CN102681357B

CN102681357B - Design method for extreme ultraviolet photoetching projection lens

Info

Publication number: CN102681357B
Application number: CN201210097574.6A
Authority: CN
Inventors: 李艳秋; 刘菲
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2012-04-01
Filing date: 2012-04-01
Publication date: 2014-02-05
Anticipated expiration: 2032-04-01
Also published as: CN102681357A

Abstract

The invention provides a design method of an extreme ultraviolet lithography projection objective lens. The specific steps are: determining that the projection objective lens in the lithography system has a six-mirror structure, and setting the optical system parameters of the projection objective lens; selecting six reflector mirrors and a diaphragm Set between the mask and the silicon wafer in the photolithography system, determine the ratio parameters between the mirrors; according to the given object-side numerical aperture and the incident angle of the object-side chief ray, calculate the ratio of the second mirror (M2) and The space where the light emitted by the first reflector (M1) is not blocked and/or the incident angle of the chief ray of the first reflector, and judge whether the set optical system parameters are reasonable according to the calculated parameters, and finally complete the lithography projection objective lens the design of. The invention can design and search according to different user requirements, avoiding the blindness of modification and trial and error in the existing structure by the traditional optical design method.

Description

A design method of projection objective lens for extreme ultraviolet lithography

技术领域 technical field

本发明涉及一种极紫外光刻投影物镜设计方法，属于光学设计技术领域。The invention relates to a design method of an extreme ultraviolet lithography projection objective lens, belonging to the technical field of optical design.

背景技术 Background technique

在超大规模集成电路的制造工艺中，需要使用高精度投影物镜将掩膜上的图形精确倍缩到覆盖有光刻胶的硅片上。当前深紫外光刻技术使用波长为193nm的激光光源，辅助以离轴照明、相移掩膜、光学边缘效应校正等分辨率增强技术，可实现45nm技术节点的产业化要求，但是对于32nm或更高技术节点的产业化需求，半导体行业普遍寄希望于极紫外光刻技术。极紫外光源波长约为11~15nm，与深紫外光刻技术相同，极紫外光刻也采用步进-扫描模式。In the VLSI manufacturing process, it is necessary to use a high-precision projection objective lens to accurately scale the pattern on the mask to the silicon wafer covered with photoresist. The current deep ultraviolet lithography technology uses a laser light source with a wavelength of 193nm, assisted by off-axis illumination, phase shift mask, optical edge effect correction and other resolution enhancement technologies, which can meet the industrialization requirements of the 45nm technology node, but for 32nm or more To meet the industrialization needs of high-tech nodes, the semiconductor industry generally places its hopes on extreme ultraviolet lithography technology. The wavelength of the extreme ultraviolet light source is about 11~15nm, which is the same as the deep ultraviolet lithography technology, and the extreme ultraviolet lithography also adopts the step-scan mode.

极紫外光刻系统由等离子光源，反射式照明系统，反射式掩膜，反射式投影物镜，涂覆有极紫外光刻胶的硅片以及同步工件台等部分组成。光束由光源出射后，经照明系统整形和匀光，照射到反射式掩膜上。经掩膜反射后，光线入射至投影物镜系统，最终在涂覆有极紫外光刻胶的硅片上曝光成像。The extreme ultraviolet lithography system consists of a plasma light source, a reflective lighting system, a reflective mask, a reflective projection objective lens, a silicon wafer coated with extreme ultraviolet photoresist, and a synchronous workpiece table. After the light beam emerges from the light source, it is shaped and homogenized by the lighting system, and then irradiates on the reflective mask. After being reflected by the mask, the light enters the projection objective lens system, and finally exposes the image on the silicon wafer coated with extreme ultraviolet photoresist.

典型的EUV投影物镜为共轴光学系统，物面、像面及所有反射镜均关于光轴旋转对称，这一设计有利于装调并且尽量避免了可能的像差。由于反射系统中存在光路折叠和遮挡，投影物镜应采用环形离轴视场设计。一般来说，除给定的设计指标外，EUV投影物镜设计还需要满足下列要求：1.可实现的光阑面设置，一般位于第2～5个反射面的某一面上；2.足够大的物方、像方工作距，保证掩膜和硅片的轴向安装空间；3.无遮拦设计，每个反射面的反射区域和通光区域之间都要留有一定的边缘余量；4.能够配合反射式掩膜使用，光线以小角度入射到掩膜上；5.高分辨率；6.极小的畸变；7.像方远心。A typical EUV projection objective lens is a coaxial optical system. The object plane, image plane and all mirrors are rotationally symmetrical about the optical axis. This design facilitates installation and avoids possible aberrations as much as possible. Due to optical path folding and occlusion in the reflective system, the projection objective should be designed with a circular off-axis field of view. Generally speaking, in addition to the given design indicators, the EUV projection objective lens design also needs to meet the following requirements: 1. Realizable diaphragm surface setting, generally located on one of the 2nd to 5th reflective surfaces; 2. Large enough The working distance of the object space and image space ensures the axial installation space of the mask and the silicon wafer; 3. Unobstructed design, there must be a certain margin between the reflection area and the light transmission area of each reflection surface; 4. It can be used with reflective masks, and the light is incident on the mask at a small angle; 5. High resolution; 6. Minimal distortion; 7. Telecentric image.

现有技术（M.F.Bal,Next-Generation Extreme Ultraviolet Lithographic ProjectionSystems[D],Delft:Technique University Delft,2003）公开了极紫外光刻投影物镜设计方法，该方法通过对EUVL投影物镜的近轴结构参数（反射镜半径、各光学面间距等）进行穷举式搜索，将系统的放大倍率、光阑共轭关系等条件作为约束，并编制程序对其光线光路进行光路遮挡判定，将无遮挡的光路进行分析拣选，从而选出合适的初始结构，作为进一步优化和计算的基础。这一方法的缺点在于：计算量过大，以现有的计算机计算速度，平均一星期才能找到一个可用设计。The prior art (M.F.Bal, Next-Generation Extreme Ultraviolet Lithographic ProjectionSystems[D], Delft: Technique University Delft, 2003) discloses a design method of extreme ultraviolet lithography projection objective lens. reflector radius, the distance between each optical surface, etc.) to carry out an exhaustive search, taking the magnification of the system, the conjugate relationship of the diaphragm and other conditions as constraints, and programming the optical path occlusion judgment of its light path, and the unoccluded optical path Analytical sorting to select a suitable initial structure as the basis for further optimization and calculations. The disadvantage of this method is that the amount of calculation is too large, and with the existing computer calculation speed, it takes an average of one week to find a usable design.

发明内容 Contents of the invention

本发明提供一种极紫外光刻投影物镜设计方法，该方法可根据不同的参数要求设计出极紫外光刻投影物镜，其计算量小，实现速度快。The invention provides a method for designing an extreme ultraviolet lithography projection objective lens. The method can design an extreme ultraviolet lithography projection objective lens according to different parameter requirements, and the calculation amount is small and the realization speed is fast.

实现本发明的技术方案如下：Realize the technical scheme of the present invention as follows:

一种极紫外光刻投影物镜的设计方法，具体步骤为：A method for designing an extreme ultraviolet lithography projection objective lens, the specific steps are:

步骤101、确定光刻系统中投影物镜为六反射镜结构，并设定该投影物镜的光学系统参数；选取六枚反射镜和光阑设置于光刻系统中掩膜和硅片之间，六枚反射镜及光阑的设置位置：从掩膜开始沿光路方向依次为第一反射镜M1、光阑、第二反射镜M2、第三反射镜M3、第四反射镜M4、第五反射镜M5以及第六反射镜M6，且光阑放置于第二反射镜M2上；确定各反射镜之间的比例参数；Step 101, determine that the projection objective lens in the lithography system has a six-mirror structure, and set the optical system parameters of the projection objective lens; select six reflectors and apertures to be arranged between the mask and the silicon wafer in the lithography system, and six The setting positions of mirrors and diaphragms: starting from the mask along the optical path, they are the first mirror M1, the diaphragm, the second mirror M2, the third mirror M3, the fourth mirror M4, and the fifth mirror M5 And the sixth reflector M6, and the aperture is placed on the second reflector M2; determine the ratio parameter between each reflector;

步骤102、计算掩膜到第一反射镜M1的距离为-l₁和第二反射镜M2到第一反射镜M1的距离为-d₁，并获取第一反射镜M1的当前半径为r₁；Step 102, calculate the distance from the mask to the first mirror M1 as -l ₁ and the distance from the second mirror M2 to the first mirror M1 as -d ₁ , and obtain the current radius of the first mirror M1 as r ₁ ;

步骤103、给定物方数值孔径NAO和物方主光线入射角度CA，根据所述-d₁和r₁，判断出步骤101中给定的光学系统参数是否合理，具体的判断过程为：Step 103, given the object-space numerical aperture NAO and the object-space chief ray incident angle CA, according to the -d ₁ and r ₁ , judge whether the optical system parameters given in step 101 are reasonable, and the specific judgment process is as follows:

步骤201、计算所述比例参数中第二反射镜M2到第一反射镜M1距离与掩膜到第一反射镜M1距离之比radio₂的上限值Uradio₂；Step 201, calculating the upper limit value Uradio ₂ of the ratio radio 2 of the distance from the second mirror M2 to the first mirror M1 and the distance from _the mask to the first mirror M1 in the ratio parameter;

Uradio₂＝1-FWDI·radio₁/YOBUradio ₂ = 1-FWDI·radio ₁ /YOB

其中，FWDI为投影物镜最小工作距，YOB为物方视场高度，radio₁为物方视场高度与掩膜到第一反射镜M1距离的比例参数；Among them, FWDI is the minimum working distance of the projection objective lens, YOB is the height of the field of view on the object side, and radio ₁ is the ratio parameter between the height of the field of view on the object side and the distance from the mask to the first mirror M1;

步骤202、给定物方数值孔径NAO和物方主光线入射角度CA，设定radio₂的搜索步长为ξ_r2，设定循环次数k＝1，radio₂(1)=0，radio₂的下限值Dradio₂=0；Step 202, given the object-space numerical aperture NAO and the object-space chief ray incident angle CA, set the search step size of radio ₂ to ξ _r2 , set the number of cycles k=1, radio ₂ (1)=0, radio ₂ ’s Lower limit Dradio ₂ =0;

步骤203、判断radio₂(k)是否小于Uradio₂，若是，则进入步骤204，否则进入步骤209；Step 203, judge whether radio ₂ (k) is less than Uradio ₂ , if so, then enter step 204, otherwise enter step 209;

步骤204、根据所述-d₁和r₁，根据光线追踪原理，计算出利用radio₂(k)所设计的投影系统的CLEAPE2(k)和/或CA₁(k)，其中CLEAPE2(k)表示第二反射镜M2与第一反射镜M1出射的光线不发生遮挡的空间，CA₁(k)表示第一反射镜M1主光线入射角度；Step 204: Calculate CLEAPE2(k) and/or CA ₁ (k) of the projection system designed using radio ₂ (k) according to the -d ₁ and r ₁ , according to the principle of ray tracing, where CLEAPE2(k) Indicates the space where the rays emitted by the second reflector M2 and the first reflector M1 are not blocked, and CA ₁ (k) represents the incident angle of the chief ray of the first reflector M1;

步骤205、对步骤204计算出参数的类型进行判断，当仅计算出CLEAPE2(k)时，则进入步骤206，当仅计算出CA₁(k)时，则进入步骤207，当同时计算出CLEAPE2(k)和CA₁(k)时，则进入步骤208；Step 205, judge the type of parameter calculated in step 204, when only CLEAPE2(k) is calculated, then enter step 206, when only CA ₁ (k) is calculated, then enter step 207, when simultaneously calculate CLEAPE2 (k) and CA ₁ (k), then enter step 208;

步骤206、判断CLEAPE2(k)＞0是否成立，若是，则将此时radio₂(k)确定为radio₂的下限值Dradio₂，即令Dradio₂＝radio₂(k)，进入步骤209，否则令k＝k+1，令radio₂(k)＝radio₂(k-1)+ξ_r2，返回步骤203；Step 206, judge whether CLEAPE2(k)>0 is set up, if so, radio ₂ (k) is then determined as the lower limit value Dradio ₂ of radio ₂ at this moment, promptly makes Dradio ₂ =radio ₂ (k), enters step 209, otherwise Make k=k+1, make radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , return to step 203;

步骤207、判断CA₁(k)＜MAXCA1是否成立，若是，则将此时radio₂(k)确定为radio₂的下限值Dradio₂，即令Dradio₂＝radio₂(k)，进入步骤209，其中MAXCA1为事先给定的第一反射镜最大主光线入射角，否则令k＝k+1，令

返回步骤203；Step 207, judging whether CA ₁ (k)＜MAXCA1 is established, if so, radio ₂ (k) is then determined as the lower limit value Dradio ₂ of radio ₂ at this moment, promptly makes Dradio ₂ =radio ₂ (k), enters step 209, Among them, MAXCA1 is the maximum chief ray incident angle of the first reflector given in advance, otherwise let k=k+1, make

Return to step 203;

步骤208、判断CA₁(k)＜MAXCA1与CLEAPE2(k)＞0是否皆成立，若是，则将此时的radio₂(k)确定为radio₂的下限值Dradio₂，即令Dradio₂＝radio₂(k)，进入步骤209，否则令k＝k+1，令radio₂(k)＝radio₂(k-1)+ξ_r2，返回步骤203；Step 208, judging whether CA ₁ (k)<MAXCA1 and CLEAPE2(k)>0 are all established, if so, then determine radio ₂ (k) at this time as the lower limit value Dradio ₂ of radio ₂ , that is, make Dradio ₂ =radio ₂ (k), enter step 209, otherwise let k=k+1, make radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , return to step 203;

步骤209、判断Dradio₂=0是否成立，若是，则判定所给定的投影物镜的光学系统参数不合理，不存在第二反射镜M2到第一反射镜M1距离与掩膜到第一反射镜M1距离的比例参数radio₂，并结束，若否，输出Dradio₂并进入步骤104；Step 209, judging whether Dradio ₂ =0 is established, if so, judging that the given optical system parameters of the projection objective lens are unreasonable, and there is no distance from the second mirror M2 to the first mirror M1 and the distance from the mask to the first mirror The ratio parameter radio ₂ of M1 distance, and end, if not, output Dradio ₂ and enter step 104;

步骤104、根据所述第二反射镜M2到第一反射镜M1的距离-d₁，计算第二反射镜M2的半径为r₂；Step 104, according to the distance -d ₁ from the second mirror M2 to the first mirror M1, calculate the radius of the second mirror M2 as r ₂ ;

步骤105、计算出第五反射镜M5到第六反射镜M6之间的间距为d₅，以及根据所述d₅获取第五反射镜M5的半径r₅和第六反射镜M6的半径r₆；Step 105, calculate the distance between the fifth mirror M5 and the sixth mirror M6 as d ₅ , and obtain the radius r ₅ of the fifth mirror M5 and the radius r ₆ of the sixth mirror M6 according to the d ₅ ;

步骤106、选取第三反射镜M3的半径r₃，根据物象共轭关系、放大倍率关系、匹兹万和条件以及光瞳共轭关系，并利用上述确定的第一反射镜M1、第二反射镜M2、第五反射镜M5以及第六反射镜M6的半径以及相互之间的距离，利用近轴迭代算法获取第四反射镜M4的半径r₄、第三反射镜M3与第四反射镜M4的间距d₃、第三反射镜M3与第二反射镜之间的距离d₂、以及第四反射镜M4的像距l′₄；Step 106: Select the radius r ₃ of the third mirror M3, according to the object-image conjugate relationship, magnification relationship, Petzwan sum condition and pupil conjugate relationship, and use the first mirror M1 and the second reflection The radii of the mirror M2, the fifth mirror M5, and the sixth mirror M6 and the distances between them, using the paraxial iterative algorithm to obtain the radius r ₄ of the fourth mirror M4, the third mirror M3 and the fourth mirror M4 The distance d ₃ between the third reflector M3 and the second reflector d ₂ , and the image distance l′ ₄ of the fourth reflector M4;

步骤107、根据上述步骤计算的6枚反射镜的半径以及相应的位置关系，得到极紫外光刻投影物镜。Step 107 , according to the radii and corresponding positional relationships of the six mirrors calculated in the above steps, the EUV lithography projection objective lens is obtained.

进一步地，当判定Dradio₂=0不成立时，本发明在radio₁可取范围内对其进行更新，利用更新后的radio₁重复步骤201-209，获取Dradio₂，进而判断出步骤101给定的光学系统参数是否合理。该判断的具体过程为：Further, when it is determined that Dradio ₂ =0 is not established, the present invention updates radio ₁ within the acceptable range, uses the updated radio ₁ to repeat steps 201-209 to obtain Dradio ₂ , and then determines the optical value given in step 101 Whether the system parameters are reasonable. The specific process of the judgment is as follows:

步骤301、设定radio₁的搜索步长为ξ_r1，设定循环次数k′＝1，radio₁(1)=YOB/TTL，设定N为大于(YOB/FWDI-YOB/TTL)/ξ_r1的最小整数，令radio₁的上限Uradio₁＝YOB/TTL+(N-1)×ξ_r1，令radio₁的下限Dradio₁＝YOB/TTL+(N-1)×ξ_r1，其中YOB为投影光刻物镜的物方视场高度，TTL为投影光刻物镜总长度，FWDI为投影光刻物镜的最小前工作距；Step 301, set the search step size of radio ₁ to ξ _r1 , set the number of cycles k'=1, radio ₁ (1)=YOB/TTL, and set N to be greater than (YOB/FWDI-YOB/TTL)/ξ The smallest integer of _r1 , let the upper limit of radio ₁ Uradio ₁ =YOB/TTL+(N-1)×ξ _r1 , let the lower limit of radio ₁ Dradio ₁ =YOB/TTL+(N-1)×ξ _r1 , where YOB is the projection light The height of the object field of view of the engraving objective, TTL is the total length of the projection lithography objective, and FWDI is the minimum front working distance of the projection lithography objective;

步骤302、判断循环次数k′＞N是否成立，若是，则进入步骤306，否则令k′＝k′+1，令radio₁(k′)＝radio₁(k′-1)+ξ_r1，并进入步骤303；Step 302, determine whether the number of cycles k'>N is established, if so, then enter step 306, otherwise let k'=k'+1, make radio ₁ (k')=radio ₁ (k'-1)+ξ _r1 , And go to step 303;

步骤303、更新投影系统中的参数radio₁为radio₁(k′)，重复步骤201至209，判断Dradio₂＝0是否成立，若是则返回步骤302，否则令Dradio₁＝radio₁(k′)，并进入步骤304；Step 303, update the parameter radio ₁ in the projection system to be radio ₁ (k'), repeat steps 201 to 209, judge whether Dradio ₂ =0 is established, if so then return to step 302, otherwise make Dradio ₁ =radio ₁ (k') , and enter step 304;

步骤304、判断循环次数k′＞N是否成立，若是，则进入步骤306，否则令k′＝k′+1，令radio₁(k′)＝radio₁(k′-1)+ξ_r1，并进入步骤305；Step 304, determine whether the number of cycles k'>N is established, if so, then enter step 306, otherwise let k'=k'+1, make radio ₁ (k')=radio ₁ (k'-1)+ξ _r1 , And go to step 305;

步骤305、更新投影系统中的参数radio₁为radio₁(k′)，重复步骤201至209，判断Dradio₂＝0是否成立，若是则进入步骤306，否则令Uradio₁＝radio₁(k′)，并返回步骤304；Step 305, update the parameter radio ₁ in the projection system to be radio ₁ (k'), repeat steps 201 to 209, judge whether Dradio ₂ =0 is established, if so then enter step 306, otherwise make Uradio ₁ =radio ₁ (k') , and return to step 304;

步骤306、判断Dradio₁＝Uradio₁是否成立，若是，则判定步骤101中给定系统参数不合理，并结束，若否，输出Uradio₁和Dradio₁并进入步骤104。Step 306 , judging whether Dradio ₁ =Uradio ₁ holds true, if yes, then judging that the given system parameters in step 101 are unreasonable, and end, if not, output Uradio ₁ and Dradio ₁ and enter step 104 .

进一步地，本发明当计算出r₂后，进一步对设定的第一反射镜M1与第二反射镜M2出射的光线不发生遮挡的空间CLEAPE1进行判断，当CLEAPE1＞0且CLEAPE1＜UCLEAPE1都成立时，则进入步骤105，否则判定根据所给定的系统参数不合理，并结束；其中Further, after calculating _r2 , the present invention further judges the space CLEAPE1 in which the light emitted by the set first reflector M1 and the second reflector M2 is not blocked. When CLEAPE1>0 and CLEAPE1<UCLEAPE1 are both established , then enter step 105, otherwise it is determined that it is unreasonable according to the given system parameters, and end; where

$UCLEAPE UCLEAPE 11 = = {h h}_{b b 11} - - \frac{- - {d d}_{11} \cdot \cdot {l l}_{11}^{' '} \cdot \cdot {radio radio}_{11}}{{l l}_{22}}$

其中h_b1为上光线与第一反射镜M1交点的高度，l′₁为掩膜图形经过第一反射镜M1的像距，l₂＝l₁′-d₁。Where h _b1 is the height of the intersection of the upper ray and the first mirror M1, l′ ₁ is the image distance of the mask pattern passing through the first mirror M1, l ₂ =l ₁ ′−d ₁ .

有益效果Beneficial effect

本发明提出了一套完整的初始结构设计方案，能够根据不同的用户要求进行设计和搜索，避免了传统光学设计方法在现有结构上进行修改和试错的盲目性。对整个系统进行分组光路搜索，大大节省了搜索时间。同时基于实际光线追迹，避免了近轴光路与实际光路的差别导致的光路遮挡情况误判。The invention proposes a complete set of initial structure design schemes, which can be designed and searched according to different user requirements, and avoid the blindness of modification and trial and error in the existing structure by traditional optical design methods. Carry out group optical path search on the whole system, which greatly saves the search time. At the same time, based on the actual ray tracing, the misjudgment of the occlusion of the optical path caused by the difference between the paraxial optical path and the actual optical path is avoided.

其次，充分考虑了“掩膜阴影效应”、各反射面的主光线入射角度、最大光束口径，以及视场宽度等因素，通过给出近似的函数关系、迭代计算和遍历筛选等方法得到了各参数的可用范围，为精细的搜索提供了可靠的依据，便于提高搜索的精度，规避不合理的参数要求。Secondly, fully considering the "mask shadow effect", the incident angle of the chief ray of each reflective surface, the maximum beam aperture, and the width of the field of view and other factors, the various The available range of parameters provides a reliable basis for fine search, which facilitates the improvement of search accuracy and avoids unreasonable parameter requirements.

附图说明 Description of drawings

图1为EUVL六反射投影物镜分组设计示意图；Figure 1 is a schematic diagram of the group design of the EUVL six-reflection projection objective lens;

图2为第一镜组G1光路示意图；Fig. 2 is a schematic diagram of the optical path of the first mirror group G1;

图3为第一反射镜M1的光路计算示意图；3 is a schematic diagram of optical path calculation of the first mirror M1;

图4为radio₂的下限Dradio₂的计算流程图；Fig. 4 is the calculation flowchart of the lower limit Dradio ₂ of radio ₂ ;

图5为radio₁的上限Uradio₁与下限Dradio₁的计算流程图；Fig. 5 is the calculation flowchart of upper limit Uradio ₁ and lower limit Dradio ₁ of radio ₁ ;

图6为第二反射镜M2的光路计算示意图；Fig. 6 is the optical path calculation schematic diagram of the second mirror M2;

图7为第三镜组G3逆向光路示意图；7 is a schematic diagram of the reverse optical path of the third mirror group G3;

图8为第六反射镜M6的光路计算示意图；Fig. 8 is a schematic diagram of optical path calculation of the sixth reflector M6;

图9为第五反射镜M5的光路计算示意图；Fig. 9 is a schematic diagram of optical path calculation of the fifth reflector M5;

图10为第二镜组G2光路示意图；Fig. 10 is a schematic diagram of the optical path of the second mirror group G2;

图11(a)为第二镜组参数d₃随M3的半径r₃改变而变化的情况；Fig. 11 (a) is the situation that the second mirror group parameter d ₃ changes with the radius r ₃ of M3;

图11(b)为第二镜组参数-l₃-ENP₂随M3的半径r₃改变而变化的情况；Fig. 11(b) shows how the second lens group parameter -l ₃ -ENP ₂ changes with the change of the radius r ₃ of M3;

图11(c)为第二镜组参数l′₄随M3的半径r₃改变而变化的情况；Fig. 11 (c) is the situation that the second mirror group parameter l' ₄ changes with the radius r ₃ of M3;

图11(d)为第二镜组参数r₄随M3的半径r₃改变而变化的情况；Fig. 11 (d) is the situation that the second mirror group parameter r ₄ changes with the radius r ₃ of M3;

图12(a)为第二镜组参数d₃的筛选情况；Fig. 12 (a) is the screening situation of the second lens group parameter d ₃ ;

图12(b)为第二镜组参数-l₃-ENP₂的筛选情况；Figure 12(b) is the screening situation of the second lens group parameter -l ₃ -ENP ₂ ;

图13为第二镜组的实际放大倍率M随迭代次数增加的收敛情况；Fig. 13 is the convergence of the actual magnification M of the second mirror group as the number of iterations increases;

图14(a)为本发明的一个实施范例所选定G1镜组光路图；Fig. 14 (a) is the selected G1 lens group optical path diagram of an embodiment of the present invention;

图14(b)为本发明的一个实施范例所选定G3镜组光路图；Fig. 14 (b) is the selected G3 lens group optical path diagram of an embodiment of the present invention;

图14(c)为本发明的一个实施范例得到的三种G2镜组光路图；Fig. 14 (c) is the optical path diagram of three kinds of G2 mirror groups obtained by an embodiment of the present invention;

图14(d)为本发明的一个实施范例得到的三种EUVL六反射物镜光路图；Fig. 14 (d) is the optical path diagram of three kinds of EUVL six-reflection objective lens obtained by an embodiment example of the present invention;

图15(a)为应用本发明设计方法得到的第四种EUVL六反射物镜光路图；Fig. 15 (a) is the optical path diagram of the fourth EUVL six-reflection objective lens obtained by applying the design method of the present invention;

图15(b)为应用本发明设计方法得到的第五种EUVL六反射物镜光路图；Fig. 15 (b) is the optical path diagram of the fifth EUVL six-reflection objective lens obtained by applying the design method of the present invention;

图15(c)为应用本发明设计方法得到的第六种EUVL六反射物镜光路图；Fig. 15 (c) is the optical path diagram of the sixth EUVL six-reflection objective lens obtained by applying the design method of the present invention;

图16为EUVL投影光刻系统示意图。FIG. 16 is a schematic diagram of an EUVL projection lithography system.

具体实施方式 Detailed ways

下面结合附图进一步对本发明进行详细说明。The present invention will be further described in detail below in conjunction with the accompanying drawings.

首先对本发明使用的参数定义进行说明。Firstly, the definition of parameters used in the present invention will be described.

实际物点/像点定义为两条边缘光线的交点，实际像高/物高定义为实际像点/物点的高度；实际像面/物面定义为过实际像点/物点与光轴垂直的面；实际入瞳距为实际物面与实际入瞳面的距离；实际出瞳距为实际像面与实际出瞳面的距离；这里的实际入瞳面和实际出瞳面由离轴视场的主光线与光轴的交点确定。为了方便起见，以后的论述中，上述参量就简称为物点/像点、物高/像高、物面/像面、出瞳/入瞳等，若该参量为近轴参量时，会特别指出。为了直观起见，本发明中所涉及的光线角度均视为正角度，对于不同方向的光线角度（逆时针或者顺时针）不采用符号规则加以区分，而仅在计算公式中使用运算符号表示。The actual object point/image point is defined as the intersection of two edge rays, the actual image height/object height is defined as the height of the actual image point/object point; the actual image plane/object plane is defined as passing through the actual image point/object point and the optical axis Vertical surface; the actual entrance pupil distance is the distance between the actual object surface and the actual entrance pupil surface; the actual exit pupil distance is the distance between the actual image surface and the actual exit pupil surface; the actual entrance pupil surface and the actual exit pupil surface here are determined by the off-axis The intersection of the chief ray of the field of view and the optical axis is determined. For convenience, in the following discussions, the above parameters are referred to as object point/image point, object height/image height, object plane/image plane, exit pupil/entrance pupil, etc. If the parameter is a paraxial parameter, it will be particularly pointed out. For the sake of intuition, the ray angles involved in the present invention are regarded as positive angles, and the ray angles in different directions (counterclockwise or clockwise) are not distinguished by symbol rules, but are only expressed by operational symbols in the calculation formula.

步骤101、确定该光刻系统中投影物镜为六反射镜结构，并设定该投影物镜的光学系统参数；所述参数包括投影物镜的放大倍率M，物方视场高度YOB，物方视场宽度FWOB，像方视场高度YIM，像方视场宽度FWIM，像方曝光视场弦长CL，各反射镜最大主光线入射角度MAXCA1～MAXCA6，投影物镜的总长度TTL，最小前工作距FWDI，以及最小后工作距BWDI（即硅片到第五反射镜M5之间的距离）。Step 101. Determine that the projection objective in the lithography system has a six-mirror structure, and set the optical system parameters of the projection objective; the parameters include the magnification M of the projection objective, the height of the object-side field of view YOB, and the object-side field of view Width FWOB, height YIM of image square field of view, width FWIM of image square field of view, chord length CL of image square exposure field of view, maximum chief ray incident angle MAXCA1～MAXCA6 of each mirror, total length TTL of projection objective lens, minimum front working distance FWDI , and the minimum back working distance BWDI (that is, the distance between the silicon wafer and the fifth mirror M5).

由于光刻系统的设计要求，极紫外投影光刻物镜的系统放大倍率M通常为1/4或1/5。Due to the design requirements of the lithography system, the system magnification M of the EUV projection lithography objective lens is usually 1/4 or 1/5.

由几何光学原理可知：According to the principle of geometric optics:

YOB＝YIM/|M|YOB=YIM/|M|

FWOB＝FWIM/|M|FWOB＝FWIM/|M|

若物方数值孔径为NAO，像方数值孔径为NAI，则有If the object-space numerical aperture is NAO, and the image-space numerical aperture is NAI, then we have

NAO＝NAI·|M|NAO＝NAI·|M|

选取六枚反射镜和光阑设置于光刻系统中掩膜和硅片之间，六枚反射镜及光阑的设置位置：从掩膜开始沿光路方向依次为第一反射镜M1、光阑、第二反射镜M2、第三反射镜M3、第四反射镜M4、第五反射镜M5以及第六反射镜M6，且光阑置于第二反射镜M2上，这样可以保证光阑在加工时可以实现。Select six reflectors and apertures and set them between the mask and the silicon wafer in the photolithography system. The positions of the six reflectors and apertures are: starting from the mask along the direction of the optical path, they are the first reflector M1, aperture, The second reflector M2, the third reflector M3, the fourth reflector M4, the fifth reflector M5 and the sixth reflector M6, and the aperture is placed on the second reflector M2, which can ensure that the aperture is can be realised.

为了后续便于描述，可将EUVL六反射投影物镜系统PO分为三个镜组，第一反射镜组G1包括第一反射镜M1和第二反射镜M2；第二反射镜组G2包括第三反射镜M3和第四反射镜M4；第三反射镜组G3包括第五反射镜M5和第六反射镜M6，如图1所示。For the convenience of subsequent description, the EUVL six-reflection projection objective system PO can be divided into three mirror groups, the first mirror group G1 includes the first mirror M1 and the second mirror M2; the second mirror group G2 includes the third mirror The mirror M3 and the fourth mirror M4; the third mirror group G3 includes the fifth mirror M5 and the sixth mirror M6, as shown in FIG. 1 .

进一步确定各反射镜之间的比例参数，所述比例参数包括物方视场高度与掩膜到第一反射镜M1距离的比例参数radio₁，第二反射镜M2到第一反射镜M1距离与掩膜到第一反射镜M1距离的比例参数radio₂，第一反射镜M1与第二反射镜M2出射的光线不发生遮挡的空间CLEAPE1，第五反射镜M5到第六反射镜M6间距与硅片到第五反射镜M5距离BWDI的比例参数radio₃，第六反射镜M6与第五反射镜M5的入射光线不发生遮挡的空间CLEAPE6，第六反射镜M6出射的光线与第五反射镜M5不发生遮拦的空间CLEAPE5。Further determine the ratio parameter between the mirrors, the ratio parameter includes the ratio parameter radio ₁ of the height of the object field of view and the distance from the mask to the first mirror M1, the distance from the second mirror M2 to the first mirror M1 and The ratio parameter radio ₂ of the distance from the mask to the first mirror M1, the space CLEAPE1 where the light emitted by the first mirror M1 and the second mirror M2 does not block, the distance between the fifth mirror M5 and the sixth mirror M6 and the silicon The ratio parameter radio ₃ of the distance BWDI from the sheet to the fifth reflector M5, the space CLEAPE6 where the incident light of the sixth reflector M6 and the fifth reflector M5 does not block, the light emitted by the sixth reflector M6 and the fifth reflector M5 Space CLEAPE5 where occlusion does not occur.

步骤102、获取掩膜到第一反射镜M1的距离为-l₁，则Step 102, obtain the distance from the mask to the first mirror M1 as -l ₁ , then

radio₁＝YOB/|-l₁|radio ₁ ＝YOB/|-l ₁ |

|-l₁|＝YOB/radio₁ |-l ₁ |=YOB/radio ₁

设第二反射镜M2到第一反射镜M1的距离为-d₁，则Assuming that the distance from the second mirror M2 to the first mirror M1 is -d ₁ , then

radio₂＝|-d₁|/|-l₁|＝|-d₁|·radio₁/YOBradio ₂ ＝|-d ₁ |/|-l ₁ |＝|-d ₁ |·radio ₁ /YOB

|-d₁|＝YOB/radio₁·radio₂ |-d ₁ |=YOB/radio ₁ radio ₂

进一步获取第一反射镜M1的半径为r₁；Further obtain the radius of the first mirror M1 as r ₁ ;

r₁的获取原理和过程如下：The principle and process of obtaining r ₁ are as follows:

如图2所示，主光线104自掩膜入射至第一反射镜M1，再由M1反射至第二反射镜M2上的情况。为了确保系统的光阑能够物理实现，保证系统无杂光，通常EUVL反射光刻物镜的光阑均位于第二反射镜M2上，即主光线通过M2的中心。根据物方主光线入射角度CA和光阑STOP位于第二反射镜M2的条件，可以计算出不同radio₁和radio₂所对应的M1的半径r₁。As shown in FIG. 2 , the chief ray 104 is incident on the first mirror M1 from the mask, and then reflected by M1 to the second mirror M2 . In order to ensure that the diaphragm of the system can be realized physically and the system is free of stray light, the diaphragm of the EUVL reflective lithography objective lens is usually located on the second mirror M2, that is, the center of the chief ray passing through M2. The radius r ₁ of M1 corresponding to different radio ₁ and radio ₂ can be calculated according to the condition that the chief ray incident angle CA on the object side and the stop STOP is located at the second mirror M2.

如图3所示，根据实际光线追迹公式，有As shown in Figure 3, according to the actual ray tracing formula, there is

${h h}_{z z 11} / / {r r}_{11} = = tan the tan {θ θ}_{z z 11}$

$= = tan the tan (({I I}_{z z 22} - - {I I}_{}^{z z 11}))$

$= = tan the tan (({I I}_{z z 22} - - \frac{((CA CA + + {I I}_{z z 22}))}{22}))$

$= = tan the tan ((\frac{{I I}_{z z 22}}{22} - - \frac{CA CA}{22}))$

$= = tan the tan ((\frac{arctan arctan (({h h}_{z z 11} / / ((- - {d d}_{11} + + {z z}_{z z 11}))))}{22} - - \frac{CA CA}{22}))$

于是有So there is

${r r}_{11} = = {h h}_{z z 11} / / tan the tan ((\frac{arctan arctan (({h h}_{z z 11} / / (({- - d d}_{11} + + {z z}_{z z 11}))))}{22} - - \frac{CA CA}{22}))$

其中，θ_z1为M1上的主光线的入射点法线与光轴的夹角；h_z1为主光线与M1交点的高度；I_z1为入射至M1上的主光线的入射角；I′_z1为入射至M1上的主光线的反射角；I_z2为M1上出射的主光线与光轴的夹角；z_z1为M1上主光线入射点与M1顶点的轴向距离。Among them, θ _z1 is the angle between the normal of the incident point of the chief ray on M1 and the optical axis; h _z1 is the height of the intersection point between the chief ray and M1; I _z1 is the incident angle of the chief ray incident on M1; I′ _z1 is the reflection angle of the chief ray incident on M1; I _z2 is the angle between the chief ray exiting on M1 and the optical axis; z _z1 is the axial distance between the incident point of the chief ray on M1 and the apex of M1.

当r₁确定后，则可以利用光学设计软件CODEV计算出M2反射镜附近的光路无遮挡空间CLEAPE2。When r ₁ is determined, the optical path unobstructed space CLEAPE2 near the M2 mirror can be calculated by using the optical design software CODEV.

步骤103、给定物方数值孔径NAO以及物方主光线入射角度CA，根据所述-d₁和r₁，利用radio₂判断出步骤101中给定的光学系统参数是否合理。Step 103 , given the object-side numerical aperture NAO and the object-side chief ray incident angle CA, according to the -d ₁ and r ₁ , use radio ₂ to determine whether the optical system parameters given in step 101 are reasonable.

以下首先对CA的选取进行分析，再具体给出判断的过程；The following first analyzes the selection of CA, and then specifically gives the process of judgment;

根据以往光刻仿真分析的结果表明，掩膜上的主入射光线角度不为0°时，将会产生掩膜的“阴影效应”，从而引起硅片上曝光线条位置的偏移，仿真结果表明当掩膜上的主光线入射角度小于6°时，“阴影效应”能够得到补偿和校正。所以有物方主光线入射角度的上限为6°。According to the results of previous lithography simulation analysis, when the angle of the main incident light on the mask is not 0°, the "shadow effect" of the mask will occur, which will cause the position shift of the exposure lines on the silicon wafer. The simulation results show that When the chief ray incident angle on the mask is less than 6°, the "shadow effect" can be compensated and corrected. Therefore, the upper limit of the incident angle of the chief ray on the object side is 6°.

由于极紫外光刻的掩膜为反射式掩膜，照明系统入射至掩膜的光路与自掩膜入射至投影物镜的光路不能相互遮挡。所以，光束的主光线104，上光线105，下光线106应该同时高于物方视场高度YOB，或同时低于物方视场高度YOB，如图1所示，以保证光路不发生遮挡，此时物方主光线入射角度的范围为Since the mask of extreme ultraviolet lithography is a reflective mask, the light path of the illumination system incident on the mask and the light path from the mask to the projection objective cannot be blocked from each other. Therefore, the chief ray 104, the upper ray 105, and the lower ray 106 of the light beam should be higher than the height of the field of view YOB at the object side, or lower than the height of the field of view YOB at the object side at the same time, as shown in Figure 1, to ensure that the optical path is not blocked. At this time, the range of the incident angle of the object-space chief ray is

|CA|＞arcsin(NAO)|CA|＞arcsin(NAO)

即物方主光线入射角度的下限为arcsin(NAO)。表1-1为几种典型物方数值孔径的物方主光线入射角度范围。That is, the lower limit of the incident angle of the chief ray on the object side is arcsin(NAO). Table 1-1 shows the incident angle range of object space chief ray for several typical object space numerical apertures.

表1-1几种典型物方数值孔径的主光线入射角度范围Table 1-1 Chief ray incidence angle range of several typical object space numerical apertures

NAO NAO 最小CA Minimum CA 最大CA Maximum CA 0.04 0.04 2.292443 2.292443 6.0000006.000000 0.05 0.05 2.865984 2.865984 6.0000006.000000 0.06 0.06 3.439813 3.439813 6.0000006.000000 0.07 0.07 4.013987 4.013987 6.0000006.000000 0.08 0.08 4.588566 4.588566 6.0000006.000000 0.09 0.09 5.163607 5.163607 6.0000006.000000 0.10 0.10 5.739170 5.739170 6.0000006.000000 0.1045 0.1045 6.000000 6.000000 6.000000 6.000000

由表1可知，对于六反射EUVL投影物镜，当光阑为第二面反射镜M2上时，物方数值孔径越大，其可用的物方主光线入射角度范围就越小，能够达到的最大物方数值孔径为0.1045。It can be seen from Table 1 that for the six-reflection EUVL projection objective lens, when the aperture is on the second mirror M2, the larger the object-side numerical aperture, the smaller the available object-side principal ray incident angle range, and the maximum that can be achieved The object space numerical aperture is 0.1045.

如图4所示，以下对步骤103的判断过程进行具体说明：As shown in Fig. 4, the judgment process of step 103 is described in detail below:

Uradio₂＝1-FWDI·radio₁/YOBUradio ₂ = 1-FWDI·radio ₁ /YOB

其中，FWDI为投影物镜最小前工作距，YOB为物方视场高度，radio₁为物方视场高度与掩膜到第一反射镜M1距离的比例参数。Among them, FWDI is the minimum front working distance of the projection objective, YOB is the height of the field of view on the object side, and radio ₁ is a proportional parameter between the height of the field of view on the object side and the distance from the mask to the first mirror M1.

由于第二反射镜M2与物方入射光线之间不能发生遮挡，所以步骤101在给定比例参数时需保证CLEAPE2＞0，同时第一反射镜上主光线的入射角必须小于MAXCA1，根据这两条件中的至少一个可以粗略地确定在一定物方数值孔径NAO和物方主光线入射角度CA，确定radio₂的下限Dradio₂，具体步骤为：Since the second reflector M2 cannot block the incident light from the object side, it is necessary to ensure that CLEAPE2 > 0 when the ratio parameter is given in step 101, and at the same time, the incident angle of the chief ray on the first reflector must be smaller than MAXCA1. According to these two At least one of the conditions can roughly determine the lower limit Dradio ₂ of radio ₂ at a certain object-space numerical aperture NAO and object-space chief ray incident angle CA, and the specific steps are:

步骤202、给定物方数值孔径NAO和物方主光线入射角度CA，设定radio₂的搜索步长为ξ_r2，设定循环次数k＝1，radio₂(k)=0，radio₂的下限值Dradio₂=0。Step 202, given the object-space numerical aperture NAO and the incident angle CA of the object-space chief ray, set the search step size of radio ₂ to ξ _r2 , set the number of cycles k=1, radio ₂ (k)=0, radio ₂ ’s The lower limit Dradio ₂ =0.

步骤203、判断radio₂(k)是否小于Uradio₂，若是，则进入步骤204，否则进入步骤209。Step 203 , judging whether radio ₂ (k) is smaller than Uradio ₂ , if yes, go to step 204 , otherwise go to step 209 .

步骤204、根据所述-d₁和r₁，根据光线追迹原理，计算出利用radio₂(k)所设计的投影物镜的CLEAPE2(k)和/或CA₁(k)，其中CLEAPE2(k)表示第二反射镜M2与第一反射镜M1上的入射光线不发生遮挡的空间，CA₁(k)表示第一反射镜M1上主光线入射角度。Step 204: Calculate CLEAPE2(k) and/or CA ₁ (k) of the projection objective lens designed using radio ₂ (k) according to the -d ₁ and r ₁ , according to the principle of ray tracing, wherein CLEAPE2(k ) represents the space where the incident light rays on the second reflector M2 and the first reflector M1 are not blocked, and CA ₁ (k) represents the incident angle of the chief ray on the first reflector M1.

步骤205、对步骤204计算出参数的类型进行判断，当仅计算出CLEAPE2(k)时，则进入步骤206，当仅计算出CA₁(k)时，则进入步骤207，当同时计算出CLEAPE2(k)和CA₁(k)时，则进入步骤208。Step 205, judge the type of parameter calculated in step 204, when only CLEAPE2(k) is calculated, then enter step 206, when only CA ₁ (k) is calculated, then enter step 207, when simultaneously calculate CLEAPE2 (k) and CA ₁ (k), go to step 208.

步骤206、判断CLEAPE2(k)＞0是否成立，若是，则将此时radio₂(k)确定为radio₂的下限值Dradio₂，即令Dradio₂＝radio₂(k)，进入步骤209，否则令k＝k+1，令radio₂(k)＝radio₂(k-1)+ξ_r2，返回步骤203。Step 206, judge whether CLEAPE2(k)>0 is set up, if so, radio ₂ (k) is then determined as the lower limit value Dradio ₂ of radio ₂ at this moment, promptly makes Dradio ₂ =radio ₂ (k), enters step 209, otherwise Let k=k+1, let radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , return to step 203 .

步骤207、判断CA₁(k)＜MAXCA1是否成立，若是，则将此时radio₂(k)确定为radio₂的下限值Dradio₂，即令Dradio₂＝radio₂(k)，进入步骤209，否则令k＝k+1，令radio₂(k)＝radio₂(k-1)+ξ_r2，返回步骤203。Step 207, judging whether CA ₁ (k)＜MAXCA1 is established, if so, radio ₂ (k) is then determined as the lower limit value Dradio ₂ of radio ₂ at this moment, promptly makes Dradio ₂ =radio ₂ (k), enters step 209, Otherwise, let k=k+1, let radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , and return to step 203 .

步骤208、判断CA₁(k)＜MAXCA1与CLEAPE2(k)＞0是否皆成立，若是，则将此时的radio₂(k)确定为radio₂的下限值Dradio₂，即令Dradio₂＝radio₂(k)，进入步骤209，否则令k＝k+1，令radio₂(k)＝radio₂(k-1)+ξ_r2，返回步骤203。Step 208, judging whether CA ₁ (k)<MAXCA1 and CLEAPE2(k)>0 are all established, if so, then determine radio ₂ (k) at this time as the lower limit value Dradio ₂ of radio ₂ , that is, make Dradio ₂ =radio ₂ (k), go to step 209, otherwise set k=k+1, let radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , return to step 203.

步骤209、判断Dradio₂=0是否成立，若是，则判定所给定的投影物镜的光学系统参数不合理，不存在第二反射镜M2到第一反射镜M1距离与掩膜到第一反射镜M1距离的比例参数radio₂，并结束，若否，输出Dradio₂并进入步骤104。Step 209, judging whether Dradio ₂ =0 is established, if so, judging that the given optical system parameters of the projection objective lens are unreasonable, and there is no distance from the second mirror M2 to the first mirror M1 and the distance from the mask to the first mirror The ratio parameter radio ₂ of the M1 distance, and end, if not, output Dradio ₂ and enter step 104 .

上述步骤的操作流程图如图4所示。The operation flowchart of the above steps is shown in FIG. 4 .

表2为物方数值孔径NAO为0.06，几个典型物方主光线入射角度CA及相应的给定的较为典型的radio₁时；此表中给出步骤204中仅计算出CLEAPE2(k)和步骤204中仅计算出CA₁(k)这两种情况，当计算出CLEAPE2(k)时，所获取的上下限限赋值为：Dradio₂₁=Dradio₂；当计算出CA₁(k)时，所获取的上下限限赋值为：Dradio₂₂=Dradio₂，表2-1中给定步进值ξ_r2为0.005。Table 2 shows that the object space numerical aperture NAO is 0.06, several typical object space chief ray incident angles CA and the corresponding given more typical radio ₁ ; this table shows only CLEAPE2(k) and In step 204, only these two cases of CA ₁ (k) are calculated, when CLEAPE2 (k) is calculated, the upper and lower limit assignments obtained are: Dradio ₂₁ =Dradio ₂ ; when CA ₁ (k) is calculated, The obtained upper and lower limits are assigned as: Dradio ₂₂ =Dradio ₂ , and the given step value ξ _r2 in Table 2-1 is 0.005.

表2-1table 2-1

当判定Dradio₂=0不成立时，本发明可进一步在radio₁可取范围内对其进行更新，利用更新后的radio₁重复步骤201-209，获取Dradio₂，进而判断出步骤101给定的光学系统参数是否合理。该判断的具体过程为：When it is determined that Dradio ₂ = 0 is not established, the present invention can further update it within the acceptable range of radio ₁ , repeat steps 201-209 by using the updated radio ₁ , obtain Dradio ₂ , and then determine the optical system given in step 101 Whether the parameters are reasonable. The specific process of the judgment is as follows:

步骤301、设定radio₁的搜索步长为ξ_r1，设定循环次数k′＝1，radio₁(k′)=YOB/TTL，设定N为大于(YOB/FWDI-YOB/TTL)/ξ_r1的最小整数，令radio₁的上限Uradio₁＝YOB/TTL+(N-1)×ξ_r1，令radio₁的下限Dradio₁＝YOB/TTL+(N-1)×ξ_r1。Step 301, set the search step size of radio ₁ to ξ _r1 , set the number of cycles k'=1, radio ₁ (k')=YOB/TTL, set N to be greater than (YOB/FWDI-YOB/TTL)/ The smallest integer of ξ _r1 , let the upper limit of radio ₁ Uradio ₁ =YOB/TTL+(N-1)×ξ _r1 , let the lower limit of radio ₁ Dradio ₁ =YOB/TTL+(N-1)×ξ _r1 .

步骤305、更新投影系统中的参数radio₁为radio₁(k′)，重复步骤201至209，判断Dradio₂＝0是否成立，若是则进入步骤306，否则令Dradio₁＝radio₁(k′)，并返回步骤304；Step 305, update the parameter radio ₁ in the projection system to be radio ₁ (k'), repeat steps 201 to 209, judge whether Dradio ₂ =0 is established, if so then enter step 306, otherwise make Dradio ₁ =radio ₁ (k') , and return to step 304;

表3-1为几种典型物方数值孔径及相应的典型物方主光线入射角度CA取值时，radio₁的上限Uradio₁下限Dradio₁的值。在Dradio₁，Uradio₁的计算中，步进值ξ_r1为0.0225。Table 3-1 shows the values of the upper limit Uradio ₁ and the lower limit Dradio ₁ of radio ₁ when several typical object space numerical apertures and corresponding typical object space chief ray incident angles CA are selected. In the calculation of Dradio ₁ and Uradio ₁ , the step value ξ _r1 is 0.0225.

表3-1Table 3-1

具体过程如下：The specific process is as follows:

如图6所示，由于极紫外光刻物镜的离轴光路在空间中完全无遮挡，并且要根据元件加工工艺和水平给反射镜的反光区域和通光区域之间留出一定的余量（即CLEAPE1），根据实际光线追迹公式和几何关系，有As shown in Figure 6, since the off-axis optical path of the EUV lithography objective lens is completely unobstructed in space, and a certain margin should be left between the reflective area and the light-transmitting area of the mirror according to the component processing technology and level ( That is CLEAPE1), according to the actual ray tracing formula and geometric relationship, we have

$\frac{{h h}_{a a 22}}{{r r}_{22}} = = tan the tan {θ θ}_{a a 22}$

$= = tan the tan (({U u}_{a a 22} - - {I I}_{a a 22}))$

$= = tan the tan (({U u}_{a a 22} - - \frac{(({I I}_{a a 22} + + {I I}_{a a 22}^{' '}))}{22}))$

$= = tan the tan ((\frac{{U u}_{a a 22}}{22} - - \frac{{U u}_{a a 22}^{' '}}{22}))$

$= = tan the tan ((\frac{{U u}_{a a 22}}{22} - - \frac{arctan arctan ((\frac{{h h}_{b b 11} - - CLEAPE CLEAPE 11 - - {h h}_{a a 22}}{{- - d d}_{11}}))}{22}))$

于是有So there is

${r r}_{22} = = {h h}_{a a 22} / / tan the tan ((\frac{{U u}_{a a 22}}{22} - - \frac{arctan arctan ((\frac{{h h}_{b b 11} - - CLEAPE CLEAPE 11 - - {h h}_{a a 22}}{{- - d d}_{11}}))}{22}))$

其中，θ_a2为第二反射镜M2上的上光线的入射点法线与光轴的夹角；h_a2为上光线与第二反射镜M2交点的高度；h_b1为下光线与第一反射镜M1交点的高度；I_a2为第二反射镜M2上的上光线入射角；I′_a2为第二反射镜M2上的上光线反射角；U_a2为入射至第一反射镜M1上的上光线与光轴的夹角；U′_a2为第一反射镜M1出射的上光线与光轴的夹角。Among them, θ _a2 is the angle between the normal line of the incident point of the upper ray on the second reflector M2 and the optical axis; h _a2 is the height of the intersection point of the upper ray and the second reflector M2; h _b1 is the height of the intersection between the lower ray and the first reflection The height of the intersection point of mirror M1; I _a2 is the incident angle of the upper ray on the second reflector M2; I' _a2 is the reflection angle of the upper ray on the second reflector M2; U _a2 is the upper ray incident on the first reflector M1 The angle between the light and the optical axis; U′ _a2 is the angle between the upper light emitted by the first reflector M1 and the optical axis.

当确定-l₁、-d₁、r₁以及r₂后，则可计算第一镜组G1的实际像高YIM1,实际出瞳距EXP1，实际出瞳直径EXD1，其中计算过程为现有技术，因此在此不进行累述。After determining -l ₁ , -d ₁ , r ₁ and r ₂ , the actual image height YIM1, actual exit pupil distance EXP1, and actual exit pupil diameter EXD1 of the first mirror group G1 can be calculated, and the calculation process is the prior art , so it will not be described here.

在本实施例中当计算出r₂后，进一步对设定的CLEAPE1进行判断，具体判断过程为：In this embodiment, after _r is calculated, the set CLEAPE1 is further judged, and the specific judgment process is as follows:

步骤401、由光路无遮挡的条件可知，一般情况下，CLEAPE1的下限DCLEAPE1为0。Step 401 , it can be seen from the condition that the optical path is not blocked, generally, the lower limit DCLEAPE1 of CLEAPE1 is 0.

步骤402、设掩膜图形经过第一反射镜M1的像距为l′₁，根据近轴光学原理，有Step 402, set the image distance of the mask pattern passing through the first mirror M1 as l′ ₁ , according to the principle of paraxial optics, there is

$\frac{11}{((YOB YOB / / {radio radio}_{11}))} + + \frac{11}{{l l}_{11}^{' '}} = = \frac{22}{{r r}_{11}}$

${l l}_{11}^{' '} = = \frac{{r r}_{11} \cdot \cdot ((YOB YOB / / {radio radio}_{11}))}{22 ((YOB YOB / / {radio radio}_{11})) - - {r r}_{11}}$

第一反射镜所成的像至第二反射镜M2的物距为l₂，根据近轴光学原理，有The object distance from the image formed by the first reflector to the second reflector M2 is l ₂ , according to the principle of paraxial optics,

l₂＝l₁′-d₁ l ₂ =l ₁ ′-d ₁

当CLEAPE1取得最大值时，掩膜图形经第二反射镜M2成像后的像距为-d₁。此时CLEAPE1的上限UCLEAPE1为：When CLEAPE1 reaches the maximum value, the image distance of the mask pattern after being imaged by the second mirror M2 is -d ₁ . At this time, the upper limit UCLEAPE1 of CLEAPE1 is:

$UCLEAPE UCLEAPE 11 = = {h h}_{b b 11} - - \frac{{- - d d}_{11} \cdot &Center Dot; {l l}_{11}^{' '} \cdot &Center Dot; {radio radio}_{11}}{{l l}_{22}}$

其中h_b1为下光线与第一反射镜M1交点的高度；Where h _b1 is the height of the intersection point between the lower light and the first reflector M1;

于是CLEAPE1的可用范围上限UCLEAPE1为

下限DCLEAPE1为0。Then the upper limit of the usable range of CLEAPE1 UCLEAPE1 is

The lower limit DCLEAPE1 is 0.

步骤403、判断CLEAPE1＞0且CLEAPE1＜UCLEAPE1是否成立，若成立，则进入步骤105，否则判定步骤101所给定的系统参数不合理，结束本方法。Step 403, judging whether CLEAPE1>0 and CLEAPE1<UCLEAPE1 are true, if true, proceed to step 105, otherwise, judge that the given system parameters in step 101 are unreasonable, and end the method.

步骤105、计算出第五反射镜M5到第六反射镜M6之间的间距为d₅，以及根据所述d₅获取第五反射镜M5的半径r₅和第六反射镜M6的半径r₆。Step 105, calculate the distance between the fifth mirror M5 and the sixth mirror M6 as d ₅ , and obtain the radius r ₅ of the fifth mirror M5 and the radius r ₆ of the sixth mirror M6 according to the d ₅ .

具体的过程为：The specific process is:

设第五反射镜M5到第六反射镜M6之间的间距为d₅，则|d₅|＝BWDI·radio₃。Assuming that the distance between the fifth mirror M5 and the sixth mirror M6 is d ₅ , then |d ₅ |=BWDI·radio ₃ .

第三镜组位于六反光刻物镜的像面（即硅片）一方。在实际的设计中，G3镜组的光路采取反向设计方法。如图7所示，G3镜组光路与EUVL投影物镜的正向光路方向相反。为了避免引起混淆，G3镜组中各参数仍然采用正向光路中的表示方法。The third lens group is located on the side of the image plane (that is, the silicon wafer) of the six-mirror lithography objective lens. In the actual design, the optical path of the G3 lens group adopts the reverse design method. As shown in Figure 7, the optical path of the G3 lens group is opposite to the forward optical path of the EUVL projection objective. In order to avoid confusion, the parameters in the G3 lens group still use the expression method in the forward optical path.

确定像方数值孔径NAI，在确定系统参数时已知Determine the image square numerical aperture NAI, which is known when determining the system parameters

NAO＝NAI·|M|NAO＝NAI·|M|

确定像方视场高度YIM，在确定系统参数时已知Determine the field of view height YIM of the image side, which is known when determining the system parameters

YOB＝YIM/|M|YOB=YIM/|M|

确定第五反射镜M5第六反射镜M5之间的间距d₅为：Determine the distance _d between the fifth reflector M5 and the sixth reflector M5 as:

|d₅|＝BWDI·radio₃ |d ₅ |＝BWDI·radio ₃

在光路中设置虚拟面D1，虚拟面D1的空间位置与第五反射镜M5的空间位置相同，设M6上出射的主光线与光轴OA平行，进一步设第六反射镜M6的半径为r₆；A virtual plane D1 is set in the light path, the spatial position of the virtual plane D1 is the same as that of the fifth mirror M5, the chief ray emitted on M6 is set to be parallel to the optical axis OA, and the radius of the sixth mirror M6 is further set to _r6 ;

在逆向光路中，其位于硅片与第六反射镜M6之间，在第六反射镜M6前方。根据像方远心的条件和硅片入射光线与第五枚反射镜之间无遮挡的条件，以及由radio₃确定的r₆，可计算出M6处于不同位置时的半径r₆，如图8所示。In the reverse light path, it is located between the silicon wafer and the sixth mirror M6, and in front of the sixth mirror M6. According to the condition of the telecentricity of the image, the condition that there is no shielding between the incident light of the silicon wafer and the fifth reflector, and the r ₆ determined by radio ₃ , the radius r ₆ of M6 at different positions can be calculated, as shown in Figure 8 shown.

${h h}_{b b 66} / / {r r}_{66} = = tan the tan {θ θ}_{b b 66}$

$= = tan the tan (({U u}_{b b 66} - - {I I}_{b b 66}))$

$= = tan the tan (({U u}_{b b 66} - - \frac{(({I I}_{b b 66} + + {I I}_{}^{b b 66}))}{22}))$

$= = tan the tan ((\frac{{U u}_{b b 66}}{22} + + \frac{{U u}_{}^{b b 66}}{22}))$

$= = tan the tan ((\frac{arctan arctan (((({h h}_{b b 66} - - (({h h}_{bD bD 11} - - CLEAPE CLEAPE 55)))) / / (({- - d d}_{55} - - {z z}_{b b 66}))))}{22} + + \frac{{U u}_{}^{b b 66}}{22}))$

于是有So there is

${r r}_{66} = = {h h}_{b b 66} / / tan the tan ((\frac{arctan arctan (((({h h}_{b b 66} - - (({h h}_{bD bD 11} - - CLEAPE CLEAPE 55)))) / / ((- - {d d}_{55} - - {z z}_{b b 66}))))}{22} + + \frac{{U u}_{}^{b b 66}}{22}))$

其中in

θ_b6为入射至第六反射镜M6上的下光线入射点法线与光轴的夹角；h_b6为入射至第六反射镜M6上的下光线与第六反射镜M6交点的高度；h_bD1为下光线与虚拟面D1交点的高度；I_b6为第六反射镜M6上的下光线入射角；I′_b6为第六反射镜M6上的下光线反射角；U_b6为第六反射镜M6入射下光线与光轴的夹角；U′_b6为第六反射镜M6出射下光线与光轴的夹角；z_b6为第六反射镜M6上主光线入射点与第六反射镜M6顶点的轴向距离。θ _b6 is the angle between the normal line of the incident point of the lower light incident on the sixth reflector M6 and the optical axis; h _b6 is the height of the intersection of the lower light incident on the sixth reflector M6 and the sixth reflector M6; h _bD1 is the height of the intersection of the lower ray and the virtual surface D1; I _b6 is the incident angle of the lower ray on the sixth reflector M6; I′ _b6 is the reflection angle of the lower ray on the sixth reflector M6; U _b6 is the sixth reflector The angle between the light ray and the optical axis under the incident M6; U′ _b6 is the angle between the light ray and the optical axis under the exit of the sixth reflector M6; z _b6 is the incident point of the chief ray on the sixth reflector M6 and the vertex of the sixth reflector M6 axial distance.

设第五反射镜的半径r₅。Let the radius r ₅ of the fifth mirror be.

如图9所示，在光路中设置虚拟面D2，虚拟面D2的空间位置与第六反射镜M6的空间位置相同，但在逆向光路中，位于第五反射镜M5与第二镜组G2之间，在第五反射镜M5后方。在计算出第六反射镜M6的半径r₆的基础上，根据第五反射镜入射光线和第六反射镜之间的无遮挡空间CLEAPE6，可以计算处M6处于不同位置时M5的半径r₅。As shown in Figure 9, a virtual surface D2 is set in the optical path, and the spatial position of the virtual surface D2 is the same as that of the sixth reflecting mirror M6, but in the reverse optical path, it is located between the fifth reflecting mirror M5 and the second mirror group G2 Between, behind the fifth mirror M5. On the basis of calculating the radius r ₆ of the sixth reflector M6, according to the unobstructed space CLEAPE6 between the incident light of the fifth reflector and the sixth reflector, the radius r ₅ of M5 when M6 is in different positions can be calculated.

${h h}_{b b 55} / / {r r}_{55} = = tan the tan {θ θ}_{b b 55}$

$= = tan the tan (({U u}_{b b 55} - - {I I}_{55}^{' '}))$

$= = tan the tan (({U u}_{b b 55} - - \frac{(({I I}_{b b 55}^{' '} + + {I I}_{b b 55}))}{22}))$

$= = tan the tan ((\frac{{U u}_{b b 55}}{22} + + \frac{{U u}_{b b 55}^{' '}}{22}))$

$= = tan the tan ((\frac{arctan arctan (((({h h}_{b b 55} - - (({h h}_{a a 66} - - CLEAPE CLEAPE 66)))) / / (({- - d d}_{55} - - {z z}_{a a 66}))))}{22} + + \frac{{U u}_{b b 55}^{' '}}{22}))$

于是有So there is

${r r}_{55} = = {h h}_{b b 55} / / tan the tan ((\frac{arctan arctan (((({h h}_{b b 55} - - (({h h}_{a a 66} - - CLEAPE CLEAPE 66)))) / / (({- - d d}_{55} - - {z z}_{a a 66}))))}{22} + + \frac{{U u}_{b b 55}^{' '}}{22}))$

其中，θ_b5为入射至第五反射镜M5上的下光线的入射点法线与光轴的夹角；h_b5为入射至第五反射镜M5上的下光线与第五反射镜M5交点的高度；h_a6为经第五反射镜M5反射的上光线与第六反射镜M6交点的高度；I_b5为第五反射镜M5上的下光线的入射角；I′_b5为第五反射镜M5上的下光线的反射角；U_b5为第五反射镜M5入射下光线与光轴的夹角；U′_b5为第五反射镜M5出射下光线与光轴的夹角；z_a6为第六反射镜M6处上光线入射点与第六反射镜M6顶点的轴向距离；Wherein, θ _b5 is the angle between the normal line of the incident point of the lower light incident on the fifth reflecting mirror M5 and the optical axis; h _b5 is the angle between the lower light incident on the fifth reflecting mirror M5 and the intersection point of the fifth reflecting mirror M5 Height; h _a6 is the height of the intersection point of the upper ray reflected by the fifth reflector M5 and the sixth reflector M6; I _b5 is the incident angle of the lower ray on the fifth reflector M5; I′ _b5 is the fifth reflector M5 The reflection angle of the upper and lower rays; U _b5 is the angle between the incident lower ray and the optical axis of the fifth reflector M5; U′ _b5 is the included angle between the fifth reflector M5 and the lower ray and the optical axis; z _a6 is the sixth The axial distance between the incident point of the upper ray at the reflector M6 and the vertex of the sixth reflector M6;

当确定d₅、r₆、r₅、BWDI后，则可计算第三镜组G3的实际物高YOB3，实际入瞳距ENP3，其中计算过程为现有技术，因此在此不进行累述。After determining d ₅ , r ₆ , r ₅ , and BWDI, the actual object height YOB3 and actual entrance pupil distance ENP3 of the third lens group G3 can be calculated. The calculation process is a prior art, so it will not be described here.

步骤106、选取第三反射镜M3的半径r₃，根据物象共轭关系、放大倍率关系、匹兹万和条件以及光瞳共轭关系，并利用上述确定的第一反射镜M1、第二反射镜M2、第五反射镜M5以及第六反射镜M6的半径以及相互之间的距离，利用近轴迭代算法获取第四反射镜M4的半径r₄、第三反射镜M3与第四反射镜M4的间距d₃、第三反射镜M3与第二反射镜M2之间的距离d₂即第三反射镜M3的物距l₃、以及第四反射镜M4的像距l′₄。Step 106: Select the radius r ₃ of the third mirror M3, according to the object-image conjugate relationship, magnification relationship, Petzwan sum condition and pupil conjugate relationship, and use the first mirror M1 and the second reflection The radii of the mirror M2, the fifth mirror M5, and the sixth mirror M6 and the distances between them, using the paraxial iterative algorithm to obtain the radius r ₄ of the fourth mirror M4, the third mirror M3 and the fourth mirror M4 The distance d ₃ between the third mirror M3 and the second mirror M2 is the distance d ₂ between the third mirror M3 and the object distance l ₃ of the third mirror M3, and the image distance l′ ₄ of the fourth mirror M4.

本步骤的具体过程为：The specific process of this step is:

如图10所示，将第二镜组作为独立的光学系统来看，其待确定的参数主要包含光学系统参数和光学结构参数。光学系统参数有第二镜组入瞳直径END2、第二镜组入瞳距ENP2（即第二镜组实际物面1001到第二镜组入瞳1002的距离）和第二镜组物高YOB2；光学结构参数包含第二镜组物面1001到第三反射镜M3的距离（l₃），第三反射镜M3到第四反射镜M4的距离（d₃），第四反射镜M4到第二镜组像面IM2的距离（l′₄），M3的半径（r₃），M4的半径（r₄）五个参数。As shown in FIG. 10 , considering the second lens group as an independent optical system, the parameters to be determined mainly include optical system parameters and optical structure parameters. The parameters of the optical system include the entrance pupil diameter END2 of the second mirror group, the entrance pupil distance of the second mirror group ENP2 (that is, the distance from the actual object plane 1001 of the second mirror group to the entrance pupil 1002 of the second mirror group) and the object height YOB2 of the second mirror group ; The optical structure parameters include the distance (l ₃ ) from the object surface 1001 of the second mirror group to the third mirror M3, the distance (d 3 ) from the third mirror M3 to the fourth mirror M4, and the distance (d ₃ ) from the fourth mirror M4 to the third mirror M3. The distance (l′ ₄ ) of the image plane IM2 of the second mirror group, the radius of M3 (r ₃ ), and the radius of M4 (r ₄ ) are five parameters.

由于第一镜组G1的结构参数已经选定，G1的出瞳直径EXD1即为G2的入瞳直径END2，即END2=EXD1；Since the structural parameters of the first lens group G1 have been selected, the exit pupil diameter EXD1 of G1 is the entrance pupil diameter END2 of G2, that is, END2=EXD1;

第一镜组G1的实际像高YIM1为第二镜组G2的实际物高YOB2，即YOB2=YIM1；The actual image height YIM1 of the first mirror group G1 is the actual object height YOB2 of the second mirror group G2, that is, YOB2=YIM1;

第一镜组G1的出瞳距EXP1即为第二镜组G2的入瞳距离ENP2，即ENP2=EXP1；The exit pupil distance EXP1 of the first mirror group G1 is the entrance pupil distance ENP2 of the second mirror group G2, that is, ENP2=EXP1;

由于第三镜组G3的结构参数已经选定，G3的入瞳距离ENP3即为第二镜组G2的出瞳距离EXP2（即第二镜组实际像面1403到第二镜组出瞳1404的距离），即EXP2=ENP3；Since the structural parameters of the third mirror group G3 have been selected, the entrance pupil distance ENP3 of G3 is the exit pupil distance EXP2 of the second mirror group G2 (that is, the distance from the actual image surface 1403 of the second mirror group to the exit pupil 1404 of the second mirror group distance), ie EXP2=ENP3;

G3的实际物高YOB3即为第二镜组G2的实际像高YIM2，即YIM2=YOB3；The actual object height YOB3 of G3 is the actual image height YIM2 of the second mirror group G2, that is, YIM2=YOB3;

使用近轴计算和迭代计算结合的方式，由上述参数可以计算出G2的结构参数。Using the combination of paraxial calculation and iterative calculation, the structural parameters of G2 can be calculated from the above parameters.

考虑G2镜组的结构参数求解，待求结构需要满足四个已知条件，即物象共轭关系，放大倍率，匹兹万和，光瞳共轭关系四个已知条件。若给出M3的半径r₃，即可求得符合相应条件的近轴解。Considering the solution of the structural parameters of the G2 lens group, the structure to be obtained needs to meet four known conditions, namely, object-image conjugate relationship, magnification, Petzwan sum, and pupil conjugate relationship. If the radius r ₃ of M3 is given, the paraxial solution meeting the corresponding conditions can be obtained.

由物象共轭关系有According to the object-image conjugation relationship, there is

$\frac{11}{{l l}_{33}} + + \frac{11}{{l l}_{33}^{' '}} = = \frac{22}{{r r}_{33}}$

l₄-l′₃＝-d₃ l ₄ -l′ ₃ =-d ₃

$\frac{11}{{l l}_{44}} + + \frac{11}{{l l}_{44}^{' '}} = = \frac{22}{{r r}_{44}}$

其中，l₃为第三反射镜M3的物距；l′₃为第三反射镜M3的像距；d₃为第三反射镜M3与第四反射镜M4的间距；l₄为第四反射镜M4的物距；l′₄为第四反射镜M4的像距；Wherein, l ₃ is the object distance of the third reflector M3; l' ₃ is the image distance of the third reflector M3; d ₃ is the distance between the third reflector M3 and the fourth reflector M4; l ₄ is the fourth reflection The object distance of mirror M4; l ' ₄ is the image distance of the 4th mirror M4;

由放大倍率关系有（这里的倍率的），From the relationship of magnification (the magnification here),

$\frac{{l l}_{44}^{' '}}{{l l}_{44}} \cdot &Center Dot; \frac{{l l}_{33}^{' '}}{{l l}_{33}} = = β β$

β为G2系统的近轴放大倍率；β is the paraxial magnification of the G2 system;

由匹兹万和条件有By Petzvan and the condition has

${pizsum pizsum}_{22} = = - - ((\frac{11}{{r r}_{11}} - - \frac{11}{{r r}_{22}} + + \frac{11}{{r r}_{55}} - - \frac{11}{{r r}_{66}}))$

则可得到then you can get

$\frac{11}{{r r}_{33}} - - \frac{11}{{r r}_{44}} = = {pizsum pizsum}_{22}$

由光阑共轭关系有By the aperture conjugate relationship, we have

$\frac{11}{(({l l}_{33} - - {enp enp}_{22}))} + + \frac{11}{{l l}_{p p 33}^{' '}} = = \frac{22}{{r r}_{33}}$

l_p4-l′_p3＝-dl _p4 -l' _p3 = -d

$\frac{11}{{l l}_{p p 44}} + + \frac{11}{{l l}_{44}^{' '} + + {exp exp}_{22}} = = \frac{22}{{r r}_{44}}$

其中，enp₂为第二镜组G2的近轴入瞳距，即令enp₂为G1的出瞳距离；l′p₃为第二镜组G2的入瞳经M3成像的近轴像距；l_p4为第二镜组G2的出瞳镜M4成像的近轴物距；exp₂为第二镜组G2的出瞳距，即令exp₂为G3的入瞳距离；Wherein, enp ₂ is the paraxial entrance pupil distance of the second mirror group G2, that is, enp ₂ is the exit pupil distance of G1; l'p ₃ is the paraxial image distance of the entrance pupil of the second mirror group G2 through M3 imaging; l _p4 is the paraxial object distance of the imaging of the exit pupil mirror M4 of the second mirror group G2; exp ₂ is the exit pupil distance of the second mirror group G2, that is, exp ₂ is the entrance pupil distance of G3;

由物象共轭关系、放大倍率关系，匹兹万和条件以及光瞳共轭关系可以解出From the object-image conjugate relationship, the magnification relationship, the Petzwan sum condition and the pupil conjugate relationship, it can be solved

${d d}_{33} = = \frac{11}{44} \cdot &Center Dot; \frac{{r r}_{33}^{22} \cdot &Center Dot; ((22 \cdot &Center Dot; {enp enp}_{22} \cdot \cdot β β \cdot \cdot {exp exp}_{22} \cdot &Center Dot; {pizsum pizsum}_{22} - - {exp exp}_{22} + + {enp enp}_{22} \cdot \cdot {β β}^{22}))}{β β \cdot \cdot {enp enp}_{22} \cdot &Center Dot; {exp exp}_{22} \cdot \cdot ((11 + + {pizsum pizsum}_{22} \cdot \cdot {r r}_{33}))}$

${l l}_{33} = = \frac{11}{22} \cdot \cdot \frac{22 \cdot &Center Dot; {enp enp}_{22} \cdot \cdot β β \cdot \cdot {exp exp}_{22} \cdot \cdot {pizsum pizsum}_{22} \cdot \cdot {r r}_{33} - - {r r}_{33} \cdot &Center Dot; {exp exp}_{22} + + {r r}_{33} \cdot \cdot {enp enp}_{22} \cdot &Center Dot; {β β}^{22} + + 22 \cdot &Center Dot; {enp enp}_{22} \cdot \cdot β β \cdot &Center Dot; exp exp + + 22 \cdot \cdot {enp enp}_{22} \cdot \cdot β β \cdot &Center Dot; {exp exp}_{22}}{- - {exp exp}_{22} + + {enp enp}_{22} \cdot &Center Dot; {β β}^{22}}$

${l l}_{33}^{' '} = = \frac{11}{44} \cdot \cdot \frac{((22 \cdot \cdot {enp enp}_{22} \cdot \cdot β β \cdot &Center Dot; {exp exp}_{22} \cdot &Center Dot; {pizsum pizsum}_{22} \cdot &Center Dot; {r r}_{33} - - {r r}_{33} \cdot &Center Dot; {exp exp}_{22} + + {r r}_{33} \cdot \cdot {enp enp}_{22} \cdot \cdot {β β}^{22} + + 22 \cdot \cdot {enp enp}_{22} \cdot \cdot {exp exp}_{22} + + 22 \cdot &Center Dot; {enp enp}_{22} \cdot &Center Dot; β β \cdot &Center Dot; {exp exp}_{22})) \cdot &Center Dot; {r r}_{33}}{((β β \cdot \cdot {r r}_{33} {\cdot \cdot pizsum pizsum}_{22} + + 11 + + β β)) {\cdot \cdot enp enp}_{22} \cdot \cdot {exp exp}_{22}}$

${l l}_{44} = = \frac{11}{44} \cdot \cdot \frac{(({r r}_{33} \cdot &Center Dot; {exp exp}_{22} + + 22 \cdot \cdot {enp enp}_{22} \cdot \cdot β β \cdot &Center Dot; {exp exp}_{22} - - {r r}_{44} \cdot &Center Dot; {enp enp}_{22} \cdot \cdot {β β}^{22} + + {22 β β}^{22} \cdot &Center Dot; {exp exp}_{22} \cdot &Center Dot; {enp enp}_{22} + + {22 β β}^{22} \cdot &Center Dot; {exp exp}_{22} \cdot \cdot {enp enp}_{22} \cdot &Center Dot; {pizsum pizsum}_{22})) \cdot &Center Dot; {r r}_{33}}{{enp enp}_{22} \cdot \cdot β β \cdot &Center Dot; {exp exp}_{22} \cdot &Center Dot; ((11 + + β β + + 22 β β \cdot \cdot {r r}_{33} \cdot \cdot {pizsum pizsum}_{22} + + {pizsum pizsum}_{22} \cdot &Center Dot; {r r}_{33} + + {pizsum pizsum}_{22}^{22} \cdot \cdot {r r}_{33}^{22} \cdot &Center Dot; β β))}$

${l l}_{44}^{' '} = = - - \frac{11}{22} \cdot &Center Dot; \frac{{r r}_{33} \cdot \cdot {exp exp}_{22} + + 22 \cdot &Center Dot; {enp enp}_{22} \cdot \cdot {β β}^{22} - - {r r}_{33} \cdot &Center Dot; {enp enp}_{22} \cdot \cdot {β β}^{22} + + {22 β β}^{22} \cdot &Center Dot; {enp enp}_{22} \cdot &Center Dot; {exp exp}_{22} + + 22 \cdot &Center Dot; {β β}^{22} \cdot \cdot {r r}_{33} \cdot \cdot {enp enp}_{22} \cdot &Center Dot; {exp exp}_{22} \cdot &Center Dot; {pizsum pizsum}_{22}}{{enp enp}_{22} \cdot &Center Dot; {β β}^{22} - - {exp exp}_{22} - - {exp exp}_{22} \cdot \cdot {pizsum pizsum}_{22} \cdot \cdot {r r}_{33} + + {r r}_{33} \cdot \cdot {β β}^{22} \cdot \cdot {pizsum pizsum}_{22} \cdot \cdot {enp enp}_{22}}$

${l l}_{p p 33}^{' '} = = \frac{11}{44} \cdot \cdot \frac{((22 \cdot &Center Dot; {enp enp}_{22} \cdot &Center Dot; β β \cdot \cdot {exp exp}_{22} \cdot &Center Dot; {pizsum pizsum}_{22} \cdot &Center Dot; {r r}_{33} - - {r r}_{33} \cdot \cdot {exp exp}_{22} + + {r r}_{33} \cdot &Center Dot; {exp exp}_{22} \cdot \cdot {β β}^{22} + + 22 \cdot &Center Dot; {enp enp}_{22} \cdot \cdot β β \cdot &Center Dot; {exp exp}_{22} + + {22 enp enp}_{22}^{22} \cdot &Center Dot; {β β}^{22}))}{(({exp exp}_{22} \cdot \cdot {pizsum pizsum}_{22} \cdot &Center Dot; {r r}_{33} + + {exp exp}_{22} + + {enp enp}_{22} \cdot &Center Dot; β β)) \cdot &Center Dot; {enp enp}_{22} \cdot &Center Dot; β β}$

${l l}_{p p 44} = = - - \frac{11}{44} \cdot &Center Dot; \frac{((- - 22 \cdot \cdot {exp exp}_{22}^{22} \cdot \cdot {pizsum pizsum}_{22} \cdot &Center Dot; {r r}_{33} - - {r r}_{33} \cdot \cdot {exp exp}_{22} - - 22 \cdot &Center Dot; {enp enp}_{22} \cdot \cdot β β \cdot \cdot {exp exp}_{22} - - 22 \cdot \cdot {exp exp}_{22}^{22} + + {r r}_{33} \cdot &Center Dot; {enp enp}_{22} \cdot \cdot {β β}^{22}))}{((22 \cdot \cdot {exp exp}_{22} \cdot &Center Dot; {pizsum pizsum}_{22} \cdot &Center Dot; {enp enp}_{22} + + {pizsum pizsum}_{22}^{22} \cdot \cdot {r r}_{33}^{22} \cdot \cdot {exp exp}_{22} + + {enp enp}_{22} \cdot \cdot β β + + {enp enp}_{22} \cdot &Center Dot; β β \cdot \cdot {pizsum pizsum}_{22} \cdot &Center Dot; {r r}_{33} + + {exp exp}_{22}))}$

r₄＝r₃/(1+pizsum₂·r₃)r ₄ =r ₃ /(1+pizsum ₂ ·r ₃ )

则可计算出第四反射镜M4的半径r₄、第三反射镜M3与第四反射镜M4的间距d₃、第三反射镜M3的物距l₃以及第四反射镜M4的像距l′₄。Then the radius r ₄ of the fourth mirror M4, the distance d ₃ between the third mirror M3 and the fourth mirror M4, the object distance l ₃ of the third mirror M3 and the image distance l of the fourth mirror M4 can be calculated ' ₄ .

步骤107、根据上述步骤计算的6枚反射镜的半径以及相应的位置关系，得到极紫外光刻投影物镜。Step 107, according to the radii and corresponding positional relationships of the six mirrors calculated in the above steps, obtain the EUV lithography projection objective lens.

上述r₃是人为根据经验随机选取，但是由于输入的条件参数均为非近轴参数，上式计算得到的参数一般不符合非近轴参数的要求，但是可以借助这一近轴参数的变化趋势，判断G1和G3的组合条件下，是否存在合理的G2与之匹配，并依据这一变化趋势确定r₃的范围。The above r ₃ is randomly selected based on experience, but since the input condition parameters are all non-paraxial parameters, the parameters calculated by the above formula generally do not meet the requirements of non-paraxial parameters, but the change trend of this paraxial parameter can be used , to determine whether there is a reasonable G2 to match under the combination of G1 and G3, and determine the range of _r3 according to this trend.

本发明将第二镜组G2作为独立的光学系统，将G2系统的近轴放大倍率β＝M₂，这里M₂＝YOB3/YIM1、第二镜组G2的近轴入瞳距enp₂等于G1的出瞳距离即enp₂＝ENP2、第二镜组G2的出瞳距exp₂等于G3的入瞳距离即exp₂＝EXP2、1500mm＞(-l₃-enp₂)＞0以及0＞d₃＞1500mm作为约束条件，根据物象共轭关系、放大倍率、匹兹万和以及光瞳共轭关系，确定r₃的范围，从获取的范围中选取一值作为第三反射镜M3的半径。In the present invention, the second mirror group G2 is used as an independent optical system, and the paraxial magnification of the G2 system is β=M ₂ , where M ₂ =YOB3/YIM1, and the paraxial entrance pupil distance enp ₂ of the second mirror group G2 is equal to G1 The exit pupil distance of enp ₂ =ENP2, the exit pupil distance exp ₂ of the second mirror group G2 is equal to the entrance pupil distance of G3, namely exp ₂ =EXP2, 1500mm>(-l ₃ -enp ₂ )>0 and 0>d ₃ >1500mm is used as a constraint condition, and the range of _r3 is determined according to the object-image conjugate relationship, magnification, Petzwan sum and pupil conjugate relationship, and a value is selected from the acquired range as the radius of the third mirror M3.

下面举例说明有G2镜头组的近轴解选择r₃的范围。输入参数的值如表1所示。The following example illustrates the range of r ₃ selected for the paraxial solution with the G2 lens group. The values of the input parameters are shown in Table 1.

表1Table 1

1/r₃ 1/r ₃ -0.002~0.002 -0.002~0.002 入瞳距离ENP2 Entrance pupil distance ENP2 -1883.508480 -1883.508480 出瞳距离EXP2 Exit pupil distance EXP2 352.613104 352.613104 匹兹万和pizsum₂ pizwan and pizsum ₂ -0.000811 -0.000811 放大倍率M₂ Magnification M ₂ -0.496181 -0.496181

入瞳直径END2 Entrance pupil diameter END2 143.574801 143.574801 物高YOB2 Wugao YOB2 -174.424131 -174.424131

令make

enp₂＝ENP2 _enp2 = ENP2

exp₂＝EXP2exp ₂ = EXP2

β＝M₂ β=M ₂

得到各参数随1/r₃的变化而变化的图表如图11(a)~图11(d)所示。对于可用的EUVL光刻投影系统，要求系统长度控制在一定范围内。这里将系统物理总长控制在2000mm以内，且M3应位于M2后方，M4位于M3前方，且间距应比系统总长稍短，所以1500mm＞(-l₃-enp₂)＞0且0＞d₃＞1500mm。The graphs obtained for each parameter changing with the change of 1/r ₃ are shown in Fig. 11(a) ~ Fig. 11(d). For available EUVL lithography projection systems, the system length is required to be controlled within a certain range. Here, the total physical length of the system is controlled within 2000mm, and M3 should be located behind M2, and M4 should be located in front of M3, and the spacing should be slightly shorter than the total system length, so 1500mm＞(-l ₃ -enp ₂ )＞0 and 0＞d ₃ ＞ 1500mm.

为了方便起见，我们将可用区间以外的物距和间距都设为零，图11(a)和图11(b)即变为图12(a)和图12(b)，得到的图表即可较为清晰地看到r₃的可用范围，比较图12(a)和图12(b)，可知在这一组实际条件下，是否存在可用的G2解。For the sake of convenience, we set the object distance and spacing outside the available range to zero, and Figure 11(a) and Figure 11(b) become Figure 12(a) and Figure 12(b), and the obtained charts can be To see the available range of r ₃ more clearly, compare Figure 12(a) and Figure 12(b), to know whether there is an available G2 solution under this set of actual conditions.

由上面图表可知，1/r₃的可用范围约为0.0005~0.002。即r₃的范围为500mm~2000mm。As can be seen from the above chart, the usable range of 1/r ₃ is about 0.0005~0.002. That is, the range of r ₃ is 500mm~2000mm.

由于给定G2系统的近轴放大倍率β与实际放大倍率M₂不同，G2系统的近轴出瞳距离exp₂与实际出瞳距离EXP₂不同，上述计算得到的光学系统参数并不能直接作为第二组参数计算的结果。Since the paraxial magnification β of the given G2 system is different from the actual magnification M ₂ , and the paraxial exit pupil distance exp ₂ of the G2 system is different from the actual exit pupil distance EXP ₂ , the optical system parameters obtained by the above calculation cannot be directly used as the first The result of calculating the two sets of parameters.

事实上，对于任意两个球面反射镜组成的视场离轴光学系统，上述两个参量的近轴值与实际值都不可能相同。In fact, for an off-axis optical system of field of view composed of any two spherical mirrors, the paraxial and actual values of the above two parameters cannot be the same.

但是对于任意一个两球面反射镜组成的视场离轴光学系统，当其实际的参数符合要求时，必定存在一组相应的近轴参数值。我们可以通过比较逼近的方法求得。具体方法如下：But for any field of view off-axis optical system composed of two spherical mirrors, when its actual parameters meet the requirements, there must be a set of corresponding paraxial parameter values. We can obtain it by the method of comparison and approximation. The specific method is as follows:

下面进一步对G2光学参数进行优化，具体步骤为：Next, further optimize the optical parameters of G2, the specific steps are:

步骤501、选取第三反射镜M3的半径r₃，设定误差因子ξ_B和

，并令β(1)＝M₂，令exp₂(1)＝EXP2，设定循环次数k＝1；Step 501, select the radius r ₃ of the third mirror M3, set the error factor ξ _B and

, and let β(1)=M ₂ , let exp ₂ (1)=EXP2, set the number of cycles k=1;

步骤502、利用β(k)、exp₂(k)以及所选取的r₃，根据物象共轭关系、放大倍率关系、匹兹万和条件以及光瞳共轭关系，求出G2系统的结构参数d₃(k)、l₃(k)、l₄′(k)以及r₄(k)；Step 502, using β(k), exp ₂ (k) and the selected r ₃ , according to the object-image conjugate relationship, magnification relationship, Petzwan sum condition and pupil conjugate relationship, find the structural parameters of the G2 system _d3 (k), _l3 (k), l4 _' (k) and _r4 (k);

步骤503、r₃、d₃(k)、l₃(k)、l₄′(k)以及r₄(k)输入到光学设计软件CODEV中，获取第二反射镜组G2的实际放大倍率M₂(k)以及实际出瞳距离EXP2(k)；Step 503, r ₃ , d ₃ (k), l ₃ (k), l ₄ ′(k) and r ₄ (k) are input into the optical design software CODEV to obtain the actual magnification M of the second mirror group G2 ₂ (k) and the actual exit pupil distance EXP2(k);

步骤204、判断且|M₂(k)-M₂|≤ξ_B是否成立，若是则结束优化，将此时的r₃、d₃(k)、l₃(k)、l₄′(k)以及r₄(k)作为第二反射镜组G2的结构参数，若否，则进入步骤505；Step 204, judge And whether |M ₂ (k)-M ₂ |≤ξ _B is true, if so, then the optimization will end, and r ₃ , d ₃ (k), l ₃ (k), l ₄ ′(k) and r ₄ (k) as the structural parameters of the second mirror group G2, if not, enter step 505;

步骤505、令β(k+1)＝β(k)·[M₂/M₂(k)]^σ，exp₂(k+1)＝exp₂(k)·[EXP2/EXP2(k)]^σ，其中σ≤1，令k加1，返回步骤502。Step 505, set β(k+1)=β(k)·[M ₂ /M ₂ (k)] ^σ , exp ₂ (k+1)=exp ₂ (k)·[EXP2/EXP2(k)] ^σ , where σ≤1, add 1 to k and return to step 502.

本发明

这里我们称[M₂/M₂(k)]^σ和[EXP2/EXP2(k)]^σ为逼近因子；若此时的G2解空间较小，当σ＝1时，[M₂/M₂(k)]¹和[EXP2/EXP2(k)]¹以这一对逼近因子对近轴放大倍率和近轴出瞳距进行处理，可能导致结果跳出合理的结构参数范围，或使得逼近结果不收敛。所以可以选取即逼近因子为[M₂/M₂(k)]^1/2和[EXP2/EXP2(k)]^1/2，或

即逼近因子为[M₂/M₂(k)]^1/4和[EXP2/EXP2(k)]^1/4，第三组逼近因子搜索过程比较稳定，但是其迭代次数较多，第二种因子介于第一组因子和第三组因子之间，应用范围比较广，一般能够满足计算的要求。this invention

Here we call [M ₂ /M ₂ (k)] ^σ and [EXP2/EXP2(k)] ^σ as approximation factors; if the G2 solution space at this time is small, when σ=1, [M ₂ /M ₂ (k)] ¹ and [EXP2/EXP2(k)] ¹ use this pair of approximation factors to process the paraxial magnification and paraxial exit pupil distance, which may cause the results to jump out of the reasonable range of structural parameters, or make the approximation results incorrect. convergence. so you can choose i.e. approximation factors of [M ₂ /M ₂ (k)] ^1/2 and [EXP2/EXP2(k)] ^1/2 , or

That is, the approximation factors are [M ₂ /M ₂ (k)] ^1/4 and [EXP2/EXP2(k)] ^1/4 . The search process of the third group of approximation factors is relatively stable, but the number of iterations is relatively large. The second group Factors are between the first group of factors and the third group of factors, and have a wide range of applications, generally meeting the calculation requirements.

图13为σ＝1时，第二镜组的实际放大倍率M2随迭代次数增加的收敛情况。FIG. 13 shows the convergence of the actual magnification M2 of the second mirror group as the number of iterations increases when σ=1.

本发明的实施实例：Implementation example of the present invention:

图14(a)为任意选定了一组G1的结构，该结构的光阑位于第二面反射镜上。物方主光线入射角度定为5°。该结构的元件排布合理，加工难度比较低，G1的光学系统参数和光学结构参数如表2所示，其中

Fig. 14(a) shows a structure in which a group of G1 is randomly selected, and the diaphragm of the structure is located on the second mirror. The incident angle of the chief ray on the object side is set at 5°. The components of this structure are arranged reasonably, and the processing difficulty is relatively low. The optical system parameters and optical structure parameters of G1 are shown in Table 2, where

表2Table 2

NAO NAO 0.05 0.05 CA CA 5.00000 5.00000 radio₁ radio ₁ 0.153 0.153 radio₂ radio ₂ 0.352 0.352 YOB YOB 132.5000 132.5000 -l₁ -l ₁ 304.7500 304.7500 -d₁ -d ₁ -304.749986 -304.749986 r₁ r ₁ -1160.173602 -1160.173602 r₂ r ₂ -9301.878824 -9301.878824 l₂′l ₂ ' 1970.7450 1970.7450 YIM1 YIM1 -368.998492 -368.998492 EXP1 EXP1 1970.744988 1970.744988 pizsum₁ pizsum ₁ -0.000754435 -0.000754435

图14(b)为任意选定了一组G3的结构,G3的光学系统参数和光学结构参数如表3所示,其中

Figure 14(b) shows the structure of a group of G3 selected arbitrarily, and the optical system parameters and optical structure parameters of G3 are shown in Table 3, where

表3table 3

NAI NAI 0.25 0.25 CA CA telecentricity telecentricity radio₃ radio ₃ 9.000000 9.000000 YIM YIM 26.5000 26.5000 l₆′l ₆ ' 320.0000 320.0000 d₅ d ₅ -288.0000 -288.0000 r₆ r ₆ -358.854572 -358.854572 r₅ r ₅ -411.048060 -411.048060 -l₅ -l ₅ 273.972300 273.972300

YOB3 YOB3 -76.985423 -76.985423 ENP3 ENP3 354.566741 354.566741 pizsum₃ pizsum ₃ -0.000354 -0.000354

根据上述G1和G2的结构参数，得到G2计算所需的参数如表4所示。According to the above structural parameters of G1 and G2, the parameters required for the calculation of G2 are obtained as shown in Table 4.

表4Table 4

1/r₃ 1/r ₃ -0.002~0.002 -0.002~0.002 入瞳距离ENP2 Entrance pupil distance ENP2 -1970.744988 -1970.744988 出瞳距离EXP2 Exit pupil distance EXP2 354.566741 354.566741 匹兹万和pizsum₂ pizwan and pizsum ₂ -0.001108 -0.001108 放大倍率M² Magnification M ² -0.208633 -0.208633 入瞳半径END2 Entrance pupil radius END2 72.144399 72.144399 物高YOB2 Wugao YOB2 -368.998492 -368.998492

计算得到r₃半径为500mm，450mm，-500mm的G2结构三种，其光路图如图14(c)所示。Three types of G2 structures with r ₃ radii of 500mm, 450mm, and -500mm are obtained through calculation, and their optical path diagrams are shown in Figure 14(c).

衔接上述三个镜组，对于不同的G2镜组，得到的六反射投影物镜结构如图14（d）所示。比较图14（d）中的几种结构，表7为下面表5、表6和表7中参数确定的三个结构的系统总长和最大反射镜口径的比较，其中c₁＝1/r₁，c₂＝1/r₂，c₃＝1/r₃，c₄＝1/r₄，c₅＝1/r₅，c₆＝1//r₆，d₁。d₁为掩膜与第一反射镜M1的间距，d₂～d₆为第一至第五反射镜M1~M5与相应后一反射镜的间距，d₇为第六反射镜M6与硅片的间距。M3位于物面（掩膜101）的前方，不利于步进工件台的工作。结构一（embodiment1）的系统总长比较短，但最大元件口径较大。结构三（embodiment3）的最大元件口径比较小，但是系统总长相对较长。可以根据工程实际的需要选择适当的M3半径。Connecting the above three mirror groups, for different G2 mirror groups, the structure of the obtained six-reflection projection objective lens is shown in Fig. 14(d). Comparing the several structures in Figure 14(d), Table 7 shows the comparison of the total system length and maximum mirror aperture of the three structures determined by the parameters in Table 5, Table 6 and Table 7 below, where c ₁ =1/r ₁ , c ₂ =1/r ₂ , c ₃ =1/r ₃ , c ₄ =1/r ₄ , c ₅ =1/r ₅ , c ₆ =1//r ₆ , d ₁ . d ₁ is the distance between the mask and the first mirror M1, d ₂ to d ₆ are the distances between the first to fifth mirrors M1 to M5 and the corresponding subsequent mirrors, d ₇ is the distance between the sixth mirror M6 and the silicon wafer Pitch. M3 is located in front of the object plane (mask 101), which is not conducive to the work of stepping on the workpiece table. The overall system length of structure one (embodiment1) is relatively short, but the maximum component diameter is relatively large. Structure 3 (embodiment3) has a relatively small maximum component diameter, but the overall system length is relatively long. The appropriate M3 radius can be selected according to the actual needs of the project.

表5table 5

表6Table 6

表7Table 7

表8Table 8

System# System# Total length Total length Max diameter Max diameter

System1 System1 1737.1874 1737.1874 888.3862 888.3862 System2 System2 1779.8679 1779.8679 771.7360 771.7360 System3 System3 1769.1643 1769.1643 407.6502 407.6502

其他几种通过分组择选的系统如图15(a)、图15(b)、图15(c)所示。其结构参数如表9、表10、表11所示。其中某些结构可能并不利于工程实现，此处仅作为分组择选搜索法的实施示例。Other systems selected by grouping are shown in Figure 15(a), Figure 15(b), and Figure 15(c). Its structural parameters are shown in Table 9, Table 10, and Table 11. Some of these structures may not be conducive to engineering implementation, and this is only used as an implementation example of the group selection search method.

表9Table 9

表10Table 10

表11Table 11

图16为典型的极紫外光刻系统示意图，光束由光源1601出射后，经照明系统1602整形和匀光，照射到反射式掩膜101上。经掩膜101反射后，光线入射至投影物镜系统1603，最终在涂覆有极紫外光刻胶的硅片102上曝光成像。本发明设计得到的EUVL投影光刻物镜可以应用于该系统当中。波长为13.5nm的极端紫外光源发射激光，经照明系统后，照射到掩膜上，经掩膜反射后，沿光路方向依次经第一反射镜M1、第二反射镜M2、第三反射镜M3、第四反射镜M4组成，成中间像，中间像经第五反射镜M5、第六反射镜M6成像于硅片上。FIG. 16 is a schematic diagram of a typical EUV lithography system. After the light beam exits from the light source 1601 , it is shaped and homogenized by the illumination system 1602 and irradiates onto the reflective mask 101 . After being reflected by the mask 101, the light enters the projection objective lens system 1603, and is finally exposed and imaged on the silicon wafer 102 coated with EUV photoresist. The EUVL projection lithography objective lens designed by the present invention can be applied to the system. An extreme ultraviolet light source with a wavelength of 13.5nm emits laser light. After passing through the illumination system, it irradiates onto the mask. After being reflected by the mask, it passes through the first reflector M1, the second reflector M2, and the third reflector M3 in sequence along the optical path. , the fourth mirror M4 to form an intermediate image, and the intermediate image is imaged on the silicon wafer through the fifth mirror M5 and the sixth mirror M6.

虽然结合附图描述了本发明的具体实施方式，但是对于本技术领域的技术人员来说，在不脱离本发明的前提下，还可以做若干变形、替换和改进，这些也视为属于本发明的保护范围。Although the specific implementation of the present invention has been described in conjunction with the accompanying drawings, for those skilled in the art, without departing from the premise of the present invention, some modifications, replacements and improvements can also be made, and these are also considered to belong to the present invention scope of protection.

Claims

1. a design method of extreme ultraviolet lithography projection objective lens, is characterized in that, concrete steps are:

Step 101, determine that the projection objective lens in the lithography system has a six-mirror structure, and set the optical system parameters of the projection objective lens; select six reflectors and apertures to be arranged between the mask and the silicon wafer in the lithography system, and six The setting positions of mirrors and diaphragms: starting from the mask along the direction of the optical path are the first mirror (M1), the diaphragm, the second mirror (M2), the third mirror (M3), and the fourth mirror ( M4), the fifth reflector (M5) and the sixth reflector (M6), and the diaphragm is placed on the second reflector (M2); determine the ratio parameter between each reflector; wherein

The optical system parameters include the magnification M of the projection objective lens, the object-side field of view height YOB, the object-side field of view width FWOB, the image-side field of view height YIM, the image-side field of view width FWIM, the image-side exposure field of view chord length CL, The maximum chief ray incident angle MAXCA1～MAXCA6 of each reflector, the total length TTL of the projection objective lens, the minimum front working distance FWDI, and the minimum rear working distance BWDI;

The ratio parameters between the mirrors include the ratio parameter radio ₁ of the height of the field of view on the object side and the distance from the mask to the first mirror M1, the distance from the second mirror M2 to the first mirror M1 and the distance from the mask to the first mirror M1. The ratio parameter radio ₂ of the distance of the mirror M1, the space CLEAPE1 where the light emitted by the first mirror M1 and the second mirror M2 is not blocked, the distance between the fifth mirror M5 and the sixth mirror M6 and the distance from the silicon wafer to the fifth mirror The ratio parameter radio ₃ of the mirror M5 to BWDI, the space where the incident light of the sixth reflector M6 and the fifth reflector M5 does not block CLEAPE6, the space where the light emitted by the sixth reflector M6 and the fifth reflector M5 do not block CLEAPE5;

Step 102, calculating the distance from the mask to the first reflector (M1) is -l ₁ and the distance from the second reflector (M2) to the first reflector (M1) is -d ₁ , and obtain the first reflector ( The current radius of M1) is r ₁ ;

Step 103, given the object-space numerical aperture NAO and the object-space chief ray incident angle CA, according to the -d ₁ and r ₁ , judge whether the optical system parameters given in step 101 are reasonable, and the specific judgment process is as follows:

Step 201, calculating the upper limit value Uradio ₂ of the ratio radio ₂ of the distance from the second reflector (M2) to the first reflector (M1) and the mask to the distance from the first reflector (M1) in the ratio parameter;

Uradio ₂ = l-FWDI·radio ₁ /YOB

Among them, FWDI is the minimum object working distance of the projection objective, YOB is the height of the object field of view of the projection objective, and radio ₁ is the ratio parameter between the height of the object field of view and the distance from the mask to the first mirror (M1);

Step 202, given the object-space numerical aperture NAO and the object-space chief ray incident angle CA, set the search step size of radio ₂ to ξ _r2 , set the number of cycles k=1, radio ₂ (1)=0, radio ₂ ’s Lower limit Dradio ₂ = 0;

Step 203, judge whether radio ₂ (k) is less than Uradio ₂ , if so, then enter step 204, otherwise enter step 209;

Step 204: Calculate CLEAPE2(k) and/or CA ₁ (k) of the projection system designed using radio ₂ (k) according to the -d ₁ and r ₁ , according to the principle of ray tracing, where CLEAPE2(k) Indicates the space where the rays emitted by the second reflector (M2) and the first reflector (M1) are not blocked, and CA ₁ (k) represents the incident angle of the first reflector (M1 main) light;

Step 205, judge the type of parameter calculated in step 204, when only CLEAPE2(k) is calculated, then enter step 206, when only CA ₁ (k) is calculated, then enter step 207, when simultaneously calculate CLEAPE2 (k) and CA ₁ (k), then enter step 208;

Step 206, judge whether CLEAPE2(k)>0 is set up, if so, radio ₂ (k) is then determined as the lower limit value Dradio ₂ of radio ₂ at this moment, promptly makes Dradio ₂ =radio ₂ (k), enters step 209, otherwise Make k=k+1, make radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , return to step 203;

Step 207, judging whether CA ₁ (k)＜MAXCA1 is established, if so, radio ₂ (k) is then determined as the lower limit value Dradio ₂ of radio ₂ at this moment, promptly makes Dradio ₂ =radio ₂ (k), enters step 209, Wherein MAXCA1 is the maximum chief ray incident angle of the first reflector given in advance, otherwise let k=k+1, make radio ₂ (k)=radio ₂ (k-1)+ξ _{r 2} , return to step 203;

Step 208, judge whether CA ₁ (k)<MAXCA and CLEAPE2(k)>0 are all established, if so, determine radio ₂ (k) at this time as the lower limit value Dradio ₂ of radio ₂ , that is, make Dradio ₂ =radio ₂ (k), enter step 209, otherwise let k=k+1, make radio ₂ (k)=radio ₂ (k-1)+ξ _r2 , return to step 203;

Step 209, judging whether Dradio ₂ = 0 is established, if so, then judging that the optical system parameters of the given projection objective lens are unreasonable, there is no distance from the second reflector (M2) to the first reflector (M1) and the distance from the mask to The proportional parameter radio ₂ of the first mirror (M1) distance, and end, if not, output Dradio ₂ and enter step 104;

Step 104, according to the distance- _d1 from the second reflector (M2) to the first reflector (M1), calculate the radius of the second reflector (M2) as _r2 ;

Step 105, calculate the distance between the fifth reflector (M5) and the sixth reflector (M6) as _d5 , and obtain the radius _r5 and the sixth reflector of the fifth reflector (M5) according to _d5 The radius _r6 of the mirror (M6);

Step 106: Select the radius r ₃ of the third reflector (M3), according to the conjugate relationship of the object image, the relationship of magnification, the Petzwan sum condition and the conjugate relationship of the pupil, and use the first reflector (M1) determined above , the radii of the second reflector (M2), the fifth reflector (M5) and the sixth reflector (M6) and the distances between them, and the radius r ₄ of the fourth reflector (M4) is obtained using the paraxial iterative algorithm , the distance d ₃ between the third mirror (M3) and the fourth mirror (M4), the distance d ₂ between the third mirror (M3) and the second mirror, and the image of the fourth mirror (M4) Distance l'₄;

Step 107 , according to the radii and corresponding positional relationships of the six mirrors calculated in the above steps, the EUV lithography projection objective lens is obtained.

2. according to the described extreme ultraviolet projection lithography objective lens design method of claim 1, it is characterized in that, when judging that Dradio ₂ =0 is not established, before entering step 104, utilize radio ₁ to further judge the given optical system parameter of step 101 Whether it is reasonable; the specific process is:

Step 301, set the search step size of radio ₁ to ξ _r1 , set the number of cycles k'=1, radio ₁ (1)=YOB/TTL, set N to be greater than (YOB/FWDI-YDB/TTL)/ξ The smallest integer of _r1 , let the upper limit of radio ₁ Uradio ₁ =YOB/TTL+(N-1)×ξ ₁ , let the lower limit of radio ₁ Dradio ₁ =YOB/TTL+(N-1)×ξ _r1 , where YOB is the projection light The height of the object field of view of the engraving objective, TTL is the total length of the projection lithography objective, and FWDI is the minimum front working distance of the projection lithography objective;

Step 302, determine whether the number of cycles k'>N is established, if so, then enter step 306, otherwise let k'=k'+1, make radio ₁ (k')=radio ₁ (k'-1)+ξ _r1 , And go to step 303;

Step 303, update the parameter radio ₁ in the projection system to be radio ₁ (k'), repeat steps 201 to 209, judge whether Dradio ₂ =0 is established, if so then return to step 302, otherwise make Dradio ₁ =radio ₁ (k') , and enter step 304;

Step 304, determine whether the number of cycles k'>N is established, if so, then enter step 306, otherwise let k'=k'+1, make radio ₁ (k')=radio ₁ (k'-1)+ξ _r1 , And go to step 305;

Step 305, update the parameter radio ₁ in the projection system to be radio ₁ (k'), repeat steps 201 to 209, judge whether Dradio ₂ =0 is established, if so then enter step 306, otherwise make Uradio ₁ =radio ₁ (k') , and return to step 304;

Step 306 , judging whether Dradio ₁ =Uradio ₁ holds true, if yes, then judging that the given system parameters in step 101 are unreasonable, and end, if not, output Uradio ₁ and Dradio ₁ and enter step 104 .

3. according to the described extreme ultraviolet projection lithography objective lens design method of claim 1, it is characterized in that, after calculating r ₂ , the output of the first reflecting mirror (M1) and the second reflecting mirror (M2) to setting is further Judgment is made by CLEAPE1 in the space where light is not blocked, and when CLEAPE1>0 and CLEAPE1<UCLEAPE1 are both established, then enter step 105, otherwise the judgment is unreasonable according to the given system parameters, and end;

UCLEAPEl UCLEA El = = {h h}_{b b 11} - - \frac{- - {d d}_{11} \cdot \cdot {l l}_{11}^{' '} \cdot \cdot {radio radio}_{11}}{{l l}_{22}}

Where h _b1 is the height of the intersection of the upper ray and the first mirror (M1), l' ₁ is the image distance of the mask pattern passing through the first mirror (M1), l ₂ =l ₁ ′-d ₁ .