Publications Details
Mechanics of interfacial crack propagation in microscratching
There are two main issues regarding thin film debonding. The first is the nucleation of interfacial cracks, while the second is the propagation of cracks. From a mechanical testing point of view, scratch testing primarily serves to address the former issue, while indentation testing is a method of addressing the latter. A new probing technique has been developed to test thin film mechanical properties. In the Microwedge Scratch Test (MWST), a wedge shaped diamond indenter tip is drawn along a fine line, while simultaneously being driven into the line. The authors compare microwedge scratching of Zone 1 and Zone T thin film specimens of sputtered W on SiO{sub 2}. Symptomatic of its poor mechanical properties, the Zone 1 film displays three separate crack systems. Because of its superior grain boundary strength, the Zone T film displayed only one of these--an interfacial crack system. Using bimaterial linear elastic fracture mechanics, governing equations are developed for propagating interfacial cracks, including expressions for strain energy release rate, bending strain, and mode mixity. Grain boundary fracture strength information may be deduced from the Zone 1 films, while adhesion may be inferred from the Zone T films.