<title>Formation of reversible and irreversible structural defects on silicon surface under laser-pulsed influence</title>

Modeling Laser Effects on the Final Optics in Simulated IFE Environments

“…The results of experimental studies of laser irradiation of single crystal silicon wafers have been reported in (Emel'yanov, 1992;Banishev et al, 1992). On increasing laser intensity in normal irradiation, the following succession of patterns has been reported.…”

“…Comparing to the experimental conditions of (Banishev et al, 1992), this corresponds to a vacancy density of the order of C + 5.10 18 cm −3 , or a film top surface temperature T + of about 1000 K ( 0.7T m ). This temperature is given by :…”

“…Diffusion along the z-direction is neglected, since "bulk" diffusion is much slower than surface diffusion (in usual experimental conditions, D τ 10 −5 cm 2 and |θ v | 10 −10 erg (Emel'yanov, 1992;Banishev et al, 1992). The displacement vector , U, and the deflection of the film's neutral surface, ξ, are related by :…”

“…For example, in the case of thin films under laser irradiation, regular deformation patterns may appear on the film surface when the laser intensity exceeds some threshold. In spatially extended irradiation zones, one-and two-dimensional gratings have been widely observed (Banishev, Emel'yanov, and Novikov, 1992;Young, Preston and van Driel, 1983b). Figure 31: Geometry of the thin film-substrate system subjected to a uniform laser beam, showing a schematic illustration of the proposed surface deformation mechanism.…”

“…However, in these papers, defect generation and transport have been considered as isotropic, which is not applicable for crystals with strong covalent bonding. For example, deformation patterns formed on Si surfaces depend on the laser field orientation in relation to crystallographic axes (Banishev et al, 1992;Young et al, 1983b;Emel'yanov, 1992). This effect is of practical importance, since the corresponding defect accumulation induces a local decrease in the melting temperature, and can also influence the Laser Induced Damage threshold (LIDT) (Wood, 1986;Bennett, Guenther, Kozlowski, Newnam and Soileau, 1995).…”