arXiv subjects

Wan Dong

Publications and source records attributed to Wan Dong.

4 recordsLinked to original sources

arXiv2026

Hybrid simulation of the energy cost of O($^1$D) and O($^3$P) generation in a capacitive Ar/O$_2$ discharge driven by sawtooth-type voltage waveforms

Low-pressure radio-frequency capacitively coupled plasmas operated in Ar/O$_2$ gas mixtures are widely adopted in critical semiconductor manufacturing processes. O($^3$P) and O($^1$D) are key highly reactive species for oxidation or as oxygen sources for deposited thin films. Optimizing external parameters to realize efficient generation of these species under limited energy deposition is essential for improving process yield.Based on a one-dimensional (1D) fluid/electron Monte Carlo (EMC) hybrid model, this study investigates the energy cost of O($^1$D) and O($^3$P) generation driven by sawtooth up-type voltage waveforms at a fixed peak-to-peak voltage, focusing on the effects of the harmonic number ($N$) and the O$_2$ ratio. The results show that O($^3$P) generation is consistently more efficient than that of O($^1$D). The generation energy cost decreases with increasing O$_2$ ratio, yet increases as $N$ increases. However, in the specific scenario of 10% O$_2$, an inflection point can be observed at $N = 2$. As $N$ increases from 1 to 2, the discharge mode shifts from the DA mode to the $\alpha$-DA hybrid mode, expanding the effective spatio-temporal range of the ionization rate and enhancing its peak, which increases electron density. Consequently, the generation rates are significantly enhanced, leading to a reduction in the generation energy cost.Moreover, as discussed above, monotonically increasing the harmonic number $N$ does not reduce the generation energy cost of O($^1$D) and O($^3$P) associated with medium-energy (8-20 eV) electrons. Only by selecting the appropriate $N$ to sustain the discharge in the hybrid $\alpha$-DA mode, thereby increasing the electron density and promoting the generation of these species, can the generation energy cost be reduced.

physics.plasm-ph↗

arXiv2026

The effect of surface quenching coefficients of $O_2(a^{1}{\Delta}g)$ and $O_2(b^{1}{\Sigma}g^{+})$ on capacitively coupled $Ar$/$O_2$ discharge: A global/equivalent circuit model study

Capacitively coupled discharges operated in mixtures of $Ar$ and $O_2$ are extensively utilized in plasma etching and deposition processes due to the oxidative properties and precursor functionality of the reactive species produced in the discharge. In $Ar$/$O_2$ discharges, the surface quenching coefficient of $O_2(a^{1}{\Delta}g)$ is known to affect this metastable density, which, in turn, affects the electronegativity and other important plasma characteristics. In this work, in addition to $O_2(a^{1}{\Delta}g)$, $O_2(b^{1}{\Sigma}g^{+})$ and its associated reactions are incorporated into a global/equivalent circuit model of an $Ar$/$O_2$ discharge. By independently adjusting the quenching coefficients of both metastable species, changes of these surface coefficients are found to significantly affect the discharge characteristics, indicating that the role of $O_2(b^{1}{\Sigma}g^{+})$ cannot be neglected. The effects of their respective surface quenching coefficients of these metastables based on various wall materials on the discharge are revealed including their effects on different particle species densities, plasma impedance, voltage drops across the sheaths, as well as plasma power absorption.

physics.plasm-ph↗

arXiv2024

Electron dynamics and SiO2 etching profile evolution in capacitive Ar/CHF3 discharges driven by sawtooth-tailored voltage waveforms

The electron dynamics and SiO2 etching profile evolution in capacitively coupled Ar/CHF3 plasmas driven by sawtooth-waveforms are investigated based on a one-dimensional fluid/Monte-Carlo (MC) model coupled with an etching profile evolution model. The effects of the sawtooth-waveforms synthesized from different numbers of consecutive harmonics, N, of a fundamental frequency of 13.56 MHz on the electron dynamics, ion and neutral transport, as well as the etching profile evolution are revealed in different mixtures of Ar/CHF3. By increasing N, a reduction in electronegativity, a decrease of the DC self-bias voltage, and a transition of the discharge mode from the Drift-Ambipolar (DA) to an {\alpha}-DA hybrid mode is observed accompanied by an enhanced plasma asymmetry. As the CHF3 gas admixture increases, the electronegativity initially increases and then decreases, following a similar trend as the absolute value of the DC self-bias voltage. This is mainly caused by the change in ionization, attachment and de-attachment reaction rates. The obtained results show that placing the substrate on the grounded electrode and using a higher number of harmonic frequencies (N) can achieve a faster etching rate, since higher ion fluxes can be obtained in these scenarios. Additionally, the Ar/CHF3 gas mixing ratio impacts the neutral surface coverage, which in turn affects the etching rate. Therefore, selecting an appropriate gas mixture is also essential for optimizing etching results.

physics.plasm-ph↗

arXiv2024

Electron dynamics and particle transport in capacitively coupled Ar/O2 discharges driven by sawtooth up voltage waveforms

One dimensional fluid/electron Monte Carlo simulations of capacitively coupled Ar/O2 discharges driven by sawtooth up voltage waveforms are performed as a function of the number of consecutive harmonics driving frequencies of 13.56 MHz, N (1-3), pressure (200-500 mTorr) and gas mixture (10-90 % admixture of O2 to Ar). The effects of these external parameters on the electron dynamics, and the transport of ions and neutrals are revealed at constant peak-to-peak driving voltage. The electronegativity is found to decline as the number of consecutive harmonics increases and the DC self-bias voltage decreases. Increasing the pressure also leads to a decrease in electronegativity. The combination of a decrease in the mean free path of electrons and the presence of the Electrical Asymmetry Effect (EAE) result in different spatio-temporal distributions of the ionization rate, which lead to a reduction in the amplitude of the DC self-bias at higher pressure. As the admixture of electronegative O2 increases, the electronegativity is enhanced, and the discharge mode changes from an {\alpha}-Drift Ambipolar (DA) hybrid to DA mode. This work focuses on linking these fundamental changes of the plasma physics induced by changing external parameters to process relevant charged particle and neutral fluxes to the electrodes. Particular attention is paid to O(1D) flux, because it is a precursor of deposition. In discharges driven by sawtooth up voltage waveforms, placing the substrate on the grounded electrode and increasing the number of consecutive harmonics, N, can facilitate the deposition process, since the O(1D) flux to the substrate is higher in these scenarios. Moreover, at an O2 admixture of 20%, the O(1D) flux is nearly as high as that at an O2 admixture of 90%, indicating that a higher O(1D) flux can be achieved without excessively increasing the O2 admixture.

physics.plasm-ph↗