Control of ion energy at the substrates during plasma processing

Ion bombardment plays a significant role in many aspects of plasma processing in integrated circuit manufacturing, including etch rate, etch selectivity, etched feature profiles, differential charging, deposited film quality, damage, etc. Some of these have emerged as new challenges as device sizes continue shrinking. Since those challenges are somewhat related to the ion trajectory (or ion energy), more precise control of ion bombarding energy is critical and necessary. This study combined plasma model simulation and experimental implementation to develop an ion energy distribution function (IEDF) control technique by carefully tailoring the bias voltage waveform applied to the substrate.; A time-dependent, spherical-shell, whole-region plasma fluid model was constructed first to investigate the factors that affect the ion energy distribution. The simulation results show that a greatly narrowed IEDF can be obtained by applying a specially tailored bias voltage waveform composed of a series of pulses and a slow negative linear slope between pulses. The simulation also demonstrates that the IEDF produced with this technique is independent of ion mass, the technique does not induce a non-uniform substrate potential, and does produce a more precisely controllable ion energy compared to the conventional sinusoidal bias voltage power supply design. Experiments in a helicon argon plasma show good agreement with simulation results. Not limited to electropositive plasmas, this technique also demonstrates similar performance in an electronegative SF₆ plasma.; Experiments related to the applications of this technique in a real-time non-intrusive ion bombarding flux measurement as well as to SiO₂/Si etching selectivity improvement have also been performed. The real-time non-intrusive ion bombarding flux measurements show more accurate results than are obtainable with Langmuir probes and the output can serve as a meaningful control variable for etching processes. This technique also presents the capability to raise the etching selectivity of SiO₂/Si across the range of the investigated DC self-bias voltage in both CHF₃/H₂ and CF₄/H ₂ plasmas. Most importantly, the high selectivity range of self-bias voltage, between the threshold ion energies for etching of SiO₂ and Si, are also increased, showing an attractive technique for plasma etching processes in the semiconductor industry.