High Density Polymer RDL and Glass Core Interposers Based on a Plasma Dry Process for Scale-Up

ABSTRACT As Moore's Law approaches its limits, heterogeneous integration technology is gaining significant attention. In particular, “3D chiplet integration,” which combines front-end and back-end processes, is seen as promising new architecture. Advancing this technology requires glass core substrates with through-glass vias (TGV) and high-density redistribution layer (RDL) interposers. However, glass substrates with TGV face challenges “SEWARE” from multi-stacked build-up (BU) films. Meanwhile, stacked photo-imageable dielectric (PID) layers as RDLs on a glass substrate gives warpage and cracking due to CTE mismatch and also waviness of the RDLs from spin-on materials. This work reports initial experiments addressing these issues: developing Cu-TGV wiring using sputtering technology for glass substrates, and plasma etching technology for PIDs with good aspect ratio and fine patterns to improve RDL performance. The thickness of the glass core is 430 μm (size : 50 mm by 40 mm), and the TGV has a cross-shaped structure. The top diameter and constriction diameter are 80 μmφ and 55 μmφ, respectively. Therefore, the aspect ratio is approximately 5 to 7. Double-sided deposition on this glass core was performed by PVD sputtering. After PVD deposition of Ti 200 nm and Cu 2000 nm, Cu electroplating was carried out, resulting in completely filled Cu TGVs. This suggests that introducing the sputtering process can reduce thermal budget risks while ensuring good adhesion. Next, using plasma dry etching, vertical etching of PID with a line and space of 2.5 μm, an etching depth of 4.3 μm, and an aspect ratio of 1.72 was achieved. This presents a new fine processing technology for multilayer RDL interposer processes.