Grain exfoliation and control thereof in ultra-precision plane honing of AlN substrates

Aluminium Nitride (AlN) has been in high demand for semiconductor substrates and heat-radiation packaging materials. However, in planarisation processing such as grinding and loose abrasive methods, material characteristics deteriorate because of generation of cracks and exfoliation of AlN grains. Therefore, the authors have investigated machining of AlN by means of an ultra-precision plane honing method. This method can realise high-efficiency and low-damage machining of hard and brittle materials, by virtue of total contact between the workpiece and the grinding wheel. In this study, microindentation and scratch tests were performed in order to understand the mechanism of brittle fracture and to obtain basic knowledge for setting optimum machining conditions. The results show that the rough grinding process is accompanied by generation of surface or internal cracks and that the ductile mode, where scratch depth is less than 0.3 μηι, is characterised by few cracks and exfoliation of AlN grains.