To provide a method of treating semiconductor wafer which reliably removes particles from a treating chamber and substrate surface in a treating cycle, without adding a long time.

A treating chamber 210 has an isolation region 252. An electrically controlled grid 250 is inserted between the region 252 and liner 220 and has independently voltage-controllable segments 250a, 250b, 250c, 250d. Power is fed between treating steps of a semiconductor substrate 230 to attract particles 235 floating in the chamber 210 toward the grid 250 away from the substrate. While a gas flow or pressure lowering is made in the treating chamber the voltage on the grid is changed to move the particles 235 to a pumping port 239 owing an electric force and remove the particles through this port from the chamber.