JP2637950B2 - Surface cleaning method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for cleaning a silicon surface.

[Conventional technology]

In recent years, for the purpose of application to high-speed bipolar devices, microwave devices, superlattice structure devices, etc., growth has been performed at lower temperatures compared to conventional silicon thin film growth technology,
Therefore, a silicon molecular beam epitaxy (SiMBE) technique in a high vacuum, which has a characteristic that the impurity distribution is hardly disturbed, has been actively researched and developed.

In such a silicon molecular beam growth technique, the crystallinity of a silicon film grown thereon is greatly affected by the cleanliness of the surface of the single crystal silicon substrate. Accordingly, a number of methods for cleaning the substrate surface have been studied. For example, the Japan Electronic Industry Progress Association, "Survey and Research Report 1 on New Silicon Devices (Showa
(March, 1957) ”from page 52 to page 66, entitled“ Si Molecular Beam Growth Technology ”, the first method for surface cleaning is to heat at high temperature in a high vacuum.
A method for sputtering a substrate surface with an ion beam as a second method, a method for irradiating a gallium beam as a third method, and a method for performing laser irradiation as a fourth method are described.

Recently, the viewpoint, "Ultra High Vacuum Wafer Purification (2)" was announced on page 502 of the proceedings of the 30th Applied Physics-related Lecture Meeting (April 1983) by Viewpoint, Inoue and Takasu. At the lecture, silicon was deposited extremely thinly on the thin silicon oxide film formed on the surface during substrate cleaning, and the ultra-thin silicon film reacted with the thin oxide film at a low temperature of 710 ° C, and both evaporated and clean. A fifth method has been shown in which a surface is obtained. In addition, Aizaki, Tatsumi, and Tsuya have published the 45th Annual Meeting of the Japan Society of Applied Physics (10 October 1984).
Monday) As a new sixth method, a gas containing ozone in the cleaning bath liquid during cleaning was presented as a new method in a lecture entitled "Defect density reduction of SiMBE-ozone treatment and growth rate dependence" on page 651. The method has been shown to reduce contamination at the interface between the protective oxide film on the surface and the silicon substrate.

[Problems to be solved by the invention]

In the first, third, fourth, fifth, and sixth methods described above, since the silicon substrate is previously cleaned in the cleaning solution, the degree of cleaning in this cleaning step is the final wafer. Affects the degree of cleaning. In the sixth method, considerable pollution can be removed by the effect of ozone (10
On the (0) plane, defects in the silicon epitaxial film due to silicon molecular beam growth can be eliminated, but on the (111) plane, defects of about 10 ² cm ⁻² still exist. In the second method, the surface can be etched in an ultra-high vacuum, which is effective in removing contamination. However, there is a disadvantage that high-temperature heat treatment is required to recover the surface by damaging the surface by sputtering. .

An object of the present invention is to eliminate such conventional drawbacks and to obtain an epitaxially grown film having sufficiently good crystallinity by a silicon molecular beam, or to a general integrated circuit manufacturing process. It is another object of the present invention to provide a method for cleaning a surface which can be applied to a method such as the above.

[Means for solving the problem]

The present invention provides a method of cleaning the surface of a substrate having silicon on at least the surface, exposing the silicon surface, irradiating a germanium molecular beam to form a mixed crystal layer of silicon and germanium, and then heating the mixed crystal to form the mixed crystal layer. Is a surface cleaning method characterized by evaporating water.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. In a normal silicon wafer, as shown in FIG. 1A, a natural silicon oxide film 20 having a thickness of more than 10 mm is formed on the surface of a silicon substrate 10, and contaminant impurities such as carbon are formed on the surface of the silicon oxide film 20. There is also a contaminant impurity 31 such as carbon at the interface between the silicon oxide film 20 and the silicon substrate 10.

Next, 28% ammonia water, 30% hydrogen peroxide water and water are used as 1:
When mixed at a ratio of 4:20 and the silicon wafer is washed in a boiling solution for 5 to 10 minutes, the etching action of the ammonia water and the action of forming the silicon oxide film in the hydrogen peroxide solution are repeatedly performed. As shown in FIG. 1B, the silicon oxide film 20 is removed, and a new high-quality silicon oxide film 21 having a very small amount of contaminant impurities such as carbon is formed at a thickness of about 10 mm. At this time, the contaminant impurities 31 such as carbon existing at the interface between the silicon oxide film 20 and the silicon substrate 10 are mostly removed but partly remain, and are newly adhered, so that they are at least less than before cleaning. There is, but there is. Furthermore, carbon is attached to the surface as a contaminant 32 by being exposed to the air.

Next, in a vacuum vessel having a good degree of vacuum of about 10 ⁻¹⁰ Torr, for a short time, for example, 1 minute to 2 minutes, 600 ° C. to 850 ° C.
Then, carbon 32 is desorbed from the surface of the silicon oxide film 21 as shown in FIG. When heated further to 850 ° C. or more, as shown in FIG.
21 evaporates. However, the carbon contaminants 31 existing at the interface do not desorb and remain on the surface. In this state, when the substrate temperature is lowered to the growth temperature of 400 ° C. to 800 ° C. and molecular beam growth is performed, crystal defects are generated with carbon contaminants 31 remaining on the surface as nuclei. In order to remove the carbon contaminants 31, the substrate temperature must be raised to 1200 ° C. or higher to thermally etch silicon on the surface to cut the surface. However, when the temperature is raised to such a high temperature, the doping profile of the substrate is changed, and the characteristic of low temperature growth, which is a great advantage of molecular beam growth, is lost.

Then, after removing the protective oxide film 21 on the surface, the substrate temperature is kept at 200 ° C. or more and four or more atomic layers of germanium are applied, as shown in FIG. 1 (e), the surface layer becomes a mixed crystal of silicon and germanium. It becomes layer 40. When the substrate temperature is set to 900 ° C. or higher, the mixed crystal layer 40 evaporates, and as a result, the substrate surface layer is etched. At this time, contaminants such as carbon remaining on the surface are also detached from the surface, and an extremely clean surface is obtained.

Next, an example in which this surface cleaning method is actually used for silicon molecular beam growth will be described more specifically. A P-type silicon substrate having a plane orientation of (111) and a specific resistance of 10 to 20 Ω · cm is prepared by mixing 28% ammonia water, 30% hydrogen peroxide water and water with 1:
Wash for 10 minutes in a mixed and boiled solution at a ratio of 4:20,
Then, after removing the oxide film on the surface at a cleaning temperature of 780 ° C. by using the silicon pre-deposition method as the fifth method in an ultra-high vacuum of 10 ⁻¹⁰ Torr, the substrate temperature is lowered to 650 ° C., which is the growth temperature. After lowering the temperature and then heating the substrate at 900 ° C for 1 minute to remove the mixed crystal layer of silicon and germanium after depositing 4 atomic layers at a cell temperature of 1150 ° C from the normal K-cell installed in the growth chamber, Table 1 shows the results of evaluation based on the crystal defect density of the silicon molecular beam grown film of Example 1. That is, Table 1
This is a result of obtaining a crystal defect density of a sample after growing a silicon molecular beam having a thickness of 1.0 μm by a commonly used zirtol etching.

The values of the crystal defect density in Table 1 show that the method of the present invention is superior to the conventional method by comparing the method of the present invention with the conventional method.

In this embodiment, the thickness of germanium to be deposited is 4
Although the thick layer is used, the thickness is preferably 4 to 10 atomic layers. Film thickness 4
If the thickness is less than the atomic layer, silicon and germanium do not react and a mixed crystal layer is not formed, so that the silicon surface cannot be etched. If the film thickness is more than 10 atomic layers, the surface after evaporating the mixed crystal layer of silicon and germanium becomes rough.

Furthermore, although the present embodiment is directed to a silicon wafer, the method of the present invention is applied to an SOS in which silicon exists only on the surface.
(Silicon on Sapphire) substrates and more generally SOI (Silico on Sapphire)
n on Insulator) Of course, it can also be applied to substrates and the like.

In the above description, the case where the present invention is applied to a cleaning method in a silicon molecular beam growth technique is described as an example. However, the present invention is not limited to this, and is widely applied to wafer processing steps such as integrated circuit manufacturing. it can.

〔The invention's effect〕

As described above in detail, the present invention is to etch a silicon surface by depositing germanium on a silicon surface, forming a surface layer of a mixed crystal layer of silicon and germanium, and then evaporating the mixed crystal layer. When an epitaxial film is formed by the silicon molecular beam growth method, a high-quality film with very few crystal defects can be obtained. Further, the film has an effect that it can be applied not only to the molecular beam growth method but also to a general integrated circuit manufacturing process. is there.

[Brief description of the drawings]

1 (a), 1 (b), 1 (c), 1 (d) and 1 (e) are schematic sectional views of a silicon wafer showing an embodiment of the present invention in the order of steps. In the figure, 10: silicon substrate, 20: silicon oxide film, 21: silicon oxide film after cleaning, 30, 32 ... contaminant impurities such as carbon on the silicon oxide surface, 31 ... silicon oxide film and silicon substrate Contaminant impurities, such as carbon, at the interface with silicon, 40 ... a mixed crystal layer of silicon and germanium

Claims (1)

(57) [Claims] In a method for cleaning a surface of a substrate having silicon on at least the surface, the silicon surface is exposed,
A surface cleaning method comprising irradiating a germanium molecular beam to form a mixed crystal layer of silicon and germanium on a silicon surface, and thereafter heating the mixed crystal to evaporate the mixed crystal.