3rd INTERNATIONAL SYMPOSIUM ON SiAlONs AND NON-OXIDES

Abstract

The high thermal conductivity and low electrical conductivity, coupled with its nontoxic nature, make AlN ceramics the best materials for the insulating substrate applications. It is recently important issue to control the electrical conductivity of AlN ceramics in an appropriate levels as well as thermal conductivity, especially for the applications of the major chamber components for semiconductor manufacturing equipments. Sintering additives have been used for the densification of highly thermal-conductive AlN ceramics. It is well known that the additives leave residual grain-boundary phases and affect on the thermal conductivity of the polycrystalline AlN. However, the effects of sintering additives and processing parameters on the electrical conductivity of AlN ceramics are less understood. In this study, calcium fluoride (CaF2) is chosen as a sintering additive, which is known to leave minimum residual grain boundary phases. The effects of calcium fluoride on microstructural development and related electrical conductivity of AlN ceramics were examined. Electrical conductivity of CaF2-doped AlN ceramics was characterized at high temperature, typically up to 700oC, by AC impedance spectroscopy. Microstructural investigations showed the grain boundaries free of any second phase. The analysis of the complex impedance spectra showed three arcs corresponding to the resistances of the bulk, the grain boundary, and the electrode. CaF2-doped AlN ceramics revealed a variation in electrical resistivity of 5 orders of magnitude at different amount of additives and sintering conditions at the range of rt to 700oC. The grain boundary blocking and segregation effects in electrical conductivity will be discussed.