Study On CD Uniformity In ArF Immersion Lithography

According to the trend of next generation lithography (NGL) and InternationalTechnology Roadmap for Semiconductors 2005 Edition (ITRS 2005), the ArF immersionlithography is one of the most potential technologies to achieve 65-45 nm criticaldimension (CD) node. The large numerical aperture (NA>1) can be achieved usingimmersion technology. But, under the condition of large NA and low process coefficient,the impacts on CD uniformity, which come from the flare, aberration and polarized light,are becoming more prominent and complex.Focusing on how to control the CD errors, which are caused by flare, aberration andpolarized light, and how to improve the CD uniformity, we start this study with calculatingthe impacts of flare, aberration and polarized light on CD uniformity. Then, wecomprehensively study the impacts of flare, aberration and polarized light on patterns'imaging quality and CD uniformity (such as binary pattern, L-pattern, butting pattern andH-pattern), as well as the mutual impacts of the three factors on CD uniformity usingvector and full physical model. Both of the CD uniformity and process window in ArFimmersion lithography are improved through these methods such as in-situ adjustingexposure dose to compensate CD error, using the characteristics of polarized light toimprove CD uniformity and adopting polarized light, phase shifting mask to reduceaberration sensitivity. The feasibility of these methods is supported by practical data whichwe got in this study. The detailed work and according results which we got through thisresearch are as following:Firstly, We studied the flare's impact on the imaging quality and CD uniformity of criticalfeatures (such as binary pattern, L-pattern, butting pattern and H-pattern) using vector andfull physical model. The CD error is compensated to some extent by properly adjusting theexposure dose, then the full field CD uniformity is improved by appropriatly adjustingexposure dose of every field one by one. After the exposure dose being adjusted, the CDerrors can be controlled within ±1.2%, which means that the CD errors caused by flarehave been assuredly compensated without adding any cost.Secondly, We studied the aberration's impact on imaging quality and CD uniformity ofcritical features (such as binary pattern, L-pattern and butting pattern) using vector and fullphysical model. The impact of aberration on isolated pattern's CD uniformaity is largerthan that on semi-dense pattern's CD uniformity. When alt-PSM (alternate phase shiftingmask) is used, the impact of aberration on overlay error is higher than that on otherlithography performances;while when attenuated PSM (att-PSM) is used, the impact ofaberration on CD error is higher than that on other lithography performances. Therefore,the emphases of CD control are different under different conditions.According to the requirement of lithography performances (such as CD uniformity,overlay, sidewall angle and resist loss), the aberration tolerances for 45 nm CD node areobtained through calculation with saving allowances for other impact factors. The data canbe regarded as important references in designing the tools of next generation ArFimmersion lithography.We also found the impartant relation of the geometrical aberrations' combination and CDuniformity. The good CD uniformity is achieved by optimizing the combination ofgeometrical aberrations.Thirdly, We studied the polarized light's impact on imaging quality and CD uniformity ofcritical features (such as binary pattern, L-pattern and butting pattern) using vector and fullphysical model. According to the rules of CD's variation, the CD uniformity and processwindows are improved with appropriate polarized light. The impacts of flare on processwindow are also reduced by appropriate polarized light. The butting pattern's gap-widtherrors are compensated by adjusting the state of polarized light. These foregoing methodsare supported by practical data which we got in this study.Fourthly, We studied the impact of flare, polarized light and resolution enhancetechnologies (RET) on aberration sensitivity and the interactional impacts of these factorson aberration sensitivity. Accroding to the rules of aberration sensitivity, the methods ofreducing aberration sensitivity have been studied.By optimizing polarization state, adopting appropriate optical parameters and usingatt-PSM, the aberration sensitivities are reduced, which means that the CD errors caused byaberration have been assuredly compensated without adding any cost. These methods aresupported by practical data through our study.According the need of this research, we design the optimize optical parameters program,batch calculate aberration sensitivities program and optimize polarization state program tooptimize the optical parameters, analyse the aberration sensitivities and optimize the settingof polarization state respectively. These programs enrich the function of commerciallithography softwares and play important roles in our study.