Research And Verification Of Phase Signal Processing System For The Grating Interferometer

Lithography machine is the core equipment of IC manufacturer.With the development of IC to advanced manufacturing process,the requirement of lithography precision is greatly increased.At present,there are two kinds of tools for positioning and measuring the stage:laser interferometer and grating ruler.The environment robustness of grating ruler is relatively good.At present,the research of grating scale phase signal processing system is relatively scarce in China,especially the high-resolution grating scale phase signal processing technology which can be applied to 28 nm immersion lithography machine.In this paper,the signal preprocessing model based on the biorthogonal phase locked amplification method is established for the first class of nonlinear error,cosine missing term and the influence of laser frequency uncertainty of grating ruler phase signal.The above signal defects are eliminated by DC offset compensation,DDS mixing,FIR filter and phase difference The cosine signal of the moving information is used for phase calculation.At the same time,combined with the specific engineering requirements of 28 nm immersion lithography,the overall design scheme of grating ruler phase signal processing system with resolution of 200 pm and maximum measuring speed of 1.2 m/s is proposed.A new real-time direction judgment design is proposed in this paper,which is used to solve the problem of low update rate of data in the existing grating ruler discrimination method.The scheme combines the symbol position and the change trend of the phase signal of grating ruler.By describing the jump relationship between the direction states by Moore state machine,the updating rate of grating ruler discrimination is increased from 4 times per cycle to 1024 times per cycle.The problem of insensitive direction switching in short range caused by low update rate of traditional directional method data is solved.In this paper,the electrical analog signal calibration method is used to calibrate the system based on the output signal of the signal generator.Firstly,the performance standard and function completeness of each module are tested.The experimental results show that each system module has reached the expected design index.Then the resolution,accuracy and standard deviation of the system are tested respectively.The results show that the resolution of the system can reach 200 pm,the accuracy can reach 82 pm/3 ?,and the standard deviation is 153 pm,the system has no abnormal data in continuous 24 hours,which proves the reliability and stability of the system performance.