Planar plasma etching of chromium

Cr and CrOx etching using SF6 and O2 plasma

“…The plasma etching of Cr is currently almost exclusively reserved for chlorine-oxygen-based chemistry by forming chromyl chloride (CrO 2 Cl 2 ) as the final etch product. [29][30][31][32][33][34][35][36][37][38][39][40][41] The consensus is that both chlorine (e.g., Cl 2 plasma) and oxygen radicals (e.g., O 2 plasma) are needed to create the volatile chromyl chloride product. It was demonstrated by Abe et al 29 roughly 45 years ago and a few years later explained by Nakata et al 30 As both O and Cl radicals are needed to remove a Cr atom, possibly allowing any intermediate CrO x Cl y reaction path, the etch rate (ER) shows an optimum for a specific ratio between the supplied Cl 2 and O 2 gas.…”

“…This ratio is typically around 30% O 2 in the Cl 2 + O 2 mixture, but depends on the temperature and other plasma parameters. 33,40 Indeed, at low O 2 content, the formed CrCl x species have a very high melting temperature (CrCl 2 and CrCl 3 ) or simply decompose (CrCl 4 ). At high O 2 concentrations, the CrO x species are difficult to evaporate as well.…”

“…31,32 Another troublesome feature is the influence of the total amount of Cr (and resist)-called loading effect-on the (local) etch rate. [1][2][3]33,[36][37][38] This will negatively affect the etch uniformity as over etching is required and profiles start to vary across the wafer and between wafers in barrel etchers. 3,37,38 During this overetch, the feature sidewalls tend to straighten, but at the expense of expanding the trench size and shrinking the feature.…”