Chapter Thirty Six - Non-destructive Bond Strength Testing of Anodic Bonded Wafers

Abstract

In this chapter, the nondestructive bond strength testing of anodic bonded wafers are discussed in detail. The bonding strength and hermeticity are the main quality aspects in wafer bonding; also, true for anodic bonding, which is widely used because it is normally a very robust and reproducible process. In order to detect this, a test structure introduced here, allows inline evaluation of the quality of an anodic bonding interface in terms of surface energy, as a standard test on every wafer during production processing. Using Finite Element Analysis (FEA) simulations, it was possible to calculate the surface energy of the monitored bonding processes. From practical experience it is known that nonbonded areas occur in the bonding interface around elevated structures, such as particle contamination or surface steps from wafer processing. In order to determine the surface energy from the measured length of the nonbonded areas, FEAs were performed. Using FEA, the dependency between the surface energy and the length of the unbonded area were calculated, with the wafer thicknesses and the step height being constant. For the multi-step structures it was assumed that the initial bonding contact occurs in the center between two lines, and that the bonding area will be enlarged during the bonding process. The multiple-step bond test structure provides a very good bonding strength measurement method for immediate quality checking after the anodic bonding of each wafer.