Characterization of plasma etch processes using measurements of discharge impedance

Abstract

Actual power delivered to the discharge, rf voltage, rf current, phase angle, and dc bias have been measured using commercially available impedance and power meters placed directly on the powered electrode of a parallel-plate diode etcher. The variation of these electrical quantities as discharge parameters such as power, pressure, electrode spacing, gas mixing ratio, and total flow are varied has been investigated for both electropositive and electronegative gases. It was found that the transfer efficiency of the matching network depends significantly on the process conditions and can be as low as 55% of the generator output. Polysilicon etch rate experiments were performed to determine the effect of varying the actual power delivered to the discharge and possible interaction with other process parameters such as pressure, as opposed to considering solely the rf generator output. End point was detected by measuring the change in the discharge impedance while etching through a polysilicon film. The sensitivity of this technique was compared with that of more commonly used optical emission methods.