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Impurity gettering in silicon using cavities formed by helium implantation and annealing

United States Patent

*** EXPIRED ***
November 24, 1998
View the Complete Patent at the US Patent & Trademark Office
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Impurity gettering in silicon wafers is achieved by a new process consisting of helium ion implantation followed by annealing. This treatment creates cavities whose internal surfaces are highly chemically reactive due to the presence of numerous silicon dangling bonds. For two representative transition-metal impurities, copper and nickel, the binding energies at cavities were demonstrated to be larger than the binding energies in precipitates of metal silicide, which constitutes the basis of most current impurity gettering. As a result the residual concentration of such impurities after cavity gettering is smaller by several orders of magnitude than after precipitation gettering. Additionally, cavity gettering is effective regardless of the starting impurity concentration in the wafer, whereas precipitation gettering ceases when the impurity concentration reaches a characteristic solubility determined by the equilibrium phase diagram of the silicon-metal system. The strong cavity gettering was shown to induce dissolution of metal-silicide particles from the opposite side of a wafer.
Myers, Jr.; Samuel M. (Albuquerque, NM), Bishop; Dawn M. (Albuquerque, NM), Follstaedt; David M. (Albuquerque, NM)
Sandia Corporation (Albuquerque, NM)
08/ 160,704
December 1, 1993
The United States Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 between the Department of Energy and American Telephone and Telegraph Company.