A method for manufacturing an electronic device includes locally implanting ionic species into a first region of a silicon nitride layer and into a first region of an electrically insulating layer located under the first region of the silicon nitride layer. A second region of the silicon nitride layer and a region of the electrically insulating layer located under the second region of the silicon nitride layer are protected from the implantation. The electrically insulating layer is disposed between a semi-conducting substrate and the silicon nitride layer. At least one trench is formed extending into the semi-conducting substrate through the silicon nitride layer and the electrically insulating layer. The trench separates the first region from the second region of the electrically insulating layer. The electrically insulating layer is selectively etched, and the etch rate of the electrically insulating layer in the first region is greater than the etch rate in the second region.