(A) study on thermal and electrical conductivity characterization of aluminum nitride

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 appropriate levels at high temperature 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. In single-crystal and polycrystalline AlN, the most dominant defects are oxygen-related defects that consist of oxygen substitutions for nitrogen ($O_N$), aluminum vacancies ($V_Al$), and $O_N - V_Al$ complexes. The large accommodation of oxygen contents in AlN grain is important to know the thermal conductivity of AlN. However, the role of the oxygen related defects on the thermal conductivity of AlN has not been clearly understood, because of the poor treatment of anharmonic effects which take place together with the defects effects in controlling phonon lifetimes. Furthermore, the role of defects on the electrical conductivity and the electrical conduction mechanism of AlN ceramics have not been studied. In chapter 3, in order to understand and measure the thermal conductivity of AlN ceramics via FT-Raman spectroscopy, polycrystalline AlN ceramics which have high thermal conductivity were sintered with different powder sizes of yttria additives and different mixing method. As controlling the size or dispersion of sintering additives, AlN ceramics with similar grain boundary morphology, interconnected grain boundary, and different thermal conductivity were produced. The thermal conductivity of AlN grain is generally affected by phonon dynamics and interaction. In AlN crystal, some de...