We have performed diagnostic measurements and polysilicon etching experiments using a halfwave radio frequency helical resonator (HR) source with a 150 mm ? discharge to develop and characterize this technology for low-pressure, high density plasma processing. This discharge source was applied to submicron, anisotropic etching of polysilicon gates using Cl2 and Cl2 /HBr at low pressure (~ 10-3 torr). A solenoidal magnetic field ~60 G along the discharge tube axis enhances plasma density between the source and wafer by a factor of 3–4 to > 1011 cm-3 in a 1000W discharge. In a Cl2/20% HBr feed gas mixture we obtain >3000 Å/min for undoped polysilicon, vertical profiles, and no proximity effects using -10 Vdc additional bias imposed on the wafer. Selectivities for polysilicon over gate oxide and trilevel resist were 50:1 and 4:1, respectively, with no bias during the overetching step.