Anisotropic Si Etching by a Supersonic Cl₂ Beam

Abstract

Perpendicular etching profiles of n⁺-Si(100) are obtained with a supersonic Cl₂ beam at substrate temperature of 900°C. Although small undercuts are observed just below the SiO₂ mask, the side wall etching caused by the background Cl₂ is almost negligible. An aspect ratio of greater than 6 and selectivity of greater than 8000 are obtained with 0.5 µm line & space mask pattern. From Arrhenius plots of etch rates, an effective activation energy of the nozzle beam etching is determined to 0.53 eV. Assuming that the reaction product is SiCl₂, the reaction probability is estimated to be 19% at 900°C. Highly anisotropic etching of the Si(100) obtained here is due to the large reaction probability.