Thermodynamic Analysis, a Useful Tool for MOCVD
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ABSTRACT Although the decomposition of metalorganic compounds is in itself an irreversible phenomenon, the nature and proportions of the deposited phase in a MOCVD process are none the less in agreement with predictions made on the basis of a thermodynamic analysis. This theoretical approach is particularly attracting in the case of relatively complicated systems, where many phases are susceptible to appear and very often the wanted compound is difficult to obtain as a single phase material. The control of the parasitic phases is extremely important in order to obtain or to maintain a given physical property of the deposited film. A correct thermodynamic description of the chemical system under investigation to simulate a given MOCVD process is therefore a useful tool for a deeper understanding of the on-going reactions at the substrate surface and to optimise the process conditions. The simulation results are often presented as deposition diagrams which allow an easy comparison between theoretical predictions and actual experimental results. Different examples for this thermodynamic analysis including the comparison with experiences in the field of electronic ceramics will be given.
INTRODUCTION Thermodynamics - only a fashion ? An ab-initio thermodynamic approach of CVD experiences was for a long time almost non-existent. Then, from 1975 to 1985, the initiative of a certain number of researchers has slowly accustomed the experimentators with the positive output which can be obtained by a preliminary thermodynamic simulation of their experiments. From 1985 to 1991, this approach has been used a little bit throughout the world, often in a satisfying way. Since 1991, this evolution stopped without any obvious reason. Is this due to the decline of teaching chemical thermodynamics of materials ? This loss of influence of a thermodynamic approach in material science can be very bad, even in the field of MOCVD where the irreversibility of the experimental phenomena could justify, in the first place, that one is not preoccupied by the phase equilibria in the studied chemical system. The variety of applications where thermodynamic simulation is a useful tool and which benefit from this approach will be developed in the following sections of this contribution. 137 Mat. Res. Soc. Symp. Proc. Vol. 415 01996 Materials Research Society
THERMODYNAMIC CHARACTERISATION OF A GASEOUS PRECURSOR MATERIAL USED IN A MOCVD PROCESS For a few years now, metalorganic compounds have been used intensively as gaseous precursor materials in a MOCVD process in various fields like electronics, optoelectronics,.... Unfortunately, an industrial use of these precursors having numerous potential applications are hindered by the fact that a database with commercially available materials, which has been approved scientifically, is not available. There is a whole list of metalorganic precursors which can be synthesised by the chemists, but their thermodynamic and kinetic properties including their decomposition behaviour has never been determined. T
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