相移点衍射干涉仪中参考球面波的质量取决于小孔的直径、圆度和厚度，其中小孔的直径是最主要的因素，在实际加工前，需给出小孔直径的要求。基于矢量衍射理论，分析计算了三维结构小孔的衍射。分析了在均匀的TE偏振光和TM偏振光入射情况下，小孔直径大小对衍射波面质量的影响。入射光的线性偏振，给衍射波面中引入了像散和彗差。分析计算得出，为了获得数值孔径(NA)为0.1，相对于理想球面波的均方根(RMS)偏差不大于0.005 λ(λ=13.55 nm)，强度均匀性为0.4的参考球面波，对90 nm厚的小孔选择直径大小为70 nm较为适宜。

The quality of the reference wave front in phase shifting point diffraction interferometer depends on the pinhole diameter, roundness and thickness, where the first one is the most critical factor. The requirement for pinhole diameter should be known before the manufacture in actual maching. Three-dimensional pinhole diffraction is calculated based on the vector diffraction theory. How the pinhole diameter affects the diffracted wave-front quality is analyzed under the uniform incident light with TE and TM polarization. The appearance of the astigmatism and coma in the wave front is brought about by the linear polarization of incident light. The calculation and analysis show that in order to obtain reference wave front with 0.1 numerical aperture (NA), the root mean square of (RMS) wave-front error below 0.005 λ (λ=13.55 nm), together with 0.4 intensity uniformity, for a 90 nm thickness pinhole, the diameter of 70 nm is suitable.