A device includes a semiconductor substrate. A step is formed at a periphery of the semiconductor substrate. A first layer, made of polysilicon doped in oxygen, is deposited on top of and in contact with a first surface of the substrate. This first layer extends at least on a wall and bottom of the step. A second layer, made of glass, is deposited on top of the first layer and the edges of the first layer. The second layer forms a boss between the step and a central area of the device.