Etching with electron beam generated plasmas

Abstract

A modulated electron beam generated plasma has been used to dry etch standard photoresist materials and silicon. Oxygen–argon mixtures were used to etch organic resist material and sulfur hexafluoride mixed with argon or oxygen was used for the silicon etching. Etch rates and anisotropy were determined with respect to gas compositions, incident ion energy (from an applied rf bias) and plasma duty factor. For 1818 negative resist and i-line resists the removal rate increased nearly linearly with ion energy (up to 220nm∕min at 100eV), with reasonable anisotropic pattern transfer above 50eV. Little change in etch rate was seen as gas composition went from pure oxygen to 70% argon, implying the resist removal mechanism in this system required the additional energy supplied by the ions. With silicon substrates at room temperature, mixtures of argon and sulfur hexafluoride etched approximately seven times faster (1375nm∕min) than mixtures of oxygen and sulfur hexafluoride (∼200nm∕min) with 200eV ions, the difference is attributed to the passivation of the silicon by involatile silicon oxyfluoride (SiOxFy) compounds. At low incident ion energies, the Ar–SF6 mixtures showed a strong chemical (lateral) etch component before an ion-assisted regime, which started at ∼75eV. Etch rates were independent of the 0.5%–50% duty factors studied in this work.