JPS60257122A - Semiconductor device - Google Patents

Abstract

PURPOSE:To prevent diffusion of an impurity in a surface layer of a semiconductor substrate formed under an insulating film beforehand, by appropriately controlling the thickness of the insulating film when a polycrystalline or amorphous Si layer on the insulating film is transformed into a single crystal. CONSTITUTION:An impurity-diffused N<+> layer 3 is formed on a P-single crystal Si substrate 1. An oxide film 4 is formed so as to cover the layer 3, and a polycrystalline Si film 5 is formed on the film 4 and the exposed surface of the substrate 1. The film 5 is irradiated with a scanning laser beam 6 so that the film 5 is transformed into a single crystal. In this case, when the film 5 is relatively thick, it becomes difficult to grow a crystal, whereas, when the film 5 is relatively thin, the fusion reaches the substrate 1 when the laser beam 6 is applied, so that the impurity in the layer 3 is undesirably diffused. Therefore, the thickness of the film 4 is set at 0.3-0.9mum. Thus, it is possible to transform the film 5 into a single crystal without diffusing the impurity in the layer 3.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to the structure of a semiconductor device, and more specifically, to forming a single crystal silicon layer on an insulating film without diffusing an impurity layer previously formed on the surface of a semiconductor substrate. Concerning the structure for.

[Background of the invention]

(1) One method for converting a polycrystalline or amorphous silicon layer on an insulating film into a single crystal is the bridging epitaxy method. In this method, an insulating film region is provided on a part of a single crystal substrate, and the polycrystalline or amorphous silicon layer formed on this is melted by irradiation with an energy beam, and during reassimilation, the crystal growth is reduced to a single crystal. This takes advantage of the fact that it progresses from the top of the substrate to the amorphous region and onto the insulating film. Therefore, in this method, crystal growth proceeds from the upper part of the single crystal substrate onto the insulating film, so if the insulating film is thick, crystal growth becomes difficult. Therefore, it is necessary to make the insulating film thinner.

However, if the insulating film is made very thin, there is a drawback that when the energy beam is irradiated, the melting will extend to the lower substrate under the insulating film, and the impurity layer formed there will be diffused.

[Purpose of the invention]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, an object of the present invention is to provide an insulating film with a thickness that prevents impurities on the surface of a semiconductor substrate formed in advance from being diffused in the production of a single crystal film on an insulating film by a bridging epitaxy method. It is in.

(2) [Summary of the Invention] In order to achieve the above object, the present invention provides a method for monocrystallizing a polycrystalline or amorphous silicon layer on an insulating film, by forming a layer on the surface of a semiconductor substrate previously formed under the insulating film. In this method, an insulating film is formed with a thickness that prevents the impurity layer from being diffused, and bridging epitaxy is performed.

[Embodiments of the invention]

An embodiment of the present invention will be described below.

First, a resist pattern 2 was formed on a P-type crystal silicon (100) substrate 1, and then an impurity-diffused n upper layer 3 was formed by implanting phosphorus (P) ions of 5×10 cm − , and the resist pattern 2 was removed. . This sample is shown in FIG. Next, the well-known LOCO is applied to cover the impurity diffusion layer.
An oxide film 4 was formed by the 5I oxidation method, and a polycrystalline silicon film 5 with a thickness of 0.4 μm was formed by thermal decomposition of 5IH4. (
(See FIG. 2) Thereafter, continuous wave argon ion laser light 6 was irradiated while scanning as shown in the figure, thereby converting the polycrystalline silicon film 5 into a single crystal. The irradiation conditions were as follows: Sample (3) substrate temperature was 500° C., beam diameter was 100 μm, irradiation power was 5 to 16 W, and beam scanning speed was 1 to 100 m/s.

For example, FIG. 3 shows the results of examining the presence or absence of diffusion of the impurity layer 3 under conditions of insulating film thickness and laser power when the beam scanning speed is 10a+/s. In the figure, region A is the non-melting condition for polycrystalline silicon, region B is the diffusion condition for the impurity layer, and line C is the maximum insulating film thickness condition for crystal growth to occur from the single crystal substrate to the polycrystalline silicon on the insulating film. , the area RI is the optimum condition area. That is, laser power 11.
In the case of region A of 5W or less, the polycrystalline silicon film 5 on the insulating film is not melted, so crystal growth does not occur, and in region B, the impurity layer is diffused. Therefore, it can be seen that it is necessary to select the conditions for the D region in order to prevent diffusion of the impurity layer. In addition, the reason why the polycrystalline silicon film on the above insulating film was crystal-grown from the top of the single crystal silicon was that the insulating film had a thickness of 0.9 μm.
The film thickness was as follows.

From the above results, crystal growth occurs from the top of the single-crystal silicon substrate to the polycrystalline silicon on the insulating film (4), resulting in single-crystal silicon with uniform crystal orientation, and impurities in the lower layer of the insulating film do not diffuse. For 0.3-0.9μm
It can be seen that a thickness of the insulating film is required. This 0.3~0
．． When the polycrystalline silicon film 5 was irradiated with laser using the 9 μm thick insulating film 4, the polycrystalline silicon film 5 could be made into a single crystal without diffusing the impurity layer 3.

〔Effect of the invention〕

As is clear from the above explanation, the glabella insulating film is 0.3 to 0.9
By having .mu.m, the impurity layer on the surface of the substrate is not diffused when forming a single crystal silicon film in the same orientation as the single crystal substrate.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of the sample, and FIG. 3 is a graph showing the relationship between the thickness of the insulating film and the diffusion of the impurity layer under laser power conditions. DESCRIPTION OF SYMBOLS 1... Single crystal silicon substrate, 2... Resist pattern, 3... Impurity layer, 4... Oxide film, 5... Polycrystalline silicon film, 6... Continuous wave argon ion laser beam. (5)

Claims (1)

[Claims] A semiconductor device in which a polycrystalline or amorphous silicon film that continuously covers an exposed surface of a semiconductor substrate and an insulating film deposited on a semiconductor substrate having an impurity layer on the surface is made into a single crystal by local heating and melting. In order to prevent the diffusion of the impurity layer on the surface of the semiconductor substrate during single crystallization and to standardize the crystal orientation by using the exposed surface of the semiconductor substrate as a seed for crystal growth, the insulating film is Thickness 0.3
A semiconductor device characterized in that the thickness is 0.9 μm.