Process for assembling substrates with low-temperature heat treatments

Abstract

The invention relates to a process for producing a bond between a first and a second substrate (2, 4), comprising:a) a step of preparing surfaces (6, 8) to be assembled,b) an assembly of these two surfaces, by direct molecular bonding,c) a heat treatment step involving at least maintaining the temperature within the range of 50° C. to 100° C. for at least one hour.

Description

TECHNICAL FIELD AND PRIOR ART[0001]The invention relates to techniques for assembling substrates.[0002]In general, a bond between two substrates or surfaces can be obtained after a preparation of the surfaces giving them a hydrophilic or hydrophobic character.[0003]The use of heat treatments to reinforce the direct bonding can cause, for a certain number of bonded structures, the appearance of defects at the bonding interface. These defects are due to the degassing of by-products of the molecular bonding reaction: for example, water, hydrogen or hydrocarbon molecules.[0004]For a certain number of bonded structures, it is known that these defects can be resorbed by heat treatments performed at very high temperatures. These temperatures are, for example, between 900° C. and 1300° C. and are based on the preparation of surfaces before bonding. Unfortunately, for other bonded structures, this solution cannot be used.[0005]The limitation of the surface oxide thickness or the presence of ...

AI Technical Summary

Benefits of technology

[0019]This heat treatment according to the invention enables good preparation of the conditions for degassing the surfaces in contact by molecular adhesion.

[0061]A process according to the invention also makes it possible to obtain very thin layers of Si (thickness below 150 nm) or of SiO2 (thickness below 50 nm) directly bonded on Si or SiO2 plates.

Problems solved by technology

The use of heat treatments to reinforce the direct bonding can cause, for a certain number of bonded structures, the appearance of defects at the bonding interface.

These defects are due to the degassing of by-products of the molecular bonding reaction: for example, water, hydrogen or hydrocarbon molecules.

Unfortunately, for other bonded structures, this solution cannot be used.

In the case of thin films (with a thickness below around ten μm or several dozen nm), heat treatments, at temperatures below 1000° C., for example between 600° C. and 800° C., cause the formation of bonding defects in the form of blisters or zones without adherent film.

These defects cannot be suppressed by higher-temperature heat treatments.

These defects make the structures produced unusable.

Currently, this phenomenon limits the production of oxide film structures, embedded at the bonding interface, that are fine (thickness below 50 nm) or ultra-fine or even Si layers directly bonded to Si plates.

Similarly, for heterostructures (for example P-doped Si bonded to N-doped Si), heat treatments cause the formation of bonding defects under certain conditions.

For certain heterostructures, if the damage is excessive in heat treatments within the temperature range below 800° C., this damage can no longer be repaired by a treatment between 1100° C. and 1300° C.

When the heat treatments at higher temperatures cannot be used (incompatibility with the component production process in progress, for example), the bonding defects are then prohibitive.

This therefore raises the problem of reducing or even eliminating, in the case of (direct) molecular bonding, the defects due to degassing at the bonding interface.

However, these techniques are not suitable for industrial use.

Unfortunately, such techniques are destructive and present usage problems.

A problem is therefore to find a treatment solution for reducing defects that enables industrial implementation while using the entire surface.

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