Density and deposition rates of amorphous CVD-Si3N4 including carbon

Amorphous Si₃N₄ containing uniformly distributed carbon was prepared by chemical vapour deposition [Am. CVD-(Si₃N₄-C)] using SiCl₄ vapour and NH₃, H₂ and C₃ H₈ gases at deposition temperatures (T _dep) of 1100 to 1300° C and at total gas pressures (P _tot) of 30 to 70 torr. The density of Am.CVD-(Si₃N₄-C) is between 2.80 and 3.00 g cm⁻³, depending upon the deposition conditions. Rate of growth in thickness increases with increasingT _dep andP _tot, and has the largest value of 0.6 mm h⁻¹ atT _dep=1300° C,P _tot=70 torr and propane gas flow rates [FR(C₃H₈)] of 0 to 20 cm³ min⁻. The activation energy of the formation decreases from 38 to 20 kcal mol⁻¹ with increasingP _tot andFR(C₃H₈).     

Density and deposition rate of chemical-vapour-deposited boron nitride

A study is made on the density and deposition rate characteristics of chemical-vapour-deposited boron nitride (CVD-BN) plates synthesized by use of the BCl₃-NH₃-H₂ system at a deposition temperature (T _dep) of 1200 to 2000°C and a total gas pressure (P _tot) of 5 to 60 torr. At aP _tot of 5 torr, all the CVD-BN plates synthesized at eachT _dep above 1300°C had a density greater than 2.O g cm^–3, and thus showed no noticeable dependence onT _dep. Over theP _tot range from 10 to 60 torr. on the other hand, the density of the plates reached the maximum of 2.08g cm^–3 at aT _dep of 2000° C. AsT _dep was lowered, the density decreased down to a minimum of 1.40 g cm^–3 The deposition rate varied with bothT _dep andP _tot and showed a maximum value under a certainP _tot at a givenT _dep. The value ofP _tot where the deposition rate becomes maximum changed depending on theT _dep. The maximum deposition rate was 0.6 mm h^–1 for the CVD-BN plates when the density was less than 2.0 g cm^–3, and 0.4 mm h^–1 when the density was above 2.0 g cm^–3 The effects of deposition conditions on the characteristics of density and deposition rate are discussed in terms of the structure and deposition mechanism.     

Synthesis and structure of chemically vapour-deposited boron nitride

Chemically vapour-deposited boron nitride (CVD-BN) plates have been synthesized on a graphite substrate by the reaction of the BCl₃-NH₃-H₂ gas system in a deposition temperature (T _dep) range from 1200 to 2000° C, with a total gas pressure (P _tot) which was varied from 5 to 60 torr. The effects ofP _tot andT _dep on the crystal structure and the microstructure of the CVD-BN plate were investigated. Turbostratic BN(t-BN) was deposited above 10 torr, at anyT _dep in the range investigated. The interlayer spacing (c ₀/2), the crystallite size (Lc) and the preferred orientation (PO) were strongly affected byT _dep. The t-BN obtained at lowT _dep had largec ₀/2 and smallLc andPO. AsT _dep increased,c ₀/2 tended to decrease whereasLc increased and thec-plane of the crystallites became oriented parallel to the deposition surface. At aP _tot of 5 torr, a mixture of t-BN and h-BN (hexagonal BN) was deposited at anyT _dep above 1700° C, and two kinds of t-BN different inc ₀/2 co-deposited at aT _dep below 1600° C. Moreover, it was indicated that r-BN (rhombohedral BN) was included in the deposits obtained at aP _tot of 5 torr and aT _dep of 1500 to 1600° C.     

Stability to moisture for chemically vapour-deposited boron nitride

Chemically vapour-deposited boron nitride (CVD-BN) plates prepared by use of the BCl₃-NH₃-H₂ gas system were investigated as to their stability to moisture. Infrared (IR) spectroscopic measurement, chemical analysis and thermal gravimetric analysis were used in this study. The synthesis conditions of CVD-BN plates have a large influence on their stability to moisture. The stability of CVD-BN plates prepared under a total gas pressure (P _tot) of 10 to 60 torr degraded as the deposition temperature (T _dep) was lowered. The CVD-BN plates with transparent and isotropic properties, which were prepared at below 1400° C and above 10 torr, showed poor stability to moisture, The CVD-BN plates synthesized under 5 torr had high moisture-resistance, even at aT _dep as low as 1400° C. An IR absorption spectral study revealed that the unstable species existing in CVD-BN plans had changed to ammonium borate hydrates by reacting with moisture in the atmosphere. The stability to moisture for CVD-BN plates degraded as the deposition roe was raked, especially for the CVD-BN plates prepared at 1400° C.     

Preferred orientation of TiB2 plates prepared by CVD of the TiCl4 + B2H6 system

Titanium diboride (TiB₂) plates (about 1 mm maximum thickness) were prepared by chemical vapour deposition (CVD) using a TiCl₄, B₂H₆ and H₂ system at deposition temperatures,T _dep of 1323–1773 K. The B/Ti atomic ratio in the deposits was 2, and the composition is strictly stoichiometric. Chlorine was not detected. The measured lattice parameters werea=0.3029 nm andc=0.3229 nm. Density is in close agreement with the theoretical value (4.50 g cm⁻³). Preferred orientation of the CVD TiB₂ plates varies mainly with total gas pressures,P _tot. AtP _tot=4 kPa the (1 0 0) plane and atP _tot=40 kPa the (1 1 0) plane is preferably oriented parallel to the substrates. The effect ofP _tot on the preferred orientation is discussed thermodynamically, and explained by supersaturation in the gas phase.     

Preparation and some properties of chemically vapour-deposited Si3N4-TiN composite

Chemically vapour-deposited (CVD) Si₃N₄-TiN composite (a plate with the maximum thickness of 1.9 mm) has been prepared on a graphite substrate using a mixture of SiCl₄, TiCl₄, NH₃ and H₂ gases. The CVD was carried out at deposition temperatures,T _dep, in the range of 1050 to 1450 ° C, total gas pressures,P _tot, from 1.33 to 10.7 kPa and gas flow rates of 136 (SiCl₄), 18 (TiCl₄), 120 (NH₃) and 2720 (H₂) cm³ min^–1. The deposits thus obtained appeared black. The Ti content in the composites ranged from 2.1 to 24.8 wt % and was found in the form of Tin. The structure of the Si₃N₄ matrices varied from amorphous (initially) to the- and-type, with increasingT _dep. Most of the- and-type deposits had a preferred orientation (001) parallel to the deposition surface. While the deposition surface of the amorphous deposits showed a pebble structure, the surfaces of the- and-type deposits were composed of various kinds of facets. The heat-treating experiment suggested that-Si₃N₄ obtained in the present work was formed directly via a vapour phase, and not from crystallization of amorphous Si₃N₄ or from transformation of-Si₃N₄.     

Thermodynamics for the preparation of SiC-C nano-composites by chemical vapour deposition

SiC-C nano-composites covering every possible combination of carbon and SiC were prepared by chemical vapour deposition. The specific compositions of the deposits were controlled by changing the Si/C molar ratio in the source gases at deposition temperatures (T _dep) of 1673 to 1873 K and total gas pressures (P _tot) of 6.7 to 40 k Pa using the SiCl₄-C₃H₈-H₂ system. The prediction, based on the thermodynamic calculation on composition, morphology and deposition rate, was compared with experimental results. The optimal deposition conditions predicted by the calculations were nearly in agreement with the experimental results.     

Preferred orientation of AlN plates prepared by chemical vapour deposition of AlCl3 + NH3 system

Aluminium nitride (AlN) plates about 1 mm thick (maximum) were prepared by chemical vapour deposition (CVD) at the maximum deposition rate of 430 nm s⁻¹ using AlCl₃, NH₃ and H₂ gases at deposition temperatures,T _dep, of 873–1473 K. The effects of deposition conditions on the preferred orientation, morphology and micro-structure were investigated. WhenT _dep was less than 1073 K, the resulting CVD AlN plates contained some impurity chlorine and the aluminium content exceed the nitrogen content. WhenT _dep exceeded 1173 K, no chlorine was detected, and the Al/N atomic ratio matched the stoichiometric value. The lattice parameters (a=0.311 nm,c=0.4979 nm) and density (3.26×10³ kgm⁻³) were in agreement with values reported previously. The crystal planes oriented parallel to the substrates changed from (1 1 ˉ2 0) to (1 0 ˉ1 0) to (0001) with increasing total gas pressure (P _tot) and decreasingT _dep. This tendency is discussed thermodynamically and is explained by the change of supersaturation in the gas phase.     

Chemical vapour-deposited silicon nitride

The massive amorphous and crystalline pyrolytic silicon nitride (Py-Si₃N₄) have been prepared under various conditions of production using SiCl₄, NH₃ and H₂. The structural features such as the crystal structure, lattice parameters, grain size, preferred orientation and infra-red absorption are related to the deposition conditions, namely deposition temperature (T_dep) and total gas pressure (P _tot). The X-ray and electron diffraction data for the crystalline Py-Si₃N₄ show that onlyα-Si₃N₄ is deposited even at a T_dep of 1500° C. The lattice parameter c increases with increasingT _dep andP _tot, while the lattice parameter a is independent ofT _dep andP _tot. The parameter c depends strongly upon the oxygen content. All the massive Py-Si₃N₄ reveal the strong (110), (210) and (222) orientations, depending uponP _tot andT _dep. Fine grained Py-Si₃N₄ (about 1μm) is obtained in the amorphous-crystalline boundary region. The infra-red absorption spectra indicate the stretching vibrations of Si-N compounds. The structure of the massive amorphous Py-Si₃N₄ is also discussed.     

Chemical vapour-deposited silicon nitride

Pyrolytic Si₃N₄ has been deposited on a graphite substrate, using a mixture of SiCl₄, NH₃ and H₂. The pyrolysis is performed with deposition temperatures of 1100 to 1500° C, total gas pressures of 5 to 300 Torr, and flow rates of H₂=700, NH₃=60 and SiCl₄ (liq.)=0.8 cm³ min^–1. Massive amorphous and crystalline pyrolytic forms of Si₃N₄ are prepared at a maximum thickness of 4.6 mm. The effects of deposition conditions on some properties of the deposited products and the dependence of formation of amorphous or crystalline deposits on deposition temperature and total pressure were investigated. The surface and cross-sectional structures show growth cones and oriented crystals which are strongly dependent on the deposition conditions. The thin deposits are translucent; the thick deposits vary in colour from white to black. The silicon content is close to the theoretical composition and independent of the deposition conditions, while the oxygen content increases with decreasing deposition temperature and total pressure. No segregation of silicon and nitrogen at cone boundaries was found.     

Morphology and preferred orientation of titanium nitride plates prepared by chemical vapour deposition

Thick titanium nitride (TiN _x ; x = 0.74–1.0) plates (up to 2 mm thick) were prepared by chemical vapour deposition using TiCl₄, NH₃ and H₂ as source gases at a total gas pressure, P _tot, of 4 kPa, deposition temperatures, T _dep, from 1373–1873 K, and NH₃/TiCl₄, m _N/Ti, gas molar ratio from 0.17–1.74. The effects of deposition conditions on morphology, preferred orientation and composition of CVD-TiN _x plates were investigated. Surface morphology changed from faceted to nodular texture with increasing m _N/Ti and T _dep. The faceted and nodular deposits showed columnar and shell-like fracture cross-sections, respectively. The composition (x = N/Ti) increased with increasing m _N/Ti and T _dep below m _N/Ti = 1.0, and was constant above m _N/Ti = 1.0. Three kinds of preferred orientations were observed: (100) orientation at low T _dep, (110) orientation at intermediate T _dep and low m _N/Ti, and (111) orientation at high T _dep and high m _N/Ti. This tendency is discussed thermodynamically, and explained as being due to changes in the degree of supersaturation in the gas phase.     

Deposition characteristics and properties of iron nitride films by CVD using organometallic compound

Iron nitride films were prepared by chemical vapour deposition from the gas mixture of Fe(C₅H₅)₂-NH₃-H₂-CO₂. The effects of deposition parameters on the deposition characteristics were investigated. Iron nitride films were deposited above 500 ° C and the films of -Fe₄N single phase were deposited above 700 ° C. At 700 ° C and under the total gas flow rate from 1 to 8 l min^–1, the deposition rate of the film may be controlled by the transport of Fe(C₅H₅)₂ molecules to the surface of the deposits. At 700 °C and under the total gas flow rate of 4 l min^–1, the phases and nitrogen contents of the films were determined bypNH₃/pH₂ ^3/2, the controlling factor of the nitrogen contents of the films. Decreasing of the total gas flow rate and increasingpCO₂ increased the nitrogen contents of the films and phases with higher nitrogen were deposited. On the other hand, increasingpFe(C₅H₅)₂ and the absence ofpCO₂ increases the carbon contents of the films, and the phase with a greater solubility in carbon, i.e. -Fe₂N, was codeposited with -Fe₄N. The saturation magnetization of the films deposited at 700 ° C was in good agreement with that reported for the bulk iron nitride, which depended not on the deposition conditions but on the nitrogen contents of the films.     

Ideal Gas Thermodynamic Properties of Propyl tert-Butyl Ethers from Density Functional Theory Results Combined with Experimental Data

Ideal gas thermodynamic properties, S°(T), C _p°(, T), H°(T)–H°(0), _f H°(T), and _f G°(T), are obtained on the basis of density functional B3LYP/6-31G(d,p) and B3LYP/6-311 + G(3df,2p) calculations for two propyl tert-butyl ethers. All torsional motions about C–C and C–O bonds were treated as hindered internal rotations using the independent-rotor model. An empirical approximation was assumed to account for the effect of the coupling of rotor potentials. The correction for rotor–rotor coupling was found by fitting to entropy values determined from calorimetric measurements. Enthalpies of formation were calculated using isodesmic reactions.     

Influence of the calcining temperature on the sintering and properties of PZT ceramics

Niobia-doped PZT powders were prepared by both hydroxide and oxalate coprecipitation methods. The resulting amorphous powders were calcined at two different temperatures (550 and 700 °C) and the morphology and size of the calcined particles were studied. It was found that hydroxide powders, when calcined at 700 °C, gave 98% theoretical density,d _th, bodies at a sintering temperature as low as 1100°C in air. The high agglomeration present in oxalate powders strongly retarded densification. Of the piezoelectric properties, ak _p higher than 60% and ad ₃₃ constant of 360 × 10^–12 CN^–1 were measured. Dielectric parametersT _c andk _3T, 310° C and 1100, respectively, were determined.     

Thermodynamic properties of NaZr<Subscript>2</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The heat capacity C _p ⁰ of crystalline NaZr₂(AsO₄)₃ has been measured in the range 7–650 K using precision adiabatic calorimetry and differential scanning calorimetry. The experimental data have been used to calculate the standard thermodynamic functions of the arsenate: C _p ⁰, enthalpy H ⁰(T) − H ⁰(0), entropy S ⁰(T), and Gibbs function G ⁰(T) − H ⁰(0) from T → 0 to 650 K. The standard entropy of its formation from elements is Δ_f S ⁰(NaZr₂(AsO₄)₃, cr, 298.15 K) = −1087 ± 1 J/(mol K).     

Proton conduction at the surface of Y-doped BaCeO3 and its application to an air/fuel sensor

25 mol% Y³⁺-doped BaCeO₃ (BCY25) showed an extremely low activation energy of 0.3 eV for proton conduction at the surface. The resulting overall conductivity at the surface reached 8.24 × 10^–3 S cm^–1 at 400°C, which was 3, 8, and 28 times higher than those in the bulk of BCY25, 20 mol% Sm³⁺-doped ceria, and 8 mol% yttria-stabilized zirconia, respectively. Such fast proton conduction enabled an air/fuel (A/F ) sensor using BCY25 as the solid electrolyte to work above 150°C for H₂ and above 250°C for C₂H₄.     

Effect of post-annealing on thin YBCO films deposited from a nanocrystalline target

Pulsed laser deposition is used to ablate thin superconducting YBCO films on SrTiO ₃ substrates. The most important parameters of thin superconducting films are high critical current density, ability to stand magnetic fields and smoothness of surfaces. Smoothness is important in fabrication of layered structures and for research of basic properties of thin superconducting structures. The target sintered from YBCO nanopowder is a promising material for making films which meet most of the requirements above. Investigations by AFM show that our target has grains about one order of magnitude smaller than usual grain size of commercial targets. At optimal deposition parameters, the oxygen pressure of 0.4 torr in the chamber and the substrate temperature 725°C, films with T _c = 90 K, J _c =8 × 10⁶ A/cm ² (77 K) and RMS surface roughness = 1.5 nm are obtained. Thermal annealing of the deposited films for 18 h at 900°C further increases the value of J _c .     

The parameters of nonequilibrium microwave discharge in nitrogen in a tube in a rectangular waveguide

Computer codes are developed for the processing of emission spectra of nonequilibrium plasma in nitrogen for the purpose of obtaining information about the translational T _g and rotational T _rot temperatures, the populations of vibrational levels in the ground electron and electron-excited states, the electron energy distribution function, the electron concentration N _e , and the electric field intensity E. The computer codes are used to determine the parameters of microwave-discharge plasma in nitrogen in discharge systems of two types, namely, in a discharge tube (with a radius of 1 cm), which crosses a rectangular waveguide (plasmatron on the H ₁₀ wavelength, at a pressure of 1.7 torr and absorbed power density of 1.5 W/cm³), and in a discharge section of similar structure on the basis of prismatic resonator (at a pressure of 1.0 torr and absorbed power density of 0.4 W/cm³). The mechanisms of population of the N₂(C ³Π_u) state are treated.     

Comparative study on the properties of amorphous carbon layers deposited from 1-hexene and propylene for dry etch hard mask application in semiconductor device manufacturing

Amorphous carbon layers (ACLs) were prepared by plasma enhanced chemical vapor deposition (PECVD) from 1-hexene (C₆H₁₂) and propylene (C₃H₆) as a carbon source at different temperatures for dry etch hard mask of semiconductor devices manufacturing process. The deposition rate of ACL deposited at 550 °C from C₆H₁₂ and C₃H₆ was 5050 Å/min and 6360 Å/min. Although the deposition rate of ACL deposited from C₆H₆ was lower than that from C₃H₆, normalized deposition rate of ACL deposited from C₆H₁₂ was 1.64 times higher than that from C₃H₆. The relative amount of hydrocarbon contents measured by FTIR (Fourier transformation infrared) and TDS (thermal desorption spectroscopy) was decreased with the increase of deposition temperature. Raman results showed that the numbers and size of graphite cluster of ACLs deposited from each source were increased with the increase of deposition temperature. The extinction coefficient of ACL deposited at 550 °C from C₆H₁₂ was 0.51 and that from C₃H₆ was 0.48. The density of ACL deposited at 550 °C from C₆H₁₂ was 1.48 g/cm³ and that from C₃H₆ was 1.45 g/cm³. The dry etching rate of ACL deposited at 550 °C from C₆H₁₂ was 1770 Å/min and that from C₃H₆ was 1840 Å/min. The deposition rate, dry etch rate and the amount of hydrocarbon contents of ACLs deposited from each carbon source were decreased with the increase of deposition temperature but extinction coefficient and density were increased with the increase of deposition temperature. We concluded that the variation behavior of the deposition characteristics and film properties of ACLs from C₆H₁₂ with the increase of deposition temperature was the same as those of ACLs from C₃H₆. The high density and low dry etch rate of ACL from C₆H₁₂ can be explained by less hydrocarbon incorporation during deposition and these properties are more favorable for the dry etch hard mask application in semiconductor device fabrication.     

Kinetics of Redox Reactions of U, Pu, and Np in TBP Solutions: VII. Kinetics of Reduction of Pu(IV) and Np(VI) with Butanal Oxime in Undiluted TBP

The kinetics of reduction of Pu(IV) and Np(VI) with butanal oxime in undiluted TBP containing HNO₃ was studied spectrophotometrically. In the range [HNO₃] = 0.08-0.75 M the rate of Pu(IV) reduction is described by the equation -d[Pu(IV)]/dt = k[Pu(IV)]²[C₃H₇CHNOH]/{[Pu(III)][HNO₃]²} with the rate constant k = 0.068±0.017 mol l^-1 min^-1 at 20°C. The kinetic equation of the reduction of Np(VI) to Np(V) in the range [HNO₃] = 0.01-0.27 M is -d[Np(VI)]/dt = k[Np(VI)][C₃H₇CHNOH][H₂O]²/[HNO₃]0.5, where k = 0.058±0.007 l2.5 mol-2.5 min^-1 at 25°C, and the activation energy is 79±9 kJ mol^-1.