Weibull fracture probability for silicon wafer bond evaluation

This work presents a strategy toward determining the mechanical reliability of bonded silicon microsystems. The fracture strength of a bond has been examined using burst tests and Weibull statistics. The testing method in itself exhibits small errors, is independent of operator, and works for weak and strong bonds alike. By the Weibull fracture probability approach, bond characteristics can be derived, which makes comparisons and predictions of differently sized and shaped structures possible. The fracture probability tests were made on differently treated bonded silicon microstructures. It was shown that the fracture probability is dependent on both annealing temperature and specimen shape. The fracture probability of differently sized structures was successfully predicted from experimental results. Furthermore, the bond fracture probability degrades by thermal cycling and vibration at 700 degreesC annealing. The quality of the bond is characterized by the Weibull modulus, m, and the mean fracture stress of unit length, <(<sigma>)over bar>(fc). At annealing temperatures between 120 and 1050 degreesC, m falls in the range 20-60 and <(<sigma>)over bar>(fc) increases from 18 to 55 MPa. The Griffith condition is used to correlate the fracture pressure and surface energy to the crack size responsible fur fracture. The crack half-length is approximately 21 mum for most test series. (C) 2000 The Electrochemical Society. S0013-4651(00)05-038-2. Ail rights reserved.