Sheath Voltage Estimation for Inductively Coupled Plasma Etcher by Impedance Analysis

A thick quartz glass is etched using an inductively coupled plasma device under constant antenna power. Sheath voltage, which is the RF voltage from the plasma edge to the sample surface, is estimated by impedance analysis. Sheath resistance and sheath capacitance are determined from some experimental bias voltage, which is the RF voltage applied to the sample bed electrode. Once they are determined, the bias and sheath voltages for arbitrary thick samples and bias power can be calculated. The calculated bias voltages agree with the experimental ones within 5%. Etching rate is proportional to sheath voltage for various etching conditions. A quartz sample 5-mm-thick can be etched at the same etch rate as a thin quartz sample using a thick quartz sample bed with a hole where the quartz sample is placed.