Influence of substrate metals on the crystal growth of AIN films

AIN films were deposited by reactive radio frequency (RF) sputtering on various bottom electrodes, such as Al, Ti, Mo, Au/Ti, and Pt/Ti. The effects of substrate metals on the orientation of A1N thin films were investigated. The results of X-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy show that the orientation of A1N films depends on the kinds of substrate metals evidently. The differences of A1N films deposited on various metal electrodes are attributed to the differences in lattice mismatch and thermal expansion coefficient between the A1N material and substrate metals. The A1N film deposited on the Pt/Ti electrode reveals highly the c-axis orientation with well-textured columnar structure. The positive role of the Pt/Ti electrode in achieving the high-quality A1N films and high-performance film bulk acoustic resonator (FBAR) may be attributed to the smaller lattice mismatch as well as the similarity of thermal expansion coefficient between the deposited A1N material and the Pt/Ti electrode substrate.