JP3489217B2 - Method for manufacturing thin film transistor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor.

[0002]

2. Description of the Related Art As a method of manufacturing a thin film transistor, there are a bottom gate method in which a gate electrode is first formed on an insulating substrate such as a glass substrate, and a top gate method in which a gate electrode is later formed. For example, in the method of manufacturing a bottom gate type thin film transistor, a blocking layer for an etching stopper is formed on an intrinsic semiconductor layer such as amorphous silicon which will be a channel region formed on an insulating substrate, and impurities are further introduced on the blocking layer. An impurity semiconductor layer such as n ₊ silicon is formed. Then, the source and drain electrodes are formed on this impurity-introduced semiconductor layer. The thin film transistor manufactured in this manner is widely used as a display driving means of an active matrix type liquid crystal device.

[0003]

However, in the thin film transistor manufactured by the conventional manufacturing method described above, the interface between the intrinsic semiconductor layer and the impurity semiconductor layer and the interface between the impurity semiconductor layer and the source / drain electrodes are slightly different. There is an impurity layer due to silicon oxide (SiOx) or dirt. Therefore, there is a problem that the contact resistance becomes large, the current is lowered particularly at a low drain voltage, and the characteristic of the drain current with respect to the drain voltage, that is, the ohmic characteristic of the channel region is deteriorated. When such a thin film transistor having poor ohmic characteristics is used as a switching element which is a display driving means of a liquid crystal display device, it causes gradation defects in a data line and causes point defects in display. The present invention is to solve such a conventional problem, and an object thereof is to provide a method of manufacturing a thin film transistor having excellent ohmic characteristics by a specific manufacturing process.

[0004]

In order to achieve the above-mentioned object, the present invention forms a blocking layer for an etching stopper on the upper surface of a semiconductor layer formed on a substrate corresponding to a channel region, An area in which an impurity semiconductor layer is formed on the upper surface of the blocking layer , an electrode is formed on the upper surface of the impurity semiconductor layer, and which is blocked by the blocking layer.
Hydrogen ion or inert gas in the region of the semiconductor layer other than
It is characterized in that it introduces ions .

[0005]

According to the present invention, a thin film transistor having excellent ohmic characteristics can be obtained by introducing ions between the semiconductor layer and the impurity semiconductor layer and between the impurity semiconductor layer and the electrode.

[0006]

1 to 5 are sectional views showing a bottom gate type manufacturing process of a thin film transistor according to the present invention. A method of manufacturing a thin film transistor will be described with reference to these drawings in order. The thin film transistor in the case of this embodiment is used as a switching element which is a display driving means of an active matrix type liquid crystal device.

First, a chromium (Cr) layer having a thickness of about 100 nm is formed on the upper surface of the insulating substrate 1 by sputtering, and the gate electrode 2 is formed by photolithography as shown in FIG. Insulating substrate 1 including the formed gate electrode 2
The gate insulating film 3, such as silicon nitride (SiN), having a thickness of about 500 nm, is formed on the entire upper surface by plasma CVD to about 50
nm non-doped amorphous silicon (a-S
i) silicon layer (i-Si) 4, which is an intrinsic semiconductor layer,
And a silicon nitride (SiN) layer having a thickness of about 200 nm is continuously formed. Further, an unnecessary portion of this silicon nitride layer is removed by photolithography to form a blocking layer 5 for an etching stopper. Figure 2
Shown in. Then, on the silicon layer 4 including the blocking layer 5, an n ⁺ amorphous silicon layer 6 into which phosphorous ions have been introduced is formed by plasma CVD to a thickness of about 25 nm.
As shown in FIG. 5, the n ⁺ amorphous silicon layer 6 and the silicon layer 4 on the lower surface thereof are removed by photolithography at unnecessary portions. Then, a chromium layer having a thickness of about 25 nm is formed on the upper surface of the n ⁺ amorphous silicon layer 6 by sputtering, and unnecessary portions are removed by photolithography to remove the source electrode 7a and the drain electrode 7b, as shown in FIG. To form.

Next, as shown in FIG. 5, an ion doping apparatus (not shown) is used to add hydrogen ions (H ⁺ ) to the intrinsic semiconductor layer at an acceleration voltage of about 10 kv and a dose of about 10 ¹⁶ atm / cm ^2. Is doped (introduced) into the silicon layer 4.
As a result of this ion doping, hydrogen ions are implanted into a region other than the region blocked by the blocking layer 5, and the amorphous silicon layer 4 and the n ⁺ amorphous silicon layer 6, or the n ⁺ amorphous silicon layer 6 and the source electrode 7a or The contact resistance at the interface between the n ⁺ amorphous silicon layer 6 and the drain electrode 7b is reduced, and the ohmic characteristics between the source and drain of the thin film transistor are improved. FIG. 6 shows data of ohmic characteristics improved by the present invention. In FIG. 6, A is an ohmic characteristic of a thin film transistor manufactured by a conventional manufacturing method,
B is the ohmic characteristic of the thin film transistor according to the manufacturing method of the present invention. As is apparent from this figure, it can be seen that the ohmic characteristics of the thin film transistor are improved by the manufacturing method of the present invention.

In the above embodiment, hydrogen ions were used as the doping ions, but helium (H
The same effect can be obtained by doping an inert gas ion such as e), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), or radon (Rn). Further, as another example, it is possible to improve the ohmic characteristics by performing pretreatment with a hydrofluoric acid-based solution instead of performing ion doping.

Although the thin film transistor in the above embodiment is of the bottom gate type, the present invention can be applied to a top gate type thin film transistor. Although the thin film transistor used in the liquid crystal device is taken as an example, the present invention is also effective as a method for manufacturing an IC such as a microprocessor or a memory.

[0011]

According to the present invention, a thin film transistor having excellent ohmic characteristics can be obtained by adding a manufacturing process of introducing ions between the semiconductor layer and the impurity semiconductor layer and between the impurity semiconductor layer and the electrode. When such a thin film transistor is used for the display driving means of a liquid crystal display device, it is possible to improve the gradation defect of the data line, and high quality image display can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view (1) showing a manufacturing process of a thin film transistor of the invention.

FIG. 2 is a sectional view (No. 2) showing the manufacturing process of the thin film transistor of the invention.

FIG. 3 is a cross-sectional view (3) showing the manufacturing process of the thin film transistor of the invention.

FIG. 4 is a cross-sectional view (4) showing the manufacturing process of the thin film transistor of the invention.

FIG. 5 is a diagram showing how the silicon layer 4 is doped with hydrogen ions after the step of FIG. 4;

FIG. 6 is a diagram showing ohmic characteristics of a thin film transistor according to a conventional example and a manufacturing method of the present invention.

[Explanation of symbols]

1 Insulating Substrate 2 Gate Electrode 3 Gate Insulating Film 4 Amorphous Silicon Layer 5 Blocking Layer 6 n ⁺ Amorphous Silicon Layer 7a Source Electrode 7b Drain Electrode

Claims (3)

(57) [Claims] 1. A blocking layer for an etching stopper is formed on an upper surface of a semiconductor layer formed on a substrate corresponding to a channel region, and an impurity semiconductor layer is formed on the upper surface of the semiconductor layer and the blocking layer. Area formed by forming electrodes on the upper surface of the layer and blocked by the blocking layer
Hydrogen ion or inert gas in the region of the semiconductor layer other than
A method of manufacturing a thin film transistor, which comprises introducing a positive ion . 2. The method of manufacturing a thin film transistor according to claim 1 , wherein the semiconductor layer is an amorphous silicon layer. 3. A gate electrode is formed on the upper surface of the insulating substrate, a gate insulating film is formed on the upper surface of the insulating substrate including the gate electrode, and the semiconductor layer is formed on the upper surface of the gate insulating film. method of manufacturing a thin film transistor according to claim 1 or 2, characterized.