Research On Synchronous Phase-shift Microscopic Interferometric Focusing Technology In Laser Direct Writing System

With the continuous improvement of the manufacturing requirements of micro-optical devices and micro electro mechanical systems,there are very high requirements for the writing accuracy and lithography resolution of the laser direct writing technology.It is effective to reduce the direct writing wavelength and increase the numerical aperture of the direct writing objective.The focal depth range of the direct writing objective lens is also becoming smaller.It makes it more difficult to focus the direct beam accurately on the surface of the element.It puts forward an urgent need for high-precision focus detection technology in the laser direct writing system.The current inspection focus technology is mainly for direct writing objectives with small and medium numerical apertures,and the accuracy of defocus detection is low.At present,there is no ideal solution for the aberration correction of the composite objective lens at the working wavelength of the inspection focus and the direct writing wavelength.In this thesis,a synchronous phase shift microscopic interference focal detection technique was proposed.A pair of objective lenses with the same NA and a plane reference mirror placed at the focal point of the reference arm objective were used to form a Linnik-type microscopic interference system.The color focus shift of the objective lens was eliminated and compensated for the constant focus error caused by the difference between the direct writing wavelength and the focus wavelength.The advantages of high wave aberration detection sensitivity and the strength of synchronous phase shift technology in real-time were integrated.The aberration information of the interference wave containing defocus was obtained from the four synchronous phase shift interferogram.Then the magnitude and direction of defocus were both analyzed from the aberration data of objective lens with large numerical aperture(NA).High precision and real-time focal plane detection could be achieved.In this thesis,the theoretical analysis,the establishment of experimental equipment simulation verification,experiment verification and error analysis were implemented.When NA=0.5,the sensitivity of the system to defocus detection could be up to 8 nm and the accuracy of focusing could be better than 10 nm within the effective focal depth range.The resolution and focal accuracy requirements of the laser direct writing equipment had been met.This system was verified to have high precision and real-time focusing ability.It was proved that this method can be used in laser direct writing.