Evaporation loss and diffusion of antimony in silicon under pulsed laser irradiation

Abstract

We have studied the loss and diffusion of Sb in Si from a 750 Å thick Sb layer evaporated on 〈111〉 Si wafers under pulsed laser irradiation. A 7 ns (fwhm) duration pulse from a Nd : glass laser ( λ = 1.06 μm) was used. RBS analysis with a 1.8 MeV He + beam was done to obtain depth profiles of Sb in Si. The loss of Sb increases with laser energy density upto 1.7 J/cm 2 without appreciable diffusion. At higher energy densities, the evaporation loss of Sb saturates as diffusion sets in. Large diffusion tails up to depths ≳1.2 μm are observed at 8.9 J/cm 2. Surface topography of laser-treated region was studied with a Scanning Electron Microscope. The surface topography varies dramatically with the incident laser energy density. A novel feature is the appearance of a curious ‘criss-cross’ line pattern with spacings close to wavelength of laser light at lower energy densities. At high energy densities, considerable damage to the Si surface is observed. Our results indicate that a careful choice of the laser energy density and pulse duration has to be made for a practical application of the technique of doping in semiconductors by laser treating an evaporated dopant layer.