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高端芯片制造所需要的极紫外光刻技术位于我国当前面临35项“卡脖子”关键核心技术之首. 高转换效率的极紫外光源是极紫外光刻系统的重要组成部分. 本文通过采用双激光脉冲打靶技术实现较强的6.7 nm极紫外光输出. 首先, 理论计算Gd18+—Gd27+离子最外层4d壳层的4p-4d和4d-4f能级之间跃迁、以及Gd14+—Gd17+离子最外层4f壳层的4d-4f能级之间跃迁对波长为6.7 nm附近极紫外光的贡献. 其后开展实验研究, 结果表明, 随着双脉冲之间延时的逐渐增加, 波长为6.7 nm附近的极紫外光辐射强度呈现先减弱、后增加、之后再减弱的变化趋势, 在双脉冲延时为100 ns处产生的极紫外光辐射最强. 并且, 在延时为100 ns处产生的光谱效率最高, 相比于单脉冲激光产生的光谱效率提升了33%. 此外, 发现双激光脉冲打靶技术可以有效地减弱等离子体的自吸收效应, 获得的6.7 nm附近极紫外光谱宽度均小于单激光脉冲打靶的情形, 且在脉冲延时为30 ns时刻所产生的光谱宽度最窄, 约为单独主脉冲产生极紫外光谱宽度的1/3. 同时, Gd极紫外光谱的变窄提高了波长为6.7 nm (0.6%带内)附近的光谱利用效率.The extreme ultraviolet (EUV) lithography technology, which is required for high-end chip manufacturing, is the first of 35 “neck stuck” key core technologies that China is facing currently. The EUV source with high conversion efficiency is an important part of EUV lithography system. The experiment on dual-pulse irradiated Gd target is carried out to realize the stronger 6.7 nm EUV emission output. Firstly, we compute the contribution of transition arrays of the form 4p-4d and 4d-4f from their open 4d subshell in charge states Gd18+−Gd27+, and transition arrays of the form 4d-4f from their open 4d subshell in charge states Gd14+−Gd17+ on the near 6.7 nm EUV source. Subsequently, the experimental results of the dual pulse laser irradiated Gd target show that the intensity of 6.7 nm peak EUV emission decreases first, then increases and drops again due to the plasma density decreasing gradually when the delay time between the pre-pulse and main-pulse increases from 0−500 ns. The strongest intensity of 6.7 nm peak EUV emission is generated when the delay time is 100 ns. At the same time, the spectrum efficiency is higher when the delay time is 100 ns, which is 33% higher than that of single pulse laser. In addition, the experimental results show that the half width of EUV spectrum produced by dual pulse in the delay between 10−500 ns is narrower than that of signal laser pulse due to the fact that the method of dual pulse can suppress the self-absorption effect. The half width is the narrowest when the delay is 30 ns, which is about 1/3 time of EUV spectrum width generated by a single pulse. At the same time, the narrowing of Gd EUV spectrum improves the spectral utilization efficiency near 6.7 nm wavelength (within 0.6% bandwidth).
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Keywords:
- extreme ultraviolet source /
- dual pulse laser /
- laser produce Gd plasma /
- spectrum efficiency
[1] Schmitz C, Wilson D, Rudolf D, Wiemann C, Plucinski L, Riess S, Schuck M, Hardtdegen H, Schneider C M, Tautz F S, Juschkin L 2016 Appl. Phys. Lett. 108 234101
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[31] Li B W, Dunne P, Higashiguchi T, Otsuka T, Yugami N, Jiang W H, Endo A, O'Sullivan G 2011 Appl. Phys. Lett. 99 231502
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[32] National Institute of Standards and Technology https://nlte.nist.gov/FLY/ [2018-8]
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图 1 双激光脉冲打靶形成Gd等离子体的极紫外光谱辐射实验装置图
Fig. 1. Experimental setup for the characteristics of EUV emission from Gd plasma produced by dual laser.
图 2 Gd靶激光等离子体极紫外光辐射实验曲线(黑色)和理论计算Gd不同离子价态自发辐射速率与波长之间的关系(红色). 图中的14+—27+表示Gd离子阶数. Gd18+—Gd27+离子的跃迁类型为Δn = 0, n = 4, 4p64dm-4p54dm+1 + 4dm–14f (m = 1—10), Gd14+—Gd17+离子的跃迁类型为Δn = 0, n = 4, 4d104fm-4d94fm+1 (m = 1—4)和Δn = 1, n = 4, n = 5, 4d104f-4d94fm–15d + 4d94fm–15g (m = 1—4)
Fig. 2. Experimental waveform of laser produced Gd plasma EUV emission (black line), and the transition probabilities of Gd14+−Gd27+ computed with the Cowan code including the effects of CI (red line). The transition type of Gd18+− Gd27+ is Δn = 0, n = 4, 4p64dm-4p54dm+1 + 4dm–14f (m = 1−10). And the transition type of Gd14+− Gd17+ is Δn = 0, n = 4, 4d104fm-4d94fm+1 (m = 1−4), and Δn = 1, n = 4, n = 5, 4d104f-4d94fm–15d + 4d94fm–15g (m = 1−4).
图 3 不同延时下, (a) 6.7 nm极紫外光辐射曲线以及(b) 6.7 nm峰值附近处辐射强度. 主脉冲激光功率为2 × 1012 W/cm2、预脉冲激光功率为2.2 × 1010 W/cm2
Fig. 3. (a) The impendence of 6.7 nm EUV spectrum radiation and (b) the radiation intensity of the 6.7 nm peak on the different delay time with the main pulse laser density of 2 × 1012 W/cm2 and pre-pulse laser density of 2.2 × 1010 W/cm2.
图 4 延时为30, 100 ns和主脉冲三种情况下的极紫外光谱宽度对比图
Fig. 4. Comparisons of EUV spectral widths under the delay of 30, 100 ns and main pulse.
图 5 在电子密度为1019 (a)和1020 cm–3 (b)条件下, 离子丰度与电子温度之间的关系, 图中的14+—25+表示Gd 离子阶数
Fig. 5. Ionic populations of Gd plasma as a function of Te under the electron density of 1019 (a) and 1020 cm–3 (b). The numbers in the figure are represented the ion stages of Gd plasma.
图 6 固定电子温度为100 eV条件下, Gd18+离子丰度与电子密度之间的关系
Fig. 6. The Gd18+ ion population dependence of electron density under the electron temperature of 100 eV.
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[1] Schmitz C, Wilson D, Rudolf D, Wiemann C, Plucinski L, Riess S, Schuck M, Hardtdegen H, Schneider C M, Tautz F S, Juschkin L 2016 Appl. Phys. Lett. 108 234101
Google Scholar
[2] Barkusky F, Bayer A, Döring S, Flöter B, Großmann P, Peth Cn, Reese M, Mann K 2010 The International Society for Optical Engineering. Prague, Czech Republic April 20, 2009 p7361
[3] Wagner C, Harned N 2010 Nat. Photonics 4 24
Google Scholar
[4] Torretti F, Sheil J, Schupp R, Basko M M, Bayraktar M, Meijer R A, Witte S, Ubachs W, Hoekstra R, Versolato O O, Neukirch A J, Colgan J 2020 Nat. Commun. 11 1
[5] Torretti F, Liu F, Bayraktar M, Scheers J, Bouza Z, Ubachs W, Hoekstra R, Versolato O O 2019 J. Phys. D: Appl. Phys. 53 055204
Google Scholar
[6] Versolato O O 2019 Plasma Sources Sci. Technol. 28 083001
Google Scholar
[7] Huang Q S, Medvedev V, Kruijs R V D, Yakshin A, Louis E, Bijkerk F 2017 Appl. Phys. Rev. 4 011104
Google Scholar
[8] Wu B Q, Kumar A 2007 J. Vac. Sci. Technol., B 25 1743
Google Scholar
[9] Sasaki A, Nishihara K, Sunahara A, Furukawa H, Nishikawa T, Koike F 2010 Appl. Phys. Lett. 97 231501
Google Scholar
[10] Wezyk A V, Andrianov K, Wilhein T, Bergmann K 2019 J. Phys. D: Appl. Phys. 52 505202
Google Scholar
[11] Chkhalo N I, Künstner S, Polkovnikov V N, Salashchenko N N, Schäfers F, Starikov S D 2013 Appl. Phys. Lett. 102 011602
Google Scholar
[12] Yoshida K, Fujioka S, Higashiguchi T, Ugomori T, Tanaka N, Kawasaki M, Suzuki Y, Suzuki C, Tomita K, Hirose R, Eshima Takeo, Ohashi H, Nishikino M, Scally E, Nshimura H, Azechi H, O'Sullivan G 2016 J. Phys. Conf. Ser. 688 012046
Google Scholar
[13] Yoshida K, Fujioka S, Higashiguchi T, Ugomori T, Tanaka N, Ohashi H, Kawasaki M, Suzuki Y, Suzuki C, Tomita K, Hirose R, Ejima T, Nishikino M, Sunahara A, Scally E, Li B W, Yanagida T, Nishimura H, Azechi H, O'Sullivan G 2014 Appl. Phys. Express. 7 086202
Google Scholar
[14] Cummins T, Otsuka T, Yugami N, Jiang W H, Endo A, Li B W, O'Gorman C, Dunne P, Sokell E, O'Sullivan G, Higashiguchi T 2012 Appl. Phys. Lett. 100 061118
Google Scholar
[15] Yin L, Wang H C, Reagan B A, Baumgarten C, Gullikson E, Berrill M, Shlyaptsev V N, Rocca J J 2016 Phys. Rev. Appl. 6 034009
Google Scholar
[16] Xu Q, Tian H, Zhao Y, Wang Q 2019 Symmetry 11 658
Google Scholar
[17] Wang J W, Wang X B, Zuo D L, Zakharov V S 2021 Opt. Laser Technol. 138 106904
Google Scholar
[18] Fujioka S, Nishimura H, Nishihara K, Sasaki A, Sunahara A, Okuno T, Ueda N, Ando T, Tao Y Z, Shimada Y, Hashimoto K, Yamaura M, Shigemori K, Nakai M, Nagai K, Norimatsu T, Nishikawa T, Miyanaga N, Izawa Y, Mima K 2005 Phys. Rev. Lett. 95 235004
Google Scholar
[19] Higashiguchi T, Li B W, Suzuki Y, Kawasaki M, Ohashi H, Torii S, Nakamura D, Takahashi A, Okada T, Jiang W H, Miura T, Endo A, Dunne P, O'Sullivan G, Makimura T 2013 Opt. Express 21 031837
Google Scholar
[20] Higashiguchi T, Otsuka T, Yugami N, Jiang W H, Endo A, Li B W, Kilbane D, Dunne P, O'Sullivan G 2011 Appl. Phys. Lett. 99 191502
Google Scholar
[21] Freeman J R, Harilal S S, Hassanein A 2011 J. Appl. Phys. 110 083303
Google Scholar
[22] Higashiguchi T, Dojyo N, Hamada M, Sasaki W, Kubodera S 2006 Appl. Phys. Lett. 88 201503
Google Scholar
[23] Freeman J R, Harilal S S, Hassanein A, Rice B 2013 Appl. Phys. A 110 853
Google Scholar
[24] Dou Y P, Sun C K, Liu C Z, Gao J, Hao Z Q, Lin J Q 2014 Chin. Phys. B 23 075202
Google Scholar
[25] Kilbane D, O'Sullivan G 2010 J. Appl. Phys. 108 104905
Google Scholar
[26] Cowan R D 1981 The Theory of Atomic Structure and Spectra (University of California Press) pp619–625
[27] Aota T, Tomie T 2005 Phys. Rev. Lett. 94 015004
Google Scholar
[28] Hassanein A, Sizyuk T, Sizyuk V, Harilal S S 2011 J. Micro/Nanolithgr. MEMS MOEMS 10 033002
Google Scholar
[29] Higashiguchi T, Kawasaki K, Sasaki W, Kubodera S 2006 Appl. Phys. Lett. 88 161502
Google Scholar
[30] Churilov S S, Kildiyarova R R, Ryabtsev A N, Sadovsky S V 2009 Phys. Scr. 80 045303
Google Scholar
[31] Li B W, Dunne P, Higashiguchi T, Otsuka T, Yugami N, Jiang W H, Endo A, O'Sullivan G 2011 Appl. Phys. Lett. 99 231502
Google Scholar
[32] National Institute of Standards and Technology https://nlte.nist.gov/FLY/ [2018-8]
[33] Higashiguchi T, Yamaguchi M, Otsuka T, Nagata T, Ohashi H, Li B W, D'Arcy R, Dunne P, O'Sullivan G 2014 Rev. Sci. Instrum. 85 096102
Google Scholar
[34] Favre A, Morel V, Bultel A, Godard G, Idlahcen S, Benyagoub A, Monnet I, Semerokc A, Dinescu Maria, Markelj S, Magaud P, Grisolia C 2021 Fusion. Eng. Des. 168 112364
Google Scholar
[35] Beyene G A, Tobin I, Juschkin L, Hayden P, O'Sullivan G, Sokell E, Zakharov V S, Zakharov S V, O'Reilly F 2016 J. Phys. D: Appl. Phys. 49 225201
Google Scholar
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