Optimal pulse shaping for plasma processing

Thin-film etching and deposition using low-pressure plasma reactors is an integral part of the fabrication of very-large-scale integrated (VLSI) circuits. Standard operation of plasma reactors uses an RF power source with constant average power to excite a plasma in the vacuum chamber. Recently, several researchers have shown empirically that operation of plasma reactors with a periodic power input has the promise to increase the flexibility of plasma processing, in the sense that a greater range of operating conditions is achievable. This paper presents a numerical analysis of a global model for an argon plasma with the aim of answering the following questions: First, can a periodic input achieve effective operating conditions that cannot be achieved using steady-state inputs? Second, if the answer to the first question is yes, what is the shape of the periodic input required to achieve a particular operating point? This technique was utilized to give answers to these questions in one particular case. It was shown that periodic operation of an argon plasma can create variations in the ratio of metastable argon density to ionized argon density beyond that achievable using constant power. In addition, strong evidence is given that arbitrarily shaped modulating waveforms have advantages over simple pulse width modulation.