Fabrication of silicon diaphragms by mechanical thinning

In order to allow greater freedom in MEMS designing, there is increasing interest in SOI wafers with buried structures (cavities, different support structures). A fabrication process for such wafers is presented in figure 1. Fabrication of the pre-patterned SOI wafers requires cavity fabrication on one or both of the wafers before bonding. During cavity fabrication, special care should be taken to keep the surfaces smooth and particle free. It should be emphasized that there are a wide range of different MEMS devices. Different MEMS devices place different demands on pre-patterned SOI wafers concerning cavity location (top, bottom or on both wafers), oxide location (top, bottom, both, on cavity), cavity shape and size, possible support structures (number, shape, size, locations), cavity atmosphere etc. Therefore, the fabrication process for pre-processed SOI also depends on the device.