Non-contact COS charge analysis for in-line monitoring of wet cleaning processes

Contamination levels in chemical cleaning equipment and wafer cleanliness in general are very critical to semiconductor manufacturers. In this work, a Keithley Instruments non contact electrical tester (Quantox) is used to measure the mobile ion (Qm) contamination in a variety of cleaning processes. Results show that photoresist strip cleaning process has a higher mobile ion concentration than standard pre-diffusion cleaning process. RCA1, RCA2 and HF solutions are good cleaning agents for removing mobile ion contaminants in wet chemical cleaning processes. Surface voltage mapping measured by the Quantox indicates some negative static charges on the surface after cleaning. This negative field appears to assist Qm removal during wet chemical cleaning. The dependence of flatband voltage (Vfb) and other oxide charges on various cleaning processes has also been investigated using the Quantox. The data suggests that a dipole layer has been formed by a surface reaction during chemical cleaning.