Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas

Abstract

Control of ion energy distributions (IEDs) onto the surface of wafers is an ongoing challenge in microelectronics fabrication. The use of capacitively coupled plasmas (CCPs) using multiple radio frequency (rf) power sources provides many opportunities to customize IEDs. In dual-frequency CCPs using a fundamental frequency and its second harmonic, varying the relative voltages, powers, and phases between the fundamental and second harmonic biases have demonstrated potential as control mechanisms for the shape of the IEDs. In this paper, we report on computational and experimental investigations of IED control in dual-frequency and triple-frequency CCPs where the phase between the fundamental and second harmonic frequency voltage waveform is used as a control variable. The operating conditions were 5–40 mTorr (0.67–5.33 Pa) in Ar and Ar/CF4/O2 gas mixtures. By changing the phase between the applied rf frequency and its second harmonic, the Electrical Asymmetric Effects was significant and not only shifted the dc self-bias but also affected plasma uniformity. When changing phases of higher harmonics, the energies and widths of the IEDs could be controlled. With the addition of a 3rd high-frequency source, the plasma density increased and uniformity improved. Computed results for IEDs were compared with experimental results using an ion energy analyzer in systems using rf phase locked power supplies.

Electron neutral collision frequency measurement with the hairpin resonator probe

“…A diagram of the experimental setup is shown in figure 1. A more complete description of the setup has been given previously by Zhang et al [10].…”

Controlling plasma properties under differing degrees of electronegativity using odd harmonic dual frequency excitation

“…The ion flux is comparatively insensitive to the change in the phase shift meaning that the two quantities can be controlled independently of one another. Since the original study many investigations have demonstrated this effect through both simulation and experiment and extended it to the use of more than two frequencies to increase the amplitude asymmetry of the waveform [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. It has also been demonstrated that an electrical asymmetry can be generated using sawtooth-like waveforms where the rise and fall times of the voltage waveform differ [41][42][43][44][45][46][47][48].…”

Disrupting the spatio-temporal symmetry of the electron dynamics in atmospheric pressure plasmas by voltage waveform tailoring

“…Here, we demonstrate that Voltage Waveform Tailoring (VWT) i.e. the construction of specific waveform shapes by the summation of multiple rf harmonics [13,14,15,16,17,18,19,20], is capable of disrupting the temporal and spatial symmetries of electron heating in APPs. This, in turn leads to spatio-temporal confinement of the electron heating, and significantly enhanced control of the EEPF.…”