Titanium Nitride Surface Research Articles

Surface chemistry and film growth during TiN atomic layer deposition using TDMAT and NH 3

Surface chemistry and film growth were examined during titanium nitride (TiN) atomic layer deposition (ALD) using sequential exposures of tetrakis-dimethylamino titanium (TDMAT) and NH 3. This ALD system is shown to be far from ideal and illustrates many potential problems that may affect ALD processing. These studies were performed using in situ Fourier transform infrared (FTIR) techniques and quartz crystal microbalance (QCM) measurements. Ex situ measurements also analyzed the properties of the TiN ALD films. The FTIR studies revealed that TDMAT reacts with NH x * species on the TiN surface following NH 3 exposures to deposit new Ti(N(CH 3) 2) x * species. Subsequent NH 3 exposure consumes the dimethylamino species and regenerates the NH x * species. These observations are consistent with transamination exchange reactions during the TDMAT and NH 3 exposures. QCM studies determined that the TDMAT and NH 3 reactions are nearly self-limiting. However, slow continual growth occurs with long TDMAT exposures. In addition, the TiN ALD growth rate increases progressively with growth temperature. The resistivities of the TiN ALD films were ⩾10 4 μΩ cm and the densities were ⩽3 g/cm 3 corresponding to a porosity of ∼40%. The high porosity allows facile oxidation of the TiN films and lowers the film resistivities. These high film porosities will seriously impair the use of these TiN ALD films as diffusion barriers.

Fibroblast growth on surface-modified dental implants: an in vitro study.

A major consideration in designing dental implants is the creation of a surface that provides strong attachment between the implant and bone, connective tissue, or epithelium. In addition, it is important to inhibit the adherence of oral bacteria on titanium surfaces exposed to the oral cavity to maintain plaque-free implants. Previous in vitro studies have shown that titanium implant surfaces coated with titanium nitride (TiN) reduced bacterial colonization compared to other clinically used implant surfaces. The aim of the present study was to examine the support of fibroblast growth by a TiN surface that has antimicrobial characteristics. Mouse fibroblasts were cultured on smooth titanium discs that were either magnetron-sputtered with a thin layer of titanium nitride, thermal oxidized, or modified with laser radiation (using a Nd-YAG laser). The resulting surface topography was examined by scanning electron microscopy (SEM), and surface roughness was estimated using a two-dimensional contact stylus profilometer. A protein assay (BCA assay) and a colorimetric assay to examine fibroblast metabolism (MTT) were used. Cellular morphology and cell spreading were analyzed using SEM and fluorescence microscopy. Fibroblasts on oxidized titanium surfaces showed a more spherical shape, whereas cells on laser-treated titanium and on TiN appeared intimately adherent to the surface. The MTT activity and total protein were significantly increased in fibroblasts cultured on titanium surfaces coated with TiN compared to all other surface modifications tested. This study suggests that a titanium nitride coating might be suitable to support tissue growth on implant surfaces.

Development of human mesenchymal stem cells on DC sputtered titanium nitride thin films.

The biocompatible properties of titanium nitride (TiN) have opened a new field of applications for this material. In the present work, TiN coatings with thicknesses around 1 microm have been prepared by DC magnetron sputtering. The aim has been to evaluate the adherence, growth and proliferation of human pluripotent mesenchymal stem cells (hMSCs) on the surface of TiN films with contrasted structural, electrical, and mechanical properties. For this purpose, the films were characterized by X-ray diffraction, scanning electron microscopy, sheet resistance measurements, and nanoindentation. Biological tests show that hMSCs adhere and proliferate onto TiN surfaces. The combination of the mechanical, electrical, and biological responses suggest that TiN coatings present appropriate properties to induce the in vitro stimulated differentiation of hMSCs. This possibility gives an added value to TiN based biomaterial coatings.

Surface nitridation of titanium by pulsed Nd:YAG laser irradiation

Surface nitridation of titanium is an adequate method to improve the hardness and wear resistance of the material. We report experimental results concerning the surface treatment of titanium by pulsed Nd:YAG (λ=1.064 μm) laser irradiation in nitrogen atmosphere. Titanium foils were scanned with constant velocity by high repetition rate (1 kHz) laser beam pulses, and the most appropriate irradiation conditions were determined to obtain titanium nitride surface layers without defects or corrugations. The best results were obtained at laser intensities just under the transition from surface melting to ablation. The obtained layers were characterised by surface profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and spectrophotometry. In the XRD spectra of the films the positions of the ( h k l) reflections reproduce the standard data of the tetragonal δ′-Ti 2N phase. In the literature films containing tetragonal Ti 2N phases are described as having better mechanical properties, corrosion and wear resistance in comparison with cubic TiN.

Fatiga oligocíclica de la aleación Ti<sub>6</sub>Al<sub>4</sub>V nitrurada termoquímicamente

The use of titanium and its alloys in applications with the presence of friction is limited, due to low hardness and reduced tribological properties. Some surface treatments are available in order to correct these problems, like the thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Oligocyclic fatigue behaviour in air of Ti6Al4V alloy has been studied. Results show a reduction of oligocyclic fatigue loads up to 10 % compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.

Low cycle fatigue behavior of Ti6Al4V thermochemically nitrided for its use in hip prostheses.

Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Besides, titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes difficult the use of titanium and Ti6Al4V in some biomedical applications, like articulating components of prostheses. Some surface treatments are available in order to correct these problems, like thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Low cycle fatigue behavior in air of Ti6Al4V alloy has been studied. Results show a reduction of low cycle fatigue life up to 10% compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.

Characterization of magnetron sputtering deposited thin films of TiN for use as a metal electrode on TiN/SiO2/Si metal–oxide–semiconductor devices

Titanium nitride (TiN) thin films were deposited by dc magnetron sputtering on SiO2/n-Si substrates in order to study their use as gate electrodes in metal–oxide–semiconductor (MOS) devices. Rutherford backscattering spectroscopy was used to determine the composition of the films and the results were correlated to those obtained by electrical measurements of the constructed MOS devices. Oxygen contamination of the TiN layers was observed, with percentage and spatial variations depending on the various deposition parameters such as the deposition temperature and the substrate bias. The best electrical performance was achieved for devices where the exposed TiN surface had low oxygen contamination. From these samples, the TiNx–Si barrier height was calculated to be equal to 0.52 eV.

Density-functional study of bulk and surface properties of titanium nitride using different exchange-correlation functionals

The adsorption and diffusion of hydrogen on the (100) surface of titanium nitride was studied using density-functional theory (DFT) and the generalized gradient approximation (GGA) for the exchange and correlation energy. The adsorption site was found to be on top of the titanium atom with the chemisorption energy of -2.88 eV. The diffusion barrier was determined as 0.73 eV along the path connecting the neighboring titanium atoms. The surface energies and surface relaxations of the three most important surfaces of TiN were studied. The surface energies have the following order: ${S}_{100}<{S}_{110}<{S}_{111}.$ Three different GGA functionals, the Perdew-Wang 1991 (PW91), the Perdew-Burke-Ernzerhof (PBE), and the revised PBE (RPBE) functionals, were tested on crystals, small molecules and TiN surfaces. The RPBE functional when applied to the surface studies of TiN was found to produce slightly lower values of surface energies and of hydrogen adsorption energies than the PW91 functional.

Quantum chemical study of aluminum CVD reaction for titanium nitride (111) surface with terminal fluorine

Reaction mechanisms and interface structures in aluminum (Al) chemical vapor deposition (CVD) have been investigated in terms of the surface termination models for TiN by ab initio quantum chemical approach. The B3LYP density functional calculations and coupled-cluster calculations were carried out by using the local structural models in order to investigate reaction mechanisms, and we found Al can be deposited on F-terminated TiN (111) surface via the substitution of hydrogen for terminal fluorine. Energetics of the reaction processes has also been discussed by the local density approximation (LDA) with the periodic boundary models. The result that total reaction enthalpy is exothermic has been obtained for the local structural models calculations and the periodic boundary calculations. In particular, a series of reactions by the successive attack of AlH3 proceed with no energy barrier for the periodic models.

Interface analysis of CVD diamond on TiN surfaces

We prepared polycrystalline diamond thin films on smooth silicon substrates with the help of a titanium nitride (TiN) buffer layer. TiN layers of different thickness were deposited first on crystalline silicon substrates with mirror finish. The TiN layers were placed by physical vapor deposition (PVD) assisted by direct current reactive magnetron sputtering. Later, diamond thin films were grown by hot filament chemical vapor deposition (HF-CVD). Scanning electron microscopy observations show a notable increase in the size of diamond particles on the substrates with the TiN buffer layer, as opposed to the plain, only scratched substrates. The diamond films were characterized by high-resolution transmission electron microscopy (HRTEM), electron energy loss (EELS) and energy dispersive spectroscopies (EDS). A buffer layer ∼0.8 nm thick is observed between the diamond particles and the TiN layer. EDS experiments reveal a carbon nitride compound at the interphase. There is no evidence of degradation (cracking, delamination, etc.) of the TiN layers for thickness below 0.5 μm.

Adsorption and desorption kinetics of tetrakis(dimethylamino)titanium and dimethylamine on TiN surfaces

Titanium nitride (TiN) can be deposited using the organometallic precursor tetrakis(dimethylamino)titanium (Ti[N(CH 3) 2] 4) (TDMAT). Deviations from conformal TiN film growth have been observed in trench structures using TDMAT. This nonconformal deposition may be associated with readsorption and site blocking by the dimethylamine (HN(CH 3) 2) (DMA) reaction product. To understand the deviations from conformal TiN deposition in trench structures, the adsorption and desorption kinetics for TDMAT and DMA were measured on a sputter-deposited TiN surface using laser induced thermal desorption (LITD) techniques. The LITD measurements revealed that DMA has a higher sticking coefficient than TDMAT. The sticking coefficients for both TDMAT and DMA were also dependent on surface coverage. The initial sticking coefficient for TDMAT is S 0=0.23 with a coverage-dependence approximated by S( θ)=0.25 exp(−4.7 θ) where θ is the normalized surface coverage. The initial sticking coefficient for DMA is S 0=0.70 and the coverage-dependence is approximated by S( θ)=0.86 exp(−3.7 θ). The observed desorption kinetics of DMA following TDMAT and DMA exposures on TiN were also coverage-dependent. The isothermal desorption measurements could be fit using a simple first-order desorption rate expression, k d= ν dexp[− E d( θ)/ RT] where E( θ) is the coverage-dependent desorption energy, E d( θ)= E 0− E 1 θ. Assuming a desorption preexponential of ν d=1×10 13 s −1, the observed isothermal desorption measurements for DMA desorption following both TDMAT and DMA exposures could be fit using E 0=29.1 kcal mol −1 and E 1=8.2 kcal mol −1. These measured adsorption and desorption kinetics are consistent with DMA readsorption as a major contributor to nonconformal TiN growth in trench structures using TDMAT.

Friction and wear of TiN-4140 steel couples in methanol

Titanium nitride (TiN) surface layers have the potential to decrease wear and increase the working life of methanol fuel injector components. A number of studies have been conducted on the wear-resistance of TiN in various lubricants. However, the friction and wear characteristics of TiN coatings in a methanol environment have not been investigated. For this research, TiN coatings were obtained by pressure vapor deposition (PVD), chemical vapor deposition (CVD) and ion implantation (ION) processes. The friction and wear characteristics of the TiN surfaces, coupled with a nitrided 4140 steel and in a methanol environment, were determined using reciprocating sliding tests. In general, the coatings protected their substrates from wear, but many caused extensive wear on the 4140 steel sample. The ION layer did not provide adequate wear protection during long-term testing. Wear due to the roughest PVD and CVD coatings increased with applied contact force. The two smoothest PVD coatings exhibited the best tribological performance under the conditions investigated.

UV irradiation effects in Al chemical vapor deposition on titanium nitride

UV irradiation effects on Al chemical vapor deposition on titanium nitride (TiN) was investigated by using dimethylaluminum hydride at 150 °C. Al films grew thermally at a rate of 6.3 nm/min, while the UV light generated by a deuterium lamp reduced the rate to 5.2 nm/min. When TiN surfaces were oxidized, Al films started to grow only under UV irradiation. Using x-ray photoelectron spectroscopy (XPS), we showed that the adsorbates formed on the oxidized surfaces could be dissociated only when the UV light was irradiated. The XPS results also suggested involvement of photoinduced desorption in reducing the growth rate.

Chemical vapor deposition of copper from CuI hexafluoroacetylacetonate trimethylvinylsilane for ultralarge scale integration applications

In this article, the authors report the results of a study aimed at optimizing a manufacturable thermal copper-chemical vapor deposition process, using (tmvs) CuI (hfac) as the source, where tmvs=trimethylvinylsilane and hfac=hexafluoroacetylacetonate, and establishing associated material and process characteristics and performance. This study employed a two-stage design of experiments approach in conjunction with actual deposition runs on unpatterned silicon (Si) and titanium nitride (TiN) surfaces, as well as SEMATECH patterned TiN structures with feature sizes as small as 0.30 μm with aspect ratio 6:1. All samples were analyzed by Auger electron spectroscopy, Rutherford backscattering, four-point resistivity probe, and cross-section scanning electron microscopy. The results of these analyses showed that precursor concentration, substrate temperature, and in situ predeposition substrate surface plasma treatment play a key role in achieving good conformality and complete filling at high growth rates in aggressive via and trench structures. Based on these findings, an optimum process window was identified and employed to demonstrate complete high growth rate (∼2000 Å/min) filling of 0.3 μm, 6:1 aspect ratio, devices structures with pure copper at as-deposited resistivities of 1.8 μΩ cm.

Electrochemical and thermal oxidation of TiN coatings studied by XPS

AbstractX‐ray photoelectron spectroscopy (XPS) has been used to investigate the electrochemical and thermal oxidation of titanium nitride (TiN) coatings prepared by physical vapour deposition (PVD) at 200°C. Electrochemical oxidation of TiN was carried out at various potentials in phthalate buffer solution (pH 5.0). Evaluation of the XPS Ti 2p and N 1s spectra showed the presence of nitride, oxynitride and oxide species in the layer formed by anodic oxidation. The electrochemical oxidation of TiN to TiO2 proceeds through the formation of a mixed oxynitride/oxide layer, which transforms into oxide (TiO2) at sufficiently positive potentials (E > 1.1 V vs. SHE). The oxidation of TiN to TiO2 is accompanied by the formation of molecular nitrogen (N2). The thickness of the oxide layer reaches ∼7 nm after oxidation at the highest potential (1.9 V). A complete coverage of the TiN surface by TiO2 leads to an anodic peak in the polarization curve. On the basis of angle‐resolved XPS measurements, two types of oxynitride species are identified, which are distributed differently throughout the oxidized layer.X‐ray photoelectron spectroscopy depth profiles of TiN oxidized at 450°C and 600°C in an oxygen flow reveal that at the lower temperature an oxynitride layer is formed, whereas a thick TiO2 layer appears on top of TiN at the higher temperature. The interface between the nitride and oxide phases is relatively sharp. It is suggested that the mechanism of TiN oxidation proceeds by a progressive replacement of nitrogen by oxygen. The TiN coatings can be used up to 600°C as a protective coating in an oxygen atmosphere.Valance band spectra of TiN, as well as of electrochemically and thermally oxidized TiN, are presented and discussed.

Influence of Wafer Preclean before Selective Tungsten CVD on Surface Properties of Interconnect and Intermetal Dielectric Materials

Results of selective tungsten CVD on titanium nitride (TiN) are summarized. The investigations are focused on the influence of precleaning and tungsten nucleation on the TiN and SiO2 surface, the CVD-W/TiN interface and the electrical properties of the contacts (via resistance). After a combination of HF dip and NF3 plasma a remarkable amount of fluorine was detected at the TiN surface which was not bound to Ti. This process showed the best effect on the reproducible nucleation of tungsten. No interfacial layer could be found by cross section TEM after the tungsten nucleation. But in the case of nucleations starting with SiH4 gas inlet tungsten growth begins with the formation of a mixture of α- and β-phase tungsten. More far away from the interface region only α-W was detected. The lowest via resistances in filled vias were measured for nucleations starting with WF6 gas inlet. For introducing SiH4 first the via resistance could be decreased using a H2 plasma conditioning of the wafer in the deposition chamber after dry pretreatments. For this case no remarkable change of the deposition surface was found by XPS. At wafers pretreated with BCl3/N2 plasmas on both surfaces (TiN and SiO2) boron nitride was found.

Surface and Interface Study of Titanium Nitride on Si Substrate Produced by Dynamic Ion Beam Mixing Method

Crystal growth of TiN on Si substrate under dynamic ion beam mixing (DIBM) processing was monitored by reflection high-energy electron diffraction (RHEED) and the interface was studied by transmission electron microscope (TEM). The TEM observation has revealed that the intermixed layer between the Si substrate and TiN film is composed of three different types of sublayers. The thicknesses of the first and the second sublayers were same as ∼7–8 nm and ∼3–4 nm, respectively, independent of different arrival ratios of Ti/N. The thickness of the third layer, however, was ∼6 nm for the arrival ratio of nearly unity whereas it was ∼14 nm for the arrival ratio greater than unity. Characterization of these sublayers with a field-emission analytical electron microscope (AEM) has revealed that these three sublayers are of an amorphous structure, composed of a mixture of Si and N, of a mixture of Si, N and small amount of recoil-implanted Ti, and of a mixture of Si, N, and Ti, for the 1st, 2nd and 3rd sublayers, respectively. TiN (001) is epitaxially grown on Si (001) along the incident direction of nitrogen ions even though the intermixed layer exists inbetween the TiN film and Si substrate.

Nucleation of Tungsten on Titanium Nitride with Hydrogen Reduction of Tungsten Hexafluoride

ABSTRACTIn this work, a hydrogen (H2) reduction process has been developed which gives tungsten (W) nucleation on titanium nitride (TiN) adhesion layers with a very short incubation time, eliminating the need for a silane (SiH4reduced seed layer. The nucleation was found to be strongly dependent on the following factors: temperature of the substrate, total pressure in chamber, and gas introduction sequence into the reactor. Theenhanced nucleation rate has been explained based on two competing reactions: dissociation of H2, and formation of titanium subfluorides on the TiN surface.

Determination of the Roughness of CVD Surfaces by Laser Scattering

AbstractA laser scattering apparatus was developed for the determination of surface roughness and other surface statistical parameters of chemically vapor-deposited coatings. Visual examination of HeNe laser scattering patterns reflected from polished sapphire and CVD titanium nitride surfaces showed a sensitivity to roughness differences of tens of nanometers. The scattering apparatus was integrated with a cold-wall CVD reactor. The root mean square roughness of silicon carbide deposits on silicon in the early stages of growth was determined from the intensity of the specularly reflected beam. Changes in roughness and the spatial arrangement of depositing crystallites were monitored in situ by angular resolution of the scattered light spectra. Both ex situ and in situ results were in good agreement with profilometric examinations of the rough surfaces.

Titanium nitride deposition on hardened high speed steel by reactive magnetron sputtering

Hardened W-Mo-Co high speed steel SIS-2723 (Swedish standard) used for the manufacture of cutting tools was deposited with titanium nitride by reactive magnetron sputtering. In this work we have studied the influence of the substrate deposition temperature on the chemical composition, hardness and adhesion at the interface and in the bulk of the TiN film.At an approximately 400°C deposition temperature the critical load CL is at maximum. At the TiN film-substrate interface and at a 400°C deposition temperature it was also found that the ratios Si:N, C:N, C:Ti, Mo:N and Cr:N are at maxima and N:Ti is at a minimum. At a 200°C deposition temperature the O:Fe ratio at the interface is at a maximum and between 400 and 500°C this ratio is at a minimum. The titanium nitride surface hardness as well as the ultramicrohardness in cross-section reach maxima at a 400°C deposition temperature. Further analysis of the TiN film adhesion shows that it is adhesive at deposition temperatures below 350°C and cohesive at higher temperatures.