Experimental and theoretical study of ion distributions near 300 μm tall steps on rf-biased wafers in high density plasmas

Abstract

We present an experimental and theoretical study of ion fluxes, energy distributions, and angular distributions close to 300 μm tall “steps” on rf-biased wafers in high-density argon plasmas. This feature size is important in the etching of microelectromechanical systems. The theory and data show good agreement in most of the trends in the ion distributions as our sampling point approaches the foot of the step: (1) the ion flux decreases, (2) the ions move away from vertical, turning towards the step, and (3) the widths of the double-peaked ion energy distributions become narrower. The theory predicts that the hot neutral flux near the foot of the step is comparable to the ion flux. These hot neutrals may have important effects on the etching process.