388 Diamond and Related Materials, 3 (1994) 388-392 The growth of (100) orientated diamond films P. John, D. K. Milne and W. C. Vijayarajah Department of Chemistry, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS ( UK) M. G. Jubber and J. I. B. Wilson Department of Physics, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS (UK) Abstract Quasi-equilibrium calculations were performedon the C-H and C-H-O systemsto calculatethe thermodynamicstability of diamond and graphite phases under CVD conditions. Exclusive diamond growth is dependent, in part, on the increased thermodynamic stability of H-terminated crystallographicsurfaces. This feature was included in the methodology by estimating the surfaceenthalpies by group additivity methods. The lower boundary in the Bachmann ternary diagram which defines the demarcation line between the growth and non-growth regions was calculated. The gradient of the line is a strong function of the degree of stabilization of the H-terminated diamond surfaces. Using mixtures of CH4-CO-H 2 of compositions close to the CO line of the phase diagram, (100) faeeted films were grown by microwaveassisted CVD at rates of 1.5-2.0 ~tmh -~. 1. Introduction 2. Experimental details The empirical Bachmann diagram Ell successfully The diamond films were prepared by microwave collates the requisite growth conditions for the formation plasma assisted CVD in an ultrahigh vacuum reactor of diamond. The remarkable feature of the diagram is previously described [5]. The range of growth condi- that the boundary between the growth and non-growth tions is given in Table 1. The silicon (100) wafers and regions does not appear to depend on the particular molybdenum plates were polished with 0.75-1.5 ixm deposition technique. Quasi-equilibrium (QE) thermo- diamond dust prior to growth. dynamic calculations [2] have been applied to many gas-solid interactions. Latterly, they have been extended to diamond growth [31 modified to include a term to 3. Results accommodate the enhanced etching of graphite in a H-atom environment. Whilst a thermodynamic model 3.1. Computational procedures is unlikely to explain complex CVD processes, such The concentrations of gaseous species in equilibrium with graphite and diamond were calculated by free calculations provide a valuable insight into the pro- cesses occurring in the immediate vicinity of the energy minimization [6] as a function of pressure, growth surface, temperature and initial composition of hydrogen-meth- In the present study we have extended the QE theory of diamond growth by incorporating the increased sta- TABLE 1. Deposition conditions bility of H-terminated diamond surfaces rather than treating explicity the relative etch rates of diamond and Parameter Condition graphite. The thermodynamic functions were calculated for individual unreconstructed diamond surfaces using Microwave Power a (W) 803 the thermochemical additivity principles adopted by Temperature b (°C) 854 Pressure (Tort) 45.1 Yarbrough [-4]. In this way, the results of QE theory H2 flow (standard cm 3 min -1) 66.5 have been used to predict the lower bound of the ternary CH4 flow (standard cm 3 min- 1) 3.5 Bachmann diagram which describes the transition from c o flow (standard cm 3 min-1) 70.0 etching to growth of the diamond phase. The predictions Time (h) 8.5 of the modified QE theory were tested by growing aReflected power is 8W. polycrystalline diamond films from CH4-CO-H 2 mix- bThermocouple measurement; the surface temperature (calibrated with tures onto single-crystal silicon and molybdenum, a pyrometer) is approximately 333°C lower with the plasma off. 0925-9635/94/$7.00 © 1994 - - Elsevier Sequoia. All rights reserved SSDI 0925-9635 (93)05067-M