Song Zhen, Zhang Libin, Yang Shang, Su Yajuan, Wei Yayi, Ye Tianchun
Appl Opt. 2023 May 20;62(15):3839-3847. doi: 10.1364/AO.487682.
Different from traditional lithography, metal material with high absorptivity and high reflectivity is introduced into plasmonic lithography technology. In particular, a silver/photo resist/silver film stack can form a Fabry-Perot (F-P) resonator structure, which can greatly change the behavior of the light reflection and transmission. Since the silver layer has a strong absorption ability to the alignment probe light with a wavelength of 532 or 633 nm, the quality of the alignment signal is seriously affected. In this paper, a thin film Fourier transfer model is established to quantitatively calculate the amplitude and phase information of the diffraction light with different orders. The results show that the diffraction optical power can be enhanced by the thickness optimization of all film stacks, and the maximum wafer quality (normalized diffraction efficiency) can be increased to 25.7%. The mechanism analysis of alignment signal enhancement is based on the F-P resonator phase oscillation amplification effect. However, it can also bring the reverse of both the power and phase for the alignment probe signal when the thickness fluctuation of the F-P resonator exists, which will be a great challenge for through-the-mask moiré fringe alignment technology. To obtain the optical power distribution of the structure surface and image of moiré fringes, a transfer matrix method is given to point-by-point calculate the incidence and reflection of the probe light in the vertical direction. The finite-difference time-domain method is also used to demonstrate alignment performance. It is proved that the subtle fluctuation of the photoresist thickness can make a huge difference to moiré fringes. A balance between the diffraction efficiency and process robustness can be achieved for plasmonic lithographic alignment technology by controlling the thickness range of the F-P resonator structure. In addition, the metal-insulator-metal structure has excellent thickness sensitivity and is applicable to optical signal detection and material property monitoring.
与传统光刻不同，具有高吸收率和高反射率的金属材料被引入到等离子体光刻技术中。特别是，银/光刻胶/银膜堆栈可以形成法布里-珀罗（F-P）谐振器结构，这可以极大地改变光的反射和透射行为。由于银层对波长为532或633nm的对准探测光具有很强的吸收能力，因此对准信号的质量受到严重影响。本文建立了薄膜傅里叶传递模型，定量计算不同阶次衍射光的振幅和相位信息。结果表明，通过优化所有膜堆栈的厚度可以提高衍射光功率，最大晶圆质量（归一化衍射效率）可提高到25.7%。对准信号增强的机理分析基于F-P谐振器的相位振荡放大效应。然而，当F-P谐振器存在厚度波动时，也会使对准探测信号的功率和相位发生反转，这对透掩模莫尔条纹对准技术来说将是一个巨大的挑战。为了获得结构表面的光功率分布和莫尔条纹图像，给出了一种传递矩阵方法，逐点计算探测光在垂直方向上的入射和反射。还采用时域有限差分法来演示对准性能。结果表明，光刻胶厚度的细微波动会对莫尔条纹产生巨大影响。通过控制F-P谐振器结构的厚度范围，可以实现等离子体光刻对准技术在衍射效率和工艺稳健性之间的平衡。此外，金属-绝缘体-金属结构具有优异的厚度敏感性，适用于光信号检测和材料性能监测。
