JPS632891A - Vapor phase epitaxy - Google Patents

Abstract

PURPOSE:To obviate the need for exposing a silicon substrate to a high temp. as in the conventional method and to eliminate the influence of a thin oxide film to be formed on silicon surface after RCA cleaning by growing the silicon film first at a high temp. in an atmosphere where hydrogen chloride exists in a vapor phase then growing the vapor phase at a low temp. CONSTITUTION:The silicon film is once grown at the high temp. in the atmosphere where the hydrogen chloride exists in the vapor phase, then the silicon film is grown at the low temp. Since the silicon is formed first at the high temp., the thin oxide film 2 on the silicon substrate 1 formed by RCA cleaning is removed by the reaction: Si+SiO2 2SiO which takes takes place at the boundary face 4 between the surface 3 of the oxide film and the silicon substrate in the initial period of the growth. The defect-free epitaxial film is obtd. by removing such oxide film.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for selective vapor phase epitaxial growth of silicon.

(Prior art) Conventionally, pre-growth treatments for silicon vapor phase epitaxial growth include: 1) gas etching at high temperature using HCI, 2) pre-baking at high temperature in a hydrogen atmosphere, 3) ionization using Ar, etc. Methods such as etching are known.

Silicon processes are trending toward lower temperatures to form smaller devices. Furthermore, lowering the growth temperature is desirable for the realization of three-dimensional devices and the crystallinity of selectively grown films. Methods 1) and 2) go against the trend of lower silicon process temperatures and have drawbacks such as a sloping impurity profile. Ion etching in 3) leaves damage on the surface, but this damage causes lattice defects, and high temperature annealing is required to remove the damage, so the same drawbacks as 1) and 2) become apparent. I will do it.

(Problem to be solved by the invention) RCA cleaning (soaking in a mixture of hydrochloric acid or ammonia, hydrogen peroxide, and water) is usually performed as a pre-growth treatment on the silicon surface, but after this treatment, a thin oxide film is formed on the silicon surface. is formed. Since this thin oxide film plays the role of protecting the silicon surface from contamination, it is preferable not to remove it until immediately before growth. If the growth temperature is high, a thin oxide film will have no effect on the crystallinity of the grown film, but if the growth temperature is lowered, lattice defects such as stacking faults and dislocations will occur at the interface between the substrate and the grown film. become. An object of the present invention is to provide a vapor phase epitaxial growth method that does not expose a silicon substrate to high temperatures as in the prior art and is not affected by a thin oxide film formed on the silicon surface after RCA cleaning.

(Means for Solving the Problems) The present invention is characterized in that a silicon thin film is once grown at a relatively high temperature in an atmosphere containing HCI, and then the silicon is grown at a low temperature to a desired film thickness.

(Operation) In vapor phase growth using dichlorosilane or silane added with HCI, it is often possible to selectively grow silicon only on silicon by using a silicon substrate on which a partially thick oxide film is formed. Are known. Therefore, a state occurs in which silicon is not deposited on the surface of the oxide film for a certain period of time. Furthermore, since active silicon atoms decomposed on the substrate surface or in the gas phase exist in the gas phase, the reaction of Si + 5i02-2 SiO↑ occurs on the 5i02 surface and the interface between SiO2 and the silicon substrate, and even if it is a thin oxide film, It is thought that it will be removed if In order to make this reaction work effectively, it is desirable to use a thin oxide film at low pressure as the secondary growth. As for temperature, a high temperature is better in order for the reaction to proceed quickly, but if you are thinking about lowering the temperature of the process, it is desirable to carry out the reaction at the lowest possible temperature and in the shortest possible time. This reaction causes RCA
If the thin oxide film formed by cleaning is completely removed,
That is, by growing a thin silicon film at a relatively high temperature and then growing a thick silicon film at a low temperature, a silicon film free from lattice defects can be obtained.

(Example) FIG. 1 shows the present invention. (a) shows a state in which silicon has begun to grow at a relatively high temperature. The thin oxide film 2 on the silicon substrate 1 was made by RCA cleaning, and the film thickness is thought to be about 20. At the surface 3 of the oxide film and at the interface 4 between the oxide film and the silicon substrate, Si+5i02-2S
An iO↑ reaction occurs, and the oxide film is removed at the initial stage of growth. (b) shows a state in which a silicon film is further grown at a lower temperature after the second growth, and 5 shows a film grown at a high temperature, and 6 shows a film grown at a low temperature.

As a result of using dichlorosilane as the raw material gas and performing the growth at 40 Torr, if the primary growth was performed at 900°C for 10 seconds and the film thickness was grown to about 100A, there would be no defects even if the growth was performed at a lower temperature of 800°C. It was possible to obtain an epitaxial film free of generation. 900 when grown under normal pressure
During the primary growth at a temperature of about 10.degree. C., a large number of defects were generated, and the results suggested that the oxide film could not be removed. When grown at only 850°C, defects occurred at the interface between the substrate and the shrimp film, resulting in insufficient removal of the oxide film. The fact that it is sufficient to remove the oxide film can be seen from the fact that almost no defects are observed in the film grown at 850° C. by removing the oxide film with hydrofluoric acid immediately before growth and then placing the film in a growth furnace.

If the growth pressure is lowered, a defect-free epitaxial film can be obtained even if the primary growth temperature is further lowered.

FIG. 2 is an example of selective epitaxial growth. As a raw material gas, dichlorosilane to which HCI was added was used. Openings 9 of oxide film 8 formed on silicon substrate 7 can be selectively filled with single crystal silicon film 10. In this case, growing at a lower temperature is effective in suppressing the generation of lattice defects on the sidewalls, but simply lowering the growth temperature will cause the interface between the substrate and the epitaxial film to deteriorate as shown in Figure 1. Defects occur from this. As a result of setting the growth pressure to 20 Torr, the secondary growth temperature to 900°C, and the secondary growth temperature to 800°C, there were no defects at the interface between the substrate and the epitaxial film, and there were very few defects at the interface between the sidewall and the epitaxial film. A small epitaxial film was obtained.

The structure shown in Figure 2 can be adapted to extremely fine element isolation by reducing the width of the oxide film.
In the conventional method, when a high temperature heat treatment is applied when the width of the oxide film is as small as about lpm or less, a phenomenon has been observed in which the oxide film separates from the substrate and floats up. When the present invention was used, such a phenomenon was not observed, and it was possible to apply the method to submicron element isolation.

FIG. 3 is an example in which the method shown in FIG. 2 is applied to lateral growth on an oxide film. Selective growth was performed in the opening 13 of the oxide film 12 formed on the silicon substrate 11, and a silicon film 14 was laterally grown on the oxide film. In this case as well, no defects occurred at the interface between the substrate and the epitaxial film, there were very few defects at the interface between the sidewall and the epitaxial film, and an epitaxial film with very few defects on the oxide film was obtained.

(Effects of the Invention) As described above, according to the present invention, there are no problems caused by high-temperature heat treatment, such as 1) degrading the impurity profile, 2) suppressing the generation of defects during selective growth, etc.
It is possible to provide a vapor phase growth method that suppresses the occurrence of defects even in the case of many substrate structures that may be applied to fine device structures.

[Brief explanation of drawings]

1 to 3 are cross-sectional views showing embodiments of the present invention. In the figure, 1 is a silicon substrate, 2 is a thin oxide film, and 3 is a silicon substrate.
is the surface of the oxide film, 4 is the interface between the oxide film and the silicon substrate, and 5 is the surface of the oxide film.
is a film grown at high temperature, 6 is a film grown at low temperature, 7 is a silicon substrate, 8 is an oxide film, 9 is an opening, 10 is a single crystal silicon film, 11 is a silicon substrate, 12 is an oxide film, 13 is an opening Sections and 14 indicate silicon films, respectively. Fig. 1 Fig. 6 Fig. 2 Opening grown at low temperature

Claims (1)

[Claims] A vapor phase epitaxial growth method that is characterized by first growing a silicon film at high temperature in an atmosphere where hydrogen chloride is present in the gas phase, and then growing the silicon film at low temperature.