NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
Most wet processes in modern fabs involve cleaning of surfaces. Some of these cleans also involve etching.
The number of cleans in a process flow is typically 20-25% of the total steps in the process and involve all parts of the flow.
Cleans typically precede all diffusion steps and film deposition steps, and they follow all RIE or plasma etch steps and plasma strip processes.