JPS60236210A - Junction of semiconductor wafers - Google Patents

Abstract

PURPOSE:To easily attain rigid junction of semiconductor wafers having large areas by finishing the surface of two sheets of semiconductor wafers like the mirror-surface, placing the ground surfaces of them in the close contact under a reduced pressure, placing them again under the atmospheric pressure and executing the heat processing at a particular temperature. CONSTITUTION:It is desirable that the surface roughness of ground surfaces is set to 500Angstrom or less and after the grinding the surfaces are washed sufficiently, the surfaces are dried up and placed in close contact within a chamber under the reduced pressure. When a pressure within the chamber of reduced pressure is set to 10mTorr or less, good contactness can be attained because residual gas such as air can substantially be disregarded. The heat processing under the atmospheric pressure brings about effective increase in injuction strength of wafers when temperature is 200 deg.C or hither. Particularly, the heat processing at a temperature of about 1,000 deg.C is desirable in order to attain good electrical characteristics. When temperature rises upto 1,300 deg.C or higher, deformation of wafer such as creep is generated as in the case of conventional hot-press method. If a foreign matter such as dust is adhered to the bonding surface, good junction body cannot be obtained. Therefore, purification of ambient is very important for the processes from washing of wafer to junction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for bonding semiconductors such as silicon.

[Technical background of the invention and its problems]

Various techniques are known for forming other semiconductor layers of the same type or of different compositions and impurity concentrations on the surface of a semiconductor wafer. Examples include a vapor phase growth method applying a chemical vapor deposition method or a physical vapor deposition method, a liquid phase epitaxial growth method, an alloy bonding method, and an adhesion method using an adhesive layer such as solder. However, various conventional vapor deposition methods have a problem in that the deposition rate is slow and it takes an extremely long time to form a semiconductor layer of, for example, several hundred micrometers. Furthermore, in the method of bonding semiconductor wafers using an adhesive layer of different materials, there is a disadvantage that when the temperature rises, the adhesive layer material diffuses into the semiconductor, and compounds are generated, causing deterioration. Furthermore,
There is a so-called Houtgeres method in which semiconductor wafers are heated and pressurized together in a vacuum, but this method requires special equipment and also requires high temperatures of around 1300°C, which is close to the melting point, resulting in deformation such as cleavage. .

On the other hand, the present inventors have discovered that by pressing the polished surfaces of mirror-polished semiconductor wafers together in a clean atmosphere, they can be bonded extremely firmly, and have previously proposed this (%
(Gan Sho 58-159276). According to this method, a bonded body of semiconductor wafers can be easily obtained with virtually no intervening foreign matter.

However, when this method was used to bond semiconductor cubes with a diameter of several inches, it was found that it was extremely difficult to bond the entire surface due to the mutual influence of the sea urchins. This is considered to be mainly due to the presence of residual gas in a part of the adhesive surface.

[Purpose of the invention]

The present invention provides a semiconductor wafer that can easily and firmly bond even large-area semiconductor wafers together.
The purpose of this invention is to provide a method for joining.

[Summary of the invention]

The present invention mirror-polishes the surfaces of two semiconductor sea urchins,
The polished surfaces are brought into close contact with each other under reduced pressure, and then returned to atmospheric pressure and heat treated at a temperature not exceeding 1300° C. to obtain a wafer bonded body.

The surface roughness of the polished surface is preferably 500X or less, and after the polished surface has been thoroughly cleaned and dried, it is brought into close contact in a vacuum chamber. The pressure inside the vacuum chamber is 10
If it is below rn Torr, residual gas such as air can be virtually ignored, and good adhesion is possible.

Heat treatment at atmospheric pressure can be applied to sea urchins at temperatures above 200°C.
The effect of increasing the bonding strength is recognized.

In particular, in order to improve the electrical characteristics, i oo
Heat treatment at around 0°C makes it a good freeze. When the temperature is increased to about 1300° C. or higher, wafer deformation such as creep occurs, as in the conventional Hotrus method.

Note that the method of the present invention cannot obtain a good bonded body if foreign matter such as demi is present on the adhesive surface. Therefore, the cleanliness of the atmosphere is important in the process from wafer cleaning to adhesion.

〔Effect of the invention〕

According to the present invention, since the semiconductor wafers are closely attached under reduced pressure, even if the semiconductor wafer has a large area, no residual gas is left on the bonding surface, and it is possible to firmly bond the semiconductor wafers.

The semiconductor urchin bonded body obtained by the present invention can be widely applied to various semiconductor devices. For example, by bonding a high impurity concentration semiconductor wafer with a low impurity concentration semiconductor, it is possible to
Moreover, a high-concentration collector-forming diffusion process can be omitted.

This can be expected to have significant effects such as shortening the process and preventing the introduction of defects. Furthermore, if a high-resistance active layer, which was conventionally formed by epitaxial growth, is realized as an IC substrate by the method of the present invention, the IC manufacturing process can be significantly shortened, and it will also contribute to improving the characteristics of devices such as high-voltage devices. .

[Embodiments of the invention]

3-inch n-type silicon sea urchin with specific resistance of 0.050-
・I prepared two sheets and polished their surfaces to a mirror finish.

The surface roughness of the polished surface is 100X or more], the flatness is 10 μm8
It was degree. These wafers were cleaned using mixed acid in a clean room with a flow rate of 20 particles/- or less, dried, and placed in a vacuum chamber at 0.1 Torr.
The polished surfaces were brought into close contact.

This silicone wafer is then returned to the atmosphere,
Heat treatment was performed at 1150° C. for 2 n, y.

(()) The wafer bonded body was etched into a mesa shape with three orifices using a hydrofluoric acid-based etching solution to expose the end face of the bonded surface. The conductivity characteristics of the joint were inspected while keeping the joint end surface clean.The results showed that the ohmic characteristics were good over the entire wafer area, and the resistance value matched the value of the sea urchin itself within the error range. .

Further, as a result of observation using an infrared microscope, no air bubbles or the like were observed on the bonding surface.

Claims (1)

[Claims] The surfaces of two semiconductor wafers are mirror-polished, the polished surfaces are brought into close contact under reduced pressure, and then heated at 1300°C under atmospheric pressure.
A method for joining semiconductor wafers characterized by heat treatment at a temperature not exceeding .