Naik, R. S., et al. Journal of The Electrochemical Society 146.2 (1999): 691.
VLSI, complementary metal oxide semiconductor (CMOS) compatible piezoelectric materials such as aluminum nitride (AlN) have great potential for application in micro bandpass filters. The quality of AlN thin films largely determines the quality factor of such devices. In order to integrate the devices into VLSI CMOS processes with Al electrodes, low temperature deposition techniques are required. A direct current (dc) magnetron sputtering system was modified to deposit high-quality polycrystalline AlN thin films on Si and Al substrates at a temperature of about 1508°C. X-ray diffraction rocking curves of 2.38 were obtained on silicon substrates and 5.78 on thin film aluminum substrates. Due to the relatively low deposition rate and the low deposition temperature required, the quality of AlN thin films is limited by the oxygen content within the film. For a deposition rate of 1 mm/h and a deposition temperature of 1508°C, the partial pressure of oxygen-containing species must be less than about 5×3×10Torr for this narrow rocking curve material. The amount of oxygen contamination depends on various system and process related factors such as deposition rate, deposition temperature, base pressure, oxygen and water partial pressures, target purity, and gas purity. Therefore, the quality of AlN films is highly system dependent. All films are tensile in nature, with stresses of 300-600 MPa for 1 mm of film on either substrate. Minimal stress control is achieved using a DC magnetron source.
The load lock can accommodate up to 14 4-inch wafers, but only one wafer can be processed at a time. There is no direct temperature control. The plasma-induced temperature at the wafer surface determines the deposition temperature. For typical deposition conditions, the surface temperature measured using thermal lacquer is about 125-150°C. The deposition pressure is regulated by a flapper valve. This valve is located between the cryopump and the high vacuum valve. An O-ring isolation valve is used to isolate the chamber from the load lock. Before loading, the wafers are rinsed with deionized water and blown dry. All deposited AlN films have a thickness of about 1 mm. The quality factor for AlN films is the fwhm rocking curve.