Surface morphologies of excimer-laser annealed BF 2+ implanted Si diodes

Abstract

Laser-induced surface roughness and damage formation in ultra-shallow n +–p and p +–n junctions, formed by low energy (5 keV) As + and BF 2 + implantations in Si, respectively, with a dose of 1 × 10 15 cm −2 have been investigated by atomic force microscopy (AFM) and Positron Annihilation Doppler Broadening (PADB) technique. The Si surface roughness is found to increase with laser energy density, and reaches a value of 3.5 nm after excimer-laser annealing (ELA) at 1100 mJ/cm 2. However, anomalous behavior is witnessed for BF 2 +-implanted Si sample at 800 mJ/cm 2, at which energy very high surface protrusions up to 9 nm high are observed. By PADB this behavior is correlated to extensive deep microcavity formation in the Si whereby the volatile F 2 fraction can accumulate and evaporate/out-diffuse, leading to Si surface roughening. The consequences for the diode characteristics and contact resistivity are examined.