Ronchi剪切干涉采用扩展光源调制光场空间相干性，具有干涉仪结构简单、共光路、零条纹检测等优点，适合用于光刻机投影物镜波像差原位检测。基于Ronchi剪切干涉的投影物镜波像差检测技术及系统，根据光栅衍射和空间相干性理论推导了Ronchi剪切干涉场的表达式。针对Ronchi剪切干涉仪多级衍射光寄生干涉对相位提取精度的影响，提出了一种十步相移算法，有效地消除±9 级以内多级衍射的影响，理论上相位提取误差峰谷(PV)值为0.0046 λ ，均方根(RMS)值为0.0019 λ ，实验数据验证了理论推导的正确性和相位提取算法的有效性。

Ronchi shearing interferometry modulates the spatial coherence of light field with extended source. With the advantages of simple structure, common- path, null- fringe detection, and so on the Ronchi shearing interferometer can be used for in situ aberration measurement of lithography projection lens. Ronchi shearing interferometry for wave-front aberration measurement of lithography projection lens is studied. The interference model of Ronchi shearing interferometer is derived by theories of grating diffraction and spatial coherence. A tenstep phase-shifting algorithm is proposed to eliminate negative effects of unwanted interference from the high order diffraction light, which limits the accuracy of phase retrieval. The effects of the first ±9 orders interference on phase retrieval accuracy can be eliminated. The peak-valley (PV) value and root mean square (RMS) value of theoretical phase retrieval error are less than 0.0046 λ and 0.0019 λ respectively. The theoretical interference model and the phase retrieval algorithm are validated.