Real-Time XRD Characterization of Growth of Sputtered Tantalum Films
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Real-Time XRD Characterization of Growth of Sputtered Tantalum Films S.L. Lee∗, J. Mueller, D. Windover+ US Army Armament Research Development and Engineering Center Benét Labs, Watervliet, NY 12189-4050 ABSTRACT An in-situ DC magnetron sputter deposition system was constructed on the goniometer of an X-ray diffractometer for investigation of thin film nucleation and growth in real time. Tantalum films were deposited on silicon and A723 steel substrates under various deposition conditions. This paper showed: 1) Ta films evolved in single or mixed α-Ta and β-Ta phase on Si and Fe with very different growth characteristics. 2) Crystalline phase was sensitive to deposition mechanics, Ta film changed phase spontaneously without external parameter changes. 3) In pressure range 0.65-13 Pa at 100 watts, phase was not sensitive to pressure variations, but deposition rate and degree of texture decreased at high gas pressure. 4) Depositions using heavier gas showed higher α-Ta concentrations. 5) Reverse sputter cleaning of target and substrate surfaces improved Ta film adhesion. INTRODUCTION A dry sputtering process is being developed to deposit clean refractory coatings to replace electrolytic Cr deposition process.1-8 Bulk Ta, which is bcc in structure, has high melting temperature (2996°C), elastic modulus compatible with steel substrate, and is resistant to aggressive propellant chemicals. Electrochemically deposited 120µm Ta coatings grown in 850ºC molten salt solution6 and triode sputtered Ta bore coatings7 demonstrated excellent protection for the steel bore against cyclic high temperature and pressure wear and erosion. However, vapor deposited Ta exists in two phases: soft and ductile α-Ta (bcc, a= 0.33058 nm), and hard and brittle β- Ta (tetragonal, a=b=1.0194 nm, c=0.5313 nm). β-Ta transforms to α-Ta at 750ºC, and stress relaxation accompanies the transformation.9 Substrate temperature, gas species, bias affected phase and microstructure in Ta coatings.2-4, 8-11 Ductile α-Ta is favored over β-Ta as candidate for future bore coatings, to avoid brittle failure under high mechanical and thermal stresses.2-8 In-situ magnetron sputtering using 1D Inel array detector was used to study microstructure evolution of Ta films on Si, all β-Ta films were observed.12-13 Real time Xray diffraction and X-ray reflectivity techniques were developed to monitor Ta thin film growth.14-15 In this paper, we investigate Ta evolution on Si and Fe substrates and discuss various deposition parameters affecting Ta growth. EXPERIMENT METHOD Figure 1 shows the DC planar magnetron sputter deposition system, with a beryllium window for X-ray transmission, constructed on the goniometer of a 4-circle X-ray diffractometer.14-15 1D and 2D detectors recorded film growth history. In-situ depositions were made using 99.995% ∗ +
Corresponding Author- Dr. S.L. Lee, 518-266-5503, [email protected] Dr. D. Windover is currently a National Research Council Fellow, NIST, Gettysburg, MD
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Figure 1. In-Situ Magnetron Sputter Deposition Syste
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