Low temperature interconnect technology using surface activated bonding (SAB) method

SAB is a process for bonding surfaces which have been cleaned and activated by ion beam bombardment or plasma irradiation. The concept is based on the reactivity of atomically clean surfaces of solids and the formation of chemical bonds on contact between such clean and activated surfaces. The bonding procedure consists of cleaning followed by contact in ultra-high vacuum or in a certain ambient atmosphere. The highly activated surfaces enable them to bond to each other at a lower temperature than the conventional bonding process. This paper reviews the development and current status of the SAB process. A high-density bumpless interconnect for Cu electrodes (3 μm in diameter, 10 μm pitch) of 100,000 pieces at room temperature, and its application on the assembly of a flash memory card are demonstrated. Two new additional processes using a nano-layer adhesion and a sequential activation process are proposed for bonding of ionic materials such as SiO₂, glass and LiNbO₃.