Thermodynamics and Kinetics of SiC CVD Epitaxy

The ultimate goal of process modeling in the context of thin film growth is not only to predict the growth rate at a reactor scale, but also to provide details of other aspects that are crucial in process development, such as the microstructure and the epitaxial quality of the films. With the fundamental aspects of reactor-scale CFD simulations already well established, chemistry becomes the key issue that needs to be addressed in order to achieve predictive reactor-scale simulations. The problem is not just the complexity of SiC CVD epitaxy in terms of the number of reactions and/or species, but the fact that the kinetics of some of these processes, especially those involving surface reactions, is not known beyond the most common precursor combinations. This lack of knowledge limits the predicting abilities of simulations in two ways: 1) they introduce an uncertainty in the model results that needs to be accounted for, especially when unknown coefficients are determined by fits to experimental data, and 2) they prevent us from understanding the impact of chemistry on film microstructure and epitaxial quality, where heterogeneous processes play a central role.

In this talk, I will present our research on non-halogenated and halogenated chemistries for SiC CVD. As part of a greater effort aimed at developing multiscale simulations of ALD and CVD for predictive scale up,[1] we are carrying out both thermodynamic and kinetic analyses of the gas phase and surface kinetics in SiC CVD epitaxy in order to identify the main sources of uncertainty. In addition to using standard sets of reactions previously compiled in the literature for SiC CVD,[2,3] we are exploring the combustion chemistry, etching, and Si CVD and PECVD literature to understand the consistency and uniqueness of the different rate coefficients, and its impact in the main predicted species in the gas phase. The goal of this work is to quantify the level of uncertainty and ultimately to improve the predictive abilities of our models as our knowledge progresses, using for instance Bayesian analysis. Likewise, we seek to identify gaps in the experimental data that will help us drive experimental research towards those reactions/pathways that have a greater weight on the synthesis processs. Finally, we will address the impact of surface chemistry on film microstructure. Besides reviewing the underlying assumptions of previous models in the literature,[2,3,4] we will explore the impact of kinetics on the roughness and the stability of step-flow growth. These could be used to establish limits on unknown heterogeneous kinetic processes based on the experimental characterization of the film microstructure and the stability of the step-flow growth as a function of the miscut angle.

[1] Yanguas-Gil and Elam, Simple ALD Multiscale Simulation (SALMS), ANL-SF-13-073, Argonne National Laboratory (2013).

[2] Danielsson, Henry and Janzen, J. Crystal Growth 243, 170 (2002).

[3] Nichizawa and Pons, Chem. Vap. Deposition 12, 516 (2006).

[4] Camarda et al, J. Crystal Growth 310, 971 (2008).