By Ultrasonic Systems, Inc. (USI)
Photoresists are light sensitive materials used in photolithography to produce a patterned coating on a substrate.Photoresists are widely used in the electronics industry including the fabrication of multi-layer high density interconnects for advanced packaging. In the case of wafer-level and panel-level packaging photoresist is used to create the intra-layer horizontal connections. The photoresist must be applied in a uniform layer at a specified thickness to ensure that these connections can be properly formed. Traditionally, photoresists are applied to wafers by spin coating. However, with the advent of the panel-level process, spin coating is not practicable for achieving a uniform coating on a large rectangular panel. Additionally, these panels are often warped which poses serious challenges for application methods like slot-die coating. In order to demonstrate the efficacy of using t CAT to apply photoresist for the creation of high density interconnects a study comparing t CAT with spin coating was conducted. In this study the USI Prism 800 system was used to produce 2 micron line/space pattern in a 7 micron thick layer of photoresist using a 300 mm diameter copper seeded silicon wafer as the test substrate. The photoresist layer thickness was measured across the surface of a 300 mm diameter wafer for the spin coating process. A statistical analysis of the photoresist film thickness data for the spin coated wafer is shown above. The photoresist layer thickness was measured across the surface of a 300 mm diameter wafer for the spray coating process. A statistical analysis of the photoresist film thickness data for the spin coated wafer is shown above. The photoresist thickness uniformity of the wafer coated with t CAT is significantly better than for the spin coated wafer. The next step is to demonstrate that the imaging performance is not adversely impacted by the t CAT spray coating process. A 2 micron line/space pattern is achieved in a 7 micron thick layer of photoresist applied with the spin coating process. A 2 micron line/space pattern is achieved in a 7 micron thick layer of photoresist applied with the t CAT spray coating process wit h no adverse impact on performance. The same results have also been achieved on panel size substrates up to 650 mm x 650 mm. Please contact us directly to receive a detailed technical presentation and paper on this promising new process. Contact us to discuss your coating process requirements.
