Water Vapor Delivery for Thin Film Vacuum Processes

May 24, 2011

Water vapor is known to play a significant role during thin film deposition in ALD, MOCVD, and sputtering processes. Such processes are commonly used to generate transparent conductive layers (TCO) and modify crystal structures via grain size or defect repair. The ability to supply water vapor free from atmospheric contaminants is critical to film integrity. A novel method for control and delivery of water vapor using ionic fluoro-polymer membranes has been tested and results are presented in this paper. One side of the membrane was exposed to ambient air and then de-ionized (DI) water. The other side of the membrane was exposed to high vacuum where a miniature mass spectrometric Residual Gas Analyzer (RGA) was used to monitor pressures of individual gas species. When the membrane was exposed to air the water-to-nitrogen ratio was 10:1 by volume. When the outer surface of membrane was submerged in water the ratio increased to 200:1. Separately on a humidity test stand and under a 20 sccm purge flow of dry nitrogen, 2.8x10-3 sccm of water was added, raising the concentration of water to 1400 ppm from less than 1 ppm.

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