Thin film adhesion characterization by microwedge scratching of precracked fine lines

A new procedure for obtaining accurate work of adhesion values for stiff films as thin as 0.5 μm or less is presented in this paper. The technique is based on fabrication of a two-dimensional test structure using a photolithographic alignment sequence. With precracks of variable length at the end of a fine line, a well known stress state is imposed before delamination. The test structure allows simple analytical equations to be applied to approximate the strain energy release rate, G. Finite element method is used to obtain more accurate values of G as well as of mode mixity. For short crack lengths, no buckling occurs, and the phase angle is near mode II. Kinking into the glass substrate is observed when the measured critical strain energy release rate, G_c, is greater than glass, but not when G_c is less than glass. When the precrack is lengthened, buckling may occur before delamination. In this case the phase angle has a large mode I component, and the crack remains in the interface even in the case of the strong interface.