A reactor scale gas dynamics model of an industrial multi-wafer atomic layer deposition reactor using direct simulation Monte Carlo approach

Atomic layer deposition (ALD) using multi-wafer batch reactors has now emerged as the manufacturing process of choice for modern microelectronics at a massive scale. Stringent process requirements of thin film deposition uniformity within wafer (WiW) and wafer-wafer (WTW) in the batch, film conformity along submicron wafer features, thin film quality, and the utilization of expensive precursors in the reactor dictate ALD reactor design and process parameter optimization. This research discusses a particle-based direct-simulation Monte Carlo (DSMC) of the full reactor scale simulation that overcomes the low Knudsen number limitation of typical continuum computational fluid dynamics (CFD) approaches used for modeling low-pressure ALD reactors. A representative industrial multi-wafer batch reactor used for the deposition of Si-based thin films with N₂ and Si₂Cl₆ (hexachlorodisilane - HCD) as process feed gases with pressures in the range 43 Pa to 130 Pa and uniform reactor temperature of 600°C is simulated. The model provides detailed insights into the flow physics associated with the transport of the precursor species from the inlets, through wafer feed nozzles, into the inter-wafer regions, and finally through the outlet. The reactor operating conditions are shown to be in the slip/transitional flow regime for much of the reactor volume and especially the feed gas nozzle and inter wafer regions (where the Knudsen number approaches ~0.2), justifying the need for a high-Knudsen number DSMC approach as in this work. For the simulated conditions, the non-uniformity of precursor species immediately above the wafer surface is predicted to be within < 1% for a given wafer and < 2% across the entire multi-wafer stack. Results indicate that higher pressure degrades WiW and WTW uniformity. A precursor-wafer interaction efficiency of ~99% is observed, irrespective of chamber pressure.