The role of stiff base substrates in warpage reduction for future high-density-wiring requirements

The role of warpage on future high density wiring requirements is investigated. These studies also show the impact of the gap between mask and the substrate arising out of warpage on the width of fine lines when vacuum cannot reduce the effect of warpage. For 100 micron wide lines, substrates with warpage greater then 50 microns are found to result in 30% error in the actual transferred pattern, while warpage greater than 200 microns results in the complete elimination of photoresist openings. The via-pad misalignment for a 300 mm substrate was measured to be 116 microns for FR4 substrate while the value is less than 25 microns for AlN. The % displacement, defined as the distance between the via center and pad center normalized with respect to the pad diameter, is hence more than 25% in case of a warped substrate, while it is found to be less than 10% for stiffer substrates. Hence, as feature size becomes smaller, accurate translation of mask features on to the substrate during photolithography will be limited by the warpage of the substrate and hence stiffer substrates are required to meet next-generation high-density wiring needs.