The disclosure relates to a method for manufacturing recessed micromechanical structures in a MEMS device wafer. First vertical trenches in the device wafer define the horizontal dimensions of both level and recessed structures. The horizontal face of the device wafer and the vertical sidewalls of the first vertical trenches are then covered with a self-supporting etching mask which is made of a self-supporting mask material, which is sufficiently rigid to remain standing vertically in the location where it was deposited even as the sidewall upon which it was deposited is etched away. Recess trenches are then etched under the protection of the self-supporting mask. The method allows a spike-preventing aggressive etch to be used for forming the recess trenches, without harming the sidewalls in the first vertical trenches.