【作者】 芮大为；

【导师】 杨怀江；

【作者基本信息】 中国科学院大学(中国科学院长春光学精密机械与物理研究所) ， 光学工程， 2022， 博士

【摘要】 作为超大规模集成电路的核心制造装备,光刻机长期以来都是中国半导体产业的一块短板。近年来,在国家的大力支持和科技工作者的不懈努力下,虽然取得了一些阶段性成就,但相对于国外科技巨头长达数十年的技术积累,差距依然巨大。因此,基础科研攻关就成为光刻机研发领域不可逾越的一道坎。照明系统作为光刻机的重要组成部分,其性能优劣直接决定芯片的制造水平。与投影物镜相比,照明系统无论在设计难度还是制造公差方面都具备很大优势,但在功能模块的种类和数量上、在学科应用的深度和广度上却有着更高的要求。按照这一认知,本文在方案设计与补偿策略两个层面,对光刻照明系统开展了基础研究工作,技术路线涵盖i线与ArFi。设计层面包括建立指标体系和生成设计方案;补偿策略层面,通过理解与掌握关键技术,实现性能指标的提升。指标体系的准确建立是良好设计的前提和保障。由于曝光系统设计并非成熟学科,缺少现成经验可循,需要在需求层面加深理解,将调研成果转化为具体的设计指标。首先,依据物理光学相关原理,面向光刻应用,对关键技术指标进行了原理层面的分析论证和量化推导,为设计工作的开展奠定了理论基础。在曝光视场能量分布方面,针对刻线质量,提出了照度均匀性需求;瞳分布方面,提出了单视场的周向分布对称性与整场一致性需求;面向套刻,提出远心度匹配需求。此外,对照明指标量化与解耦等方面也提出了见解。一个合格的设计者应充分考虑如何在各个层面上实现均衡优化。相应地,一个优秀的设计方案需要做出各种折衷和妥协,避免冗余,将优化变量的有限自由度发挥到极致。对标具体设计指标,阐述了设计方法,识别出关键技术。对光瞳角谱离散性的成因也进行了溯源,基于积分器的工作原理,量化了离散性并提出了改善措施,以实验数据验证了改善效果。光瞳能量分布对称性对曝光分辨率和对准过程有着极其重大影响,是照明设计需要优先确保的指标,相应的设计方法涵盖像差分解以及远心度匹配。在照明像差控制方面也进行了思考:照明系统像差矫正到何种程度完全取决于曝光需求,并非越高越好。冗余设计不仅增加设计与制造成本,还会降低系统透过率。因此对像质不必苛求,应以等晕照明为前提,确保设计结果具备高度的整场一致性与远心度匹配水平。公差分析也是光学设计重要的一环,对应提出明确的公差分析策略,为设计收敛提供重要保障。在仿真工具的使用和数据处理方法上,也提出了一些见解。数据处理过程可以窥见整个照明仿真分析工作的严谨性,需要仔细斟酌。在规则、定义、概念方面不得含糊。不同于设计工作取舍的灵活性,仿真分析工作本身更像是一把衡量别人的尺子,重在自身的准确性。只有把“刻度”找准,才能评价他人,才能具备长远的价值。i线光刻技术在当前依然拥有广阔的市场和成长空间,从自主研发的战略需求出发则更显重要,值得在设计层面深耕。随着非球面透镜制造技术的日益发展,i线光学结构可极大精简,实现轻量化,从而提升整个曝光系统的光效和产率。首先进行了指标分解,详细讨论了子模块设计概念和关键技术,提出了一种侧重于远心匹配的设计方案,并以照明仿真仿真对该方案进行了评价。结果表明,掩模面的匹配误差优于-1.44 mrad,硅片面的合成远心度优于4 mrad。满足需求,符合预期。ArFi处于DUV曝光领域的最前沿,在各种分辨率增强技术的联合加持下,其应用极限可拓展到7nm制程。相应地,照明系统的需求和设计难度都极大地提升了,主要体现在严格的照明指标、灵活的照明模式切换以及强大的补偿能力上。研究内容侧重于浸没系统严格指标下的指标分解和解决策略:如远心匹配传递、面向微透镜阵列的场分布补偿等等。阐述了功能原理和设计方法,分解了各功能模块的设计指标、完成了方案设计及公差分析,并通过光线追迹详尽评估了系统级指标的满足度。提升了ArFi系统设计与评价能力,积累了经验。光刻照明中,各种功能模块的量化控制以及照明指标补偿方面的研究,相对于光路设计更为复杂。重点论述了离轴光瞳的形貌筛选与变焦控制方法、以及光瞳均匀性补偿策略。离轴控制方面,通过LightTools宏语言编写及matlab外部调用,以穷举法获得所有可能的光瞳形貌及其变焦位置信息,然后筛选并重构数据库,剔除无用变焦组合,建立起明确的变焦-驱动关系。光瞳补偿方面,建立了补偿目标参数化模型,以约束条件优化解的方式求解超定方程组,获得补偿器的最小化行程,理论计算和仿真结果符合度较高。更多还原

【Abstract】 As the core fabricating equipment of ultra-large-scale integrated circuits(VLSIC),lithographic exposure tools have long been the fatal flaw in China’s semiconductor industry.Recent years,with the strong support by central government and the unremitting efforts of researchers,some milestones are achieved.However,there is still a huge gap compared with those foreign giants whose lithographic technologies accumulated for decades.Therefore,basal research has still been an insurmountable hurdle in front of China’s lithography development.As an important part of lithography tools,the illuminator impacts significantly on chip manufacturing.Compared with projection objectives,the illumination system has great advantages in terms of design difficulties and manufacturing tolerances,but it strongly demands more complicated modules and higher level of discipline applications.In this paper,basal research on illuminator design and compensation is proposed,and the technical routes for both i-line and ArFi type are given in detail.The design work aims for performance specification and the specific light path,and the compensation targets for performance improvement through understanding and mastering key technologies.A solid establishment of the design target is the premise and guarantee of an excellent design.Since lens design for exposure system is lack of ready-made experience,it is necessary to deepen the understanding of design target and then convert the research results into specific target data.First,based on the relevant principles of physical optics,the key targets of lens design are analyzed and demonstrated at the level of principle deduction,which put the design work to a more theoretical level.To meet the CDU requirements,uniformity of field energy distribution is recommended.To meet the balanced exposing requirements,pupil uniformity and consistency are recommended.To meet the overlay requirements,telecentrisity in a certain matching level is recommended.In addition,the insights of the quantification and decoupling of the above illumination design targets are also presented,too.A qualified designer should fully consider how to achieve balanced optimization at all levels.Accordingly,an excellent design solution has to make various tradeoffs and compromises,avoid redundancy,and maximize the degrees of freedom of optimization variables under a series of constraints.To fully meet the above design target,the design method is proposed,and the key technologies are identified.The root cause of pupil map discreteness is illustrated,and a series of compensation proposed based on the analysis of rod and lenslet integrator,with some verification through an experiment.The pupil energy imbalance has an extremely significant impact on exposure resolution and wafer alignment,which should be considered as a priority in lens design,corresponding to lens aberration decomposition and telecentric matching.Considerations have also been made about aberration control.The level of illumination aberration correction depends entirely on the exposure requirements,rather than “the higher the better”,because of the fact that,the redundant design not only increases design and manufacturing costs,but also reduces system transmittance.Therefore,don’t be too mean to illuminator’s aberration,just make sure of the high level of telecentrisity and consistency across the entire exposure field.Besides,tolerance analysis is an important part of optical design,and a clear tolerance requirement should be listed to provide a solid guarantee for the rest of design work.Some suggestions are also presented on the use of simulation tools and data processing methods.The data process exhibits the rigor of the entire quality of analysis work,which deserves great patience.There should be no ambiguity in the understanding of rules,definitions and concepts.Different from the flexible of design work,the simulation analysis work itself is more like a ruler to measure others,focusing on its own accuracy.Only by calibrating its own "scale" can it precisely measure others,which makes a durable value.At present,i-line lithography technology still has a prosperity and market share.Moreover,with a strong strategic significance in independent research and development,i-line illumination is worthy of deep cultivation in lens design.With the increasing development of aspheric lens manufacturing,i-line optical structure can be greatly simplified and lightweight,thereby improving the transmittance and productivity of the entire exposure system.In this paper,the design target is specifically decomposed,the sub-module design concept and key technology are discussed in detail,and then a lens design solution focusing on telecentric matching is proposed.After the ray tracing simulation,the results show that the matching error at reticle level is better than 1.44 mrad,and the synthetic telecentricity at wafer level is better than 4mrad,which fully meets the requirement,and meets our expectations,too.ArFi lays on the forefront of DUV exposing technology.With the joint efforts of various resolution enhancement technologies(RETs),its application limit can even reach the 7nm process.Accordingly,the requirements and design difficulties have also been greatly improved,mainly on the stricter targets,the more flexible illumination mode transformation and more complicated compensation ability.The research content focuses on the decomposition and solution strategies under the strict requirements,such as telecentric matching,field distribution compensation after lenslet array,etc.The specific design method are expounded with the decomposition of design target on sub modules,then the lens design and its tolerance analysis are completed,with the detailed evaluation through ray tracing simulation.All of which improves the ArFi system design and analysis capabilities.In lithographic illumination,the research of mathematic control and exposure compensation on various sub modules are more complicated than the optical design.The sifting method on pupil shape with its corresponding zoom status for off-axis control is fully studied,and the compensation strategy for pupil uniformity is discussed,too.For off-axis control,by using LightTools macro programming and external execution of Matlab,all possible pupil shapes and their zoom position information are obtained through exhaustive method,and then the database is filtered and reconstructed by erasing useless zoom status,and then a clear zoom-drive connection are established.For pupil compensation,a parametric model of the compensation target is rebuilt,and the overdetermined equation is solved in a way of constrained optimization solution,then a series of the minimum stroke of the compensator are obtained.Besides,the theoretical calculations are in good agreement of simulation results.更多还原