Development of ultra-thin Chip-on-Wafer process using bumpless interconnects for three-dimensional memory/logic applications

Chip-on-Wafer (COW) stacking structure using stack-first and bumpless interconnects was successfully fabricated for the first time. Chips were arrayed and bonded onto the wafer by back-to-face and gap filling between chips were carried out using organic material without void formation. Chips on the wafer were thinned down to 5 μm. Via-holes were formed at off-chip area (outside the chip). Copper redistribution line was formed using the via-first Damascene method. Lower leakage current as low as back ground was found between pads. No failure and an approximate 100% yield were achieved in the vertical wiring for multi-chips COW stacking.