Study On High Precision Measurement Technology Of Wafer Focus Based On Polarization Modulation

Chips-the developing basis of information society.According to Moore's law,it has been developing towards the direction of smaller line size and larger device size.Lithography is the key technology of chip manufacturing,and smaller line size means the improvement of lithography resolution,larger device size means larger lithography exposure field.From the development of lithography technology,the main ways to improve the resolution of lithography are to increase the numerical aperture(NA),reduce the exposure wavelength and reduce the process factor.However,the effective depth of focus of lithography is greatly shortened by increasing the objective NA or shortening the exposure wavelength.Therefore,in modern high-precision projection lithography,focal plane detection and control is one of the key technologies,which is the premise of realizing high precision exposure.In high projection lithography,the focal plane measure and control accuracy needs tens of nanometers.The existing research on focal plane detection only focuses on the accuracy of the detection technology itself,and the research and analysis focuse on the systematic control of the focal plane of lithography are insufficient,;at the same time,the existing focal plane detection technology is mostly based on the image detection of mark or mark array.The detection accuracy is greatly affected by the process conditions,which is not enough to support the high projection lithography technology especially in extreme ultraviolet lithography(EUVL).Based on the above requirements,focusing on the high-precision focal plane detection technology,this paper carried out a systematic research on the focal plane detection and control technology of lithography system.Firstly,the theory of focal plane control in lithography system is analyzed.The relationship between depth of focus and lithography performance and the main methods to improve the depth of focus are systematically researched.Then,aiming at the advanced projection lithography system,the actual optimal focal plane positioning method and main application scenarios are studied.In this paper,a focal plane detection system is designed and simulated by analyzing polarization modulation and the adaptability of EUVL.Under the support of related projects,the focal plane detection system was established,the relevant test environment and test platform were built,and the experimental verification of the focal plane detection system was carried out.Under the EUV environment,the focal plane detection ability of measuring range > 1 mm and detection accuracy is ± 3.9 nm(3?),which met the focal plane detection requirements of 32 nm resolution EUVL.In order to further explore the new technology of focal plane detection,this paper also carried out the research of nano focal plane detection method based on grating shearing interferometry.The advantage of this method is without reference plane,low environmental sensitivity,strong anti-interference ability and high measurement accuracy.A simple experiment system is set-up to verify the feasibility of this method.The measurement procession is 28.1nm(PV)and 9.8nm(RMS).Finally,the application of focal plane detection data in lithography system is studied,and the theoretical model and method of leveling and focusing process are also analyzed.