In an apparatus for etching a semiconductor wafer or sample (101), the semiconductor wafer or sample is placed on a sample holder (104) disposed in a first chamber (103). The combination of the semiconductor wafer or sample and the sample holder is enclosed within a second chamber (130) inside the first chamber. Gas is evacuated from the second chamber and an etching gas is introduced into the second chamber, but not into the first chamber, to etch the semiconductor wafer or sample.