Patent ID: 6852371

Claim:
A method of dissociation, dissolution, and gettering of precipitate impurities in a silicon wafer that has a front face and a back face substantially opposite each other and a layer of gettering metal selected from a group consisting of Al, Pd, Ni, or Pt on the back face which forms a silicon/metal interface, comprising: propagating light energy through the silicon wafer from the front face to the silicon/metal interface with sufficient optical power density to melt the gettering metal at the silicon/metal interface, while keeping the temperature of the silicon wafer less than 550° C. for a sufficient first period of time to cause interstitial silicon Si(i) insertion into the gettering metal to thereby create and insert enough vacancies V in the silicon wafer to saturate& the silicon wafer with vacancies V; increasing the optical power density level for a sufficient second time period to increase the silicon wafer temperature to at least 700° C., but not more than 900° C., to activate the vacancies V in the silicon wafer to induce dissociation and dissolution of the precipitate impurities in the silicon and to achieve the dissociation and dissolution of the precipitate impurities; allowing the dissolved impurities resulting from such dissociation of the precipitate impurities to diffuse and migrate to the melted gettering metal; and ramping down the optical power density and cooling the silicon wafer enough to solidify the gettering metal and capture the impurities that have diffused and migrated to the gettering metal.