Pulsed CO(sub 2) laser processing of thin ion-implanted silicon layers

摘要

We show that extremely shallow ((approx lt) 800 (Angstrom)) melt depths can be easily obtained by irradiating a thin heavily doped silicon layer with a CO(sub 2) laser pulse. Since the absorption of the CO(sub 2) laser pulse is dominated by free-carrier transitions, the beam heating occurs primarily in the thin degenerately doped film. For CO(sub 2) pulse-energy densities exceeding a threshold value, surface melting occurs and the reflectivity of the incident laser pulse increases abruptly to about 90%. This large increase in the reflectivity acts like a switch to reflect almost all of the energy in the remainder of the pulse, thereby greatly reducing the amount of energy available to drive the melt front to deeper depths in the material. Transmission electron microscopy shows no extended defects in the near-surface region after laser irradiation, and van der Pauw electrical measurements verify that 100% of the implanted arsenic dopant is electrically active. 8 refs., 3 figs., 1 tab.