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Surface Analysis of Amorphous Carbon Thin Film for Etch Hard Mask.

When the aspect ratio of a high aspect ratio (HAR) etching process is greatly increased, an amorphous carbon layer (ACL) hard mask is required for dynamic random-access memory (DRAM). To improve the durability of an etch hard mask, an understanding of the plasma deposition mechanisms and the deposited film properties associated with the plasma conditions and atomic structure, respectively, is required. We performed a series of plasma depositions, material characterizations and dry-etching to investigate the effect of the deposition process condition on the surface characteristics of an ACL film to be used as a dry etch hard mask in an HAR etch process. We found that a lower chamber pressure at a higher temperature for the plasma deposition process yielded higher film hardness, and this infers that higher plasma ion energy in lower pressure regions helps to remove hydrogen atoms from the surface by increased ion bombardment. It was postulated that a higher substrate temperature gears the bake-out of hydrogen or hydroxide contaminants. From the results of inductively coupled plasma-reactive ion etching of the deposited ACL film, we observed that the etch selectivity over the silicon dioxide film was improved as C═C sp₂ and C-C sp₃ bonds increased.