Process conditions and lithographic performance of arch durimide polyimides in the ultra-thick film regime

Abstract

Polyimides are readily known to possess superior mechanical resistance and adhesion, better chemical inertness in strong acids and bases and, when cured, a higher thermal stability than thick novolak-based resists. They fit well in advanced buffer coat applications to release the mechanical stress between the microchip and the epoxy mould compound and represent promising candidates for recent wafer level packaging developments where they can serve either as interlayer dielectrics or as a mould for solder bumps plating. However, in MEMS fabrication and micromachining they are often perceived as over-engineered for etch processes and as under-performing as to produce high aspect ratio structures for advanced metal plating applications.We optimized coating, exposure and develop conditions for reaching Arch Durimide TM 7500 polyimide layers between 6 and 85 microns thick and investigated their photolithographic performance on the ASML SA 5200/55 stepand-repeat systems. Dense line features were analyzed from extensive focus-exposure matrices and demonstrated very wide process window capabilities and excellent CD linearity behaviors. The highly transparent backbone polymer enabled to achieve very low sizing doses and near-vertical sidewall profiles over a considerably wide process window. The aspect ratio of the lines increased linearly with thickness, reaching over 4.2 in the 85 micron film.From additional dense plasma etch and strip tests, we conclude that the Arch Durimide TM polyimides compare very advantageously to thick novolak systems to meet the robust process and high throughput requirements of future large-volume MEMS and micromachining applications, especially in the ultra-thick film regime.