Influence of Process Parameters on Surface Activated Aluminum-to-Aluminum Wafer Bonding

Abstract

Aluminum-to-aluminum wafer bonding is a promising technique for future wafer-level packaging and heterogeneous integration. The main challenge for a successful Al-to-Al thermocompression bonding is the fast oxidation of the aluminum surface. In this article, a surface-activated Al-to-Al wafer bonding process for patterned 200-mm wafers is presented, which removes the oxide in an argon plasma and enables a high bond quality with an accurate alignment. The influence of the bonding parameters’ temperature (200 °C–300 °C), force (20–40 kN), and activation time (2.5–5 min) on the contact resistances and bonding yield is analyzed. Additionally, we modified an etch mask during wafer fabrication and thereby improved the condition of the Al pad surface, which resulted in a higher bonding quality. Based on this optimized wafer fabrication process, we achieved a high bonding yield of >85% and contact resistances in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega $ </tex-math></inline-formula> range for bonding temperatures as low as 250 °C. This demonstrates the potential of Al-to-Al wafer bonding to create reliable interconnects for 3-D wafer-level integration.