| CPC H01L 21/31144 (2013.01) [H01L 21/31116 (2013.01); H01L 21/67069 (2013.01)] | 12 Claims |

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1. A method comprising:
providing, within an etch chamber, a base structure comprising a target layer disposed on a substrate, and an etch mask disposed on the target layer, wherein the target layer comprises carbon;
dry etching, within the etch chamber at a sub-zero degree Celsius temperature, the target layer using thionyl chloride to obtain a processed base structure, the processed base structure comprising a plurality of features and a plurality of openings defined by the etch mask, wherein each feature of the plurality of features has an aspect ratio greater than or equal to about 60:1; and
removing the processed base structure from the etch chamber.
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