Characterization of front- to backwafer bulk micromachining using electrical overlay test structures

Abstract

MEMS device fabrication can benefit from accurate front- to backwafer alignment (FTBA) using wafersteppers. To characterize FTBA an electrical overlay test structure is designed and fabricated to measure front- to backwafer overlay in a bulk micromachining process. The measurement results not only show that the front- to backwafer overlay accuracy in bulk micromachining is limited by non-lithographic process errors but also give an insight into the locations and size of the defects in wet anisotropic silicon etching.