Low Nitrogen Flow Rate Research Articles

Band gap energy fluctuations in InGaN films grown by RF‐MBE with changing nitrogen supply rate investigated by a piezoelectric photothermal spectroscopy

AbstractIn this study, non‐radiative recombination center in InGaN films with varying III/N ratio grown by rf‐molecular beam epitaxy was investigated directly by piezoelectric photothermal spectroscopy (PPTS). To clarify the influence of the III/N supply ratio during the InGaN layer growth, the nitrogen flow rate was changed from 1.0 to 2.0 sccm. Since metallic‐indium droplets and phase separation were observed for the samples grown by low nitrogen flow rate, it was found that these have been grown under a group‐III‐rich condition. With increasing nitrogen flow rate, the indium content in InGaN films increased. The estimated non‐radiative recombination edges determined from PPTS method (PPT edge) red‐shifted with increasing the nitrogen flow rate. The energy difference between estimated band edge and the PPT edges increased with increasing flow rate under group‐III rich condition, and became saturated under the N‐rich condition. It is considered that the existence of the phase separation is related to this behavior. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural properties and electrical resistivity of TiNx and Ti1−xAlxN films prepared by reactive dc magnetron sputtering: effect of nitrogen flowrate

Nanocrystalline thin films of titanium nitride and titanium aluminium nitride were deposited on (111) Si substrates by reactive dc magnetron sputtering under various nitrogen flowrates and at constant substrate temperature. The effect of nitrogen flowrate on the structural and electrical properties of TiNx and Ti1−xAlxN thin films deposited at substrate temperatures of 973 and 773 K respectively is investigated. TiNx films are polycrystalline at all N2 flowrates and there is a change of preferred orientation from (200) to (111) with increasing nitrogen flowrates. In contrast, Ti1−xAlxN thin films are polycrystalline only at low nitrogen flowrates (<5 sccm) and show a tendency to become more nanocrystalline with weak (200) preferred orientation at higher nitrogen flowrates. The variation of lattice parameter showed opposite behaviour in these two types of films. Auger electron spectroscopy indicated that the nitrogen concentration of both types of the films gradually increased with increasing nitrogen flowrate and almost reached a constant value at a flowrate of nitrogen ≥5 sccm. While the resistivity of TiNx films showed a minimum at a nitrogen flowrate of 5 sccm, the resistivity of Ti1−xAlxN films increased with increasing nitrogen flowrate. The variation in the electrical resistivity could be explained on the basis of structural changes occurring in these two types of films.

Relationship between composition, bonding constitution and microstructure in unbalanced magnetron sputtered Ti–B–N thin films

Two types of Ti–B–N thin films with different B contents were deposited on Si(100) at room temperature at different nitrogen flowrates. Their phase configurations and microstructures were subsequently characterised. The results indicated that the nitrogen flowrate greatly affected phase configuration and film composition. At a low nitrogen flowrate, TiN bonding was preferentially formed, accompanying with small amounts of TiB and TiB2 bonds. Formation of TiB2 bonding was accelerated with increasing B content. Nanocomposite thin films mainly consisting of nanocrystalline (nc-) TiN/amorphous (a-) TiB2 were finally formed. At a high nitrogen flowrate, TiN followed by BN was first formed, accompanying with small amounts of TiB and TiB2 bonds. Formation of BN bonding was further accelerated with increasing B content. Nanocomposite thin films mainly consisting of nc-TiN and a-BN were finally produced. The present thin films are the nanocomposite of nc-TiN embedded in the a-matrix with a dense microstructure despite of the nitrogen flowrate.

Damage-Free Ultradiluted HF / Nitrogen Jet Spray Cleaning for Particle Removal with Minimal Silicon and Oxide Loss

There has been a trade-off between efficient particle removal and damage minimization to fragile device structures when using mixed-liquid/gas jet spray cleaning of silicon wafers. We have developed an ultradiluted HF/nitrogen jet spray cleaning procedure for single-wafer spin-cleaning, which can efficiently remove particles on both silicon and silicon-dioxide surfaces even at a low nitrogen flow rate without causing damage to fragile 45-nm polysilicon gate structures in a short period. The use of ultradiluted HF can make silicon and oxide loss negligible, below 0.003 nm and 0.03 nm, respectively. This very simple single-step cleaning procedure drastically reduces chemical consumption.

Properties of MoN xO y thin films as a function of the N/O ratio

The main purpose of this work is the preparation of single layer films of molybdenum oxynitride, MoN x O y . The films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure Mo target and varying the flow rate of reactive gases. This allowed tuning of the crystallographic structure between insulating oxides and metallic nitrides and consequently changes in the electronic, mechanical and optical properties of the material. X-ray diffraction (XRD) results revealed the presence of molybdenum nitride for the films with low oxygen fraction: face-centered cubic phases (γ-Mo 2N) for low nitrogen flow rate or cubic MoN x and hexagonal phase (δ-MoN) for high nitrogen flow rate. The increase of oxygen content induces an amorphization of the nitride phases and the appearance of MoO 3 phases. The increase of the oxygen fraction in the films induces also a high decrease in the film's hardness. Residual stresses were compressive, in the range of very few tenths of GPa to − 2 GPa. These results will be presented as a function of the deposition parameters, the chemical composition and the structure of the films.

Sputtered FeCoN soft magnetic thin films with high resistivity

Fe/sub 70/Co/sub 30/N thin films with thickness from 20 to 1100 /spl Aring/ were prepared by radio- frequency reactive sputtering in an N/sub 2/--Ar mixture. The FeCoN films prepared in a low nitrogen flow rate percentage (<6%) and sputtering pressure (<8 mTorr) have a high B/sub s/ of about 24.0 kG, but a moderate hard-axis coercivity H/sub ch/ of 5-30 Oe. With further increase in N/sub 2/ percentage or sputtering pressure, films become significantly softer, with H/sub ch/ of about 0.1-0.6 Oe, and have a higher resistivity of up to about 160 /spl mu//spl Omega//spl middot/cm. The change in the magnetic properties with nitrogen flow rate percentage and sputtering pressure can be attributed to the formation of an ultrafine grain size nanocrystalline FeCoN thin film as observed by high-resolution transmission electron microscope. The soft properties of FeCoN films with nano-sized crystallites remain stable even after being annealed at 270/spl deg/C.

Influence of Bias Voltage on Copper Nitride Films Deposited by Reactive Sputtering

This paper investigates the effect of negative bias voltage applied to substrates on the structure and electrical resistivity of films deposited with rf sputtering on a copper target in reactive Ar-N2 mixtures. To show the influence of the nitrogen content in the film, four different nitrogen flow rates have been chosen from the results of a previous study. Whatever the nitrogen flow rate when a negative bias voltage is applied to the substrates, copper diffraction peaks are detected. This is due to nitrogen resputtering during the film growth. This resputtering phenomenon can be so significant that films deposited with a low nitrogen flow rate and high bias voltage are composed only of copper. With other deposition conditions, the films are biphased: Cu + Cu3N. In these films, the Cu3N crystal orientation is also dependent on the bias voltage. Since the nitrogen content of the films evolves and since copper crystals are formed, the electrical resistivity of the films decreases when a bias voltage is applied. However, the electrical resistivity of biphased coatings does not reach that of copper and therefore, copper grains do not percolate in these films.

Reactively sputtered Ti–B–N nanocomposite films: correlation between structure and optical properties

Ti–B–N nanocomposite coatings were deposited on silicon, glass and steel substrates by DC magnetron sputtering of a TiB 2 target in various Ar–N 2 reactive mixtures. In this report, some optical properties of the films were investigated in connection with their structure. At low nitrogen flow rate, coatings contain nanocrystals of titanium diboride. On the other hand, at high nitrogen flow rate, only titanium nitride nanocrystals are detected by grazing angle X-ray diffraction. Whatever the nitrogen flow rate, Fourier-transform infrared spectroscopy shows the occurrence of an amorphous boron nitride phase. Moreover, the number of BN bonds continuously increases with the nitrogen flow rate, even if the boron and nitrogen concentrations in the film become nearly constant. Colour measurements show a progressive decrease of the coating brilliance vs. the nitrogen flow rate. Thus, Ti–B–N nanocomposite coatings are suitable for decorative applications. The UV-visible transmittance of Ti–B–N coatings increases with the nitrogen flow rate due to an increase in the number of BN bonds. Finally, the shape of the transmittance curve for a Ti–B–N coating is similar to that of a TiN coating, as soon as TiN nanocrystals are detected in Ti–B–N coatings.

Characterisation of reactively sputtered Ti–B–N and Ti–B–O coatings

The effect of oxygen or nitrogen incorporation into sputtered titanium–boron based coatings was investigated. The coatings are deposited by reactive magnetron sputtering of a TiB 2 target in Ar–N 2 or Ar–O 2 mixtures. The composition, structure, hardness and electrical resistivity of these films were compared. Ti–B–N films crystallise in a TiB 2-like structure at low nitrogen flow rate ( Q(N 2)) and in a TiN one at high Q(N 2). Whatever Q(N 2), BN bonds are detected by Fourier transform infrared spectroscopy. Then, Ti–B–N films are nanocomposite coatings: nc-TiB 2/a-BN and nc-TiN/a-BN vs. Q(N 2). On the other hand, grazing angle X-ray diffraction and X-ray photoelectron spectroscopy analyses show that Ti–B–O films are nanocomposite coatings at low oxygen flow rate (i.e. nc-TiB 2/a-oxides) and become amorphous for higher oxygen content. For both systems, the hardness of the films decreases when the reactive gas flow rate increases. Highly oxygenated Ti–B–O films are electrical insulators whereas highly nitrided Ti–B–N films conserve their metallic character.

Nitrogen flow rate dependence of the growth morphology of TiAlN films deposited by reactive sputtering

The dependence of the growth morphology of TiAlN films deposited by reactive sputtering on Si(100) substrates was investigated using scanning and transmission microscopy, X-ray diffraction and atomic microscopy. The TiAlN films deposited by this technique have the (200) preferred orientation of the NaCl structure. However, at lower nitrogen flow rates the (200) intensity peak in the XRD spectra decreases in intensity and broadens as an additional peak of 10 1 ̄ 1 wurtzite structure alloys overlaps at the same 2θ value. The TiAlN film has a columnar structure. The columns become denser as the nitrogen flow rate increases. Atomic force microscopy indicates a fluctuating surface morphology mainly arising from the grain domain distribution in a random fashion.

Structural and electrical properties of sputtered titanium boronitride films

Titanium boronitride (TiBN) films are deposited on steel and glass substrates by DC magnetron sputtering of a TiB 2 target in various Ar–N 2 mixtures. In this report the electrical properties of TiBN films are investigated in connection with their structure. At low nitrogen flow rate, the films are nanocrystallized in a TiB 2-like structure. On the other hand at high nitrogen flow rate, TiBN films contain nanocrystals of TiN probably embedded in a boron nitride amorphous matrix. The electrical resistivity of TiBN films increases continuously with the nitrogen flow rate. The thermal behaviour of the electrical resistance shows that coatings with a TiB 2-like structure have a positive temperature coefficient of resistance, whereas samples obtained under high nitrogen flow rate exhibit a negative one. These results are discussed together with those obtained from high-resolution photoemission spectroscopy, which gives evidence to the metallic character for all deposits.

Magnetostriction in FeTaN thin films

Magnetostriction is studied in FeTaN single layer thin films deposited by high power density, high growth rate, DC magnetron sputtering. Magnetostriction is found to increase linearly with the nitrogen content of the films, passing from negative to positive with increasing nitrogen content. Thinner films exhibit larger positive magnetostriction than thicker films deposited at the same nitrogen flow rate. Film stress is found to be tensile in as-deposited films grown at zero nitrogen pressure. As the nitrogen content in the films increases, the film stress changes from tensile to compressive and increases in magnitude, while annealing at 300 degrees C reduces the magnitude of film stress without affecting magnetostriction. Stress anisotropy is found to reach a minimum at low nitrogen flow rate, and stripe domain formation accompanies large stress anisotropy at high nitrogen flow rates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sputter deposition of decorative coatings based on ZrB 2 and ZrB 12

Decorative coatings of zirconium boride and zirconium boron nitride were deposited onto steel and molybdenum substrates employing non-reactive and reactive d.c. magnetron sputter deposition using zirconium diboride (ZrB 2) and zirconium dodecaboride(ZrB 12) targets. The characterization of the coatings was by scanning electron microscopy and X-ray diffraction. The results are discussed in connection with measured mechanical and optical film properties such as microhardness and CIE-L *a *b * values. By means of non-reactive sputtering, fine-columned films with a predominantly (00l)-orientated ZrB 2 phase were formed; in the case of sputtering from the ZrB 12 target the ZrB 2 phase was accompanied by the rhombohedric B phase. Reactive deposition at low nitrogen flow rates leads to the formation of a hexagonal Zr−B−N phase based on ZrB 2 (using the ZrB 2 target), accompanied by a highly distorted B phase (using the ZrBu target). The further incorporation of nitrogen leads to amorphous film growth. The maximum Vickers microhardness of the coatings was found to be approximately 2300 HV 0.01. These coatings offer an excellent choice for decorative applications with colours from silver-grey to black combined with outstanding corrosion and abrasion resistance.

Sputter deposition of wear-resistant coatings within the system ZrBN

Wear-resistant coatings of zirconium boride and zirconium boron nitride were deposited on steel and molybdenum substrates employing non-reactive as well as reactive d.c. magnetron sputtering using zirconium diboride targets. The characterization of the coatings was done by means of scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results are discussed in connection with measured mechanical coating properties such as microhardness and adhesion. The optical properties of the coatings were determined using a CIE-L *a *b * colorimeter and specialized corrosion and abrasion tests. Non-reactive sputtering using ZrB 2 targets results in the formation of coatings with a columnar structure and predominantly (001)-orientated ZrB 2 crystals. Coatings deposited at low nitrogen flow rates exhibit very fine-grained or even fracture amorphous structures with a hexagonal ZrBN phase derived from the ZrB 2 lattice. A further increase of the nitrogen flow leads to an amorphous film growth. The maximum Vickers microhardness of the coatings was found to be approximately 2300 HV 0.02 ZrB and ZrBN coatings offer a wide range of interesting colours as well as good corrosion and wear resistance.

Direct quantitatitve analysis using the flame-ionization detector: Some operating parameters and the fidoh detector

The effect of varying carrier gas (nitrogen) flow-rate on the absolute molar and weight responses of a flame-ionization detector operated under conditions of a hydrogen-rich flam using oxygen as the supporter of combustion has been investigated and shows that a considerable degree of flexibility is available for achieving these detector responses. Selective detection of chlorine has been shown to depend upon high hydrogen and low nitrogen flow-rates with intermediate to high oxygen flow-rates. Additional compounds have been shown to respond equally to carbon content in the molar mode of operation.