Finding a fast and precise method to measure the side-wall angle of periodic (or non-periodic) structures is still a very challenging problem in lithographic applications. For this reason, over the years, many techniques have been proposed to circumvent this limitation, with the final goal to give the most precise geometrical description of particular targets. Recently, the investigation of the optical angular momentum, which is encoded in the light's spiral spectrum, has brought new ways to acquire information about objects. In this work, we built an optical setup to put forward a new method to detect the side-wall angle in a fast and reliable way. The novelty of this work is the use of the spiral spectrum of a light beam for angle measurements, i.e. the light transmitted by a particular structure is projected onto properly tailored spatial modes and only the most sensitive mode to the side wall angle is detected and processed.