Monitoring wafer cleanliness and metal contamination via VPD ICP-MS: Case studies for next generation requirements

The importance of metal contamination in semiconductor processing and the ultimate yield effects has long been discussed in literature, the ITRS, and most importantly in the fab. Analysis methods including TXRF, VPD ICP-MS, and TOF-SIMS have been used to verify that wafers are properly “clean,” and that cross-contamination has not been imparted via process chemicals, environment, people, processing tools, and a host of other and still evolving sources. Analysis choice has often been chosen via an instrument that is most convenient and quickest for the fab. This trend is still present with a focus on the most automation, speed and lowest detection limits bringing quick answers to the newest generation fabs. In this paper, we discuss the use of an automated vapor phase decomposition (VPD) process in conjunction with inductively coupled plasma mass spectrometry (ICP-MS) to gauge analysis capability in conjunction with new process materials as well as contamination via contact transfer to indicate whether incoming wafers are clean or not.The role of the VPD collection solution and its composition has been examined before [1], most recently with the advent of copper processing in the semiconductor industry. Solutions with varying concentrations of hydrofluoric acid (HF), hydrogen peroxide (H2O2), nitric acid (HNO3) and water have been touted as a best means for collection efficiency. The role of this solution is most important, as an improper solution will “collect” less contaminant and “dirty” wafers then judged as “clean.” Relative newer applications of Pd, Pt, and Ag in process, and the importance of Au as a major player in minority carrier lifetime make these elements important for contamination control and ensuring collection solutions are properly selected.Discussed in the 2007 ITRS Yield Enhancement section and again in the 2008 update, the importance of the edge and bevel to process yield is a critical challenge going forward [2]. From a metal contamination standpoint, the edge and bevel have been looked at and reported on specifically for copper and via TXRF and ICP-MS [3] and using an innovative mechanical system to look specifically at these areas of the wafer. We extend these initial discussions by using an automated system to look at the edge and bevel and looking at contamination for a host of metals.