Critical issues in post Cu CMP cleaning

Application of dilute HF with respect to post Cu CMP cleaning showed evidence of some critical issues that may seriously impact process performance. First of all it was seen that due to the heterogeneity of the surface after CMP drying problems can occur due to differences in wettability or due to topography. The cleaning of alumina slurry by under-etching with HF showed possible redeposition of these particles on the surface in case of a non-optimised rinsing and drying step. Furthermore a pattern dependent form of corrosion of the Cu was observed. Since single lines were more seriously impacted than dense meander/fork structures extrapolation of the latter to give process yield data may result in erroneous results. Finally it was shown that megasonic energy was very efficient in order to remove deposited slurry residues from the wafer surfaces.