Role of Photons, Ion Implantation and Mixing in Sub-threshold Selective Etching of Si

As device sizes shrink, control of selectivity and damage during plasma etching becomes important. Recent literature reports the role of photons in the cleaving of surface and sub-surface Si-Si bonds which may initiate Si etching by radicals, even below the threshold energies needed for ion-assisted etch.\footnote{H. Shin, W. Zhu, V. M. Donnelly, and D. J. Economou, J. Vac. Sci. Technol. A \textbf{30(2)}, 021306 (2012).} Simultaneous effects of photons and ion~penetration can degrade the selectivity. Photon assisted Si etching in below-threshold ion energies in Cl$_{2}$ plasmas reported 4-10 nm/Min. etch rate.\footnote{Ibid.} We investigated the effects of photons in sub-threshold etching of Si in HBr/He/O$_{2}$ plasmas. As photons with wavelengths $<$170 nm have enough energy to cleave Si-Si bonds, we concentrated on 58.4 nm photons emitting from He(2 $^{1}$p) and 130nm photons emitted by O(3s) which can penetrate $\sim $10nm intoe Si.\footnote{J. R. Woodworth, M. E. Riley, V. A. Amatucci, T. W. Hamilton, and B. P. Aragon, J. Vac. Sci. Technol. A \textbf{19}, 45 (2001).} This paper will discuss the role of photons and mixing in silicon-dioxide/silicon etching using modeling {\&} simulation, experiments and diagnostics.