JP2603553B2 - Thin film growth method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film growth method in which a raw material gas containing silicon is introduced into a vacuum vessel, and a silicon epitaxial film is grown on the surface of a heated silicon substrate.

(Prior Art) A selective growth technique capable of forming a finely integrated structure in a two-dimensional plane direction of a silicon substrate surface by patterning and forming a silicon epitaxial layer only on any part of the two-dimensional structure. Is one of the methods that can promote high integration of silicon semiconductors in the future and increase added value.

Conventionally, as an example of such selective growth, a silicon oxide film (SiO ₂ ) is formed on the surface of a silicon substrate, and then the surface of the silicon substrate, that is, a window for exposing a silicon crystal is formed at a predetermined position by patterning. , And a patterning substrate, for this patterning substrate,
There is known a selective growth technique in which gas source epitaxy using a source gas containing silicon is performed, a silicon epitaxial film is grown only on a silicon crystal exposed in the window, and nothing is grown on an oxide film. I was

In the conventional selective growth, after a patterning substrate is housed in a vacuum vessel, heating is first performed at 850 ° C. for 1 minute, and a thin oxide film (formed in air) is formed on the silicon surface exposed through the window. After removing the natural oxide film, the silicon substrate kept at 750 ° C. is irradiated with disilane gas to grow a silicon epitaxial film selectively on the exposed portion. In the initial stage of the growth, an epitaxial silicon film is grown on the silicon substrate exposed by the formation of the window, that is, on the silicon crystal by a reaction with disilane, while on the silicon oxide film left by patterning. Because disilane is difficult to react, nothing grows.

(Problems to be Solved by the Invention) In the above-mentioned selective growth method, if a long-time epitaxy is performed to obtain a desired thickness of the silicon epitaxial film, the silicon oxide film is also covered with silicon, and the formation of silicon nuclei is prevented. This has led to the formation of polycrystalline silicon, and it has been known that selective growth, which is a feature of this technique, is prevented.

As a method of preventing the growth of polycrystalline silicon on such a silicon oxide film, chlorine or chloride silane gas is introduced into a vacuum vessel to remove silicon nuclei or polycrystalline silicon on the silicon oxide film by etching. Therefore, a method of realizing selective growth has been known, but in this method, the temperature during the growth of the silicon substrate must be 900 ° C. or higher in order to perform etching sufficiently, so that a thermal diffusion method is used in the silicon substrate. There is a problem that the built-in fine device structure is destroyed.

Also known is a method in which the temperature of the silicon substrate is set to 650 ° C. or less during the growth of the silicon epitaxial film, and the introduction flow rate of the source gas containing silicon is set to 1 sccm or less to lengthen the time for selective growth. in case of,
The growth rate of the silicon epitaxial film is as low as 0.5Å / sec, and there is a problem in adopting it for the production of semiconductor devices.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems in the selective growth, and has been developed for manufacturing a semiconductor device without heating a patterned silicon substrate to a high temperature (a temperature at which a structure in the substrate is broken). It is another object of the present invention to provide a thin film growth method capable of growing a silicon epitaxial film having an arbitrary thickness at a growth rate (10 ° / sec) that can cope with the above.

(Means for Solving the Problems) According to a thin film growth method of the present invention for achieving the above object, in a method of introducing a silicon-containing source gas into a vacuum vessel and growing a silicon epitaxial film on a silicon substrate surface, The method is characterized in that the introduction of the raw material gas is performed intermittently, and the silicon substrate is heated during the introduction cutoff period to evaporate silicon adhered on an oxide film formed in advance on the substrate.

In such a method, the period for blocking the introduction of the raw material is to secure the time required for the silicon attached on the oxide film to evaporate, but the time is longer or shorter depending on the temperature of the silicon substrate. For example, if the temperature of the silicon substrate is 85
When the temperature is set to 0 ° C., a time of 30 seconds or more is secured. On the other hand, during the introduction period of the source gas, it is necessary to prevent the growth of the polycrystalline silicon film on the oxide film of the silicon substrate and to prevent the selective growth from being impaired. It is good to repeat with

(Function) According to the method of the present invention, the introduction of the source gas is performed intermittently, and the silicon adhering to the oxide film is evaporated during the introduction interruption period, so that the growth rate of the silicon epitaxial film is not reduced, and It can be grown to a desired film thickness. In addition, silicon adhering to the oxide film due to the introduction of the raw material gas reacts with oxygen in the oxide film during the introduction cutoff period, and silicon monoxide (SiO) having a relatively high vapor pressure.
Because a mechanism that generates and evaporates can be used,
Processing can be performed without a high temperature that would destroy the internal structure of the silicon substrate.

(Examples) Hereinafter, the present invention will be described based on examples. FIG. 1 shows a main part of a gas source epitaxial apparatus used in the embodiment.
A substrate heating device 3 is installed, and a source gas supply port 4 is provided through the side wall of the vacuum vessel 1. A source gas 5 supplied through the supply port 4 is supported by the substrate holder 2. It is configured so that it can be sprayed on the substrate 6. In the figure, reference numeral 7 denotes an exhaust port to which an exhaust device (not shown) is connected so that the inside of the vacuum vessel 1 can be evacuated.

Using such a gas source epitaxial device,
Selective growth of a silicon thin film was performed on the patterned silicon substrate 6 using disilane gas as a source gas.

After setting the silicon substrate 6 on the substrate holder 2 in the vacuum vessel 1, the inside of the vacuum vessel 1 was first evacuated to an ultrahigh vacuum region. Next, first, the silicon substrate 6 is heated at 850 ° C. for one minute by the substrate heating device 3, and the silicon substrate exposed to the window formed by patterning the silicon substrate 6, that is, a thin oxide film (natural After removing the oxide film, the silicon substrate 6 was maintained at 750 ° C., and 100% disilane gas was introduced at a flow rate of 30 sccm through the supply port 4 to grow a silicon epitaxial film for 3 minutes. At the time when three minutes had elapsed, the supply of the source gas disilane gas was stopped, and the temperature of the silicon substrate 6 was maintained at 850 ° C. for 30 seconds.

The introduction (3 minutes) and cutoff (30 seconds) of such a source gas were repeated five times to complete the growth of the silicon epitaxial film. FIG. 2 is a time chart of the temperature of the silicon substrate 6 and the supply amount of the source gas (disilane gas) in the above process.

When the silicon substrate 6 after growth is taken out and the surface is observed with a scanning electron microscope, no polycrystalline silicon nuclei are adhered on the oxide film pattern formed by patterning, and complete selective growth is realized. It was confirmed that it was done. The oxide film pattern of the silicon substrate 6 was etched with a BHF solution, and the thickness of the silicon epitaxial film was measured to be 1.2 μm.

FIG. 3 and FIG. 4 schematically show the surface of the silicon substrate 6 in the above embodiment.

In FIG. 3A, 8 is an oxide film (SiO ₂ ) left by patterning, 9 is a window, and a natural oxide film 10 is formed on the surface of the silicon substrate 6 exposed from the window 9. This natural oxide film 10 is removed by heating at 850 ° C. for one minute.

When a disilane gas (Si ₂ O ₆ ), which is a raw material gas, is blown onto such a silicon substrate 6, a silicon epitaxial film 11 is selectively grown on the surface of the silicon substrate 6 exposed from the window 9, and the third layer is formed. The result is as shown in FIG.

If the silicon epitaxial film is continuously grown,
The oxide film 8 is also covered with silicon, and as shown in FIG. 3 (c), the polycrystalline silicon nucleus 12 is formed to prevent the selective growth, as described above. In the embodiment, the supply of the source gas was stopped before the polycrystalline silicon nuclei 12 were formed.

When the silicon substrate 6 is heated to 850 ° C. during the cutoff period of the source gas, the silicon atoms 13 on the oxide film 8 react with the oxygen 14 in the oxide film 8 as shown in FIG. It can be described that silicon monoxide (SiO) 15 having a high density is formed, the silicon material for forming polycrystalline silicon is evaporated from the oxide film 8 into a vacuum, and disappears from the oxide film 8.

(Effects of the Invention) As described above, according to the present invention, it is possible to perform selective growth without heating to a high temperature at which the internal structure of a silicon substrate is destroyed, and to grow a required film thickness at a high growth rate. Therefore, the present invention can be applied to the production of semiconductor devices, and has the effect of improving the degree of freedom in the structural design of semiconductor devices.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus used in an embodiment of the present invention, and FIG.
FIG. 3 is a time chart of the embodiment of the present invention, and FIG.
(B) and (c) are diagrams schematically showing the surface of the silicon substrate in the example, (a) is a diagram showing a state in which a natural oxide film is formed, and (b) is a silicon epitaxial film grown. FIG. 4C is a view showing a state in which a polycrystalline silicon nucleus is formed on an oxide film, and FIG. 4 is an explanatory view of a step of heating a silicon substrate in the same embodiment with the source gas shut off. is there. DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 2 ... Substrate holder, 3 ... Substrate heating device, 4 ... Supply port, 5 ... Source gas, 6 ... Substrate, 8
...... Oxide film, 9 ... Window, 10 ... Natural oxide film, 11 ... Silicon epitaxial film

Claims (3)

(57) [Claims] In a method of introducing a source gas containing silicon into a vacuum vessel and growing a silicon epitaxial film on the surface of a silicon substrate, the source gas is intermittently introduced, and the silicon substrate is introduced during a cut-off period. Heating the substrate to evaporate silicon adhering to the oxide film previously formed on the substrate. 2. The method according to claim 2, wherein the supply and cutoff period of the source gas is 30 seconds or more,
2. The method for growing a thin film according to claim 1, wherein the heating temperature of the silicon substrate is 850 ° C. or higher. 3. The thin film growth method according to claim 1, wherein the introduction period of the source gas is 20 minutes or less per time.