Metallization of High-Aspect Ratio Vias on Advanced IC-Substrates Using a Novel Liquid Metal Ink

The semiconductor industry is at an inflection point. The traditional miniaturization of transistor circuitry and its associated interconnect architecture is becoming physically and economically more difficult, while the demand for increased performance is experiencing explosive growth driven by Artificial Intelligence (AI) and other advanced computing applications. To meet the demands, novel technology solutions are required through the continued development of system level and semiconductor packaging functionalities. A key enabler of these advancements can be achieved through improvements in packaging in which affordable fine-pitch interconnect metallization is critical. Currently, most advanced IC-substrates consist of a composite of dielectric materials and epoxy, of which the most widely used is Ajinomotos Build-up Film (ABF). Herein we demonstrate a dry process approach to fabricating high aspect ratio vias and the subsequent copper metallization utilizing a novel liquid metal ink (LMI) on ABF. We outline a maskless patterning technique to fabricate vias with a diameter 8um using either a hard mask or a photoresist mask with an aspect ratio of 5:1. The dry etching parameters such as power, pressure, and gas chemistry will be discussed regarding ABF etch performance. The metallization via LMI, a novel organic based Pd catalyst system, for Cu seeding is compared to traditional Pd-based Cu seeding approaches, namely ionic and colloidal palladium. LMI demonstrates better surface wettability as evidenced by contact angle measurements. In addition, LMI shows a more desirable Pd morphology with a thinner more dispersed catalyst layer and limited inhomogeneous aggregation, as compared to traditional ionic and colloidal palladium-based approaches. LMI variations and coating processes on ABF are explored, and the subsequent electroless copper adhesion strength is evaluated. A subsequent comparison of a physical vapor deposition (PVD) Cu seed and a LMI Cu seed is conducted. The Cu seed roughness, adhesion, stress, and thickness uniformity are evaluated. This work demonstrates the feasibility of metalizing high aspect ratio vias using a novel LMI chemistry with a dry etch process in addition to comparing traditional Cu seeding approaches with LMI.