Abstract: In semiconductor device fabrication processes which include the formation of hardmask elements 17 including Al2O2, unwanted Al2O3 is left between the hardmask elements 17. The unwanted Al2O3 includes a layer 9 of Al2O3which is not homogenous across the surface of the structure 3 it overlies, and Al2O3 deposits on the sides of the hardmask elements 17. A method is proposed in which any such unwanted Al2O3 between the hardmask elements 17 is removed by a wet etching step in which the unwanted Al2O3 is exposed to an etchant liquid which etches the Al2O3 at a faster rate than other portions of the structure. This step allows the unwanted Al2O3 to be removed substantially completely without causing significant detriment to those other portions of the structure. Subsequently, an RIE etching step can be performed using the hardmask elements 17 as a mask, without the unwanted Al2O3 obstructing the RIE etching step.