Plasma damage and restoration of a spin-on organic ultra low-k material (k=2.3)

As interconnect dielectrics, spin-on polymers might offer some advantages over OSG materials. In particular, a lower k-value is possible with less porosity, smaller pore size. They also have greater resistance to plasma damage due to their mono-component nature. However, some chemical modifications during the plasma exposure cannot be avoided. In this work, we study the changes caused by a N$_{2}$-H$_{2}$-C$_{2}$H$_{4}$ CCP discharge used for damascene patterning, on a spin-on k=2.3 organic low-k material. It is shown that this plasma forms amine and ester groups, leading to hydrophilization and k-value degradation. Several restoration treatments are studied on blanket wafers, trying to restore the chemical composition, minimize the k-value and hydrophilization. Those treatments include exposure to in-situ He-H$_{2}$ discharge, high temperature He-H$_{2}$ afterglow and combinations thereof, low- and high-temperature VUV treatments. It is found that the best k-value gain is around 50{\%}, and the most promising repair treatment results from the short exposure to a combination of low temperature in-situ He-H$_{2}$ discharge and high temperature He-H$_{2}$ afterglow. Applying such restoration process to an array of 30nm trenches, the integrated k-value showed a gain of 13{\%} in RC constant, indicating efficient restoration to pristine k-value, although the chemical composition was not completely restored in all evaluated conditions.