Investigating TDDB Reliability in Next-Generation Packaging Technology: Nano-Twinned Cu RDL

Due to the performance improvement and miniaturization of semiconductor devices, the size of input/output (I/O) has decreased while their number has rapidly increased, surpassing the capacity of conventional printed circuit board (PCB) substrates. To address this issue, recent advanced packaging technology for 2.5D integration has applied a redistribution layer (RDL), which enables a larger number and smaller size of I/O, significantly improving signal process performance. However, as RDL becomes increasingly fine-pitched, the interlayer dielectric spacing between RDLs decreases rapidly, resulting in an increased effective electric field and raising concerns about potential dielectric breakdown. Notably, since the dielectric in RDL is organic dielectric polyimide (PI) instead of the SiO₂-based inorganic dielectric used in the conventional backend-of-line (BEOL), it is expected to be more vulnerable to time-dependent dielectric breakdown (TDDB). Therefore, this presentation will showcase the TDDB assessment of fine-pitch RDL interconnect for different RDL linewidth/space (L/S) and RDL line patterns. In particular, we compare the TDDB of interconnect with random microstructures to that with nanotwinned Cu interconnect, which is known to possess superior strength, ductility, thermal conductivity, and electromigration (EM) resistance due to its microstructure that incorporates a few nanometers thick twin boundaries within grains. Interestingly, we observed a clear difference in TDDB results between random Cu interconnect and nanotwinned microstructure. We will also discuss the cause of the difference in TDDB reliability according to the microstructure, based on the analysis of the leakage current conduction mechanism through voltage-ramping dielectric breakdown (VRDB) tests at various temperatures.<br/><br/>Keywords: 2.5D/3D integrated circuit (IC) integration, redistribution layer(RDL), Time-dependent dielectric breakdown (TDDB), Nano-twinned Cu