Precise Sputter Control by Tailored Waveform Biasing for Selective Ablation in Future 2D Electronics Manufacturing

Precise control of ion energy in plasma processes is pivotal for the selective, damage-free etching that future two-dimensional (2D) electronics demand. Conventional equipment technology with RF sinusoidal waveform biasing is unable to generate the monoenergetic ion energy distribution function (IEDF) required for the selective sputtering of materials that exhibit only marginal differences in threshold ion energy for sputtering. Applying a low-frequency tailored pulse-wave-shaped bias voltage waveform to the substrate electrode of a commercial 200 mm inductively coupled plasma (ICP) plasma reactor results in an IEDF with a full width at half maximum (FWHM) of just 10 eV even at higher ion energies. These narrow IEDFs are used within this study to determine the sputtering thresholds of molybdenum disulfide ( ${\mathrm{MoS}}_2$ ) and selected dielectrics: ${\mathrm{HfO}}_2$ , ${\mathrm{Ta}}_2{O}_5$ , ${\mathrm{Al}}_2{O}_3$ and ${\mathrm{SiO}}_2$ , with the aim of enabling the efficient selective physical etching of dielectric materials relative to 2D materials, and vice versa. Armed with this knowledge, the dielectric environment and layer structure can be designed specifically to the application at hand, ensuring the highest possible selectivity in the patterning process. Additionally, a tailored waveform bias allows ${\mathrm{MoS}}_2$ layers of varying quality to be plasma cleaned below the sputtering threshold energy.