Influence of metal electrodes on crystal orientation of aluminum nitride thin films

We have investigated the influence of various bottom metal electrodes on the crystallinity and crystal orientation of aluminum nitride (AIN) thin films prepared on them in order to develop thin film bulk acoustic wave resonators. AIN films were prepared on 15 kinds of bottom metal electrode (Ag, Al, Au/Ti, Co, Cr, Cu, Fe, Mo, Nb, Ni, Pt/Ti, Ti, W, Zn, Zr) using rf magnetron reactive sputtering method. The crystallinity and crystal orientation of the AIN films strongly depend on the bottom metal electrodes. The AIN films prepared on the metal electrodes with the face centered cubic lattice structure show high c-axis orientation, except Ni. The AIN films prepared on Au/Ti and Pt/Ti show the highest crystallinity and orientation among them. The high crystallinity and orientation are due to the fact that the crystallinity of the Au/Ti and Pt/Ti electrodes is high, the surface roughness of the Au/Ti and Pt/Ti is low, and An and Pt (I 1 1) planes match well with hexagonal AIN crystal structure. These results suggest that the crystallinity and orientation of AIN films are strongly influenced by bottom metal electrodes. (C) 2004 Elsevier Ltd. All rights reserved.