Method in etching of a substrate

In etching, an etchant for etching of a substrate is applied in a given pattern. Before etching, a resist layer is applied to the substrate in said pattern to define at least one exposed portion of the substrate. In order to minimize under etching, a passivating substance is arranged, before etching, on the substrate to also define said pattern, i.e., at the periphery of the exposed portion. The passivating substance is such as to form, during etching, an etch-protecting compound at the periphery.