JPS62111420A - Method for forming cosi2 film - Google Patents

Abstract

PURPOSE:To obtain a solid phase epitaxial method having less effect on the Si substrate by alternately stacking Co and Si films on a Si monocrystalline substrate with a specific composition ratio and at a substrate temperature of 450 deg. or less. CONSTITUTION:On a Si substrate 2, multilayer films 1, 3 of Si and Co are formed so that the composition ratio becomes that of CoSi2, at a substrate temperature of 450 deg.C or less which is hard to cause the reaction with the ground, preferably, 25-300 deg.C. For the composition ratio of Co and Si, Si/Co>2, the excess Si precipitates on the CoSi2 film at the time of epitaxial growth, so it is not desirable. For Si/Co<1.8, Si atoms diffuse from the ground to supply insufficient Si atoms in forming the CoSi2 film, which adversely affects the surface morphology of the CoSi2 film.

Description

[Detailed Description of the Invention] Western Description of the Invention [Field of Application of the Invention] The present invention relates to a method for forming a CoSi2 film. CoS is suitable for semiconductor devices because it can easily form a COS j 2 single crystal film with particularly good crystallinity, and at the same time there is little influence of impurity diffusion from CoSi2 into the Si substrate.
This invention relates to an in-phase epitaxial growth method for i2 films.

[Background of the invention]

Conventionally, as a method for epitaxially growing a CoSi2 single crystal film on a Si single crystal, a solid-phase epitaxial method in which a Co film and a Si substrate are reacted has been described, for example, by R.T. 1-Lang et al. in Applied Physics Letters, No. 40. Volume, page 684, published 1982 (R,
T., Tunget al., Appl., Phys.
, Lett, 40 (1982).

p. 684) was known.

The solid-phase epitaxial method is easy to form, but the reaction involves diffusion, which may cause Co to diffuse into Si,
The disadvantage was that the surface morphology of the membrane was poor.

[Purpose of the invention]

An object of the present invention is to provide a method for forming a CoSi2 film using an in-phase epitaxial method that is as easy as the conventional solid-phase epitaxial method and has less influence on the Si substrate.

[Summary of the invention]

The disadvantages of the conventional solid-phase epitaxial method are that film growth occurs due to nucleation due to reaction with the underlying Si substrate, and because a diffusion reaction of Si and CO is essential, Co atoms may become impurities in the Si substrate. It turned out that it was dissolved in solid solution. Therefore, if the in-phase reaction with the Si substrate is prevented and the epitaxial growth is made to follow the underlying Si substrate, the above-mentioned drawbacks of the in-phase epitaxial method can be overcome. For this reason, the substrate temperature is preferably 450°C or lower, where reaction with the underlying layer is less likely to occur on the Si substrate, preferably 25°C.
At ~300°C, Si was added to the composition ratio of CoSi2.
A multilayer film of Co and Co is formed. Composition ratio is CoSi2
If it deviates from this, it is not desirable because the reaction between the underlying Si substrate and the film formed thereon becomes significant at a substrate temperature of 450° C. or higher, especially 550° C. or higher. The composition of the multilayer film as a whole is such that there is little lattice mismatch with Si, epitaxial growth occurs easily, and CoSi2 is stable as a coexisting phase with Si. At this time Co and S
When the composition ratio with i is Si/Co)2, excess S is added to the CoSi2 film during epitaxial growth.
i becomes precipitated, which is undesirable. Also S i /
When G o <1, 8, Si atoms diffuse from the base to cover the insufficient Si atoms when forming the CoSi2 film, but this is undesirable because the surface morphology of the CoSi2 film deteriorates.

A multilayer film of Si and Co formed at a temperature below 200°C.

Each layer is very thin with 30 to 300 layers, and contains a large number of lattice defects compared to the single crystal substrate, so it is difficult to diffuse t<,4
Even by annealing at a low temperature of 50° C. for 30 minutes, a uniform CoSi2 phase is easily formed without reacting with the underlying Si. The annealing temperature for forming CoSi2 is as described above.
450-550℃ from the viewpoint of preventing reaction with the substrate
It is. Note that the step of forming a CoSi2 film from this multilayer film may be omitted.

Next, add CoSi2 film or Co-Si multilayer film.

The base Si single crystal substrate was heated to 450° C. to 1000° C. in order to perform in-phase epitaxial growth.

Single crystal growth is possible at 450°C if the Si substrate surface is clean.
However, the crystallinity is not very good. 600-75
At 0° C., it is possible to obtain a single crystal film with good crystallinity and a very smooth surface with irregularities on the order of atomic layers.

When heated to 800°C or higher, especially 900°C, the crystallinity is good, but the surface becomes rough, and in extreme cases.

A hole may be formed in the CoSi2 film and the underlying Si substrate may be exposed. Therefore, 600~
A substrate heating temperature of 800° C. is the optimal temperature range for solid phase epitaxial growth.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to Examples.

Example 1 A Si (111) single crystal substrate was inserted into a molecular beam growth apparatus, and the surface was cleaned by low-temperature thermal etching in an ultra-high vacuum of 10-10 torr. Next, the substrate temperature was lowered to room temperature, and the Si layer and Co layer were
Four layers were alternately formed at intervals of 0 people. The substrate was then raised to 600°C for 30 minutes. When the crystallinity was determined by reflection electron beam diffraction, a single crystal pattern was obtained, and it was found that epitaxial growth of the (111) plane had similarly occurred on the (111) plane of the underlying Si substrate. Next, analysis by Auger electron spectroscopy showed that CoSi
A 5itvv peak with a line shape characteristic of CoSi2 was obtained, indicating that CoSi2 was generated. When the cross section was observed, it was found that CoSi2 did not grow eating away at the underlying Si substrate, as shown in FIG. 1(b), unlike in the case of normal solid phase epitaxial method.

Note that FIG. 1(a) is a cross-sectional view showing a state in which a 00 layer is formed on a Si substrate 2, and FIG. 1(b) is a cross-sectional view after solid phase epitaxial growth. On the other hand, FIG. 2(a) shows the result using the method of the present invention, with a Co layer (1) and a Si layer (3).
This shows a state in which these are alternately stacked on a Si substrate (2). Second
Figure (b) shows a state in which solid phase epitaxial growth was performed in this state. Also.

The morphology of the surface was so mirror-like that no structure could be seen even when viewed with a Nomarski optical microscope. When IMA analysis was performed in the depth direction, as shown in Figure 3, in the case of the ordinary in-phase epitaxial method, the sag at the interface was 2000, as was the case with the solid-phase epitaxial method of the present invention. In the case of , the amount of sagging at the interface was about 400. This sagging is the extent of sagging due to ion bombardment accompanying ion sputtering in analysis, and it is clear that in the method according to the present invention, the diffusion of Co atoms into the Si substrate is extremely small.

〔Effect of the invention〕

As described above, according to the present invention, (1) a film quality equivalent to that obtained by simultaneous vapor deposition can be formed without eating Si atoms from the Si substrate, and with the same ease as the conventional in-phase epitaxial method. .

(2) Moreover, it has the characteristic that the diffusion of Co atoms into the semiconductor layer is small.

CoSi2 can be used for semiconductors, which has an extremely large effect.

[Brief explanation of drawings]

Figures 1 (a) and (b) are cross-sectional views of layers grown by the conventional in-phase epitaxial method. FIGS. 2(a) and 2(b) are cross-sectional views of layers grown by the solid-phase epitaxial method according to the present invention, and (a) is a cross-sectional view after forming a multilayer film of CoSi□ film; b) is a cross-sectional view of this after solid-phase epitaxial growth. Fig. 3 is a diagram showing the results of CO depth direction analysis by secondary ion mass spectrometry. 1...CO film, 2...Si Substrate, 3...Si film, 4...
...CoSi2 film.

Claims (1)

[Claims] 1. On a Si single crystal substrate, at a substrate temperature of 450°C or less, Co and Si films are alternately formed at a desired periodicity with a thickness of 30 to 300 Å, and the composition ratio of the entire laminated film is It is characterized by epitaxially growing a CoSi_2 single crystal film by forming a laminated film so that ▲ is ▼, and then heating it to 450 to 1000°C to form a CoSi_2 film. C
Method for forming oSi_2 film. 2. The laminated film of the Si film and Co film is annealed to
A method for forming a CoSi_2 film according to claim 1, characterized in that an oSi_2 film is formed and then a CoSi_2 single crystal film is epitaxially grown.