JPH0638430B2 - Method of manufacturing thin film transistor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a thin film transistor, particularly a thin film transistor using a cadmium selenide film (hereinafter referred to as a CdSe film) as a semiconductor film.

[Conventional technology]

In recent years, as semiconductor manufacturing technology has advanced, attempts have been made to apply thin film transistors as switching elements for displays, for example. There are various structures of this thin film transistor, but an inverted staggered type using a CdSe film is widely used, and its basic structure is shown in FIG.

As shown in FIG. 4, this inverted staggered thin film transistor has a gate electrode 2, a gate insulating film 3, a CdSe film 4 as a semiconductor film, and a CdSe film 4 as a semiconductor film, which are sequentially stacked on an insulating glass substrate 1. 4 and the source and drain electrodes 5 and 6 which are formed at a predetermined interval with respect to 4, and C between the source and drain electrodes 5 and 6 is formed.
It is known as a kind of field effect transistor in which the current flowing in the dSe film 4 is controlled by the voltage of the gate electrode 2.

[Problems to be solved by the invention]

However, in such a conventional inverted staggered thin film transistor, since the overcoat layer as the passivation film is not formed on the CdSe film 4, the electrical characteristics of the thin film transistor are easily affected by the ambient temperature and humidity. The conditions of use were extremely limited. Therefore, after the thin film transistor element shown in FIG. 4 is formed, the element is annealed in a non-oxidizing atmosphere such as N ₂ and then SiO 2 is deposited on the CdSe film 4 by, for example, a sputtering method, an electron beam evaporation method, a plasma CVD method or the like. ₂ , A ₂ O ₃
There is also a type in which an overcoat layer is formed by depositing an insulating material such as, but it has a drawback that the electrical characteristics of the thin film transistor are deteriorated. That is, in the inverted staggered CdSe thin film transistor formed by the conventional method, when an overcoat layer is formed on the CdSe film 4 after annealing in a non-oxidizing atmosphere, the CdSe film has a high resistance. Oxygen in the film is gettered in the overcoat layer and the resistance of the CdSe film becomes low. For example, when the thin film transistor is used as a transistor for a switching element, the off resistance becomes extremely small, and it cannot be put to practical use. I got it.

The present invention has been made in view of the above points, and an object thereof is to provide a method of manufacturing a thin film transistor having good characteristics.

[Means for solving problems]

A method of manufacturing a thin film transistor according to the present invention, a thin film transistor element is formed by exposing a semiconductor film on an insulating substrate, and then the thin film transistor element is annealed in an oxidizing atmosphere such as air or a mixed gas of oxygen and nitrogen, and then, This method is characterized in that an overcoat layer made of an insulating material is deposited on the surface of the semiconductor film to protect the semiconductor film, and then annealed in a non-oxygen atmosphere.

[Action]

In the method of the present invention, the thin film transistor element is annealed in an oxidizing atmosphere, and then an overcoat layer is deposited on the exposed surface of the semiconductor film to form a semiconductor formed by the annealing in the oxidizing atmosphere. It was found that the oxide on the film surface has a function of preventing gettering of oxygen by the overcoat layer.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a sectional view showing a method of manufacturing an inverted staggered type thin film transistor according to an embodiment of the present invention, and the same reference numerals as those in FIG. 4 indicate the same or corresponding portions. In this example,
First, a gate electrode 2 made of A having a thickness of 500 Å is formed in a predetermined shape on a glass substrate 1, and a gate insulating film 3 made of SiO _{2 having a} thickness of 3000 Å is formed on the entire surface including the gate electrode 2. Then, as a semiconductor film, a CdSe film 4 having a thickness of 2000 Å, for example, is selectively formed in a region on the gate insulating layer 3 facing the gate electrode 2. Next, the source and drain electrodes 5 and 6 made of Cr having a thickness of 700 Å, for example, are formed on the CdSe film 4 at intervals corresponding to the width of the gate electrode 2 to form a part of the CdSe film 4. A thin film transistor element having an exposed portion is formed. Then, after forming the source and drain electrodes 5 and 6, for example, in an oxidizing atmosphere in air,
0 to 450 ° C, several minutes to several hours, 400 ° C, 30 in a typical example
Then, the thin film transistor element is annealed. Then, on the CdSe film 4, for example, a thickness of
The reverse staggered thin film transistor as shown in FIG. 1 was produced by depositing an overcoat layer 7 of 2000 Å made of SiO ₂ . When the overcoat layer 7 is formed by a sputtering method, an electron beam evaporation method, a plasma CVD method, or the like, CdSe is formed at the time of forming the film.
Since the film 4 is damaged and the characteristics are deteriorated, after forming the overcoat layer, 350 to 500 in a non-oxidizing atmosphere such as N _2.
It is necessary to anneal at a temperature of several minutes to several hours, typically 450 ° C. for 30 minutes.

FIG. 2 shows the gate voltage V applied to the gate electrode of the thin film transistor according to the present invention thus formed.
FIG. 3 is a characteristic diagram showing a result of measuring a drain current I _D with respect to a drain voltage V _D when _G (V _G = 0, 20 V) is used as a parameter, and a characteristic diagram according to a conventional example corresponding to FIG. Shown in the figure. Here, FIG. 3 shows that after the above-mentioned conventional source and drain electrodes are formed, they are annealed in a non-oxidizing atmosphere such as N ₂ at 350 to 400 ° C. for several minutes to several hours and then overcoated on the CdSe film. a characteristic diagram obtained when measuring a drain current I _D with respect to the drain voltage V _D on the reverse staggered thin film transistor deposited form a layer, as can be seen from the figure, the off-current ((V _G
= 0 V) is on the order of mA, and cannot be put to practical use for a switching element, for example. On the other hand, as is clear from FIG. 2, the thin film transistor according to the present example has better saturation characteristics than the conventional one, and the off current (V _D = 10 V, V _G = 0 V) is Two
nA, ON current (V _D = 10V, V _G = 20V) is 120μA
And the on / off ratio is 10 ⁴ or more. This value is sufficient for use as a transistor for a switching element of a matrix display, for example.

Considering the reason why the thin film transistor according to the present invention exhibits good characteristics in this way, it is not clear why annealing in an oxidizing atmosphere prevents gettering of oxygen by the overcoat layer, but after annealing in an oxidizing atmosphere, the CdSe film is not clear. When the surface was examined by Auger analysis, C
r and O were detected, and Cr and O were hardly detected on the surface of the CdSe film in the sample annealed in the non-oxidizing atmosphere. From this result, it is presumed that the Cr oxide on the surface of the CdSe film formed by the annealing in the oxidizing atmosphere may act as a barrier for preventing the gettering of oxygen by the overcoat layer.

In addition, in the above-described embodiment, the case of applying to the inverted staggered thin film transistor using the CdSe film as the semiconductor film is shown, but the present invention is not limited to this, and a semiconductor film other than the CdSe film may be used, Needless to say, the same applies to other types than the inverted staggered type.

〔The invention's effect〕

As described above, according to the method for manufacturing a thin film transistor of the present invention, after annealing the thin film transistor element in an oxidizing atmosphere, an overcoat layer is formed on the exposed semiconductor film of the element, and a non-oxygen atmosphere is further applied. By annealing in the inside, it is possible to obtain a thin film transistor having good characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a method of manufacturing a thin film transistor according to the present invention, FIG. 2 is a drain voltage / drain current characteristic diagram of a thin film transistor according to the present invention, and FIG. 3 is a drain voltage / drain of a conventional thin film transistor. FIG. 4 is a sectional view showing the basic structure of a generally known inverted staggered thin film transistor. 1 ... Glass substrate, 2 ... Gate electrode, 3 ... Gate insulating film, 4 ... CdSe film (semiconductor film), 5 ... Source electrode, 6 ... Drain electrode, 7 ... Overcoat layer.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Tokuhide Shimojo 700 Wada, Ueno Town, Ise City, Mie Prefecture, Ise Denshi Kogyo Co., Ltd. (56) Reference JP-A-57-109377 (JP, A)

Claims (2)

[Claims] 1. A step of forming a thin film transistor element by exposing a semiconductor film on an insulating substrate, a step of annealing the thin film transistor element in an oxidizing atmosphere, and an overcoat layer deposited on the semiconductor film. A method of manufacturing a thin film transistor, comprising: a step of annealing the thin film transistor in a non-oxidizing atmosphere. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the semiconductor film is a cadmium selenide film.