JPH09307084A - Method for forming semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an etch back method and to provide a forming method of an SOI substrate having a thin film SOI layer whose film thickness is uniform and which does not have a crystalline defect. SOLUTION: A device substrate 10 where a monocrystalline silicon film 3 is epitaxy-gown in a state where a thin silicon oxide film 2 exists on the surface of a monocrystalline silicon substrate 1 is adhered to a support substrate 11 constituted of a substrate 5 having a silicon oxide film 4 on the surface with the epitaxial growth film 3 as a junction face. The device substrate 10 is removed from a monocrystalline silicon substrate 1 side until it reaches the thin silicon oxide film 2. Then, an SOI substrate where the epitaxial grown film 3 is left on the supporting substrate 11 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate used for manufacturing a semiconductor device, and more particularly to an SOI (Semicondu) having a single crystal silicon layer on an insulating film.
The present invention relates to a method for forming a semiconductor substrate having a center on insulator structure.

[0002]

2. Description of the Related Art A conventional SOI substrate has a silicon oxide film 2 on the surface of a supporting substrate 25, as shown in a sectional view of FIG.
4 is formed, and the SOI layer 23 made of single crystal silicon is formed on the silicon oxide film 24. When a low power consumption, high speed CMOS device is constructed using such an SOI substrate, the SOI layer 23 has a thickness of 0.01 to
A thin film of 0.03 μm is required. As a method of manufacturing an SOI substrate having such a thin SOI layer, “S bonding method” and “S method using oxygen ion implantation method” have been conventionally used.
IMOX (Separation by example)
"Ted oxygen) method" has been proposed.

In the bonding method, a single crystal silicon plate is integrally bonded to a supporting substrate, and the surface of the single crystal silicon is polished thereon to control the film thickness of the SOI layer. However, this bonding method is not suitable for manufacturing an SOI substrate for a CMOS having a thin SOI layer because the in-plane film thickness uniformity of polishing by a normal polishing method is ± 0.3 μm. When polishing is performed by etching using plasma called pace processing, the film thickness accuracy can be increased to ± 0.01 μm, but the uniformity is still insufficient for the SOI layer 7 having a thickness of 0.1 μm or less. On the other hand, the SIMOX method controls the depth position of the silicon oxide film by changing the implantation energy of oxygen implanted from the surface of the single crystal silicon substrate, and controls the film thickness of the SOI layer thereabove. Since this method uses ion implantation, a thin SOI
The SOI substrate of the layer can be formed with good film thickness uniformity. However, the SOI substrate formed by the SIMOX method has a crystal defect of 10 ³ cm ^{-2 in} the SOI layer and a pinhole of 10 cm ^{-2 in} the silicon oxide film. For this reason,
The characteristics and performance of the element formed in the SOI layer are likely to deteriorate.

As described above, the conventional bonding method,
The SIMOX method has advantages and disadvantages, has no crystal defects, and it is difficult to form an SOI substrate having a thin SOI layer of about 0.1 μm. In order to solve this, several improved methods of bonding called an etching back method have been reported. As shown in FIG. 5, the etching back method is a device substrate in which silicon to be an SOI layer 23 is epitaxially grown on an etching layer 22 formed on a single crystal silicon substrate 21 as shown in (a). Form 30. Also, the substrate 2
Support substrate 3 having silicon oxide film 24 formed on the surface of substrate 5
1 and then the SOI layer 2 as described in (b) above.
3 and the silicon oxide film 24 so as to face each other.
Stick 1 together. Then, as in (c), the single crystal silicon substrate 21 is ground from the back surface of the device substrate 30 to expose the etching layer 22. Further, as shown in (d), the etching layer 22 is etched using the SOI layer 23 as a stopper layer under the condition that the etching ratio between the etching layer 22 and the SOI layer 23 is large. As a result, the remaining SOI layer 23 is formed as a thin film SOI layer having good film thickness uniformity.

In such an etching back method,
A method using a SiGe film for the etching layer 22 (D. FEIJOO et al., Journal of Electronic Materials Vol.
6, 1994) or a method using a silicon layer heavily doped with B (Cynthia A Desmond).
Et al., Journal of Electrochemical Society, Vol. 141, No. 1,178-184,1
994) etc. have been reported. In addition, Yonehara et al. Suppress the film thickness variation within the substrate surface within ± 0.003 μm by a bonding method using porous silicon as the etching layer 22 even if the SOI layer is as thin as 0.1 μm. (Nikkei Microdevice, October 1994 issue). In this method, porous silicon is formed on the device substrate 30 by anodic oxidation, and silicon is epitaxially grown on the porous silicon.

[0006]

However, in the former technique using a SiGe film as an etching layer, a high-temperature treatment of about 1000 ° C. is performed for bonding, and therefore a misfit dislocation occurs when the SiGe film is used. However, there is a problem that defects occur in the SOI layer, or when high-concentration B doping is used, B diffusion occurs in addition to the occurrence of misfit dislocations, and the SOI layer also becomes a B doping layer. Also, in the latter technique using porous silicon for the etching layer,
Since defects are generated during epitaxial growth on porous silicon, 2 × 10 ³ cm ^-2 defects are SOI.
The problem of being in layers remains. As described above, in the etching back method as well, it is difficult to form a thin film SOI layer having a good film thickness uniformity and a crystal defect of about 0.1 μm.

An object of the present invention is to improve the above-mentioned etching back method and to provide a thin film SOI having a uniform film thickness and no crystal defects.
A method for forming an SOI substrate having a layer is provided.

[0008]

According to the present invention, a device substrate in which single crystal silicon is epitaxially grown in the state where a thin silicon oxide film is present on the surface of a single crystal silicon substrate, and a support substrate are formed by using the epitaxial growth film as a bonding surface. The method is characterized by including the steps of bonding and removing the device substrate until the thin silicon oxide film is reached. For example, the device substrate exposes the surface of the single crystal silicon substrate and then epitaxially grows at a low temperature by the UHV-CVD method to form an epitaxial film of single crystal silicon. Alternatively, the device substrate is LPC
Epitaxial growth is performed at a high temperature by the VD method to form an epitaxial film of single crystal silicon.

Further, when removing the device substrate, the device substrate is ground from the single crystal silicon substrate side to leave the single crystal silicon substrate thin, and thereafter, the single crystal silicon substrate is etched and removed by hydrazine until a thin silicon oxide film is reached. . Alternatively, the device substrate is ground from the single crystal silicon substrate side to leave the single crystal silicon substrate thin, and then polished with an aqueous amine solution until a thin silicon oxide film is reached.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a forming process according to an embodiment of the present invention. First, as shown in FIG. 1A, a thin silicon oxide film 2 is formed on the surface of a single crystal silicon substrate 1, and a silicon epitaxial film 3 is grown on the surface of this silicon oxide film 2 to manufacture a device substrate 10. To do.
On the other hand, on the other hand, the support substrate 11 made of an arbitrary substrate 5 having the silicon oxide film 4 on the surface is formed. Then, as shown in FIG. 4B, the epitaxial film 3 and the silicon oxide film 4 are opposed to each other, and the substrates 10 and 11 are bonded together.

Next, as shown in FIG. 3C, the device substrate 10 is polished from the back surface side so that the single crystal silicon substrate 1 is left to have a thinness of about several μm.
As described above, the single crystal silicon 1 is removed by etching using the silicon oxide film 4 as a stopper under the condition that the etching ratio of silicon and the silicon oxide film is large. As a result, the thin epitaxial film 3 having the silicon oxide film 2 on its surface is formed.
Is formed as an SOI layer.

In this forming method, since the thin silicon oxide film 2 of the device substrate 10 is a thin film, there are pinholes, and the surface is covered with the thin silicon oxide film 2 having the pinholes. By selectively growing silicon on the single crystal silicon substrate 1, crystal growth occurs only from the pinholes, and the silicon epitaxial growth film 3 is formed on the thin silicon oxide film 2. This epitaxial film 3 is a single crystal silicon substrate 1
Since it is grown from, it is defect-free. The device substrate 10 thus formed is bonded to the support substrate 11 and polished and etched from the back surface. By using a liquid having a high selection ratio between the silicon oxide film and the silicon film, the silicon oxide film is formed. It is possible to stop the etching of the single crystal silicon substrate 1 at 2. For example, with hydrazine, the selectivity ratio between silicon and silicon oxide film is 500: 1.
Therefore, even if the silicon oxide film thickness is 0.0015 μm, the surface roughness of silicon ± 0.01 μm can be flattened. At that time, the film thickness uniformity of the 0.1 μm SOI layer is ± 0.
003 μm, which can be improved from the conventional ± 0.01 μm. The SOI substrate formed in this manner can form elements similarly to the conventional SOI substrates,
At this time, if the thin silicon oxide film left on the surface is unnecessary, it may be removed by etching.

[0013]

【Example】

(First Embodiment) Referring to FIG. 1, first, a single crystal silicon substrate 1 to be a device substrate was immersed in an HF aqueous solution to remove a silicon oxide film on the substrate. After that, the ultimate vacuum degree is 1 × 10 ⁻⁹ or less, and UHV-CVD (Ultra high
h vaccum chemical vapor de
The epitaxial film 3 was grown on the single crystal silicon substrate under the selective growth condition using a positioner. here,
Disilane (Si ₂ H ₆ ) at growth pressure of 1 × 10 ^-4 Torr
0.01 μm was grown using only The high temperature treatment before the growth was not performed, and the growth was performed at a low temperature of 640 ° C.

As described above, there is no step of forming the thin silicon oxide film 2 on the surface of the single crystal silicon substrate 1 in particular, but the thin silicon oxide film 2 is automatically formed during the above steps. Will be formed. That is, FIG. 2 shows the relationship between the growth temperature and the amount of oxygen existing at the interface between the epitaxial film and the single crystal silicon substrate in the growth of the present UHV-CVD apparatus. In this case, 2 × 1
O ¹⁴ cm ⁻² oxygen is present at the interface. By observing the cross section of the transmission electron beam at this interface, as shown in FIG. 3, the interface between the single crystal silicon substrate 1 and the epitaxial film 3 is 0.00
It was confirmed that a 15 μm natural oxide film (thin silicon oxide film) 2 was present. Furthermore, it was also confirmed that the natural oxide film 2 has pinholes having a size on the order of several atoms, and epitaxial growth was carried out between the pinholes, so that the epitaxial film 3 had no defects. The film thickness uniformity of the epitaxial film 3 is ± 0.003 μm.

The device substrate 10 formed as described above
1 was bonded to a support substrate 11 made of a substrate 5 having a silicon oxide film 4 as shown in FIG. 1C, and the single crystal silicon substrate 1 was ground from the back surface to a thickness of 1 μm.
The surface level difference after grinding is ± 0.3 μm. Next, grinding was performed by a method using plasma called pace processing, and the surface step was ± 0.01 μm, and the single crystal silicon substrate 1 was thinly cut to 0.05 μm. After that, the single crystal silicon substrate 1 was further etched by etching using hydrazine to form a thin film. Since the etching selectivity of hydrazine between silicon and silicon oxide film is 500: 1 or more, it is ± 0.0 with a natural oxide film 2 of 0.0015 μm.
It is possible to sufficiently flatten the unevenness of 1 μm. Since hydrazine has a small number of atoms, it passes through some pinholes in the natural oxide film 2, but since the etching is performed after thinning the single crystal silicon substrate 1 to 0.05 μm, the etching time can be shortened. Can be suppressed. After the selective etching, light polishing was performed to eliminate the surface step.
In this way, as shown in FIG. 3, the SOI substrate having the SOI layer composed of the epitaxial film 3 could be formed. As a result, the uniformity of the SOI layer of ± 0.003 μm was realized.

(Second Embodiment) In the second embodiment, formation of the epitaxial film 2 is performed by LPCVD (Low pressure).
re chemical vapor deposit
Ion). Also in this embodiment, the single crystal silicon substrate 1 was immersed in an HF aqueous solution before growth to remove the silicon oxide film on the substrate. After that, the epitaxial film 3 is grown under the selective growth condition, but here, the high temperature treatment before the growth is not performed, and the growth condition is 750 ° C., the pressure is 10 Torr, and dichlorosilane (SiH ₂ Cl ₂ ) is hydrogen-reduced to 0.01 μm.
m. Hydrogen chloride (HCl) was simultaneously introduced in order to obtain further selectivity.

In the second embodiment, the reaching pressure is 1 To.
Since rr is high, oxygen is present at the interface between the epitaxial film 3 and the single crystal silicon substrate 1 even at 750 ° C., unlike the case of UHV-CVD of the first embodiment. The observation of the cross section of the transmitted electron beam also confirmed that the natural oxide film 2 having 0.0015 μm pinholes was present at the interface between the single crystal silicon substrate 1 and the epitaxial film 3 as in the first embodiment. . No defect was present in the epitaxial film 3 grown from between the pinholes. Also in this embodiment, the film thickness uniformity of the epitaxial film 3 is ± 0.003.
μm.

The device substrate 10 thus formed is bonded to the support substrate 11 and thinned to form an SOI layer. Also in this case, the single crystal silicon substrate 1 was roughly ground from the back surface to a thickness of 1 μm, and then the single crystal silicon substrate 1 was thinly cut to 0.1 μm by pace processing. The surface step at that time is ± 0.01 μm. After that, silicon was thinned by polishing with an aqueous amine solution. The etching selectivity between amine silicon and silicon oxide film is 5
Since it is 0: 1 or more, it is possible to flatten the unevenness of ± 0.01 μm with the native oxide film 3 of 0.0015 μm. As described above, by using the secondary amine having a large molecule as the amine, etching could be stopped by the natural oxide film 3 without passing through the pinholes of the natural oxide film 3 at the atomic level. As a result, the SOI layer having the film thickness uniformity of ± 0.003 μm made of the epitaxial film 3 was realized.

[0019]

As described above, the present invention uses a device substrate in which single crystal silicon is epitaxially grown in the state where a thin silicon oxide film is present on the surface of the single crystal silicon substrate, and this is bonded to a support substrate, and The device substrate is removed until reaching the thin silicon oxide film, and SOI is removed.
Since the substrate is formed, the film thickness uniformity is ± 0.01 μm to ± 0.003 μm compared with the conventional bonding method.
It can be more than doubled. In addition, SIMOX method and an improved bonding method using porous silicon are 2 × 10.
Nearly defect-free SOI for a crystal defect density of ³ cm ^-2
Layers can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method for forming an SOI substrate of the present invention in the order of steps.

FIG. 2 is a graph showing the relationship between the growth temperature in UHV-CVD and the amount of interfacial oxygen between the substrate and the epitaxial film.

FIG. 3 is a cross-sectional view of a device substrate used in the present invention.

FIG. 4 is a cross-sectional view of an SOI substrate.

FIG. 5 is a cross-sectional view showing a method of manufacturing a conventional SOI substrate in the order of steps.

[Explanation of symbols]

 1 Single crystal silicon substrate 2 Natural oxide film (silicon oxide film) 3 Epitaxial film 4 Silicon oxide film 5 Substrate 10 Device substrate 11 Support substrate

Claims (5)

[Claims] 1. A method for forming a semiconductor substrate (hereinafter referred to as an SOI substrate) having a single crystal silicon film on an insulating film, wherein the single crystal is formed in the state where a thin silicon oxide film is present on the surface of the single crystal silicon substrate. A method for forming a semiconductor substrate, which comprises a step of bonding a device substrate on which silicon is epitaxially grown and a support substrate with the epitaxial growth film as a bonding surface, and removing the device substrate until the thin silicon oxide film is reached. . 2. The method for forming a semiconductor substrate according to claim 1, wherein the device substrate exposes the surface of the single crystal silicon substrate and then epitaxially grows at a low temperature by a UHV-CVD method to form an epitaxial film of single crystal silicon. 3. The method for forming a semiconductor substrate according to claim 1, wherein the device substrate is epitaxially grown at a high temperature by an LPCVD method to form an epitaxial film of single crystal silicon. 4. The device substrate according to claim 1, wherein the device substrate is ground from the single crystal silicon substrate side to leave the single crystal silicon substrate thin, and thereafter, etching is performed using hydrazine until the thin silicon oxide film is reached. And a method for forming the semiconductor substrate. 5. The device substrate according to claim 1, wherein the device substrate is ground from the side of the single crystal silicon substrate to leave the single crystal silicon substrate thin, and then polished with an aqueous amine solution until a thin silicon oxide film is reached. Method for forming semiconductor substrate.