As front end transistor scaling by Moore's law faces economic and technical challenges, interconnect scaling by advanced packaging technologies has started to add value at system level for a variety of electronics applications including consumer, high performance computing and automotive. The focus on yield improvement at every node that has enabled transistor scaling is now becoming a very critical need for high volume manufacturing of advanced packaging technologies such as 2.5D interposers and high density fanout [1]. This paper describes the first demonstration of a novel atmospheric approach based on ozone as an alternative to vacuum-based plasma treatment for photoresist cleaning to enhance the re-distribution layer (RDL) yields in advanced semi-additive process (SAP) processes. The ozone process is applicable to wafers as well as large panels, and is suited for small feature sizes down to 1um that are required for interposers and future fan-out packages. Ozone process provides an environmentally fr...