Crack initiation in ultra thin patterned films

We present an investigation of the unique cracking problems associated with patterned thin film devices fabricated via soft lithographic methods. Decohesion and fracture of the patterned films is dominated by two key properties: interfacial failure strength and processing induced stresses/shrinkage. We utilize several experimental methods for characterizing these properties and their relationship to cracking in patterned films. Thin film interfacial strength is measured using a laser induced pulsed loading technique. Laser pulse absorption generates a high amplitude, short duration stress waves from the substrate side of the sample, providing a loading force that does not damage or otherwise affect the test film before the failure event occurs. The rapid, high strain-rate loading minimizes inelastic deformation in the films, providing an intrinsic estimate of the interfacial strength. Processing induced residual stress in the films is determined by in situ laser reflectance measurements of wafer curvature. A dynamic edge delamination test is underdevelopment to obtain the fracture toughness of the interface. The link to meaningful fracture parameters is achieved with the aid of appropriate analytical and numerical tools to support the experiments.