The magnetized helical resonator plasma etcher has been built. Electron density and temperature were measured as functions of rf source power, axial magnetic field, and pressure. The results show electron density increases as the magnetic field increases and reached <TEX>$2 imes1012cm^{-3}$,/TEX>. The oxide etch rate and selectivity to polysilicon were investigated as the above mentioned conditions and self-bias voltage. We can obtain the much improved oxide etch selectivity to polysilicon (60 : 1) by applying the external axial weak magnetic field in magnetized helical resonator plasma etcher.