JPS6167268A - Thin film transistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve TFT characteristic by forming the first semiconductor region of a low resistivity through a gate insulating film on a region which contains a gate electrode, and forming the second semiconductor region of high resistivity around the first region, thereby improving the boundary between the insulating layer and the semiconductor layer in the same degree as a metal mask type. CONSTITUTION:After a gate electrode 8 made of aluminum is formed on an insulating substrate 7 of glass or the like, aluminum is sputtered on the substrate 7 and the electrode 8 to form an Al2O3 film 9, and a CdSe film is formed thereon. A photoresist is coated on the overall surface of the high resistance CdSe film 10, the pattern of a photoresist film 14 of the prescribed shape is formed, and an impurity 15 for imparting an N type conductivity is formed on the films 10, 14. After the film 14 and the impurity 15 thereon are removed, the impurity 15 adhered onto the film 10 is heat treated, uniformly diffused in the film 10, and converted into a low resistance CdSe film 11. Since this region is used as the channel region of a thin film transistor, an element having a high gm can be obtained. Then, source and drain electrodes 12, 13 made of aluminum or the like are formed on the region which contains the film 11.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in thin film transistors, and particularly to a thin film transistor with a good interface between a gate insulating film and a semiconductor layer, and a method for manufacturing the same.

(Structure of a conventional example and its problems) A conventional example of a thin film transistor using CdSe as a semiconductor layer is shown in FIG. A gate electrode 2 formed of a metal layer such as Ag on a glass substrate 1, a gate insulating film 3 made of AN, O, etc., an impurity 1 imparting n-type conductivity, such as In, Ga, etc.
It is composed of a semiconductor layer 4 made of CdSe containing AN, etc., and a source electrode 5 and a drain electrode 6 made of a metal layer such as A&. As a method for forming a semiconductor layer in a predetermined region in a thin film transistor having such a structure,
There are two methods: a metal mask method in which areas other than the area to which the semiconductor is attached are covered with a metal thin piece, and a photolithography method using a photoresist film, which is well known as IC technology. When the shape of the region to which CdSe is deposited by vapor deposition or the like is less than several tens of microns, the metal mask method becomes difficult in terms of accuracy, and the photolithography method must be used. In this case, Cd
In order to reliably and easily form Se only in predetermined areas, a photoresist film or a foot-off method is usually used. In this method, a photoresist film is coated on the entire surface of the gate insulating film 3, and then Cd
The photoresist film is removed only from the region where Se is to be attached. After that, CdSe is deposited on the entire surface by vapor deposition, etc., and then the photoresist film and the CdSe on the photoresist film are deposited.
This is a method of removing e. In this conventional method, CdS
If there is residue of the photoresist film, impurities contained in the photoresist film, or contamination from the exposure and development processes in the area where the CdSe film is deposited, the insulating layer and CdSe layer, which will become the channel region of the thin film transistor, will be damaged. The interface with the substrate becomes extremely dirty, and many trap levels of carriers occur, making it impossible to obtain good transistor characteristics. For example, Cd5e with the same configuration and shape
-The table shows a comparison of the electrical characteristics of TPT manufactured using a metal mask method and a photolithography method.

In the case of the table, the threshold voltage V increases, and the mobility μ of CdSe determined from the transistor characteristics extremely decreases.

In addition, the electron mobility μ in the CdSe film decreases and the drain current decreases. There are also fewer brackets. The stability is also poor. It is clear that the influence of the photoresist film process on the interface between the gate insulating film and the CdSe layer has a large effect on the deterioration of the TPT characteristics.

(Objective of the Invention) In view of the above-mentioned conventional techniques, an object of the present invention is to improve the characteristics of a TFT by making the interface between an insulating layer and a semiconductor layer as good as that of a metal mask method.

(Structure of the Invention) In order to achieve the above object, the present invention includes forming a first semiconductor region having a predetermined shape and having a low resistivity over a region including at least a gate electrode with a gate insulating film interposed therebetween; A second semiconductor region with high resistivity is formed around the first semiconductor region on the gate insulating film, and source and drain electrodes are formed on at least the first semiconductor region on the gate electrode. A thin film transistor and a method for manufacturing the same are provided. That is,
In the thin film transistor according to the present invention, a photoresist film is patterned by a photolithography method on a high-resistance CdSe film formed on the entire surface of a gate insulating film, and an impurity that gives n-type conductivity is deposited only in a predetermined region.
A heat treatment is performed to diffuse the impurity into CdSe to form a CdSe film with low resistivity, which becomes the active region of the TPT. With this method, the interface between the gate insulating film and the CdSe film, which forms the channel region of the TPT, is almost completely free of contamination caused by the photoresist film process using the photolithography method, which was seen in conventional examples, and the characteristics of the TFT are similar to those of the metal mask method. The same V as in the case of ? ＋μ、■. I was able to get

(Explanation of Examples) Hereinafter, the present invention will be explained in detail according to examples.

FIG. 2 is a cross-sectional view showing the structure of a single-film transistor that constitutes an embodiment of the present invention. An insulating substrate 7 made of glass or the like is provided with a gate electrode 8 made of a metal such as Aρ having a thickness of about 2000, and Al having a thickness of about 4000,
A gate insulating film 9 made of 03 or the like is formed. A high-resistance semiconductor layer 10 made of CdSe or the like is formed on the gate insulating film 9 and has a thickness of about 1,000 Ω and a resistivity of about 10 6 to 10' Ω·■. On the region including at least the gate electrode 8 in the layer 10, a low resistance film of a predetermined shape made of CdSe or the like having a resistivity of about 103 to IO4Ω including impurities such as Ga, In, 1, etc. that gives n-type conductivity is placed. A semiconductor region 11 is formed. A source electrode 12 and a drain electrode 13 made of AN or the like having a thickness of approximately 2,000 mm are formed on a region including at least the low-resistance semiconductor region 11. In the structure according to the present invention, since the semiconductor layer 10 is formed on the gate insulating film 9 without defining a fine region, a photoresist film is directly applied and formed on the insulating film.
Since there is no process of creating a fine pattern, there is no contamination of the interface between the gate insulating film 9 and the semiconductor layer 10 due to the photoresist film process, which has been a problem in the past. Thin 11
1; The fine channel and region of the J transistor are determined by introducing an impurity giving n-type conductivity into the fine semiconductor region 11 formed on the high-resistance semiconductor layer 10 by photolithography. This is done by forming a low-resistance semiconductor region that is actively active. At this time, a photoresist film is directly applied and formed on the high resistance semiconductor layer 10, but contamination at this time is limited to the surface of the high resistance semiconductor layer, and there is no adverse effect on the interface between the insulating film and the semiconductor layer. did not give. Further, there was no apparent adverse effect on the source electrode or drain electrode that would cause problems in the operation of the thin film transistor.・V7 of the thin film transistor having the structure according to the present invention is approximately 1V, and μ is approximately 200aJ.
Almost the same characteristics were obtained for the thin film transistor manufactured by the metal mask method as /v,s.

As a result, in the thin film transistor of the present invention, despite having a fine channel shape using the photolithography method, the interface between the insulating film and the semiconductor layer is as clean as that in the case of the metal mask method. It is clear that the electrical characteristics are significantly improved compared to thin film transistors with conventional structures.

Next, an example of a method for manufacturing a thin film transistor according to the present invention will be described with reference to FIG.

On an insulating substrate 7 made of glass or the like, a gate electrode 8 made of AQ or the like having a thickness of about 2,000 wafers is fabricated in a predetermined shape by vacuum evaporation using a resistance heating method or the like. After that, Ar:O,=3:1,4 is applied on the insulating substrate 7 and gate electrode 8.
At'2 with a thickness of about 4000 by sputtering, for example, AQ in an atmospheric gas of
0. A film 9 is formed. Next, the above 1. heated to about 300°C. O, a CdSe film with a thickness of about 1,000 layers is deposited on the film 9 by vacuum deposition using, for example, a resistance heating method.
It is formed at a speed of about sec. The composition of the CdSe film produced in this manner is very close to the stoichiometric ratio, and its electrical resistivity is as high as 10' to 10' Ω. Further, the mobility μ shows a small value of about 0.1a(/v,s) due to the influence of the potential barrier at the polycrystalline grain boundary (FIG. 3(A)).

A photoresist (
For example, after applying AZ1300 (trade name) to a thickness of about 1.5 μm, a pattern of a photoresist film 14 having a predetermined shape is formed by a well-known photolithography method.

After that, for example, by vacuum deposition using a resistance heating method,
Impurity 151 that provides n-type conductivity, such as Ga, I
The high-resistance CdSe is coated with a thickness of several layers, such as AN, AN, etc.
Formed on the film 1O and the photoresist film 14 (third
Figure (B)).

After removing the photoresist film 14 and the impurities 15 thereon by ultrasonic cleaning in acetone, etc., the impurities 15 adhering to the high resistance CdSe film 10 are heated at 200° C.-1 in a non-oxidizing atmosphere. A heat treatment is performed for about an hour to uniformly diffuse the impurity 15 into the high-resistance CdSe film 10 and convert the high-resistance CdSe film 10 into a low-resistance, electrically active CdSe film 11.

The resistivity of this low resistance CdSe@ll is 103~10'Ω
・■, and its mobility becomes a very large value of about 200 alt/v,s because the potential barrier that was inverted to n-type at each polycrystalline grain boundary is reduced by n-type impurities. Since this region is used as a channel region of a thin film transistor, a high g1 element can be obtained (FIG. 3(C)).

Thereafter, a source electrode 12 and a drain electrode 13 made of AQ or the like having a predetermined shape are formed in a region including the low resistance CdSe film 11 using, for example, a well-known photolithography method (FIG. 3(D)).

As described above, according to the method of manufacturing a thin film transistor according to the present invention, there is no need to apply a photoresist film on the gate insulating film 9, so that conventionally, the photoresist film and impurities therein are not coated on the gate insulating film 9. Problems in the characteristics of thin film transistors, which were caused by adhesion of particles or contamination during the formation of a predetermined pattern, have completely disappeared.

(Effects of the Invention) As is clear from the above description, according to the present invention, a thin 1
The electrical characteristics of the simulated transistor can be easily improved to the same level as the characteristics of a thin film transistor manufactured by the metal mask method, and can be widely used for driving various display devices.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional thin film transistor, FIG. 2 is a sectional view of a thin film transistor of the present invention, and FIG. 3 is a diagram showing an example of a method for manufacturing a thin film transistor of the present invention. 2.8...Gate electrode, 4,11...Low resistivity semiconductor region, 10...High resistivity semiconductor layer, 5゜1
2... Source electrode, 6.13... Drain electrode. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 Figure 3 (A) (B)

Claims (3)

[Claims] (1) A first semiconductor region of a predetermined shape with low resistivity is formed on at least a region including a gate electrode via a gate insulating film, and a first semiconductor region of a predetermined shape with low resistivity is formed around the first semiconductor region on the gate insulating film. A thin film transistor characterized in that a second semiconductor region having a high resistivity is formed, and a source and a drain electrode are formed at least on the first semiconductor region above the gate electrode. (2) Claim (1) characterized in that the first semiconductor region is made of a CdSe film containing an impurity giving n-type conductivity, and the second semiconductor region is made of a CdSe film. The thin film transistor described in Section 1. (3) A step of forming a gate insulating film in a region including a gate electrode formed on an insulating substrate, after forming a first semiconductor layer on the gate insulating film, applying a photoresist on the first semiconductor layer. a step of applying a film to form a pattern of a predetermined shape; a step of depositing an impurity imparting n-type conductivity on the first semiconductor layer and the photoresist film, and then removing the photoresist film; A thin film transistor comprising the steps of: diffusing impurities into the first semiconductor layer to form a second semiconductor layer; and forming source and drain electrodes in at least a region including the second semiconductor layer. Production method.