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We have performed diagnostic measurements and polysilicon etching experiments using a halfwave radio frequency helical resonator (BR) source with a 150 mm b 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 I HBr at low pressure (-io 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 ? 10 cm3 in a 1000 W discharge. In a Cl2/20% HBr feed gas mixture we obtain > 3000 A/mm for undoped polysiicon, 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.

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