JPS61212017A - Solid-phase epitaxial growth method for nisi2 film - Google Patents

Abstract

PURPOSE:To easily obtain the crystallizability of good quality by a method wherein a multilayer film consisting of Si and Ni is formed in such a manner that the compositional ratio of NiSi2 is obtained at the substrate temperature of 350 deg.C or below, and a single crystal film is formed by performing a solid-state epitaxial growth method at the temperature range of 350-750 deg.C. CONSTITUTION:After a laminated film of 30-300Angstrom in thickness is formed on an Si single-crystal substrate 2 at the substrate temperature of 350 deg.C or below in such a manner that an Ni film 1 and an Si film 3 are superposed alternately at the desired cycle and that the entire compositional ratio is brought to Si/Ni=2-1.8, which said laminated film is turned into an NiSi2 film by performing an annealing, and then an NiSi2 single crystal film 4 is epitaxially grown by heating the above-mentioned NiSi2 film at the temperature range of 350-750 deg.C. As a result, the film of the same quality as the film obtained by performing a simultaneous vapor-deposition method in the degree of simplicity the same as the solid-phase epitaxial growth method heretofore in use can be obtained without removal of Si atoms from the Si substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for forming a NiSi2 film. In particular, the present invention relates to a solid-phase epitaxial growth method for NiSi2 films suitable for semiconductor devices, in which an N15il single crystal film with good crystallinity can be easily formed, and at the same time, the influence of impurity diffusion from NiSi2 into a Si substrate is small.

[Background of the invention]

Conventionally, as a method for epitaxially growing a NiSi2 single crystal film on a Si single crystal, solid phase epitaxial growth (for example, S, 5aitoh
et al, Japan JAPA
, 20 (1981).

1649) and the simultaneous evaporation method (for example, J, C, Beana
tal, APL, 37 (1980),
643~) was known. Although the in-phase epitaxial method is easy to form, one reaction involves diffusion, and it has drawbacks such as diffusion of Ni into Si and poor morphology of the surface of the film.

On the other hand, the co-evaporation method has the advantage of producing a film with good crystallinity, good morphology on the surface, and less diffusion of Ni atoms into the Si substrate.
It was difficult to keep the ratio of i and Ni constant over time to the stoichiometric composition. This is a practical difficulty.

[Purpose of the invention]

The object of the present invention is to provide a method for forming a NiSi2 film.

The object of the present invention is to provide a solid phase epitaxial method that is as easy as the conventional solid phase epitaxial method, has good crystallinity comparable to that of the simultaneous vapor deposition method, and has less influence on the Si substrate.

[Summary of the invention]

The disadvantages of the conventional in-phase epitaxial method are that film growth occurs due to nucleation due to reaction with the underlying Si substrate, and because a diffusion reaction between Si and Ni is essential, Ni atoms may become fixed as impurities in the Si substrate. It was said that it would be dissolved. Therefore, similarly to the simultaneous vapor deposition method, 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 solid phase epitaxial method can be overcome. For this purpose, a multilayer film of Si and Ni is formed on a Si substrate at a substrate temperature of 350° C. or lower, preferably 25 to 200° C., where reaction with the underlying layer is less likely to occur, so as to have a composition ratio of NiSi2. When stable NiSi2 phase is not formed, the temperature is 350℃ or higher,
In particular, a substrate temperature of 450°C or higher is undesirable because the reaction between the underlying Si substrate and the film formed thereon becomes significant.
The overall composition of the multilayer film has little lattice mismatch with Si, and epitaxial growth occurs easily.
NiSi2 was made to be stable as a coexisting phase with i. At this time, when the composition ratio of Ni and Si is Si/N1)2,
Excess S is added to the NiSi2 film during epitaxial growth.
i becomes precipitated, which is undesirable, and Si/Ni
>1.8, Si atoms diffuse from the underlying layer to cover the insufficient Si atoms when forming the NiSi2 film, but this is undesirable because the surface morphology of the NiSi2 film deteriorates. Multilayer films of Si and Ni formed at temperatures below 200°C are extremely thin, with each layer having 30 to 300 layers, and contain a large number of lattice defects compared to single crystal substrates, so they are easily diffused and do not remain stable even below 100°C. A uniform Ni51g phase is formed, and even by annealing at a low temperature of 350° C. for 30 minutes, it easily becomes a uniform Ni51g phase without reacting with the underlying Si. The annealing temperature for forming this NiSi2 is 350°C from the viewpoint of preventing reaction with the Si substrate as described above.
~450°C. Note that the step of forming the NiSi2 film from this multilayer film may be omitted.

Next, apply a NiSi2 film or a Ni-Si multilayer film to the base layer S.
i A single crystal substrate was heated to 350° C. to 750° C. for solid phase epitaxial growth. Single crystal growth can occur even at 350° C. if the Si substrate surface is clean, but the crystallinity is poor.

Good crystallinity at 500-650°C.

A very smooth single crystal film with surface irregularities on the order of atomic layers can be obtained. When heated to 650° C. or higher, especially 750° C., the crystallinity is good, but the surface becomes rough, and in extreme cases, holes are formed in the NiSi2 film, exposing the underlying Si substrate. Therefore, 500-650
A substrate heating temperature of °C is the optimum temperature range for in-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-'' torr.

Next, the substrate temperature was lowered to room temperature, and the Si layer and Ni layer were each
Five people alternately formed four layers at a period of 50λ. Thereafter, the substrate was heated to 600° C. for 30 minutes.

When the crystallinity was determined by reflected electron beam diffraction, a single crystal pattern was obtained, and with respect to the underlying Si substrate (ni) surface,
Similarly, it was found that epitaxial growth of the (111) plane occurred. Next, when analyzed by Auger electron spectroscopy, it was found that the line shape Si t peculiar to NiSi2
, vv peaks are obtained.

It was found that N15iz was generated. When the cross section was observed, unlike in the case of the normal solid phase epitaxial method, as shown in FIG. 1(b), there was no growth of N15iz eating into the underlying Si substrate. Note that FIG. 1(a) is a cross-sectional view showing a Ni layer formed on a Si substrate 2, and FIG. 1(b) is a cross-sectional view of this after solid phase epitaxial growth.

On the other hand, FIG. 2(a) shows the result using the method of the present invention, with N
A state in which i-layers (1) and Si layers (3) are alternately stacked on a Si substrate (2) is shown. FIG. 2(b) shows a state in which in-phase epitaxial growth is performed in this state. Furthermore, the surface morphology 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 normal solid-phase epitaxial method, the sag at the interface was 2000 as shown above, whereas in the case of the in-phase epitaxial method of the present invention, the sag was 2000. In the case of engineering, there were about 500 regular sag marks on the interface. 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 N1J7i molecules into the Si substrate is extremely small.

〔Effect of the invention〕

According to the above first invention, (1) Without eating Si atoms from the Si substrate.

Moreover, it is possible to form a film with the same quality as that obtained by simultaneous vapor deposition with the same degree of ease as the conventional solid phase epitaxial method.

(2) It is also characterized by less diffusion of Ni atoms into the semiconductor layer.

There is an extremely large effect that N15iz can be used for semiconductors.

[Brief explanation of the drawing]

Figures 1(a) and 1(b) are cross-sectional views of a layer grown by conventional solid-phase epitaxial method, in which (a) is a cross-sectional view after forming a Ni film on a substrate, and (b) is a cross-sectional view of a layer grown by solid-phase epitaxial growth. FIG. FIGS. 2(a) and 2(b) are cross-sectional views of a layer grown by the solid phase epitaxial method according to the present invention;
A cross-sectional view of the film after the multilayer film is formed, and (b) is a cross-sectional view of the film after solid-phase epitaxial growth. FIG. 3 is a diagram showing the results of depth direction analysis of Ni by secondary ion mass spectrometry. 1...Ni film, 2...Si substrate, 3...Si film. 4...NiSi2 film.

Claims (1)

[Claims] 1. On a Si single crystal substrate, at a substrate temperature of 350°C or less, Ni 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 changed. NiSi_2 is characterized by epitaxially growing a NiSi_2 single crystal film by forming a laminated film so that ▲ is ▼ and then heating it to 350 to 750°C to form a NiSi_2 film. Solid-phase epitaxial growth of films. 2. The laminated film of the Si film and Ni film is annealed to
A solid phase epitaxial growth method for a NiSi_2 film according to claim 1, characterized in that an iSi_2 film is formed and then a NiSi_2 single crystal film is epitaxially grown.