Jian-Yun Zhang

Thermodynamics analyses of the effect of CH3 and C2H2 on morphology of CVD diamond films

CH 3 and C 2 H 2 are the dominant growth precursors during chemical vapor deposition diamond process. The ratio of C 2 H 2 to CH 3 concentration will affect the growth orientation of diamond film. In this paper the dependence of C 2 H 2 and CH 3 concentrations on substrate temperature is calculated under 4 kPa pressure according to a non-equilibrium thermodynamic coupling model reported previously. The concentrations of C 2 H 2 and CH 3 increase when the substrate temperature rises. C 2 H 2 concentration rises more highly. The dependence of the ratio of C 2 H 2 to CH 3 concentration ([C 2 H 2 ]/[CH 3 ]) on substrate temperature is also calculated. Diamond (111) and (100) facets growth is discussed with the ratio of C 2 H 2 to CH 3 concentration under various substrate temperatures and CH 4 concentrations. With the increase of substrate temperature or CH 4 concentration, the value of [C 2 H 2 ]/[CH 3 ] will rise. So the growth rate of diamond (111) facets controlled by C 2 H 2 concentration is higher than that of diamond (100) facets controlled by CH 3 , and thus (100) facets appear. These results are well consistent with many experiments reported by other researchers.

Density functional theory study of adsorption and dissociation of HfCl4 and H2O on Ge∕Si(100)-(2×1): Initial stage of atomic layer deposition of HfO2 on SiGe surface

We have investigated adsorption and dissociation of water and HfCl4 on Ge/Si(100)-(2x1) surface with density functional theory. The Si-Ge heterodimer and Ge-Ge homodimer are employed to represent the Si1-xGex surface. The activation energy for adsorption of water on Ge-Ge homodimer is much higher than that on Si-Ge heterodimer. No net activation barrier exists during the adsorption of HfCl4 on both SiGe surface dimers. The differences in the potential energy surface between reactions on Si-Ge and Ge-Ge dimers are due to different bond strengths. It should also be noticed that the activation energy for HfCl4 is quite flat, thus HfCl4 adsorbs and dissociates on Ge/Si(100)-(2x1) easily.

Effects of fluorine addition on driving force for CVD diamond growth

The driving force for the diamond growth from the vapor phase with fluorine addition was studied according to a non-equilibrium thermodynamic coupling model. There exists a temperature range that the driving force for diamond growth is positive but that for activated graphite is negative. Inside the temperature range, the growth of diamond under low pressures is possible. The effects of fluorine content on driving force for the diamond growth were also discussed. The theoretical results can offer quantitative predictions for optimizing experimental conditions.

Phase diagrams for CVD diamond deposition from halogen-containing gas phase

Abstract Thermodynamics of diamond film deposition at low pressure from C (carbon)–H (hydrogen)–X (halogen) system has been studied according to a non-equilibrium thermodynamic coupling model proposed by Wang in previous papers. Projective and sectional temperature–gas composition phase diagrams of diamond growth are obtained. Diamond growth regions, which represent the constraints of temperature, pressure and gas composition suitable for diamond growth, are predicted in our phase diagrams. Diamond growth regions agree with many experimental data reported in the literature. Thermodynamic analyses show that the substrate temperature range suitable for diamond film deposition moves towards lower temperature with increasing X addition, and becomes narrower. The effect of system pressure on the diamond growth region is also discussed.

Evaluation of the growth condition of chemical vapour deposition diamond under fluorine addition

Abstract Effects of fluorine addition on the growth conditions of chemical vapour deposition (CVD) diamond are discussed in the light of thermodynamics. Phase diagrams in the C-H-F system for low-pressure diamond growth are calculated in the usual conditions: 0.1–6.67 kPa, 900–1100 K. The effects of substrate temperature and fluorine addition on the diamond growth region are explored. From these phase diagrams, we find that the diamond growth region is small and near the CH4-HF line at low temperature; it gradually moves to the H-HF line with increasing temperature.

Projective phase diagrams for CVD diamond growth from C-H and C-H-O systems

Abstract Phase diagrams for chemical vapor deposition (CVD) diamond growth from C–H and C–H–O systems were calculated according to the non-equilibrium thermodynamic coupling model. As compared with a large quantity of experimental facts, the theoretical predictions agreed well with the experiments. The theoretical results can not only solve the conflict between the classical equilibrium thermodynamics and CVD diamond growth under low pressure, but also give quantitative predictions for optimizing experimental conditions.

Quantum chemical study of adsorption and dissociation of HfCl 4 and H 2 O on Ge/Si(100) − (2×1): Initial stage of atomic layer deposition of HfO 2 on SiGe surface

We investigated adsorption and dissociation of water and HfCl 4 on a Ge/Si(100) −(2 × 1) surface with a density-functional theory. The Si–Ge and Ge–Ge homodimers are used to represent the Si 1− x Ge x surface. (i) Water first adsorbs on the bare Ge/Si(100) − (2 × 1) surface and then dissociates into OH and H. The activation energy for adsorption of water on the Ge–Ge homodimer is much higher than that on the Si–Ge heterodimer. (ii) HfCl 4 dissociates upon adsorption on the Ge/Si(100) − (2 × 1) surface into HfCl 3 and Cl. No net activation barrier exists during the adsorption of HfCl 4 on both SiGe surface dimers. The molecular adsorption state is found to be metastable according to the calculation, which implies that the reaction tends to move toward to the product rather than trapping in HfCl 4 adsorbed state. The difference in the potential energy surface between reactions on Si–Ge and Ge–Ge dimers is due to different bond strengths.

Reaction mechanism of ZrCl/sub 4/ with Ge/Si(100)-(2/spl times/1): A density functional theory study of initial stage of ZrO/sub 2/ atomic layer deposition on SiGe alloy surface

The reaction mechanism of ZrCl/sub 4/ adsorption and dissociation on Ge/Si(100)-(2/spl times/1) surface is investigated with density functional theory. The Si-Si, Si-Ge and Ge-Ge one-dimer cluster models are employed in the calculation to represent Ge/Si(100)-(2/spl times/1) surface with different Ge composition. The reaction of ZrCl/sub 2/ with hydroxylated Ge/Si(100)-(2/spl times/1) surface forms a bridged ZrCl/sub 2/ site, while on H-passivated surface ZrCl/sub 3/ site is formed. The reaction energy barrier of ZrCl/sub 2/ with H-passivated SiGe surface is much higher than ZrCl/sub 4/ with hydroxylated SiGe surface, which indicates that the reaction proceeds more slowly on H-passivated surface than on OH-terminated surface. The adsorbates and products on Ge-Ge dimer cluster model of Ge/Si(100)-(2/spl times/1) are most stable while structures on Si-Si dimer cluster model are least stable.

Thin film growth conditions for CVD diamond under low pressure

Non-equilibrium stationary phase diagrams for diamond growth with nitrogen addition into the reaction system were calculated and coordinate well with published experimental results. Therefore they can direct the experimental research on the subject. The effects of nitrogen addition on the deposition of diamond films were discussed by using the phase diagrams. The nitrogen addition can accelerate the deposition rate of diamond films in two aspects: enhance the CH/sub 3/ concentration at the growth surface and accelerate the abstraction of H atoms covering the growth surface sites.

Structure Stability in Plasma Chemistry

Diamond is a metastable phase, while graphite is a stable phase in low pressure equilibrium phase diagrams of carbon. However, diamond with saturated structure of π bonds is more stable than graphite with unsaturated structure of n bonds during the existence of activated particles generated by plasma. That provides an excellent explanation for the plasma and other activated CVD diamond growth under low pressure taking place with simultaneous graphite etching.