JPH01214014A - Manufacture of soi substrate - Google Patents

Abstract

PURPOSE:To prevent a silicon nitride nucleus from being stripped off without working the silicon nitride nucleus minutely and to form falt, easy-to-work and homogeneous single-crystal silicon on an insulating substrate by a method wherein a polycrystalline silicon layer and a silicon dioxide layer are laminated on a silicon nitride layer and a single-crystal silicon layer is formed inside a trench. CONSTITUTION:A silicon nitride layer 2 is formed on an insulating substrate 1; a polycrystalline silicon layer 3 is laminated on it; in addition, a silicon dioxide layer 4 is laminated on it; a trench 5 ranging from the surface of the silicon dioxide layer 4 to the silicon nitride layer 2 is formed. Then, a single-crystal silicon layer 6 is formed inside said trench 5 by a selective epitaxial growth operation by making use of the silicon nitride layer 2 as a growth nucleus. By this setup, when the selective epitaxial growth operation of silicon is executed by making use of the silicon nitride layer 2 as the growth nucleus, it is affected by a crystal lattice of the polycrystalline silicon layer 3 constituting sidewalls of the trench 5; accordingly, the growth orientation can be controlled; priority is given to the growth only in the direction perpendicular to the surface of the insulating substrate 1; as a result, a flat single-crystal silicon layer 6 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an SOI substrate in which a crystalline silicon layer is formed on an insulating substrate.

[Conventional technology]

An example of a conventional SOI substrate manufacturing method is r EXtend.
ed Abstracts of the 19th
Conference on 5otidstate
DeViCe and Materials, Tokyo
o, 1987. pp, i91~194/5 select
ive Growth of Nuclei on A
2(a) to (C) described in "Morphous 5 Substrates". In FIG. 2(a), an insulating substrate 1 made of silicon dioxide
A rectangular parallelepiped silicon nitride core 7 having a film thickness of 0.1 to 0.2 μm is formed thereon to serve as a core for later growing single crystal silicon. The area of the plane of the silicon nitride core 7 that is horizontal to the surface of the insulating base 1 is about 7 μm 2 or less. When this area becomes 16 μm2 or more, multiple silicon crystals grow around the silicon nitride core 7 and become polycrystalline, and do not become a single crystal. , a selective epitaxial growth reaction is carried out in an epitaxial reactor, and single crystal silicon grains 8 are formed around silicon nitride nuclei 7 as shown in FIG. 2(b). The single-crystal silicon grains 8 that continued to grow eventually become as shown in Figure 2 (c
), the grains collide to form crystal grain boundaries 9, forming an uneven silicon layer on the insulating substrate. Furthermore, when a semiconductor device is formed using this uneven silicon layer, it is necessary to polish the surface to make it flat and easy to process.

[Problem to be solved by the invention]

However, in the conventional technology, it is necessary to pattern the area of the surface of the silicon nitride core horizontal to the surface of the insulating substrate to about 7 μm2 or less, and due to the small size, the surface in close contact with the insulating substrate 1 may peel off. The silicon nitride core 7 was often lost.

Furthermore, since silicon begins to grow equidistantly from the silicon nitride core 7, large irregularities occur on the final silicon surface. This had the problem of requiring a machining process to make it flat. Furthermore, since the silicon nitride nucleus, which is the center of growth, and the growing single-crystal silicon grain 8 have different compositions and crystal lattice constants, it is not possible to control the orientation of the growth plane of the growing single-crystal silicon grain 8. However, there was also the problem that growth proceeded in various directions simultaneously, making it impossible to obtain homogeneous silicon crystal grains.

Therefore, the method for manufacturing an SOI substrate of the present invention eliminates the peeling of silicon nitride nuclei without performing fine processing of silicon nitride nuclei, and forms homogeneous single crystal silicon that is flat and easy to process on an insulating substrate. The purpose is to provide a manufacturing method that

[Means to solve the problem]

The method for manufacturing an SOI substrate of the present invention includes forming a silicon nitride layer on an insulating substrate, laminating a polycrystalline silicon layer on the silicon nitride layer, and laminating a silicon dioxide layer on the polycrystalline silicon layer. A trench is formed from the surface of the silicon dioxide layer to the silicon nitride layer, and a single crystal silicon layer is formed in the trench by selective epitaxial growth using the silicon nitride layer as a growth nucleus.

〔Example〕

Embodiments of the method for manufacturing an SOI substrate of the present invention will be described below with reference to the drawings.

In FIG. 1(a), a film of silicon nitride N2 is formed on an insulating substrate 1. In FIG. The silicon nitride layer 2 may be formed by either a normal chemical vapor phase reaction under reduced pressure or a chemical vapor phase reaction using plasma. As the gas, a mixed gas of silane gas and ammonia is reacted at a temperature of 600° C. or higher.

Next, in FIG. 1(b), polycrystalline silicon 3 is formed to a thickness of 5 μm to 0.5 μm on the silicon nitride layer thus formed.

After laminating the polycrystalline silicon layer 3, a silicon dioxide layer 4 is laminated as shown in FIG. There is a method of thermally oxidizing the surface, or a method of forming a film using a mixed gas of silane and oxygen through a chemical vapor phase reaction.

Next, as shown in FIG. 1(d), a trench 5 extending from the surface of the silicon dioxide layer 4 to the silicon nitride layer 2 is formed using an anisotropic drama etching technique using RIE. Since the polycrystalline silicon layer 3 and the silicon nitride layer 2 exposed at the bottom of the trench 5 have different compositions, even if etching is continued after the silicon nitride layer 2 is not exposed at the bottom of the trench 5, the exposed silicon nitride layer 2. Etching does not progress to the inside of trench 5, and etching has high selectivity to silicon nitride. Therefore, the setting range of the etching time is wide, and even if the etching time exceeds the standard, it will have no effect on the shape of trench 5. There are almost no

After the trench 5 is formed, as shown in FIG. 1(e), silicon is selectively epitaxially grown using the silicon nitride layer 2 as a growth nucleus so as to fill the trench 5. During this epitaxial growth, the side walls of the trench 5 are It is possible to control the growth direction because it is influenced by the crystal lattice of the polycrystalline silicon layer 3 constituting the insulating substrate 1, and the growth direction is prioritized only in the direction perpendicular to the surface of the insulating substrate 1. Unlike isotropic crystal growth, a flat single crystal silicon layer 6 is formed.

〔Effect of the invention〕

As is clear from the above examples, according to the method for manufacturing a Sol substrate according to the present invention, there is no need for the step of buttering the silicon nitride film, which serves as a crystal nucleus, into a minute shape, and peeling of the silicon nitride film also occurs. It is also possible to easily control the effective area during growth of the silicon nitride film by adjusting the size of the trench. Additionally, since the trench sidewalls are surrounded by a polycrystalline silicon layer, it is also possible to control the growth direction of the single crystal silicon that grows inside the trench, preferentially growing in the direction perpendicular to the surface of the insulating substrate. Therefore, the surface of the obtained single crystal silicon layer is flat. For this reason, unlike in the case of crystal growth that grows isotropically from a nucleus, there is no need to reprocess the obtained single crystal silicon layer to make it flat. The silicon nitride layer, which serves as a crystal growth nucleus, acts as an etching stopper, has a wide etching time margin, and has the advantage of being easy to process.

[Brief explanation of the drawing]

FIGS. 1(a) to (e) are cross-sectional views of essential parts showing an embodiment of the method for manufacturing an SOI substrate of the present invention, and FIGS. 2(a) to (c) show a conventional method for manufacturing an SOI substrate. It is a sectional view of the main part. 1... Insulating substrate 2... Silicon nitride layer 3... Polycrystalline silicon layer 4... Silicon dioxide layer 5... Trench 6... Single crystal silicon layer 7... Silicon nitride core 8 ...Single-crystal silicon grain 9...Above the grain boundary 1 Old

Claims (1)

[Claims] A silicon nitride layer is formed on an insulating substrate, a polycrystalline silicon layer is laminated on the silicon nitride layer, a silicon dioxide layer is laminated on the polycrystalline silicon layer, and the nitride layer is laminated from the surface of the silicon dioxide layer. 1. A method for manufacturing an SOI substrate, comprising forming a trench reaching a silicon layer, and forming a single crystal silicon layer in the trench by selective epitaxial growth using the silicon nitride layer as a growth nucleus.