Low throughput is a major limitation for industrial level atomic layer deposition (ALD) applications. Spatial ALD is regarded as a promising solution to this issue. With numerical simulations, this paper studies an in-line spatial ALD reactor by investigating the effects of gap size, temperature, and pumping pressure on the flow and surface chemical deposition processes in Al2O3 ALD. The precursor intermixing is a critical issue in spatial ALD system design, and it is highly dependent on the flow and material distributions. By numerical studies, it's found that bigger gap, e.g., 2 mm, results in less precursor intermixing, but generates slightly lower saturated deposition rate. Wafer temperature is shown as a significant factor in both flow and surface deposition processes. Higher temperature accelerates the diffusive mass transport, which largely contributes to the precursor intermixing. On the other hand, higher temperature increases film deposition rate. Well-maintained pumping pressure is beneficial to decrease the precursor intermixing level, while its effect on the chemical process is shown very weak. It is revealed that the time scale of in-line spatial ALD cycle is in tens of milliseconds, i.e., similar to 15 ms. Considering that the in-line spatial ALD is a continuous process without purging step, the ALD cycle time is greatly shortened, and the overall throughput is shown as high as similar to 4 nm/s, compared to several nm/min in traditional AID. (C) 2016 Elsevier Ltd. All rights reserved.