Pseudomorphic substrates
AssigneeIntevac, Inc.
InventorsRoger T. Green, Gary A. Davis, Verle W. Aebi
Life of this patent
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Abstract
High quality epitaxial layers can be grown on a multi-layer substrate which has a crystalline pseudomorphic layer with an exposed surface used for the epitaxial growth. The pseudomorphic layer of the substrate has a thickness at or below the pseudomorphic limit so it will be deformed as stress forces are developed during epitaxial growth of heteroepitaxial structures. A plastically deformable layer is bonded to the pseudomorphic layer, This plastically deformable layer is made of material that plastically flows at epitaxial growth temperatures.
Claims12
An article comprising:
- a substrate;
- and
- an epitaxial layer grown on the substrate;
- said substrate including:
- (a) a crystalline pseudomorphic material layer having a thickness no greater than a pseudomorphic limit for said crystalline pseudomorphic material layer and said epitaxial layer, the crystalline pseudomorphic material layer and the epitaxial layer having differing lattice constants to provide a tendency for a deformation to be imposed on the epitaxial layer;
- (b) a plastically deformable layer having a thickness sufficient to structurally withstand stress forces induced by the epitaxial layer on the pseudomorphic layer bonded to the crystalline layer prior to the epitaxial layer being grown on the crystalline pseudomorphic material layer so the crystalline layer is between the plastically deformable layer and the epitaxial layer, the plastically deformable layer being a material that plastically flows at the epitaxial layer growth temperature and having a coefficient of thermal expansion approximately equal to the coefficient of thermal expansion of the pseudomorphic material layer over a temperature range of approximately room temperature to the annealing temperature of the plastically deformable layer, the layers being such that the tendency for the epitaxial layer to be deformed is overcome without causing substantial crystal defects in the epitaxial layer.
A substrate with an exposed surface from which an epitaxial layer can be grown, said substrate including the combination of an about 0.040 inch thick sapphire mechanical support layer bonded to an about 0.008 inch thick glass plastically deformable layer characterized by an annealing temperature of about 581.degree. C. and a coefficient of expansion of about 62.times.10.sup.-7/ .degree.C. bonded to an about 300 .ANG. thick Si.sub.3 N.sub.4 encapsulating layer deposited on an about 150 .ANG. thick In.sub.0.49 Ga.sub.0.51 P pseudomorphic material layer.
Dependencies are inferred from the claim text.