Microstructure‐Mechanical Property Correlation in Size Controlled Nanocrystalline Molybdenum Films

Abstract

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 ≈100 nm thick with a variable microstructure are deposited under variable argon (Ar) sputtering pressure (PAr), 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 PAr due to difference in the adatom mobility. The average crystallite size (d) of the nc‐Mo films is in the range of 5–20 nm; size decreases with increasing PAr. 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 (Er) of nc‐Mo films deposited at lower PAr are higher but decreases continuously with increasing PAr. Under optimum sputtering conditions, the best mechanical characteristics obtained for Mo films are: H = 25 GPa, Er = 360 GPa, H/Er = 0.07, and H3/ = 0.13 GPa. A size‐microstructure‐mechanical property correlation in nc‐Mo films is derived based on the results presented and discussed.

Correlation between Crystal Structure, Surface/Interface Microstructure, and Electrical Properties of Nanocrystalline Niobium Thin Films

“…A 2" Nb metal target (Plasmaterials Inc., Livermore, CA, USA) was used for deposition. Details of the deposition system employed in this work for Nb films were described previously elsewhere [39,40]. The deposition processing parameters employed for Nb film fabrication along with the characteristics of the Si(100) substrates are summarized in Table 1.…”

“…Therefore, and since thin film quality and properties are fully dependent on deposition rate, the sputtering pressure, sputtering power applied to Nb-target and target to substrate distance were kept constant throughout the experimental study. As such, the effect of deposition rate and/or sputtering gas pressure is not within the scope of the present study while the optimum parameters were chosen based on extensive work performed either on Nb films and/or other metal films as reported previously elsewhere [40,43]. Remarks: Substrates were rotated at speed of 6 rpm to ensure uniformity on the Nb films Si(100) substrates, which were cut from the large area substrates for the purpose of various measurements.…”

“…The grazing incidence X-ray diffraction (GIXRD) studies were carried out on Bruker D8 Advance (Bruker, Billerica, MA, USA) using Cu-Kα radiation (λ = 1.5418 Å) at room temperature. We employed the standard procedures for structural characterization of metal and alloy thin films as reported elsewhere [39,40]. However, for clarity and continuity, the details of the XRD measurements made is as follows.…”

“…The surface topology and roughness analysis were carried out by Atomic force microscopy (Nanoscope iiia, Santa Barbara, CA, USA) using a standard commercial tip (Bruker DNP-S10) with a spring constant of 0.24 N/m by raster scanning across the film surface. We adopted the experimental procedures and approaches, which were quite successful to characterize the surfaces of metal/alloy thin films, as reported widely in the literature from our previous works [40,45]. The instrument was calibrated prior to any measurements being taken.…”

“…The performance of thin metal and alloy films in technological applications is dependent upon a myriad of features, like thickness, surface and grain morphology, crystallographic nature, structural imperfections, chemical composition, and residual stresses [ 37 , 38 , 39 ]. The electronic and mechanical properties of the metal and alloy thin films fabricated using the physical vapor deposition methods, especially the well-adopted and industry compatible sputtering, depends on their processing parameters [ 40 , 41 , 42 , 43 ]. The conditions during sputter-deposition processing, like substrate temperature, working pressure, target-substrate distance and sputter power, are most relevant in influencing the thin film quality, structure, and properties [ 37 , 38 , 39 , 40 ].…”