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Time-resolved measurement of surface displacement in excimer laser ablation of Si

The mechanism for removal of a single-crystal silicon in laser drilling using a KrF excimer laser was investigated. A time-resolved interference analysis was carried out to measure the surface profile of the Si during and after laser irradiation at a laser fluence in the range of 4 - 11 J/cm2. The 2nd harmonic output of a Q-switched Nd:YAG laser, the pulse duration of which was 10 ns, was used as the light source of the interferometer. The volume change of Si by melting and thermal expansion was directly observed. The formation and the growth of a sharp projection surrounding the laser-irradiated area was also observed during and after irradiation.