Imaging Performance Compensation Strategy And Compensation Technology Of Lithography Lens

Step-and-scan lithography system is the core equipment for ultra large scale integrated circuit,and lithography lens is the key component of the lithography system,its imaging performance such as wavefront aberration,distortion,field curvature,telecentricity,directly determines the critical dimension of the integrated circuit.The lithography lens is one of the most precision and complex optical systems.It has characteristics such as large field,high NA and precision imaging quality,which make it difficulty in design,manufacturing,and assembly period.By using the aberration compensation strategy,the strict tolerances can be reduced and therefore improves its manufacturability and cost-performance.The 193 nm lithography lenses in ASML and Nikon have been industrialized,while China started the relevant research late and thus weak in manufacturing process and lack of relative patents.So,developing high-performance lithography lens independently has important strategic significance.This paper focus on 193 nm,NA0.75 lithography lens to study imaging performance strategy and aberration compensation technology.The main research contents are as follows:1.Study on imaging theory and analyze the imaging performance of lithography lens.The imaging theory and its quality evaluation parameters of lithography lens are studied.Then the design of NA0.75 lithography lens is carried out based on the constraint conditions,such as working environment,laser light source,and optical materials.Results show the wavefront aberration(RMS)is less than 1.2nm;the distortion is less than 3.1nm;the field deviation is less than 16nm;the telecentricity is less than ±1mrad,and the magnification error is less than 0.3ppm,which satisfy the requirements and provide sufficient margin for later manufacturing and assembling periods.2.Study on the compensation strategy of lithography lens.This paper analyzes the influence of various tolerances on the imaging performance during the period of optical redesign,computer-aided adjustment and working condition,and studies the compensation strategies to improve imaging quality.Tolerances of optical re-design period mainly include material and manufacturing errors.Compensators are the air spacers of each optical element,and the compensated wavefront is less than 1.51 nm,and distortion is less than 5.6nm.Tolerances of computer-aided alignment period included alignment and measurement errors.Compensators are the lens X-Y movement,lens axial movement,object and image movements.The compensated wavefront is less than 3.76 nm,and distortion is less than 8.6nm.For thermal aberration under circular illumination,Z5 astigmatic active lens,lens axial movement,object and image movements,and wavelength changing are selected as the compensators,and the final wavefront is better than 5.55 nm,distortion is better than 9.9nm.Results show the compensation strategy has significant effect.3.Research on the lens X-Y compliant mechanism compensation technology.According to the requirements of lens X-Y compensator for NA0.75 lithography lens,the X-Y compliant mechanism based on 1RR-2RRR configuration is studied.And its Jacobian matrix,flexibility matrix,coupled errors are studied.Results show that mechanism X and Y coupling is less than 1%,and can be controlled to less than 7nm using displacement closed-loop;tip/tilt rigid motion is better than 0.22 sec,z-axis rigid motion is better than 50 nm.The mechanism has high precision and small coupling,and can be used as an effective compensator for lithography lens.4.Research on the compensation technology of deformable lens element.For the demand of thermal aberration compensation,a Z5 astigmatism deformable lens element based on axial force is proposed;its operational principle is analyzed.Experimental results show that the Z5 coefficient stroke is more than 600nm;Z5 coefficient accuracy is better than ±1nm;coupled rigid motions z/x/y/tip/tilt are respectively 48.6nm/342.9nm/223.5nm/ 317.5msec/287.5msec.The compensator has the advantages of large stroke,high precision and small coupling errors,and it can satisfy the requirements of lithography lens.A complex active deformable lens based on axial force,radial moment and tangent moment is simulated,results show Zernike term Z4,Z5,Z6,Z7,Z8,Z10,Z11,Z12,Z13,Z17,Z18,Z19,Z20,Z26,Z27,Z28,Z29 deformations can be realized,the compensator can be used for lithography lens complex thermal aberration compensation.