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.