Quantitative Analysis of Mono-Energetic Ion Flux Control in Atomic Layer Etching via Tailored Waveform Profiles

Atomic layer etching (ALE) is increasingly critical in semiconductor manufacturing due to its superior control over etching profiles compared to traditional methods. Many ALE techniques utilize plasmas, either to generate neutral radicals for surface modification or ions for removing the altered layer. Independent control of ion flux and energy is highly desirable for ALE processes; however, single frequency capacitively coupled discharges (CCPs) lack this capability, as input power affects both parameters. While dual frequency discharges offer limited control, traditional CCPs produce broad ion energy distribution functions with sharp peaks, making it challenging to confine ion energy to a specific range. This precise energy control is crucial in ALE to selectively remove the top layer without damaging the underlying material.

Initially, the phenomenon of wafer charging, characterized by charge accumulation impeding the penetration of electric fields into the plasma region, was investigated. This investigation was conducted through the application of a steplike waveform while systematically varying the wafer conductivity and dielectric constant. Simulated observations revealed that conductivity exerts a considerably more substantial influence on the ion energy distribution compared to the dielectric constant. Specifically, elevated conductivity levels were correlated with a broadening of the ion energy distribution, attributed to the enhanced penetration of the electric field into the plasma, which subsequently resulted in a wider spectrum of ion acceleration energies. Conversely, the strategic implementation of a voltage slope during the negative phase, in conjunction with low conductivity conditions, facilitated the identification of optimal parameters for achieving independent ion energy control. This finding enables a more refined manipulation of the etching process and improved selectivity.