A model for spectroscopic ellipsometry analysis of plasma-activated Si surfaces for direct wafer bonding
A model for spectroscopic ellipsometry analysis of plasma-activated Si surfaces for direct wafer bonding
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DOI：
10.1063/5.0101633
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发表时间：
2022-08-22
影响因子：
4
通讯作者：
Groiss, H.
中科院分区：
文献类型：
--
作者：
Rauch, N.;Andersen, E.;Groiss, H.
本工作利用椭圆偏振光谱系统地研究了等离子体处理对顶部带有自然氧化物的硅片的影响。提出了一种适用于椭偏测量数据拟合的通用三层光学模型结构，并将其应用于经N-2、O-2和N-2/O-2混合等离子体处理的样品。检测到氧化物生长、晶态Si的非晶化以及在SiO_2和非晶态Si之间形成过渡层。通过互补性方法确认了所产生的层的估计厚度，从而可以精确地检测超薄层的厚度，即角度分辨x射线光电子能谱和透射电子显微镜。产生的非晶态结构的深度分辨化学成分和直接厚度测量显示出明显的元素梯度，并且没有尖锐的界面。等离子体过程中使用的氮气主要以Si3N4的形式注入在SiO_2/过渡层的界面上。然而，由于Si3N4浓度相对较低，且其折射率n和吸收系数k与SiO_2相似，因此对所有等离子体物种采用由SiO_2/过渡层/非晶态Si组成的通用椭圆偏振测量模型是可行的。椭圆偏振光谱是无损的，不需要任何样品制备，可以有效地用于分析整个晶片。可以得出结论，本椭偏测量模型的开发和验证方法非常适合于等离子体激活的直接晶片键合工艺。(C)2022年作者(S)。
In this work, the impact of plasma treatment on Si wafers with native oxide on top was systematically investigated using spectroscopic ellipsometry. A general applicable three-layer optical model structure for ellipsometry data fitting was developed and employed on samples treated with the N-2, O-2, and N-2/O-2 mixture plasma. Oxide-growth, amorphization of crystalline Si, and the formation of a transition layer between the SiO2 and the amorphous Si were detected. The estimated thicknesses of produced layers were confirmed by complementary methods, which allow precise ultra-thin layers thicknesses detection, namely, angle-resolved x-ray photoelectron spectroscopy and transmission electron microscopy. The depth-resolved chemical composition and the direct thickness measurements of the produced amorphous structure revealed pronounced elemental gradients and the absence of sharp interfaces. Nitrogen gas used in the plasma process was found to be implanted mainly at the interface of the SiO2/transition layer in the form of Si3N4. However, it was verified that it is feasible to employ one general ellipsometry model consisting of SiO2/transition layer/amorphous Si on crystalline Si for all plasma species due to comparably low Si3N4 concentrations as well as its refractive index n and absorption k similarity to SiO2. Spectroscopic ellipsometry is nondestructive and can be efficiently applied to analyze whole wafers without any sample preparation. It can be concluded that the present approach to ellipsometry model development and verification is well suited for plasma-activated direct wafer bonding processes. (C) 2022 Author(s).