Ionic liquids – a new path to form nanothin seed films for CMOS applications

The scaling of feature size in micro-electronics becomes difficult below 32 nm. At this stage, the copper seed layer occupies a considerable fraction of the feature size which makes the bottom-up filling difficult. Therefore, attempts are made to avoid the deposition of this copper seed and to electrodeposit directly on the barrier layer. However, the currently used Ta/TaN barrier layer forms an insulating oxide layer when it comes in contact with water, resulting in bad nucleation densities and poor adhesion of the deposited copper. Hence, people have started to look for alternatives such as replacing the Ta/TaN barrier material by ruthenium. The research reported here takes an alternative approach. Rather than changing the barrier material, the possibility of direct electrodeposition of copper on Ta is studied using electrolytes that do not contain water. More specifically, we have studied the direct electrodeposition of copper from ionic liquids on Ta/TaN barriers.