Abstract: An alignment mark is formed in a planar semiconductor IC structure coated by a layer opaque to the radiations of the photo-stepper used to perform a photolithographic step. First, there is provided a structure comprised of a silicon substrate (11) having at least one shallow isolation trench (17A) in the chip region (13) and one shallow alignment trench (17B') in the kerf region (14) of the substrate wherein said alignment trench has a determined width (W'). Then, a layer (18) of an insulating material is conformally deposited onto the structure. Its thickness is adequate to over fill the trenches so that depressions (18A, 18B') are created above the locations of said isolation and alignment trenches. Next, the structure is planarized by filling the depression over said isolation trench but not the depression (18B') formed over said alignment trench to preserve it.