JPS59182569A - Polycrystalline silicon thin-film transistor - Google Patents

Abstract

PURPOSE:To obtain excellent output characteristics with superior reproducibility by forming source and drain electrodes on a polycrystalline silicon film constituting a polycrystalline silicon thin-film transistor and inactivating the surface of the film through heat treatment in a mixed gas containing hydrogen when the transistor is formed on an insulating substrate. CONSTITUTION:A polycrystalline silicon semiconductor film 2 is deposited on an insulator substrate 1, source and drain regions are formed to the film 2, and a source electrode 4 and a drain electrode 5 are shaped on the film 2. The whole surface containing these electrodes is coated with a gate insulating film 3, and a gate electrode 6 is shaped on the film 3 while being made correspond to a channel region between the source and drain regions, but the next heat treatment is executed before the whole surface is coated with the film 3. That is, the surface of the film 2 is inactivated previously through heat treatment in hydrogen or a mixed gas of hydrogen and nitrogen, and pollution during the formation of the film 3 is avoided. When the mixed gas is used at that time, the quantity of hydrogen shall be 1mol% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a polycrystalline silicon thin film transistor, and particularly to a polycrystalline silicon thin film transistor that provides good output characteristics.

[Background of the invention]

A thin film transistor is an active element made by depositing a semiconductor thin film on an insulating substrate by vapor deposition or other methods.
Similar to ET. However, unlike M9S-FETs, which are usually formed using a single crystal substrate, NIN thin film transistors have the advantage of being able to fabricate large-area transistor layers because they are constructed from a semiconductor thin film formed on an insulator substrate. ing. Therefore, it is extremely suitable as, for example, a switching element for preventing crosstalk in a liquid crystal matrix display. In other words, in recent years, liquid crystal matrix displays have been developed as devices for pocket TVs and computer terminals, and there is a need for even higher definition images, but in order to prevent crosstalk due to the increase in the number of pixels, An effective method is to provide a switching element in each pixel. This is disadvantageous because the vortex film transistor can be formed on one substrate of the display panel. In this case, compounds such as c(1s l Cd86) and amorphous silicon can also be used as the semiconductor constituting the thin film, but polycrystalline silicon is the best from the viewpoint of stability of characteristics and non-polluting. 2 and 2 are main part sectional views showing an example of this type of thin film transistor that is commonly used. In the figure, 1 is an insulating substrate made of glass or the like, 2 is a semiconductor film, and 3 is an insulating film. , 495 are source and drain electrodes, and 6 is a gate electrode.

However, in a thin film transistor that has the above structure, when the semiconductor film 2 is made of polycrystalline silicon, if the film is thin, the crystallinity is insufficient and good operating characteristics cannot be obtained. It is. However, if the thickness of the semiconductor film 2 is increased in this way, in the structure shown in FIGS.
Another disadvantage is that carriers are not sufficiently excited in the semiconductor film 2 near the drain electrode t1, making it difficult to operate. Therefore, when polycrystalline silicon is used as the semiconductor film 2, it is advantageous in terms of carrier excitation as shown in FIG.

The structure shown in FIG. 4 is considered desirable. In addition, Figure 3,
In FIG. 11, the same part as in FIGS. 1 and 2 will be formed, and later a polycrystalline silicon semiconductor film 2 will be formed.
It is necessary to raise the temperature to 00°C or higher, and the temperature is high when the silicon film is formed.

The disadvantage is that the electrode material diffuses into the silicon or reacts with the silicon, making it practically unusable. After all, when polycrystalline silicon is used as the semiconductor film 2, the fourth
I am forced to adopt the structure shown in the figure.

In the case of the structure shown in FIG. 4, the source electrode 4. Although the drain electrode 5 can be formed by mask vapor deposition, there are drawbacks such as insufficient precision of the electrode pattern and leakage between the source electrode 4 and the drain electrode 5. On the other hand, photoetching can easily form a predetermined electrode pattern and produce desirable results. Further, considering the conditions that the electrode material should not easily react with polycrystalline silicon and that good electrical contact can be made, the electrode material is limited to M. As a result, it is desirable that the source electrode 4° drain electrode 5 of the polycrystalline silicon thin film transistor be formed with an At pattern formed by photoetching.

However, when such a Hiko polycrystalline silicon thin film transistor was manufactured, the following problems were found. That is, the source electrode 4. Since the polycrystalline silicon surface after forming the drain electrode 5 is extremely active, if it is exposed to the outside air before the gate insulating film 3 is formed, it will undergo some deterioration, causing damage to the completed polycrystalline silicon thin film transistor. Output characteristics change. As a result, it has been extremely difficult to manufacture polycrystalline silicon thin film transistors with good reproducibility.

[Purpose of the invention]

Therefore, the present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a polycrystalline silicon thin film transistor that has good output characteristics and can be obtained with good reproducibility. .

[Summary of the invention]

In order to achieve this object, the present invention subjects the surface of polycrystalline silicon to inactivation treatment after forming the source and drain electrodes.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail using the drawings.

First, in FIG. 4, the source electrode 4. Drain electrode 5
After forming the polycrystalline silicon semiconductor film 2, the surface of the polycrystalline silicon semiconductor film 2 is heat-treated in hydrogen or a mixed gas of hydrogen and an inert gas, such as nitrogen. With this method, the surface of the polycrystalline silicon semiconductor film 20 is inactivated, and even if the surface of the polycrystalline silicon semiconductor film 2 is exposed to the outside air until the gate insulating film 3 is formed, it will not be contaminated. As long as this is not done, the output characteristics of the completed polycrystalline silicon thin film transistor will not change. As a result, it becomes possible to manufacture polycrystalline silicon thin film transistors with good reproducibility.

Here, if the processing atmosphere is 100 moz% hydrogen, there will be no problem, and in the case of a mixed gas with active gas, good results can be obtained if the hydrogen amount is 1 m□t% or more. . In addition, when the heat treatment temperature is lower than 120℃,
If a sufficient effect is not obtained, and if the temperature exceeds 440°C, At in the source and drain' electrodes will diffuse into the grain boundaries of polycrystalline silicon and deteriorate the output characteristics of the polycrystalline silicon thin film transistor. A suitable temperature range is 250°C to 380°C, more preferably 250°C to 380°C.

Furthermore, if the surface of the polycrystalline silicon semiconductor film is treated with oxygen plasma before or after heat treatment in hydrogen or a mixed gas of hydrogen and inert residue, the output characteristics of the completed polycrystalline silicon thin film transistor can be stabilized for a long period of time. It is possible to turn it into a fossil.

〔Effect of the invention〕

As explained above, according to the present invention, after forming the source electrode and the drain electrode, the bare surface of the polycrystalline silicon semiconductor film is heat-treated with hydrogen or a mixture of hydrogen and an inert gas. : Since the surface of M can be stabilized, it has an extremely excellent effect in that a polycrystalline silicon thin film transistor with good output characteristics and high reproducibility can be obtained.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of main parts of conventional polycrystalline silicon thin film transistors, and FIG. 4 is a cross-sectional view of main parts for explaining an example of a polycrystalline silicon thin film transistor according to the present invention. 1... insulator substrate, 2... polycrystalline:/ IJ contact semiconductor film, 3... insulating film, 4... source electrode, 5... do 1/ In-electrode 6 a * +1 ・
gate electrode.

Claims (1)

[Claims] In a polycrystalline silicon thin film transistor made of a polycrystalline silicon film formed on an insulating substrate, after forming source and drain electrodes on the polycrystalline silicon film, the polycrystalline silicon film is heat-treated in a mixed gas containing at least hydrogen. A polycrystalline silicon thin film transistor characterized by having an inactivated surface.