An apparatus includes a susceptor, a first piping, a second piping, a liquid source, a third piping and a gas source. The susceptor is suitable for placing a wafer, and the first piping is configured to dispense a chemical to the wafer on the susceptor. The second piping communicates with the first piping. The liquid source is configured to deliver a cleaning liquid to the first piping through the second piping to wash a portion of the first piping. The third piping communicates with the first piping. The gas source is configured to flow a purge gas to the first piping through the third piping to purge the portion of the first piping.