Molecular-beam study of the plasma-surface kinetics of silicon dioxide and photoresist etching with chlorine

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The plasma-surface kinetics of silicon dioxide and photoresist etching in chlorine were measured by beam scattering in which the Ar+, Cl, and Cl2 beams were independently controlled at fluxes comparable to a high-density plasma etching process. The etching was characterized as a function of Ar+ ion energy, ion flux, chlorine-to-ion flux ratio, and the ion impingement angle. Molecular chlorine did not enhance the etching of silicon dioxide, but atomic chlorine enhanced the etching of oxide by a factor of 4 at flux ratios around 100. The ion energy dependence for oxide was a linear function of (Eion1/2−Eth1/2), where the threshold energy Eth was found to be approximately 40 eV. The oxide angular dependence showed a maximum etching yield at ∼60° off-normal ion incident angle, indicating that physical sputtering is the rate limiting mechanism. Angular resolved x-ray photoelectron spectroscopy analysis suggests that ion bombardment sputters oxygen and allows atomic chlorine to bond to silicon. The etching of chlorinated silicon is assumed to be enhanced by subsequent ion bombardment in a manner similar to ion enhanced polysilicon etching with chlorine. The angular dependence of photoresist etching exhibited a maximum at ∼60° off-normal ion incident angle, indicating that sputtering is the important etching mechanism.