Properties of laser-assisted doping in silicon

Abstract

Ohmic contacts and p‐n junctions in p‐ and n‐type silicon are generated with the aid of a laser. Doping was achieved by covering the surface of the silicon with a layer of dopant and melting locally with pulses from either a Nd : YAG or a CO₂ laser. Typical residual resistances of the Ohmic contacts are of the order of 0.1–1 Ω cm² and backward/forward resistance ratios of 10⁴ were measured for the diodes. A model which takes account of segregation during the cooling process is discussed and shown to agree with the resulting distribution of dopant. Highly doped material was found in a surface layer of a thickness less than 0.5 μm. This thickness was independent of laser parameters.