because of this according to this embodiment it is possible to reduce the damage to the underlayer film 31 and to increase the etching rate while an nd 2 ion and a d ion are being applied to the underlayer film 31 side walls of the organic film 32 removed by etching are exposed to an nd 2 radical and a d radical because the d radical is more active than the nd 2 radical mainly the d radical reacts with the carbon in the organic film 32 and carbon deuterium cd generated as a reaction product therefore the organic film 32 is etched in a horizontal direction of the substrate in order to form an undercut region fig5 is a sectional view which shows an example in which side wall parts of the organic film 32 are etched mainly by a d radical and an undercut region 36 is formed on the other hand fig6 is a sectional view which shows an undercut region 36 of the organic film 32 when plasma etching has been performed by using a gas which contains a hydrogen compound nh 3 the d radical enters into the undercut region 36 with the depth x 5 because of a mass difference between the d radical and the h radical the temperature of the h.