Ion Energy Control by Voltage Waveform Tailoring in ICPs with Substrate Bias for Plasma Etching

Hybrid discharges, which are a combination of capacitively and inductively coupled plasmas, are widely used for etching semiconductor materials. To achieve the required selectivity, the ion energy distribution function (IEDF) is a key parameter, which additionally affects other properties such as the etch rate and anisotropy. In hybrid discharges, the IEDF is mostly determined by the substrate bias at the capacitively coupled electrode.  A low-frequency (100 kHz) pulse wave-shaped tailored voltage waveform is used as substrate bias in a commercial reactive ion etching reactor. The IEDF is measured using a retarding field energy analyzer (RFEA). To investigate the influence of the tailored substrate bias on the electron dynamics and density, phase-resolved optical emission spectroscopy (PROES) and a multipole resonance probe (MRP) were used. The energy-dependent etch rates of physical sputtering were quantified for different materials. The results of the RFEA measurements show that the tailored substrate bias leads to tunable, mostly mono-energetic IEDFs. By adding another voltage plateau-level to the tailored waveform, two independently controllable IEDF peaks are generated. The electron density, as well as the electron dynamics were mostly unaffected by the substrate bias.