JPH04125936A - Forming method of thin film transistor - Google Patents

Abstract

PURPOSE:To exclude the overlapping parts between electrodes of a base, a source, and a drain, and reduce capacitances between the electrodes, by diffusing impurities by the effect of temperature rise of a semiconductor layer caused by projecting laser light from the substrate side while using a gate electrode as a mask. CONSTITUTION:A gate insulating film 4, a semiconductor layer 3, a impurity containing layer 7 are formed in order on a gate electrode 2 on a substrate 1. From the substrate 1 side, laser light 11 is projected; the impurities in the layer 7 are diffused in the semiconductor layer 3 by the effect of temperature rise in the layer 3, thereby forming a source.drain region, on which a source electrode 5 and a drain electrode 6 are formed. The temperature rise caused by the laser light 11 is restricted within a region which does not overlap at all with the gate electrode 2 irradiated with the laser light 11 while the gate electrode 2 is used as a mask, so that overlapping parts between the gate electrode and the source and the drain electrodes are not generated. Thereby capacitances between electrodes are reduced, and the rise time characteristics of a gate signal can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a thin film transistor used, for example, in a liquid crystal space luminosity wI4 device.

[Prior Art] FIG. 4 is a sectional view of a conventional inverted staggered thin film transistor disclosed in, for example, Japanese Patent Laid-Open No. 174673/1983. In the figure, (11 is a transparent insulating substrate, (2) is a gate electrode, (3) is a semiconductor layer, (4) is a gate insulating film, (5) is a source electrode, and (6) is a drain electrode.

Next, the operation will be explained. When a voltage is applied to the gate electrode (2), carriers are induced in the semiconductor layer (3) and the thin film transistor is turned on.

OF when no voltage is applied to the gate electrode (2)
It is in F state.

[Problems to be Solved by the Invention] The conventional inverted stagger type thin film transistor is configured as described above, and the source electrode (5) or the drain electrode (
6) and the gate electrode (2), the capacitance between the gate electrode (2) and the source electrode (5) (hereinafter referred to as gate-source capacitance) and the gate electrode (2) and the drain electrode ( 6) There was a drawback that the capacitance between them (hereinafter referred to as gate-drain capacitance) became large. For this reason, ■ When the gate signal falls, discharge occurs due to the gate-drain capacitance and the drain voltage decreases.
There were problems such as a slow rise of the gate signal due to the source capacitance, gate/drain capacitance, and gate resistance.

The second invention was made to solve the above-mentioned problems, and its purpose is to eliminate the overlap between the source electrode or drain electrode and the gate I electrode.

[Means for Solving the Problems] A method for manufacturing a thin film transistor according to the present invention involves injecting light from the substrate side using the gate electrode as a mask, increasing the temperature of the semiconductor film, diffusing impurities, and forming the source region and the drain. It forms a region.

[Operations] In the method for manufacturing a thin film transistor according to the present invention, impurities are diffused using the gate electrode as a mask to form the source region and the drain region, so it is possible to eliminate the overlapping portions of the gate electrode, the source electrode, and the drain electrode.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
Figures (a), (b), and (c) are cross-sectional views showing steps in a method for manufacturing a thin film transistor according to an embodiment of the present invention. In this figure, (1) is a transparent insulating substrate.

(2) is a gate electrode, and generally a high melting point metal such as Cr is used. (3) is a semiconductor layer, which is generally made of amorphous silicon, polycrystalline silicon, or the like. (4) is a Kate insulating film. (7) is PSG in the impurity-containing layer
etc. may be used.

Next, the creation method will be explained. First, as shown in FIG. 1(a), a gate insulating film (4) is placed on a gate electrode (2),
After forming the semiconductor layer (3), an impurity-containing layer (7) is formed. Next, as shown in FIG. 1(b), this substrate (
When excimer laser light (11) is incident on 1) from the substrate side, the excimer laser light (11) using the gate electrode (2) as a mask enters the semiconductor 11m1 (3) and is absorbed, causing a temperature rise. This temperature rise causes impurities in the impurity-containing layer (7) to diffuse into the semiconductor film (3), forming source and drain regions. The temperature rise occurs in the portions that are irradiated with the excimer laser beam (11) using the gate electrode (2) as a mask, and these portions do not overlap with the gate electrode (2) at all. Therefore, the gate electrode (2), the source electrode (5) and the drain electrode (6)
The overlapping part can be eliminated. After this, Figure 1 (
As shown in C), source and drain electrodes (5) and (6) may be formed on the source and drain regions.

In the above embodiment, an excimer laser was used as the light source, but other lasers (for example, Ar laser, Any light source may be used, from a Q-switch to a CW light source.Furthermore, a light source other than a laser, such as a flash lamp, may be used.

Furthermore, although an impurity-containing layer (7) such as PSG was used as the impurity supply source this time, the impurity-containing layer may be a semiconductor layer doped with an impurity, a resin containing an impurity, or the impurity itself. To create a semiconductor layer doped with impurities, film formation using a CVD method or the like or ion implantation can be used.

Further, as shown in FIG. 2(a), by providing an insulating film (8) on the semiconductor layer (3) with a width that covers the gate electrode (2), it is possible to prevent impurities from diffusing into the surface of the semiconductor layer. At the same time, the region in which impurities are diffused into the semiconductor layer (3) can be controlled more precisely. The other steps shown in FIGS. 2(b) and 2(c) are the same as those in FIGS. 1(b) and (C).

In addition, as shown in FIG. 3, the gate electrode (2) is formed by light.
To prevent damage to the gate electrode [i! (2) and an insulating substrate (
A reflective film (9) may be provided between 1).

[Effects of the Invention] As described above, according to the present invention, light is incident from the substrate side using the gate electrode as a mask to increase the temperature of the semiconductor film and diffuse impurities, thereby forming a source region and a drain region. Therefore, it is possible to eliminate the overlap between the gate electrode, source electrode, and drain electrode, reduce the source-gate capacitance and drain-gate capacitance, and improve the rise characteristics of the gate signal and the retention characteristics of the drain voltage. It is possible to obtain a product with good performance.

[Brief explanation of drawings]

Figures 1(a), (b), and (c) are cross-sectional views showing the method for manufacturing a thin film I transistor according to an embodiment of the present invention in the order of steps, and Figures 2(a), (b), and (c) are sectional views of this method, respectively. FIG. 3 is a sectional view showing a part of the manufacturing process of a thin film transistor according to still another embodiment of the invention, and FIG. FIG. 3 is a cross-sectional view showing a thin film transistor manufactured by the method. In the figure, (1) is a transparent insulating substrate, (2) is a gate electrode, (3) is a semiconductor layer, (4) is a gate insulating film, (5) is a source electrode, (6) is a drain electrode,
(7) is an impurity-containing layer, (8) is an insulating film, and (9) is a reflective film. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masu Oiwa M2 figure

Claims (1)

[Claims] A gate electrode provided on a substrate at least the surface of which is made of an insulator, a gate insulating film provided on this gate electrode, a semiconductor film provided on this gate insulating film, and this semiconductor film. In the method for manufacturing an inverted stagger type thin film transistor, the thin film transistor is formed of a source region and a drain region formed on the substrate, and a source electrode and a drain electrode provided on the source region and the drain region, respectively. 1. A method of manufacturing a thin film transistor, comprising the steps of: applying light using an electrode as a mask to increase the temperature of the semiconductor film and diffusing impurities to form the source region and the drain region.