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Method to produce germanium layers
| Details |
Inventors: Seifert, Werner;
Assignee: BTG International Limited (London, GB)
Primary Examiner: Nelms; David
Assistant Examiner: Lee; Calvin
Attorney, Agent or Firm: Miles & Stockbridge P.C.
A method of producing a very large area germanium layer on a silicon substrate, comprises forming an initial layer of germanium on the silicon substrate such that rounded S—K protuberances are produced by lattice mismatch. Oxidation produces silicon dioxide between the protuberances, and a subsequent reduction step exposes the tops of the protuberances. Since the top regions are almost perfectly relaxed and free of stress, these form nucleation sites for the subsequent growth of a final layer of germanium, formed as single crystals each extending from a nucleation site. |
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DETAILED DESCRIPTION It is an object of the invention to provide an improved method for producing germanium or other layers of large area.
In a first aspect, the present invention provides a method of producing a layer of a desired material, the method comprising: a) providing a substrate of silicon, having a different lattice constant from said desired material, and depositing said desired material on the substrate such that rounded protuberances are produced; b) filling the areas between the protuberances with a non-crystalline material; and c) depositing again said desired material, the rounded protuberances serving as growth sites whereby to produce a layer of said material.
In a second aspect, the invention provides a semiconductor structure comprising a substrate of silicon, protuberances of a desired material formed on the substrate surface, said protuberances having a rounded shape, and the desired material having a different lattice constant from that of silicon, a layer of non-crystalline material being formed between the protuberances, and a layer of said desired material being formed on top of, and in contact with, the rounded protuberances.
The layer of material is essentially formed in step c) as single crystals extending from each protuberance.
Depending on the intended application, the crystals may extend to form a more or less continuous layer; alternatively the growth may continue to form a layer of uniform thickness.
The protuberances may be formed on the substrate in any desired way.
For example the substrate may be prepared to define sites on which the desired material may be deposited, by lithography or other methods (for example, that described in our copending application WO 01/84238).
However it is preferred to grow an initial layer of the material uniformly on the substrate, and this creates in known manner, once the layer exceeds a certain thickness, Stranski Krastanov (SK) pyramidal shaped bumps caused by buckling of the layer under strain.
In accordance with the invention, these pyramidal-shaped bumps are increased in size until they become rounded in shape, in the form of a dome
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MEMS 
