Demonstration of 2µm RDL wiring using dry film photoresists and 5µm RDL via by projection lithography for low-cost 2.5D panel-based glass and organic interposers

High-density packages and 2.5D interposers require 2µm trace widths and gaps, and less than 10µm ultra-small microvias to achieve 20–40µm I/O pitch interconnections. Silicon interposers with through-silicon-vias (TSVs) have been used for such ultra-high density interconnections between logic and memory chips with sub-micron multi-layer copper wiring. However, the high cost of silicon interposers coming from back end of line (BEOL) processes have limited their applicability to mobile systems like smart phones and wearables. Glass and organic interposers have been investigated as a lower cost solution coming from large panel processes and dry film lithography for semi-additive copper metallization. However, achieving high wiring density with low-cost package substrate processes remains a challenge. This paper presents the first demonstration of high resolution photo-lithography processes to achieve 2µm copper line widths and 5–10µm microvias with panel-based processes using newly developed large field projection lithography tools and advanced dry film photoresists. A two-metal layer redistribution layer (RDL) structure integrating 2µm line and space wiring and less than 10µm ultra-small microvias was demonstrated on ultra-thin glass and organic substrates.