Fracture probability and Weibull statistic analysis is introduced as a new method to evaluate the reliability of anodically bonded structures. The method enables comparison of anodic bonding performance for various bonding conditions. Fracture strength for samples bonded at different temperatures have been evaluated and found to agree with previously reported results. The strength of anodic bonds, processed at temperatures between 300 and 450°C, are comparable to silicon fusion bonds annealed at temperatures above 800°C. Shock and ramp bonding are compared regarding their fracture probability.

A strategy towards determining the mechanical reliability of bonded silicon microsystems is presented. The fracture probability has been analysed by the Weibull statistical approach. Fracture probability tests have been made on differently treated bonded silicon microstructures. The fracture probability of differently sized structures is successfully predicted from experimental results. It is shown that the bond fracture probability degrades by thermal cycling and vibration. Furthermore, the fracture probability is dependent on both annealing temperature and cavity shape.

In this paper, the oxygen plasma bonding process for fusion bonded silicon wafers has been characterized by a new approach. The mechanical reliability of bonded microstructures was determined using burst tests and Weibull statistic analyses. The fracture characteristic of the bonded system is considered to depend on the stress distribution, the defect distribution and the fracture surface energy at the bond. Using Weibull theory, it is possible to extract the Weibull modulus m and the mean fracture uniform tensile stress per unit length <()over bar>(fc), from the measured data. These quantities make it possible to compare the joint defect distribution and the fracture surface energy at the bonded interface for the processing conditions under observation. These experiments also demonstrate that it is possible to distinguish between these quantities under certain conditions.The fracture probability for different annealing temperatures has been evaluated and found to agree with previous results from surface energy measurements. It is shown that the bond fracture probability increases with annealing times in the range of 10-100 h. The saturated bond strength value is considerably enhanced by oxygen plasma activation prior to bonding. In this study, plasma activations at room temperature and 300 degreesC compare to chemical activations in hot nitric acid annealed at 120 degreesC and 700 degreesC respectively. The tendency to form voids at elevated temperatures, e.g. 300 degreesC. is increased by the oxygen plasma treatment.If the surface energy is considered to be homogeneous over the bonded interface, the Weibull modulus In is an indirect measure of the defect distribution, low m values indicate a wide spectrum of defect types, whereas a high in value narrows the defect distribution responsible for fracture. The Weibull modulus in is shown to be valuable for evaluation of the bonded interface. It is demonstrated that a more scattered defect distribution emerges for in situ bonded wafers as compared to ex situ, and annealing at 300 degreesC for 90 h as compared to room-temperature storage. However. the defect distribution becomes increasingly more narrow with storage time. These variations may be due to either changes in microcracks or void configuration or inhomogeneities in the fracture surface energy over the bond interface.