ICMCTF2009 Session B3-2: CVD Coatings and Technologies

Atomic Layer Deposition (ALD) is applied in many advanced technologies that require control of film properties in the nanometer or sub-nanometer scale. ALD finds use mainly in semiconductor applications but also in solar energy, catalysis, micro-systems and biological applications. ALD films can be used to improve oxidation resistance, corrosion resistance, to improve electrical or optical properties … Atomic layer deposition (ALD) , which is based on the sequential self-limiting surface reactions from generally two gaseous precursors, provides an ideal technique for depositing ultrathin and conformal films.

To develop and optimize an ALD process for a new material requires knowledge of the reactions mechanisms. Most of the studies on ALD modeling have been dedicated on the two precursors surface reactions. However, the most commonly use of organometallic molecule precursors with the occurrence of thermal decomposition requires an understanding of the gas-p hase chemical reactions. Information on physical and chemical behavior of this kind of precursor is scarce and namely species that were transported to the ALD deposition chamber are generally unknown. Mass spectrometer coupled with a Knudsen effusion cell has already proved to be a powerful tool for studying the stability of gaseous molecules, thermodynamics of condensed phases and, more generally vaporization processes. The identification and quantification of the actual species present in the gaseous phase can be determined using a specific system composed of a Knudsen effusion cell coupled with a mass spectrometer. This presentation describes the application of such approach for TaN and ZrO₂ ALD deposition processes.

The tungsten diphenylhydrazido complex Cl₄(CH₃CN)W(NNPh₂) (1) was used to deposit tungsten carbonitride (WN_xC_y) by metal-organic chemical vapor deposition (MOCVD) in the temperature range 300 to 700 °C. The effect of deposition temperature on the film microstructure, surface morphology, chemical composition, bonding states, growth rate, electrical resistivity, lattice parameter, and grain size was studied. The microstructure of films deposited using 1 was amorphous below 500°C and polycrystalline above this temperature. Between 500 and 700°C the lattice parameter varied from 4.15 to 4.20 Å, while the average grain size increased from 25 to 55 Å. XPS results for films deposited using 1 indicate that W is primarily bonded to N and C for films deposited over the entire deposition temperature range. The growth rates of films deposited using 1 varied from 1.0 to 25.4 Å/min and showed Arrhenius behavior in the rang e 300 to 450°C with an apparent activation energy of 0.49 eV. The barrier quality of Cu/WN_xC_y/Si stacks was evaluated using XRD patterns and cross-sectional TEM images along with EDS. The integrity of both Cu/WN_xC_y and WN_xC_y/Si interfaces was retained after annealing at 500 °C for 30 min. XRD spectra revealed no Cu₃Si peaks and EDS qualitative analysis showed a sharp decrease in the Cu K_α peak at the Cu/WN_xC_y interface. Hence, WN_xC_y films deposited at 400°C are viable materials to serve as a Cu diffusion barrier. The properties of films deposited with 1 are compared to those deposited from tungsten piperidylhydrazido complex Cl₄(CH₃CN)W(N-pip) and tungsten imido complexes Cl₄(CH₃CN)W(NR) (R = Ph, ⁱPr, and allyl)¹ to provide insight into the effect of incorporating hydrazido and imido ligands on film properties.

¹ O. J. Bchir, K. M. Green, H. M. Ajmera, E. A. Zapp, T. J. Anderson, B. C. Brooks, L. L. Reitfort, D. H. Powell, K. A. Abboud, L. McElwee-White, J. Am. Chem. Soc. 127 (2005) 7825-7833.

Polycrystalline silicon carbide (SiC) is widely used in a range of commercial applications due to its resistance to extreme conditions. This resistance is improved by increasing the crystallinity and purity of the silicon carbide.

High temperature Chemical Vapour Deposition as a process allows greater control over a wider range of reaction parameters (temperature, pressure, ratio of injected gaseous precursors) when compared to other techniques such as Physical Vapor Transport. The variation of these parameters allows control over properties of the final material such as its morphology, crystalline quality and composition. As such it is preferable for the growth of pure, highly crystalline SiC.

Thermodynamic calculations have been performed on a CVD system employing H₂ and methyltrichlorosilane (MTS) for a temperature range of 1200-1600°C, a pressure range of 150-250 mbar and H₂/MTS ratios of 5-150. The corresponding data was u sed to calculate the theoretical supersaturation of the gaseous system at equilibrium and the composition of the solid deposit also at equilibrium, which were correlated to experimental data obtained for the HT-CVD process within these ranges of reaction parameters. Characterization techniques such as FEG-SEM, EBSD, XRD, profilometry were used to evaluate film roughness and film morphology, especially grain size and orientations.