A Study on Optimized Conditioner for Soft Pad in Cu Barrier Removal

In removing the Cu barrier in Cu CMP process, high-porosity soft pads have been commonly used. However, due to its high surface roughness of its initial state, the high-porosity pads have caused the continuous increase in wafer removal rate until being conditioned by diamond conditioners for a certain period of time which results in process instability and the excessive waste of consumables including slurries and dummy wafers. In this paper, the mechanism that soft pads causes the increase in wafer removal rate at the early stage of Cu barrier polishing and the methodology to stabilize the polishing process by minimizing the period of increase in wafer removal rate are studied. In order to do so, the pad morphology, pad wear rate, wafer removal rate, wafer non-uniformity of soft pads were evaluated as a function of the configurations of diamond conditioners, diamond protrusion, diamond density, grit size, diamond distributions.