JP2964546B2 - 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 prior art, in the case of epitaxial lateral overgrowth, when epitaxial growth proceeds laterally from the seed region onto SiO ₂ , the growth rate in the film thickness direction and the growth rate in the lateral direction are increased. It is difficult to give a big difference to
As the growth in the lateral direction progressed, the film thickness increased, and it was 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 a large area, a further SiO ₂ is deposited a polycrystalline Si on the SiO ₂ during the formation of the tunnel Since the polycrystalline Si is deposited and removed by gas etching with HCl, irregularities reflecting the surface shape of the polycrystalline Si occur on the lower surface of the upper SiO ₂ film, and irregularities occur on the surface of the resulting SOI There was a disadvantage.

According to (SUMMARY for a) the present invention, it is exposed and forming a first SiO ₂ film on the Si substrate surface, the Si substrate by removing a partial region of the first SiO ₂ film Process, a process of epitaxially growing Si only in the region where the Si substrate is exposed, and forming a seed so that the height of the growth surface and the surface of the SiO ₂ film are substantially the same, and depositing and patterning amorphous Si Process and the Si ₃ N ₄ film or the second S
depositing an iO ₂ film, removing a portion of the Si ₃ N ₄ film or the second SiO ₂ film to form a window,
HCl gas is introduced to remove amorphous Si, and S
introducing a growth gas containing i and growing epitaxial Si on the first SiO ₂ film from the seed to obtain an SOI substrate forming method.

(Operation) Hereinafter, the reason why the present invention makes it possible to form a thin SOI with a small surface unevenness and a large area will be described.

In the present invention, amorphous Si is used in place of polycrystalline Si for tunnel epitaxy. Since polycrystalline Si is a collection of fine crystal grains of Si, irregularities corresponding to the crystal grains appear on the surface.Since amorphous Si has completely randomly arranged Si atoms, It is extremely flat compared to crystalline Si. Therefore, a second SiO ₂ film or Si ₃ N ₄ to be an upper part of a tunnel formed by etching this amorphous Si
The lower surface of the film is also flatter than that of polycrystalline Si,
The resulting SOI surface is also flat. Also, once the amorphous Si is deposited, even if the substrate temperature rises in the process of forming an SiO ₂ film or a Si ₃ N ₄ film thereon and the amorphous Si is transformed into polycrystalline Si,
The surface roughness is sufficiently flat compared to depositing polycrystalline Si from the beginning. Irregularities on the surface of the SOI are not preferred because they hinder lithography techniques when forming devices on the SOI, but the present invention overcomes such disadvantages.

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

1 (a) to 1 (e) are schematic sectional views for explaining an embodiment of the present invention. Plane orientation (100), (110), (11
1) A dry or wet oxidation method at a substrate temperature of 900 to 1100 ° C and a substrate temperature of 500 to 900 ° C
An SiO ₂ film 20 is formed to a thickness of 0.2 to 0.8 μm by LPCVD,
A part of the _two films was removed by ordinary photolithography and dry etching to form a seed 30 (FIG. 1A). Next, an 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. 1B).
The growth is SiH ₂ Cl ₂ (which may be SiH ₄ or Si ₂ H ₆ ) / HCl / H ₂
The test was performed at a substrate temperature of 800 to 1,050 ° C. using a mixed gas. Next, the amorphous Si240 was deposited by molecular beam deposition in ultra-high vacuum.
0.05 to 0.6 μm was deposited and patterned. For comparison, a sample in which polycrystalline Si was deposited by LPCVD instead of amorphous Si was also fabricated. After that, SiO ₂ film or
A Si ₃ N ₄ film 250 was deposited to a thickness of 0.1 to 0.5 μm, and a gas introduction window 260 was formed at a position 5 to 50 μm away from the seed by a normal dry etching technique (FIG. 1C). Next, the amorphous Si240 is removed by gas etching using HCl, and a tunnel 37 in which the upper portion is sandwiched by the SiO ₂ or Si ₃ N ₄ film 250 and the lower portion by the SiO ₂ film 20 is used.
0 was obtained (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). Obtained SO
I measured its surface roughness using SEM and STM.

As a result, when the tunnel height is 0.05 μm, the surface roughness of SOI
In contrast to 0.01 to 0.02 μm, in the case of amorphous Si, the measurement limit was 0.005 μm or less. When the tunnel height is 0.5 μm, the surface roughness is
0.05 to 0.1 μm, compared to 0.01 to 0.02 μm in the case of amorphous Si, and in any case, the reduction in surface roughness by using amorphous Si rather than using polycrystalline Si The effect was confirmed.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain a tunnel epitaxy technique capable of forming a SOI with a flat surface and a large area more than the conventional technique, and supply a substrate for forming a high-performance SiLSI. Became possible.

[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: Amorphous Si, 250: SiO ₂ or Si ₃ N ₄ film, 260: Gas introduction window , 370 …… Tunnel, 480 …… SOI area

Claims (1)

(57) [Claims] A step of forming a first SiO ₂ film on the surface of the Si substrate, a step of removing a partial region of the first SiO ₂ film to expose the Si substrate, and a step of exposing the Si substrate to a region where the Si substrate is exposed. A step of forming a seed so that the height of the growth surface and the surface of the SiO ₂ film are substantially the same by epitaxially growing Si, a step of depositing and patterning amorphous Si, and a step of forming a Si ₃ N ₄ film or Second SiO ₂
Depositing a film, removing a part of the Si ₃ N ₄ film or the second SiO ₂ film to form a window, and removing HC from the window.
l A process to remove amorphous Si by introducing gas and
Introducing a growth gas containing Si and growing epitaxial Si on the first SiO ₂ film from the seed.