MEASUREMENT OF THIN FILM STRENGTH

PURPOSE:To determine the strength of a thin film by pressing a steel ball or the like on a thin film on a substrate to measure distortion of the substrate (equal to distortion of the film) at a possible cracked portions. CONSTITUTION:As a steel ball 1 is pressed on a thin film 3 of a substrate, the substrate 2 and the thin film 3 both deform causing a concentric crack 4 through the thin film 3. When the steel ball 1 is pressed on the thin film 3 in a virtually static manner, the distortion of a dented boundary 5 increases with the diameter (d) of the dent. But in the film once tensioned, the distortion at a desired point in the dent won't change after the pressing of the steel ball because the distortion can be preserved by friction with the steel ball and hence, the distortion is determined primarily by the distance (x) from the center of the dent. When the diameter of the minimum circle of the concentric crack is presented by (d) and measured, the fracture distortion epsilon of the film can be measured from the formula.