Low-temperature deposition of highly textured aluminum nitride by direct current magnetron sputtering for applications in thin-film resonators

Very large scale integration (VLSI), complementary metal on oxide semiconductor (CMOS) compatible piezoelectric materials such as AlN have great potential for applications as miniature bandpass filters. The AlN film quality strongly determines the figures of merit for such devices. For device integration into a VLSI CMOS process with Al electrodes, a low-temperature deposition technique is necessary. A direct current (dc) magnetron sputtering system was reconstructed to deposit high-quality polycrystalline AlN films on Si and Al substrates at temperatures of approximately 150 degrees C. X-ray diffraction rocking curves of 2.3 degrees on Si substrates and 5.7 degrees on thin-film Al substrates were achieved. Due to the relatively low deposition rates and the required low deposition temperature, the AlN film quality was found to be limited by the oxygen content within the film. For a deposition rate of 1 mu m/h and a deposition temperature of 150 degrees C, the partial pressure of oxygen-containing species must be less than approximately 5 X 10(-10) Torr for such narrow rocking curve material. The amount of oxygen contamination is dependent on various system- and process-related factors such as the deposition rate, deposition temperature, base pressure, oxygen and moisture partial pressure, target purity, and gas purity. Therefore, the AlN film quality is strongly system dependent. All films were tensile in nature, with stress es of 300-600 MPa for 1 mu m films on either substrate. Minimal stress control was possible with the de magnetron source. (C) 1999 The Electrochemical Society. S0013-4651(98)03-017-1. All rights reserved.