Characterization of neutral species densities in dual frequency capacitively coupled photoresist ash plasmas by optical emission actinometry

Reactive neutral species densities for various conditions in dual frequency capacitively coupled discharges of $Ar∕O2$⁠, $Ar∕N2$⁠, and $Ar∕H2$ were determined using optical emission spectroscopy, Kr actinometry, and modeling. The reactive neutral species probed in this work include O, $O2$⁠, N, $N2$⁠, H, and $H2$⁠. Densities are reported as a function of pressure $(5–60mTorr)$⁠, percent Ar in the feed gas (1%–86%), source power $(50–800W)$⁠, and bias power (⁠$0W$⁠, $200W$⁠). It was found that increasing the pressure from $5to60mTorr$ resulted in order of magnitude increases in atomic species densities for all ash chemistries. At $30mTorr$⁠, percent dissociation is relatively low $(⩽15%)$ for all species. Also, at $30mTorr$⁠, the addition of Ar resulted in a small decrease in N and H densities, but an order of magnitude increase in O density. Based on modeling, it is proposed that the increase in O density is due to an increasing contribution of Penning dissociation with increasing Ar density. Only the source power contributed significantly to O and N radical densities, but $200W$ bias power generated a significant H radical density above that generated via the source power. Details of these results are discussed in comparison with theory and literature.