Evaluation of ICP Sputter Etch with Reducing Atmosphere for the Improvement of Rc in UBM/RDL Applications

In UBM/RDL manufacturing, the process challenge to keep low contact resistance in high-density interconnects increases with the ongoing scaling towards miniaturization of the critical design dimensions. Moreover, the ubiquitous use of organic passivation layers and the increasingly popular polymer-based substrates require advanced wafer pre-treatment processes prior the sputter deposition of adhesion/seed layers. Typically, a dedicated strategy combining Degas and Sputter Etch is mandatory to keep Rc low and stable in high-volume manufacturing. In this paper, beside the well-established ICP-Etch BKM based on physical sputtering in a pure Ar plasma, we investigate the impact of a reducing Ar/H2 atmosphere on the Rc of contacts ranging from 5.0 μm to 30.0μm. A very sensitive Rc test vehicle with Kelvin structures was built. The results have shown that Ar/H2 atmosphere can be beneficial in certain conditions to improve Rc in 5.0 μm and 10.0 μm opening; whereas, no benefit compared to the BKM process is seen for larger contacts.