Step height measurements in micro and nano scale are essential to the micro-technology. The interferometric measurement is carried out using two main techniques: white light scanning interferometry (WLI) and phase stepping interferometry (PSI). A step height standard sample of nominal step height value h of 90.1 nm has been studied using the PSI mode with an optical filter light of λ = 633.4 nm against three parameters: vertical distance (z) between objective and sample, intensity of the incident light and the inclination angles of the sample to the incident light. The effect of numerical aperture of objectives has been referenced to some literature. The total budget of studied parameters for the sample 90.1 nm leads to expanded uncertainty of 0.46 nm.