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Pure silicon nano-powder was successfully synthesized via gas-phase sodium reduction of silicon tetrachloride, exhibiting 100% conversion of the reactants and achieving >95% yield of the final product. The interactions of the process conditions and tin-doping with the particle morphology were investigated. The produced powders were analyzed by nitrogen adsorption, transmission and scanning electron microscopy, X-ray diffraction, inert gas fusion analysis and glow discharge mass spectroscopy. The washed polycrystalline silicon particles had a BET surface area in the range of 23–44 m 2 /g. The silicon aciniform aggregates consisted of relatively homogeneous primary particles in the range of 20–100 nm. The silicon was protected by a 2–3 nm thick passivation layer established during the washing step resulting in an oxygen content of less than 3 wt.%. Electrochemical testing demonstrated a high inherent capacity for the pure Si powders. The initial capacity and 1st cycle charge efficiency of Si-containing anode electrodes was dependent on the initial powder surface area. The highest capacity was achieved for Si powders with intermediate BET surface area of 28.5 m 2 /g and cells with this anode material delivered capacity of 2651 mA h/g (normalized to Si) and 82.4% efficiency at first charge.

The influence of precursor characteristics and synthesis conditions on the formation of yttrium aluminum garnet, Y3Al5O12 (YAG), was investigated using “single-source” precursors (cohydrolyzed yttrium and aluminum alkoxides and yttrium aluminum glycolates) and “multiple-source” precursors (mixtures of metal nitrates and mixtures of separately hydrolyzed yttrium and aluminum alkoxides). Phase-pure YAG was formed only in the solid-state thermal decomposition experiments. The lack of formation of YAG in all the spray-pyrolysis experiments was ascribed to the short heating times and fast heating rates, which resulted in the formation of kinetic products. In the case of the metal nitrates, an additional factor that influenced product formation was the difference in thermal reactivity of the precursors. It was concluded that the formation of complex metal oxide materials by conventional or aerosol routes is not necessarily achieved by the use of a chemically homogeneous precursor, such as a single-source precursor. It also was necessary to ensure that the precursors and intermediates have similar thermal decomposition temperatures to avoid phase segregation in the initial stages of thermal decomposition.

The formation of ZrO2, Al2O3/ZrO2, and SiO2/ZrO2 coatings on TiO2 particles by a continuous gas-phase process was studied. Titania particles were formed by the reaction of TiCl4 vapor with O2 in a hot-wall tubular reactor at 1300°C and were mixed with ZrCl4 and AlCl3 or SiCl4 vapors near the end of the reactor. The ZrCl4/TiCl4 molar ratio was varied from 6.7 x 10-4 to 5 x 10-3 while the AlCl3/TiCl4and SiCl4/TiCl4 molar ratios varied in the ranges 8 x 10-3-8 x 10-2 and 2 x 10-2-8 x 10-2, respectively. Discrete tetragonal ZrO2 nanoparticles of average diameter 20 nm were formed on the surfaces of the titania particles at a surface concentration that increased with the ZrCl4 gas-phase concentration. The sequential introduction of AlCl3 and ZrCl4 vapors resulted in composite coatings. These consisted of dense, coherent, amorphous, and smooth Al2O3 layers approximately 10 nm thick, on top of which ZrO2 nanocrystalline particles were dispersed in a similar pattern as in the absence of Al2O3. Concentration depth...

Chemical vapor co-deposition of Cu–Co films has been demonstrated using (1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)Cu(II) [Cu(hfac)2] [hfac=hexafluoroacetylacetonate] and (acetylacetonate)Co(II) [Co(acac)2] [acac=acetylacetonate] as precursors. The deposition was performed at the substrate temperature of 270°C in a warm-wall impinging jet type reactor. The precursor Co(acac)2 was sublimed at 140°C to achieve reasonable precursor delivery rates and avoid decomposition of precursor in the sublimator. Films with varying Cu content from 17 wt.% to 98 wt.% were deposited by subliming Cu(hfac)2 in the temperature range of 40–100°C with a fixed Co(acac)2 delivery rate. The morphologies and crystallinities of the binary films were strongly dependent on the film stoichiometry. Overall, this study provides insights into the mechanism of Cu–Co binary film formation by CVD.

A new method for synthesis of composite films was developed and used to synthesize ZnO—SiO2 and Cu—SiO2 composite films where the silica particle size was varied from 40 nm to 520 nm. The process consists of sequential deposition of particles and the matrix material (using chemical vapor deposition) and can be used for any material system. The morphology of the composite films can be controlled and varied from dense to porous and laminated structures can be formed. The film formation process can be explained in terms of the Thiele modulus. In order to obtain dense films the Thiele modulus for such systems should be 1.5.

The reactions of Co2(CO)8 and submicron cobalt particles with Cu(hfac)2 (hfac = hexafluoroacetylacetonate) were studied in toluene. Reactions between these species in the gas phase were studied in a hot-wall, parallel-plate chemical vapor deposition (CVD) reactor. Similar results were obtained with both methods. The overall chemical reactions can be expressed by the following equations: 2Cu(hfac)2 + Co2(CO)6 → 2Cu + 2Co(hfac)2 + 8CO and Cu(hfac)2 + Co → Cu +Co(hfac)2. These results suggested that Co2(CO)8 is not a good source precursor for CVD of Cu−Co binary films when used in conjunction with copper(II) and some copper(I) hexafluoroacetylacetonate compounds and that chemical etching of cobalt metal by Cu(hfac)2 needs to be taken into account when depositing this binary film with copper(I) and copper(II) hexafluoroacetylacetonate compounds as copper source precursors.

Zinc oxide films were deposited by CVD in air and nitrogen under atmospheric conditions using zinc acetate and zinc oxyacetate as the precursors. Factors for obtaining reproducible depositions were identified. The activation energies using zinc acetate as the precursor were ∼ 45 kJ mol–1 (±20%) both in air and in nitrogen, and ∼ 45 kJ mol–1 (±20%) in air, using zinc oxyacetate as the precursor. The concentration dependence of the deposition rate was ≤ 1/3. Crystalline films with lower carbon content were deposited at lower substrate temperatures under atmospheric conditions than at reduced pressures. Water enhanced the (002) orientation of the films and increased the deposition rate only in nitrogen (not in air). Overall, this study provides the first quantitative information about the kinetics of the deposition of ZnO from zinc acetate and zinc oxyacetate.

Doped group 12 metal sulfides are important materials in the phosphor display industry. Control over the host lattice phase, composition, and dopant concentration is crucial for controlling the luminescence characteristics of these materials. Ternary thin films of CdxZn1-xS and ZnS:Mn were deposited by aerosol-assisted chemical vapor deposition (AACVD) using liquid delivery of toluene solutions of new single-source Zn−S and Cd−S precursors M(SOCC(CH3)3)2TMEDA (M = Cd, Zn; TMEDA = N,N,N,N-tetramethylethylenediamine) and Mn2(CO)10 as a source of Mn. Control over film composition, wherein the precursor solution and film stoichiometries were identical, was achieved by using feed-rate-limited deposition conditions. Films with compositions Cd0.75Zn0.25S, Cd0.50Zn0.50S, and Cd0.25Zn0.75S were deposited at 225 °C from 10 mmol solutions with the same Cd:Zn precursor mole ratios, respectively. A series of control experiments in which the precursor feed rate was varied confirmed the presence of feed-rate-limited fil...

Ashes from an industrial bubbling fluidized bed (BFB) and a circulating fluidized bed (CFB) boilers burning biomass and paper mill sludges are characterized. Bulk sampling was carried out with a simultaneous low pressure impactor sampling (BLPI) and with on-line monitoring of submicron ash gas phase size distribution. The principal ash forming mechanism was sintering of 1–10 μ m inorganic paper filler particles, into 5–200 μ m ash agglomerates. Despite few spherical particles no ash melting was detected. The fraction of vaporized and condensed ash was below 0.1 mass% in both units as determined with BLPI and with on-line monitoring. According to elemental mass size distributions no significant vaporization of any main element occurred including sodium and potassium. Wall deposit observed on refractory lining in BFB furnace was composed of sintered ash binding large ash and sand particles in the structure. No molten phases were detected to participate in the layer growth. Most quartz sand grains in the bed were covered by a thin layer of small ash particles, below 5 μ m in size.

We have examined the formation of copper films alloyed with small quantities of palladium. Independent control studies of palladium and copper deposition from palladium bis(hexafluoroacetylacetonate) [Pd(hfac)2] and (hexafluoroacetylacetonato)copper(I)(vinyltrimethylsilane) [(hfac)Cu(I)(vtms)], both in the presence and absence of H2, were carried out. The growth kinetics for both metals were feed-rate-limited under similar reactor conditions. No significant variation in deposition rate (100 nm/min, Pd; 100−500 nm/min, Cu), morphology, resistivity, and purity of the copper films was observed due to the addition of H2. Simultaneous introduction of both precursors yielded Cu−Pd alloy films. The absence of pure palladium grains was confirmed by X-ray diffraction analysis which showed binary solid solutions (Cu99.5Pd0.5−Cu80Pd20) as the only crystalline phases. Auger electron spectroscopy analysis showed a significant reduction in the palladium content of the films as compared to that expected on the basis of ...

The precursor (1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) palladium(II) [Pd(hfac)2] was used to deposit high-purity, polycrystalline palladium films under low-pressure CVD conditions at high growth rates (1000–4000 A/min) over a substrate temperature range of 80–200°C in the presence of H2. Mixing of the precursor and H2 streams near the substrate was required to avoid reactions of the precursor with H2 at locations other than the substrate surface. Auger electron spectroscopy (AES) showed that the films were impurity free when sufficient H2 was used. Resistivity values of 20 μΩcm were obtained at the higher deposition temperatures (∼200 °C) while high values of 50 μΩ cm were observed at the lower deposition temperatures (∼ 90 °C). The deposition rate was feed-rate limited even at the lowest deposition temperatures and highest precursor delivery rates, suggesting that even higher deposition rates could be obtained with higher feed rates. A high precursor conversion of 50–60 % was observed. The high surface reaction probability of Pd(hfac)2 in the presence of H2 was reflected qualitatively by trench fill studies which showed a greater film thickness on the top of sub-micrometer trenches than in the bottom.

The oxidation kinetics of submicron Ca-containing Pd powders produced by spray pyrolysis were studied in the temperature range 600 to 675 C using thermogravimetric analysis. The oxidation of pure Pd powder had an activation energy of {approximately}230 kJ/mol in the region 27% 70%. The activation energies for Pd particles containing 0.01 weight percent (w/o) and 0.4 w/o Ca in the region 27% < oxidation < 70% were {approximately}230 kJ/mol and {approximately}50 kJ/mol, respectively. Transmission electron microscopy suggested that the conversion of Pd to Pd{sup II}O (stoichiometric PdO) proceeds from the particle surface into the interior and not homogeneously throughout the particle. The predictions of a variety of models and rate laws (shrinking core, parabolic, cubic, logarithmic, and inverse logarithmic) were compared with the data. The comparison suggested a mechanism in which oxidation of pure Pd proceeds by chemisorption and diffusion of oxygen to form a substoichiometric oxide, followed by the conversion of substoichiometric PdO to Pd{sup II}O. Oxidation of pure Pd is then probably limited by the diffusion of oxygen through the substoichiometric PdO and/or Pd{sup II}O. The addition of Ca increased the oxidation resistance of Pd most likely bymore » inhibiting oxygen diffusion through the metal oxide layers surrounding the Pd.« less

In situ coating of titania aerosol particles with alumina and alumina−silica mixtures by chemical vapor deposition, cluster deposition, and sintering was demonstrated in a hot-wall, continuous flow tubular reactor. Titania particles with diameters in the range 0.2−0.8 μm were produced by the reaction of TiCl4 with O2 at 1300 and 1500 °C and were passed through a coating region where they were mixed with AlCl3 or mixtures of AlCl3 and SiCl4. Uniform and dense coatings of Al2O3 were obtained at both 1300 and 1500 °C using AlCl3 inlet concentrations that corresponded to Al2O3 mass loading of less than 1 wt %. The coating thickness could be controlled from 5 to 20 nm which corresponded to deposition rates up to 50 nm/s. Uniform and dense coatings of Al2O3/SiO2 were obtained at 1300 °C when the SiO2/Al2O3 weight ratio was less than 2:1. It is proposed that coating takes place in two modes: (a) chemical vapor deposition of AlCl3 and SiCl4 on the particle surface and (b) gas-phase reactions of the metal chlorid...

The feasibility of in situ coating of titania particles with silica using a high-temperature, gas-phase process was demonstrated. Titania was produced from the reaction of TiCl4 and O2 in a hot-wall, tubular, aerosol reactor and directly coated in the gas phase via the reaction of O2 with SiCl4 vapor. Rough SiO2 coatings were obtained at 1300 °C while uniform, dense coatings were obtained at all conditions examined for 1500 °C. The presence of water in the reactor significantly influenced the morphology of the coatings and resulted in smooth, dense, and uniform coatings at 1300 °C. Coating thicknesses could be controlled from 5 nm to roughly 100 nm, corresponding to growth rates on the order of 10–100 nmys. The characteristics of the coatings depended upon the concentration of SiCl4 and the coating temperature. These process variables influenced the coating mechanism, growth rate, and densification which directly influenced the coating uniformity and thickness.

Fine particles of dense, high-purity, crystalline BaTiO 3 were produced by flame-spray pyrolysis. A 0.5-M (Ba:Ti = 1:1) solution of barium acetate, titanium lactate, and water was aerosolized using an ultrasonic generator and the droplets were delivered into the core of an annular diffusion flame (H 2 /air) reactor. For all investigated temperatures [∼1,000- ∼2,000°C adiabatic], the generated powders were chemically pure, crystalline (primarily tetragonal phase with hexagonal and cubic polymorphs), and unagglomerated. At a low-flame temperature (∼1,000°C ad.), the particles produced were hollow and irregularly shaped. Particles produced at higher flame temperatures ( > ∼1,500°C ad.) were dense and homogeneous. Particles showed a transition from a nonspherical porous morphology to a spherical dense morphology with increasing temperature. By increasing residence time, the temperature at which particles became spherical and dense was reduced. Flame-spray pyrolysis provides a useful method for forming dense particles of high melting point materials by aerosol-phase densification.

This work is a review of the experimental results from the literature for single-component metal and simple metal-oxide particles. Criteria for correlating particle morphology, i.e., whether the particles are solid or hollow, with process parameters and material properties during spray pyrolysis are presented and compared with the data available in the literature. The materials were classified into two categories for which the precursor: (1) melts and (2) does not melt before chemical reaction takes place, and separate criteria were used for each category based on the work of Jayanthi et al. (1993) J. Aerosol Sci. 19:478. In systems where the precursor melts before chemical reaction occurs, e.g., decomposition of nitrates of Mg, Al, Fe, Zn, Pb, Ni, Co, Pd, Mn, Cu, Sr, and Ag, the particle morphology is determined primarily by the densities and formula weights of the reactant and product compounds unless high temperature densification or puffing up of the particles due to gases evolved during the ...

The role of surface reaction in the synthesis of titanium dioxide from TiCl 4 in aerosol reactors was studied theoretically using a one-dimensional log-normal model in which particle growth occurred by coagulation and surface reaction. The surface reaction kinetics were obtained from chemical vapor deposition studies of TiO 2 from TiCl 4 reported in the literature and the gas-phase kinetics from data for aerosol reactors. The effect of surface reaction rate on the TiO 2 particle size distribution was studied for different axial temperature profiles and for laboratory and industrial conditions. Within the inlet TiCl 4 concentration range of 4.7 × 10 −8 −5.5 × 10 −6 mol cm −3 and gas velocities of 30 cm s −1 −20 m s −1 at atmospheric pressure, surface reaction did not affect the average TiO 2 particle size or the spread of the distribution. Two dimensionless quantities were identified which enable the determination of the significance of surface reaction in aerosol synthesis of particles. In general, for any system where homogeneous gas-phase reaction directly forms particles, and particle growth occurs by surface reaction and coagulation, it is not possible in practice to obtain a final particle size distribution with a geometric standard deviation less than the asymptotic geometric standard deviation determined by the coagulation kinetics (e.g. 1.32 for spherical particles with a log-normal size distribution in the continuum regime (Lee, 1983), which is the value determined by coagulation kinetics)

The goal of this study was the synthesis of submicron composite and coated particles of palladium with CaO, MgO, Al{sub 2}O{sub 3}, ZnO, SiO{sub 2} and TiO{sub 2} via spray pyrolysis using aqueous solutions of precursors of the additive compounds and palladium nitrate. The solutions were atomized, the droplets transported to a furnace where they reacted at 1,000 C in a flow system of N{sub 2}, and the particles were collected on a filter. X-ray diffraction data showed that palladium was the only crystalline phase formed regardless of the type of the additive. Coatings were observed in all cases except Al{sub 2}O{sub 3} and the thickness determined by high-resolution transmission electron microscopy [{approximately} 10 nm at 2.5 weight percent (w/o) of the additive compound] was similar for all compounds. Auger electron spectroscopy analysis indicated the coatings were stoichiometric oxides and roughly 10% of the total surface was covered in the case of 2.5 w/o Zn while above 90% was covered for 2.5 w/o Ca. The oxidation compared to pure palladium powders decreased when Ca and Mg were used and increased when Zn, Ti, Si, and Al were used. Thermogravimetric analysis of the oxidation of palladium particles with CaO coatings showedmore » a weight gain of 2.5 to 4%, while 6% was observed for pure palladium powders. The extent of oxidation of CaO-coated powders was independent of the coating thickness.« less

Copper oxide powders were prepared by the spray pyrolysis of copper nitrate solutions over a range of temperatures (400–1300 °C) and residence times (3–7 s). Phase-pure [by x-ray diffraction (XRD)] copper (I) oxide was obtained at 800–1300 °C in an inert (nitrogen) atmosphere. The particles varied from smooth, solid spheres at 1300 °C to irregularly shaped and hollow particles at 800 °C with dense particles of Cu2O being made only at 1000 °C or higher. The particles were polycrystalline with an average crystallite size of 42 nm at 800 °C, while at 1000–1200 °C, the particles were single crystals. Spray pyrolysis in forming gas (7% H2–N2) atmosphere at 500–700 °C gave Cu while spray pyrolysis in air yielded CuO over 800–1000 °C and a mixture of Cu2O/CuO at 1200 °C. These results show that solid, phase-pure Cu2O particles can be produced by aerosol-phase densification at temperatures below its melting point (1235 °C).

A model for aerosol-phase densification of particles during their synthesis by spray pyrolysis is presented. The model was used to describe the evolution of the specific surface area of PdO powders synthesized at temperatures between 400 to 800 °C (residence times 27.9 to 22.7 s). Surface areas and grain sizes ranged between 56 m2/g and 4 nm at 400 °C to 3.2 m2/g and 40 nm at 800 °C The characteristic coalescence lime was determined as: τ= 1.7 x 1013T d3 exp(1.3 x 105/RT) [for lattice diffusion] and t = 2.7 x 1019Td 4exp (1.6 x 105/RT) [for grain boundary diffusion] (τ is in seconds, Tin degrees Kelvin, R is 8.314J/(mol.K)and d is in meters), but the data and model did not allow identification of the specific mechanism. The model provides a general approach for correlating changes in particle surface area with reactor operating conditions that is applicable to a wide variety of materials.

The CVD of Cu using (hfac)Cu(VTMS) (hfac = hexafluoroacetylacetonate, VTMS = vinyltrimethylsilane) and (hfac)Cu(2-butyne) in the presence of water and other reagents has been studied. The overall C...

Crystalline, submicrometer strontium ferrite powders, including SrFeO2.97, SrFe2O4, Sr2FeO4, Sr3Fe2O6.16, and SrFe12O19, were prepared by spray pyrolysis of an aqueous solution of mixed metal nitrates. The Sr:Fe mole ratio in the precursor solution was retained in the final products. Phase-pure materials were typically obtained only at the highest temperatures investigated (>1100°C) and powders prepared at lower temperatures frequently contained crystalline Fe2O3. The as-prepared particles were unagglomerated, polycrystalline, and hollow at lower temperatures, but densified in the gas phase at higher temperatures to give solid particles. The strontium ferrite (SrFe12O19) system was studied in detail as a representative example of the Sr-Fe-O system. At temperatures of 1200°C, dense, phase-pure magnetoplumbite-structure material, SrFe12O19, was obtained, while at lower temperatures, small amounts of Fe2O3 were observed. The particles prepared at 800° and 1100°C were 0.1-1.0 μm in diameter, and consisted of crystallites

A new thermal dry etch process for copper (Cu) is reported which results in isotropic removal of Cu at high rates, does not involve the use of halogens such as chlorine, and results in formation of a volatile etching product. Applications include cleaning of chemical vapor deposition reactors and the back-side of wafers. The process involves oxidation of copper by hydrogen peroxide (H2O2) vapor to form either copper(I) or copper(II) oxide depending on the etch temperature and removal of the copper oxides by reaction with hexafluoroacetylacetone (hfacH) to form volatile copper(bis-hexafluoroacetylacetonate) (Cu(hfac)2) and water. Copper was etched at temperatures as low as 150 °C and at rates of up to ~ 1 μm min−1 at 190 °C by simultaneous flow of H2O2 and hfacH over a heated substrate. The etch rate increased with substrate temperature, etchant flow rates, and chamber pressure over the range of the parameters studied. The rate-limiting regime was identified by observing the film color during etching; a dark-brown color suggested fast oxidation with slow removal of copper oxide as the rate limiting step while a copper color suggested fast removal of copper oxide from the surface with oxidation as the rate-limiting step. The partially etched copper films were less reflective and exhibited higher surface roughness compared with the sputter-deposited copper used for etching.

Submicrometer crystalline metal ruthenate powders with perovskite structure, MRuO3 (M = Sr, La), and pyrochlore structure, M2Ru2O7-x(0.5 < x < 1; M = Bi, Pb, Y, Eu, Gd, Tb, Dy, Ho, Er, Tm), were prepared by spray pyrolysis using metal nitrates and glycolates under an oxygen-gas atmosphere at temperatures up to 1100°C. Submicrometer-sized solid single crystals (SrRuO3), submicrometer-sized hollow spheres consisting of nanocrystallites (pyrochlore rare-earth ruthenates, Bi2Ru2O7, and Pb2Ru2O6.5 below 1000°C), and nanometer-sized particles (Pb2.31Ru1.69O6.5 and Bi-Pb-O above 1000°C) were observed. Particle formation proceeded by intraparticle reaction and intraparticle reaction followed by evaporation of volatile metal oxides to form metal oxide vapors followed by condensation and reaction to form particles. The former was observed for systems where no volatile metal oxides were formed, whereas the latter occurred for the Pb-Ru-O and Bi-Ru-O systems, where volatile metal oxides, such as Bi2O, PbO, and RuOx could occur. Particle morphology depended strongly on precursor properties. Submicrometer-sized single-crystal SrRuO3 particles could be formed from the metal nitrates but not from Sr(NO3)2 and ruthenium glycolate, which gave hollow polycrystalline particles. In general, crystallite size could be controlled by varying precursor properties and reactor temperature, with higher temperatures giving larger crystallite sizes.

The Selective chemical vapor deposition (CVD) of metals from metal-containing compounds is reviewed and the approaches taken are classified according to the different physicochemical phenomena which take place on the growth and non-growth surfaces. These include: an intrinsic difference in reaction rates, sacrificial solid-state co-reactant, activation of the growth surface, radiation-induced activation of the growth surface, passivation of non-growth surfaces, and a physical nucleation barrier. The results from the literature suggest that surface modification, in which the growth surface is activated or the non-growth surface is passivated, is a promising method to control selectivity. However, few results are available from experiments with well-characterized surfaces, making meaningful comparisons of the origin of selective CVD difficult to interpret.

The role of particle evaporation during synthesis of volatile metal oxide powders (Bi2O3, MoO3, PbO, and V2O5) by aerosol decomposition (spray pyrolysis) in a heated flow reactor was investigated. Solid particles (0.1–0.6 (Am) of predominantly β-Bi2O3 were formed with smooth spherical shape at all reactor temperatures (673–1173 K) employed. Solid MoO3 particles (0.1–1.2 μm) produced at low temperatures (673–773 K) had a roughly spherical or faceted morphology and at high temperatures (873 K) had a platelike or layered structure. Solid V2O5 particles produced at low temperatures (573–673 K) were spherical and at high temperatures (973–1073 K) were platelike. The PbO particles were solid and spherical for all temperatures studied (773°–1073°C). Evaporative losses of up to 100% to the reactor walls were observed for all the metal oxides, due to their substantial vapor pressures. The evaporative losses were modeled by considering simultaneous particle evaporation and mass transfer of the metal oxide vapor to the reactor walls. The calculations indicated that, for most of these volatile metal oxides, evaporative losses were limited by diffusional transport of the vapor to the reactor walls and that evaporative losses occur when the vapor pressure of the oxides in the reactor is above 10-5-10-3 mm Hg.

The chemical vapor deposition (CVD) of metals is a rapidly developing area in which metal-containing compounds are being synthesized as new precursors. This article reviews this area and discusses precursor design, reaction pathways, reactor types, and the influence of reactor operating conditions on film growth. We have gathered recent results for precursor design and CVD chemistry and show how analysis of results from CVD experiments can be used to assist in the development of new CVD precursors.

Spray pyrolysis was used to produce submicron Ag-Pd metal alloy particles for applications in electronic component fabrication. The particles were prepared in nitrogen carrier gas from metal nitrate precursor solutions with various compositions. The Ag-Pd alloy was the predominant phase for reactor temperatures of 700 °C and above for all compositions. The 70-30 Ag-Pd partcles were fully dense at 700 °C, but an increased reaction temperature was necessary to produce dense particles at higher Pd to Ag ratios. The extent of palladium oxidation was suppressed with increased amounts of Ag. Single-crystal particles could be produced at sufficiently high temperatures. These results show that particle phase composition, size, oxidation behavior, and morphology can be controlled by the Ag-Pd ratio in the precursor solution and by the reaction temperature.

A new process has been developed to produce patterned copper films with small feature sizes on polytetrafluoroethylene (PTFE). In the first step a sodium naphthalenide etching solution was used to chemically modify PTFE and also create a rough surface which provided good adhesion characteristics. In the second step a KrF excimer laser irradiated the substrate through a mask, ablating the etched layer and leaving a pattern. The typical total absorbed laser energy required to ablate the etched layer was 575 mJ cm−2 and X-ray photoelectron spectroscopy (XPS) analysis showed that the ablated region had a composition similar to that of unmodified PTFE. In the third step, high purity copper was deposited selectively on the unablated regions in a cold wall reactor using (hfac)Cu(VTMS) (hfac [ hexafluoroacetylacetonate; VTMS [ vinyltrimethylsilane) at deposition rates up to 1 μm min−1 at 180 °C and 10 mTorr partial pressure of (hfac)Cu(VTMS) to give films 15–20 μm thick of high purity copper on PTFE. Film resistivities were near bulk values. There are several advantages to this procedure compared with conventional approaches: (1) wet etching and liquid wastes are avoided; (2) conducting paths with dimensions less than 20 μm can be produced; (3) excellent adhesion is obtained; (4) owing to the high energy density available from an excimer laser, rapid throughput is possible.

The selective chemical vapor deposition (CVD) of Cu was studied using (hfac)Cu(VTMS) (hfac  1,1,1,5,5,5-hexafluoro-acetylacetonate; VTMS [ vinyltrimethylsilane) in the absence and presence of water during CVD with SiO2 surface passivation, derived from the silylating agent hexamethyldisilazane (HMDS), as a function of the nature of the carrier gas, HMDS and water vapor flow rates and chamber pressure. For CVD of Cu in the absence of water, pre-dosing with HMDS in the absence of water gave selective deposition. The deposition was feed rate limited and dense, smooth copper films were deposited selectively at rates of about 600 A min−1. The selectivity for CVD of Cu in the presence of water depended on the pre-dosing conditions. Pre-dosing with both HMDS and water vapor gave selective deposition at rates of about 1200 A min−1 in the presence of water, a factor of 2 higher compared with CVD in the absence of water vapor. Dense films with near-bulk resistivities were deposited selectively in the trenches on an underlying tungsten layer at the optimum water vapor flow rate and chamber pressure. Higher water vapor flow rates and chamber pressures resulted in porous, discontinuous films with significantly higher resistivities. An integration scheme utilizing selective CVD of Cu is proposed that allows formation of fully encapsulated copper lines without the need for a copper etch.

Selective chemical vapor deposition (CVD) on metals in the presence of SiO 2 can be achieved by passivating the SiO 2 surface using reagents which replace or shield isolated hydroxyl, hydrogen-bonded hydroxyl, and SiO four-member rings with less reactive -SiR 3 groups. This process was studied by FTIR of (hfac)CuL (where L=VTMS and 2-butyne) adsorption/desorption on unpassivated and passivated SiO 2 surfaces with varying surface concentrations of hydroxyl groups and four-member SiO rings. The passivating reagents included monofunctional trimethylchlorosilane (TMSCI), hexamethyldisilazane (HMDS), trimethyldimethylaminosilane (TMDMA), dimethyl-t-butyldimethylaminosilane (DMBDMA), and bi-functional dimethylbis(dimethylamino)silane (DMDMA) species

The reaction of (hfac)Cu(VTMS) with SiO 2 surfaces with varying surface concentrations of isolated and hydrogen-bonded surface hydroxyl groups and four-membered SiO rings has been investigated. The adsorbed (hfac)Cu(VTMS) (where hfac=1,1,1,5,5,5-hexafluoroacetylacetonate and VTMS=vinyltrimethylsilane) reacted with the hydrogen-bonded surface hydroxyl groups and the strained siloxane sites and interacted with the isolated surface hydroxyl groups. The VTMS ligand was completely liberated from the adsorbed compound between 125 and 175 o C depending on the relative ratios of the reactive surface sites. Because all SiO 2 surfaces have some combination of these reactive sites, dissociation of (hfac)Cu(VTMS) to give «(hfac)Cu» and VTMS is always expected

Nanometer-size fullerene particles were generated via vapor condensation in a continuous flow system starting from pure C60 and mixed fullerene extract (C60/C70). Vapor condensation was carried out by cooling a nitrogen gas stream containing fullerene vapors from 400–650°C to room temperature. Particles were partly amorphous at 400°C, and became crystalline C60 when processed above 500°C. The average particle diameter and particle number concentration increased with increasing processing temperature. The particles had average sizes of 30, 35 and 40 nm and total number concentrations of 2.2 × 106, 3.5 × 106, and 5.0 × 106 #/cm3, respectively at 500, 525 and 550°C.

The influence of precursor design on gas-phase and liquid/solid-phase (spray pyrolysis) aerosol materials synthesis is described. The necessity for the incorporation of reaction mechanisms that lead to complete removal of organic by-products is emphasized by the examples of aerosol-assisted CVD of Cu and Ag films and the formation of ZnS films and powders. The role of “single-source” precursors in the formation of complex materials including ZnS, perovskite phase PbTiO3 and yttrium aluminum garnet, Y3Al5O12 is described.

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)-Sr-Ca-Cu-O powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi1.8Pb0.44Sr2Ca2.2Cu3Ox composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)-Sr-Ca-Cu-O powders were (Bi,Pb)2Sr2CuOx (2201), Ca2PbO4 (plumbate), (Bi,Pb)2Sr2CaCu2Ox(2212), and (Bi,Pb)3Sr2Ca2Cu1Ox(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (

The passivation of silica surfaces and the subsequent adsorption/desorption of (hfac)Cu(2-butyne) and (hfac)Cu(VTMS) precursors were studied. The goal was to enhance the selective deposition of copper from these compounds during chemical vapor deposition (CVD). The passivation reagents were hexamethyldisilazane (HMDS) and triisobutylaluminum (TIBA). Surface passivation with HMDS shielded the hydrogen-bonded surface hydroxyl groups and the strained siloxane surface sites making them inaccessible to both (hfac)Cu(VTMS) and (hfac)Cu(2-butyne) where hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate and VTMS = vinyltrimethylsilane. The adsorbed copper(I) compounds molecularly desorbed from the HMDS-passivated surface below 125 °C. The surface groups resulting from the reaction of TIBA with the silica surface reacted with the copper compounds subsequently adsorbed at 275 °C. The reaction products were present on the surface above 450 °C. These results demonstrate the utility of SiO2 surface modification using HMDS for control of selective CVD of copper.

The process of spray pyrolysis was investigated theoretically using a model that describes the evolution of the droplet size, solvent vapor concentration in the carrier gas, and both droplet and gas temperatures along the reactor axis. The model also accounts for solute concentration profiles and solute precipitation in the solution droplets. The model was used to describe the evaporation of sodium chloride aqueous solution droplets in diffusion dryers and hot-wall reactors as a function of reactor residence time, droplet size (a few microns), solution molality (up to 2 M), droplet concentration (10 6 –10 7 cm −3 ), relative humidity of the carrier gas (0–50%) and reactor wall conditions. Decreasing initial droplet size and solution molality accelerated droplet evaporation and resulted in smaller droplets at the onset of solute nucleation. Decreasing droplet concentration and carrier gas inlet relative humidity as well as increasing wall temperature (up to 350°C) or axial wall temperature gradient (up to 100°C cm −1 ) increased the droplet evaporation rate, but did not change appreciably the droplet size at the point of precipitation for a given droplet size and solute concentration. Thus, control of droplet size at the onset of solute nucleation by varying process parameters other than the solution concentration and initial droplet size is limited.

The compound (hfac)Ag(1,5-cod) was synthesized by the reaction of 1,1,1,5,5,5-hexafluoroacetylacetone (hfacH) with Ag2O and 1,5-cyclooctadiene (1,5-cod) and characterized in the solid state by single-crystal X-ray diffraction. In contrast to the corresponding copper(I) compound (hfac)Ag(1,5-cod) exhibited lower volatility and was found to be dimeric in the solid state, containing the two unusual β-diketonate coordination modes, namely, μ4-η2-hfac and μ2-hfac. The deterioration of the crystal and extensive disorder precluded a detailed comparison of the metrical parameters of this compound with other literature data. However, the solid-state FTIR data showed substantial differences in the ν(CO) and ν(CC) stretching regions compared with the chelated hfac ligand in (hfac)Cu(1,5-cod). These data will be useful in assigning the coordination mode of β-diketonate ligands in metal-organic β-diketonate complexes by FTIR.

There is a tremendous demand for improved performance and speed in consumer electronics that is likely to continue as new applications and developments occur. This demand necessitates a reduction in the critical dimensions and an increase in the density of devices in microelectronic circuits. As a result, new materials must be considered for integration into microelectronics technology. In particular, the metal wiring or interconnects that connect different components in silicon-based semiconductor devices is a subject of great interest. As the dimensions of transistors shrink below the 0.5 μm level, their speed will become limited by the delays in the existing interconnect material, Al-Si-Cu alloy (p ~ 3 μΩ cm). Therefore, to avoid problems associated with RC (“resistance/capacitance”) time delays and voltage drops, it will be necessary to construct interconnections of materials that possess lower resistivities, resistance to electromigration and hillock formation, and resistance to diffusion into other materials (see Table I).A number of materials are possible candidates to replace the Al-Si-Cu alloy, including W, Ag, Au, and Cu. Tungsten has excellent resistance to electromigration and hillock formation, but has higher resistivity compared with the Al-Si-Cu alloy. Thus, applications of W are likely to be found where short interconnection distances are necessary. Silver has the lowest resistivity of all metals, but is easily corroded and diffuses rapidly into many materials used in semiconductor devices. However, some specific applications for silver are viable, such as the formation of contacts on ceramic superconductors. Gold has a lower resistivity than the Al-Si-Cu alloy and is inert to chemical corrosion. As a result Au is used where device reliability is the primary concern-for example, for wiring in GaAs-based semiconductors and electrical contacts in packaging.

Solid, spherical, micron-sized silver metal particles were produced by spray pyrolysis from a silver nitrate solution. The effects of reaction temperature, carrier gas type, solution concentration, and aerosol droplet size on the characteristics of the resultant silver particles were examined. Pure, dense, unagglomerated particles were produced with an ultrasonic generator at and above 600° C using N 2 carrier gas, and at and above 900°C using air as the carrier gas. Solid particle formation at temperatures below the melting point of silver (962°C) was attributed to sufficiently long residence times (3.5–54 s) which allowed aerosol-phase densification of the porous silver particles resulting from reaction of the precursor.