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dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorGall, Daniel
dc.contributorHuang, Liping
dc.contributorPicu, Catalin R.
dc.contributorShi, Jian
dc.contributor.authorOzsdolay, Brian
dc.date.accessioned2021-11-03T08:39:47Z
dc.date.available2021-11-03T08:39:47Z
dc.date.created2016-09-27T14:11:35Z
dc.date.issued2016-08
dc.identifier.urihttps://hdl.handle.net/20.500.13015/1766
dc.descriptionAugust 2016
dc.descriptionSchool of Engineering
dc.description.abstractMoNx layers, 689-980 nm thick, were deposited on 1-inch diameter oxidized-Si(111) substrates by reactive magnetron sputtering. X-ray diffraction scans show only cubic MoNx peaks for 600-900 °C with a predominantly 002 texture for Ts = 600-700 °C and weaker 111, 220, and 113 peaks which changes to a slight 111 texture and later a lack of preferred orientation as Ts increases to 800-1000 °C. In addition, BCC Mo peaks appear at 1000 °C. The out-of-plane lattice constant for the cubic 002 peak decreases from 4.283 Å to 4.151±0.004 Å with increasing Ts, while lattice constants of the 111, 220, and 113 peaks vary from 4.236±0.005 Å to 4.138±0.003 Å as Ts varies from 600-1000 °C. The N/Mo ratio x as measured by energy-dispersive x-ray spectroscopy decreases from x = 0.99-0.51 as Ts increases from 600-1000 °C. Wafer stress measurements by x-ray diffraction show a radius of curvature that ranges from 2.43±0.35 m to 4.16±0.94 m which are confirmed by optical measurements which show a radius of curvature varying from 2.51±0.19 m to 4.48±0.51 m. Stress values range from 105±28 MPa to 179±19 MPa as measured by x-ray diffraction and from 97±11 MPa to 170±31 MPa as measured by the optical method. Hardness values range between 5.3±0.6 GPa and 6.8±0.3 GPa, while the elastic modulus decreases from 109±4 GPa to 37±1 GPa as Ts increases from 600-900 °C. The elastic modulus increases again to 164±15 GPa for Ts = 1000 °C due to the appearance of BCC Mo in this sample.
dc.description.abstractThis thesis research has focused on the thin film growth, phase stability, and elastic properties of two relatively unknown nitrides: tungsten nitride and molybdenum nitride. The elastic properties and hardness are not well characterized for either material, with previous measurements showing a wide range of values. In addition, the conditions leading to growth of high quality epitaxial layers of these materials are not well known. There is also some discrepancy over the cubic crystal structure seen in both WNx and MoNx. While the presence of nitrogen vacancies are well documented, it is unclear if metal vacancies also appear and in what concentrations.
dc.description.abstractTungsten nitride layers, 1.45-μm-thick, were deposited by reactive magnetron sputtering on MgO(001), MgO(111), and Al2O3(0001) in 20 mTorr N2 at 500-800 °C. All layers deposited at Ts = 500-700 °C form a cubic phase, as determined by X-ray diffraction ω-2θ scans, and show an N-to-W ratio x that decreases from x = 1.21 to 0.83 with increasing Ts = 500-700 °C, as measured by energy dispersive and photoelectron spectroscopies. Ts = 500 and 600 °C yields polycrystalline predominantly 111 oriented β-WN on all substrates. In contrast, deposition at 700 °C results in epitaxial growth of β-WN(111) and β-WN(001) on MgO(111) and MgO(001), respectively, and a 111-preferred orientation on Al2O3(0001). Ts = 800 °C causes nitrogen loss and WNx layers with primarily BCC W grains and x = 0.04-0.06. For Ts = 700 °C, nanoindentation provides hardness values of 9.8±2.2, 12.5±1.0, and 10.3±0.4 GPa, and elastic moduli of 240±40, 257±13, and 242±10 GPa for layers grown on MgO(001), MgO(111), and Al2O3(0001), respectively. Brillouin spectroscopy measurements yield shear moduli of 120±2 GPa, 114±2 GPa and 108±2 GPa for WN on MgO(001), MgO(111) and Al2O3(0001), respectively, suggesting a WN elastic anisotropy factor of 1.6±0.3, consistent with the indentation results. The combined analysis of the epitaxial WN(001) and WN(111) layers indicate Hill’s elastic and shear moduli for cubic WN of 251±17 and 99±8 GPa, respectively. The resistivity of WN(111)/MgO(111) is 1.9×10-5 and 2.2×10-5 Ω-m at room temperature and 77 K, respectively, indicating weak carrier localization. The room temperature resistivity is 16% and 42% lower for WN/MgO(001) and WN/Al2O3(0001), suggesting a resistivity decrease with decreasing crystalline quality and phase purity.
dc.description.abstractDensity functional theory calculations indicate an increase in structural stability by the introduction of either W or N vacancies into the cubic WN rock-salt structure, reducing the formation energy per W atom from 0.63 eV for the rock-salt structure to 0.16 eV for WN0.75 and -0.16 eV for WN1.33, to -0.83 eV for stoichiometric WN in the NbO structure. The out-of-plane lattice constant decreases from 4.357-4.169 Å with increasing Ts = 500-700 °C. Comparing these values with calculated lattice constants indicates that the W vacancy concentration increases from 6-11% for Ts = 500-600 °C to 11-18% for Ts = 700 °C, while the N vacancy concentration also increases from negligible to 18-29%. The simultaneous increase of both vacancy types is attributed to thermally activated N2 recombination and desorption and atomic rearrangement towards the thermodynamically favorable cubic NbO structure which contains 25% of both W and N vacancies. The measured elastic modulus ranges from 110-260 GPa for 500-700 °C and decreases with increasing N-content, and increases to 350 GPa for Ts = 800 °C. The room temperature resistivity decreases with increasing Ts = 500-700 °C from 4.5-1.1×103 µΩ-cm, indicating a resistivity decrease with decreasing nitrogen content and increasing crystalline quality and phase purity.
dc.description.abstractMoNx layers were deposited epitaxially on MgO(001) substrates by reactive magnetron sputtering in 20 mTorr N2 at 600-1000 °C. X-ray diffraction showed that all layers were 001 oriented cubic crystals with lattice constants that decrease from 4.26-4.16 Å with increasing deposition temperature. Rutherford Backscattering Spectrometry (RBS) showed that x decreased from 1.25 to 0.69 with increasing deposition temperature. RBS measurements confirmed a constant Mo area density across all samples, consistent with the use of a constant deposition time. X-ray reflectivity measurements showed a drastic decrease in layer thickness between samples from 98 nm to 69 nm, indicating an increasing overall film density due to Mo-vacancy filling within the cubic structure. Indeed, the Mo-site occupancy increases from 0.70-0.89 with increasing Ts while N-site occupancy ranges from 0.88-0.60 over the same range. The Ts = 800 °C layer shows a Mo-site occupancy of 0.78±0.05 and a N-site occupancy of 0.74±0.05, consistent with density functional theory predictions of a stable NbO-structure at Mo- and N-site occupancies of 0.75. Time resolved pump-probe reflectivity and surface Brillouin spectroscopy measurements show C11 values ranging from 360-502 GPa and C44 values ranging from 73-100 GPa.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectMaterials engineering
dc.titleWNx and MoNx layers: elastic properties and crystal structure
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid177523
dc.digitool.pid177524
dc.digitool.pid177525
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreePhD
dc.relation.departmentDept. of Materials Science and Engineering


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