Control of ion flux-energy distribution at dielectric wafer surfaces by low frequency tailored voltage waveforms in capacitively coupled plasmas

Abstract

Capacitively coupled plasmas are routinely used in an increasing number of technological applications, where a precise control of the flux and energy distribution of ions impacting boundary surfaces is required. In the presence of dielectric wafers and targets the accumulation of charges on these surfaces can significantly alter the time evolution of the sheath electric field that is accountable for ion acceleration from the plasma bulk to the surfaces and, thus, lead to parasitic distortions of process relevant ion flux-energy distributions. We apply PIC/MCC simulations to provide insights into the operation, ion acceleration mechanisms, and the formation of such distributions at dielectric wafers for discharges in argon gas. The discharges are driven by a combination of a single high frequency (27.1~MHz) voltage signal and a low frequency (100~kHz) customized pulsed voltage waveform. The low frequency waveform includes a base square signal to realize narrow and controllable high energy peaks of the ion distribution, and steady-slope ramp voltage components. We discuss the distorting effect of dielectric surface charging on the ion flux-energy distribution and provide details about how the voltage ramps can restore its narrow peaked shape. The dependence of the surface charging properties on the low frequency pulse duty cycle and amplitude, as well as the high frequency voltage amplitude is revealed. The radial homogeneity of the ion flux is found to be maintained within ± 10 % around the mean value for all quantities investigated. The radial electric field developing at the edge of the dielectric wafer with finite width has only a small influence on the overall homogeneity of the plasma across the whole surface, its effect remains localised to the outermost few mm-s of the wafer.

Experimental validation of particle-in-cell/Monte Carlo collisions simulations in low-pressure neon capacitively coupled plasmas

“…Limitations of the separate control of the ion flux and the mean ion energy at the electrodes in dualfrequency CCPs operated at strongly different frequencies were revealed based on such simulations as well, explained by the effects of frequency coupling and secondary electrons (SEs) [23,24]. Both by means of experiments and simulations, voltage waveform tailoring was demonstrated to overcome such limitations and provide an improved separate control of the mean ion energy and flux [23,[25][26][27][28] as well as control over the IEDF shape [29][30][31][32].…”

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode

“…3,4 The behaviors of ions near the electrode and substrate where the tailored-waveform AC voltages are applied has been investigated numerically. [5][6][7][8][9] In addition, experimental studies pertaining to the tailored-waveform approach primarily focus on the analysis of timeaveraged IVDFs. 7,8,10,11 Previously, Wang and Wendt measured the temporal evolution of electric potential on a substrate.…”

Contribution of Ion Energy and Flux on High-Aspect Ratio SiO2 Etching Characteristics in a Dual-Frequency Capacitively Coupled Ar/C4F8 Plasma: Individual Ion Energy and Flux Controlled

“…For instance, Kim et al [ 17 ] proved the capability of the individual control of ion flux and energy distribution by varying dual-frequency voltages through a two-dimensional particle-in-cell Monte Carlo collisions (PIC-MCC) simulation. Schulze et al [ 18 ] proved the voltage pulse wave tailoring technology for individual control of the ion flux and energy through a two-dimensional PIC-MCC simulation in dual-frequency voltage sources. In addition, most experimental studies analyzed the coupled influence of ion flux and energy for etching based on the ion parameter measurement [ 3 , 10 , 19 ].…”