Determination of the Oxygen Permeability of Metal Oxide Thin Films
Various metals such as Ta, Ti, W and their nitrides are often applied as thin films in integrated circuits as supportive and protective layers. For those films to be effective, they must remain unoxidized. During IC manufacturing, thermal cycling would often oxidize the thin film even with trace amount of oxygen in the environment. Once the metal/metal nitride oxidized, they would no longer remain its functionality. Therefor diffusion barrier with low oxygen diffusion flux and permeability is needed in a thermally active environment. This work investigated the oxygen permeability of Y2O¬3 and Al2O3 thin films utilizing optical study of a Zr indicator layer. Diffusion barriers were deposited on a Zirconium layer and were thermally oxidized in an oxygen environment. Optical thickness measurement of the formed ZrO2 layer were measured and the oxygen diffusion flux and permeability were experimentally determined. Cubic bixbyite Y2O3 was determined to be a poor diffusion barrier against oxygen. Its oxygen permeability ranged from 1.40E-12 to 2.32E-9 mol/cm*sec with different oxidation temperature, time and barrier thickness. The oxidation and oxygen diffusion behavior at 500°C were significantly different than the 300°C and 400°C oxidations. It was experimentally determined that the oxygen diffusion flux in Y2O3 had little dependency with Y2O3 barrier thickness below 400°C and the flux decreases with increasing Y2O3 thickness at 500°C. Possible diffusion mechanism involves Fick’s diffusion and pipe diffusion but requires future experiment to be testified. Experiments had also shown that Y2O3 diffusion barrier reacted differently to repeating heating and cooling at different temperatures and generally could not be applied as an oxygen diffusion barrier. Corundum bixbyite Alumina films were tested using the same procedure as the Y2O3 films. Experiments showed that complete coverage Alumina film with thickness greater than 2nm had negligible oxygen diffusion flux and permeability at 300°C, 400°C and 500°C. Therefore, Alumina thin film could be applied as oxygen diffusion barrier at below 500°C environment.
Materials Science; thin film; metal oxide; oxygen diffusion; Permeability
Van Dover, Robert B.
Xing, Huili Grace
Materials Science and Engineering
M.S., Materials Science and Engineering
Master of Science
dissertation or thesis