Removing a resist film

A hardened layer 4 formed over unhardened layer 3 of a resist film 2, layer 4 is formed as a result of ion implantation of a semiconductor substrate 1 is removed by bombarding the layer with positively charged ions, e.g. of oxygen, an oxygen/hydrogen mixture, argon or helium generated by an hf coil 22, the substrate being negatively biased by electrode 25 and the temperature being low enough to avoid popping. The temperature may be 120{C or below, the substrate being heated by heater such as a lamp 33. After removal of the hardened layer, layer 3 of the resist film can be removed by bombardment with the same ions, but with the substrate being unbiased and at an elevated temperature, e.g. 150-300{C. Temperature control may be effected by using pins 32 to vary the distance between the heater 33 and the substrate 1.