JPS63207181A - semiconductor materials - Google Patents

Abstract

PURPOSE:To enable the high-speed operation of a transistor when a TFT is manufactured, and to obtain the excellent reproducibility of electric physical properties by forming a polysilicon layer in a thin layer of 1000Angstrom or less and bringing the smoothness of the polysilicon layer to + or -20Angstrom or less. CONSTITUTION:In a semiconductor material in which a poly-Si layer 2 used as an active layer for a TFT (a thin-film transistor) is shaped onto a transparent insulating substrate l, the poly-Si layer 2 is formed in a thin-film of 1000Angstrom or less, and the smoothness of the layer 2 is brought to + or -20Angstrom or less. That is, grain size can be scaled up by a change into the thin-film, thus increasing mobility. Leakage currents from a gate electrode at the time of the formation of the TFT can be reduced extremely by the smoothing of the surface while the film having excellent reproducibility can be shaped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a semiconductor material in which a polysilicon (hereinafter referred to as poly-3i) layer used as an active layer of a thin film transistor is formed on a transparent insulating substrate.

[Prior art]

In general, thin film transistors (hereinafter referred to as TPTs) or S'
The most important aspect of OI is its high-speed response performance. Usually, T
Semiconductor films constituting the active layer of PT and the Si film of S○ process include amorphous Si (hereinafter referred to as a-5i:H) film and p
Although an oly-5i film is used, when a high switching speed is required, a poly-Si film, which has higher carrier mobility than an a-si:H film, is used. In order to further increase the carrier mobility of such a poly-Si film, poly-S
Attempts have been made to make the i-film thinner and subject it to heat treatment to increase the crystal grain size. However, since the poly-Si film is usually formed on a transparent insulating substrate by low pressure CVD or the like, its surface properties are not very good. Therefore, this p
When an oly-Si film is used as an active layer and a gate is formed thereon, problems such as gate leakage tend to occur.

〔the purpose〕

The present invention improves the above-mentioned conventional problems and enables high-speed operation of transistors, good reproducibility of electrical characteristics, and easy manufacturing when manufacturing TPTs for driving 1-magnification image sensors, crystal displays, etc. The purpose is to provide semiconductor materials with improved yield and quality.

〔composition〕

The present invention provides a semiconductor material in which a poly-Si layer used as an active layer of TPT is formed on a transparent insulating substrate, wherein the poly-Si layer is a thin layer of 1000 Å or less and has a smoothness of ±20 Å or less. It is characterized by certain things.

The present inventors have conducted various studies to achieve the above object, and as a result, the film thickness of the poly-Si layer on the transparent insulating substrate was increased to 10%.
It has been found that the following advantages can be obtained by setting the thickness to 00 Å or less and the smoothness to ±20 Å or less. That is, (1) the grain size can be increased by making the film thinner.

■Therefore, mobility increases. ■ T by smoothing the surface
When PT is formed, leakage current from the gate electrode can be minimized. ■ Smoothing creates a film with good reproducibility. The present invention was completed based on these findings.

In this way, in the present invention, poly-
The thickness and smoothness of the surface of the Si layer are set to a predetermined value, and even if only the thickness or smoothness is set to a predetermined value, the intended purpose cannot be achieved. In addition, po
The thickness of the ly -Si layer is set to be 1000 Å or less, preferably 500 Å or less. Further, the smoothness is set to be ±20 Å or less, preferably ±10 Å or less.

Below, several means for obtaining a poly-Si layer on a transparent insulating substrate having such a predetermined thickness and smoothness will be explained.

FIG. 1 is a process explanatory diagram showing an example thereof.

In FIG. 1, poly-5i is placed on a transparent insulating substrate 1.
Layer 2 is deposited (FIG. 1(a)). This poly-S
The i-layer 2 is formed to a thickness of approximately 1,600 to 1,700 layers by, for example, a low pressure CVD method under the following conditions.

Temperature = 560~730°C SiH4 concentration = concentration -10~100% Gas: N, o
rH,) Flow rate = 75 to 700 sec Pressure: 0.1 to 0.5 Torr Next, on the poly-8i layer 2, coated Sin, layer 3,
For example, Tokyo Ohka Layer OCD-S 1-80000 is applied so that the surface is smooth (FIG. 1(b)).

(b) The SiO2 layer 3 obtained in step
The -5i layer 2 is removed by etching to the extent that its convex portions coincide with the surface of the SiO layer 3 (FIG. 1(C)).

At this time, the surface is made smooth by the upper end of the convex portion of the poly-Si layer and the remainder of the SiO□ layer 3.

The material obtained in step (c) is thermally oxidized, for example, under the following conditions.

Temperature: 1025°C 0□Flow rate: 300sec, temperature rising: 30scc
mN2 flow rate: I Q /win (when temperature decreases) Due to this thermal oxidation, a SiO□ layer 3' of a predetermined thickness is formed from the smooth surface, and as a result, the SiO□ layer 3' layer surface 1 surface O□
The interface between N3' and poly-Si layer 2 also becomes smooth (
Figure 1(d)).

(d) Etching the material obtained in step 5 of the surface layer.
Removal of in2J'ii3' creates p with a smooth surface.
An oly-Si layer 2 is obtained (FIG. 1(e)). The thickness of the obtained poly-Si layer 2 is about 1000 mm, and its surface smoothness is about ±20 mm.

FIG. 2 is a process explanatory diagram showing another example.

In FIG. 2, a relatively thick poly-Si layer 2 of, for example, about 4,000 to 5,000 layers is formed on a transparent insulating substrate 1 by low pressure CVD (FIG. 2(a)). poly
The conditions for forming the -5i layer 2 may be the same as those in the process of FIG. 1(a).

The poly-5i layer 2 obtained in step (a) is removed little by little by dry etching (FIG. 2(b)).

This process is continued until the surface of the poly-Si layer 2 has a desired smoothness of about 1, for example, ±20 degrees, and the etching is finished when the film thickness is less than 1000 Å. As a result, a desired material as shown in FIG. 2(c) can be obtained.

The semiconductor material thus obtained is placed on the transparent insulating substrate 1.
This is because the ly-Si layer 2 has a thickness of 1000 Å or less and a surface smoothness of ±20 Å or less.

When TPT is produced using this material according to a conventional method, p
The oly-Si layer becomes an active layer, and since this active layer has a large crystal grain size, carrier mobility becomes large,
Moreover, since the surface is smooth, leakage current from the gate electrode can be minimized, and a TPT with good reproducibility of electrical characteristics can be obtained.

〔effect〕

According to the present invention as described above, when a TPT is manufactured, the transistor can operate at high speed, quality and manufacturing yield are improved, and a semiconductor material with good reproducibility of electrical properties can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a process explanatory diagram showing an example of manufacturing a semiconductor material according to the present invention. FIG. 2 is a process explanatory diagram showing another example of manufacturing the semiconductor material according to the present invention. 1...Transparent insulating substrate 2...poly-Si layer 3.3'...5i02 layer

Claims (1)

[Claims] 1. In a semiconductor material in which a polysilicon layer used as an active layer of a thin film transistor is formed on a transparent insulating substrate, the polysilicon layer is a thin layer of 1000 Å or less and its smoothness is ±20 Å or less. Characteristic semiconductor materials.