Optimization of structural parameters and fabrication of monocrystalline silicon gratings with small blazed angle
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摘要:
本文开展了对单晶硅小闪耀角光栅的各向异性湿法刻蚀制备工艺研究，制备了适用于软X射线中波波段的闪耀光栅，以满足国家同步辐射光源的需要。首先，基于严格耦合波法对小闪耀角光栅进行了结构参数优化及工艺容差分析。在晶向对准过程中，先通过环形预刻蚀确定硅片晶向，再基于倍频调整法实现光栅掩模与单晶硅<111>晶向的对准。研究了光刻胶灰化技术及活性剂对光栅槽形质量的影响，并通过单晶硅各向异性湿法刻蚀工艺成功制备了接近于理想锯齿槽形的闪耀光栅。实验结果证明：所制备光栅闪耀角为1°，刻线密度为
1200 gr/mm，闪耀面均方根粗糙度在0.5 nm以内。此方法可以应用于软X射线中波波段闪耀光栅的制作，在获得较高衍射效率的同时可以大大减少制作难度及成本。Abstract:In order to meet the requirements of the national synchrotron radiation source, the anisotropic wet-etching technology of monocrystalline silicon grating with small blazed angle is studied, and the blazed grating suitable for the medium wave soft X-ray band is prepared. Based on the rigorously coupled wave theory, the structural parameters and process tolerance of the small blazed angle grating are designed. In the crystal alignment process, the crystal orientation of the silicon wafer is determined by ring-preetching, and then the grating mask is aligned with the crystal direction of monocrystalline silicon <111> based on the frequency doubling adjustment method. At the same time, the effect of the photoresist ashing technique and the active agent on the groove quality of the grating is investigated, and the scintillating gratings close to the ideal sawtooth groove shape are successfully prepared by the monocrystalline silicon anisotropic wet etching process. The experimental results show that the blazed angle of the prepared grating is 1°, the linear density is
1200 gr/mm, and the root mean square roughness of the blazed surface is less than 0.5 nm. This method can be applied to the fabrication of the medium wave soft X-ray blazed grating, which can greatly reduce the difficulty and cost of fabrication while achieving high diffraction efficiency.-
Key words:
- blazed grating /
- monocrystalline silicon /
- crystalline alignment /
- wet etching
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图 1 不同状态入射光随波长变化的衍射效率
Figure 1. Diffraction efficiency of incident light as a function of wavelength under different states
图 2 不同刻线密度光栅随波长变化的衍射效率
Figure 2. Diffraction efficiency of gratings with different grating densities as a function of wavelength
图 3 不同闪耀角光栅随波长变化的衍射效率
Figure 3. Diffraction efficiency of gratings with different flare angles as a function of wavelength
图 5 不同平台占宽比下光栅随波长变化的衍射效率
Figure 5. Diffraction efficiency of grating with different platform ratios as a function of wavelength
图 6 不同平台高度h光栅随占宽比f变化的衍射效率
Figure 6. Diffraction efficiency of grating with different platform height h as a function of aspect ratio f
图 7 不同平台高度h下光栅衍射效率随占宽比f变化情况
Figure 7. Diffraction efficiency of grating with different platform height h as a function of aspect ratio f
图 14 光栅制备工艺流程。（a）硅片清洁；（b）氧化层制备；（c）旋涂光刻胶；（d）对准曝光；(e)显影；（f）光刻胶图形转移；（g）氧化层掩模制备；（h）湿法刻蚀；（i）去除表面掩模
Figure 14. Grating preparation process. (a) Silicon wafer cleaning; (b) preparation of oxide layer; (c) spin coated photoresist; (d) alignment exposure; (e) development; (f) photoresist pattern transfer; (g) preparation of oxide mask; (h) wet etching; (i) remove the surface mask
图 15 光刻胶掩模（a）灰化前与（b）灰化后掩模占宽比对比结果
Figure 15. Comparison results of mask expansion ratio for photoresist mask (a) before and (b) after ashing
图 16 (a)未添加及(b)添加异丙醇活性剂的光栅表面粗糙度对比结果
Figure 16. Comparison results of grating surface roughness (a) before and (b) after using isopropanol
图 18 实际槽型和设计槽形对比
Figure 18. Comparison of actual groove shape and designed groove shape
图 19 设计光栅与制备光栅的衍射效率对比
Figure 19. Comparison results of diffraction efficiencies for designed grating and fabricated grating
表 1 光栅技术指标
Table 1. Specification of grating
指标参数 数值 波长范围/nm 3~6 衍射级次 −1 入射状态 掠入射 衍射效率 >40% 
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表 2 光栅槽形参数
Table 2. Grating groove parameters
槽形参数 数值 闪耀角/(°) 1±0.1 周期/nm 833 f 0<f<0.3 h/nm 0<h<8
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表 3 AFM粗糙度测量结果
Table 3. AFM roughness measurement results (Unit: nm)
测量点 Rq 1 0.287 2 0.436 3 0.365 4 0.253 5 0.220 6 0.379 7 0.409 8 0.293 9 0.333 10 0.400 平均值 0.3375
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表 4 闪耀角测量结果
Table 4. Blazed angle measurement results
测量点 闪耀角 1 0.969° 2 1.023° 3 0.974° 4 1.015° 5 1.009° 平均值 0.998°
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