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Method for Increasing Grain Size in Silicon and Germanium by Successive Doping

IP.com Disclosure Number: IPCOM000042952D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Grovenor, C: AUTHOR [+3]

Abstract

The presence of grain boundaries in semiconductors is often undesirable, but tolerated for reason of economy and ease of fabrication. Grain boundaries increase the resistivity of semiconductors by scattering majority carriers and by trapping dopants, by segregation, in an electrically inactive state. A technique is described for the migration of grain boundaries to produce polycrystalline semiconductors with exceptionally large grain size. The method of this invention is the alloying of semiconductors, specifically Si and Ge, to cause grain boundary migration. Two or more successive doping treatments used in the temperature range, 0.3Tm < T < 0.5Tm, where Tm is the absolute melting temperature of the semiconductor.

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Method for Increasing Grain Size in Silicon and Germanium by Successive Doping

The presence of grain boundaries in semiconductors is often undesirable, but tolerated for reason of economy and ease of fabrication. Grain boundaries increase the resistivity of semiconductors by scattering majority carriers and by trapping dopants, by segregation, in an electrically inactive state. A technique is described for the migration of grain boundaries to produce polycrystalline semiconductors with exceptionally large grain size. The method of this invention is the alloying of semiconductors, specifically Si and Ge, to cause grain boundary migration. Two or more successive doping treatments used in the temperature range, 0.3Tm < T < 0.5Tm, where Tm is the absolute melting temperature of the semiconductor. The temperature T is selected to be in the range where bulk diffusion is very slow but grain boundary diffusion is rapid. The dopants are selected to be substitutional solutes which have increasing affinities for the solvent, so that the earlier deposited dopants are displaced by the later deposited dopants. As an example of this process, a treatment to provide very large grained polysilicon is to dope with Sb, then to dope with As, and finally to dope with P. This produces polysilicon with grain sizes in the range 100-1000 times larger than those in intrinsic polysilicon. This process yields polysilicon semiconductors with exceptionally large grain sizes. The electrical pro...