Epitaxial TiN Research Articles

Effect of crystal defects on the electrical properties in epitaxial tin dioxide thin films

Epitaxial (101) tin dioxide thin films with thickness ranging from 6 and 100 nm were deposited on the (101̄2) α-Al2O3 substrate by femtosecond pulsed laser ablation. Due to the lattice and thermal expansion mismatch with the substrate, the SnO2 film shows interfacial misfit dislocations, antiphase boundaries (APBs), and partial dislocations. The APBs lie along the (1̄01) planes with a displacement of 1/2[101]. The densities of APBs and partial dislocations vary with film thickness, whereas the average spacing of misfit dislocations remains constant. Hall effect measurements showed that both electron concentration and mobility decrease with a reduction in the film thickness, which is ascribed to the scattering of electrons by crystal defects and interfaces and the effect of a native space charge region at the near-surface region of the films. The response of the films to reducing gases was found to depend on the electron concentration of the film and the relative fraction, with respect to film thickness, of material that is depleted of electrons.

Absolute orientation-dependent TiN( [formula omitted]) step energies from two-dimensional equilibrium island shape and coarsening measurements on epitaxial TiN( [formula omitted]) layers

In situ high-temperature (1030–1223 K) scanning tunneling microscopy was used to determine the equilibrium shapes of two-dimensional TiN vacancy islands on atomically smooth terraces of epitaxial TiN(0 0 1) layers. Inverse Legendre transformations of the equilibrium island shapes yield relative step energies as a function of step orientation within an orientation-independent scale factor λ, the equilibrium chemical potential of the island per unit TiN molecular area. We then use quantitative TiN(0 0 1) adatom island coarsening measurements to determine λ and, hence, absolute orientation-dependent step energies β and step stiffnesses β ̃ . For 〈1 1 0〉 and 〈1 0 0〉 steps on TiN(0 0 1), we obtain: β 1 1 0 =0.21±0.05 eV/Å, β 1 0 0 =0.25±0.05 eV/Å, β ̃ 1 1 0 =0.9±0.2 eV/Å, and β ̃ 1 0 0 =0.07±0.02 eV/Å. From the β ̃ values, we calculate kink formation energies ε 1 1 0 =0.40±0.2 eV and ε 1 0 0 =0.11±0.1 eV based on the unrestricted terrace-step-kink model.

Epitaxial Growth of Magnetic Nickel Nanodots by Pulsed Laser Deposition

ABSTRACTEpitaxial nickel magnetic nanodots were obtained by pulsed laser deposition (PLD) technique on Si (100) substrate using epitaxial TiN film as the template. Characterization methods include: high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) Z-contrast imaging, selected area electron diffraction (SAD), and X-ray diffraction (XRD) techniques. The results showed that as long as no coalescence between neighboring dots occurred, the dots are all single crystal. The predominant orientation relationship observed is Ni (100) // TiN (100) // Si (100), the so-called “cube-on-cube” orientation relationship. Other rotational orientation relationships, where the nickel crystal rotates an angle with respect to TiN (011) directions, were also observed. The dots are in faceted island shapes, bounded by (111) and (001) facets. The actual size of dots varies from a few nanometers to tens of nanometers, depending on the deposition time and temperature. The shape of a certain dot was found to be closely related to its epitaxial orientation. Effects of deposition temperature and template crystalline quality were studied. It was found that deposition temperature in a certain range does not have much influence on the epitaxial orientation of dots, while the crystalline quality of titanium nitride (the underlying template) is primarily responsible for the orientation variation. At the optimum condition, samples with a large fraction of cube-on-cube orientated nickel dots could be obtained in a rather wide temperature range (up to 250 °C), as evidenced by the strong reflections from both SAD and XRD. Samples containing more than one layer of nickel and titanium nitride matrix were also studied. The results showed that the degree of orientation perfection could be greatly improved by decreasing the size of dots.

Growth of YBCO thin films on TiN( [formula omitted]) and CeO 2-coated TiN surfaces

Epitaxial growth of YBa 2Cu 3O 7− x (YBCO) layers on TiN(0 0 1) surfaces was explored, both with and without CeO 2 intermediate layers. The epitaxial TiN layers were grown on MgO(0 0 1) and textured Ni substrates. Thin CeO 2 (∼200 nm thick) and YBCO (∼300 nm thick) layers were grown on TiN-coated MgO substrates, using pulsed laser deposition. While YBCO grown directly on TiN was of poor quality, a good epitaxial YBCO layer was obtained using a thin CeO 2 cap layer on the TiN. A superconducting critical transition temperature ( T c) of 89 K was measured by AC susceptibility. The critical current density ( J c) was 6×10 5 A/cm 2 obtained at 77 K by whole body transport current measurement in self-field using a 1 μV/cm criteria. These results suggest that transition metal nitrides, such as TiN, are potentially useful as buffer layers for YBCO thin films. Advantages of the nitride buffer layers compared to conventional oxide buffers include high electrical and thermal conductivity, better mechanical toughness, good diffusion barrier characteristics, and relative ease of deposition.

Mechanical properties of nanocrystalline and epitaxial TiN films on (100) silicon

We investigated mechanical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25 to 700 °C during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having a uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using x-ray diffraction and high-resolution transmission electron microscopy. Hardness measurements were made using nanoindentation techniques. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant at less than 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size. This behavior was modeled recently involving grain boundary sliding, which is particularly relevant in the case of hard materials such as TiN.

Oxidation and phase transitions of epitaxial tin oxide thin films on (1̄012) sapphire

We studied the structural behavior and electrical transport properties of epitaxial α-SnO thin films grown on the (1̄012) α-Al2O3 (sapphire) substrate. Hall effect measurements revealed that the epitaxial as-deposited SnO film is a p-type semiconductor. In situ x-ray diffraction studies show that the α-SnO phase is metastable and will transform into SnO2 with the rutile type structure when annealed at high temperatures in air. The onset of this phase transformation was observed to begin approximately at 300 °C during heating. Shortly thereafter, rutile SnO2 was observed to coexist with α-SnO and intermediate products such as Sn and Sn3O4. After being annealed at temperatures above 600 °C, the film then fully transformed into the rutile SnO2 phase. Our results show that the α-SnO to SnO2 structural transformation proceeds initially by the localized disproportionate redistribution of internal oxygen at low temperature, followed by the transformation of the remaining SnO phase and intermediate phases into SnO2 via the inward diffusion of external oxygen at higher temperatures. Most of the SnO2 crystallites nucleate epitaxially on α-SnO with the orientation relationship of (101)SnO2//(001)SnO and their growth processes are controlled by the (101)SnO2//(001)SnO interfaces, leading to a (101) texture and a laminar grain shape for SnO2. The relationship between the electrical transport properties and the structural evolution of the film has also been investigated.

Nickel Nanocomposite Thin Films

ABSTRACTNickel was deposited on epitaxial TiN matrix layer grown on Si (100) substrate by pulsed laser deposition process (PLD). Transmission electron microscopy (TEM) study shows that nanoparticles formed are single crystals with two kinds of epitaxial relationship with respect to matrix TiN. One is cube on cube, where (200) Ni // (200) TiN // (200) Si and (022) Ni // (022) TiN // (022) Si. The particles grown in this orientation have a trapezoidal morphology in [011] projection. The other involves a 90 ° rotation with respect to [011] direction of TiN matrix (zone axis), where (022) Ni // (200) TiN // (200) Si and (200) Ni // (022) TiN // (022) Si. The particles grown in this rotated orientation have a triangular morphology in [011] projection and a smaller lattice constant compared with that of pure nickel. The possible mechanism of forming these two epitaxial orientations is discussed. Superconducting quantum interference device (SQUID) magnetometer was used for magnetic measurements. In order to investigate the effect of texturing on magnetic properties of nanoparticles, results were compared with those obtained from Ni nanoparticles grown on amorphous Al2O3 matrix layer in previous research. It was found that both blocking temperature and coercivity of Ni nanoparticles grown on epitaxial TiN matrix are significantly higher than that of Ni grown on amorphous Al2O3. The higher value of coercivity is possibly associated with the stronger tendency of crystallographically oriented particles to retain their magnetic moments in the presence of reversing magnetic field.

Mechanical and Electrical Properties of Nanocrystalline and Epitaxial TiN Films

AbstractHigh-temperature materials such as TiN have been successfully applied as wear corrosion protection, decorative coatings, electrical contacts and diffusion barriers in electronic devices. However the poor toughness and ductility have limited some of these applications. To alleviate some of these problems, reduction of grain size can enhance grain boundary sliding and grain boundary diffusion related creep phenomena. We have investigated mechanical and electrical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25oC to 700oC during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Hardness measurements were made using nanoindentation techniques. Resistivity measurements were performed by van der Pauw method. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size in nanoscale. This behavior has been modeled recently involving grain boundary sliding which is particularly relevant in the case of hard materials such as TiN. The dependence of resistivity of TiN as a function of the substrate temperature is discussed and correlated with hardness results.

Epitaxial TiN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial TiN(001) layers grown in situ. The films were deposited by ultrahigh vacuum reactive magnetron sputtering on MgO(001) at 850 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα x-ray sources were used to obtain the XPS spectra, while the UPS data was generated by He I and He II UV radiation. The spectra show that the TiN(001) surfaces are free of O and C. The films were found to be stoichiometric in agreement with Rutherford backscattering spectroscopy (RBS) results, yielding a N/Ti ratio of 1.02 ± 0.02.

Epitaxial TiN(001) Grown and Analyzed In situ by AES After (1) Deposition and (2) Ar+ Sputter Etching

In situ Auger electron spectroscopy (AES) spectra were obtained on single-crystal TiN(001) layers grown on MgO(001)1 × 1 in a multichamber ultrahigh vacuum (UHV) system. A turbomolecular-pumped magnetron sputter deposition chamber was attached to a Physical Electronics model 660 scanning Auger system to allow spectra to be collected on the as-deposited film without exposure to air. The spectra show that the film surfaces are free of O and C. Spectra are also presented following sputter etching with a 3 keV Ar+ beam at an incident current density of 0.3 mA cm−2. The film was sputtered until the N/Ti peak height ratio reached equilibrium, then spectra were acquired for the after sputter condition. AES spectra were collected for both the as-deposited and the Ar+ sputter etched films using primary beam energies of 3, 5, 10, and 20 keV. The as-deposited bulk film composition was analyzed by Rutherford backscattering spectroscopy (RBS) and found to be stoichiometric with a N/Ti ratio of 1.02 ± 0.02.

Epitaxial TiN(001) Grown and Analyzed In situ by XPS and UPS. II. Analysis of Ar+ Sputter Etched Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to study epitaxial TiN(001) layers grown in situ which were Ar+ sputter etched. The films were deposited on MgO(001) at 850 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa) and shown to have a N/Ti ratio of 1.02 ± 0.02 by Rutherford backscattering spectroscopy (RBS). The films were sputter etched with 3 keV Ar+ at an angle of 40° to a constant nitrogen-to-titanium ratio. A Mg Kα x-ray source was used to obtain the XPS data, while the UPS data was generated by He I and He II radiation. The sputter etched films were found to have a N/Ti ratio of 0.73, indicating a preferential removal of nitrogen.

A Comparison of Auger Electron Spectra from Stoichiometric Epitaxial TiN(001) After (1) UHV Cleaving and (2) Ar+ Sputter Etching

We present Auger electron spectroscopy (AES) spectra from epitaxial B1-NaCl-structure TiN(001) layers grown on MgO(001)1×1 by ultrahigh vacuum magnetron sputter deposition. The layers are stoichiometric with a N/Ti ratio of 1.01 ± 0.02 as shown by Rutherford backscattering spectroscopy (RBS). AES spectra were obtained from clean TiN(100) surfaces by cleaving 5-μm-thick layers in situ in the Auger spectrometer at a vacuum of 2 × 10−10 Torr. For comparison, we also show spectra obtained following sputter etching for 5 min with a 3 keV Ar+ beam at an incident current density of 0.11 mA cm−2 in order to simulate typical “sputter cleaning” conditions following sample air exposure. The Ar+ beam was incident at an angle of 58° with respect to the cleaved surface normal [100]. We show that sputter etching reduces the N/Ti ratio to 0.89 due to preferential sputtering. In the experiments, the AES spectra were collected using primary electron beam energies of 3, 5, 10, and 20 keV.

Pulsed-laser-deposited AlN films for high-temperature SiC MIS devices

We report on the fabrication of device-quality AlN heterostructures grown on SiC for high-temperature electronic devices. The AlN films were grown by pulsed laser deposition (PLD) at substrate temperatures ranging from 25 °C (room temperature) to 1000 °C. The as-grown films were investigated using x-ray diffraction, Rutherford backscattering specttroscopy, ion channeling, atomic force microscopy, and transmission electron microscopy. The AlN films grown above 700 °C were highly c-axis oriented with rocking curve FWHM of 5 to 6 arc-min. The ion channeling minimum yields near the surface region for the AlN films were ∼2 to 4%, indicating their high degree of crystallinity. TEM studies indicated that AlN films were epitaxial and single crystalline in nature with a large number of stacking faults as a results of lattice mismatch and growth induced defects. The surface roughness for the films was about 0.5 nm, which is close to the unit cell height of the AlN. Epitaxial TiN ohmic contacts were also developed on SiC, GaN, and AlN by in-situ PLD. Epitaxial TiN/AlN/SiC MIS capacitors with gate areas of 4 * 10−4 cm2 were fabricated, and high-temperature current-voltage (I-V) characteristics were studied up to 450 °C. We have measured leakage current densities of low 10−8 A/cm2 at room temperature, and have mid 10−3 A/cm2 at 450°C under a field of 2 MV/cm.

Microstructural evolution and Poisson ratio of epitaxial ScN grown on TiN(001)/MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition

ScN layers, 60–80 nm thick, were grown at 800 °C on 220-nm-thick epitaxial TiN(001) buffer layers on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition in pure N2 discharges. The films are stoichiometric with N/Sc ratios, determined by Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy, of 1.00±0.02. Plan-view and cross-sectional transmission electron microscopy analyses showed that the films are single crystals which appear defect free up to a critical thickness of ≃15 nm, above which an array of nanopipes form with their tubular axis along the film growth direction and extending to the free surface. The nanopipes are rectangular in cross section with areas of ≃1.5×5 nm2 and are self-organized along 〈100〉, directions with an average separation of ≃40 nm. Their formation is the result of periodic kinetic surface roughening which leads to atomic self-shadowing and, under limited adatom mobility conditions, to deep cusps which are the origin of the nanopipes. The ScN layers are nearly relaxed, as determined from x-ray diffraction θ-2θ scans in both reflection and transmission, with only a small residual compressive strain due to differential thermal contraction. The Poisson ratio of ScN was found to be 0.20±0.04, in good agreement with ab initio calculations.

Pulsed-Laser-Deposited AlN Films for High-Temperature SiC MIS Devices

AbstractWe report on the fabrication of device-quality AlN heterostructures grown on SiC for high-temperature electronic devices. The AlN films were grown by pulsed laser deposition (PLD) at substrate temperatures ranging from 25 °C (room temperature) to 1000 °C. The as-grown films were investigated using x-ray diffraction, Rutherford backscattering specttroscopy, ion channeling, atomic force microscopy, and transmission electron microscopy. The AlN films grown above 700 °C were highly c-axis oriented with rocking curve FWHM of 5 to 6 arc-min. The ion channeling minimum yields near the surface region for the AlN films were ∼2 to 4%, indicating their high degree of crystallinity. TEM studies indicated that AlN films were epitaxial and single crystalline in nature with a large number of stacking faults as a results of lattice mismatch and growth induced defects. The surface roughness for the films was about 0.5 nm, which is close to the unit cell height of the AlN. Epitaxial TiN ohmic contacts were also developed on SiC, GaN, and AlN by in-situ PLD. Epitaxial TiN/AlN/SiC MIS capacitors with gate areas of 4 * 10-4 cm2 were fabricated, and high-temperature current-voltage (I-V) characteristics were studied up to 450 °C. We have measured leakage current densities of low 10-8 A/cm2 at room temperature, and have mid 10-3 A/cm2 at 450°C under a field of 2 MV/cm.

Ohmic contacts to p-6H–SiC using focused ion-beam surface-modification and pulsed laser epitaxial TiN deposition

The development of low-resistance Ohmic metallizations to p-type 6H–SiC, using a focused ion-beam (FIB)-Ga surface-modification and ex situ pulsed laser (PLD) epitaxial TiN deposition without further annealing, is reported. The FIB-Ga surface-modification and PLD epitaxial TiN metallizations showed a minimum value of contact resistance of 4.4×10−5 Ω cm2 at an ion dose and energy of 5.0×1016 ions/cm2 and 20 keV, respectively. Auger analysis data indicated well-defined interfaces between the metal and the semiconductor, and a significant subsurface Ga concentration.

Fabrication and characterization of epitaxial AlN/TiN bilayers on sapphire

We have grown high quality AlN/TiN heterostructures on sapphire (0001) substrates using the pulsed laser deposition (PLD) technique. The X-ray diffraction studies revealed that the AlN (0002) and TiN (111) planes were parallel to the sapphire (0006) plane and the rocking curve full widths at half maximum (FWHM) were 0.2°–0.3° for these layers. The AlN/TiN interface was found to be sharp from secondary ion mass spectrometry (SIMS) studies. The electrical resistivity of the epitaxial TiN buffer layer was as low as 14 μΩ cm at room temperature, indicating that TiN could be an excellent contact material for nitride based wide bandgap semiconductor devices. The reflection spectrophotometry measurements showed that the AlN layer deposited on top of the TiN buffer retained its bulk optical properties having a refractive index of 2.25 and an energy gap larger than 5.9 eV. The electrical transport across the TiN/AlN/TiN capacitor could be explained with the ionic conduction model.

Preferred growth of epitaxial TiN thin film on silicon substrate by pulsed laser deposition

Epitaxial TiN thin films on silicon substrates were prepared by pulsed excimer laser (KrF, 34 ns) ablation of a hot-pressed TiN target in nitrogen gas atmosphere. X-ray diffraction (XRD) showed that the preferred orientations of TiN thin films did not change with substrate temperatures, nitrogen gas pressure and film thickness; however, they did change with the orientations of substrates. The epitaxial orientation relationships between high-quality epitaxial TiN thin films and silicon substrates [2 4 2] TiN∥ [2 4 2] Si, (1 1 1) TiN∥(1 1 1) Si and [3 1 1] TiN∥ [3 1 1] Si, (1 0 0) TiN∥(1 0 0) Si. The full-width at half-maximum (FWHM) of the rocking curve of XRD and the minimum channelling yield of Rutherford backscattered spectroscopy (RBS) of the epitaxial TiN thin film were estimated to be 0.3 ° and 7.3%, respectively, indicating excellent crystalline quality of the grown film. X-ray photoelectron spectroscopy confirmed that the binding energies of Ti 2p 3/2 and N 1s core levels in epitaxial thin film were 455.2 and 397.1 eV, respectively, corresponding to those of TiN bulk. By calibrating the RBS spectra, the chemical composition of TiN thin films was found to be titanium-rich. The typical surface roughness of TiN thin film observed by scanning probe microscopy was about 1.5 nm. © 1998 Chapman & Hall

In situ scanning tunneling microscopy studies of the evolution of surface morphology and microstructure in epitaxial TiN(001) grown by ultra-high-vacuum reactive magnetron sputtering

The group IV-B transition metal nitride TiN is widely employed as a wear-resistant coating on mechanical components and as a diffusion barrier in microelectronic devices. We use the epitaxial growth of TiN as a model system for insight on the evolution of surface morphology and microstructure in more complex polycrystalline films. Atomically-flat MgO(001) substrates, prepared by air annealing at 950 °C for 12 h, are verified by atomic force microscopy (AFM). Epitaxial TiN layers are grown by reactive magnetron sputter deposition in pure N 2 at 650 - T s ≤750 °C. Scanning tunneling microscopy (STM) results show that the development of surface morphology is dominated by growth mounds with an aspect-ratio of ≈ 0.006; both the roughness amplitude and average separation between mounds follow an approximate power law dependence on film thickness, t γ, with γ = 0.25 ±0.07. The films grow in a two-dimensional multilayer mode in which island edges exhibit dendritic geometries characteristic of limited step-edge mobility. Transmission electron microscopy (TEM) shows that the films are epitaxial with dislocation loops on 111 planes and 01misfit dislocations at the interface. Low-energy N 2 + ion irradiation during film growth leads to surface smoothing with the smoothest layers, having a surface width of ≅0.22 nm, obtained with V s = 43 V. Increasing V s ≥43 V leads to surface roughening with decreased in-plane length scales.

Morphology of epitaxial TiN(001) grown by magnetron sputtering

The evolution of surface morphology and microstructure during growth of single crystal TiN(001) is characterized by in situ scanning tunneling microscopy and postdeposition plan-view transmission electron microscopy. The TiN layers are grown on MgO at 650<T<750 °C using reactive magnetron sputter deposition in pure N2. The surface morphology is dominated by growth mounds with an aspect ratio of ≃0.006; both the roughness amplitude and average separation between mounds approximately follow a power law dependence on film thickness, tα, with α=0.25±0.07. Island edges show dendritic geometries characteristic of limited step-edge mobility at the growth temperature.