JP3011741B2 - Semiconductor substrate manufacturing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor substrate used in a semiconductor integrated circuit. More specifically, the present invention relates to a method for manufacturing a semiconductor substrate. The present invention relates to a method for forming a film having both of the above, and forming a polycrystalline silicon layer thereon by depositing and solidifying molten silicon.

(Prior Art) A method of forming a film having both insulating properties and wettability with molten silicon on a surface of a semiconductor substrate, and then forming a polycrystalline silicon layer by solidifying the molten silicon on the film. For example, the present invention is applied to a method of manufacturing a dielectric isolation substrate.
Therefore, as a conventional method, a conventional method of manufacturing a dielectric isolation substrate will be described with reference to FIG. The method of manufacturing this dielectric isolation substrate is disclosed in Japanese Patent Application Laid-Open No. 2-135754.

First, as shown in FIG. 2A, a single crystal silicon substrate 1 is oxidized to form a silicon dioxide film 2 having a thickness of about 1 μm on the surface thereof.

Next, as shown in FIG. 2 (b), the silicon dioxide film 2 is partially opened by photolitho etching, and the single crystal silicon substrate 1 is anisotropically formed using the remaining silicon dioxide film 2 as a protective mask. Etching to a depth of 50
A V-shaped groove 3 of about μm is formed.

Next, as shown in FIG. 2 (c), after removing the silicon dioxide film 2, the single-crystal silicon substrate 1 is oxidized again to form an insulating film having a thickness of about 2 μm on the substrate surface including the V-shaped groove 3. Of silicon dioxide film 4 is formed.

Next, silicon oxynitride (S) having a thickness of about 0.2 μm is formed on the silicon dioxide film 4 by a known CVD method.
An iO _x N _y ) -based thin film 5 is formed from the silicon dioxide film 4 side toward the surface to be formed.
It is formed so that x increases. Here, the thin film 5 may be made of complete silicon oxide at the portion in contact with the silicon dioxide film 4 and may be made of complete silicon nitride on the surface. The silicon oxynitride thin film is obtained by thermal decomposition of a mixed gas of SiH ₄ , NH ₃ and N ₂ O, and NH ₃ / N ₂ O
By increasing the mixing ratio, the silicon oxynitride-based thin film 5 having the above-mentioned film configuration can be formed. In addition, silicon oxynitride exhibits intermediate properties between silicon dioxide and silicon nitride according to the composition ratio of oxygen and nitrogen. By adopting the above-mentioned film configuration, molten silicon can be converted into silicon oxynitride in a later step. Nitride thin film 5
When it is dropped on the surface, the film does not peel off at the interface with the silicon dioxide film 4 for insulation separation because of the same thermal expansion coefficient as the silicon dioxide, and the surface has the same wettability to molten silicon as silicon nitride. Thereby, the filling of the molten silicon into the V-shaped groove 3 is ensured.

Next, molten silicon at a temperature of about 1440 ° C.
The silicon substrate 1 is kept at 00 ° C. and supplied onto the thin film 5 by dripping or spraying from a nozzle, spread over the entire surface, and further cooled to form a 550 μm thick film on the silicon oxynitride-based thin film 5. Polycrystalline silicon layer 6
To adhere.

During the solidification of the molten silicon, the (100) plane preferentially grows from the substrate surface due to the fact that the temperature of the silicon substrate 1 is lower than the temperature of the molten silicon and the anisotropy of the surface energy of the crystal. I do. Therefore, on the main plane excluding the V-shaped groove 3 of the silicon substrate 1, a crystal whose orientation is aligned to (100) in the vertical direction as shown by an arrow a grows. However, the orientation in a plane parallel to the main plane is arbitrary because there is no restricting element, and as a result,
As is clear from the crystal grain boundary indicated by the dashed line B, a crystal having a large grain size in the direction perpendicular to the main plane and having a small grain size in the parallel direction is formed. On the V-shaped groove 3, a crystal grows in an orientation different from that on the main plane for the same reason.

Then, after the surface of the polycrystalline silicon layer 6 is ground to a flat processing reference plane c, the back side of the single-crystal silicon substrate 1 is removed by grinding and polishing until the tip of the V-shaped groove 3 is exposed. 2 As shown in FIG. 2D, a dielectric isolation substrate in which the single crystal silicon islands 7 are electrically separated from each other is completed.

(Problems to be Solved by the Invention) However, in the above-described conventional manufacturing method, the direction parallel to the main plane of the single crystal silicon substrate 1 (horizontal direction)
In this case, since the polycrystalline silicon layer 6 has a small grain size, the polycrystalline silicon layer 6 and the single-crystal silicon substrate 1 have different coefficients of thermal expansion. At the time of cooling, there was a problem that the entire body was warped. This warpage has led to a problem that a single-crystal silicon island 7 having a uniform thickness cannot be obtained in the dielectric isolation substrate shown in FIG.

The present invention has been made in view of the above points, and it is possible to reduce the occurrence of warpage due to a difference in thermal expansion coefficient between a semiconductor substrate and a polycrystalline silicon layer, and to manufacture a semiconductor substrate capable of obtaining a high-quality semiconductor substrate. The aim is to provide a method.

(Means for Solving the Problems) According to the present invention, a film having both insulating properties and wettability with molten silicon is formed on the surface of a single crystal silicon substrate, and a part of the surface of the film is etched. A groove having a period and a depth smaller than the diameter of the molten silicon droplet is formed on the surface of this film, and a polycrystalline silicon layer is formed on the film by solidifying the molten silicon.

(Operation) When a polycrystalline silicon layer is formed on the above-mentioned film on the surface of the single crystal silicon substrate by solidification of molten silicon, when the molten silicon is solidified, silicon is formed on the side and bottom surfaces of the groove and on the upper surface between the grooves. (100) plane and its equivalent (010)
The surface or (001) surface comes into contact and solidifies,
In this case, a crystal having a uniform orientation grows not only in a direction perpendicular to the surface of the single crystal silicon substrate but also in a plane parallel to the surface, so that a grain boundary hardly occurs. A polycrystalline silicon layer having a large grain size also in the direction. Therefore, the coefficient of thermal expansion of this polycrystalline silicon layer approximates the coefficient of thermal expansion of the semiconductor substrate of single-crystal silicon. As a result, after the formation of the polycrystalline silicon layer, the semiconductor substrate is entirely cooled when cooled to room temperature. Warpage does not occur.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows an embodiment of the present invention, in which the present invention is applied to a method of manufacturing a dielectric isolation substrate.

In this embodiment, first, as shown in FIG. 1A, a single crystal silicon substrate 11 is oxidized, and a silicon dioxide film 12 having a thickness of about 1 μm is formed on the surface thereof.

Next, as shown in FIG. 1 (b), the silicon dioxide film 12 is partially opened by photolitho etching, and the single crystal silicon substrate 11 is anisotropically formed using the remaining silicon dioxide film 12 as a protective mask. 50μm depth by etching
A V-shaped groove 13 is formed.

Next, after the silicon dioxide film 12 is removed, the single crystal silicon substrate 11 is oxidized again to form an insulating film having a thickness of about 2 μm on the surface of the substrate including the V-shaped groove 13 as shown in FIG. A silicon dioxide film 14 is formed.

Subsequently, as shown in FIG.
A silicon oxynitride-based thin film with the same composition as the conventional example with a film thickness of about 0.3 μm by the known CVD method above
Form 15.

Then, the silicon oxynitride-based thin film 15
Of the surface of the substrate 11 except for the V-shaped groove 13 on the main plane, by etching a part of the surface of the substrate 11 by dry etching with CF ₄ + O ₂ using a resist as a mask.
On the surface, equally spaced grooves 16 with a period of 3.8 μm and a depth of 0.1 μm
To form Here, the droplet diameter of the molten silicon, which will be described later, is several mm in the case of dropping, and several tens of μm in the case of ejection from a nozzle.Therefore, the period and depth of the groove 16 are smaller than the droplet diameter. It can be said that it is small enough.

After that, molten silicon at about 1440 ° C,
While maintaining the silicon substrate 11 at 00 ° C., the polycrystalline silicon layer having a thickness of about 550 μm is provided on the thin film 15 by supplying the solution onto the thin film 15 by dropping or spraying from a nozzle, spreading over the entire surface, and further cooling. 17 is formed as shown in FIG. 1 (c). At this time, in the portion of the thin film 15 where the grooves 16 are formed at regular intervals and whose period and depth are sufficiently smaller than the droplet diameter of the molten silicon, the side and bottom surfaces of the grooves 16 and the upper surface between the grooves (100) The plane and its equivalent (010) plane or (001) plane come into contact with each other, so that the silicon is solidified. Therefore, in this example, the V-shaped groove of the silicon substrate 11 is used.
On the main plane excluding 13, crystals having a uniform orientation grow not only in a direction perpendicular to the main plane of the silicon substrate 11 but also in a plane parallel thereto, as shown in FIG. Since a grain boundary is less likely to be formed (a space between crystal grain boundaries indicated by a one-dot chain line B is widened), a polycrystalline silicon layer having a large grain size not only in the vertical direction but also in the horizontal direction is obtained.

Thereafter, after the surface of the polycrystalline silicon layer 17 is ground to a flat processing reference plane, the back side of the single crystal silicon substrate 11 is removed by grinding and polishing until the tip of the V-shaped groove 13 is exposed. Then, as shown in FIG. 1 (d), a dielectric isolation substrate in which the single crystal silicon islands 18 are electrically isolated from each other is completed.

Although the above embodiment is an example in which the present invention is applied to a dielectric isolation substrate, the present invention can be applied to other similar semiconductor substrate manufacturing methods.

Further, in the above-described embodiment, the film that secures insulation isolation and wettability to molten silicon is composed of the silicon dioxide film 14 and the silicon oxynitride-based thin film 15,
If one sheet is enough, it may be enough.

(Effects of the Invention) As described above in detail, according to the manufacturing method of the present invention, the liquid of molten silicon is deposited on the surface of the single crystal silicon substrate surface, which secures insulation isolation and wettability to molten silicon. A groove with a period and depth smaller than the droplet diameter was formed, and a polycrystalline silicon layer was formed on the film by solidification of molten silicon. A crystal having a uniform orientation grows not only in a direction perpendicular to the surface of the substrate but also in a plane parallel to the substrate, and it becomes difficult to generate grain boundaries. Thus, a polycrystalline silicon layer can be formed. Therefore, the difference in the coefficient of thermal expansion between the polycrystalline silicon layer and the semiconductor substrate made of single crystal silicon can be reduced, and the entire structure can be prevented from being warped when cooled down to room temperature after the polycrystalline silicon layer is formed. According to the dielectric isolation substrate of the embodiment, a single crystal silicon island having a uniform thickness can be obtained.

In the dielectric isolation substrate of the embodiment, a groove is formed on the surface of the film at a single crystal silicon island portion forming a grid line, and a polycrystalline silicon region having a large grain size is formed at that portion (grid line portion). If you do
Since the polycrystalline silicon region having a small grain size generated on the V-shaped groove is divided at the grid line portion by the polycrystalline silicon region having a large grain size on the grid line, the adverse effect can be reduced. A single crystal silicon island having a more uniform thickness can be obtained with a smaller warpage.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing one embodiment of a method of manufacturing a semiconductor substrate according to the present invention, and FIG. 2 is a process sectional view showing a conventional method of manufacturing a dielectric isolation substrate. 11 ... single crystal silicon substrate, 14 ... silicon dioxide film,
15 ... Silicon oxynitride thin film, 16 ...
Groove, 17 ... polycrystalline silicon layer.

Claims (1)

(57) [Claims] A step of forming a film having both insulating properties and wettability with molten silicon on a surface of a single crystal silicon substrate; and etching a part of the surface of the film to form a film on the surface of the film. ,
Forming a groove having a width and depth smaller than the droplet diameter of the molten silicon and a forming cycle smaller than the droplet diameter; and forming a polycrystalline silicon layer on the film by solidifying the molten silicon. Forming a semiconductor substrate.