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

TL;DR

This study investigates how sawtooth-waveform-driven Ar/CHF3 plasmas influence electron behavior and SiO2 etching profiles, revealing how waveform harmonics and gas mixtures affect etching efficiency and plasma characteristics.

Contribution

It introduces a combined fluid/Monte Carlo model to analyze the effects of waveform harmonics on plasma dynamics and etching profiles in Ar/CHF3 discharges, highlighting optimization strategies.

Findings

Higher waveform harmonics reduce electronegativity and self-bias voltage.

Increasing CHF3 initially raises then lowers electronegativity.

Using grounded substrates and more harmonics enhances etching rates.

Abstract

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.