JPH0613321A - Forming method for silicon thin film - Google Patents

Abstract

PURPOSE:To selectively form a silicon film having a clean front surface without contamination on a substrate by forming a tantalum oxide thin film patterned in a shape necessary for the substrate, and selectively coating a region in which the oxide film is not exposed with a silicon thin film by a chemical vapor growing method. CONSTITUTION:A clean glass substrate SBS is covered with a tantalum oxide TOX by a sputtering method. Then, a resist film RSL is formed on the tantalum oxide film TOX. Thereafter, a resist is photosensed and developed so as to allow the resist of a necessary part to remain, and a partial tantalum surface is exposed. Then, the tantalum oxide of the exposed part is removed by etching. Subsequently, a surface PTX of contaminated tantalum oxide is removed by a dry etching method using CF4 gas. Then, a silicon thin film SFL is formed by low pressure chemical vapor deposition(LPCVD). Thus, the silicon thin film having no contamination of impurity of the resist can be formed on the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to formation of a silicon thin film of a MOS transistor of an integrated circuit on a silicon substrate or an active matrix type flat display.

[0002]

2. Description of the Related Art A silicon thin film is used as an active layer of a thin film transistor which is an element of an active matrix type liquid crystal display. Impurities such as sodium that deteriorate the electrical characteristics are a serious enemy for the silicon thin film of this thin film transistor.

As shown in FIG. 2 (a), a silicon thin film of a coplanar thin film transistor is formed by first forming a silicon thin film PSL on a clean glass substrate SBS having a passivation film on its surface by a low pressure chemical vapor deposition method. Then, a resist RSL is applied as shown in FIG. 2 (b), and then the resist is patterned PRS by a photolithography method as shown in FIG. 2 (c).
The exposed silicon film is removed by etching as shown in (d),
Further, as shown in FIG. 2E, the resist remaining on the silicon film is removed to form the patterned silicon thin film DSS.

In this conventional method, when a resist is applied on a silicon thin film as shown in FIG. 2 (b), impurities such as Na contained in the resist adhere to the surface of the silicon film or the resist is resisted. The molecules and carbon atoms of the organic substance that constitute the silicon atom are bonded to the silicon surface to form a silicon surface SIP contaminated with impurities. In the thin film transistor formed of this silicon film, the interface state between the silicon film and the gate insulating film is large, and the electrical characteristics are deteriorated.

In addition, the contaminated surface of the silicon thin film is
There have been attempts to wash with a mixed solution of hydrogen peroxide solution, ammonia and water, but it was difficult to completely remove the contamination.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for producing a patterned silicon thin film without surface contamination as described in "Prior Art" and an interface between a silicon active layer and a gate insulating film. A method for manufacturing a thin film transistor without contamination is provided.

[0007]

The present invention is characterized in that a step of forming a tantalum oxide thin film patterned into a required shape on a substrate and a selective deposition of a silicon thin film by chemical vapor deposition. A method of forming a silicon thin film is provided.

Further, according to the present invention, a step of forming a tantalum oxide film on a substrate, a step of patterning this tantalum oxide film, and a silicon film selectively in a region where the tantalum oxide film is not exposed by a chemical vapor deposition method. And a step of forming a silicon oxide film on the silicon film, and a step of forming a gate electrode on the silicon oxide film.

[0009]

The details of the present invention will be described below with reference to the illustrated embodiments.

First, as shown in FIG. 1A, a tantalum oxide film TOX having a thickness of 200 nm is formed by sputtering on a clean glass substrate SBS whose surface is covered with an insulating film PBL. Next, a resist film RSL is formed on this tantalum oxide film TOX. At this time, for the same reason as in the conventional example, the surface PTX on the tantalum oxide film TOX is contaminated with impurities such as Na in the step of depositing the resist.

Next, as shown in FIG. 1 (b), the resist is exposed to light and developed so as to leave a necessary portion of the resist,
Expose some tantalum oxide surface.

Next, as shown in FIG. 1C, the exposed portion of tantalum oxide is removed by etching by a dry etching method using CF ₄ gas, and the resist film P is further removed.
RS is dissolved and removed with concentrated sulfuric acid containing hydrogen peroxide solution at 98 ° C. At this time, the exposed surface SFS of the insulating film PBL is not contaminated.

Next, as shown in FIG. 1D, the surface PTX of tantalum oxide contaminated by the impurities contained in the resist is removed by the dry etching method using CF ₄ gas. By this step, contamination by the resist on the substrate SBS is completely removed.

Next, as shown in FIG. 1E, low pressure chemical vapor deposition (LPC) is performed on the substrate processed up to FIG. 1D.
The silicon thin film SLF is formed by the VD) method. When the substrate temperature is 600 ° C. and the flow rate of monosilane is 40 sccm, the insulating film P formed of a silicon oxide film is formed.
A polycrystalline silicon film is formed in the region where BL is exposed, but no silicon film is formed on the tantalum oxide thin film.

The LPCVD method can form a silicon thin film having a thickness of 20 nm on a substrate having a diameter of 200 mm with a variation of 10% or less.

That is, according to the method of the present invention, it is possible to selectively form a silicon thin film having a thickness of only about 20 nm on a substrate without contamination of resist impurities.

[0017]

According to the present invention, a silicon film, which is a clean surface without contamination, can be selectively formed on a substrate. By using the silicon film formed by this method, an electrically excellent thin film transistor in which the interface state between the active layer and the gate insulating film is small can be manufactured.

[Brief description of drawings]

FIG. 1 is a process drawing of a method for manufacturing a silicon thin film according to an embodiment of the present invention.

FIG. 2 is a diagram of a conventional example.

[Explanation of symbols]

 SBS ... Substrate PBL ... Insulating film TOX ... Tantalum oxide thin film PTX ... Tantalum oxide thin film containing resist impurities RSL ... Resist film PRS ... Patterned resist film SFS ... Exposed insulating film surface SLF, PSL ... Silicon thin film SIP ... Contamination Surface of patterned silicon thin film DSS ... Patterned silicon thin film

Claims (2)

[Claims] 1. A step of forming a tantalum oxide thin film patterned into a required shape on a substrate, and selectively depositing a silicon thin film on a region where the tantalum oxide film is not exposed by a chemical vapor deposition method. A method for forming a silicon thin film, comprising: 2. The method for forming a silicon thin film according to claim 1, wherein the chemical vapor deposition method is a low pressure chemical vapor deposition method.