IN-SITU CHEMICAL CONCENTRATION CONTROL FOR WAFER WET CLEANING

This paper demonstrates the use of conductivity sensors to monitor and control the concentration of RCA cleaning and hydrofluoric acid (HF) etching solutions. Commercially available electrodeless conductivity s ensors were used to monitor and control the concentration of these pro cess solutions. A linear relationship between the conductivity of the solution and the chemical concentration was obtained within the range studied A chemical injection scheme was developed to maintain the chem ical concentration within specified limits. Different concentrations o f RCA-based cleaning solutions and HF solutions were investigated. Res ults show that these techniques are suitable for monitoring and contro lling the concentration of chemicals in the process tanks for better p rocess control. These techniques provide low cost of ownership of the process by using dilute chemicals and longer bath life (i.e., a more e nvironmentally sound process).