JPH0257342B2 - - Google Patents

Description

[Detailed Description of the Invention] <<Industrial Application Field>> The present invention is directed to an LSI that can handle high voltages.
The present invention relates to a method for manufacturing a so-called dielectric isolation substrate in which the elements are electrically isolated by an electrical insulator.

<<Prior Art>> The basic methods that have been adopted so far as methods for manufacturing dielectrically isolated substrates are as follows.

That is, as shown in FIG. 2, a single-crystal Si substrate c is prepared in which a V-shaped groove a is previously formed on the upper surface b, and the upper surface b is oxidized by means such as thermal oxidation. An electrical insulating layer e having a predetermined layer thickness d is formed following the unevenness of the upper surface b, and further, C.
By applying polycrystalline silicon (poly-Si) using the VD method, a polycrystalline Si layer g having a smooth upper surface f is formed.

Incidentally, the dielectric isolation substrate A thus formed is a wafer that moves from the state shown in FIG. As is known, by polishing, the lower end a' of the apex angle of the V-shaped groove a is removed by polishing, and in this way the next LSI manufacturing process is carried out.

By the way, when using the above manufacturing method, since the polycrystalline Si layer g is formed by the CVD method as described above, not only does it take a considerable amount of time to form the layer, but also Since the dielectric isolation substrate C obtained as described above must be subjected to wafer polishing, it must have enough strength as a support to withstand the external force applied during the polishing. ~
A thick polycrystalline Si layer of approximately 500 μm is required.

However, when attempting to form the polycrystalline Si layer g using the CVD method as described above, not only does it take time as described above, but the thickness is limited to around 100 μm even if it takes a long time, and as a result, the strength condition described above is not satisfied. I can't do it.

Therefore, in order to improve the above means, a single crystal Si substrate c having an electrically insulating layer e as described above was prepared,
This is rotated by a turntable h or the like as shown in Fig. 3, and the molten polycrystalline silicon applied onto the electrically insulating layer e is spread by centrifugal force, and is cooled and solidified at appropriate times to create a smooth surface as described above. A so-called spin method has also been proposed in which a polycrystalline Si layer g having a top surface f is formed.

However, when using the spin method described above, although it is true that a polycrystalline Si layer g of the desired thickness is obtained, the molten polycrystalline silicon that spreads due to centrifugal force flows sufficiently into the groove a to the bottom and fills it. In such a case, the dielectric isolation substrate A is removed along the removal line B as described above.
When the wafer is polished to the point where there is no electrical insulator between the resulting isolated islands j and j, the product becomes defective in terms of electrical insulation.

<<Problems to be Solved by the Invention>> The present invention was studied in view of the above-mentioned difficulties of the conventional spin method. By applying an electrical insulator from the outside rather than by forming SiO ₂ through oxidation, it is possible to not only fill the groove with the electrical insulator, but also to add more electrical insulation with a smooth surface. Then, by applying molten polycrystalline silicon on this smooth surface by a spin method, a polycrystalline Si layer is formed. The purpose is to make it possible to eliminate problems such as the occurrence of unfilled areas of silicon, and to easily obtain a withstand voltage of several hundred volts in terms of electrical insulation.

<<Means for Solving the Problems>> In order to achieve the above-mentioned object, the present invention fills the grooves by applying an electrical insulator on a single-crystal Si substrate with grooves formed on the upper surface. and forming an electrically insulating layer that covers the upper surface to expose the smooth surface, and by rotating the thus obtained insulating substrate, spreading the molten polycrystalline silicon provided on the smooth surface, The present invention provides a method for manufacturing a dielectric isolation substrate, characterized in that a polycrystalline Si layer of a required thickness is formed by a spin method that is cooled and solidified at appropriate times.

《Function》 Since the electrical insulation layer applied to the single crystal Si substrate completely fills the grooves, there is no deterioration of electrical insulation due to the generation of voids in this area as in the conventional method. Since the upper surface of the electrical insulating layer is formed as a smooth surface, when forming the polycrystalline Si layer by the spin method, the flow of molten polycrystalline silicon is smoothly spread, and the grooves are not formed as in the conventional method. There is no need to consider whether or not molten polycrystalline silicon will flow deep, and the spin method can be performed easily and quickly.

<<Example>> The present invention will be explained in detail below with reference to FIG. 1. First, as shown in FIG. A single-crystal Si substrate 2 is prepared, and an electrical insulating layer 3 is formed on the upper surface 2a. In the present invention, as a means for obtaining the electrical insulating layer 3, CVD method,
It is preferable to use a PVD method or a method in which a coating agent is applied and then baked.

Here, as the above-mentioned coating agent, a coating-baking type insulating inorganic compound forming agent is used, and a suitable example thereof is a silanol liquid that forms SiO ₂ .In this case, the silanol liquid is applied with a brush. The silanol solution is applied to the upper surface 2a by a spraying method or the like, and in this case, the silanol solution is filled into the groove 1 and the entire upper surface 2a is covered with the same solution. It is.

In this state, a SiO ₂ film, that is, an electrical insulating layer 3, is formed by baking at 500°C for about 20 minutes.
The electrical insulating layer 3 is filled in the groove 1 and is stacked up by a thickness D from the flat portion 2b of the upper surface 2a, and the upper surface is a smooth surface 3a.

Next, the insulating substrate 4 formed as described above is set in a known spin method mold (not shown), and while maintaining the temperature at 800 to 1400°C,
As illustrated in FIG. 3, melted polycrystalline silicon is rotated using a turntable or the like to flow down onto the smooth surface 3a of the electrically insulating layer 3 of the insulating groove 4, or the solid polycrystalline silicon is By means of placing the polycrystalline silicon on the smooth surface 3a and heating and melting them, the polycrystalline silicon in both fluid states is expanded by the centrifugal force of a turntable, etc., and the desired flow expansion is obtained. If so, by stopping the heating, for example, stopping high-frequency heating, the molten polycrystalline silicon is solidified, thereby forming a polycrystalline Si layer 5 having a smooth upper surface 5a to the required thickness. As a result, a dielectric isolation substrate 6 is obtained.

The dielectric isolation substrate 6 obtained in this way is
As illustrated in FIG. 2B using the conventional method, the single crystal Si substrate 2 is removed by wafer polishing up to the removal line B, thus forming the isolation islands 7, 7.

<<Effects of the Invention>> Since the present invention is carried out as described above, the polycrystalline Si layer can be formed to a desired thickness by utilizing the advantages of the spin method, unlike the conventional means using the CVD method. It is possible to form a polycrystalline Si layer easily and quickly, and therefore it is possible to form a polycrystalline Si layer that can fully play its role as a support for a dielectric separation substrate, and therefore provides a layer that does not hinder wafer polishing work at all. It is possible.

Moreover, since the spin method is carried out as a spreading flow of molten polycrystalline silicon onto a smooth surface, not only smooth and rapid implementation is ensured, but also the grooves are completely filled with electrical insulator beforehand. Because of this, there is no room for the conventional problem of air bubbles forming in the concave grooves.
The isolation island can easily and reliably obtain a withstand voltage of several hundred volts, which is of great benefit in manufacturing LSIs and the like with high withstand voltages.

[Brief explanation of the drawing]

Figures 1a, b, and c are longitudinal sectional front views of the processed product in each process for explaining the steps of the manufacturing method according to the present invention, and Figures 2 a and b are longitudinal sectional front views of the processed product in each process of the past conventional method. 3 are longitudinal cross-sectional front explanatory views of a workpiece processed by the spin method as an improved conventional method. DESCRIPTION OF SYMBOLS 1... Concave groove, 2... Single crystal Si substrate, 2a... Upper surface, 3... Electrical insulating layer, 3a... Smooth surface, 4...
...Insulating substrate, 5...Polycrystalline Si layer, 6...Dielectric separation substrate.

Claims (1)

[Claims] 1. A single crystal Si substrate having grooves formed on its upper surface is coated with an electrical insulator to fill the grooves and cover the upper surface to expose a smooth surface. By rotating the thus obtained insulating substrate, the molten polycrystalline silicon provided on the smooth surface is spread, and the required thickness is obtained by a spin method in which the molten polycrystalline silicon is spread at appropriate times and solidified. Polycrystalline Si
A method for manufacturing a dielectric isolation substrate, characterized in that a layer is formed. 2 The method of forming the electrical insulating layer is CVD method, PV
D. method, a coating agent application-baking method, and the method for manufacturing a dielectrically separated substrate according to claim 1, wherein the electrical insulator is SiO ₂ .