Recent Developments of Photolithography Equipment for Wafer Bumping and Wafer Level Packaging

摘要

Photolithography is increasingly used for wafer bumping, wafer-level packaging and multichip module technology (MCM-D). Here, proximity printing meets practically all requirements regarding resolution, overlay accuracy, thick resist exposure (liquid or dry film) and fine patterning of standard Silicon, GaAs or flexible and warped substrates. This paper introduces the latest developments in proximity lithography focussing on thick resist exposure. Results in common resist materials like AZ4620, AZ9000 (Clariant), PMER P-LA900 (Tokyo Ohka), THB-130N (JSR), and DuPont MRC dry film are presented. Additionally new results in photo-BCB as used for multichip modules and chip scale packages are discussed. Another import issue in wafer level packaging is the availability and price of 9" masks. In order to reduce process costs, low cost soda lime masks will be increasingly used especially for prototyping. Since the CTE of soda lime is relatively high, run-out compensation will be a critical issue in the future when overlay requirements get tighter. Run-out can be compensated for by controlling the temperature of mask and wafer. Thermal management in mask aligners has to be different from projection systems, since mask and substrate are in close proximity to each other.