Etching experiments have been conducted on phosphorus doped Si 〈100〉 samples in low pressure SF6/Ar microwave multipolar plasmas which have been characterized. The influence of SF6partial pressure on anisotropy has been determined. Strictly anisotropic etching of silicon was obtained under SF6pressure of about 3×10−4Torr in an SF6/Ar gas mixture, the total pressure being (3–5)×10−3Torr. An etching rate of ∼150 nm/min, without any undercutting, has been achieved under low energy ion impact. The anisotropic etching mechanisms involved in the SF6/Ar system are discussed.