Zhang Lei, Thomas Joseph P, Guan Xiaoyi, Heinig Nina F, Leung Kam Tong
WATLab, and Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Nanotechnology. 2020 Aug 7;31(32):325301. doi: 10.1088/1361-6528/ab8d69. Epub 2020 Apr 27.
Resist-based ion beam lithography has been studied by exposing different species of ions (He, Si, Ga and Au) on 700 and 2000 Å thick poly(methyl methacrylate) (or PMMA) films supported on Si substrates. By comparing the resist sensitivities to different ions and the cross-sectional shapes of the developed features with the simulation outputs from the TRIM (TRansport of Ions in Matter) software, long-chain scissoring in PMMA can be largely attributed to ion-initiated electron cascades (as evaluated by ion energy loss to the electrons) and recoil atom cascades (as evaluated by vacancy distribution in TRIM). The ion-initiated electron cascades contribute more to the resist sensitivity for the lighter ions, while the recoil atom cascades are more important for the heavier ions. A proportional relation between the resist sensitivity and the product of the ion energy loss to electrons and vacancy number is obtained semi-empirically for heavy ions. The He ion is the only ion species that can travel through and therefore expose the entire 2000-Å thick PMMA resist film, while the heaviest ion, Au, provides the highest resist sensitivity. The effective energy and momentum impartment to the resist by the ion, as revealed by recoil atom cascades and vacancy formation, is important to significantly expanding the material types suitable for ion beam lithography.
通过在硅衬底上支撑的700埃和2000埃厚的聚甲基丙烯酸甲酯（或PMMA）薄膜上曝光不同种类的离子（氦、硅、镓和金），对基于抗蚀剂的离子束光刻技术进行了研究。通过将抗蚀剂对不同离子的灵敏度以及显影特征的横截面形状与TRIM（物质中离子传输）软件的模拟输出进行比较，PMMA中的长链剪接在很大程度上可归因于离子引发的电子级联（通过离子对电子的能量损失来评估）和反冲原子级联（通过TRIM中的空位分布来评估）。离子引发的电子级联对较轻离子的抗蚀剂灵敏度贡献更大，而反冲原子级联对较重离子更为重要。对于重离子，半经验地获得了抗蚀剂灵敏度与离子对电子的能量损失和空位数乘积之间的比例关系。氦离子是唯一能够穿透并因此曝光整个2000埃厚PMMA抗蚀剂薄膜的离子种类，而最重的离子金则提供了最高的抗蚀剂灵敏度。反冲原子级联和空位形成所揭示的离子对抗蚀剂的有效能量和动量赋予，对于显著扩展适用于离子束光刻的材料类型非常重要。
