Defect mitigation of plasma-induced delamination of TiW/Cu from SiN_x layer in thin si interposer processing with glass carriers

Abstract

Glass is widely used as a carrier substrate for processing thin silicon wafers for 3D applications. Moreover, the use of glass as an interposer material has recently attracted significant attention in both research and development. For silicon interposer applications, the silicon wafer with through silicon vias (TSVs) is first bonded to a temporary glass handler and subsequently subjected to wafer thinning to reveal the TSVs. After TSV reveal, wiring layers are patterned on the 'grind-side' using photoresist, with sputtered TiW/Cu as the metal seed-layer and SiNx as the dielectric separating the metal layers. This paper reports a new 'resistdependent' delamination phenomenon that occurs at the interface between TiW/Cu and SiNx surfaces, which is triggered during the plasma process. The delamination manifests as small blisters of raised TiW/Cu over the SiNx surface, and was observed while using glass wafers, either as a handler or as the actual electronic substrate. In this study, the root cause of delamination is identified as the Ar plasma used for clamping the wafers. The defect intensity is minimized by lowering the power of Ar plasma. Finally, defects are completely mitigated by substituting O2 gas in place of Ar during plasma processing.