on the substrate placing table 23 in the etching chamber 21 then nh 3 gas is introduced into the plasma generating chamber 25 through the gas introduction pipe 26 and the microwave is introduced into the plasma generating chamber 25 through the waveguide 28 at the same time the electrons that have been put in cyclotron motion in advance by applying the magnetic field of intensity of 875 gauss generated with the electromagnetic coil 27 resonates with the microwave and acquires high energy and collides with nh 3 gas and supplies the energy thereof to the nh 3 gas thus forming the nh 3 gas into plasma the nh 3 gas formed into plasma passes to the downstream etching chamber 21 through the conduction hole 24 and etches the hgcdte substrate 10 besides an ecr plasma etching apparatus is used in the foregoing in this ecr plasma etching apparatus microwave electric power with magnetic field is supplied so as to form etching gas into plasma and etching is performed by the plasma gas but a plasma chamber separation type etching apparatus may also be used in this etching apparatus microwave electric power having the same frequency as the above is simply supplied so as to form the etching gas in a plasma generating chamber 34 into plasma and the plasma gas is introduced into an etching chamber 31 so as.