Effects of friction and loading parameters on four-point bend adhesion measurements of low-k thin film interconnect structures

The four-point bend method has become an established metrology for quantitatively examining interfacial fracture energies of thin film multi-layers. However, despite the widespread use of the technique, relatively little is known about how four-point measurements are affected by loading point friction and variations in readily adjustable loading parameters. In this study we demonstrate that four-point measurements can be sensitive to applied loading geometry and factors that affect the rate of steady state debond propagation. These effects can be experimentally significant, particularly for fracture energy measurements above similar to 5 J/m(2). We show that this behavior is due to a combination of Coulomb friction and stress corrosion effects. Good practice testing guidelines are suggested to systematically improve accuracy and consistency of four-point data.