Ultra Low-k Damage Control and k Recovery for 28nm RC Improvement

Abstract

To improve resistance-capacitance delay, porous ultra low-k dielectric materials are used in advanced copper damascene integration. However, the BEOL processes often lead to low-k film damage by removing the hydrophobic groups Si-CH3, and convert partially low-k materials surface from hydrophobic to hydrophilic one. During the wet related processes, the hydrophilic porous low-k film surface is easy to absorb moisture and potentially increase k-value. In this work, we developed the processes that can maintain ultra low-k film k-value either by repairing low-k damage or by removing moistrue. Dry etch plasma process is one of the main steps to result in low-k film damage. Post etch treatment (PET) was optimized to repair porous low-k film surface due to the etch damage. This improved process with less low-k damage can significantly reduced the moisture absorption in the following wet process and improve the capacitance by about 10%. Various thermal treatments post wet and post CMP processes were studied, including temperature, gases and pressures. From our results, post wet clean heat treatment can improve capacitance by about 5% and post CMP heat treatment can improve capacitance by about 10%. To decrease moisture absorption from atmosphere after the wafers were processed thru CMP, queue time from CMP to NDC deposition also was studied and the safe specification was also defined.