous silicon film 15 separated by the recessed portions by doping N-type impurities at a high concentration. This N+ type amorphous silicon region 16 serves as a source.
This becomes the drain region.

Further, a source electrode 17 and a drain electrode 18 are selectively formed on the N + type amorphous silicon region 16.

[Problems to be Solved by the Invention] However, in the conventional thin film transistor described above, it is difficult to process the cross-sectional shape of the gate electrode 12 into a tapered shape. Source electrode 17 and drain electrode 1
8's step coverage becomes worse. Therefore, there are problems in that the withstand voltage of the gate insulating film 14 is lowered, and the manufacturing yield of the thin film transistor is lowered due to disconnection of the source electrode 17 and drain electrode 18. Further, there is a problem in that contamination by alkali metals contained in the glass substrate 11 causes drift in transistor characteristics.

The present invention has been made in view of such problems, and includes:
An object of the present invention is to provide a thin film transistor that can improve step coverage and prevent contamination by alkali metals contained in an insulating substrate.

[Means for Solving the Problems] A thin film transistor according to the present invention includes a gate electrode and a tantalum oxide film patterned by selectively oxidizing a tantalum film deposited on an insulating substrate, and a gate electrode and a tantalum oxide film. A gate insulating film deposited on the tantalum oxide film, an amorphous silicon film deposited on the gate insulating film, and a source/drain selectively disposed on the surface of the amorphous silicon film. and source/drain electrodes provided on the source/drain regions.

[Function] In the present invention, the gate electrode is patterned by selectively oxidizing a tantalum film (Ta film) deposited on an insulating substrate. Therefore, unlike the conventional case where the gate electrode is formed by removing unnecessary Ta film, the Ta film in the portion other than the gate electrode remains as a tantalum oxide film (Ta203 film). Therefore, since no step is formed between the gate electrode and the Ta2O3 film in other parts, the gate insulating film and the source/drain electrodes, which are sequentially formed on the gate electrode and the Ta2O3 film, Step coverage can be improved. Thereby, the withstand voltage of the gate insulating film can be improved, and the source
Disconnection of the drain electrode, etc. can be prevented, and the manufacturing yield of thin film transistors can be improved.

Furthermore, since the Ta film and the Taz 03 film have barrier properties against alkali metals such as Na, the gate electrode (Ta film) and the Ta2O3 film are placed between the insulating substrate and the gate insulating film. By intervening, contamination by alkali metals contained in the insulating substrate can be prevented. Therefore, drift in transistor characteristics can be prevented, and reliability of the thin film transistor can be improved. Furthermore, since it is not necessary to use an expensive alkali-free glass substrate or the like as the insulating substrate, manufacturing costs can also be reduced.

In addition, in the present invention, the tantalum film has a film thickness of 10
Preferably, the number is 00 to 2000 people. Further, in the selective oxidation treatment of the tantalum film, it is preferable that the tantalum film is selectively anodized using a photoresist film deposited on the tantalum film as a mask. In this case, a desired gate electrode can be easily formed.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an N-channel thin film transistor according to a first embodiment of the present invention.

As shown in FIG. 1, first, a tantalum film (Ta film) having a film thickness of, for example, 1,000 to 2,000 is deposited on a glass substrate 1, and a photoresist film is deposited on the Ta film using photolithography. (not shown) A pattern is formed. Then, using this photoresist film as a barrier, the T
The gate electrode 2 and the Ta2O3 film 3 are patterned by selectively anodizing the a film. A gate insulating film 4 is deposited on the gate electrode 2 and the Ta2O3 film 3. An amorphous silicon film 5 is deposited on the gate insulating film 4, and a recess is formed in the amorphous silicon film 5 directly above the gate electrode 2. The two regions on the surface of the amorphous silicon film 5 separated by this recess are doped with N+ impurities at a high concentration.
A molded concrete crystalline silicon region 6 is selectively formed. This N+ type crystalline silicon region 6 becomes a source/drain region. Furthermore, a source electrode 7 and a drain electrode 8 are selectively formed on the N++ amorphous silicon region 6.

In the thin film transistor constructed in this way, unlike the conventional case where the gate electrode is formed by removing unnecessary Ta film, the gate electrode 2 is patterned by anodizing the Ta film, and the gate electrode 2 is patterned by anodizing the Ta film. T in other parts
The a film remains as the Ta2O3 film 3. For this reason,
Since no step portion is formed between the gate electrode 2 and the Ta20a film 3 in other parts, the gate insulating film 4, which is sequentially formed on the gate electrode 2 and the TazO+ film 3,
The step coverage of the source electrode 7 and drain electrode 8 can be improved. As a result, the gate insulating film 4
The withstand voltage of the source electrode 7 can be improved.
And it is possible to prevent the drain electrode 8 from breaking, etc.
The manufacturing yield of thin film transistors can be improved.

Furthermore, since the Ta film and the Ta2O3 film have barrier properties against alkali metals such as Na, the gate electrode (Ta film) 2 and the Ta film are provided between the glass substrate 1 and the gate insulating film 4.
By interposing the 2O3 film 3, contamination by alkali metals contained in the glass substrate 1 can be prevented. Therefore, drift in transistor characteristics can be prevented, and reliability of the thin film transistor can be improved.

FIG. 2 is a sectional view showing an N-channel thin film transistor according to a second embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, and detailed explanations of those parts will be omitted.

A Ta film is deposited on the glass substrate 1, and this Ta film is coated using a patterned photoresist film (not shown) as a barrier.
The gate electrode 2 and the Ta2O3 film 3a are patterned by selectively anodizing the film. After removing the photoresist film, the surface of the gate electrode 2 is oxidized by anodization, thereby forming a Ta2O3 film 3a also on the gate electrode 2.

A gate insulating film 4 is then formed on the entire surface of this Ta2O+ film 3a.
is formed.

In this embodiment, the Ta 203 film 3a is used as part of the gate insulating film, and the same effects as in the first embodiment can be obtained.

[Effects of the Invention] As explained above, according to the present invention, the gate electrode and the tantalum oxide film are patterned by selectively oxidizing the tantalum film deposited on the insulating substrate. It is possible to improve the step coverage of the gate insulating film and source/drain electrodes that are sequentially formed on the oxide film and the tantalum oxide film. Therefore, the withstand voltage of the gate insulating film can be improved, and
Disconnection of the source/drain electrode can be prevented, and the manufacturing yield of thin film transistors can be improved.

Furthermore, the gate oxide film and the tantalum oxide film can prevent contamination caused by alkali metals contained in the insulating substrate. Therefore, drift in transistor characteristics can be prevented, and reliability of the thin film transistor can be improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an N-channel thin film transistor according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view showing an N-channel thin film transistor according to a second embodiment of the present invention, and FIG. 1 is a cross-sectional view showing an example of an N-channel thin film transistor with an inverted staggered structure. 1.11; Glass substrate, 2.12; Gate electrode, : 3+
3 a; Ta20G film, 4, 14; gate insulating film, 5.15; amorphous silicon film, 6.16; N+ type amorphous silicon region, 7.17; source electrode, s, is
;Drain electrode

Claims (3)

[Claims] (1) A gate electrode and a tantalum oxide film patterned by selectively oxidizing a tantalum film deposited on an insulating substrate, and a gate insulating film deposited on the gate electrode and the tantalum oxide film. , an amorphous silicon film deposited on this gate insulating film, a source/drain region selectively placed on the surface of this amorphous silicon film, and a source/drain region provided on this source/drain region. A thin film transistor characterized by having source and drain electrodes. (2) The tantalum film has a thickness of 1000 to 2000 Å.
The thin film transistor according to claim 1, characterized in that: (3) The selective oxidation treatment of the tantalum film is characterized in that the tantalum film is selectively anodized using a photoresist film deposited on the tantalum film as a mask. 2. The thin film transistor according to any one of 2.