As the advanced packaging community continues to grow with the successful integration of FOWLP and 2.5D/3D interposer technologies, equipment manufacturers must also continue to expand and integrate system-scaling technologies to deliver on next generation demands. This paper presents the results of a variable high NA projection system for the imaging of high-density redistribution layers and thick film via formation as it applies to micro bump and interposer technologies.
The development effort provides the industry with the highest numerical aperture solution over a 71mm field with broader bandwidth for high aspect ratio printing needed for thick photo-imageable films. This paper demonstrate the system’s ability to image 1um RDL in thin films and 2um to 5um RDL in thick films with varying aspect ratios. This paper also demonstrates the versatility a variable NA system can provide by imaging thick film via’s with high aspect ratio’s ranging from 2.5:1 to 7:1 with near 90 degree side wall angles. To achieve both high resolution RDL and high aspect ratio vias, wavelength, numerical aperture, and partial coherence settings are considered in an optimization process.
In addition to resolution performance, CD uniformity across large fields is of particular interest and shown to maintain less than ±10% variation for a 50mm square exposure. The large exposure field is a critical aspect in throughput considerations when modifying a packaging line for large panel substrates. This paper demonstrates the ability for a panel level lithography system to overcome large substrate limitations and image 1um features for RDL applications on varying substrates.