Paper PS-TuP24
Effects of Etching-Mask Geometry and Charging on Etching Profile Evolution

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Two-dimensional etching profile evolution in two different geometries, an axisymmetric hole and an infinitely long trench, has been calculated to clear effects of etching-mask geometry and charging on etching profile evolution. In the simulation, SiO₂ etching by fluorocarbon plasmas is assumed because of widely employed processes for the fabrication of contact and via holes in the SiO₂ film. The model takes into account the transport of particles in microstructures, together with surface reactions therein through sputtering, ion-assisted etching, chemical etching, and deposition. The model includes ions and neutrals (CF_x⁺, CF_x, F; x=1-3) coming from the plasma, under different conditions of particle temperature, density, and ion energy. The neutral particles from the plasma onto substrate surfaces are assumed to travel in microstructures with diffusive reflections on feature surfaces, while the ions accelerated through the sheath on the substrate travel with specular reflections on feature surfaces. The cell removal method is employed to represent the feature profile evolution, where the SiO₂ is represented by two-dimensional discrete cells. Numerical results indicate that the etching profiles of hole and trench have the similar tendency under varying input parameters such as plasma species densities, ion energy, and mask aspect ratio. However, the etching-mask geometry shows some differences in the two structures; the resulting profile is narrower and shallower in the hole than in the trench, where the incident neutral fluxes are more reduced in the hole. Moreover, the profile of the trench has lateral etches such as undercut and bowing on sidewalls. The velocity distribution of neutral particles contributes to the difference of the etching profile evolution in the two structures; in effect, the velocity distributions are the more isotropic in the trench, because less neutral particles interact with mask sidewalls in the trench. Thus, it follows that geometrical structures contribute significantly to the behavior of neutral particles therein, and characterize the resulting etched profiles. The etching-mask geometry and the SiO₂-etched feature also make the differences in charging potential at the feature bottom in the trench being lower than in the hole, because the trench feature surface obtains more electron flux owing to its geometrically smaller shadowing effect.