The grazing incidence X-ray reflectivity is used to determine the multilayer thickness ofGaAs/AlAs supperlattice. The measurement process includes the fitting model and themeasurement conditions (different powers of 45 kV × 40 mA, 40 kV × 40 mA and 35 kV × 40mA, different step sizes of 0.005°, 0.008° and 0.010°,and different times per step of 1 s, 2 s, 3 s). In order to obtain the valid measurementprocess, the combined standard deviation is used as the normal of the fitting resultsselection. As a result, the measurement condition of 0.008° step size and 2 stime per step with the power 40 kV × 40 mA is selectable with the operation stability offacilities and smaller error.
