Surface smoothing and increase of conductivity in polycrystalline silicon films by laser irradiation

For application of polycrystalline silicon in SGT processes it is necessary to have a high conductivity in the polycrystalline layer. Several thermal methods are used to increase the conductivity of polysilicon, laser annealing is one of them. Laser irradiation in the ns-regime can be also used to smooth the surface of the polysilicon layer yielding to an increase of the breakdown voltage of the polysilicon oxide. The following results are discussed: (1) a thin surface layer of polysilicon is amorphized by ion implantation to get a high absorption of the laser light (wavelength 1.06 μm). Implantation provides not only amorphization but also additionally doping; (2) laser irradiation yields supersolubility of dopants decreasing the sheet resistance for 50%. The thermal stability of the supersolubility is investigated. Substantial decrease of conductivity takes place at annealing temperatures above 700 K; and (3) surface smoothing of the polysilicon causes an increase of the breakdown voltage of the polysilicon oxide for a factor of 2-3. Because the oxide is generated by anodic oxidation no deactivation of dopants occurs during the oxidation process. (author)