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极紫外光刻技术是我国当前面临35项“卡脖子”关键核心技术之首. 高极紫外光转换效率和低离带热辐射的激光等离子体极紫外光源是极紫外光刻系统的重要组成部分. 本文通过采用激光作用固体Sn和低密度SnO2靶对极紫外光源以及其离带热辐射进行研究. 实验结果表明, 两种形式Sn靶在波长为13.5 nm附近产生了强的极紫外光辐射. 由于固体Sn靶等离子体具有较强自吸收效应, 在光刻机中心工作波长13.5 nm处的辐射强度处于非光谱峰值位置. 而低密度SnO2靶具有较弱的自吸收效应, 其所辐射光谱的峰值恰好位于13.5 nm处. 相比于固体Sn靶, 低密度SnO2靶中处于激发态的Sn离子发生跃迁所产生的伴线减弱, 使其在13.5 nm处的光谱效率提升了约20%. 另一方面, 开展了极紫外光源离带热辐射(400—700 nm)的实验研究, 光谱测量结果表明离带热辐射主要是由连续谱所主导, 低密度SnO2靶中含有部分低Z元素O(Z = 8), 导致其所形成的连续谱强度低, 同时离带辐射时间短, 因而激光作用低密度SnO2靶所产生的离带热辐射弱于固体Sn靶情况. 离带热辐射角分布测量结果表明, 随着与靶材法线夹角逐渐增加, 离带热辐射强度逐渐减弱, 且辐射强度与角度满足
$ A{\cos ^\alpha }\theta $ 的关系.The extreme ultraviolet (EUV) lithography technology required for high-end chip manufacturing is the first of 35 “bottleneck” key technologies that China is facing currently. The high conversion efficiency EUV source and low out-of-band radiation play a significant role in the application of the EUV lithography system. In this work, the EUV source and out-of-band radiation are studied by using laser irradiated solid Sn target and low-density SnO2 target. The result shows that a strong EUV radiation at a wavelength of 13.5 nm is generated when the laser irradiates the two forms of Sn targets. Owing to the self-absorption effect of the solid Sn target plasma, the maximum intensity of the wavelength is not located at the position of 13.5 nm, which is working wavelength of EUV lithography system. However, the peak radiation spectrum is located at the position of 13.5 nm with low-density SnO2 target due to its weaker plasma self-absorption effect. In addition, the satellite lines are weaker in low-density SnO2 target than in the solid Sn target, so that the spectrum efficiency of the EUV at 13.5 nm (2% bandwidth) is increased by about 20%. On the other hand, the experimental study of the out-of-band radiation is carried out. The out-of-band radiation spectral results show that the out-of-band radiation is mainly dominated by the continuum spectrum. Compared with the solid Sn target, the low-density SnO2 target contains a part of the low Z element O (Z = 8), resulting in a low-intensity continuum spectrum. In addition, the collision probability of ion-ion and electron-ion both become low when the laser irradiates the low-density SnO2 target, resulting in a short out-of-band radiation duration time. Therefore, the out-of-band radiation generated by the laser irradiated on the low-density SnO2 target is weak based on the above reasons. The angular distribution of out-of-band radiation measurement results shows that the intensity of out-of-band radiation decreases with the angle increasing. A cosine function$A \cos ^\alpha \theta$ can fit the angular distribution of the total radiation.-
Keywords:
- low-density target /
- extreme ultraviolet source /
- out-of-band radiation /
- spectral efficiency
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图 1 激光等离子体极紫外光源与其离带热辐射实验装置图
Fig. 1. Experimental setup for the radiation of extreme ultraviolet (EUV) source and out-of-band from plasma produced by a laser.
图 2 不同激光能量下的极紫外光谱曲线图 (a)固体Sn靶; (b)低密度SnO2靶
Fig. 2. The EUV spectra under different laser energy: (a) Solid Sn target; (b) low-density SnO2 target.
图 3 激光能量为400 mJ时, 固体Sn靶和低密度SnO2靶激光等离子体极紫外光谱对比图
Fig. 3. Comparison of EUV spectra of laser produced Sn and SnO2 plasma at laser energy of 400 mJ.
图 4 激光能量在200—600 mJ范围内, 固体Sn靶与低密度SnO2靶激光等离子体极紫外光谱效率对比图
Fig. 4. Spectral efficiency of the radiation around 13.5 nm (2% bandwidth) to the total radiation between 10–18 nm under laser produced Sn and SnO2 plasma with laser energy from 200–600 mJ.
图 5 激光能量为400 mJ作用下, 两种靶材等离子体光源离带热辐射对比图
Fig. 5. Comparison of out-of-band radiation of laser produced Sn and SnO2 plasma at laser energy of 400 mJ.
图 6 激光能量为400 mJ、探测角度为30°时所测量的时间分辨离带热辐射 (a)带通滤波片波长325—385 nm; (b)带通滤波片波长435—500 nm; (c)带通滤波片波长485—565 nm
Fig. 6. Out-of-band radiation of laser produced Sn and SnO2 plasma was measured at the detection angle of 30° when laser energy of 400 mJ: (a) Band pass filter wavelength of 325–385 nm; (b) band pass filter wavelength of 435–500 nm; (c) band pass filter wavelength of 485–565 nm.
图 7 激光能量为400 mJ, 两种靶材所产生离带热辐射强度的角分布 (a)带通滤波片波长325—385 nm; (b)带通滤波片波长435—500 nm; (c)带通滤波片波长485—565 nm
Fig. 7. Angle distribution of out-of-band radiation of laser produced Sn and SnO2 plasma at laser energy of 400 mJ: (a) Band pass filter wavelength of 325–385 nm; (b) band pass filter wavelength of 435–500 nm; (c) band pass filter wavelength of 485–565 nm.
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[1] 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 2334
Google Scholar
[2] Huang Q, Medvedev V, van de Kruijs R, Yakshin A, Louis E, Bijkerk F 2017 Appl. Phys. Lett. 4 011104
Google Scholar
[3] van de Kerkhof M, Liu F, Meeuwissen M, Zhang X Q, de Kruif R, Davydova N, Schiffelers G, Wählisch F, van Setten E, Varenkamp W, Ricken K, de Winter L, Mcnamara J, Bayraktar M 2020 Journal of Micro/Nanolithography, MEMS, and MOEMS San Jose, California, United States, September 22, 2020 p033801
[4] Fujioka S, Nishimura H, Nishihara K, Sasaki A, Sunahara A, Okuno T, Ueda N, Ando T, Tao Y, 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
[5] Behnke L, Schupp R, Bouza Z, Bayraktar M, Mazzotta Z, Meijer R, Sheil J, Witte S, Ubachs W, Hoekstra R, Versolato O O 2021 Opt. Express 29 4475
Google Scholar
[6] Freeman J R, Harilal S S, Verhoff B, Hassanein A, Rice B 2012 Plasma Sources Sci. T. 21 055003
Google Scholar
[7] Harilal S S, Coons R W, Hough P, Hassanein A 2009 Appl. Phys. Lett. 95 221501
Google Scholar
[8] Higashiguchi T, Rajyaguru C, Kubodera S, Sasaki W, Yugami N, Kikuchi T, Kavata S, Andreev A 2005 Appl. Phys. Lett. 86 231502
Google Scholar
[9] Higashiguchi T, Kawasaki K, Sasaki W, Kubodera S 2006 Appl. Phys. Lett. 88 161502
Google Scholar
[10] 谢卓, 温智琳, 司明奇, 窦银萍, 宋晓伟, 林景全 2022 物理学报 71 035202
Google Scholar
Xie Z, Wen Z L, Si M Q, Dou Y P, Song X W, Lin J Q 2022 Acta. Phys. Sin. 71 035202
Google Scholar
[11] 李镇广, 窦银萍, 谢卓, 王海建, 宋晓伟, 林景全 2021 中国激光 48 1601005
Google Scholar
Li Z G, Dou Y P, Xie Z, Wang H J, Song X W, Lin J Q 2021 Chin. J. Lasers. 48 1601005
Google Scholar
[12] Okuno T, Fujiokaa S, Nishimura H, Tao Y, Nagai K, Gu Q, Ued N a, Ando T, Nishihara K, Norimatsu T, Miyanaga N, Izawa Y, Mima K 2006 Appl. Phys. Lett. 88 161501
Google Scholar
[13] Harilal S S, Tillack M S, Tao Y, O'Shay B, Paguio R, Nikroo A. 2006 Opt. Lett. 31 1549
Google Scholar
[14] O'Sullivan, G D, Faulkner R 1994 Opt. Eng. 33 3978
Google Scholar
[15] Fujioka S, Nishimura H, Okuno T, Tao Y, Ueda N, Ando T, Kurayama H, Yasuda Y, Uchida S, Shimada Y, Yamaura M, Gu Q, Nagai K, Norimatsu T, Furukawa H, Sunahara A, Kang Y G, Murakami M, Nishihara K, Miyanaga N, Izawa Y 2005 Emerging Lithographic Technologies IX San Jose, California, United States, May 6, 2005 p578
[16] Torretti F, Schupp R, Kurilovich D, Bayerle A, Scheers J, Ubachs W, Hoekstra R, Versolato O O 2018 J. Phys. B: At., Mol. Opt. Phys. 51 045005
Google Scholar
[17] Stuik R, Scholze F, Tümmler J, Bijkerk F 2002 Nucl. Instrum. Methods Phys. Res. Sect. A 492 305
Google Scholar
[18] Louis E, van de Kruijs R W E, Yakshin A E, Alonso van der Westen S, Bijkerk F, van Herpen M M J W, Klunder D J W, Bakker L, Enkisch H, Müllender S, Richter M, Banine V 2006 In Emerging Lithographic Technologies X San Jose, California, United States, March 24, 2006 p887
[19] Parchamy H, Szilagyi J, Masnavi M, Richardson M 2017 J. Appl. Phys. 122 173303
Google Scholar
[20] Namba S, Fujioka S, Sakaguchi H, Nishimura H, Yasuda Y, Nagai K, Miyanaga N, Izawa Y, Mima K, Sato K, Takiyama K 2008 J. Appl. Phys. 104 013305
Google Scholar
[21] Sakaguchi H, Fujioka S, Namba S, Tanuma H, Ohashi H, Suda S, Shimomura M, Nakai Y, Kimura Y, Yasuda Y, Nishimura H, Norimatsu T, Sunahara A, Nishihara K, Miyanaga N, Izawa Y, Mima K 2008 Appl. Phys. Lett. 92 111503
Google Scholar
[22] Mbanaso C, Antohe A O, Bull H, Denbeaux G, Goodwin F, Hershcovitch A 2012 J. Micro/Nanolithgr. MEMS. MOEMS. 11 021116
Google Scholar
[23] 宋晓林, 宋晓伟, 窦银萍, 田勇, 谢卓, 高勋, 林景全 2016 光谱学与光谱分析 36 3114
Google Scholar
Song X L, Song X W, Dou Y P, Tian Y, Xie Z, Gao X, Lin J Q 2016 Spectrosc. Spect. Anal. 36 3114
Google Scholar
[24] Morris O, Hayden P, O’Reilly F, Murphy N, Dunne P, Bakshi V 2007 Appl. Phys. Lett. 91 081506
Google Scholar
[25] Tomie T 2012 J. Micro-nanolith. Mem. 11 021109
Google Scholar
[26] O'Sullivan G 1983 J. Phys. B At. Mol. Phys. 16 3291
Google Scholar
[27] Cummings A, O'Sullivan G, Dunne P, Sokell E, Murphy N, White, Hayden J P, Sheridan P, Lysaght M, O'Reilly F 2006 J. Phys. D: Appl. Phys. 39 73
Google Scholar
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