Photothermal Activation of Shallow Dopants Implanted in Silicon

Dopant impurities were implanted at high dose and low energy (10 cm, 0.5–2.2 keV) into double-side polished 200 mm diameter silicon wafers and electrically activated to form p–n junctions by 10 s anneals at temperatures of 1,025, 1,050, and 1,075 C by optical heating with tungsten incandescent lamps. Activation was studied for P, As, B, and BF2 species implanted on one wafer side and for P and BF2 implanted on both sides of the wafer. Measurements included electrical sheet resistance (Rs) and oxide film thickness. A heavily boron-doped wafer, which is optically opaque, was used as a hot shield to prevent direct exposure to lamp radiation on the adjacent side of the test wafer. Two wafers with opposing orientations with respect to the shield wafer were annealed for comparison of exposure to, or shielding from, direct lamp illumination. Differences in sheet resistance for the two wafer orientations ranged from 4% to 60%. n-Type dopants implanted in p-type wafers yielded higher Rs when the implanted surface was exposed to the lamps, as though the effective temperature had been reduced. p-Type dopants implanted in ntype wafers yielded lower Rs when the implanted surface was exposed to the lamps, as though the effective temperature had been increased. Effective temperature differences larger than 5 C, which were observed for the P, B, and BF2 implants, exceeded experimental uncertainty in temperature control.