Uniform deposition of thin film layers remains a challenge in silicon processing industries due to the lack of in situ measurements and poor distribution of deposition species across the substrate surface [1],[2]. In particular, for plasma-enhanced chemical vapor deposition (PECVD) of amorphous silicon (a-Si:H), growth rate non-uniformities greater than 20% across the surface of the wafer are common [3], which may lead to inefficient solar cells and microelectronics of poor quality. Process operators typically avoid this issue by preconditioning the reaction chamber and manually adjusting deposition conditions such that thickness non-uniformities may be reduced. Last year Crose et al. [3] developed a run-to-run-based, control scheme which has been demonstrated to reduce the offset in product thickness from 5% to less than 1% within ten batches of operation [3]; likewise, in recent years three dimensional computational fluid dynamics (CFD) models of PECVD reaction chambers have demonstrated exceptional fidelity to industrially used systems [4],[5]. Motivated by this, in this work, we investigate the application of the newly developed run-to-run control strategy to the simulated deposition of amorphous silicon (a-Si:H) thin films using a transient, three-dimensional CFD model as the process simulator. The multiscale three-dimensional CFD model recently developed by Crose et al. [5] has been shown to accurately capture the complex behavior of the PECVD reactor and to reproduce experimentally observed non-uniformities with respect to the film thickness and porosity, and will be used throughout this work. A computationally efficient parallel processing scheme allows for the application of the R2R algorithm to 20 serial batch simulations which are shown to reduce the product offset from the 300 nm thickness set-point.
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[2] O. Gabriel, S. Kirner, M. Klick, B. Stannowski, R. Schlatmann, “Plasma monitoring and PECVD process control in thin film silicon-based solar cell manufacturing,†EPJ Photovolt., 55202, 1-9, 2014.
[3] Crose, M., Kwon, JSI., Tran, A. and Christofides, P.D., “Multiscale modeling and run-to-run control of PECVD of thin film solar cells,†Renewable Energy, 100, 129-140, 2017.
[4] Crose, M., Tran, A. and Christofides, P.D., “Multiscale computational fluid dynamics: methodology and application to PECVD of thin film solar cells,†Coatings, 7 (2), 22, 23 pages, 2017.
[5] Crose, M., W. Zhang, A. Tran and P. D. Christofides, "Multiscale
Three-Dimensional CFD Modeling of PECVD of Amorphous Silicon Thin Films,†Comp. & Chem. Eng., 113, 184-195, 2018.
