Physicochemical effects of seed structure and composition on optimized TSV fill performance

Microstrike and Electroless conformal seed deposition are low-temperature alternatives to iPVD for filling high aspect ratio vias. In this paper we compare electrochemical and physical measurements of seeds deposited by iPVD, Microstrike and Electroless processes and compare their TSV filling results. Measurement methods include RDE, AFM, SIMS, XRD, FIB and SEM. For iPVD seed, TSV filling performance depends mainly on large-scale surface topography along the via sidewall, which affects adsorption behavior. This observation is consistent with previous reports. For the Microstrike process, optimization of chemistry and waveform provides continuous conformal nucleation throughout the via and adequate seed for void-free filling. Filling time for 10:1 A/R vias was similar to iPVD seed, suggesting that the seed is of equivalent quality. For Electroless Cu seed, impurities cause a significant potential rise (induction) time and a low steady-state potential. Chemical optimization or compensation by changing the current waveform increases the plating rate to be close to that of the iPVD baseline while providing sufficient suppression to prevent voids.