Optimization of structural parameters and fabrication of small blazed angle monocrystalline silicon gratings
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摘要:
为了满足国家同步辐射光源的需要，对单晶硅小闪耀角光栅的各向异性湿法刻蚀制备工艺展开了研究，制备适用于软X射线中波波段的闪耀光栅。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。同时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其制作难度及成本。
Abstract:In order to meet the requirements of the national synchrotron radiation source, the anisotropic wet-etching technology of small blazed angle monocrystalline silicon grating 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 0.5nm. This method can be applied to the fabrication of the medium wave soft X-ray band blazed grating, which can greatly reduce the difficulty and cost of fabrication while achieving high diffraction efficiency.
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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 in 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 不同平台占宽比光栅随波长变化的衍射效率
Figure 5. Diffraction efficiency of grating with different platform ratio 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光栅随占宽比f变化的衍射效率
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 16 使用异丙醇前后光栅表面的粗糙度对比
Figure 16. Comparison of grating surface roughness before and after using isopropanol
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 3 AFM粗糙度测量结果(单位：nm)
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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