engleski

Laser Induced Convection Patterns on SiON Thin Film

Laser irradiation of silicon-oxynitride (SiON) thin film generated the self organized structures (SO) characteristic for the surface parametric waves, Rayleigh-Benard convection, elekctroconvection and other phenomena were generated. The homogenized UV excimer beam of KrF laser of the wavelength 248 nm the SiON thin film of 0.8-1 µ m thick deposited on the Si <111> substrate has been irradiated. The multipulses irradiation (20-50) at the repertition frequency of 1Hz, of the pulse duration of 20 ns. The homogenization of the laser beam causes its decomposition into 210 independent beamlets which change the Gaussian power density distribution into flat one into x direction and partially into z direction. The energy of the laser beam 145 mJ was reduced due to homogenization to 65± 2 mJ which was deposited to the surface sample. The SO stuctures of various complexity levels and different orientations can be divided into the domains which comprised either regular, iregular or even chaotic structures. The Fourier spectrum (FS) of the stuctures indicate that they are determined by the wave vector band near the critical wave vector. For the irregular wave structures the preferential direction of the unstable wave vector doesn’ t exist so that FS has the form of the circle. The domains which compris regular structures the FS have the form of the arc, the position of which depends on the orientation of the structures. The meassured wave length of the regular wavy structures is about  2 µ m. The structures comprise great number of defects in the form of dislocations, disclinations, domain boundaries and other irregular formations. The numerical simulation based on the Swift Hohenberg (SH) equation gives excelent qualitative agreement of the structures. The SH equation represents the model describing the structures generated by the gradient of the thermal field perpendicular to the target surface. The domains with the regular wavy structures corresponds to the bifurcation which occur slightly above the critical point. On the other hand, domains with chaotic structures corresponds to bifurcations much above the critical point on the bifurcation diagram and include a band width a number of wave vectors which cause instability. Besides the patterns of the wavy structures the numerical simulation also generated the structural defects in very god qualitative agreement with the observed one.

laser material interaction

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