JP3060486B2 - Method for forming SOI substrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming an SOI substrate, which is a kind of Si substrate required for forming a semiconductor device.

(Prior Art) Conventionally, as a method for forming an SOI substrate using a vapor phase growth method having excellent crystallinity, for example, a method described in J. of Electrochem.
c.), Vol. 130, p. 1571, Epitaxial Lateral Overgrowt
h) and a method called tunnel epitaxy as shown in the 50th Annual Meeting of the Japan Society of Applied Physics, Proceedings of Lectures, Second Volume, page 588 (28a-C-8).

(Problems to be Solved by the Invention) In the epitaxial lateral overgrowth of the prior art, when the epitaxial growth progresses from the seed region to the SiO ₂ in the lateral direction, the growth rate in the film thickness direction and the lateral growth are increased. Since it is difficult to make a large difference in the speed, the film thickness increases as the lateral growth proceeds, and it is difficult to obtain a thin SOI (single crystal Si on SiO ₂ ) region with a large area.

Tunnel epitaxy overcomes these disadvantages of epitaxial lateral overgrowth. In tunnel epitaxy, crystal growth proceeds laterally in a tunnel region sandwiched between upper and lower portions of SiO ₂ . This method uses SOI
Since the film thickness is accurately controlled by the height of the tunnel, it is possible to form a thin SOI with a large area, but there is a disadvantage that twin defects and stacking faults exist in the SOI film.

Method of forming a SOI substrate of the present invention (Means for Solving the Problem) is (100) up and down as a seed the SiO ₂ film or the upper the Si substrate the Si ₃ N ₄ film, a lower S
Tunnel epitaxy in which Si is vapor-phase epitaxially grown on a lower SiO ₂ film in a cavity region sandwiched between iO ₂ films,
The growth direction is <100> direction.

(Operation) Hereinafter, the reason why the present invention can form a good SOI without crystal defects such as twin defects and stacking faults which are observed in the related art will be described.

In conventional tunnel epitaxy, lateral growth is <10
In the present invention, it is performed in the <100> direction, whereas in the <0> direction.
Perform lateral growth in the direction. The present inventor has studied in detail the lateral epitaxial growth in such a vertically limited gap. In the <100> direction, twin defects are generated at a very early stage of the lateral growth, It became clear that surface defects such as twin defects and stacking faults occurred one after another. Although the cause of twin defect generation is not strictly clear, since all of these defects are introduced from the interface between the epitaxial growth layer and SiO ₂ or Si ₃ N ₄ , Si / SiO ₂ or Si / Si ₃ It is expected that the stability of the N ₄ interface has the cause. As long as the (100) substrate is used as a seed, these interfaces are constant on the (100) plane regardless of the lateral growth direction, but the transition from vertical growth to lateral growth occurs in the immediate vicinity of the seed. In a region, its crystallographic orientation relationship changes with the lateral growth direction. Therefore, considering the interfacial stability in this region, it can be obtained by changing the lateral growth direction.
It is possible to control the crystallinity of SOI.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process schematic diagram for explaining an embodiment of the present invention. The substrate temperature 9 on the Si substrate 10
The SiO ₂ film 20 is formed to a thickness of 0.2 to 0.8 μm by a dry or wet oxidation method at 00 to 1100 ° C. and an LPCVD method at a substrate temperature of 500 to 900 ° C.
A seed 30 was formed by opening a portion of the SiO ₂ film by ordinary photolithography and dry etching (FIG. 1A). Seed with lateral growth direction <10
0>. For comparison, those arranged so as to be <110> and intermediate <210> were also formed. Next, the epitaxial Si 130 was selectively grown only in the seed region until the surface of the epitaxial growth and the surface of the SiO ₂ film became almost the same height. (FIG. 1 (b)) The growth was made of SiH ₂ Cl
₂ (or SiH ₄ or SIH ₆ ) / HCl / H ₂ mixed gas was used at a substrate temperature of 800 to 1,050 ° C. Next, polycrystalline Si or amorphous Si240 is LPCVD method or ultra-high vacuum deposition method 0.05 ~
0.6 μm deposition and patterning
₂ or Si ₃ N ₄ film 250 is deposited at 0.1 to 0.5 μm and gas introduction window 260
Was formed at a position 5 to 50 μm away from the seed by a normal dry etching technique (FIG. 1 (c)). Next, polycrystalline or amorphous Si was removed by gas etching using HCl to obtain a tunnel 370 in which the lower portion was sandwiched between SiO ₂ and the upper portion between SiO _{2 and} Si ₃ N ₄ (FIG. 1 ( d)). Finally, epitaxial growth was performed in the tunnel under the same selective growth conditions as in FIG. 1B to obtain an SOI region 480 (FIG. 1E). The obtained SOI was observed using a cross section and a surface TEM to evaluate its crystallinity.

As a result, in the case of a tunnel sandwiched between upper and lower portions of SiO ₂ , a large number of crystal defects (twin defects and stacking faults) were observed in the <110> lateral growth, whereas the <100> lateral direction was observed. During the growth, no crystal defects were observed in the range observed by TEM. In the case of <210> growth, crystal defects were observed although the number was smaller than that of <110> growth. Si ₃ N on top
_{4. In} the case where the lower portion was made of SiO ₂ , crystal defects were observed in all samples, but the occurrence of crystal defects was suppressed most in the case of <100> lateral growth. In this case, <100
> All the crystal defects observed in the lateral growth had a shape expected to be introduced from the Si ₃ N ₄ / Si interface.

(Effect of the Invention) As described above, according to the present invention, it is possible to obtain a tunnel epitaxy technique capable of forming an SOI having better crystallinity as compared with the conventional technique, and it is possible to supply a substrate for forming a high-performance SiLSI. It became.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view for explaining an embodiment of the present invention. 10 ... Si substrate, 20 ... SiO ₂ film, 30 ... Seed, 130 ... Epitaxial Si, 240 ... Polycrystalline Si or amorphous Si, 250 ... SiO ₂ or Si ₃ N ₄ film, 260… … Gas introduction window, 370 …… Tunnel, 480 …… SOI area

Claims (2)

(57) [Claims] 1. A method according to claim 1, wherein a (100) Si substrate is used as a seed and SiO ₂
Film or the upper and the Si ₃ N ₄ film, the Si on the lower SiO ₂ film of the cavity region sandwiched between the lower of SiO ₂ film a tunnel epitaxy to grow a vapor phase epitaxial, the growth direction <100>
A method for forming an SOI substrate, comprising: 2. A step of forming a first SiO ₂ film on a surface of a (100) Si substrate, and removing a partial region of the first SiO ₂ film to grow Si by vapor phase epitaxial growth only in a region where the Si substrate is exposed. Forming a seed so that the surface and the first SiO ₂ film have substantially the same height, and forming the lower first SiO ₂ film and the upper Si ₃ N ₄
Forming a cavity region sandwiched between the film and the _second SiO ₂ film; and forming a <100> region on the first SiO ₂ film in the cavity region from the seed.
A step of epitaxially growing Si in the direction of vapor phase.