Insight into the re-deposition equilibrium and mitigation of sn contaminant during hydrogen plasma cleaning

Abstract

This paper employed advanced precision reflector cleaning technology to study the characteristics of Sn contaminant removal on different substrates. The DFT calculation results indicate that the adsorption energy of adjacent Sn atom on Ru reaches −1.07 eV and would gradually desorb from Ru in forming SnH_n(n = 1–4) after interacting with hydrogen atoms. Meanwhile, Sn-DOS could transform from a metal of Sn/SnH/SnH₂ to a molecule of SnH₃ and SnH₄. The plasma-cleaning experiment results demonstrate that the removal rate for superficial Sn was relatively fast (reaching 6 nm/h) and would drop slowly as the contamination thickness decreased. Interestingly, the Sn contamination could not be cleared completely, although extending the treatment time to 24 h, and would reach a fixed value (with residual Sn proportion of ∼0.35 %) and remained stable. To clarify the potential catalytic effects of Ru matrix, a non-catalytic Si substrate (with adsorption energy of ∼-0.1 eV) was introduced to illustrate the dynamic equilibrium between hydrogen plasma cleaning and the re-deposition of SnH₄. In addition, residual Sn was completely removed through the gas purging method by the synergistic effect of superficial blowing and enhanced active particles.