SOI substrate and semiconductor device

Details SOI substrate and semiconductor device SOI substrate and semiconductor device

2001-10-15

2002-10-15

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Forming bipolar transistor by formation or alteration of...

On insulating substrate or layer

C438S933000

Reexamination Certificate

active

06465316

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a silicon substrate (referred to as an SOI (silicon on insulator) substrate throughout the specification) comprising a buried silicon oxide layer immediately under a silicon thin film serving as an active layer.
2. Description of the Background Art
When forming a device on the SOI substrate having the buried silicon oxide layer therein as described above, it is possible to reliably isolate the device with respect to the substrate. Therefore, a leakage current between elements is reduced and a device having excellent drivability (driving current, response speed etc.) can be formed. Further, an element isolation region such as a trench may not be deeply formed and can be inhibited from transverse spreading, to attain further refinement. Hence, the SOI substrate is applied to a high-frequency device used in the GHz band, a high-speed microprocessor or a low power consumption element, for example.
Such an SOI substrate can be manufactured by various methods such as an SOS (silicon on sapphire) method or an SIMOX (separation by implanted oxygen) method. Attention is now drawn to a bonding method for manufacturing an SOI substrate by bonding a bond wafer having a buried silicon oxide layer part and a base wafer serving, as a support substrate to each other.
A conventional method of manufacturing an SOI substrate employing the bonding method is described with reference to FIG.
26
. First, a bond wafer
1
consisting of a single crystal of silicon is dipped in an ionization solution. An electric field is applied between the bond wafer
1
and the ionization solution for ionizing silicon atoms present on the main surfaces of the bond wafer
1
and dissolving the same in the ionization solution (performing the so-called anodization). At this time, dissolution heterogeneously progresses on one of the main surfaces of the bond wafer
1
and a porous silicon layer (a silicon layer having numerous small grooves or depressions distributed in the crystal)
15
is formed on this main surface.
Then, a silicon single-crystalline layer
4
is formed on a surface of the porous silicon layer
15
by epitaxy. The overall surface of the bond wafer
1
is oxidized for forming a silicon oxide layer
5
. Then, a base wafer
2
consisting of a single crystal of silicon is bonded to the main surface of the bond wafer
1
formed with the porous silicon layer
15
. The bond wafer
1
and the base wafer
2
bonded to each other are heated to a temperature of at least 900° C., for example, for reinforcing the degree of adhesion therebetween.
The bond wafer
1
is removed by polishing the main surface opposite from that formed with the porous silicon layer
15
serving as a stopper, and thereafter the porous silicon layer
15
is removed by dipping the base wafer
2
, which is in close contact with the multilayer structure of the porous silicon layer
15
, the silicon single-crystalline layer
4
and the silicon oxide layer
5
, in a mixed solution of a hydrofluoric acid solution and aqueous hydrogen peroxide.
Thus, an SOI substrate having the silicon oxide layer
5
as a buried silicon oxide layer is obtained.
As hereinabove described, the porous silicon layer
15
is employed as a stopper when removing the bond wafer
1
in the conventional bonding method. This is because the porous silicon layer
15
has selectivity for single-crystalline silicon in polishing due to the coarse crystal state thereof.
However, the crystal state of the porous silicon layer
15
is disadvantageously irregular. When formed on the surface of the porous silicon layer
15
, therefore, the silicon single-crystalline layer
4
readily causes crystal defects. Such crystal defects in the silicon single-crystalline layer
4
may influence the crystal state of the silicon oxide layer
5
formed subsequently to the silicon single-crystalline layer
4
, to generate a leakage current between the elements again.
Further, the porous silicon layer
15
merely serving as a stopper must be removed after the bonding step. The porous silicon layer
15
cannot be employed as a layer (hereinafter referred to as a device forming layer) for forming the device on the surface of the SOI substrate due to the inferior crystal state thereof. However, this is inefficient in consideration of effective use of the raw material.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a method of manufacturing an SOI substrate comprises steps (a) to (f) of (a) forming a silicon germanium single-crystalline layer on a main surface of a bond wafer consisting of a single crystal of silicon, (b) forming a silicon single-crystalline layer on a surface of the silicon germanium single-crystalline layer, (c) oxidizing a surface of the silicon single-crystalline layer, (d) bonding a base wafer consisting of a single crystal of silicon to the oxidized surface of the silicon single-crystalline layer, (e) heating the bond wafer and the base wafer for reinforcing the degree of adhesion therebetween, and (f) removing the bond wafer.
In the method of manufacturing an SOI substrate according to the first aspect, the silicon germanium single-crystalline layer exhibiting small irregularity in its crystal state and having selectivity for the single crystal of silicon forming the bond wafer hardly causes crystal defects in the silicon single-crystalline layer and reliably enables removal of the bond wafer. Further, the silicon germanium single-crystalline layer can be employed as a device forming layer on the SOI substrate.
According to a second aspect of the present invention, the method of manufacturing an SOI substrate according to the first aspect further comprises a step (g) of reducing the thickness of the silicon germanium single-crystalline layer to a prescribed value subsequently to the step (f).
In the method of manufacturing an SOI substrate according to the second aspect, the thickness of the silicon germanium single-crystalline layer can be set to a level suitable for serving as a device forming layer. Alternatively, the silicon germanium single-crystalline layer can be completely removed for manufacturing a general SOI substrate comprising only a buried silicon oxide layer and a silicon layer on the base wafer.
According to a third aspect of the present invention, a part of the bond wafer in contact with the silicon germanium single-crystalline layer is removed by chemical mechanical polishing or wet etching in the step (f), and the silicon germanium single-crystalline layer is removed by wet etching in the step (g).
In the method of manufacturing an SOI substrate according to the third aspect, not plasma etching but chemical mechanical polishing or wet etching is employed for finishing removal of the bond wafer, whereby the silicon germanium single-crystalline layer has a small possibility of causing crystal defects. Further, the silicon germanium single-crystalline layer is removed by wet etching, whereby the silicon germanium single-crystalline layer and the silicon single-crystalline layer have a small possibility of causing crystal defects.
According to a fourth aspect of the present invention, the method of manufacturing an SOI substrate according to the first aspect further comprises steps (h), (k) and (i) of (h) forming a mask layer on the silicon-germanium single-crystalline layer after the step (f), (k) patterning the mask layer through photolithography, and (i) removing a part of the silicongermanium single-crystalline layer not covered with the mask layer by employing the patterned mask layer as a mask.
In the method of manufacturing an SOI substrate according to the fourth aspect of the present invention, the silicon germanium single-crystalline layer can be subjected to arbitrary patterning for serving as a device forming layer.
According to a fifth aspect of the present invention, the method of manufacturing an SOI substrate according to the fourth aspect further comprises a step O) of oxidizing the part of the silico

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