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Supercritical CO2 Applications in BEOL Cleaning

Introduction As the semiconductor industry prepares for the 45 and 32 nm technology nodes, supercritical fluid methods offer flexible chemistries, rapid transport, and environmentally benign alternatives to wet and dry BEOL cleans processes. In addition, supercritical methods have been demonstrated to remove photoresist and post-ash residue,[1,2,3] deposit metal lines and low-k films,[4] extract lowk porogens,[5] and repair post-ash damage to porous low-k films.[6,7,8,9] Recent work by a number of groups have demonstrated the effective removal of 248 and 193nm photoresist layers using supercritical CO2 (SC-CO2) with co-solvents.[10,11,12] First patented by researchers at Los Alamos National Lab,[13] resist removal techniques employ swelling, interfacial attack, and dissolution mechanisms. Recently, researchers at Cornell[14] and Univ. of North Carolina[15] have reported novel photoresists that can be developed and removed using supercritical CO2. Other work has examined the use of co-solvents in SC-CO2 to dissolve photoresist [1,12] and thermal oxide layers.[16] However, without significant advantages over current processes of record, the large capital expenditures necessary to introduce high pressure fluids into manufacturing environments will delay the implementation of supercritical methods in the manufacture of semiconductor devices.