JPH0773096B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] In order to improve the quality of recrystallization of silicon by adopting the zone melting method of silicon for the fabrication of SOI, mechanochemical polishing is performed when exposing a part of the silicon substrate. Use the method.

[Industrial application field]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a large number of SOI (Semiconductor On Insulator) elements on a substrate having unevenness by a zone melting method.

[Conventional technology]

Explaining the method of forming the SOI device using the zone melting method,
First, rectangular recesses are formed in a lattice pattern on the surface of a silicon substrate. Next, the uneven surface of the silicon substrate thus formed is oxidized to form a SiO ₂ film. After the silicon is deposited on the SiO ₂ film by the CDV method, the cap layer is formed for the purpose of preventing deformation during melting of the silicon deposited on the SiO ₂ film by the SiO ₂ / Si ₃ N ₄ film, etc. and preventing various contaminations. Form.
Then, the silicon on the SiO ₂ film is melted in a band shape by a lamp, a carbon heater or the like, and recrystallized. After that, when the cap layer and the recrystallized silicon layer are removed to a height where the top surface of the convex portion of the silicon substrate or the SiO ₂ film on the silicon substrate is exposed, the recrystallized silicon region is formed in the concave portion of the silicon substrate.
It is formed by being separated by the SiO ₂ film. An SOI device can be formed by using the separated recrystallized silicon region as an active region.

[Problems to be solved by the invention]

In the melt recrystallization method of silicon by the zone melting method,
Since the silicon formed on the SiO ₂ film by the CVD method is inevitably polycrystalline and a single crystal is not formed, the quality of the recrystallized layer is inferior when melted and recrystallized.

Therefore, the surface of the recess of the silicon substrate is made of Si for element isolation.
Since O ₂ is required, the SiO ₂ film on the convex surface of the silicon substrate is selectively removed, silicon is epitaxially grown on the exposed convex portion of the silicon substrate, and this epitaxially grown silicon region is used as a nucleus for recrystallization. Therefore, the quality of the recrystallized silicon can be improved. However, when a photolithographic method using a resist was adopted to selectively remove the SiO ₂ film on the convex portion of the silicon substrate, a problem occurred. That is, if the concave portion of the substrate is deep, the resist is not uniformly applied, and the adhesiveness of the resist on the shoulder portion of the unevenness is not good.
When etching SiO _2, pinholes were seen often occur until the SiO ₂ film on the bottom or side of the concave portion of the substrate is removed. Also on the convex part of the substrate, Si
Since a step due to the SiO ₂ film is generated in the boundary region where O ₂ is etched, a crystal defect may occur in the step portion during melting and recrystallization. Similarly, since the shoulder of SiO ₂ on the convex portion of the substrate is not smooth, there is a problem that a crystal defect is generated also in this portion during melting and recrystallization.

[Means and Actions for Solving Problems]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides mechanochemical polishing of an SiO ₂ film on a convex portion of a silicon substrate, generally an insulating film on the convex portion in order to selectively remove the insulating film. Do. According to this mechanochemical polishing, the problem of resist unevenness is essentially nonexistent, and the polishing marks on the convex portions of the substrate are also essentially flat, so that the exposed silicon substrate and the insulating surface that remains unpolished remain. There is no step at the boundary of the film. Furthermore, according to mechanochemical polishing,
The shoulder of the insulating film on the convex part of the substrate is also rounded and rounded,
It becomes smooth. Thus, according to the mechanochemical polishing, it is possible to prevent pinholes from being generated on the bottom and side surfaces of the concave portion of the substrate, or to prevent crystal defects from being generated in the melted / recrystallized silicon. Is obtained.

Here, the mechanochemical polishing method is a polishing method that is performed with a flexible brush (buff) having a long bristle using an alkaline solution of silica having a particle size of 10Å and is well known as a polishing method that does not cause defects in silicon. It is a technology. A relatively flexible synthetic resin plate may be used instead of the brush. The present invention takes advantage of the characteristics of the mechanochemical polishing method due to the polishing and the action on the uneven surface by the flexible brush with long hair.

〔Example〕

An example of using a SiO ₂ film as the insulating film will be described.

Referring to FIG. 1, the silicon substrate 1 (plane orientation: (10
0)) is thermally oxidized to form a SiO ₂ film 2 having a thickness of about 3000Å on the surface.

Referring to FIG. 2, a rectangular opening pattern 3 is formed in a lattice pattern on the SiO ₂ film 2 by photolithography.
Each side of the rectangular pattern 3 is perpendicular or parallel to the <110> direction of the silicon substrate 1, and the size of one side is, for example, 500 μm.
m.

Referring to FIG. 3, the silicon substrate 1 is selectively etched with a KOH solution at 80 ° C. using the SiO ₂ film 2 left in a lattice shape as a mask to form the recesses 4 having a depth of about 30 to 40 μm.

Referring to FIG. 4, after removing the SiO ₂ film 2, a SiO ₂ film 5 having a thickness of 1 to ₂ μm is formed on the front surface by thermal oxidation. At this time,
If necessary, it can be further by a CVD method or the like SiO _2, Si ₃ N4 is deposited thereon to improve the withstand voltage.

Referring to FIG. 5, the SiO ₂ film 5 on the convex portion of the silicon substrate 1 is selectively removed by mechanochemical polishing. The mechanochemical polishing is carried out, for example, using TIZO × 1300 [trade name of abrasive] in an apparatus conventionally used for mirror polishing of silicon wafers. According to this mechanochemical polishing, the shoulder portion of the SiO ₂ film 5 is sagging and has a rounded shape, and no step is formed at the boundary between the removed portion of the SiO ₂ film 5 and the exposed portion of the silicon substrate 1. Moreover, no pinhole is generated in the SiO ₂ film 5 in the recess.

Referring to FIG. 6, a silicon layer 6 having a thickness of about ₃ to 20 μm is deposited on the entire surface by the CVD method, and Si ₃ N 4 is deposited on the surface after the oxidation by the CVD method to deposit SiO ₂ / Si ₃ N 4 having a thickness of about 2 μm. A cap layer 7 made of is formed. At this time, since the SiO ₂ film 5 does not exist on the convex portion of the silicon substrate 1, the silicon layer 6 is epitaxially grown on the silicon substrate 1 to form the single crystal region 8.

After the cap layer 7 is formed, the silicon layer 6 is melted into a band shape by a rod-shaped heating source such as a lamp, a carbon heater, a tungsten heater, etc., and recrystallized. Then, since the single crystal silicon region 8 on the convex portion of the silicon substrate 1 exists, recrystallization proceeds from there, and the quality of the recrystallized silicon is improved as a whole. Further, since the polishing marks on the convex portion of the silicon substrate 1 are flat and the SiO ₂ film 5 on the shoulder portion has a gentle roundness, crystal defects are generated in the recrystallized silicon due to these portions. There is nothing to do.

Then, if deep silicon regions are needed, cap layer 7
After removing, the silicon is epitaxially grown by the CVD method to fill the recess.

Referring to FIG. 7, when the portion above the top surface of the convex portion of the silicon substrate 1 is removed by mechanochemical polishing, the recrystallized silicon region (island) separated by the SiO ₂ film 5 is formed in the concave portion of the silicon substrate 1. Region 9) is formed, and it is possible to fabricate a semiconductor device using this region as an active region.

In the above embodiment, a single recrystallized silicon region is formed in the recess of the silicon substrate. For example, in FIG. 6, the silicon to be deposited is doped with an n ^{+ type} dopant, and the n ^{+ type} silicon to be deposited is deposited. The layer thickness is made thin with respect to the depth of the recess, then melting and recrystallization is performed, the cap layer is removed, and then the n ⁻ -type silicon layer is epitaxially grown on the exposed n ^{+ -type} recrystallized silicon layer. Then, it is also possible to form the n ^{+ -type} buried layer and the n ⁻ -type epitaxial growth layer in the recess of the silicon substrate by planarizing the top surface to the height of the protrusion of the silicon substrate. This n ^{+ type} buried layer is simply
n ^- well are embedded under type layer, has the advantage of its ends extends to the surface is easily joined with the external electrodes.

〔The invention's effect〕

According to the present invention, in forming a molten / recrystallized region of silicon through an insulating film in a recess of a silicon substrate,
The quality of the recrystallized silicon is improved by using the silicon region epitaxially grown on the convex portion of the silicon substrate as the nucleus for recrystallization, and the occurrence of the step due to the removal of the insulating film on the convex portion of the silicon substrate is eliminated. By smoothing the insulating film on the shoulder of the convex part of the substrate, it is possible to prevent crystal defects from occurring in recrystallized silicon and prevent pinholes in the insulating film from degrading the withstand voltage. can do.

[Brief description of drawings]

1 to 7 are sectional views for explaining a series of steps for carrying out the method of the present invention. 1 ... silicon substrate, 2 ... SiO ₂ film, 3 ... opening, 4
...... Concave part, 5 …… SiO ₂ film, 6 …… Silicon layer, 7 …… Cap layer, 8 …… Epitaxial growth silicon region, 9
...... Recrystallized silicon area.

Claims (1)

[Claims] 1. A plurality of recesses are formed on a silicon substrate, an insulating film is formed on the uneven surface of the silicon substrate thus formed, a silicon layer is deposited on the insulating film, and the silicon deposition is performed. In a method of manufacturing a semiconductor device including a step of forming a cap layer thereon and then heating to melt and recrystallize silicon in the silicon deposition layer, a mechanochemical method is used prior to the silicon layer deposition step. In this way, the insulating film on the convex portion of the silicon substrate is selectively removed to expose the top surface of the convex portion of the silicon substrate, and the exposed silicon substrate and the insulation remaining on the side wall of the convex portion. The method is characterized in that the boundary region with the film is kept flat, and the shoulder portion of the surface of the insulating film remaining on the side wall of the convex portion different from the surface in contact with the convex portion is rounded.