Internal Stress Dependence of Aluminum-doped Zinc Oxide Thin Films Deposited by DC Magnetron Sputtering on the Deposition Conditions

The internal (growth) stress of very thin aluminum-doped Zinc Oxide (AZO) films, i.e., 30 nm in thickness, was investigated as the deposition conditions, such as sputter working pressure, applied power on the cathode and amount of O-2 addition, were varied. All of the films in this study were deposited by DC magnetron sputtering on glass substrates. The internal stress of the AZO thin films was measured by using a laser scanning technique. Because of the importance of the optical properties of the AZO dielectric films, the refractive indices were measured by using spectroscopic ellipsometry (SE), which also determined the film's thickness precisely. Also, the transmission rate was measured by using a spectrophotometer. Through this work, we confirmed that the deposition conditions, especially the total working pressures influenced the internal stress of the deposited film strongly, even in a very thin film of 30 nm. When the total working pressure was increased from 5 mTorr to 20 mTorr, about a 50% reduction of internal stress could be obtained without any substantial change in the optical properties. The dependence of the internal stress on the pressure can be explained by the "atomistic peening" effect due to the bombardment of energetic species during the deposition