Development of a through-stack-via integrated SRAM module

In this paper, a through-stack-via integration process for SRAM module was developed using wafer level pre-patterned BCB bonding. A SRAM module with a built-in decoder has been designed according to this integration process. TSVs passed through all stacked SRAM chips and common signals, including address bus, data bus, power, write and read control, were connected to the same TSV using RDL. The chip select signals are individually connected to the built-in decoder. RDL was fabricated using lift-off process prior to wafer bonding and via filling. Double-layer spin coating technology was employed to prevent photoresist residues left in TSVs. With pre-patterned BCB adhesive bonding, a bottom-up TSV filling features as the last step, which eliminates the traditional solder bumping, flip chip bonding and underfill filling processes. Preliminary results have shown that this process is promising for integration of memory chips with similar layout.