Paper PS1-ThM6
Geometrical Effects on Etching Profile Evolution

Thursday, October 18, 2007, 9:40 am, Room 606

Two-dimensional etching profile evolution in two different geometries, an axisymmetric hole and an infinitely long trench, has been calculated to clear the effects of geometrically different structures on etching profile evolution. In the simulation, SiO₂ etching by CF₄ plasmas is assumed because of widely employed processes for the fabrication of contact and via holes, which have various and unique geometrical shapes. 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 simulation domain is enclosed by the sheath-surface interfaces and the feature surfaces of SiO₂ with an inert etching mask. 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 different plasma conditions. However, the two etching profiles have some differences each other; the profile evolution is narrower and slower 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 lateral etches decrease with increasing the ratio of neutral fluorocarbon fluxes, where the neutral fluorocarbons contribute to deposition. The velocity distribution of neutral particles also contribute to the difference of the etching profile evolution in the two structures; in effect, the velocity distributions are the more anisotropic in the hole, because more neutral particles interact with mask sidewalls in the hole, so that more anisotropic particles are conducted onto bottom surfaces after passing the mask features. Thus, it follows that geometrical structures contribute significantly to the behavior of neutral particles therein, and characterize the resulting etched profiles.