Light Exposure Pre-Treatment for Copper-to-Copper Direct Bonding

Copper-to-copper (Cu-to-Cu) direct bonding is crucial for inter-chip vertical interconnections but is limited by strict processing conditions. This study explores UVC light and plasma treatments to enhance bonding under low-temperature <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{(\leq 250^{\mathrm{o}}\mathrm{C})}$</tex>, short-time <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{(\leq 5\min)}$</tex>, and low-pressure <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{(\leq 10}$</tex> MPa) conditions. Results show that UVC treatment significantly increases bonding strength from 14.57 MPa to 44.06 MPa, while excessive oxidation from plasma reduces strength. XPS analysis confirms that hydroxylation improves bonding, whereas excess Cu<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O weakens it. Controlled surface modification can enhance Cu-to-Cu bonding performance.