Properties and fracture of tungsten-alumina atomic layer deposited nanolaminates

Thin film coatings are often applied to microelectronic and MEMS devices to improve their tribological properties. However, as device complexity increases, it becomes necessary to deposit coatings over intricate structures. For these geometries, atomic layer deposition (ALD) represents an ideal method due to its inherent surface reaction growth mechanism. Interestingly, recent work has shown that nanolaminated film structures may display both increased hardness and fracture toughness as compared to single blanket films. Therefore, we have initiated a mechanical study of atomic layer deposited nanolaminate-based composites using alternating layers of nanocrystalline tungsten and amorphous aluminum oxide to take advantage of the high hardness and low frictional coefficients offered by the two-film systems. Using nanoindentation techniques, we have determined that the elastic modulus and hardness range from 183 to 284 GPa and 7.0 to 8.2 GPa respectively depending on laminate structure. Additionally, nanoscratch tests revealed a strong reverse length-scale effect in the fracture behavior of the laminated films. It was observed that as the layer period decreased, the apparent toughness of the film decreased. The results will be used to show how structure controls properties and fracture of ALD nanolaminates. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.