James D. Adolf

Novel High Molecular Weight Levelers Extending Gap Fill to Smaller Features

It has been recently demonstrated that a high molecular weight leveler can improve gap fill, in addition to minimizing the overburden (1). An analysis of this phenomenon and a quantitative model explaining the effect are presented here. The penetration of the high molecular weight leveler into the via is restricted due to its large size and slow diffusion, leading to preferential passivation of the wafer top surface. Since the leveler is a strong inhibitor, the applied current is therefore preferentially directed into the vias. Because the side walls are passivated by PEG, the majority of this current is directed to the via bottom, improving bottom-up fill. The process conditions and the distribution of features on the wafer affect this improvement. The model has been quantified using a computer implemented simulation combining empirical and analytical methods. Requirements for suitable additives for this application are specified, identifying polyethylenimine as one such additive.