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 e xamined using burst tests and Weibull statistics. The testing method in its elf exhibits small errors, is independent of operator, and works for weak a nd strong bonds alike. By the Weibull fracture probability approach, bond c haracteristics can be derived, which makes comparisons and predictions of d ifferently sized and shaped structures possible. The fracture probability t ests were made on differently treated bonded silicon microstructures. It wa s shown that the fracture probability is dependent on both annealing temper ature and specimen shape. The fracture probability of differently sized str uctures 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 Wei bull modulus, m, and the mean fracture stress of unit length, <(<sigma>)ove r bar>(fc). At annealing temperatures between 120 and 1050 degreesC, m fall s in the range 20-60 and <(<sigma>)over bar>(fc) increases from 18 to 55 MP a. The Griffith condition is used to correlate the fracture pressure and su rface energy to the crack size responsible fur fracture. The crack half-len gth is approximately 21 mum for most test series. (C) 2000 The Electrochemi cal Society. S0013-4651(00)05-038-2. Ail rights reserved.