A 3-D structure formed in a recess of a substrate delimited by walls, including a large number of rectangle parallelepipedic blades extending from the bottom of the recess to the substrate surface while being oriented perpendicularly to one another and formed in a pattern covering the whole surface of the recess, some blades being non-secant to one of the walls, each non-secant blade being connected to one of the walls by at least another perpendicular blade.