JPH08153780A - Semiconductor substrate - Google Patents

Abstract

PURPOSE: To obtain a semiconductor substrate which has no polysilicon film, but a laminated SOI structure, and to simplify the manufacturing process of the substrate. CONSTITUTION: After a silicon oxide film 13 with steps is formed on at least one surface of an active-layer substrate A, the film 13 is polished on a rigid turntable by using an abrasive composed mainly of colloidal silica. Then a silicon wafer having an SOI structure is obtained by putting and sticking the mirror surface of a supporting substrate B on and to the polished joint surface 13a of the substrate 13. Therefore, the conventional polysilicon film which has been formed on the surface of the oxide silicon film for joint is not required. The polishing of the joint surface is performed in such a way that, after the surface of the silicon dioxide film 13 is flattened by using an abrasive composed of true-spherical colloidal silica which is manufactured by a wet colloidal method and has an average particle diameter of 70nm, steps having large level differences are removed by raising the polishing rate, and then, the film 13 is polished with colloidal silica having an average particle size of 30nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate, and more particularly to a semiconductor substrate having a thin film SOI structure.

[0002]

2. Description of the Related Art SOI (Silicon on Ins)
In a semiconductor substrate having an ululator structure, the thinner the active layer forming the element, the more the parasitic capacitance of the pn junction can be reduced and the operating speed of the element can be increased.
For this reason, ultra-thin active layers are being studied.

By the way, a bonding method is known as a method for obtaining a semiconductor substrate having a thin film SOI structure.
FIG. 3 is a cross-sectional view showing a method for manufacturing a semiconductor substrate having an SOI structure by a conventional bonding method.

In this manufacturing method, first, SiO ₂ is formed on the surface of the patterned silicon substrate 1 (active layer substrate).
A film 3 is formed (see FIG. 3A), and a polysilicon layer 4 is formed on the oxide film 3 (FIG. 3B). Next, after the surface of the polysilicon layer 4 is planarized by mechanochemical polishing (FIG. 3C), another silicon substrate 5 (support substrate) is attached to the polishing surface 4a (FIG. 3C).
(D)). Finally, the surface of the active layer substrate 1 (the surface opposite to the bonding surface) is polished until the oxide film 3 is exposed (FIG. 3E).

That is, the conventional SOI structure semiconductor substrate thus manufactured has the polysilicon layer 4 on the support substrate 5, and the oxide film 3 is formed on the polysilicon layer 4. It was The single crystal silicon layer 1 was laminated on the oxide film 3, and the single crystal silicon layer 1 was insulated and separated by the patterned oxide film 3.

[0006]

However, in such a conventional semiconductor substrate having an SOI structure, the polysilicon layer 4 is provided due to the necessity of manufacturing. This is because the polysilicon layer is polished and flattened and then laminated. Therefore, there is a problem that a wasteful process is required to form a polysilicon layer that is unnecessary for a semiconductor substrate having an SOI structure.

Therefore, the inventor has noticed that the step of forming the polysilicon layer can be omitted if the silicon oxide film formed on the surface of the silicon substrate is directly polished to obtain a satisfactory flatness. As a result of diligent research and examination of a method for polishing a silicon oxide film, it was confirmed that a polishing surface capable of satisfying the flatness required for bonding can be obtained by appropriately configuring an abrasive and a polishing method. The invention was completed.

An object of the present invention is to provide an SOI structure semiconductor substrate which can be easily manufactured by omitting the step of depositing a polysilicon film by directly laminating and bonding an oxide film. .

[0009]

According to a first aspect of the present invention, there is provided a support substrate portion made of single crystal silicon, an insulating layer made of an oxide film and covering the surface of the support substrate portion, and the insulating layer. A single crystal silicon layer covering the surface of the layer, and a semiconductor substrate in which a part of the oxide film is exposed on the surface of the single crystal silicon layer.

[0010]

According to the invention of claim 1, since a part of the oxide film forming the insulating layer is exposed to insulate the single crystal silicon layers from each other, a device can be formed in each single crystal silicon layer. . Further, the unnecessary polysilicon layer as the semiconductor substrate having the SOI structure can be eliminated, and the manufacturing thereof can be easily performed.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor substrate according to an embodiment of the present invention will be specifically described with reference to the drawings. 1A to 1D are cross-sectional views showing a manufacturing process of a silicon wafer having an SOI structure according to an embodiment. As shown in FIG. 1D, in the silicon wafer having the SOI structure, the oxide insulating film 13 is laminated on the single crystal silicon substrate portion 15, and the thin single crystal silicon layer 11 has the oxide film 13 on the oxide film 13. Thirteen
Is insulated and separated into islands. That is, the thin film S in a state where the active layer 11 is separated by the island-shaped oxide film 13.
It is a silicon wafer having an OI structure.

The silicon wafer having the thin film SOI structure is formed through the following steps. First, as shown in FIG. 1A, a semiconductor substrate 11 (active layer substrate A) made of single crystal silicon is prepared, and one surface of the substrate 11 is formed to a depth, for example, by using a photolithography technique or an etching technique. The grooves 12 having a thickness of 0.1 μm are formed at intervals of 500 μm.
This surface is thermally oxidized to form a SiO ₂ film having a thickness of 0.1 μm. Furthermore, on the SiO ₂ film formed by this thermal oxidation,
A SiO ₂ film having a thickness of 0.9 μm is formed by the CVD method. As a result, the laminated SiO ₂ film 13 of 1.0 μm
Form the surface insulating layer 13 of the active layer substrate. The oxide film 13 is formed as a surface having a step according to the surface shape of the patterned active layer substrate A.

Then, the oxide film 13 is directly polished.
For polishing the oxide film 13, for example, an abrasive containing colloidal silica as a main component is used. The solid content (NV) of the colloidal silica in the abrasive is not particularly limited, but it is preferably used in the range of 1 to 10%. Further, the pH of the polishing agent is not particularly limited, but it is advantageous to the polishing performance for the silicon oxide film if it is adjusted to be neutral around pH = 7. The abrasive used in this example removes fumed silica from each of SC112 (manufactured by Cabo) or ILD1200 (manufactured by Rodel), and colloidal silica is added to the modifier. As the colloidal silica, one produced by a wet colloidal method is used. The colloidal silica in this case is a true sphere, and its diameter is 10 nm to 100 nm. Polishing is performed in two steps. That is, first, the average particle size is 70n.
The surface of the silicon dioxide film is flattened and polished by using an abrasive of m colloidal silica. This first-stage polishing increases the polishing rate and removes large steps. After that, polishing is performed with a colloidal silica abrasive having an average particle diameter of 30 nm. It is finish polishing. As a result, the silicon dioxide film having a large step can be polished flat. Further, when the wafer thus polished was bonded to a base wafer which is a support substrate, the occurrence of voids was reduced.

In the polishing step shown in FIG. 1B, the oxide film 13 is polished by using the above-mentioned polishing agent and a rigid surface plate. Rigid surface plate is flat with little mechanical and thermal deformation.
For example, it is made of ceramic or the like. The surface of the polishing surface of this rigid surface plate may be thinly coated with the hot melt wax mixed with the above-mentioned abrasive containing cerium oxide as a main component.

In the polishing method of this embodiment, since a rigid surface plate which is not elastically deformed is used, if the polishing surface has a step as shown in FIG. 1 (a), first the convex portion pressed against the surface plate is pressed. Only the pieces are gradually polished. In this way, the step between the convex portion and the concave portion is gradually reduced, and as a result, a flat polished surface can be obtained.

FIG. 2 shows the result of polishing the silicon oxide film 13 with such an abrasive and a rigid surface plate. FIG. 2A is a chart showing the surface of the silicon oxide film 13 before polishing, which is measured by a surface roughness meter, and is about 0.1 μm.
The steps of the silicon oxide film 13 are observed. On the other hand, FIG. 2 (B) uses the abrasive and the rigid surface plate,
Under the conditions that the polishing pressure is 200 g / cm ² , the relative speed between the polishing agent and the wafer is 75 rpm, and the polishing rate is 70 nm / min, the state after polishing the silicon oxide film shown in FIG. It is a chart measured by a roughness meter.
As is clear from this result, the surface roughness of the silicon oxide film 13 sufficiently satisfies the condition of 5 nm or less necessary for bonding.

Through the above steps, the active layer substrate A, which is one of the semiconductor substrates for forming the semiconductor substrate having the SOI structure, is obtained.

The joining surface 13a in a mirror state shown in FIG. 1 (b).
Then, the mirror surface of the other semiconductor substrate 15 to be the supporting substrate B is brought into close contact with the bonding surface 13a, and the two are bonded by thermal bonding by hydrogen bond of the OH group (FIG. 1 (c)).
reference). The bonding strength is, for example, 200 kg / cm ²
As described above, it is preferable that the bonding temperature is 1100 ° C. and that the same silicon substrate as the active layer substrate 11 is used as the support substrate 15 in order to prevent the warp of the SOI substrate due to the difference in thermal expansion.

As shown in FIG. 1C, after laminating the active layer substrate A and the supporting substrate B, chamfering of the side peripheral portion is performed and the thickness of the active layer substrate 11 becomes about 2 μm. Grind in advance.

Finally, as shown in FIG. 1D, the active layer substrate A is selectively polished. In this selective polishing, for example, a ceramic surface plate having a surface roughness of 0.01 μm is rotated, 5.0 wt% of fine particles of high-purity silica having a particle size of 0.02 μm are dispersed on the surface of the surface plate, pH = 10. While dropping the alkaline solution (polishing solution) of 5, the single crystal substrate portion 11 of the active layer substrate is pressed and rubbed against the surface plate at a pressure of 100 g / cm ² .

By this selective polishing, the single crystal substrate portion 11 is formed.
Is gradually polished. When the platen reaches the oxide film 13 made of SiO ₂ , the oxide film 13 serves as a stopper for the selective polishing, and the polishing rate rapidly decreases. This is because the oxide film 13 is less likely to be mechanochemically polished than the single crystal substrate portion 11. By detecting the change in the polishing rate, the oxide film 13 as shown in FIG. 1D is exposed from the surface of the single crystal substrate portion 11, that is, the active layer 16 is exposed.
It is possible to obtain a silicon wafer having a thin film SOI structure in which the islands are separated by the island-shaped oxide film 13.

[0022]

According to the present invention, the step of forming the polysilicon film for bonding, which is required in the conventional manufacturing method, becomes unnecessary. A semiconductor substrate having an SOI structure can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing each manufacturing process of a semiconductor substrate according to an embodiment of the present invention.

FIG. 2 is a view for explaining a result of polishing an oxide film on a semiconductor substrate before laminating according to an embodiment of the present invention,
(A) shows each surface roughness before polishing, and (B) shows each surface roughness after polishing.

FIG. 3 is a cross-sectional view showing a conventional method of manufacturing a semiconductor substrate.

[Explanation of symbols]

 A active layer substrate B support substrate 11 active layer substrate side silicon substrate 13 surface layer (oxide film) 13a bonding surface 15 support substrate side silicon substrate 16 active layer

Claims (1)

[Claims] 1. A semiconductor including a supporting substrate portion made of single crystal silicon, an insulating layer made of an oxide film and covering the surface of the supporting substrate portion, and a single crystal silicon layer covering the surface of the insulating layer. A semiconductor substrate in which a part of the oxide film is exposed on the surface of the single crystal silicon layer.