Improvement of photoresist etching by impedance control of a bias electrode in an inductive discharge

Abstract

To improve the photoresist (PR) etching in inductively coupled plasma (ICP) without the use of bias power, an impedance control unit is connected in series to the bias electrode of the ICP. This impedance control unit consists of an inductor and a variable capacitor to control the impedance of the bias electrode. With the series resonance of the sheath capacitance and inductance of the bias electrode impedance, the current flowing through the bias electrode increases dramatically, resulting in a higher voltage across the sheath and larger ion energy loss. The effect of series resonance on the decrease of electron density, as observed by a Langmuir probe, is illustrated by a global power balance model. As the capacitance approaches the series resonance condition, the larger ion energy leads to an enhanced PR etch rate, and the more uniform profile of the radio frequency (RF) plasma potential results in more uniform distributions of ion energy and PR etch rate. Additionally, the variation of the RF plasma potential profile is attributed to the enhanced capacitive electrical field in the ICP. These variation are analysed using an electromagnetic simulation.