Bath Stability Monitoring for Electroless Cu Seed Formation in High Aspect Ratio TSV

Three-dimensional (3D) integration technology with through-Si via (TSV) has drawn much attention in view of the more-than-Moore technology. In order to achieve high-density integration, high aspect ratio (HAR) TSV, with AR>10 will significantly assist [1,2]. However, a Physical Vapor Deposited (PVD) Cu has already shown to be close to its limits for yielding a continuous, i.e. electrically conductive, seed layer [3]. Electroless deposition (ELD) Cu can become an attractive option as alternative seed deposition method in the fabrication of semiconductor devices [4,5]. ELD has interesting characteristics, such as excellent conformality in high aspect ratio structures, selectivity towards materials already present on the wafer, low temperature processing and, possibly low cost. The application of ELD-Cu for seed layer in TSV is promising. Although, there are only a few reports in literature, which focus on controlling the bath stability for longer times, a prerequisite for implementation in an industrial context. In this presentation, we use a combination of techniques such as pH measurement, UV-VIS spectroscopy, and mixed potential monitoring to develop understanding of bath stability. For measuring any of these three parameters, solutions can be designed and implemented on a processing tool.