Patterning of silicon – differences between nanosecond and femtosecond laser pulses

Si 100.surfaces were exposed to 8 ns and 100 fs laser pulses with fluencesF3 Jrcm2and F0.5 Jrcm2, respectively. Transient stages and final patterns were investigated by pulsed photoelectron microscopy and scanning electron plus light interference microscopy. Though the pattern formation extends for both pulse lengths over the same time of some 10 ns, the patterns are different. Nanosecond pulses produce smooth craters and remove a covering oxide. Femtosecond pulses ablate an oxide-free Si surface and produce flat pits covered by nanodrops, whereas oxide-covered surfaces are converted to a foam, which solidifies to a blistered structure. q1999 Elsevier Science B.V. All rights reserved