Adhesion Promotion and Stress Buffer Layers in Metallized Glass Core

ABSTRACT Glass cores are vital for next generation semiconductors due to superior flatness, thermal stability matching silicon's CTE, low signal loss for high frequencies (6G/AI), enabling dense interconnects and offering hermeticity for sensors. However, the challenge remains the metallization of the glass core. Traditional physical vapor deposition methods may be able to deposit a few hundred nanometers of copper layer through impingement, but it fails miserably to provide a decent step coverage in high aspect ratio vias, with little to no copper at the center of vias. On the other hand, some metal oxide seed layer (MOSL) methods may facilitate electroless copper metallization of glass core however, there have been recent reports where MOSL have induced glass cracking when run through a temperature cycling tests (TCTs) due to their high Young's modulus. In this work, we have developed a new polymer brush (PB) or bottle brush approach where we grow these polymers on the glass surface with complex topographies. The PBs can be tuned to a wide range of desired thickness from 10 nm to 1500 nm. Further, the PBs can be functionalized with coordinating atoms that can facilitate copper seed layer and achieve greater than 70% step coverage in very high aspect ratio vias (AR > 20). The deposited seed layer (300-700 nm) followed by a 25-micron thick electroplated copper layer, after annealing exhibits a supreme adhesion strength >4 N/cm. Our unique PB architecture of branched bottle brush structure can grow to a high thickness of 1 micron or greater. At this thickness our PB layer can also act as a stress buffer layer (SBL) between the deposited seed layer and the glass substrate, acting as a cushion for the generated stress during the TCT. This would ensure greater reliability of the glass core-based packaging