Point-diffraction interference wave aberration measuring instrument and measuring method thereof

Abstract

A point-diffraction interference wave aberration measuring instrument consists of a light source, a light splitter, a first light intensity and polarization adjuster, a phase shifter, a second light intensity and polarization adjuster, an ideal wave front generating unit, an object precise adjusting platform, a measured optical system, an image wave front detecting unit, an image precise adjusting platform and a data processing unit. The interference instrument has the advantages of simplicity in structure, no systematic error of a phase shifting element, high interference grain visibility and capability of calibrating the systematic error.

Description

technical field [0001] The invention relates to the field of interferometry, in particular to a point-diffraction interference wave aberration measuring instrument and a detection method. Background technique [0002] Waveform aberration is an important parameter to describe the performance of small aberration imaging optical system. The wave aberration of high-quality microscope objectives and space telescopes should be less than λ / 4PV or λ / 14RMS (λ is the working wavelength, and RMS is the root mean square value). The wave aberration of the projection objective lens for deep ultraviolet lithography is required to reach several nm RMS, and the wave aberration of the projection objective lens for extreme ultraviolet lithography needs to be less than 1nm RMS. This puts high demands on wave aberration detection technology. [0003] Prior art 1 (see H. Medecki, E. Tejnil, K.A. Goldberg, "Phase-shifting point diffraction interferometer", OPTICS LETTERS Vol.21, No.19, 1526-1528...

AI Technical Summary

Problems solved by technology

However, the light intensity of the 0th-order diffracted light and the 1st-order diffracted light is determined by the diffraction efficiency of the diffraction grating and cannot be adjusted

When the 1st-order diffracted light is used to filter the reference light wave through the pinhole, the visibility of interference fringes is too low; when the 0th-order diffracted light is used to filter the pinhole to generate the reference light wave, the coma aberration generated by the grating diffraction will affect the measurement accuracy, and it is difficult to calibration

In addition, the diffraction grating is used as the phase shifting element, and the diffraction grating is located in the imaging optical path of the imaging system under test, requiring an additional displacement platform for phase shifting, resulting in a complex system structure and increased system cost

Factors such as uneven refractive index and uneven thickness of the diffraction grating base material, defects in the diffraction grating pattern, and dust will also cause wavefront distortion and system errors

Images