Analysis of measuring errors for the visible light phase-shifting point diffraction interferometer

In order to improve the measuring accuracy of the visible light phase-shifting point diffraction interferometer (PS/PDI) for the extreme ultraviolet lithography (EUVL) aspheric mirrors, the main measuring errors will be discussed in this paper. At first, the elementary configuration and measuring principle of the visible light phase-shifting point diffraction interferometer are introduced briefly, then the different errors which are possible to affect the measuring result are summed up, the errors include PZT phase-shifting error, detector nonlinearity error, detector quantization error, wavelength instability error and intensity instability error of the laser source, vibration error, air refractivity instability error and so on. Through detailed analysis and simulation, the magnitude of these errors can be obtained. By analysing the reasons which cause these errors and the relationship between these errors and interferometer configuration parameters, some methods are put forward to avoid or restrain these errors accordingly.