Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Subsequent separation into plural bodies
Reexamination Certificate
1999-10-06
2002-03-26
Lee, Eddie (Department: 2815)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Subsequent separation into plural bodies
C438S459000, C438S520000, C438S067000
Reexamination Certificate
active
06362077
ABSTRACT:
TECHNOLOGICAL FIELD
This invention relates to a structure comprising a thin layer of material made up of conductive zones and insulating zones. It also relates to the method of manufacturing such a structure.
STATE OF THE PRIOR TECHNOLOGY
Certain components created on the surface of a substrate require, in order to be used, that an electric current is able to pass through the thickness of the substrate, that is to say, in the vertical direction with respect to the plane of the substrate. One may mention as an example components with vertical operation: electroluminescent diodes, laser diodes (in particular, laser diodes with a vertical cavity), photodetectors, hyperfrequency detectors (in particular, Schottky diodes), power components, solar cells. These components are represented diagrammatically in the form of doped substrates, on which, the active or non-active layers are produced by a specific doping operation. As a general rule, the electrical contacts are made on the front facing surface and at the back of the component or at depth.
Power diodes have two contacts: the anode contact on the front face and the cathode contact on the back face. For more sophisticated power components such as the MOSFETs, the IGBTs and the thyristor structures, there is still one contact on the front face and one contact on the back face with one or more contact points at depth. However, for all these types of components, the electrical current passes between the front and rear faces of the device (see for example the synthesis article entitles “Trends in power semiconductor devices” by B. JAYANT BALIGA, that appeared in IEEE Transactions on Electron Devices, Vol. 43, No. 10, October 1996).
One of the techniques used to provide active layers on the substrate is epitaxial growth. This technique consists of causing a material to grow in an ordered manner from a crystalline substrate whilst controlling its composition. Stacks of epitaxiated semiconductor layers with variable doping levels can be produced in this way. If the epitaxiated semiconductor layers are of the same kind as the crystalline substrate, one refers to deposition by homo-epitaxy. If they are of a different kind, then this is deposition by hetero-epitaxy. This technique permits the production of semiconductor layers of very small thickness (a few tens of Angstrom units), of high purity and with interfaces of excellent quality. However, this technique is very expensive and its low rate of deposition does not enable one to obtain semiconductor layers of thickness greater than a few tens of micrometers in an industrial manner. Furthermore, the epitaxy of the layers can only be created if the substrate has crystal parameters which are close to those of the material to be epitaxiated. In effect, if the crystal parameters are not sufficiently close, the limitation to the matching the lattice parameters greatly reduces the good optical and electronic properties of the structures obtained by hetero-epitaxy. Therefore, this severely limits the number and the diversity of the layers that one is able to grow. In particular, one may mention the difficulty in obtaining components from the III-V family of semiconductors on silicon substrates. For certain components, it is of interest to combine the advantages of different semiconductors. By way of example, one can consider the cases of an active layer of GaAs or an active layer of InP on silicon. This configuration allows one to associate the good electronic properties of the GaAs or InP materials at hyperfrequency with a silicon substrate which has the advantage of being more robust, having less weight and which has better thermal conductivity than GaAs. One may also mention the case of a layer of GaN on a SiC substrate, a structure which offers many advantages for electronic power components.
In another field, solar cells for use in space are of great interest. In effect, energy for satellites is generally supplied by means of panels of solar cells. Among the various possibilities for producing solar cells for use in space, one can mention solar cells made of GaAs. The problem of gallium arsenide is its cost and above all its weight and its fragile nature. In order to resolve this problem, it has been proposed to produce solar cells from thin films of GaAs epitaxiated onto a germanium substrate. A great improvement would consist of providing thin films of GaAs or InP on a silicon substrate. This type of structure would allow one to combine the advantages of GaAs (surface properties to create the component constituting the solar cell) and the advantages of silicon as a support (weight three times less than that of GaAs and much less fragile).
In order to produce these structures made up of a thin film, integral with a substrate of a different material, processes other than hetero-epitaxy can be used. In particular, one may mention the methods of bringing semiconductor substrates into contact by bonding them using molecular adhesion or techniques for transferring thin films. The method disclosed by the document FR-A-2 681 472 offers numerous advantages. It allows one to transfer a thin semiconductor film with a large surface area (of a few thousand Angstrom units with a few micrometers of thickness), from its original substrate to the desired support by a combination of ionic implantation (using light ions), bonding by molecular adhesion and an appropriate heat treatment.
This transfer technique has been the subject of other developments. According to document FR-A-2 748 851, the ion implantation step is carried out with an ion dose which is between a minimum dose and a maximum dose. The minimum dose is that from which sufficient micro-cavities will be created to provide weakening of the substrate along the reference plane. The maximum dose, or critical dose is that above which, during the heat treatment step, there is separation of the substrate. The separation step comprises the application of mechanical forces between the two parts of the substrate.
If the thin film defined in the substrate is sufficiently rigid itself (because of its thickness or because of its mechanical properties), after the transfer annealing, one can obtain a self-supporting film. This is what is disclosed in document FR-A-2 738 671.
Document FR-A-2 767 416 discloses that it is possible to lower the annealing temperature if the thermal budget supplied to the substrate during the various steps of the method is taken into account (ion implantation step, possibly a step of bonding the substrate to a stiffener, possible intermediate treatments, an annealing step to allow separation). By the term thermal budget one understands that for a step where thermal energy is supplied (for example during an annealing step), one must not only consider the temperature but the time-temperature couple supplied to the substrate.
This technique is used now for the industrial manufacture of SOI substrates (see the article by A. J. AUBERTON et al., entitled “SOI materials for ULSI applications” that appeared in Semiconductor International, 1995, Vol. 11, pages 97-104). The feasibility of this technique to III-V semiconductor materials such as GaAs has recently been demonstrated (see the article by E. JALAGUIER et al., entitled “Transfer of 3 in GaAs Film on Silicon Substrate by Proton Implantation Process” published in Electronics Letters, Feb. 19, 1998, Vol. 34, No. 4, pages 408-409). For such a structure, made up of a thin film of GaAs on a silicon support, bonding by using an intermediate layer of silicon oxide has been used. The thin layer of GaAs is therefore electrically insulated from the silicon support. In the case of a solar cell constituted in this way, it is necessary to make an electrical connection on the front face and an electrical connection on the back face, electrical connection with the photo-voltaic thin layer being made through the substrate.
One solution to this problem can be found by choosing a conductive interface between the thin layer and its support, this interface then having also to provide the adhesion of t
Aspar Bernard
Bruel Michel
Jalaguier Eric
Burns Doane , Swecker, Mathis LLP
Commissariat a l'Atomique
Lee Eddie
Richards N. Drew
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