A hybrid fluid-Monte Carlo simulation of laser ablation of Cl/sub 2/ (s)

Summary form only given. Recently, wafer charge damage considerations in high density plasma processing reactors have prompted the development of neutral beam sources for etching. Anisotropic etching of Si has been demonstrated using a beam of vibrationally excited Cl/sub 2/. Despite this, the mechanism of anisotropic etching by neutral beam sources is still not well understood. Two requirements for any neutral beam source for etching applications are that the beam be highly directed (that there be little spread to the beam) and that the directed flux of etching precursors be sufficiently high to achieve a reasonable etch rate. Laser ablation of a target material such as frozen Cl/sub 2/ may meet these requirements. Ions, nonetheless, may be important so we consider the case in which the laser beam from an excimer laser, for example, would be incident off the normal of the pellet surface. By modifying the laser energy, the ion content and degree of dissociation of the neutral beam could be prescribed. This scheme is being investigated using a 2-dimensional hybrid fluid-Monte Carlo simulation with a plasma chemistry scheme. The fluid model is a solution of the drift-diffusion equations and Poisson´s Equation. A semi-implicit field solution is used to obtain solutions in reasonable execution times. Electron transport coefficients and reaction rates for the pertinent electron collision processes are calculated from a Monte Carlo simulation, the electric fields and species densities being supplied from the fluid model. The initial plume properties are estimates. Although a zero density boundary condition is used for charged particles after ablation occurs, a non-zero density boundary condition is considered in which the densities of charged species are calculated using a time-splitting scheme in which the rate of accumulation of charge and total charge density (at the surface) are calculated self-consistently.