Chapter Thirty Seven - Wafer-Bonding Equipment

Abstract

This chapter discusses the wafer-bonding equipment in detail. In the beginning equipment for bonding was home based was primarily a combination of semiautomated systems. Specialized wafer-bonding equipment development was the only path to ensure the levels of productivity, reliability and reproducibility required by manufacturing processes. Development of dedicated wafer-bonding equipment started in the early 1990s. Wafer-to-wafer alignment technology is a very dynamic field. For each application the right combination of wafer-bonding/alignment technology has to be selected for the best result. Two main types of wafer-to-wafer alignment methods are used in MEMS technology—mechanical alignment and optical alignment. The main quality requirements for a wafer-level bonded MEMS device include bond strength, hermeticity, alignment accuracy and overall bonding yield, given by the number of defects. In both mechanical and optical alignment methods an in situ alignment approach provides best accuracy. Two different bonding methods are frequently used with an in situ process they are direct bonds and UV bonds. Optical alignment can be performed in two different ways—direct and indirect alignment. Direct alignment has two methods—transparent and infrared. The indirect alignment uses the process of backside alignment. Two main types of bond chambers used in wafer bonding technology are thermal bond chamber and room temperature bond chambers. A few examples of equipment solutions that are used in MEMS manufacturing are presented in detail. Besides the equipment dedicated to perform the wafer-to-wafer alignment step and wafer-to-wafer bonding step, other types of equipment are sometimes necessary for performing wafer-bonding-related processes: