Depth Profiling In Alumina Ceramic By Optical Coherence Tomography

Quality inspection of multi layer ceramic micro devices is a challenging task for large-scale production. Detection of embedded cavities, metal strips or defects within a sintered multi layer alumina ceramic stack is one of the research areas under investigation in the EU-Multilayer project. Since visible light is highly scattered in the turbid alumina, traditional optical imaging techniques fails and acoustic microscopy requires the structure to be soaked in a liquid for good acoustic coupling. In this paper we investigate the performance of optical coherence tomography (OCT) as a candidate for inspection of alumina films. To understand how deep we can "see" through the alumina material, an optical scattering model is built up based on the study of microstructure of the sintered alumina sample. The investigated sample has high purity, more than 1% porosity and an average pore size of 0.8 pm. By applying optical coherence tomography (OCT) to a sintered tapered alumina ceramic sample for the first time, a depth profile of sample is obtained with high resolution. The maximum detectable thickness is 0.26 mm using an OCT system with center wavelength at 1.3 mu m and axial resolution of 12 mu m.