(711g) Three-Dimensional Multiscale CFD Modeling for PECVD of Amorphous Silicon Thin Films

Continuous strides have been made in the multiscale modeling of plasma-enhanced chemical vapor deposition (PECVD) with applications to the manufacturing of silicon thin films for use in the photovoltaic and microelectronics industries [1],[2],[3],[4]. Due to difficulties associated with continuous, in situ measurements during the deposition process, accurate modeling of thin film deposition is necessary in order to improve product quality and to cut down on manufacturing costs. Recently, Crose et al. proposed a novel multiscale computational fluid dynamics (CFD) model, which combined a macroscopic CFD domain with a microscopic surface domain [5]. While this model was successful in capturing the behavior of the PECVD reactor with regard to the non-uniform deposition of a-Si:H films and in providing a basis for multiscale CFD modeling, the two-dimensional axisymmetric nature of the model means that some features of the true three-dimensional system remain unexplored. Specifically, the showerhead holes that provide process gas to the plasma region, a key feature when considering the uniformity of thin film products, are not possible to represent using two-dimensional (2D) axisymmetric models.

Motivated by the above considerations, the 2D axisymmetric framework previously developed is extended to the three dimensional (3D) spatial domain. Using a 3D render of a typical chambered, parallel-plate PECVD reactor, a CFD model is proposed which is capable of reproducing both accurate plasma chemistry and fluid flow into the reaction zone through the showerhead region. Additionally, a detailed kinetic Monte Carlo (kMC) algorithm developed previously [3] is applied to simulate the the surface of the wafer in order to capture both the exchange of mass and energy, as well as the character of the a-Si:H thin-film. Given the computationally demanding nature of the transient simulations, a parallel computation strategy is applied which allows for the discretization of both the macroscopic CFD volume and the microscopic kMC algorithm. The outlined multiscale model is applied to the deposition of 300 nm thick a-Si:H films revealing significant non-uniformities in the thickness and porosity of the thin-film product. Additionally, comparison to the previously mentioned 2D axisymmetric model provides insight to the utility of reduced dimensional approaches.

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