Linewidth control in anisotropic plasma etching of polycrystalline silicon

Linewidth control in anisotropic plasma etching of polycrystalline silicon using CF3Cl and CF3Cl/C2F6, gas mixtures was investigated. Experiments were performed in a radial flow plasma etcher utilizing endpoint detection consisting of RF power or electrode d.c. bias monitoring. Etch rate, selectivity of etching polysilicon over SiO2and the amount of mask undercutting were all observed to be functions of the gas composition with pure CF3Cl giving the highest values for each. Lateral etching or mask undercutting was found to accelerate at the endpoint for all compositions, and was more severe for rich CF3Cl mixtures. Etching characteristics and etched polysilicon wall profiles suggest an etching mechanism domimated by surface diffusion of free Cl atoms with the Cl concentration and lifetime moderated by etching reaction and recombination reactions with CF3.