John S. Chun

Compositional and structural analysis of aluminum oxide films prepared by plasma-enhanced chemical vapor deposition

Aluminum oxide films were deposited on silicon wafers by plasma-enhanced chemical vapor deposition, using trimethylaluminum, N2O and He gases. The chemical composition, states of functional groups and microstructure of the aluminum oxide films were investigated using FTIR, XPS, AES and TEM. Etch rates were measured and related to the microstructure of the films. It was found that carbon and hydrogen atoms are incorporated less at higher deposition temperatures and are almost completely removed as gas phases, such as CO2 and H2O, by post-deposition heat treatment at 800 °C in an oxygen environment. Carbon atoms incorporated into the films are in the chemical form of AlCH3 or AlCOOH, and the atomic concentration varies from 2% at 300 °C to 5% at 120 °C. Hydrogen atoms are in the chemical form of AlOH, and the atomic concentration estimated from the absorbance FTIR band of the OH stretching mode varies from about 7% at 300 °C to about 28% at 120 °C. The aluminum oxide films deposited at 300 °C have a microcrystalline structure of hydrogen-stabilized γ-Al2O3 with an O/Al ratio of 1.6, whereas those deposited at 120 °C have an amorphous structure. Etching properties of the films were related to the change in the microstructure.

X-RAY STUDIES OF SNO2 PREPARED BY CHEMICAL VAPOUR-DEPOSITION

Abstract Deposits of SnO2 were formed on Si(100) wafers by chemical vapour deposition using direct oxidation of SnCl4. X-ray studies demonstrated that SnO2 films deposited at temperatures above 400°C are polycrystalline with the tetragonal rutile structure and grow with a (301) preferred orientation. The preferred orientation characteristics of SnO2 prepared by CVD can readily be explained using the standard deviation of texture coefficients of each crystal plane from the powder condition. It is concluded that the mechanism of SnO2 CVD at temperatures below 600°C is oriented overgrowth as a result of preferred nucleation on the growing surface and at temperatures above 600°C is affected by homogeneous nucleation.

Properties of aluminium oxide films prepared by plasma-enhanced metal-organic chemical vapour deposition

Abstract Aluminium oxide films were deposited on silicon substrates at low temperatures (150–300 °C) by plasma-enhanced chemical vapour deposition using trimethylaluminium, N 2 O and helium gases. The film properties including chemical composition, depth profile, microstructure, refractive index and step coverage were investigated, and the dependence of the film properties and deposition rate on the deposition temperature were also studied. The deposition rates of aluminium oxide films deposited at 150 and 170 °C are very high, reaching 320–400 A min −1 . On the contrary, above 200 °C the deposition rates are constant at 160 A min −1 . The film deposited at 150 °C has an amorphous structure and those above 250 °C have an extremely fine γ-alumina crystalline structure. Hydrogen is the only impurity detected in the aluminium oxide film and its concentration increases as the deposition temperature decreases. The film deposited at 250 °C exhibits a very smooth surface and fairly conformal step coverage. The temperature dependence of the deposition rate and hydrogen content is explained by the change in adsorption type and desorption rate of reactants with temperature.

A comparative evaluation method of machinability for mica-based glass-ceramics

The machinability of mica glass-ceramics is evaluated using a tool dynamometer. Several samples with different chemical compositions and microstructures were tested in turning operations using TiCN cermet tools. The cutting rate dependence of specific cutting energy has been studied to find a simple method for the evaluation of machinability. The mechanical strength, the surface roughness of the machined surface and the fracture toughness were measured to support the machining behaviour. For the determination of machinability, the specific cutting energy at low cutting rate conditions, neglecting an elastic impact effect, and the slope of the log-log plot of the specific cutting energy versus cutting rate were considered as the reasonable parameters. These results are correlated with the microstructure and the hardness of the workpiece. In particular, the microhardness of the sample is shown to control the cutting characteristic.

Microstructure and Electrical Properties of Tantalum Oxide Thin Film Prepared by Electron Cyclotron Resonance Plasma-Enhanced Chemical Vapor Deposition

High-quality tantalum oxide thin film was prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) for high-density memory devices. The tantalum oxide film deposited at 205°C showed excellent electrical properties: E bd= 4.4 MV/cm, e (Ta2O5)=25 and J< 1×10-9 A/cm2 at 2.5 V. The deposited film was annealed at various temperatures in an oxygen ambient. The microstructure and the composition of the annealed tantalum oxide film were examined and they were related to the electrical properties of the film. The growth of the interfacial silicon oxide layer was observed by using a high-resolution transmission electron microscope (TEM) and its effects on the electrical properties of the dielectric film were also studied. The electrical properties of the film could not be improved by annealing in an oxygen ambient at high temperatures due to the crystallization of the tantalum oxide film and the growth of the interfacial silicon oxide layer.

Growth and structure of chemical vapor deposited silicon carbide from methyltrichlorosilane and hydrogen in the temperature range of 1100 to 1400 °C

Silicon carbide has been grown at 1100 to 1400 °C by chemical vapor deposition using CH3SiCl3 and H2 gaseous mixture onto a graphite substrate. The effect of deposition temperature, total system pressure, and the CH3SiCl3 input fraction on growth characteristics and structure of deposits has been studied. The experimental results show that the SiC deposition reaction is a thermally activated process with the deposition rate limited by surface reactions. The apparent activation energy is about 26 kcal/mol at a system pressure of 200 Torr and decreases with the increasing total system pressure. In this experiment, polycrystalline β‐SiC always has been deposited. The preferred orientation of the deposited SiC films changes from 〈111〉 to 〈220〉 with increasing deposition temperature. The size of the polycrystalline β‐SiC grains becomes coarser as the deposition temperature and the CH3SiCl3 input fraction are increased.Silicon carbide has been grown at 1100 to 1400 °C by chemical vapor deposition using CH3SiCl3 and H2 gaseous mixture onto a graphite substrate. The effect of deposition temperature, total system pressure, and the CH3SiCl3 input fraction on growth characteristics and structure of deposits has been studied. The experimental results show that the SiC deposition reaction is a thermally activated process with the deposition rate limited by surface reactions. The apparent activation energy is about 26 kcal/mol at a system pressure of 200 Torr and decreases with the increasing total system pressure. In this experiment, polycrystalline β‐SiC always has been deposited. The preferred orientation of the deposited SiC films changes from 〈111〉 to 〈220〉 with increasing deposition temperature. The size of the polycrystalline β‐SiC grains becomes coarser as the deposition temperature and the CH3SiCl3 input fraction are increased.

Effects of the experimental conditions of chemical vapour deposition on a TiC/TiN double-layer coating☆

Abstract Deposits of titanium nitride (TiN) were formed on TiC-coated 94wt.%WC-6wt.%Co substrates by chemical vapour deposition using a TiCl4, H2 and N2 gas mixture. The effects of the deposition temperature, the total flow rate of the reactant gases and the partial pressure of TiCl4 on the deposition rate, the preferred orientation and the surface morphology of the TiN deposit were investigated. The controlling mechanism of the TiN deposition reaction and its relationship with the deposition temperature and the total flow rate of the reactant gases were also investigated. The deposition rate and the TiN crystal growth along the (220) preferred orientation are increased with an increase in the deposition temperature and an increase in the partial pressure of TiCl4 at a total flow rate of less than 700 cm3 min-1. The particle size of the TiN deposit is reduced with an increase in the partial pressure of TiCl4 and is increased with an increase in the deposition temperature at a total flow rate of less than 700 cm3 min-1. When the total flow rate is greater than 700 cm3 min-1, the deposition rate, the TiN crystal growth along the (220) preferred orientation and the particle size of the TiN deposit no longer vary. When the deposition temperature is lower than 1000 °C, the TiN deposition reaction is controlled by the surface reaction; at a temperature above 1000 °C, the reaction is controlled by mass transport. When the total flow rate is less than 700 cm3 min-1, the deposition reaction is controlled by mass transport; with a total flow rate greater than 700 cm3 min-1, the reaction is controlled by the surface reaction.

Effect of the aspect ratio of mica crystals and crystallinity on the microhardness and machinability of mica glass-ceramics

Abstract The change in the microhardness and machinability of mica glass-ceramic is related closely to its microstructural parameters. The aspect ratio of the crystals, the volume crystallinity and the spatial arrangement of the particles must be considered in order to be able to estimate the characteristics of the material. With a high aspect ratio and crystallinity, the microhardness decreases because of high connectivity. By introducing the effective crystallinity, indicating the effectiveness of disk-like crystals in forming a connected structure of crystals, the variation in microhardness can be explainable. A steep decrease in the microhardness of mica glass-ceramics occurs due to the connection of the mica crystals, leading to good machinability.

Effect of partial pressure of the reactant gas on the chemical vapour deposition of Al2O3

Abstract Films of Al 2 O 3 were deposited onto TiN-coated cemented carbide substrates by a chemical vapour deposition technique using AlCl 3 , CO 2 and H 2 gases. The effects of the deposition temperature and the partial pressures of the reactants on the final structure of the Al 2 O 3 film were investigated, especially the effect of the supersaturations of the reactants (H 2 O and AlCl 3 ) on the final structure of the Al 2 O 3 film. The supersaturations of the reactants are calculated assuming chemical equilibria. It is found that the deposition rate of Al 2 O 3 is limited by both the AlCl 3 concentration and the [H 2 ]/[CO 2 ] ratio, but the crystal size of Al 2 O 3 film decreases with increasing H 2 O supersaturation. The supersaturation of AlCl 3 , however, seems not to affect the crystal size of Al 2 O 3 film under our experimental conditions. It is also found that the crystallographic structure of the Al 2 O 3 film changes from random orientation to (10 1 4)-preferred orientation with increasing deposition temperature.

Effects of annealing in O 2 and N 2 on the electrical properties of tantalum oxide thin films prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition

The tantalum oxide thin films with a thickness of 14 nm were deposited at 95°C by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECRPECVD), and annealed at various temperatures (700∼850°C) in O2 and N2 ambients. The microstructure and composition of the tantalum oxide thin films and the growth of interfacial silicon oxide layer were investigated and were related to the electrical characteristics of the film. Annealing in an O2 ambient led to a high dielectric constant (εr(Ta2O5) = 24) as well as a small leakage current (Ebd = 2.3 MV/cm), which were due to the improved stoichiometry and the decreased impurity carbon content. Annealing in an N2 ambient resulted in poor and nonuniform leakage current characteristics. The as-deposited tantalum oxide films were crystallized into δ-Ta2O5 after annealing at above 750°C regardless of the ambient. The leakage current of the film abruptly increased after annealing at 850°C probably because of the stress caused by thermal expansion or contraction.