Optical sensor design for fast and process-robust position measurements on small diffraction gratings
Optical sensor design for fast and process-robust position measurements on small diffraction gratings
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DOI：
10.1016/j.optlaseng.2020.106267
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发表时间：
2020-11-01
影响因子：
4.6
通讯作者：
Osten, Wolfgang
中科院分区：
文献类型：
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作者：
Godecke, Maria Laura;Bett, Claudia Monika;Osten, Wolfgang
我们提出一种光学传感器设计，用于在间距范围从400纳米到约10微米的小衍射光栅上进行亚纳米精度的位置测量。干涉式位置检测基于通过180度旋转剪切引入的自参考。目标的横向扫描产生一个周期性变化的强度信号，其相位对目标位置进行编码。目标尺寸小（小至约5×5平方微米），这就要求在扫描过程中目标上的照明光斑尺寸更小。在我们的传感器中，通过用高数值孔径（NA）的显微镜物镜照亮入瞳中的大离轴区域，实现了仅2 - 3微米的光斑直径。一组两个互补的孔径光阑确保阻挡镜面反射，从而使信号对比度接近1。由于照明轮廓的大数值孔径范围，传感器对像差固有地敏感。我们通过在光瞳平面进行额外的光束监测来校正由此产生的定位误差。一项基于全面模拟研究的公差分析表明，传感器性能对典型的目标和参数变化具有鲁棒性。此外，初步的原理验证测量验证了实际可行性。
We propose an optical sensor design for position measurements with sub-nanometer precision on small diffraction gratings with a wide pitch range from 400 nm to approximately 10 mu m. The interferometric position detection is based on a self-reference introduced via 180 degrees-rotational shearing. A lateral scan of the target generates a periodically varying intensity signal whose phase encodes the target position. The small size of the target (down to approximately 5 x 5 mu m(2)) necessitates an even smaller illumination-spot size on the target for the scanning procedure. In our sensor, a spot diameter of only 2-3 mu m is realized by illuminating large off-axis areas in the entrance pupil of a microscope objective with high numerical aperture (NA). A set of two complementary aperture stops ensures blocking of the specular reflection, thus allowing for a signal contrast close to one. Due to the large NA-extent of the illumination profile, the sensor is inherently sensitive for aberrations. We correct the resulting positioning error via additional beam monitoring in the pupil plane. A tolerance analysis in terms of a comprehensive simulation study shows that the sensor performance is robust against typical target and parameter variations. Furthermore, first proof-of-principle measurements validate the practical feasibility.