SOI wafers are joined together by silicon fusion bonding, a method that brings into contact two hydrophilic, mirror-polished, flat and clean silicon surfaces and anneals them at high temperature. The CL200 processes two wafers simultaneously without separation between process steps. The closed chamber acts as splash protection and creates a mini-environment with a controlled nitrogen atmosphere for optimum process control. The semiautomatic machine can be upgraded to a fully automatic substrate bond cluster.
Optional cleaning with diluted standard cleaning chemicals is offered for process development. The final cleaning is performed by megasonic activation. The system has demonstrated the capability to remove fine particles greater than or equal to 0.1 μm from the wafer surface. The drying step is performed by spinning the wafers at high speed and incorporating infrared-heating. Alignment of the wafers is created by floating each substrate to reference pins at the flat and the edge. The CL200 initializes prebonding by performing a point contact at the edge or center position, depending on the required process.