High Cleanliness and High Hydrophobic/Hydrophilic Contrast Done by Direct Wafer Bonding for Die-to-Wafer Self-Assembly

We propose an innovative process with a high hydrophilic contrast for die-to-wafer self-assembly bonding. Dies and target wafer bonding surfaces first undergo a photolithography process to define bonding sites with a 15 µm step. An efficient cleaning is then performed for direct bonding surface preparation. A carrier is bonded to the bonding site to temporarily protect it during the hydrophobic treatment. After it, water contact angles of 18° and 110° are measured on bonding sites and on hydrophobic area, respectively. Finally, the self-assembly process compatibility is demonstrated with 8x8 mm² dies achieving alignment accuracy of less than 1 µm and excellent bonding interface quality.