RCA Clean Replacement

Abstract

A two‐step replacement for the four‐step process used to clean silicon wafers at critical steps during semiconductor microcontroller manufacture was studied and characterized in a spray tool and was shown to be an improved cleaning process. The standard four‐step process, commonly referred to as the RCA clean, consists of a treatment with an alkaline solution containing ammonium hydroxide followed by a water rinse and an acid solution containing hydrochloric acid followed by a water rinse; whereas the new clean consists of an alkaline solution containing tetraalkylammonium hydroxide followed by a water rinse. To obtain a measure of the latitude afforded by this new clean, the variables studied were chemical flow or spray rate, temperature, spray time, and concentration. The manufacturing process step used for the study was the clean prior to the growth of the tunnel oxide, and the key electrical parameter monitored was the tunnel oxide current and electrical stress breakdown for very thin oxides. The results show that the main effect of temperature had the greatest direct impact on the cleaning efficiency (measured by time to tunnel oxide break down), with the interaction effects of temperature/time and temperature/flow being most significant. The interaction of temperature and time had the largest impact on the tunnel oxide uniformity across the wafer.