Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Having diverse electrical device
Reexamination Certificate
1999-07-14
2001-03-20
Bowers, Charles (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Having diverse electrical device
C438S064000, C438S067000, C438S406000, C438S458000, C438S464000
Reexamination Certificate
active
06204079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Title of the Invention
This invention relates to the selective transfer of elements from a transfer support to a reception support.
In particular, it relates to the transfer of partially or completely finished semiconductor chips from their initial substrate on which they were produced to a new substrate (or reception support) which may itself have been treated using microelectronic techniques.
The invention can be used for the transfer of chips, for example transfer of chips with a surface area of 1 cm
2
from their initial substrate onto glass or onto a transparent substrate. It can also be used to transfer optoelectronic components such as VCSEL (vertical cavity lasers) or small pieces of III-V semiconductor from their initial substrate onto silicon wafers prepared using microelectronic techniques in order to obtain III-V semiconductor elements on silicon. In this case, the size of chips is usually smaller, for example of the order of 1 mm
2
or less.
2. Description of the Related Art
The molecular bonding technique for bonding two surfaces made of semi-conductor material is known. Molecular bonding includes two types of bonding; namely hydrophilic bonding and hydrophobic bonding. In the case of hydrophilic bonding for the example of silicon oxide, bonding is the result of a change in —OH interactions at the surface of a structure to the formation of Si—O—Si bonds. The forces associated with this type of interaction are strong. The bonding energy is of the order of 100 mJ/m
2
at ambient temperature and reaches 500 mJ/m
2
after annealing at 400° C. for 30 minutes (values obtained for bonding between native or hydrophilic SiO
2
and unpolished thermal SiO
2
). The bonding energy is usually determined by the blade method described by W. P. MASZARA et al. in the “Bonding of silicon wafers for silicon-on-insulator” article published in J. Appl. Phys. 64(10), Nov. 15, 1988, pages 4943-4950. The bonding energy for bonding between deposited, polished silicon oxide and deposited, polished silicon oxide, is of the order of 1 J/m
2
for annealing under the same conditions. However, if a hydrophilic treated surface is bonded by molecular bonding on a hydrophobic treated surface, very poor quality bonding is obtained and the bonding forces are very low; bonding energy of the order of 100 mJ/m
2
after annealing at 400° C. for 30 minutes.
Hydrophobic bonding is achieved by molecular bonding without an OH group. In the case of silicon, molecular bonding of hydrophobic wafers can also produce high bonding forces. For example, the work done by Y. BACKLUND et al. described in the “A suggested mechanism for silicon direct bonding from studying hydrophilic and hydrophobic surfaces” article published in J. Michromech. Microeng. 2 (1992), pages 158-160. This article shows that bonding forces of the order of 1 J/m
2
are obtained after annealing at 400° C., after bonding hydrophobic silicon wafers.
SUMMARY OF THE INVENTION
This invention was designed to obtain a selective transfer of elements from a first support to a reception support. In order to arrive at this result, it makes particular use of the molecular bonding technique.
Therefore, the purpose of this invention is a process for the selective transfer of elements from a transfer support to a reception support, the elements bonding through a first face to the transfer support with a defined bonding energy, each of the elements having a second face that may be put into contact with the reception support, the process comprising the following steps:
definition of at least one element to be transferred among the said elements, involving separation of the said element to be transferred from elements that are not to be transferred,
treatment of the second face of the said element to be transferred to give it a bonding energy with the reception support exceeding the bonding energy between its first face and the transfer support, retaining means being provided to retain elements not to be transferred onto the transfer support,
the second face of the element to be transferred is put into bonding contact with the reception support,
separation of the transfer support from the reception support in order to transfer the element(s) to be transferred onto the reception support and to retain other elements on the transfer support.
The process may comprise the following preliminary steps:
formation of the elements on a face of an initial substrate, the elements being supported on the said face of the initial substrate through their second face,
the face of the initial substrate comprising the elements is fixed to the transfer support such that the elements bond to it through their first face according to the said defined bonding energy,
elimination of the initial substrate so that the second face of the elements is exposed.
In some cases, it may be useful to treat wafers in thin layers several times before transferring elements. It is thus possible to make double sided devices and to choose either face as being the contact face.
Preferably, bonding of the face of the initial substrate comprising the elements with the transfer support is obtained by molecular bonding. In this case, it is useful if this molecular bonding is made by one or several treatments of the faces to be bonded to the initial substrate and/or the transfer support so as to control the hydrophilia and/or hydrophobia properties and/or a satisfactory micro-roughness to obtain the defined bonding energy. Advantageously, a heat treatment may be applied globally or locally to contribute to obtaining this bonding energy. Elements may include a layer, called the stop layer, by which they are bonded to the initial substrate. This initial substrate may be eliminated by one or several techniques including grinding, chemical etching of the initial substrate and/or the stop layer, polishing, separation subsequent to heat treatment along a cleavage plane induced by ionic implantation.
If the elements form a continuous layer on the transfer support, the definition step of at least one element to be transferred may include isolation of the element to be transferred. Advantageously, this isolation may be produced by chemical etching, blade cutting, laser etching or any other cutting means. Preferably, when this isolation is made by etching, the cut is made in a manner such that etching stands are formed close to the transfer support.
The second face of the element to be transferred can be put into bonding contact with the reception support by molecular bonding. Heat treatment may be applied globally or locally to contribute to obtaining the defined bonding energy defined between the second face of the said element to be transferred and the reception support. Molecular bonding of the second face of the said element to be transferred and the reception support may be achieved by treatment of the second face and/or all or part of the reception support. Retaining means may consist of treating elements not to be transferred and/or areas of the reception support that are not suitable for receiving elements so that there is no bond between the elements that are not to be transferred and the reception support. They may consist of modifying the surface of the elements that are not to be transferred and/or the surface of the reception support areas that are not suitable for receiving the elements, in order to make the bonding energy between elements not to be transferred and the reception support less than the bonding energy between elements to be transferred and the reception support, and less than the bonding energy between the first faces of the elements and the transfer support. The treatment resulting in the said retaining means may be chosen from one or several of the following treatments—hydrophilia, hydrophobia, roughness, heat treatment, surface shrinkage.
If the second face of elements not to be transferred comes into contact with the reception support during the bonding contact step, the retaining means may consist of treating the second face of these elements not to be
Aspar Bernard
Moriceau Hubert
Rayssac Olivier
Bowers Charles
Commissariat A l'Energie Atomique
Lee Hsien-Ming
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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