JPH0810672B2 - Flat plate bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] A method for bonding flat plates, for example, SOI (Silicon on Insulato)
r) As a method of bonding flat plates necessary for thin film transfer SOI formation, which is a type of structure formation method, an s-Si: H layer is formed on each of a pair of flat plates, and each a-Si: H layer is brought into close contact. We propose a method of firmly bonding both plates by heating them in a heated state. This enables adhesion without peeling or distortion even after a high temperature thermal cycle.

[Industrial applications]

The present invention relates to a bonding method for a flat plate made of a semiconductor or the like, and particularly to a bonding method capable of withstanding a high temperature heat cycle.

The thin film transfer SOI formation method, which is one of the above-mentioned SOI formation methods, is a method in which a Si wafer is bonded to another substrate via an insulating layer.
This is a method of thinning an i-wafer by polishing or etching.

In the case of the above SOI formation, the Si wafer is thinned to about 1 μm, and various devices are formed on this thin film.

In the device formation process, the process of heating and cooling at around 1000 ° C is performed multiple times. Therefore, a large stress is applied to the thin film, which may cause strain or crack.

There is a demand for a method that does not cause distortion or cracks in bonding for such applications, and has no impurity contamination when applied to semiconductor processes.

[Prior art and problems to be solved by the invention]

The most common conventional bonding method is to use a polymer adhesive.

In this case, the solvent is hard to escape, and the adhesive has poor heat resistance, so it cannot be applied to the semiconductor process.

On the other hand, as a bonding method applicable to the semiconductor process, there is melt bonding using phosphosilicate glass (PSG).

In this method, PSG is deposited on the adhesive surfaces of a pair of flat plates, and the PSG is melt-bonded by pressurizing and heating both adhesive surfaces together.

When the phosphorus (P) concentration of PSG increases, the softening point decreases and fusion becomes easier, but the contamination by P becomes a problem. Also, due to the difference in thermal expansion coefficient between PSG and Si, high temperature fusion (750 to 1100 ° C)
When the temperature is returned to normal temperature, distortion and cracks often occur, which hinders device formation.

[Means for solving problems]

To solve the above problems, a hydrogenated amorphous silicon layer is formed on each surface of a pair of flat plates, and the surfaces of the hydrogenated amorphous silicon layers formed on each flat plate are heated in close contact with each other. According to the present invention, the flat plate bonding method according to the present invention for bonding the pair of flat plates is achieved.

[Action]

FIG. 1 is a schematic sectional view for explaining the principle of the present invention.

In the figure, a-Si deposited on the surface of a pair of flat plates 1, 1 ':
If the temperature is raised while the H layers 2 and 2'are in close contact, hydrogen will escape and at the same time, the a-Si dangling bonds will bond and bond.

This is possible only when a-Si: H containing hydrogen is used. With a-Si that does not contain hydrogen, no dangling bond of Si occurs due to hydrogen desorption, and therefore flat plates cannot be bonded. .

As described above, the bonding method of the present invention is completely different from the conventional method in that it is separated by hydrogen which is released at high temperature.
A dangling bond is generated on the a-Si surface, and this bond is used for bonding.

Furthermore, hydrogen is easily dissipated to the outside, so there is no risk of impurity contamination, and since the adhesive layer is in an amorphous state, stress is easily absorbed, and there is little risk of adversely affecting thinned Si for device formation.

〔Example〕

FIG. 2 is a schematic sectional view for explaining an embodiment of the present invention.

In the figure, as a pair of flat plates 1, 1 ′, a 2-inch diameter Si
The wafers 11 and 11 'having the oxide films 12 and 12' having a thickness of 3000 Å formed on the surfaces are used.

Next, a 5000-Å-thick a-Si: H layer 2, 2 ′ is deposited on the surface of the oxide film 12, 12 ′ by the glow discharge CVD method.

In CVD, the substrate temperature is set to 200 ° C and SiH ₄ + is used as the reaction gas.
Using H ₂ or SiH ₄ + Ar, decompressing it to several Torr and applying power of frequency 13.56MHz to several 100W per substrate.

The pair of flat plates 1,1 ′ thus obtained was used as an a-Si: H layer.
Put 2,2 'so that they are in contact with each other, put them in an electric furnace in a nitrogen (N ₂ ) atmosphere with a load applied, and raise the temperature to 700 ° C.
Hold for 10 minutes, then turn off the electric furnace and let it cool naturally.

When the temperature was near room temperature, the sample was taken out of the furnace and the pair of flat plates 1,1 'were firmly bonded.

In addition, when the sample was crushed and examined in detail, it was confirmed that there was almost no unbonded portion, and that strong bonding was achieved over the entire surface.

In this mechanism, hydrogen in a-Si: H gradually escapes as the temperature rises, and most of the hydrogen escapes above 400 ° C, and the dangling bond of Si is bonded as described above. It is believed that

In the embodiment, the Si substrate in which an oxide film is formed on a pair of flat plates is used. Instead of this, a p-type Si substrate and an n-type Si substrate are used, and the bonding is performed through an extremely thin a-Si: H. Therefore, a large area pn junction can be formed.

In addition, although the bonding heating step was performed in an N ₂ atmosphere in the examples, if the bonding heating step is performed in an oxygen (O ₂ ) atmosphere, the bonding surface is Si—O.
-Si becomes a siloxane bond, and an adhesive layer with high insulation is obtained.

Furthermore, by adding O ₂ or N ₂ to the raw material gas for forming the s-Si: H layer, a high resistance adhesive layer (a-Si: H, O or a-Si: H, N) can be formed. Is also possible.

〔The invention's effect〕

As described above, according to the present invention, it is possible to bond flat plates that are free from impurity contamination, have heat resistance that can withstand a semiconductor process, and have less stress and strain due to heat.

This bonding method can be applied to the formation of SOI structures and the formation of large area pn junctions.

[Brief description of drawings]

FIG. 1 is a schematic sectional view for explaining the principle of the present invention, and FIG. 2 is a schematic sectional view for explaining one embodiment of the present invention. In the figure, a pair of flat plates 1,1 ', 11,11' are Si wafers, 12,12 'are oxide films, and 2,2' are a-Si: H layers.

Claims (1)

[Claims] 1. A hydrogenated amorphous silicon (a-Si: H) layer is formed on each surface of a pair of flat plates, and the surfaces of the hydrogenated amorphous silicon layers formed on each flat plate are brought into close contact with each other. A method for bonding flat plates, characterized in that the pair of flat plates are bonded by heating in a state.