(110c) Multiscale Three-Dimensional CFD Modeling and Reactor Design for ALD of SiO2 Thin-Films

Atomic layer deposition (ALD) is widely used in the semiconductor industry because of its ability to produce conformal ultra-thin films on planar surfaces as well as on complex three-dimensional surface features with stringent uniformity and defect formation criteria [1]. ALD has been used to deposit SiO₂ thin-film, which is an important material for gate oxides in MOSFET and MEMS devices, sacrificial layers, and conformal dielectric films in the front-end-of-line (FEOL) semiconductor wafer processing [2]. Although the SiO₂ thin-film deposition process using bis(tertiary-butylamino)silane (BTBAS) and Ozone as precursors is well studied experimentally and utilized industrially, there is still room for reducing the spatial non-uniformity and improving industrial throughput.

The microscopic surface reactions during the process directly influence the film quality and growth rate, which serves as the motivation for our previous work to develop a kinetic Monte-Carlo (kMC) microscopic model for the surface deposition along with a low computation cost data-driven model using standard feedforward and Bayesian regularized neural networks. The previously developed microscopic model successfully reproduces the surface deposition mechanisms and characterizing the growth per cycle (GPC) under a range of fixed boundary conditions [3].

However, the effect of the macroscopic gas phase development in the ALD reactor on the wafer surface microscopic deposition profile still remains unclear and is possible for further geometric and operational optimization [4]. Thus, in this study, we use ANSYS Fluent to create an accurate macroscopic CFD model of the ALD reactor chamber, which is linked with the microscopic kMC model through a message passing interface (MPI) using the user defined function (UDF) in Fluent [5]. The nature of the ALD process is comprehensively reproduced by the multiscale model. In addition, equipped with the multiscale workflow, optimized reactor geometries are designed and investigated, including a showerhead hole distribution optimization and an upstream shape modification. Also, operational optimizations are carried out by controlling the radial heating of the substrate surface and several reactor designs are evaluated to develop an optimal reactor design. Together, it is demonstrated that, for the deposited film, the spatial non-uniformity and required cycle-time are reduced.

[1] Schwille, M.C., Schössler, T., Barth, J., Knaut, M., Schön, F., Höchst, A., Oettel, M., Bartha, J. Experimental and simulation approach for process optimization of atomic layer deposited thin films in high aspect ratio 3D structures. Journal of Vacuum Science & Technology A:Vacuum, Surfaces, and Films. 2018, 35, 01B118.

[2] Murray, C.A., Elliott, S.D., Hausmann, D., Henri, J., LaVoie, A. Effect of reaction mechanism on precursor exposure time in atomic layer deposition of silicon oxide and silicon nitride. ACS Applied Materials & Interfaces. 2018, 6, 10534–10541.

[3] Ding, Y., Zhang, Y., Kim, K., Tran, A., Wu, Z., Christofides, P.D. Microscopic Modeling and Optimal Operation of Thermal Atomic Layer Deposition. Chemical Engineering Research and Design. 145, 159-172, 2019.

[4] George, S.M. Atomic layer deposition: An overview. Chemical Reviews 110, 111–131, 2009.

[5] Crose, M., Zhang, W., Tran, A., Christofides, P.D., “Multiscale three-dimensional CFD modeling for PECVD of amorphous silicon thin films. Computers & Chemical Engineering. 2018, 113, 184 – 195, 2018.