Compatibility of common MCM-D dielectric with scanning laser ablation via generation processes

The use of a scanning laser ablation-based via generation process for MCM-D substrate fabrication is described. The robustnesses of a variety of thin (1-5-μm-thick) conformal metal masking layers were compared by static exposure in a computer controlled XeCl excimer laser exposure tool. The relative ablation rates of commercially available dielectric materials were compared for a range of fluences from 0 to 600 mJ/cm² using static excimer laser exposure. Based on process limits established by these static test results, generic scanning laser ablation (SLA) processing parameters were established which were successfully used for the fabrication of vias in low-stress, acetylene terminated, and fluorinated polyimides as well as benzocyclobutene (BCB) and polyphenylquinoxalines (PPQs). The extent of soot accumulation during SLA was dependent on the conformal metal masking layer used. Excessive accumulation of soot resulted in mask cracking around the vias. The use of helium as a process gas was found to reduce dramatically the amount of soot that accumulated and consequently to eliminate soot-related mask damage