Etching Process Effects on Surface Structure, Fracture Strength, and Reliability of Single-Crystal Silicon Theta-Like Specimens

The etching processes used to produce microelectromechanical systems (MEMS) leave residual surface features that typically limit device strength and, consequently, device lifetime and reliability. In order to optimize MEMS device reliability, it is therefore necessary to determine the effects that these etching processes have on MEMS component strength. The microscale theta specimen, which is shaped like the Greek letter Θ, acts as a tensile test specimen when loaded in compression by generating a uniform tensile stress in the central web region of the specimen. Three sets of single-crystal silicon theta specimens are fabricated using two deep reactive ion etching recipes and a temperature-controlled cryogenic plasma etching recipe, each set resulting in a different specimen surface structure. The resulting strength distributions are analyzed in two ways. First, the strength data are fit to a three-parameter Weibull distribution function to determine the lower bound, or threshold strength, of each distribution. Second, the strength data are used in conjunction with various loading schemes to assess their effect on the lifetime spectrum of the device. In both approaches, the theta specimen is used to great effect to gain quantitative insight into the role of etching-induced surface features on the manufacturing yield and operational reliability of MEMS components.