Consequences of implanting and surface mixing during Si and SiO2 plasma etching

Summary form only given. Fluorocarbon plasmas are widely used in Si and SiO₂ etching. The generally accepted mechanism includes:1 a) ion activation of sites to produce a SiC_xF_y or SiO₂C_xF_y complex layer, b) deposition of C_xF_y polymer layer on top of the complex and c) etching the complex by releasing volatile etch products, such as COF_x and SiF_x. Since the ion energies typically used in dielectric etching can be many hundreds of eV, mixing of the surface layers and implantation can occur. The mixing can produce a more reactive surface which could increase the etch rate but the mixing is also a form of damage. Small molecular or atomic ions are capable of penetrating through the polymer and complex layers, and be trapped in the SiO₂ or Si lattices. High energy molecular ions striking the surface are partly dissociated to generate smaller molecules and atoms which, if retaining energy, can also implant. Species with lower energy may implant into the polymer or complex layer as well. These weakly bonded or interstitial species may eventually diffuse back into the plasma. These implant and mixing processes have been incorporated into the MCFPM (Monte Carlo feature profile model). Using fluxes to the surface in a capacitively coupled plasma for Ar/C₄F₈/O₂ mixtures obtained from the HPEM (hybrid plasma equipment model), the consequences of mixing and implantation on etching of Si and SiO₂ were investigated. Mixing depth, etching rate and feature profiles will be discussed as a function of incident ion energy and angular spread.