Method for making a stressed structure designed to be dissociated

Abstract

The invention concerns a method of making a complex microelectronic structure by assembling two substrates through two respective linking surfaces, the structure being designed to be dissociated at a separation zone. The invention is characterized in that is consists, prior to assembly, in producing a state difference in the tangential stresses between the two surfaces to be assembled, said difference being selected so as to obtain in the assembled structure a predetermined stress state at the time of dissociation.

Description

TECHNICAL FIELD AND PRIOR ART [0001] The invention relates to a method of producing a complex microelectronic structure by assembling two basic microelectronic structures, this complex structure being intended to be dissociated. The microelectronic structure concept must be understood hereinafter as including optoelectronic, microtechnological, nanotechnological and nanoelectronic structures. [0002] The technique of transferring a layer from an original substrate to a temporary or final target substrate is increasingly used in microelectronics. This technique has many applications, of which only two will be mentioned here by way of illustrative and non-limiting example. For example, it is used to produce SOI (silicon on insulator) substrates used in particular to produce fast components with low power consumption. It is also used to produce composite substrates that limit costs by avoiding the use of costly bulk substrates. This is the case with bulk silicon carbide substrates, for ...

AI Technical Summary

Benefits of technology

[0011] The tangential stress state difference between the two faces to be assembled is advantageously selected to minimize the stresses in the separation region at the moment of dissociation.

[0013] It is to be noted that, in an entirely different context, the paper by D. Feijoo, I. Ong, K. Mitani, W. S. Yang, S. Yu and U. M. Gösele, “Prestressing of bonded wafers”, Proceedings of the 1st international symposium on semiconductor wafer bonding, Science, Technology and applications, Vol. 92-7, The Electrochemical Society (1992) page 230, proposes a method of generating internal stresses within a complex structure with a view to improving the mechanical stability of the structure.

[0020] The tangential stress difference between the faces to be bonded of the two basic structures may advantageously be created by deforming (mainly elastically) each of said structures before assembly. A simple and easy technique for generating stresses is to curve these structures.

[0032] the substrates are assembled by direct contact, the surface of at least one of the substrates being adapted to prevent air from being trapped between the assembled surfaces,

[0040] Also, the tangential stress state difference between the two faces to be assembled is advantageously selected so that the prestresses created in this way within the complex structure enable subsequent imposition of specified internal stresses at a specified temperature. The prestresses are advantageously selected to minimize or eliminate the stresses within the complex structure.

[0046] The tangential stress state difference between the two faces to be assembled is advantageously selected to minimize the stresses in the buried layer at the moment of dissociation. This guarantees the quality of the structures obtained after dissociation.

Problems solved by technology

A problem can arise if heat treatment is required to induce some or all of the fracture in the weakened region and the source and target substrates feature materials with very different coefficients of thermal expansion.

Heat treatment can induce high internal stresses within the structure formed by assembling the two substrates, by virtue of the difference in their coefficients of thermal expansion, and these high internal stresses may damage the structure.

These stresses can also cause damage at the moment of fracture proper, since at this time the structures immediately relax when they are suddenly dissociated.

If its magnitude is too high, this jump can damage at least one of these two structures.

More generally, the problem is that of controlling the stresses within a heterostructure (i.e. a complex structure made by assembling at least two different materials) at the moment of dissociation of the heterostructure when that dissociation necessitates a change of temperature.

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