Investigation of the plasma-wave interaction in helicon plasmas near the lower hybrid frequency

The study of the characteristics of the plasma-wave interaction in helicon plasmas near the lower hybrid frequency has been carried out. The (0D) dispersion relation is derived to analyse the properties of the wave propagation and the 1D cylindrical plasma-wave interaction model is established to investigate the power deposition and implement the parametric analysis. It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates a very thin layer near the boundary. Therefore, it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks. It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.

Theoretical Modeling for Predicting Material Removal Rate through Interelectrode Gap

In EDM, the thermal energy of the discharge causing material erosion which is supplied by the power source unit as electrical input. The discharge energy may be recognized by the current and voltage pulses on time transient discharge characteristic curve (V-I curve) during machining. However, the plasma resistance is very short for a smaller interelectrode gap in micro-EDM compared to the impedance of the circuit. Hence, direct probe-based measurement of current and voltage pulses may include the voltage drop across the stray impedance which causes variation in its exact value. Here, a modeling-based approach may help to analyze the energy interaction with the interelectrode gap. This article presents a theoretical modeling approach to predict the interelectrode gap based on gap voltage, gap current, and plasma characteristics. Initially, a simplified two-dimensional heat conduction equation (cylindrical form) was studied to understand the asymmetry of heat flow in Gaussian distribution. A numerical analysis of a single discharge pulse was considered by applying some basic assumptions. A numerical model has been developed to predict gap distance and MRR considering gap voltage, gap current, and plasma properties. The predicted model was validated against previously reported data from the literature. Later on, the impact of gap voltage on gap distance, plasma resistance, and material erosion rate was analyzed and discussed briefly.

Remarkable plasma-resistance performance by nanocrystalline Y2O3·MgO composite ceramics for semiconductor industry applications

Motivated by recent finding of crystallographic-orientation-dependent etching behavior of sintered ceramics, the plasma resistance of nanocrystalline Y2O3-MgO composite ceramics (YM) was evaluated for the first time. We report a remarkably high plasma etching resistance of nanostructure YM surpassing the plasma resistance of commercially used transparent Y2O3 and MgAl2O4 ceramics. The pore-free YM ceramic with grain sizes of several hundred nm was fabricated by hot press sintering, enabling theoretical maximum densification at low temperature. The insoluble two components effectively suppressed the grain growth by mutual pinning. The engineering implication of the developed YM nanocomposite imparts enhanced mechanical reliability, better cost effectiveness with excellent plasma resistance property over their counterparts in plasma using semiconductor applications.