JPH01114080A - Thin film transistor - Google Patents

Abstract

PURPOSE:To form an extra-thin oxide film and improve the stability significantly and improve the long-term reliability of characteristics by oxidizing the amorphous silicon hydride side surface of a gate insulating film. CONSTITUTION:After a Cr film 2 is built up on a glass substrate 1, the Cr film 2 is patterned into a gate electrode pattern by photoetching. SiN3 is deposited by plasma CVD and the surface of SiN3 is oxidized by the same CVD equipment to form an oxide film 4. Then oxygen is eliminated and mixed gas of SiH4 and H2 is introduced and an a-Si film 5 is built up by plasma CVD so as to have a thickness of 0.3mum. After that, an n-type a-Si film 6 doped with P with a content about 2% is built up so as to have a thickness of 0.03mum. Then a Cr layer 7 with a thickness of 0.1mum and an Al layer 8 with a thickness of 0.3mum are built up to form a double-layer film of Cr/Al. The double-layer film is patterned by photoetching to form source and drain electrodes. After the n-type a-Si film on a channel part is removed by dry-etching, an SiN film 9 is formed as a protective film.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a thin film transistor (TPT).

In particular, the present invention relates to a transistor structure suitable for reducing the threshold voltage shift of a TPT in which silicon nitride (S i N) is used as a gate insulating film and amorphous silicon hydride (a-5i) is used as a semiconductor film.

[Conventional technology]

The conventional TPT using a-8i as a semiconductor film was disclosed in Japanese Patent Application Laid-open No. 1983.
As described in No. 3289, a method was used in which SiN and a-8i were successively deposited on the gate insulating film by the p-cvp method. This method is effective in reducing the level at the interface between SiN and a-8i, and it was therefore believed that the operational stability of the TPT made using this method is the best.

[Problem that the invention seeks to solve]

However, the problem remains that when a gate voltage is applied to a TPT manufactured by the conventional technique and left for a long time, the threshold voltage gradually shifts. Although this shift amount can be reduced by improving the film fabrication properties, such as by increasing the SiN and a-8i film deposition temperature, it is still not a sufficient value.

[Means for solving problems]

The above threshold voltage shift can be significantly reduced by forming an extremely thin oxide layer on the semiconductor layer (a-8i layer) side surface of the SiN gate insulating film.

[Effect]

When an oxide layer is formed on the SiN surface and when SiN is formed as an oxide 1
For example, when changing to 5ift, the shift of the dark value voltage is completely different, and the principle behind the improvement is unknown.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First, a Cr film 2 is deposited on a glass substrate 1, and then processed into a gate electrode pattern by photoetching. Thereafter, SiN3 was deposited by plasma CVD. A mixed gas of SiH4, NHa, and Nx was used for this deposition. Si
The thickness of the N film is 0.3 μm. After that, the same-CVD
02 gas was introduced into the apparatus. Gas pressure is 0.06T
It's o r r. High frequency power 0.02 W/l-j
Form an oxygen plasma, by applying a density of
The SiN surface was oxidized to form an oxide layer 4. The discharge time was 20 minutes, and the substrate temperature was 320°C.

Thereafter, oxygen was removed, a mixed gas of 5iHa and H2 was introduced, and an a-8i film 5 was deposited by plasma CVD. The film thickness is 0.3 μm. After that, an n-type a-8i film 6 doped with about 2% P was deposited, and the film thickness was 0.03.
Next, Cr7/AQ82 heavy films were deposited to a thickness of 0.1 μm and 0.3 pm, respectively, and processed using a photoetching method to form source and drain electrodes, and then dry etching was performed to form an n-type a layer in the channel portion. -5i film was removed. moreover.

A SiN film 9 was formed as a protective film by p-CVD method.

FIG. 2 shows the amount of shift in threshold voltage when gate voltages of +30 V and -30 V were applied for 1000 seconds to the a-S i T F T formed by this method and the TPT formed by the conventional method, respectively. In the TPT according to the present invention, in the positive direction,
Threshold voltage shift force (both in the negative direction) is small.

The thickness of this oxidized layer was in the range of several tens to hundreds of layers, and no deterioration in mobility was observed due to the formation of the oxidized layer. Furthermore, the off-state current was approximately the same or lower than that of the conventional sample.

Here, oxygen plasma was used to form the oxide layer, but the gas used here is Hz or N gas containing several percent or more of oxygen.
A similar improvement effect was seen with z, Ar, etc.

〔Effect of the invention〕

According to the present invention, by forming an oxide layer on the surface of the gate insulating film SiN, the stability of a-8iTPT can be significantly improved.

This has the effect of improving the long-term reliability of the characteristics of a liquid crystal display using this.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a TPT according to an embodiment of the present invention. FIG. 2 is a diagram showing the shift amount of the threshold voltage that shows the effect of the present invention. 1...Glass substrate, 2...Cr, 3...SiN,
4...Acid. layer, 5-a-3i, 6-a-S i n layer,
7...Cr, 8-AQ, 9-8iN. No./[! ]

Claims (1)

[Claims] 1. In a thin film transistor in which amorphous hydrogenated silicon is laminated as a semiconductor on a gate insulating film made of a compound of silicon and nitrogen, an extremely thin film is formed on the surface of the amorphous silicon side of the gate insulating film. A thin film transistor characterized by having an oxide layer. 2. The thin film transistor according to claim 1, wherein the oxide layer is formed by oxidizing the surface of the gate insulating film on the amorphous silicon side.