Etching with improved control of critical feature dimensions at the bottom of thick layers

The present invention relates to a method for etching a feature in an etch layer that has a thickness of more than 2 micrometers from an initial contact face for the etchant to an opposite bottom face of the etch layer, at a lateral feature position in the etch layer and with a critical lateral extension at the bottom face. The method includes fabricating, at the lateral feature position on the substrate layer, a mask feature from a mask-layer material, the mask feature having the critical lateral extension. The etch layer is deposited to a thickness of more than 2 micrometers, on the mask feature and on the substrate layer, from an etch-layer material, which is selectively etchable relative to the mask-layer material. Then, the feature is etched in the etch layer at the first lateral position with a lateral extension larger than the critical lateral extension, using an etchant that selectively removes the etch layer-material relative to the mask-layer material.