JPS5982744A - Manufacture of sos substrate - Google Patents

Abstract

PURPOSE:To obtain an SOS substrate having superior crystallinity even when a silicon film is thin and having satisfactorily few microtwins by a method wherein the process that the SOS substrate made the single crystal silicon film of the prescribed thickness to grow is heat treated at a temperature higher than the growth temperature and moreover in an oxygen atmosphere, and thus formed oxide film is removed, is repeated up to reach the desired silicon film thickness. CONSTITUTION:A single crystal silicon film 2 is grown epitaxially at film thickness of 1mum or more on a single crystal sphhire substrate 1. As the growth condition, SiH4 gas is used, the growth temperature is made to 950 deg.C, and the growth speed is made to 1mum/min, for example. Then, the heat treatment temperature is selected to 1,100 deg.C as the temperature higher than the growth temperature 950 deg.C, and the heat treatment is performed in an oxigen atmosphere for 1.5hr. An oxide film generated by the heat treatment thereof is etched to be removed by a dilute hydrofluoric acid liquid. The silicon film 2 is thinned as much. The heat treatment and etching thereof are repeated for the 10 cycles in total, and thickness of the silicon film is made to the necessary thickness finally.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an SO8 substrate.

5O8 (8i1icon on 5apphire) in which a silicon single crystal film is formed on a sapphire single crystal substrate
) is suitable for high density because it separates device elements through impurity control and separates the silicon film into islands, compared to the bulk silicon that makes up semiconductor devices such as VLSI. Also, since the parasitic capacitance is small, it has the advantage of being able to operate at higher speeds. It is well known that the ideal device used in SOS is ideal for low power consumption, high-speed devices with high density integration.

The SO8 substrate has a silicon single crystal film formed by heteroepitaxial growth according to the crystallographic orientation of the sapphire substrate, and is usually formed by chemical vapor deposition. Although existing SO8 substrates have some drawbacks, with current growth techniques, those formed by the chemical vapor deposition method described above have better crystallinity than those obtained by other formation methods. However, for device manufacturers, SO8 substrates formed by chemical vapor deposition are still insufficient to manufacture ideal devices with high initial performance.
Improvement of its crystallinity has been desired. When trying to manufacture a device with desired ideal characteristics using an SO8 substrate, the thinner the SOS silicon film is (for example, 0.3~0.
(about 2 μm or less) is desirable, but on the other hand, thin crystallinity deteriorates.

The thickness dependence of silicon film crystallinity and microtwins, which have been problems with conventional SO8 substrates, will be explained. First, the dependence of crystallinity on film thickness will be explained.

FIG. 1 is a cross-sectional view of an example of a conventional SO8 substrate.

By chemical vapor deposition on a 7-Aire substrate l whose main surface is the (1102) plane! l) Grow a silicon film 2 having a (100) plane. The chemical vapor deposition method uses silane (Si
The growth temperature was 950° C. using a ) gas.

It is known that when the distance from the interface 3 of the silicon film 2 is t, the crystallinity of the silicon film 2 changes as a function of t, that is, the closer it gets to the interface 3, the more the crystallinity deteriorates.

This situation has been qualitatively investigated by measuring the X-ray rocking curves of SO8 with different film thicknesses, and an analysis of the X-ray rocking curves based on the kinematics theory of the X-ray diffraction method (Edo, et al. : The 41st Academic Conference of the Japan Society of Applied Physics (198-N-6 (1,980)) was also held.

Figure 2 is a diagram explaining the half-width with respect to the crystal orientation distribution,
FIG. 3 is a curve diagram showing the relationship between the distance from the interface of the silicon film of the SO8 substrate and the half-width of the orientation distribution.

When the half-width of the orientation distribution spread (mosaicness) of a mosaic crystal is expressed as Wi, it means that the sum crystallinity is good when the half-width w1 is small.

As shown in FIG. 3, the crystallinity is worst at the interface and improves as it approaches the surface. This tendency does not change even if the silicon film thickness is changed. Furthermore, the half-width itself at a location a certain distance away from the interface 3 does not change at all depending on the silicon film thickness. Therefore, if an SOS substrate with a thick silicon film is used, the mosaicness of the silicon film near the surface is better, but as mentioned above, in order to obtain a device with good characteristics, it is preferable to use an SO8 substrate with a thin silicon film.

However, if the silicon film is thin, the mosaicness will be poor.
There is a drawback that good characteristics cannot be obtained when a device is formed.

Next, microtwins, which are another problem with the silicon film of the SOS substrate, will be explained. The microtwin exists near the interface 3 of the silicon film 2 in FIG. Therefore, when the silicon film is thick, it does not affect the characteristics of the manufactured device, but as the silicon film becomes thinner, this effect appears. Silicon film thickness is 0
．． AsoS devices have not yet been realized using SO8 substrates of 2 μm or less due to poor mosaicness and the presence of microtwins.

The present inventor investigated changes in microtwins due to heat treatment,
The following results were obtained. (1) Heat treatment in a hydrogen atmosphere does not change the strength of the four microphones.

(2) In heat treatment in a nitrogen atmosphere, microtwins are partially reduced. (3) In heat treatment in an oxygen atmosphere, microtwins in thick film SO8 are slightly reduced, and microtwins in thin film SO8 are sufficiently reduced. From the above, it is considered that the decrease in microtwins in a chlorinated atmosphere is due to the effect of excess oxygen.

That is, in thick film SO8, since the silicon film 2 is thick, sufficient excess oxygen is not supplied near the interface 3, and the number of microtwins does not decrease much, but as the silicon film 2 becomes thinner, the supply of excess oxygen becomes sufficient. It is thought that this is because of this.

In this way, the silicon film of the SO8 substrate has two problems: crystallinity and microtwins, and it was found that when the silicon film is thin, microtwins can be reduced by heat treatment in an oxygen atmosphere. There still remains the problem of poor crystallinity when thin.

Beam annealing method (LQoleckf etal, A
ppl, Phys, Lett, Volume 37, No.
1980) p. 919) has been proposed. This method is
This is a method in which a silicon film is irradiated with a laser beam to be melted and then regrown. Since this method involves high-temperature heat treatment that melts silicon, impurities such as AA from sapphire diffuse, and even though the crystallinity improves, the change in impurity concentration causes the silicon to become unsuitable for device formation. There are six disadvantages when it comes to membranes.

The present inventor investigated whether the heat treatment in an oxygen atmosphere, which was effective in reducing microtwins, was also effective in improving crystallinity.

FIG. 4 is a curve diagram showing the change in crystallinity at the edge of the silicon film of the SO8 substrate before heat treatment in an oxygen atmosphere.

The horizontal axis is the distance from the interface, and the vertical axis is the half-width of the orientation distribution. There are two types of silicon film thickness: 0.6 μm and 1.5 μm. The solid line shows the silicon film before heat treatment, and the small broken line (0.68 m film thickness product) and large broken line (1.5 μm film thickness product) after heat treatment. It was shown in Before heat treatment, 0.68m film thickness product and 1.
Since they are almost the same as the 5 μm film thickness product, both are shown by a single solid line in FIG. The processing temperature is 1100℃,
The test was carried out for 300 minutes. The half width was determined by carpet analysis of the X-ray rocking curve.

From this result, it was found that heat treatment in an oxygen atmosphere significantly improves crystallinity in the case of thicker crystallinity films, but the improvement effect is not so great in thinner films. That is, an SO8 substrate with a thin silicon film can be heat-treated in an oxygen atmosphere to reduce microtwins, but the crystallinity is not improved as desired.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a method for manufacturing an SO8 substrate that has excellent crystallinity even if the silicon film is thin and has sufficiently few microtwins.

The method for manufacturing an SO8 substrate of the present invention includes a step of manufacturing an SO8 substrate by epitaxially growing a single-crystal silicon film with a thickness of 1 μm or more on a single-crystal sapphire substrate, and a step of manufacturing the SO8 substrate at a temperature higher than the growth temperature for growing the silicon film. and a step of repeating a heat treatment step of heat treating the SO8 substrate in an oxygen atmosphere and an etching step of etching away an oxide film on the silicon film formed in the heat treatment step until a desired silicon film thickness is obtained. configured.

Next, embodiments of the present invention will be described using the drawings.

A single-crystal silicon film 2 is epitaxially grown to a thickness of 1.1 μm on a sapphire substrate 1 having a (1102) main surface in the same manner as the method for manufacturing the SO8 substrate described in FIG. The growth conditions were SiH, gas, and a growth temperature of 95%.
The temperature was 0° C. and the growth rate was 1 μm/ml. Next, a heat treatment temperature of 1100° C. is selected as a temperature higher than the growth temperature of 950° C., and heat treatment is performed for 1.5 hours in an oxygen atmosphere. The oxide film produced by this heat treatment is removed by etching with a dilute dichloromethane solution.

The silicon film 2 becomes thinner by this amount. This heat treatment and etching were repeated for a total of 10 cycles until the final silicon film thickness was 0.37 μm. For comparison,
Separately, an SO8 substrate with a silicon film thickness of 1.1 μm, which was manufactured under the same growth conditions as above, was grown in an oxygen atmosphere.
A sample was prepared by heat-treating at 100° C. for 15 hours continuously and removing the generated oxide film by etching.

The silicon film thickness of this comparative sample was 0.87 μm.

FIG. 5 is a curve diagram showing the change in the half-width with respect to the distance from the silicon film interface of the SO8 substrate before and after the heat treatment and etching of the present invention.

The solid line 4 shows the change in half width before heat treatment, and the broken line 5 shows the change in half width of the heat treatment and etching edges. A broken line 6 indicates the half width of the comparative sample after heat treatment and etching. The half width of the comparison sample before heat treatment is the same as solid line 4.

As can be seen from FIG. 4, the heat treatment value is less than half that before the heat treatment.

The comparison sample, which was subjected to repeated heat treatment and etching, also showed a slightly higher half-value width, but did not have the same effect on improving crystallinity as t1.

Figure 6+a), (bl is the X of the silicon film of the SOS substrate before and after the heat treatment and etching of the present invention.
It is 14 charts.

FIG. 6(a) is an X-ray chart of a silicon film before and after the heat treatment and etching of the present invention is performed, and FIG. 6(b) is an X-ray chart of the silicon film after the heat treatment and etching of the present invention are performed. That is, FIG. 6(a) corresponds to the solid line 4 in FIG. 5, and FIG. 6(b) corresponds to the broken line 5 in FIG.

Although the peak of microtwins is seen in Fig. 6 (at), the peak of #I is hardly seen in Fig. 6(b). That is, by performing the heat treatment and etching of the present invention, the microtwins are sufficiently Although not shown in the figure, microtwins in a comparative sample heat-treated for 15 hours continuously in an oxygen atmosphere were not sufficiently reduced. However, if d is the oxide film thickness, t is the heat treatment time, and a is the rate constant, then d=
According to the relationship aJ, the heat treatment time t is divided into n, and the heat treatment time per time is t/n?: Oxide film thickness when repeated n times (total treatment time is t) This is due to the fact that d becomes d′20・d. However, the oxide film generated in each heat treatment is removed. Therefore, the reduction in 7 recon films for a heat treatment time of 15 hours is due to the single treatment. In this case, compared to the repeated treatment, 1 E = 0.316, which is about 70 times smaller, and the effect of excess oxygen on the microtwins existing near the interface is weaker.

In the above example, a sapphire substrate whose main surface is a (1x02 angle) was used, but the present invention can also be applied to an SO8 substrate in which a single crystal silicon film having a (111) plane is formed using a sapphire substrate whose main surface is a (0001) plane. can be implemented with similar good improvement results.

As explained in detail above, according to the present invention, the silicon film has a thin film thickness of about 0.3 to 0.2 μm or less, and the crystallinity of the silicon film is excellent, and there are extremely few microtwins. The effect is great because SO8 substrates can be manufactured.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of an example of a conventional SO8 substrate, Figure 2 is a diagram explaining the half-width with respect to the crystal orientation distribution, and Figure 3 is an S
A curve diagram showing the relationship between the distance from the interface of the silicon film of the O8 substrate and the half width of the orientation distribution. Figure 4 is a curve showing the change in crystallinity of the silicon film of the SO8 substrate before heat treatment in an oxygen atmosphere. Figures 5 and 5 are curve diagrams showing changes in half-width versus distance from the interface of the silicon film of the SO8 substrate before and after the heat treatment and etching of the present invention, and Figures 6 (al) and (b) are curve diagrams showing changes in half-width with respect to the distance from the interface of the silicon film of the SO8 substrate before and after the heat treatment and etching of the present invention. and X-ray charts of the silicon film of the SO8 substrate before and after etching. 1... Sapphire substrate, 2... Silicon film, 3... Interface. 13- First country Nori, standing - Ina! The distance of the second national interface #t- Figure 3 ((L) Direction I standing fA (0) 6 Closed (b) Direction a angle (0)

Claims (1)

[Claims] A step of manufacturing an SO8 substrate by growing a single crystal silicon film with a thickness of 1 μm or more on a single crystal sapphire substrate, and growing the SO8 substrate at a temperature higher than the growth temperature of the silicon film and in an oxygen atmosphere. A method for manufacturing an SO8 substrate, comprising a step of repeating a heat treatment step and an etching step of etching away an oxide film formed on the silicon film formed in the heat treatment step until a desired silicon film thickness is obtained. .