Solving the challenges of highly outgassing substrates in advanced packaging applications such as UBM and RDL

Organic passivated silicon wafers, composite substrates such as silicon on glass or Fan-out Wafer-Level Package (FOWLP) technology all pose new challenges for UBM and RDL processes [1]-[5]. Materials used in these substrates must be adequately degassed for subsequent plasma processing under vacuum but their heat-sensitive nature necessitates careful thermal management. Selecting the proper technology for each individual step enables the definition of a high yield process, minimizing contamination from the organic materials. This paper discusses the preferred degas principles for different substrates and applications. Temperature simulation data and experimental results are presented for various heating methods including single wafer and batch processes. It illustrates the effectiveness of an atmospheric batch degasser for removal of volatile water and organic compounds (VC) at moderate temperatures below 150°C. The results will be compared with standard vacuum degas technologies and the resulting contact resistance (Rc) values after subsequent low temperature ICP etch will be reported. The paper also addresses the etch process requirements to ensure efficient pumping of remaining volatile contaminants, the required temperature management of the substrates and the particle containment and cleanliness of the process environment.