PURPOSE: To reduce the pollution of an damage to a specimen by a method wherein sputtered ions excluding the etching ion reaching the specimen is stopped by a shutter means.

CONSTITUTION: An electron sheet 7b on a specimen processing chamber 2 side out of leading-out electrodes 7 is kept in earth potential. Another electrode sheet 7a on a plasma chamber 1 side is fed and impressed with AC or pulse voltage from an AC power supply 9 provided outside a dryethcing device. The period is set up as short as possible in consideration of the difference in rate between sputtered ions 81 and chlorine gas ion 4 so that the gas ion 4 and sputtered ions 81 may be isolated spatially and sufficiently. On the other hand, a specimen base 6 is arranged in the specimen processing chamber 2 to place a specimen 3 such as GaAs wafer on the base 6. Furthermore, a shutter sheet 10 is provided on the front surface of the speciment 3 to be opened and closed so that the group of gas ion 4 may be selectively passed but the group of sputtered ions 81 may be stopped by the shutter sheet 10.