Using a low-k material with k=2.5 formed by a novel quasi-porogen approach for 65 nm Cu/LK interconnects

A porous k=2.5 low-k material (LK2.5) with its pore size distribution and mechanical properties comparable to the ones of k=3.0 low-k materials (LK3.0) was developed by a novel quasi-porogen approach for 65 nm BEOL Cu dual damascene (DD) interconnects. As compared to the Cu/LK3.0 DD, the Cu/LK2.5 DD, processed using similar etching and ashing processes and chemistries, showed a 14% line-to-line (L-L) capacitance reduction at S=0.1 μm. Other physical, electrical and reliability results show that the Cu/LK2.5 DD is comparable to the Cu/LK3.0 DD with no degradations commonly associated with conventional porous LK2.5s formed using porogens, such as peeling or LK recess in CMP, k increase or trench bottom roughening in patterning, high L-L leakage, low L-L Vbd or low SM resistance. Further process extendibility studies revealed that k<2.0 is also achievable using this quasi-porogen approach which strongly enables its applicability to current and future Cu/LK BEOL technologies.