Various embodiments include a method for providing instructions to a process tool. The method includes emitting an incident light beam at a substrate, receiving a reflected light beam from the substrate and determining a spectrum of the reflected light beam. The method further includes determining a first property of a first layer of the substrate and a second property of a second layer of the substrate, based on the spectrum determination. The method further includes comparing the first property of the first layer to a first reference property and comparing the second property of the second layer to a second reference property. The method further includes determining the instructions based on the first property comparison and the second property comparison; and providing the instructions to the process tool.