Microstructure-Mechanical Property Correlation in Size Controlled Nanocrystalline Molybdenum Films

The authors report on the microstructure, crystallography, and mechanical properties of size controlled nanocrystalline (nc) molybdenum (Mo) films deposited by sputtering. The nc-Mo films of approximate to 100nm thick with a variable microstructure are deposited under variable argon (Ar) sputtering pressure (P-Ar), which is varied in the range of 3-25 mTorr. X-ray diffraction analyses indicate that the nc-Mo films exhibit (110) preferential growth. However, the crystal-quality degradation occurs for Mo films deposited at higher P-Ar due to difference in the adatom mobility. The average crystallite size (d) of the nc-Mo films is in the range of 5-20nm; size decreases with increasing P-Ar. The effect of sputtering pressure is significant on the microstructure, which in turn influences the mechanical characteristics of Mo films. The hardness (H) and modulus of elasticity (E-r) of nc-Mo films deposited at lower P-Ar are higher but decreases continuously with increasing P-Ar. Under optimum sputtering conditions, the best mechanical characteristics obtained for Mo films are: H=25GPa, E-r=360GPa, H/E-r=0.07, and H-3/<mml:msubsup>Er2</mml:msubsup>=0.13GPa. A size-microstructure-mechanical property correlation in nc-Mo films is derived based on the results presented and discussed.