A method for producing a pillar structure in a semiconductor layer, the method including providing a structure including, on a main surface, a semiconductor layer. A patterned hard mask layer stack is provided on the semiconductor layer that includes a first layer in contact with the semiconductor layer and a second layer overlying and in contact with the first layer. The semiconductor layer is etched using the patterned hard mask layer stack as a mask. The etching includes subjecting the structure to a first plasma thereby removing a first part of the semiconductor layer and at least a part of the second layer while preserving the first layer thereby, producing a first part of the pillar structure, thereafter; and subjecting the structure to a second plasma thereby removing a second part of the semiconductor layer thereby, producing a second part of the pillar structure.