極紫外光範圍內矽鉬薄膜疊層的干涉光譜解析

Spectroscopic Characterization of Si/Mo Thin-film Stack at Extreme Ultraviolet Range

黎延垠(Yen-Yin Li)

指導教授 ： 黃升龍

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2018年)

https://doi.org/10.6342/NTU201802809

摘要

當製程節點下探7奈米，傳統浸潤式微影術進行多重圖形而造成高昂的成本，將使得極紫外光微影術的逐漸成為主流。但由於相關光罩檢測工具現在還不被使用，芯片製造商必須依靠晶圓檢測來識別光罩缺陷。基於193奈米的技術在延伸至7奈米方面，因光源波長的繞限極限以及光源的吸收而有所限制。因此，需要檢查工具光源的波長勢必朝向短波長前進。而極紫外光源具有高亮度，穩定性（空間和時間）和成本效益是未來重要的發展方向。
在雷射產生電漿的極紫外光源系統中，高強度雷射光束聚焦到目標材料上以形成發射紫外光的電漿體，這種極紫外光源的主要優點是小的電漿體體積。與放電產生的電漿的極紫外光源系統相比，雷射產生電漿的極紫外光源將使得碎片和顆粒產生減少，並且擁有更高的光收集效率和功率的提昇。使用雷射產生電漿的極紫外光源進行干涉儀的實驗研究以及模擬。利用矽鉬多層分光器和反射鏡形成的具有共同路徑的邁克森干涉儀來實現系統的緊實性。基於Wiener-Khinchin定理，通過對測量的信號自相關進行模擬分析而無需波長校準來獲得準確的極紫外光譜。該頻譜分析儀的光譜解析度為30皮米，與平場光譜儀相當。並且討論了與干涉儀中使用的多層反射鏡相關的問題。
此外，本論文提出了一種非侵入性的共路光學同調斷層掃描術，其縱向解析度為64.6奈米，用來量測分析矽鉬多層膜鏡的薄膜疊層厚度及其複合傳遞函數。矽鉬疊層的複合傳遞函數在原始的13.5奈米波長範圍內被實驗和模擬驗證。除此之外，圖像質量高度依賴於其信噪比，討論了目前共路光學同調斷層掃描術信噪比22.3分貝的成因及改善方法。
擁有這些知識和成就後，基於極紫外光源的新型光學同調斷層掃描術同時使用雷射產生電漿的極紫外光源和共路設計，顯示出極紫外光源的光學同調斷層掃描術將成為光罩檢測的非破壞性層析成像方法。

關鍵字

主從式放大器 ； 雷射產生電漿 ； 極紫外光 ； X射線光譜 ； X射線應用 ； X射線干涉學測量 ； 光學同調斷層掃描

並列摘要

Using extreme ultraviolet (EUV) radiation for nanoscale imaging has recently seen much interest. As actinic patterned mask inspection tools are not available, chipmakers must rely on wafer inspection to identify mask defects. The current 193 nm-based technologies have their limitations in terms of extending to 7 nm and beyond. Hence, there is a need to reduce the wavelength of the inspection tools. An EUV source (13.5 nm) with high brightness, stability (spatial and temporal) and cost effectiveness is needed.
The laser-produced plasma (LPP) EUV source has shown promise to be the source of the mask inspection tools. In a LPP EUV system, a high-intensity laser beam is focused onto a target material to form a plasma, which emits ultraviolet light. The main advantage of such a EUV source is the small plasma volume. Compared with the discharge-produced plasma (DPP) EUV system, LPP EUV allows for fewer fragments or particles generation, higher light collection efficiency, and better power scalability.
A compact and wavelength-calibration-free interferometric scheme was numerically and experimentally investigated using a LPP EUV source. A Michelson-type interferometer with a common path, formed by a Si/Mo-multilayer-based beam splitter and mirror, was utilized to achieve system compactness. Based on the Wiener–Khinchin theorem, an accurate EUV spectrum was obtained by numerically analyzing the measured signal autocorrelation without performing wavelength calibration. The achieved spectral resolution of 30 pm was comparable to those of flat-field spectrometers. The issues related to the multilayer mirror used in the interferometer are also discussed.
A noninvasive method for characterizing Si/Mo thin-film stack thickness and its complex transfer function using common-path optical coherence tomography (OCT) is proposed, analyzed and experimentally demonstrated. The measured complex transfer function of the Si/Mo stack was verified near the pristine 13.5 nm wavelength range. In addition to, the image quality is highly dependent on its signal-to-noise ratio (SNR). The SNR of this common-path OCT is discussed.
Having these knowledge and accomplishments, the novel EUV based OCT using both the LPP EUV source and common-path design has shown promise to be a nondestructive tomographic method for mask inspection.

並列關鍵字

Master oscillator power amplification (MOPA) ； laser-produced plasma (LPP) ； extreme ultraviolet (EUV) ； X-ray spectroscopy ； X-ray applications ； X-ray interferometry ； optical coherence tomography

參考文獻

Chapter 1

[1.1] M. Neisser and S. Wurm, “Overview of next generation lithography, advanced patterning, EUV and self assembly,” Frontiers of Characterization and Metrology for Nanoelectronics: 2013, 252–254 (2013).

[1.2] R. Es, M. Kerkhof, H. Jasper, L. Levasier, and R. Peeters, “EUV lithography industrialization progress,” Proc. SPIE 10450, 1045003-1–1045003-17 (2017).

[1.3] V. M. Borisov, A. V. Eltsov, A. S. Ivanov, Y. B. Kiryukhin, O. B. Khristoforov, V. A. Mishchenko, A. V. Prokofiev, A. Y. Vinokhodov, and V. A. Vodchits, “EUV sources using Xe and Sn discharge plasmas,” J. Phys. D. Appl. Phys. 37, 3254–3265 (2004).

[1.4] H. Mizoguchi, H. Nakarai, T. Abe, T. Ohta, K. M. Nowak, Y. Kawasuji, H. Tanaka, Y. Watanabe, T. Hori, T. Kodama, Y. Shiraishi, T. Yanagida, T. Yamada, T. Yamazaki, S. Okazaki, and T. Saitou, “Sub-hundred Watt operation demonstration of HVM LPP-EUV source,” Proc. SPIE 9048, 90480D (2014).