DSMC Simulations of Thin-Film Deposition in Vacuum

Graduate Students: A. Venkattraman and Arnab Ganguly

Vacuum processes for fabrication of thin-film materials play an increasingly important role in various technologies including manufacture of integrated circuits, N/MEMS and nanocomposites. A variety of techniques are used for thin-film deposition including molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and electron beam assisted physical vapor deposition (EBPVD). These deposition processes are performed under high vacuum leading to formation of supersonic jets which increase reactants kinetic energy and enhance surface reaction probability.

A description of such vapor flows based on non-equilibrium kinetic theory of gases is required to predict the resultant spatial variation of deposition angle and energy that determine thin film properties. Accurate modeling of vapor flows using the DSMC technique requires a suitable molecular collision model for the material of interest. Usually, collision models are based on measurements of transport properties such as viscosity or thermal conductivity. However, these measurements are extremely difficult to perform for non-volatile materials such as metal vapors. The main goal of this work is to determine metal-vapor molecular models for DSMC simulations of vacuum thin-film deposition processes. Various molecular models are compared using viscosity coefficient dependence on temperature as a metric. Three-dimensional DSMC simulations of thin-film depositions of copper using EBPVD from a 2D slit source at conditions from a previously published experiment are performed. Figure 1 shows the number density contours of the rapidly expanding copper vapor flow. The molecular model has been shown to have a significant effect on the mass flux distribution at the substrate. Based on comparison of dimensional mass fluxes obtained from the DSMC simulations and experiments, a suitable molecular model for copper has been determined.

Figure 1. Number density for flow of Cu vapor from a slit source into vacuum

Figure 2. 3D DSMC simulations of vacuum deposition using sources with complicated geometry

Publications and Conference Proceedings

1. A. Venkattraman and A.A. Alexeenko, "DSMC Simulations of E-beam Metal Deposition", Journal of Vacuum Science and Technology A, 28 (4) 2010 (also presented in AVS 56th International Symposium & Exhibit, San Jose, CA, Nov 8-13, 2009)

2. A. Venkattraman and A. A. Alexeenko, “DSMC Modeling of Metal Vapor Flows in Application to Thin Film Deposition”,Vacuum, Vol. 86 (11), pp. 1748–1758, 2012.

3. A. Venkattraman and A. Alexeenko, “DSMC Study of Effects of Thermal Non-Uniformities in Electron-Beam Physical Vapor Deposition”, Journal of Vacuum Science and Technology A, Vol. 29 (4), Jul/Aug 2011, 041509, 10 pages.

4. A. Venkattraman, A.A. Alexeenko, "DSMC Modeling of E-Beam Metal Deposition", Journal of Vacuum Science and Technology A, Vol. 28, No. 4, pp. 916-924, 2010.