Abstract: The present invention provides a method for forming a transistor on a silicon substrate, the method comprising: providing a substrate comprising: a gate electrode with a liner comprising silicon and oxygen, and with a sidewall spacer, and source and/or drain region(s) in the substrate adjacent to the gate electrode, a layer at least 5 nm thick comprising silicon dioxide covering at least the source and/or drain regions; etching the layer comprising silicon and oxygen from at least the source and/or drain regions; and forming contacts for the source and/or drain region(s), characterized in that the layer comprising silicon and oxygen is etched from the substrate by steps comprising: forming an etchant from a plasma formed from a mixture comprising nitrogen trifluoride and ammonia; exposing the substrate to the etchant; and annealing the substrate.