JPH05308064A - 'on the spot' elimination method and device of silicon natural oxide film - Google Patents

Abstract

PURPOSE:To obtain a method and device for eliminating 'on the spot' by heating at low temperature a natural film which exists on the surface of a silicon substrate immediately before treatment such as film formation. CONSTITUTION:Hydrogen gas where an extremely small amount of silane gas is added is supplied into an elimination chamber 1 and a silicon substrate 3 is placed on a substrate supporting stand 2. The silicon substrate 3 is heated while light with a wavelength for performing photo chemical decomposition of silane gas is applied from a light source 6 through a light incidence window 7, thus eliminating natural oxide film of the silicon substrate 3 'on the spot' at a lower temperature than before. At this time, heating the light incidence window 7 to nearly the same temperature of heating treatment temperature or higher of the silicon substrate 3 prevents a film from being deposited on the light incidence window 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing "in-situ" a natural oxide film of silicon, in particular, by heating a natural oxide film existing on the surface of a silicon substrate immediately before processing such as film formation at low temperature. In-situ "removal method and apparatus.

[0002]

2. Description of the Related Art The "in-situ" removal method of a natural oxide film, in which the natural oxide film existing on the surface of a silicon substrate is completely removed, and thereafter the subsequent processing such as film formation is performed without contact with the outside air, is conventionally performed by Si epitaxial growth. Although it has been regarded as the most important step in the process, this natural oxide film removal method is beginning to have decisive importance also in future LSI manufacturing processes in which miniaturization progresses. On the other hand, in the LSI manufacturing process, in order to prevent the device from being damaged, lowering the temperature should be pursued at the same time, and a natural oxide film removing process must be developed with due consideration to this point.

As a natural oxide film removing method in the conventional Si epitaxial process, a hydrogen baking method has been favored. However, according to this method, the reliable removal effect of the natural oxide film is recognized only at about 950 ° C. or higher, which is unacceptable even in the current LSI manufacturing process. Further, an etching method using HF (hydrogen fluoride) vapor is expected as a trump card for lowering the above-mentioned temperature, but in principle, it is inevitable that fluorine remains on the semiconductor surface after processing, and further, an oxide film pattern is required. The problem of controlling unwanted overetching of the part must also be solved.
Further, as a physical removal method that does not require high temperature, there is a sputter etching method using Ar or the like, but in this case, there are problems of sputter damage and loss of the removal effect in a fine pattern portion.

Among the various natural oxide film removal methods described above, the hydrogen bake method in which a very small amount of silanes is added has recently attracted attention for the purpose of lowering the temperature of the natural oxide film removal by hydrogen bake, and many reports have been made. .. Here, the mechanism of natural oxide film removal by the hydrogen bake method will be described. What is important in this case is that hydrogen does not directly reduce the natural oxide film as given by the following formula (1), but it does not provide a hydrogen atmosphere as shown in formula (2) or as a catalyst. Is considered to be greater in action.

[0005]

[Chemical 1]

That is, hydrogen does not directly reduce and remove the natural oxide film as generally considered, but merely provides a reducing atmosphere, and the natural oxide film (Si
O ₂ ) is reduced by more reducing (substrate) silicon and becomes volatile SiO, which is evaporated and removed. Based on such a mechanism, an extremely small amount of silanes such as monosilane (SiH ₄ ) and disilane (Si ₂ ) is used for the purpose of lowering the temperature of the natural oxide film removal by the hydrogen bake method.
Hydrogen bake is performed by adding a gas such as H ₆ ).

In this method, as a reducing agent for the natural oxide film in the above formula (2), SiH ₄ and Si ₂ H ₆ added in an extremely small amount in addition to the substrate silicon are thermally decomposed and are extremely reducible. SiHn (silyl radical; n = 1 to 3)
And a very small amount of silicon nuclei (seed) generated on the natural oxide film at the same time. That is,
Due to SiHn generated in the gas phase or on the substrate surface and a very small amount of silicon nuclei generated on the natural oxide film, the natural oxide film is reduced by the mechanism shown in the following formulas (3) and (4). It is removed by evaporation.

[0008]

[Chemical 2]

By using this method, an equivalent natural oxide film removing effect is about 10 as compared with a simple hydrogen baking.
0 ° C to 150 ° C lower temperature, namely 800 ° C to 850 ° C
It is obtained even at a moderate temperature. What is important in this method is that the concentration of the added silane gas is sufficiently diluted so that substantial silicon deposition does not occur. That is, if the amount of silane gas added is excessive and the concentration is too high, the generation of silicon nuclei becomes excessive,
As a result, silicon is deposited on the natural oxide film rather than the natural oxide film being removed by the mechanisms of the above formulas (3) and (4). In other words, the added silane gas also serves as a source gas for depositing silicon depending on its concentration (this is a general application), while it also serves as an etching gas for the silicon oxide film. The removal utilizes the latter property. The amount of silane gas added for such applications is actually several ppm to several tens of p
Concentrations of pm are common.

[0010]

In the "in-situ" removal method of the silicon natural oxide film as described above, since silane gases are added for thermal decomposition, it is effective for lowering the temperature of hydrogen bake. Nevertheless, a temperature of about 800 ° C. to 850 ° C. is still required, and there is a problem that further lowering of the temperature is required for application to the LSI process. The present invention has been made in order to solve such a problem, and it is possible to remove a natural oxide film at a lower temperature than the conventional hydrogen bake by adding a silane gas.
It is an object of the present invention to provide a “situ” removal method and apparatus for a native silicon oxide film that can be applied to the I process.

[0011]

According to a first aspect of the present invention, a method for "in-situ" removal of a silicon native oxide film is performed by using a silane gas in a hydrogen atmosphere containing a very small amount of silane gas. While irradiating light with a wavelength that photochemically decomposes
The silicon substrate immediately before the subsequent processing is heat-treated.

In the "in-situ" removal apparatus for a silicon native oxide film according to the second aspect of the present invention, a silicon substrate is arranged inside and hydrogen gas to which an extremely small amount of silane gas is added is supplied. A light incident window provided in the chamber and for allowing light from a light source provided outside the chamber to enter the chamber is heated to a temperature approximately equal to or higher than the heat treatment temperature of the silicon substrate, and then immediately before the subsequent treatment. A silicon substrate is heat-treated.

[0013]

According to the first aspect of the present invention, by adopting photochemical decomposition capable of supplying SiHn radicals and silicon nuclei regardless of temperature, it is possible to further reduce the effective lower limit temperature in the hydrogen bake method with addition of a trace amount of silanes. This is intended to lower the temperature.

According to the second aspect of the present invention, since the light incident window is heated to a temperature equal to or higher than the heating temperature of the silicon substrate, film deposition is prevented from occurring in the light incident window and the incident light is blocked. Can be avoided.

[0015]

[Example] In the conventional hydrogen baking method in which a very small amount of silane gas is added, it is possible to achieve a certain temperature reduction.
As described above, this is due to the SiHn radicals generated by thermal decomposition and the natural oxide film reduction effect of silicon having a size equal to or less than the critical nucleus. The thermal decomposition efficiency determines the lower limit temperature to which the conventional method is applied. It was one of the factors. Therefore, in the present invention, by further utilizing the photochemical decomposition capable of supplying the SiHn radicals and the silicon nuclei regardless of the temperature, the effective lower limit temperature in the ultra-trace amount silane gas-added hydrogen baking method is further lowered. is there. Also,
The feature of the present invention is that the concentration of the added silane gas is set to an extremely small amount, so that the added silane gas is not used for usual deposition of silicon but is used for etching removal of the silicon oxide film. Especially.

FIG. 1 is a schematic diagram showing an "in-situ" removal apparatus for a silicon native oxide film according to an embodiment of the present invention. In the figure, a silicon oxide substrate 3 mounted on a substrate support 2 having a heating device 2a is accommodated in an "in-situ" removal chamber 1 for a natural oxide film. Further, the removal chamber 1 is provided with a gas supply pipe 4 for supplying hydrogen gas to which an extremely small amount of silane gas has been added and a vacuum exhaust pipe 5 for exhausting the inside of the removal chamber 1. Further, outside the removal chamber 1, there is provided a light source 6 that generates light that photochemically decomposes the silane gas. The light source 6 may be a laser or a lamp as long as it has a radiation wavelength that photochemically decomposes a silane gas, and for example, an ArF excimer laser (for example, 19
30 Å), low-pressure mercury lamp (eg 2537 Å, 184
9Å) or deuterium lamp can be preferably used.

Light from the light source 6 is applied to the silicon substrate 3 in the removal chamber 1 through a light incident window 7 made of, for example, quartz. The light incident window 7 is heated by the heating device 8 to the same temperature as the silicon substrate 3 or higher.
A film formation chamber 10 is arranged adjacent to the removal chamber 1 via a gate valve 9. In this film forming chamber 10, the silicon substrate 3 from which the natural oxide film has been removed in the removing chamber 1 passes through the gate valve 9 in an airtight manner without coming into contact with the outside air, and is transported into the film forming chamber 10 to be transferred to the silicon substrate. The film forming process of No. 3 is performed. A substrate support 11 having a heating device 11a for mounting a silicon substrate 3 is arranged in the film forming chamber 10, and a gas supply pipe for film forming reaction for supplying a film forming reaction gas into the film forming chamber 10. 12 and a vacuum exhaust pipe 13 for exhausting the inside of the film forming chamber 10 are provided.

In the "in-situ" removal apparatus for the natural oxide film constructed as described above, first, the inside of the removal chamber 1 is evacuated by the vacuum evacuation means (not shown) through the evacuation tube 13, and then 1 ppm- Hydrogen gas to which an extremely small amount of silane gas of about 100 ppm is added is supplied from the gas supply pipe 4 into the removal chamber 1. The silicon substrate 3 and the light incident window 7 are respectively heated by the heating means 2a and 8 from 500 ° C to 600 ° C.
Heat to about ℃. Light having a wavelength that photochemically decomposes the silane gas is irradiated from the light source 6 to the silicon substrate 3 in the removal chamber 1 through the light incident window 7 that is heated to the same temperature as the silicon substrate 3. The silicon substrate 3 heated to a temperature lower than that of the conventional one is baked while being irradiated with light in a hydrogen gas containing an extremely small amount of silane gas, and the natural oxide film on the surface of the silicon substrate 3 is removed.

At this time, since the light incident window 7 is heated to a temperature equal to or higher than the heat treatment temperature of the silicon substrate 3,
The silicon to be deposited on the light incident window 7 is converted to SiO by a mechanism similar to the above formula (4) and evaporated, and as a result, the light incident window 7 is kept clean. As described above, the inhibition of the excitation light incidence due to the film deposition on the light incident window 7, which is one of the most troublesome problems in the conventional process utilizing the light energy, causes the light incident window 7 to be blocked as described above. It can be completely avoided by heating.

Silicon substrate 3 from which the natural oxide film has been removed
Are transferred to the film forming chamber 10 through the gate valve 9 without being exposed to the outside air. The inside of the film forming chamber 10 is evacuated by a vacuum exhaust pipe 13 in advance, and then a film forming reaction gas is supplied from a gas supply pipe 12. The silicon substrate 3 placed on the substrate support 11 is subjected to a predetermined film forming process.

Incidentally, the film forming chamber 10 in the above-mentioned embodiment.
It is not necessary to carry out the film formation process in
A thermal CVD method, a plasma CVD method, or another processing method may be used. Further, in the steps after the removal of the natural oxide film, various kinds of processing other than film formation can be performed.

[0022]

As described above, the invention according to claim 1 of the present invention irradiates with light having a wavelength that photochemically decomposes this silane gas in a hydrogen atmosphere to which an extremely small amount of silane gas is added. However, since the silicon substrate immediately before the subsequent processing is heat-treated, the temperature required for the "in-situ" removal of the native silicon oxide film by baking can be significantly reduced, and it is also applicable to the LSI process. Produce an effect.

The invention according to claim 2 of the present invention is provided in a chamber in which a silicon substrate is disposed inside and a hydrogen gas to which an extremely small amount of silane gas is added is supplied.
Moreover, the light incident window for entering the light from the light source provided outside the chamber into the chamber is heated to a temperature equal to or higher than the heat treatment temperature of the silicon substrate, and the silicon substrate immediately before the heat treatment is heat treated. Therefore, it is possible to prevent the film from being deposited on the light incident window and prevent the incident light from being obstructed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an “in-situ” removal apparatus for a silicon native oxide film according to an embodiment of the present invention.

[Explanation of symbols]

 1 Removal chamber 2, 11 Substrate support 2a, 8, 11a Heating device 3 Silicon substrate 4, 12 Gas supply pipe 5, 13 Vacuum exhaust pipe 6 Light source 7 Light entrance window 9 Gate valve 10 Film formation chamber 12 Gas supply pipe

Claims (2)

[Claims] 1. A silicon substrate immediately before the subsequent treatment is heat-treated while irradiating light having a wavelength that photochemically decomposes the silane gas in a hydrogen atmosphere to which an extremely small amount of silane gas is added. "In-situ" removal method of native silicon oxide film. 2. A silicon substrate is provided inside a chamber provided with a hydrogen gas to which an extremely small amount of silane gas is added, and light from a light source provided outside this chamber is introduced into the chamber. The light incident window incident on is heated to a temperature equal to or higher than the heat treatment temperature of the silicon substrate,
An "in-situ" removal apparatus for a natural silicon oxide film, which is characterized by heat-treating a silicon substrate immediately before the subsequent processing.