Bonding

Bonding is essential in layer transfer: thin slices of material can be detached from substrate wafers and bonded to other wafers. Bonding of structured wafers is used to create channels, cavities and gaps, for example for microfluidic channels, capacitive pressure sensors and RF switches. Some of the techniques are common with wafer bonding, like thermocompression bonding (TCB), but in this chapter the author concentrates on wafer-level bonding applications only. Anodic bonding of silicon to glass is the oldest bonding technique in microfabrication. Anodic bonding can be visually checked through the glass side: bonded surfaces look black, and non-bonding areas are lighter. TCB applies pressure and heat simultaneously to the samples. Adhesive bonding with a polymeric intermediate layer offers several advantages for bonding. In layer transfer methods thin slices of material are cut from a donor wafer and bonded to a handle wafer. Controlled Vocabulary Terms adhesive bonding; tape automated bonding; wafer bonding