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 sensors were used to monitor and control the concentration of these process 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 chemical concentration within specified limits. Different concentrations of RCA-based cleaning solutions and HF solutions were investigated. Results show that these techniques are suitable for monitoring and controlling the concentration of chemicals in the process tanks for better process control. These techniques provide low cost of ownership of the process by using dilute chemicals and longer bath life (i.e., a more environmentally sound process).