JPH0425178A - Manufacturing method of thin film transistor - Google Patents

Abstract

PURPOSE:To make a thin film transistor small enough in hysteresis of VG-ID characteristics so as to enable it to carry out an excellent switching action by a method wherein a very small amount of N-type impurities is diffused into a semiconductor layer. CONSTITUTION:A very small amount of N-type impurities is diffused into a semiconductor layer 14. If N-type impurities are diffused into the I-type semiconductor layer 14, the semiconductor layer 14 is lessened in band gap, so that a band gap difference between the semiconductor layer and a gate insulating film 13 becomes large. Therefore, the injection of charges between the semiconductor layer 14 and the gate insulating film 13 is of no effect, and in result a thin film transistor of this design becomes small in hysteresis. By this setup, a thin film transistor is possessed of a VG-ID characteristic very small in hysteresis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film transistor and a method for manufacturing the same.

[Conventional technology]

A thin film transistor has a gate electrode, a gate insulating film,
This thin film transistor is made up of a stack of a semiconductor layer, an ohmic contact layer made of an n-type semiconductor, and source and drain electrodes, and the structure shown in FIG. 4 is conventionally known as this thin film transistor.

This thin film transistor includes a gate electrode 2 formed on a substrate 1 made of glass or the like, and a gate insulating film 3 made of silicon nitride (SiN), a semiconductor layer 4, and an ohmic contact layer on the gate electrode 2. 5 and source and drain electrodes 6 and 7 are stacked. In addition,
The semiconductor layer 4 is made of an i-type semiconductor such as i-type amorphous, silicon or polysilicon (i-8j), and the ohmic contact layer 5 is made of an n-type semiconductor such as phosphorus (P). n-type amorphous silicon or polysilicon (n”
-8j).

By the way, the thin film transistor is mainly used as a switching element, and in order to make this thin film transistor perform a good switching operation, the VG-ID characteristic of this thin film transistor needs to be a characteristic with small hysteresis.

For this reason, in the conventional thin film transistor, the gate insulating film 3 has a composition ratio S of silicon atoms S1 and nitrogen atoms N.
It is formed of silicon nitride with j/N close to the stoichiometric ratio (Sj/N=0.75) to reduce the hysteresis of the V6ID characteristic.

[Problem to be solved by the invention]

However, even if the gate insulating film 3 of the conventional thin film transistor is formed of silicon nitride having a composition close to the stoichiometric ratio, its V. - There was a problem that the ID characteristic had a certain degree of hysteresis.

That is, FIG. 5 shows the Vc of the conventional thin film transistor.
This V6-ID characteristic is for a thin film L transistor with a gate insulating film 3 of 2000 mm thickness, drain voltage VD is 10V1, source voltage vs is Ov, and gate voltage VC is +40V ~ Change to -40V and source.

This is the result of measuring the current value flowing between the drain electrodes 6 and 7, which is V of a conventional thin film transistor. -1, the characteristics showed hysteresis with a hysteresis width W of about 3V under these measurement conditions.

The present invention has been made in view of the above circumstances, and its purpose is to provide a thin film transistor that can sufficiently reduce the hysteresis of the v6-ID characteristic and perform good switching operations. In addition, it is an object of the present invention to provide a method for manufacturing the same.

[Means to solve the problem]

The thin film transistor of the present invention is a thin film transistor in which a gate electrode, a gate insulating film, a semiconductor layer, an ohmic contact layer made of an n-type semiconductor, and source and drain electrodes are laminated. It is characterized by diffusion of impurities.

Further, in the method for manufacturing a thin film transistor of the present invention, a gate electrode is formed on a substrate, and a gate insulating film, a semiconductor layer made of an i-type semiconductor, and a semiconductor layer made of an n-type semiconductor are placed on the substrate on which the gate electrode is formed. After sequentially depositing an ohmic contact layer and metal films for source and drain electrodes, the n-type impurity contained in the ohmic contact layer above the semiconductor layer is thermally diffused into the semiconductor layer by heat treatment, and after this heat treatment, The method is characterized in that the source and drain electrode metal films and the underlying ohmic contact layer are patterned into the shapes of the source and drain electrodes.

[Effect]

That is, in the thin film transistor of the present invention, by diffusing a small amount of n-type impurity into the semiconductor layer, Vc
The hysteresis of the ID characteristic is reduced.

In addition, the method for manufacturing a thin film transistor of the present invention includes depositing an i-type semiconductor as a semiconductor layer, and then sequentially depositing an ohmic contact layer made of an n-type semiconductor and metal films for source and drain electrodes. , the n-type impurity contained in the ohmic contact layer is thermally diffused into the i-type semiconductor layer by heat treatment, and the metal film for source and drain electrodes and the ohmic contact layer thereunder are used as source and drain electrodes. If the heat treatment is performed before patterning into the shape of the semiconductor layer, the portions under the source and drain electrodes of the semiconductor layer and the source.

According to this manufacturing method, the n-type impurity contained in the ohmic contact layer can be diffused throughout the channel region between the drain electrodes.
- A transistor can be manufactured easily.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 is a cross-sectional view of the thin film transistor of this example.

This thin film transistor includes a gate electrode 12 formed on a substrate 1 made of glass or the like;
1' conductor layer 14 formed on this gate insulating film 13, and this "I" conductor layer 14,
4 Ohmic contact layer 1 on both sides of conductor layer 14
The source electrode 16 and the drain electrode 17 are formed through the electrode 5. Note that the gate insulating film 13
is the composition ratio Sj/of silicon atoms Sj and nitrogen atoms N
It is made of silicon nitride (SiN) in which N has a near stoichiometric ratio. Further, the ohmic contact layer 15 is
The semiconductor layer is formed of an n-type semiconductor, for example, n-type amorphous silicon or polysilicon (n+-5j) doped with an n-type impurity such as phosphorus (P), and the semiconductor layer]4
is a type 1 semiconductor made of i-type amorphous silicon or polysilicon (iSi) with a trace amount of n-type impurity diffused into an n-type silicon (n−-3j) layer with an extremely low concentration of n-type. has been done. The n-type impurity diffused into this semiconductor layer 14 is contained in the ohmic contact layer (
n-type impurities (phosphorus, etc.) contained in the n-type semiconductor layer) 15
The amount of diffusion of this n-type impurity is such that the semiconductor layer 14 is
The amount is said to be extremely small enough to not lose its function as a type semiconductor.

The reason why a small amount of n-type impurity is diffused into the semiconductor layer 14 over the entire area including its channel region is to make the VG-1 characteristic of this thin film transistor free from hysteresis. When a small amount of n-type impurity is diffused into the layer 14, the thin film transistor ■6-
The ID characteristic has almost no hysteresis as shown in FIG.

In addition, V6-1. shown in FIG. The characteristics were measured under the same conditions as those for measuring the v6-ID characteristics of the conventional thin film transistor shown in FIG. ~40V) to the source and drain electrodes 16
．． 17, and the V, -I characteristics of the thin film transistor of the above example exhibit only slight hysteresis with a hysteresis width W of approximately 0.5 V under these measurement conditions. It is.

When a small amount of n-type impurity is diffused into the semiconductor layer 14 in this way, V. - ■ The hysteresis of the characteristics becomes smaller when n-type impurities are diffused into the i-type semiconductor layer 14.
The bandgap of this semiconductor layer 14 becomes smaller, and the difference (barrier hide) between the bandgap of the semiconductor layer 14 and the bandgap of the gate insulating film 13 becomes large, and therefore, the difference between the bandgap of the semiconductor layer 14 and the bandgap of the gate insulating film 13 becomes large. This is thought to be because the effect of charge injection between the two is almost eliminated, and the hysteresis is reduced.

FIG. 2 shows the method for manufacturing the thin film transistor in the order of steps, and this thin film transistor is manufactured through the following steps.

First, as shown in FIG. 2(a), a metal film such as chromium (Cr) is deposited on the substrate 11-, and this metal film is patterned to form the gate electrode 12.
A gate insulating film 13 made of silicon nitride is deposited thereon, and a semiconductor layer 14 made of an l-type semiconductor is further deposited thereon.
Then, an ohmic contact layer 15 made of an n-type semiconductor and a metal film A for source and drain electrodes, such as chromium, which will become the source and drain electrodes 16 and 17 are deposited one after another.

Next, as shown in FIG. 2(b), the gate insulating film 1
A laminated film of 3, the semiconductor layer 14, the ohmic contact layer 15, and the metal film A for source and drain electrodes is patterned into the shape of a transistor element by photolithography.

Next, as shown in FIG. 2(c), the entire substrate 11 is heat-treated at a temperature higher than the deposition temperature of the semiconductor layer 14 and the ohmic contact layer 15, and the second ohmic contact is applied to the semiconductor layer 4. Layer (n-type semiconductor layer) 15
thermally diffuses the n-type impurity contained in the The heating temperature in this heat treatment is controlled to such an extent that diffusion of the n-type impurity from the ohmic contact layer 15 into the semiconductor layer 14 occurs only slightly. When a small amount of n-type impurity is diffused into the semiconductor layer 14 in this way, the semiconductor device layer 14 becomes an n-type semiconductor with a very low degree of n-type, as shown by the dotted pattern in the figure. In this case, the metal film A for the source and drain electrodes and the ohmic contact layer 15 thereunder are left over the entire surface of the semiconductor layer 14 with only their outer shape patterned into the shape of a transistor element. ]4, n-type impurities are diffused over the entire area including the portion below the source and drain electrodes 16.17 and the channel region between the source and drain electrodes 16.17.

After this, as shown in FIG. 2(d), source.

The metal film A for drain electrode and the ohmic contact layer thereunder] 5 are patterned by photolithography to form source and drain electrodes 16 and 17, thereby completing a thin film transistor.

That is, in the thin film transistor of the above embodiment, the hysteresis of the VG-ID characteristic is reduced by diffusing a small amount of n-type impurity into the semiconductor layer 14. According to this thin film transistor, the hysteresis of the V6-ID characteristic is reduced. Hysteresis can be made sufficiently small to perform good switching operations.

In addition, the method for manufacturing the thin film transistor of the embodiment described above includes depositing an i-type semiconductor as the semiconductor layer 14, and depositing an ohmic contact layer 15 made of an n-type semiconductor thereon, and a source layer and a source layer.
After sequentially depositing the metal film A for the drain electrode, the n-type impurity contained in the ohmic contact layer 15 is thermally diffused into the i-type semiconductor layer 14 by heat treatment. If the heat treatment is performed before patterning the metal film A and the ohmic contact layer 15 thereunder into the shape of the source and drain electrodes 16.17, the areas under the source and drain electrodes 16.17 of the semiconductor layer 14 will be Since the n-type impurity contained in the ohmic contact layer 15 can be diffused throughout the channel region between the source and drain electrodes 16 and 17, this manufacturing method makes it easy to manufacture the thin film transistor. I can do it.

〔Effect of the invention〕

The thin film transistor of the present invention has a trace amount of n in its semiconductor layer.
Since type impurities are diffused, the hysteresis of the v6-ID characteristic can be made sufficiently small to allow good switching operation.

Further, in the method for manufacturing a thin film transistor of the present invention, an i-type semiconductor is deposited as a semiconductor layer, an ohmic contact layer made of an n-type semiconductor and a metal film for source and drain electrodes are sequentially deposited thereon, and then the The n-type impurity contained in the ohmic contact layer is
Since heat is diffused into the semiconductor layer of the mold, the thin film transistor of the present invention can be easily manufactured.

[Brief explanation of drawings]

Figures 1 to 3 show an embodiment of the present invention. Figure 1 is a sectional view of a thin film transistor Naso, Figure 2 is a manufacturing process diagram of a thin film transistor Naso, and Figure 3 is a VG of a thin film transistor. - ID characteristic diagram. 4 and 5 are cross-sectional views of a conventional thin film transistor and its V6-I
. It is a characteristic diagram. DESCRIPTION OF SYMBOLS 11... Substrate, ]2... Gate electrode, ]3... Gate insulating film, ]4... Semiconductor layer, 15... Ohmic contact layer, 16... Source electrode, 17... Drain electrode, A...metal film for source and drain electrodes.

Claims (2)

[Claims] (1) Gate electrode, gate insulating film, semiconductor layer, n
an ohmic contact layer consisting of a type semiconductor, a source,
In a thin film transistor in which a drain electrode is laminated,
A thin film transistor characterized in that a trace amount of n-type impurity is diffused into the semiconductor layer. (2) A gate electrode is formed on a substrate, and a gate insulating film, a semiconductor layer made of an i-type semiconductor, an ohmic contact layer made of an n-type semiconductor, a source, a drain, etc. are formed on the substrate on which the gate electrode is formed. After sequentially depositing the metal films for the electrodes, the n-type impurity contained in the ohmic contact layer thereon is thermally diffused into the semiconductor layer by heat treatment, and after this heat treatment, the metal films for the source and drain electrodes are deposited. A method for manufacturing a thin film transistor, comprising patterning an ohmic contact layer thereunder into the shape of a source electrode and a drain electrode.