1. A system comprising: a stage configured to hold a wafer; a light source configured to direct a beam at a surface of the wafer on the stage; a sensor configured to receive the beam reflected off the surface and provide at least two polarization channels, each of the polarization channels providing a signal; and a controller in electronic communication with the sensor, wherein the controller is configured to: receive the signal from each of the polarization channels; normalize a difference between a pair of the signals to generate a normalized result; and determine a value of a layer on the wafer based on the normalized result and a total intensity of the pair of the signals, wherein the value is one of a thickness, a surface roughness, a material concentration, or a critical dimension.