JPS6054277B2 - Single crystallization method for non-single crystal semiconductor layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for single-crystallizing a non-single-crystal semiconductor layer formed on a semiconductor substrate by irradiating it with light.

A polycrystalline silicon layer or an amorphous silicon layer is formed on an insulating film such as a silicon dioxide SiO2 film that covers the surface of a semiconductor substrate, such as a silicon Si substrate, and is irradiated with a laser beam or a light beam such as a high-pressure xenon lamp. By doing so, the non-single crystal silicon layer can be made into a single crystal.

However, as shown in FIG. 1, when an opening 3 is provided in the SiO2 film 2 covering the silicon Si substrate 1, it is not always easy to convert the non-single crystal silicon layer 4 into a single crystal by irradiating it with light. isn't it.

That is, since the 5102 film 2 has a lower thermal conductivity than the 51 substrate 1, for example, when the laser beam 5 scans the entire non-single crystal silicon layer 4, if the beam intensity is constant, SiO has poor heat dissipation. The non-single crystal silicon on the film 2 is heated excessively, and as shown in FIG. 2, the Si() may peel off from the film 2. An object of the present invention is to provide a method for uniformly monocrystallizing a non-single-crystal semiconductor layer formed on a semiconductor substrate whose surface is selectively covered with an insulating film. The present invention is characterized in that a non-single crystal semiconductor layer is formed on a semiconductor substrate on which an insulating film having an opening is formed,
Next, when the non-single-crystal semiconductor layer is irradiated with a light beam to single-crystallize the non-single-crystal semiconductor layer, prior to irradiating the light beam, the surface of the non-single-crystal semiconductor layer has a reflectance that is higher in the opening portion than in the portion on the insulating film. The objective is to form a reflective film with a small reflection. An embodiment of the present invention will be described below with reference to main part sectional views shown in FIGS. 3 and 4.

In FIG. 3, 1 is a silicon substrate, and 12 is a silicon dioxide SiO2 film formed by a selective oxidation method.

The thickness of this SiO2 film 12 is usually selected so as to satisfy desired electrical characteristics such as withstand voltage. However, in this example, the above-mentioned SiO. The thickness of the film 12 is determined by the argon Ar laser beam (wavelength λ 0.488 [
9196, which is the thickness at which the reflectance J with respect to
It was made almost equal to [in]. A polycrystalline (or non-crystalline) silicon layer 14 is formed on the silicon substrate 1 having the insulating film 12 selectively formed on its surface by a normal chemical vapor deposition (CVD) method or the like. do.

Next, this polycrystalline silicon layer 14 is heated and oxidized to form an SiO2 film 15 with a thickness of about 1700 [8] over the entire surface, and then this SiO2 film 15 is formed with a thickness of about 1700 [8]. Silicon nitride Si3N is deposited on the film 15 at a position corresponding to the 5100 film 15 by the CVD method.
Film 16 is selectively formed to a thickness of about 1220 [A].
Next, using this Si3N4 film 16 as a mask, the surface of the polycrystalline silicon layer 14 is heated and oxidized again to form a SiO2 film 1.
2, which corresponds to the position of the opening 13.
The thickness of the O2 film 15'' is increased to approximately 2508 [A].It is well known that the thickness of the SiO2 film 15 covered with the Si3N4 film 16 does not change in this step. The thickness of the film 14 is determined in advance so that the thickness will be approximately 5096 [A] on the SiO2 film 12 when the formation of each part is completed as described above.

By forming each part as described above, the wavelength λ=0.
The following interference conditions hold for Ar laser light of 488 [μm].

That is, the reflectance of the Si3N4 film 16 and the SiO2 film 15 and the reflection at the interface between the SiO2 film 15 and the polycrystalline silicon layer 14 are almost maximum, the reflectance of the SlO2 film 12 is almost minimum, and the reflectance of the SiO2 film 15'' is almost maximum. In this example, the Si3N4 film 16 and the SiO2 films 15, 15'' are almost minimum.
This film is used as a reflective film for laser light, and by configuring the reflective film as described above, the N laser light that reaches the polycrystalline silicon layer 14 can be transferred to the SlO2 film, which has poor heat dissipation and tends to increase in temperature. It is small in the part 12 and increases in the part of the opening 13 where the temperature does not easily rise.

Furthermore, a considerable portion of the N laser light that has reached the SlO2 film 12 is transmitted through the SiO2 film 12, and only a small amount is reflected by the polycrystalline silicon layer 14. Therefore, if the reflective film is scanned with an Ar laser beam whose intensity is kept constant, the temperature of the polycrystalline silicon layer 14 will be raised almost uniformly, and the polycrystalline silicon layer 14 will become a single crystal without peeling as in the case of conventional methods. be converted into

In this example, various film thicknesses were selected so that the reflectance to Ar laser light was maximum or minimum, but the thickness is not necessarily limited to this.

The key is to make the temperature of the non-single crystal semiconductor layer almost uniform.
The thickness of the reflective film may be controlled so that the amount of irradiation light that reaches the non-single crystal semiconductor layer is large in areas where the temperature does not easily rise and is small in areas where the temperature easily rises. After the single crystallization is completed in this manner, the Si3N4 film 16 and the SiO2 films 15, 15'' are all removed to expose the single crystal layer 1C, as shown in FIG.

In the above embodiment, the reflective film is formed to have a two-layer structure, but it may be one layer or three or more layers, and the material thereof may be appropriately selected.

Further, the irradiation light source is not limited to an Ar laser, but may be another laser, an infrared lamp, or the like. In short, the material and thickness of the reflective film should be selected in consideration of the relationship with the wavelength of the light source used to satisfy the desired optical interference conditions.

As explained above, according to the present invention, even when the base layer of a non-single crystal layer is partially different, it is possible to form a saw-like single crystal by irradiation with light.

[Brief explanation of the drawing]

1 and 2 are sectional views of essential parts for explaining the conventional method, and FIGS. 3 and 4 are sectional views of essential parts showing one embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 5 is a laser beam, 12
13 is an insulating film, 13 is an opening, 14 is a non-single crystal layer, 1C is a single crystal layer, and 15, 15'', and 16 are reflective films.

Claims (1)

[Claims] 1. When a non-single crystal semiconductor layer is formed on a semiconductor substrate having an insulating film with an opening formed on its surface, and then the non-single crystal semiconductor layer is irradiated with a light beam to form a single crystal, the method of irradiating the light beam with A reflective film for the light beam is previously formed on the surface of the non-single crystal semiconductor layer, and the reflectance of the reflective film on the opening is made smaller than the reflectance of the reflective film on the insulating film. A method for single crystallizing a non-single crystal semiconductor layer.