Droplet formation during laser sputtering of silicon

High purity single-crystal silicon was ablated with nitrogen laser radiation wavelength 337 nm, pulse length 6 ns, maximal energy density 1.1 J/cm(2), nonuniform. target energy distribution. Many droplets were observed around the damaged target area, which seem to be ejected out of it and splashed vigorously onto the surrounding target surface. Their diameters are found to be in the range of a micrometer. The droplets were most probably produced within a single laser pulse as a result of hydrodynamical instability of the molten surface layer. Intense splashing occurs as a consequence of the large plume pressure generated by the most intense parts of the laser beam. The irregular power distribution on the target seems to enhance droplet formation significantly, since their abundance is drastically lower or even missing in similar experimental conditions but with uniform power distribution. (C) 1998 Elsevier Science B.V. All rights reserved.