Claude Bernard

Characterization of chromium nitride and carbonitride coatings deposited at low temperature by organometallic chemical vapour deposition

Abstract Chromium nitride and carbonitride hard coatings were deposited by organometallic chemical vapour deposition in the temperature range 350–550 °C. Bis(benzene) chromium and NH 3 or N 2 H 4 were used as chromium and nitrogen vapour sources respectively. The chemical and structural characterization of these coatings is presented. Amorphous films were obtained below 450 °C. Above this temperature, a different phase, namely Cr 7 C 3 , Cr 2 (N,C) or CrN could be prepared depending on the gas phase composition. Electron probe microanalysis and X-ray photoelectron spectroscopy gave evidence for a slight contamination of the films with free carbon. The experimental results are in good agreement with a thermodynamic calculation which has been fruitful in giving information about the feasibility of growing chromium nitride phases under these chemical vapour deposition conditions. The microhardness of the coating in each case was comparable with that of similar material deposited by other techniques.

State of the art in the modelling of SiC sublimation growth

Different computational tools have helped to provide additional information on the sublimation growth of SiC single crystals by the modified-Lely method. The modelling work was motivated by the need of a better control of the local temperature field inside the crucible. Because there is an environment of strong thermal radiation in which the SiC boule growth process occurs, heat transfer must therefore be coupled with gaseous species transport and reactivity. This highly coupled model must take into account all geometric modifications in crucibles which strongly influences the crystal growth process. Local thermochemical equilibrium linked to heat and mass transfer is the model proposed in this paper to give the magnitude of the growth rate and the shape of the crystal. This modelling field is still too young to propose a software package including all modelling aspects and a reliable material database. However, some parts of the modelling work have reached maturity like electromagnetic heating and thermal modelling coupled with simplified chemical models. We show in this paper selected examples in order to demonstrate the types of information which can be routinely available by simulation and how to approach defect formation from a macroscopic point of view. Minor geometric modifications of the holes for pyrometric measurements drastically change the magnitude of thermal gradients in the crucible. Geometric modifications of the crucible change the computed crystal shapes. The calculated results complete the experimental knowledge by a quantification of the local macroscopic fields.

Growth of AlSb on insulating substrates by metal organics chemical vapour deposition

Abstract Aluminium antimonide thin films were grown on different insulating substrates, i.e. silica, CaF 2 , BaF 2 , Al 2 O 3 , GaAs, by metal organics chemical vapour deposition (MO-CVD). Epitaxial AlSb thin films were successfully grown on CaF 2 and GaAs. In the process, the metal alkyls trimethylaluminium (TMA) and trimethylantimony (TMSb) are the sources of Al and Sb, respectively. The thermodynamic study of the system Al-Sb-C-H shows that AlSb could be deposited for given values of the partial pressures of Al, Sb and C in the vapour phase. Other condensed phases could appear, Al 4 C 3 , Sb.

Application of equilibrium thermodynamics to the development of diffusion barriers for copper metallization (invited)

Abstract The guidelines for designing a conductive, amorphous material, capable of thermodynamic equilibrium with copper, are defined using readily available thermodynamic information. The tradeoff between desired properties — equilibrium at the interfaces, amorphous microstructure, and electronic conductivity — are described, along with trends in relevant binary systems that result in these properties. These guidelines maximize the thermodynamic tendency for amorphous phase formation, in an attempt to minimize the need for nonequilibrium synthesis methods.

Thermodynamic calculations in CVD growth of GaAs compounds: I. Critical assessment of the thermodynamic properties for the gaseous molecules of the Ga-Cl system

Abstract Thermodynamic calculations of CVD growth are successful for prevision of the deposition rate, but also for selecting the main kinetic process which governs the growth rate. When changing the pressure and temperature conditions, the gaseous phase composition usually changes drastically. So, for a chemical system, the set of existing gaseous molecules must be well-known for the understanding of the CVD process. We analyse by complex equilibrium calculations the experimental works which have been performed on the Ga-Cl system and estimate or check with a dimensional model the minor species which have not been completely studied. Thermodynamic data are available for the GaCl 3 , Ga 2 Cl 6 , GaCl, Ga 2 Cl 2 , Ga 2 Cl 4 and GaCl 2 molecules, which are important in CVD-chloride deposition of GaAs .

Thermal degradation mechanisms of Nicalon fibre:a thermodynamic simulation

Thermodynamic calculations for the thermal degradation of the Nicalon fibre in inert gas flow at atmospheric pressure have been performed, based on minimization of the Gibbs energy of the Si-C-O-H chemical system. The calculations are based on a critically selected thermodynamic database of the participating compounds. The results are presented by means of diagrams illustrating the quantities of condensed and gaseous species obtained as a function of treatment temperature. These are compared with recently reported TEM studies of as-received and heat-treated material, which illustrate the sequential morphologies of its structure and nanotexture as a function of treatment temperature. The main step of the observed degradation mechanism is successfully simulated in terms of the temperature, the oxygen content and the weight loss of the material. An endogenous oxidation mechanism is proposed for degradation of the fibre.

Experimental and theoretical study of low pressure GaAs VPE in the chloride system

An experimental study of the chemical vapor transport of GaAs in a low pressure reactor was carried out using the AsCl3/GaAs/H2 method. The thermodynamic equilibrium in the Ga/As/H/Cl system was calculated by minimization of the Gibbs free energy as a function of the process parameters: temperature, total pressure, and AsCl3/H2 input ratio. The growth rate dependences on those parameters were examined. Particularly, the total pressure dependence of the growth rate shows the relative importance of surface kinetics and mass transfer through the boundary layer in the growth rate limitation. In the pressure range of 5 mbar to 1 bar, the growth rate decreases with decreasing total pressure; nevertheless growth rates of up to 12 μm/h were achieved at 100 mbar.

LPCVD and PACVD (Ti, Al)N films : morphology and mechanical properties

Abstract Coatings of (Ti,Al)N with different Ti/Al ratios have been deposited on silicon and different steel substrates by both low pressure CVD (LPCVD) and low frequency plasma-assisted CVD (PACVD) processes starting from metal chlorides generated by in situ chlorination of a TiAl alloy and the resulting gaseous products were mixed with NH 3 or N 2 , H 2 and Ar. The morphology and the microstructure of the as-deposited (Ti,Al)N films were investigated using XRD, SEM, EDS as well as glow discharge optical spectroscopy (GDOS). Microhardness and scratch tests and have also been performed in order to evaluate mechanical performance. For both techniques, dense and quite homogeneous layers with composition ranging from Ti/Al=99/1 to 30/70 have been synthesized depending on the experimental parameters. It seems that PACVD coatings have slightly higher hardness levels and a better adhesion than LPCVD coatings. Some preliminary correlations between the layer morphologies and mechanical properties were established.

Evaluation of LPCVD Me-Si-N (Me=Ta, Ti, W, Re) diffusion barriers for Cu metallizations

Abstract LPCVD MeSiN (MeRe, W, Ti, Ta) thin films were investigated for use as diffusion barriers between Cu overlayer and oxidized silicon substrates. Gaseous precursors were silane, in situ fabricated metal chloride, ammonia, hydrogen and argon. Thermodynamic simulations of the MeSiN and the CVD MeSiNClHAr systems were combined with the experimental study. It was shown that the existence (titanium and tantalum) or non-existence (rhenium and tungsten) of stable metal nitrides could explain the differences observed in the morphology of the four systems. Amorphous or nanocrystallized ReSiN and WSiN whereas crystallized TiSiN and TaSiN films were deposited. The ReSiN an WSiN layers crystallization temperature was found to be around 1173 K. Their morphology, thermal stability, resistivity and the performances of the four copper metallized MeSiN systems were evaluated. WSiN material appeared as the most promising diffusion barrier thanks to its morphology, resistivity around 1 mΩ cm and performances in blocking copper diffusion.

Evaluation of triisobutylaluminium for the epitaxial growth of AlSb compared to trimethylaluminium

Abstract Epitaxial layers of AlSb were grown from metal organics using trimethylantimony (TMSb) and either trimethylaluminium (TMA) or triisobutylaluminium (TiBA). The two Al alkyl sources were compared. Growth with TiBA resulted in epilayers of AlSb on GaSb that did not contain a second phase of Al 4 C 3 . However, AlSb formed using TMA always contained Al 4 C 3 .