Pulsed TEA CO2 laser surface modifications of silicon

Abstract

The interaction of a transversely excited atmospheric (TEA) CO2 laser, pulse duration of about 2μs (FWHM of initial spike=120ns), with p-type single crystalline silicon doped by boron, was studied. The results have shown that the silicon was surface modified by the laser beam of 12.0Jcm−2 energy density. The energy absorbed from the CO2 laser beam is converted partially into thermal energy, which generates a series of effects such as melting, vaporisation of molten material, shock waves, etc. Morphological manifestations on the silicon surface are: nonuniform modifications (central zone of interaction); wave-like periodical microstructure (inner periphery zone); hydrodynamical structure-like droplets (outer periphery zone). Wave-like microstructure consists of periodic parallel fringes with a period of about 0.8μm. Formation of these wave-like microstructures is very complex. Explanation includes a consideration of the laser-induced periodic surface structure (LIPSS) effect. The process of the CO2 laser interaction with silicon was not initially accompanied by plasma. Plasma, in the form of a spark, typically appeared after about 100 cumulated laser pulses.