Substrate with determinate thermal expansion coefficient

Abstract

A process for reducing defects during formation of a transfer layer on a composite support having a central layer with a first thermal expansion coefficient. The method includes providing the composite support with at least one pair of lateral layers about the central layer, with the layers of each pair having second thermal expansion coefficients and thicknesses that are substantially identical to one another to thus provide the composite support with an overall thermal expansion coefficient that is sufficiently close to that of the transfer layer; conducting crystalline growth of the transfer layer on a growth substrate; bonding the transfer layer to the composite support; and removing the growth substrate to provide the transfer layer on the composite support without generating an excessive number of defects in the transfer layer due to the matching of the overall thermal expansion coefficients of the composite substrate and transfer layer.

1 . A process for reducing defects during formation of a transfer layer on a composite support having a longitudinal plane of symmetry that is parallel to its principal surfaces and that passes through a central layer thereof that has a first thermal expansion coefficient at a specified temperature T, which method comprises:
 providing the composite support with at least one pair of lateral layers about the central layer, with the layers of each pair having second thermal expansion coefficients at the temperature T that are substantially identical to one another and having thicknesses that are substantially identical to one another to thus provide the composite support with an overall thermal expansion coefficient at the temperature T that is sufficiently close to that of the transfer layer at the temperature T; and   epitaxially growing the transfer layer on the composite substrate by chemical vapor deposition or molecular beam epitaxy without generating an excessive number of defects in the transfer layer due to the sufficiently close matching of the overall thermal expansion coefficient of the composite support and that of the transfer layer.   
     
     
         2 . The process of  claim 1 , wherein the transfer layer is crystalline and is epitaxially grown on a growth substrate other than the composite support; and the process further comprises bonding the transfer layer and growth substrate to the composite support; and then removing the growth substrate to provide the transfer layer on the composite support. 
     
     
         3 . The process of  claim 2 , wherein the growth substrate is removed by etching or by providing a region of weakness subjacent the transfer layer and supplying energy to the region of weakness in order to detach the transfer layer from the growth substrate. 
     
     
         4 . The process of  claim 1 , wherein the second thermal expansion coefficients of the layers of each pair at the temperature T are different from that of the central layer, and the layers of each pair made of materials, thicknesses and arrangements about the central layer to provide the composite support with symmetry of thermal expansion coefficients about the longitudinal plane of symmetry and with an overall thermal expansion coefficient at the temperature T that is sufficiently close to the thermal expansion coefficient of the material of the transfer layer to avoid substantial deflection. 
     
     
         5 . The process of  claim 1 , which further comprises providing the layer of the composite support that is intended to support the transfer layer to be of a material that has a lattice parameter that is sufficiently close to that of the material of the transfer layer to avoid generating high internal strain in the transfer layer. 
     
     
         6 . The process of  claim 1 , which further comprises providing the central layer to be made of SiC, providing each of the lateral layers to be the same and to be made of crystalline or polycrystalline AlN, SiC, sapphire, or Si material, and providing the transfer layer to be GaN. 
     
     
         7 . The process of  claim 1 , wherein each layer of the pairs of layers have a thickness on the order of 1 μm to 1000 μm. 
     
     
         8 . The process of  claim 1 , which further comprises producing electronic components in or on the transfer layer before or after bonding of the transfer layer of the temporary substrate to the composite support. 
     
     
         9 . The process of  claim 1 , which further comprises crystalline growth by epitaxy of a useful layer on the transfer layer before bonding of the transfer layer and the growth substrate to the composite support. 
     
     
         10 . The process of  claim 7 , which further comprises producing electronic components in or on the useful layer before bonding of the transfer layer and the growth substrate to the composite support. 
     
     
         11 . The process of  claim 1 , which further comprises crystalline growth by epitaxy of a useful layer on the transfer layer after removing the growth substrate. 
     
     
         12 . The process of  claim 9 , which further comprises producing electronic components in or on the useful layer. 
     
     
         13 . The process of  claim 1 , wherein the outermost pair of lateral layers are made of an oxide to assist in the bonding of the transfer layer to one of the layers of the outermost pair. 
     
     
         14 . The process of  claim 1  which further comprises epitaxially growing additional pairs of layers on the transfer layer, each pair including an additional transfer layer and an intermediate layer subjacent the additional transfer layer to provide a multilayer structure. 
     
     
         15 . The process of  claim 14 , which further comprises providing the transfer layer with an epitaxial nucleation layer for generating the additional transfer layers. 
     
     
         16 . A process for forming an epitaxy substrate having a transfer layer thereon with reduced defects which comprises:
 providing the multilayer structure of  claim 14 ; and   removing a transfer layer from the multilayer structure by:
 implanting atomic species into the intermediate layer subjacent the transfer layer in order to create therein a region of weakness in the vicinity of the implant depth; 
 bonding the transfer layer to a composite support; and 
 supplying energy to the region of weakness in order to detach the transfer layer from the multilayer structure while also providing a remaining portion of the intermediate layer on the detached transfer layer; and 
   selectively etching the remaining portion of the intermediate layer on the transfer layer, thus producing an epitaxy substrate comprising the composite substrate and the transfer layer.   
     
     
         17 . The process of  claim 16 , which further comprises preparing the surface of the multilayer structure from which the transfer layer was detached for use in a subsequent layer transfer. 
     
     
         18 . The process of  claim 17 , wherein the preparing of the surface of the multilayer structure includes providing an epitaxial nucleation layer thereupon for generating a further epitaxial layer to be transferred. 
     
     
         19 . The process of  claim 16 , which further comprises repeating the removing of additional transfer layers to create further epitaxy substrates. 
     
     
         20 . The process of  claim 16 , which further comprises providing a plurality of crystalline growth layers on the plurality of transfer layers, so as to form a plurality of respective useful layers to be transferred with the transfer layer.