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

Surface activated bonding (SAB) is a process for bonding metals, semiconductors or insulators at the surfaces which are cleaned and activated prior to bonding by ion beam bombardment or plasma irradiation. The concept of the method is based on the reactivity of atomically clean surface of solids and formation of chemical bonds on contact between such clean and activated surfaces. The bonding procedure consists of cleaning process of the surfaces by ion- or radical beam irradiation and contact in ultra-high vacuum or in a certain ambient atmosphere. The highly activated surfaces enable to bond them to each other at a lower temperature than conventional bonding process. The process has wide applications in the microelectronics, optoelectronics, and micro electro mechanical systems (MEMS) packaging. The paper reviews the development and current status of the SAB process. A high-density bumpless interconnect for Cu electrodes (3 mu m in diameter, 10 mu m pitch) of 100,000 pieces at room temperature, and its application on 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.