Research On Heterodyne Grating Interferometer With Low Periodic Nonlinear Error

Ultra-precision laser measurement technology is an indispensable basic technology for the development of cutting-edge microelectronics manufacturing equipment,and has an important supporting role for advanced manufacturing and high-end equipment.Compared with laser interferometry technology,grating interferometry technology has the advantages of high stability and convenient multi-degree-of-freedom(Do F)measurement.However,there are still problems such as excessive periodic nonlinear error and too small angular tolerance,which need to be solved to meet the urgent need for ultra-precision measurement proposed by the development of high-end equipment such as domestic lithography machine.This article "Research on heterodyne grating interferometer with low periodic nonlinear error" carries out a series of studies on the problems such as nano-scale periodic nonlinear errors,small angular tolerance and the lack of multi-Do F decoupling methods in the existing heterodyne grating interferometry systems.(1)Aiming at the problem of nanoscale optical period nonlinear errors in the common optical path heterodyne grating interference system,a heterodyne grating interference displacement measurement method based on non-co-optical path is proposed.Firstly,by analyzing each part in the common optical path heterodyne grating interference system,the nonlinear error model is established.After theoretical analysis and simulation research,it is proved that the main reason for the nonlinear error of the optical period is the optical aliasing caused by unideal factor of the measurement system.The resulting optical aliasing can produce a displacement error of up to ten nanometers.On this basis,a non-common optical path is used to build a grating interference system,so that the laser beams of the two frequencies of the heterodyne laser propagate separately before the final interference,which in principle avoids the optical aliasing and effectively supress periodic nonlinear errors.Experimental verification shows that the non-common optical path heterodyne grating interference displacement meas urement system based on this method reduces the periodic nonlinear error from 0.72 nm of the traditional common optical path to 0.17 nm,which greatly reduces the periodic nonlinear error of the system.(2)Aiming at the problem that the existing heterodyne grating interference displacement measurement system has small angular tolerance and cannot meet the measurement requirements of multi-Do F,a non-co-optical heterodyne grating interference measurement method with high angular tolerance is proposed.To solve the problem that the measurement system fails due to the mismatch of beam parallelism caused by the accompanying angular displacement of the measured target in linear displacement measurement,this method designs a second-order diffraction interference optical path with parallel reentry characteristics,which effectively increases the angular tolerance of the measurement system.And using the diffraction characteristics of the plane grating,a two-Do F high angular tolerance method of heterodyne grating interference displacement measurement method applied to non-common optical path is proposed.After experimental verification,the wide-angle adaptive non-common optical path heterodyne grating interference displacement measurement system proposed in this article increases the roll,yaw,and pitch tolerance angles to ±5.5 mrad,±2.2 mrad,and ±1.4 mrad,respectively.It can withstand an offset of ±0.6 mm in vertical direction.And two-Do F in-plane synchronous measurement without coupling can be realized.(3)Aiming at the problem that the installation error of the grating probe in the3-Do F grating interferometric measurement method seriously restricts the accuracy of angular displacement calculation,a self-compensation method for the installation error of the 3-Do F measurement system based on redundant measurement is proposed.This method converts the probe spacing from the design value to the value to be solved by introducing the redundant number of measurement axes,and in principle reduces the influence of the probe installation error in the angle measurement.The simulation experiments show that the proposed redundant measurement correction method reduces the angular displacement calculation error by two orders of magnitude compared with the uncompensated.In summary,this article successfully suppresses the periodic nonlinear error in the traditional co-optical path heterodyne grating interferometry in principle,improves the angular tolerance range of the system,and reduces the angular displacement measurement decoupling error caused by the inaccuracy of machine constants in the multi-Do F measurement.The above content provides the method basis and key technology for the next generation of ultra-high-precision multi-Do F grating interferometry,and has important potential application value in the manufacture of high-end equipment such as domestic advanced lithography machines.