Low defect density/arbitrary lattice constant heteroepitaxial layers
AssigneeInternational Business Machines Corporation
InventorsFrancoise Kolmer Legoues, Bernard Steele Meyerson
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Abstract
A multi-layered structure and process for forming it arc described, incorporating a single crystal substrate, a plurality of epitaxial layers having graded composition wherein the layers have changing lattice spacings not exceeding about 2 percent per 1000 .ANG. of thickness whereby misfit dislocations are formed to relieve strain and then move to the edges of respective layers. The invention overcomes the problem of large numbers of misfit dislocations threading to the surface of the top layer, especially during device processing at temperatures in a range from 700 to 900 degrees Celsius. Fully relaxed, incommensurate structures having low defect densities are obtained, where arbitrary combinations of materials can be used.
Claims20
A method for forming an incommensurate crystalline film of arbitrary lattice spacing above crystalline layers comprising the steps of:
- selecting a first substrate of single crystalline material having a first set of lattice parameters and a clean upper surface,
- first forming a plurality of epitaxial layers on said clean upper surface,
- said step of first forming including the step of varying the composition of a number of said plurality of epitaxial layers to change one or more lattice parameters of said number of said plurality of epitaxial layers less than 2 percent per 1000 .ANG. of thickness whereby misfit dislocations in said selected layers migrate to the respective edges of said number of said plurality of epitaxial layers during said step of first forming thereby forming said incommensurate crystalline film above said number of said plurality of layers, said step of first forming including the step of forming at a temperature less than about 650.degree. C.
A process for forming a structure including relaxed incommensurate layers including a final epitaxial layer of low crystallographic defect density, comprising the following steps:
- depositing on a single crystalline substrate a first epitaxial layer of graded composition where said composition is graded at a rate of less than 2 percent per 1000 .ANG. thickness whereby misfit dislocations formed in said first epitaxial layer migrate to the edges of this layer as it is formed to provide a top surface layer of said first epitaxial layer having crystallographic defects therein of less than about 10.sup.5 /cm.sup.2, said first epitaxial layer being formed at a temperature less than about 650.degree. C.,
- continuing the growth of said first epitaxial layer at a substantially constant composition, and
- forming a second epitaxial layer on said first epitaxial layer, said second epitaxial layer being of adequate thickness to ensure relaxation of said second epitaxial layer to an equilibrium, strain-free lattice constant substantially matched to the lattice constant of said top surface layer of essentially constant composition of said first epitaxial layer.
A method for producing a structure including a crystalline substrate and an epitaxial layer thereover including the steps of:
- providing a crystalline substrate, having a first lattice parameter,
- forming a first epitaxial layer thereon of graded lattice parameter, said first epitaxial layer having a lattice parameter substantially the same as that of said substrate at the interface of said epitaxial layer and said substrate, said lattice parameter being graded less than 2 percent per 1000 .ANG. thickness of said first epitaxial layer to produce a surface region thereof having a second lattice parameter, whereby pinning of threading dislocations in said first epitaxial layer is reduced to provide a top surface having a density of crystallographic defects of less than about 10.sup.5 /cm.sup.2,
- said step of forming including the step of forming at a temperature less than about 650.degree. C.
Dependencies are inferred from the claim text.