JPH02203567A - Thin film transistor - Google Patents

Abstract

PURPOSE:To manufacture in a short time a semiconductor device by laser CVD by a method wherein a semiconductor layer is arranged between a source electrode and a drain electrode, and the semiconductor layer comes into contact with each electrode, only through the side wall part. CONSTITUTION:Firstly, a chromium film is patterned on a glass substrate 6, thereby forming a drain electrode 1 and a source electrode 2. Patterning is performed by plasma CVD method. A semiconductor layer 4 is formed in the gap between the electrodes 1 and 2, in the manner in which the length in the gap direction becomes equal to the gap width. After a gate insulating film 5 is formed, a gate electrode 3 is formed thereon and a thin film pattern is obtained. The semiconductor layer 4 comes into contact with the electrodes 1 and 2 only through the side wall part, so that direct laser irradiation on the electrode surface is unnecessitated, and highly intense laser light irradiation is enabled. As a result, a thin film can be formed in a short time by laser CVD.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to thin film transistors.

[Prior art and its problems] In manufacturing a staggered thin film transistor, which requires fewer manufacturing steps than an inverted staggered thin film transistor, after forming drain and source metal electrodes, a metal electrode is formed that partially covers the drain and source electrodes. A semiconductor layer was formed between both electrodes. The authors have proposed a method to form a semiconductor layer with such a structure by directly irradiating patterned laser light.
It was reported in the Proceedings of the 49th Japan Society of Applied Physics Conference in 1988, page 534. Laser CVD does not require a resist process, so it has the feature that the manufacturing process can be significantly shortened compared to other methods.

However, in the case of laser CVD for forming a semiconductor layer of a conventional staggered thin film transistor structure, if the intensity of the irradiation light is not sufficiently lowered, the electrode metal will diffuse into the semiconductor layer.
This had the disadvantage of degrading the electrical characteristics of the transistor. For this reason, in conventional laser CVD semiconductor layer formation, the intensity of the irradiated light is lowered, and as a result, it takes a long time to obtain the desired film thickness, and the advantage of shortening the process by laser CVD has not been fully utilized.

The present invention has been made to solve the conventional problems as described above, and an object of the present invention is to provide a thin film transistor in which a semiconductor layer can be formed in a short time by laser CVD.

[Means for Solving the Problems] The present invention provides a thin film transistor in which a semiconductor layer is formed between a source electrode and a drain electrode, and a gate insulating film and a gate electrode are sequentially formed on the semiconductor layer. The thin film transistor is characterized in that contact with the semiconductor layer is made only at the side wall portion of each electrode.

[Operation] Laser CVD is a technology that locally promotes the decomposition reaction of the source gas only in the laser beam irradiation area to form a film.
If applied to the formation of a semiconductor layer of a thin film transistor matrix, the resist process required in the past can be omitted, and the time required for process and manufacturing can be greatly reduced.

However, in order to create a conventional type staggered film transistor with a structure in which contacts between the drain and source electrodes and the semiconductor layer are made on both the electrode surface and the side surfaces, the electrode surface must also be directly irradiated with laser light. Must be. Therefore, under a laser beam intensity that allows a sufficiently high film deposition rate, diffusion of metal into the semiconductor layer occurs, leading to deterioration in the performance of the thin film transistor. In order to prevent this, conventionally the intensity of the laser beam was sufficiently lowered and the semiconductor layer was formed at a low deposition rate. For this reason, in the conventional structure, although the number of steps can be reduced, the time required for manufacturing cannot be shortened, and the advantages of laser CVD cannot be fully utilized.

In the present invention, only the side surfaces of the electrodes are in contact with the semiconductor layer, so when fabricating by laser CVD, it is only necessary to irradiate the inter-electrode gap with laser light, and it is not necessary to irradiate the electrodes. There is no. Therefore, even if high-intensity laser light is irradiated, the electrode material will not dissolve into the semiconductor layer, so it can be manufactured in a short time. Therefore, the manufacturing process can be shortened without deteriorating the performance of the thin film transistor.

The contact resistance between the semiconductor layer and metal is the same metal film thickness.

The semiconductor film thickness is larger than the conventional structure, but the metal film thickness is greater.

By slightly increasing the thickness of the semiconductor film, the contact resistance can be kept as low as in the conventional case. At this time, even when taking into account the increased time required for film formation, a thin film transistor can be created in a much shorter time than with conventional structures.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a partial cross-sectional view of a thin film transistor according to the present invention.

In the figure, 1 is a drain electrode, 2 is a source electrode, 3 is a gate electrode, 4 is a semiconductor layer, 5 is a gate insulating film, 6 is a glass substrate, and 12 is an ohmic layer.

Chromium was used as the material for each of the electrodes 1 and 2, SiN was used as the material for the gate insulating film 5, and amorphous silicon was used for the semiconductor layer 4. Further, in order to improve ohmic contact, the surfaces of the drain and source electrodes were covered with an ohmic layer 12 made of a silicon thin film into which n-type impurities were implanted.

Next, a method for manufacturing the above thin film transistor will be described.

First, a chromium film is formed by sputtering on a glass substrate 6 shown in FIG. 1, and patterned to form a drain electrode 1 and a source electrode 2. next,
A phosphorus-doped silicon film as the ohmic layer 12 is formed by plasma CVD and patterned.

Subsequently, using the film forming apparatus shown in FIG. 2, the semiconductor layer 4 is formed in the following manner. The glass substrate 6 is fixed to the CVD chamber 11, and the light emitted from the ArF laser 7 is passed through the mask 8.
, a lens 9, and a synthetic quartz window 10 to irradiate the gap between the source electrode 2 and the drain electrode 1 with a beam pattern in which the length in the gap direction is equal to the gap width. As a result, CV
Disilane gas introduced into the D chamber 11 is photochemically decomposed by an ArF laser to form a-3i as the semiconductor layer 4:
A patterned thin film of H film is formed.

Subsequently, a SiN layer as the gate insulating film 5 is formed by plasma CVD. Finally, a chromium film is formed again by sputtering, and then patterned to form the gate electrode 3.

A thin film transistor was manufactured as described above.

In the thin film transistor structure obtained in the example, even if the laser is irradiated with an irradiation light intensity of 18 W/cm2 or more in the process of forming the semiconductor layer, the electrode metal does not diffuse into the semiconductor film, and the OFF current of the thin film transistor is It was low enough. Further, the film formation rate was more than 10 times the film formation rate obtained when the electrodes were directly irradiated with low irradiation light intensity of 0.1 songs/Cm2 or less. Furthermore, it was confirmed from the drain current-drain voltage characteristics that good ohmic contact was formed between the drain and source electrodes and the semiconductor layer.

Note that it is not necessarily necessary to use SiN for the gate insulating film, and SiO2 may also be used. Further, each electrode does not necessarily need to be made of chromium, but may be made of tantalum or aluminum. Moreover, the semiconductor layer is not necessarily a-3i:)-1
There is no need to use polysilicon, and polysilicon may be used.

[Effects of the Invention] As described above, in the thin film transistor according to the present invention, the semiconductor layer can be formed at a high deposition rate without diffusing the drain and source electrodes into the semiconductor layer.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view of an embodiment of the present invention, and FIG. 2 is a configuration diagram of an example of an apparatus used for manufacturing the thin film transistor of the present invention.

Claims (1)

[Claims] (1) In a thin film transistor in which a semiconductor layer is formed between a source electrode and a drain electrode, and a gate insulating film and a gate electrode are sequentially formed on the semiconductor layer, the contact between the source electrode and the drain electrode and the semiconductor layer is at each electrode. A thin film transistor characterized in that only a sidewall portion of the thin film transistor is formed.