Submicron-Scale Cu RDL Pattering Based on Semi-Additive Process for Heterogeneous Integration

Use of dry plasma etching rather than wet etching of a Cu-seed layer in a semi-additive process enabled more precise dimension controllability in the patterning of submicron-scale Cu traces due to no shift in the width of the traces. This controllability is comparable to that of competitive fabrication technologies such as that for damascene-based Cu redistribution layers. The dry etching enabled the patterning of Cu traces with an aspect ratio as high as 4.2 (L/S=0.7/0.7 µm, 3.0 µm in height) without any failures such as electrical shorts between traces. Simulation showed that an increase in the aspect ratio effectively reduced signal transmission loss due to a reduction in conductor loss. The dry etching provided very smooth surfaces on the Cu-trace side-wall (roughness as low as 0.05 µm). This further reduced the signal transmission loss compared to that of wet-etched Cu traces. Submicron-scale patterning of Cu traces using dry etching enables flexible design of redistribution layer lines in terms of signal integrity, in addition to increasing the number of signal I/Os cost effectively.