Study of photoresist plug etching back with CO/O2 plasma for dense-ISO via recess loading tunning

Plasma dry etching was widely used in photoresist plug etching back (PEB) in Via-first Dual Damascene process. [1-3] In the via first approach, via is required to form prior to trench pattern. Before trench patterning, the via is typically filled photoresist to form plug in via hole for preventing dielectric layer damage and Cu exposure during trench etching.[3] Normally, after via filled with photoresist, a photoresist layer thickness loading between the ISO and dense via features is always observed. This fill loading creates in hole plug recess depth loading between ISO and dense via features in PEB process, then induces fence or sidewall damages during trench etching. Carbon monoxide (CO) containing plasma is used for pre-treatment to reduce photoresist layer etching rate, which bases on the polymeric cross-linking reaction at photoresist surface in CO plasma. [4]In this work, CO/O2 mixed gas plasma is studied in PEB process, in which the recess loading between ISO and dense via features can be modified by the CO/O2 gas ratio and process pressure. The results show that the loading can be improved smaller than 100A, and keep at same level when the recess depth increasing.