Research On Resolution Enhancement Technology And The Vector Imaging Theory In Optical Lithography

Currently, the Argon Fluoride (ArF) immersion lithography has been developed as themain technique for very large scale integrated circuit (VISL) fabrication. As the shrink ofcritical dimension (CD) on VISL, the demands for the precisions of imaging model inlithography simulation, in situ aberration measurement and the resolution enhancementtechnology are higher than ever before, especially in45nm node and beyond. However, thepresent status of these three aspects cannot meet the requirements of immersion lithographywith hyper numerical aperture (NA>1) projector. With the purpose of solving theseproblems, the contents of this dissertation include four parts:(1) Research on the vector imaging theory of lithography. A rigorous vector imagingmodel is established in this dissertation. The vector effects through the lithography systemswere considered in this model, including the vector incident electric fields, the vectordiffraction of2D thin mask or3D thick mask, the polarization (vector) aberration ofprojector and the vector interference of3D electric fields on the image plane of lithographysystem. Moreover, the telecentric error of projector was incorporated by establishing newpupil function and3D polarization aberration function. Comparing with current vectorimaging model, the proposed model can be more accurate to analysis the polarized imagingperformance of practical lithography system. The simulation results show that the proposedtheory was same as that in commercial software for the lithography system with doubletelecentric projector. However, the impact of the telecentric error on the lithographyimaging performance cannot be analyzed by commercial software. These demonstrated thatthe current vector imaging theory was embedded and extended by the proposed theory, andthe accuracy of lithography simulation was improved.(2) Research on the main factors impact on the performance of lithography imaging.By using the vector imaging theory proposed in this dissertation, the main factors impactson the lithography imaging performance were firstly analyzed systematically, and theregulars were summarized. The main factors included the aberration of projector, the errorsof numerical aperture and partially coherent factor. The results show that: odd aberrationand odd retardation would cause the pattern displacement on the nominal and defocus plane,even aberration and even retardation would cause best focus shift and CD error, oddapodization and odd diattenuation merely caused the pattern placement on the defocus plane, while the even apodization and even diattenuation mainly caused the CD error on thenominal focus plane. On the other hand, the errors of numerical aperture and partiallycoherent factor would influence the performance of lithography imaging with the followingregular. Under the situation that the1storder pupil was intersect with the―effective source‖,the CD error caused by positive value of NA error was smaller than that of negative NAerror, while the CD errors caused by positive and negative coherent factor error were nearlyequal.(3) Research on the vector imaging sensing technique. As currently aerial image basedin situ aberration measurement technique were derived from the scalar imaging theory,which were not applicable to immersion lithography. By using the vector imaging theory inthis dissertation, the vector imaging sensitivity technique for the wavefront aberration insitu measurement was firstly proposed. The simulation results show that the maximalretrieval error of our proposed method is below0.5m, while that of the method based onthe scalar imaging theory is about4at NA of1.35. On the other hand, the vectorimaging sensing technique for the polarization aberration in situ measurement was alsoproposed based on the vector imaging theory. The results demonstrated that the proposedtechnique could retrieve all the information of polarization aberration quickly andaccurately. Moreover, the cost of polarization aberration in situ measurement was reducedby choosing common masks as the test marks.(4) Research on the vector resolution enhancement technique. By using the vectorimaging theory proposed in this dissertation, the vector OPC and vector SMO wereestablished for the lithography system with polarization aberration. The simulation resultsshow that the OPC and SMO based on scalar imaging theory were not accurate for thepattern in45nm node and beyond, the results acquired from vector OPC and vector SMOcould satisfy the requirements of immersion lithography much better. In addition, for thelithography system with polarization aberration, the deteriorated effects of imagingperformance could be compensated by controlling the asymmetry of the pattern on mask.