JPH01245509A - Formation of semiconductor crystal layer - Google Patents

Abstract

PURPOSE:To make it possible to single-crystallize a region wider than the region obtained by heating a substrate entirely at the same temperature by a method wherein, after an insulating film has been formed on a semiconductor substrate, an aperture is provided on the insulating film, and after an amorphous silicon layer has been formed on the whole surface, the layer is heated up for a short period from the opposite side. CONSTITUTION:A silicon oxide film 12 is formed on a silicon substrate 11, and the film 12 is removed in the stripe form of 2mum wide. A polycrystalline silicon film 14 is formed on the whole surface in such a manner that the exposed silicon surface will not be oxidized. Subsequently, the polycrystalline silicon film 14 is brought into an amorphous state by ion-implanting silicon. By heating from the rear side of a sample for one minute, for example, the single crystal region is extended by 15mum toward both sides of a seed 13.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for forming a semiconductor single crystal layer on an insulating film, and particularly to a method for forming a good semiconductor single crystal layer by solid phase growth. Regarding how to.

(Prior art) As semiconductor memories become smaller and faster, active elements are formed not only on a semiconductor substrate but also on the semiconductor single crystal layer (SOI) with an insulating film interposed therebetween. is becoming necessary.

There are two ways to form a semiconductor single crystal on an insulating film: one is to obtain a single crystal through the process of melting and solidification, which is represented by electron beam annealing and laser annealing, and the other is to form an amorphous crystal in a place where an opening (seed) is provided in the insulating film. forming a quality semiconductor film, or
After forming polycrystalline silicon, it is made amorphous by ion implantation, etc., and then heated at 500 to 600°C for a long time to sequentially crystallize it from the seed.
A single crystal layer is obtained. In the melting method, the silicon layer is temporarily melted even though an insulating film is interposed therebetween, so the temperature of the underlying substrate also rises considerably, which poses a problem in miniaturization of the underlying device. On the other hand, solid phase growth requires a long heating time.

The above problem does not occur because the temperature is low. This method is
This is achieved because it is easier in terms of energy than forming crystal grains in amorphous material in contact with crystal grains. As is clear from the above explanation, this semiconductor substrate is
Since the entire structure is kept at the same temperature, microcrystalline grains are generated even in the amorphous state by long-term heat treatment. Once these microcrystalline grains are generated, even if crystal grains from the seed grow here, it is no longer possible to incorporate this region and increase the single crystal region, and this is the limit of the single crystal region. Become. Currently, this region is several microns in size, which is a bottleneck in practical application to devices.

(Problems to be Solved by the Invention) The present invention provides a method for single-crystalizing a wider area than the current single-crystal region when obtaining a semiconductor single-crystal layer by an in-phase growth method, and provides an insulating layer by solid-phase growth. The purpose is to put devices on semiconductor single crystal films into practical use.

After forming an insulating film on a semiconductor substrate, forming an opening in the insulating film, and forming an amorphous silicon layer on the entire surface,
Heating is performed from the opposite side where the amorphous silicon is present for a short time or repeatedly for a short time.

(for production) FIG. 1 shows a schematic diagram for explaining the present invention in detail.

Here (11) is a semiconductor substrate, (12) is an insulating film, (
13) is an opening (seed) provided in the insulating film, from which the single crystal film to be grown receives the orientation of the underlying semiconductor crystal. Although (15) is a heating source, in order to accurately control the heating time, it is preferable to use a heating method such as a halogen lamp with a small heat capacity.

Assuming that amorphous silicon and silicon are used as the semiconductor layer and substrate semiconductor, respectively, silicon has a thermal conductivity about 1000 times better than a silicon oxide film at room temperature. As the temperature rises, the thermal conductivity of silicon decreases,
Although the thermal conductivity of silicon oxide film increases, it still reaches 750℃.
There is a difference of about 100 times.

Therefore, when heating is performed with the configuration shown in FIG. 1(a), heat transfer to the upper layer of amorphous silicon is mainly performed through the contact area (seed) between the silicon substrate and the amorphous silicon. The temperature distribution at a certain time is as shown in FIG. 1(b). The temperature values shown in the figure are included to make it easier to understand the high and low temperatures. For example, if in-phase growth occurs dominantly at 700°C, then
The area up to the °C isotherm is single crystallized. As time progresses, the 700°C isotherm moves further along.

Since crystallization does not occur at temperatures below 700° C., by creating a temperature gradient in this way, it is possible to single-crystallize a wider area than by heating the entire area at the same temperature.

Because of the above-mentioned reasons for how heat is transmitted to amorphous silicon, it is, in principle, conducted through the seed. However, since the silicon film thickness is at most 1km, the thermal resistance is large in the portions away from the seed. At a location far enough in front of the seed, more heat may be transmitted through the silicon oxide film, which has poor thermal conductivity, than from the seed. In such a case, the temperature gradient in the amorphous silicon portion disappears, and a large number of crystal grains are generated in a disordered manner, and the crystal grains no longer form a single crystal. In the present invention, a number of methods can be considered to alleviate this problem, and some of them will be mentioned in the embodiments.

(Example) Example 1 An example of the present invention will be described using FIG. 1(a). A 0.5-thick silicon oxide film (1) is deposited on a silicon substrate (11).
2) is formed and removed in stripes with two widths. Subsequently, a polycrystalline silicon film (14) is formed on the entire surface by low pressure CVD so as not to oxidize the exposed silicon surface. Next, apply silicon to the entire surface at 5O-380KV'.
The polycrystalline silicon film (14) is made amorphous by ion implantation from t'10'' to 101 G/ad.

Subsequently, the sample is heated from the back side for, for example, 1 minute using a configuration as shown in FIG. 4(a). After that, by selective sex,
After checking the single crystal region, the single crystal region is a seed (13)
They each extended for 15 μs on each side.

Considering the thermal resistance through the insulating film and through the seed, the thicker the insulating film and the silicon film, the larger the difference in thermal resistance. The film thickness and silicon film thickness were set to t, o, and m, respectively.

According to this, the thermal resistance when passing through the silicon through the seed is halved, and conversely, the thermal resistance through the silicon oxide film is doubled, and the temperature gradient is maintained further away from the seed. As a result, it was found that the single crystal region in this method was further extended than in Example 1, and was 50 crystals or more.

FIG. 2 shows a plan view of the polycrystalline silicon region near the seed region. FIG. 2(a) is a plan view of a case where polycrystalline silicon is coated on the entire surface in a form similar to that described in Example 1. Because heat is transmitted through certain seeds.

It is efficient to apply heat only to the necessary areas.

Therefore, depending on the form of the device region, it is preferable to remove unnecessary portions of the polycrystalline silicon by etching. For example, as shown in FIG. 2(b), a polycrystalline silicon film is left in the width of the seed and the rest is etched to prevent heat from being transferred in the width direction of the seed. Or in a polycrystalline region as shown in FIG. 2(c) and FIG. 2(d).

By leaving the polycrystalline silicon in the region that will become the crystalline region from the seed, it is possible to avoid applying heat to the polycrystalline region that is unlikely to become a single crystalline region, and to ensure that the desired polycrystalline region becomes single crystallized. can.

Further, as is clear from the discussion so far, it is preferable that the seed region be wide from the viewpoint of thermal resistance, contrary to the case of a seed in electron beam annealing in which the substrate is heated from above.

Furthermore, it is desirable that the heating method is also described below. In other words, when the substrate is heated from the back side, the effective heat is the heat that passes through the seeds. However, in a region away from the seed, heat through the thermal oxide film (12) shown in FIG. Therefore, heating the wafer from the top surface is used as auxiliary heating to prevent the generation of crystal nuclei, for example, by preheating the wafer to 500°C. It is preferable to set the beam irradiation amount and carry out single crystallization. This is due to heat radiation from the surface.

It is also desirable to reduce the effects of escaping.

Further, if preheating is performed at 500° C., the thermal conductivity ratio will be about 1:200. On the other hand, since the ratio is about 1:1000 at room temperature, it is advantageous to keep the silicon oxide film at as low a temperature as possible.

Therefore, preheating from the top surface is linked to heating from the back surface, and the oxide film temperature should be kept as low as possible.

In other words, it is desirable to perform pulse heating if necessary.

〔Effect of the invention〕

According to the present invention, by performing solid-phase growth of a semiconductor layer on an insulating film with a temperature gradient, nucleation, which is a factor inhibiting crystal growth, is suppressed and a high-quality, large-area single crystal layer is obtained. things become possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining one embodiment of the present invention,
FIG. 2 is a sectional view for explaining one embodiment of the present invention. 11... Semiconductor substrate, 12... Insulating film. 13...Seed portion, 14...Amorphous silicon film, 21...Seed, 22...Amorphous silicon. Agent Patent Attorney Noriyuki Chika Yudo Mitsuyuki Matsuyama

Claims (1)

[Claims] An insulating film having an opening that partially exposes a part of the substrate is formed on a semiconductor substrate, and then an amorphous semiconductor layer is formed on the entire surface, and then heat treatment is performed to close the opening. A method for forming a semiconductor crystal layer in which the amorphous semiconductor layer is single-crystallized from a portion thereof, wherein the heat treatment is performed from a surface of the substrate opposite to a surface of the amorphous semiconductor layer formed on the substrate. How to form.