Defect detection in films on ceramic substrates

Abstract

Disclosed is a nondestructive optical method for detecting defects (e.g., open regions) in thin opaque or non-opaque films formed on a ceramic substrate by utilizing the inherent fluoresceability of the ceramic material. The film-clad ceramic is illuminated with an intense optical radiation consisting of at least one wavelength which corresponds to the excitation band(s) of the ceramic component responsible for fluorescence. In case of an opaque film, the incident light will reach the ceramic in regions corresponding to the defects causing these ceramic regions to fluoresce at a different wavelength than that of the incident light. The fluorescent radiation emanating from the ceramic will provide a high contrast optical image of the defects particularly when viewed through a filter which transmits only the fluorescent radiation. In case the film is non-opaque, the incident light will generate fluorescent radiation over the entire substrate--both the defective and non-defective regions. However, the intensity of the fluorescent light emanating from the defective regions will be higher than that from the non-defective regions due to absence of any absorption of the incident and fluorescent light by the defective regions of the film. By analyzing the intensity of the fluorescent light emanating from the entire film-clad substrate, defects in the non-opaque film can be ascertained.