PURPOSE: To prevent the adhesion of contamination on a rear surface of one wafer to the rear surface of the other wafer by a method wherein a wafer holder is provided with stoppers for holding one of every two sheets of wafers and a wafer carrier is converted.

CONSTITUTION: A first stopper 3 blockades one of every two grooves 6 for wafers of a wafer holder 1 while the wafers are supported in the grooves 6 for wafers, which are blockaded. A second stopper 2 blockades all of the grooves 6 for wafers of the wafer holder 1 simultaneously to support the wafers in the wafers grooves 6. A wafers carrier rotating mechanism 9 converts a wafers carrier 4 about the vertical shaft thereof. Thus, the wafers, received in the wafers carrier, are treated under a condition that the front surface of the wafers is opposed to the rear surface of the other wafers.