Research On Key Technologies Of Wavefront Measurement Based On Shack-hartmann Sensor

Lithography is a very large scale integrated circuit manufacturing processes in thecore equipment. Aberrations of Lithography projection lens affect the image quality oflithography, lithography resolution and uniformity of critical dimension, have been oneof the most important indicators of lithography tools. In order to achieve the rigorousrequirements of wave-front aberration, it is necessary to carry out lithographyprojection lens aberration measurement and correction regularly. The aberrationmeasurement of lithography projection lens based on Shack-Hartmann wavefrontsensor are mainstream method and has promising structure for compact on-body lensinspection instruments. The calibration is significant to realize high accuracywavefront aberration metrology. The high quality spherical wave is indispensable tocalibration of the system errors in Shack-Hartmann wavefront sensor.After review of importance of projection lens aberration measurement to ICfabrication, there is also a view over the projection lens aberration measurementmethods, especially based on Shack-Hartmann sensor methods. It is a significantresearch focus on the high-precision spherical wavefront for projection lens aberrationmeasurement based on Shack-Hartmann sensor methods.Comparative analysis of the finite element method, the rigorous coupled wavemethod and the finite difference time domain method, we decide use FDTD method toanalysis the pinhole diffraction model. A simulation model based on Finite-DifferenceTime-Domain method is proposed to precisely analyze the pinhole diffractedwave-front. Surface Equivalence Theorem and Green function as a new near-field tofar-field method be used for the wave-front with large numerical aperture inthree-dimension. The high precision far-field wave-front fitting is realized by using thealgorithm of Gram-Schmidt.In the visible light, the related factors to the reference spherical wave-front, suchas the pinhole thickness, diameter, roundness, numerical-aperture range and theincident wave-front error, is analyzed in details based in FDTD method. The results areconsistent with the relevant aspects of domestic and foreign research results prove thecorrectness of the simulation model and self-study programs. In deep-ultraviolet light,the related factors to the reference spherical wave-front, such as the pinhole thickness, diameter, roundness, numerical-aperture range, numerical aperture, the incidentwave-front error and polarization, is analyzed in details based in FDTD method. Theresults show that the wavefront error of the spherical wave is about8.4E-4λ RMSwhen the diameter and thickness of the pinhole is200nm. Wavefront error of thediffracted spherical wave increases as the NA of the aberrant illumination beamincreasing. The filtering effect is reduced as the pinhole diameter increasing, and comaof the illumination beam is the most difficult aberration to filter. And the simulationresults provides theoretical basis for the related devices design in the projection lenstesting system.We introduce a new illumination source for Shack-Hartmann wavefront sensorused to measure the wavefront aberration of the projection objective. By using thepinhole array, the brightness and uniformity of the illumination light can besignificantly improved. The results obtained in this paper are the important referencefor determining the illumination parameters in calibration of high accuracy wavefronttesting system, and have important applications for high-precision testing oflithography wavefront aberration of the projection lens system.