Water vapor delivery for CIGSe and other thin film vacuum processes

Water vapor has been shown to have significant effect on thin film layers in ALD, MOCVD, and sputtering processes. Such processes are commonly used to generate TCO layers and modify crystal structures via grain size or defect repair. The ability to deliver water vapor free from atmospheric contaminants is critical to film integrity. A novel method for control and delivery of water vapor using Ionic Fluoropolymer membranes has been tested. One side of the vacuum 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 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. The partial pressure of water increased from 1.4e-4Torr to 3.9e-3Torr. Nitrogen increased from 1.4e-5Torr to 2.0e-5Torr while oxygen was found to increase from 6.5e-6Torr to 6.6e-5Torr. Separately on a humidity test stand and under a 20 sccm purge flow of dry nitrogen, 2.8e-3 sccm of water was added, raising the concentration of water to 1400 ppm from less than 1 ppm.