Method in etching of a substrate

In etching, an etchant (4) for etching of a substrate (1) is applied in a given pattern. Before etching, a resist layer (2) is applied to the substrate (1) in said pattern to define at least one exposed portion (3) of the substrate (1). In order to minimize under etching, a passivating substance is arranged, before etching, on the substrate (1) to also define said pattern, i.e. at the periphery of the exposed portion (3). The passivating substance is such as to form, during etching, an etch-protecting compound at the periphery.