Thick Film Lithography Techniques utilizing state-of-the-art Proximity Aligners for BEoL Applications

Wafer-level packaging is a promising technology to meet future demands of increased performance for advanced integrated circuits with tighter pitch and higher I/O counts (higher feature density). Innovative equipment technology for new full field lithography techniques is at the forefront of the technology roadmap and perfectly suited for wafer-level packaging, including bond-bad redistribution and fine pitch wafer bumping applications. Typically advanced packaging applications involve thick resist processing of films in the range of up to 100 µm, exposure of conformal films on topography and the requirement for steep, controllable sidewall angles. The smallest required resolutions are in the range of 20 µm in thick film photoresists for bumping applications and 3-5 µm for pad redistribution lines in dielectric resins, like BCB. The alignment and exposure requirements for the lithographic process in WLP will be discussed. Projection aligners are still the first choice for WLP, even if the investments are much higher compared to the 1x proximity aligner. We will demonstrate that state-of-the-art proximity aligner fulfill all requirements for WLP and embedded passives.