Urea And Ammonia Removal From De-Ionized Water Via Steam Purification

摘要

De-Ionized (DI) water is ubiquitous within the Fab. Purity and consistency of DI is critical to manufacturing process. Urea is a known contaminant that is difficult to control and has large seasonal fluctuations. Normally stable at room temperature, Urea has a high conversion rate to Ammonia when boiled. DI water is often converted to steam and then injected into cleanroom air to control humidity. We will present data that shows that Urea converts to Ammonia during boiling. Ammonia is a known airborne molecular contaminant and directly leads to photo resist T-topping and wafer image defects. We will also present data that shows the ability to remove both Urea and Ammonia from the steam. Urea was reduced from 2200 ppb to 2.6 ppb and Ammonia was removed from 1468 ppt to 116 ppt.