Yashchuk V V, Fischer P J, Chan E R, Conley R, McKinney W R, Artemiev N A, Bouet N, Cabrini S, Calafiore G, Lacey I, Peroz C, Babin S
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Center for X-Ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Rev Sci Instrum. 2015 Dec;86(12):123702. doi: 10.1063/1.4936752.
We present a modulation transfer function (MTF) calibration method based on binary pseudo-random (BPR) one-dimensional sequences and two-dimensional arrays as an effective method for spectral characterization in the spatial frequency domain of a broad variety of metrology instrumentation, including interferometric microscopes, scatterometers, phase shifting Fizeau interferometers, scanning and transmission electron microscopes, and at this time, x-ray microscopes. The inherent power spectral density of BPR gratings and arrays, which has a deterministic white-noise-like character, allows a direct determination of the MTF with a uniform sensitivity over the entire spatial frequency range and field of view of an instrument. We demonstrate the MTF calibration and resolution characterization over the full field of a transmission soft x-ray microscope using a BPR multilayer (ML) test sample with 2.8 nm fundamental layer thickness. We show that beyond providing a direct measurement of the microscope's MTF, tests with the BPRML sample can be used to fine tune the instrument's focal distance. Our results confirm the universality of the method that makes it applicable to a large variety of metrology instrumentation with spatial wavelength bandwidths from a few nanometers to hundreds of millimeters.
我们提出了一种基于二进制伪随机（BPR）一维序列和二维阵列的调制传递函数（MTF）校准方法，作为在包括干涉显微镜、散射仪、相移菲索干涉仪、扫描和透射电子显微镜以及此时的X射线显微镜等多种计量仪器的空间频率域中进行光谱表征的有效方法。BPR光栅和阵列固有的功率谱密度具有类似确定性白噪声的特性，能够在仪器的整个空间频率范围和视场内以均匀的灵敏度直接确定MTF。我们使用具有2.8 nm基本层厚度的BPR多层（ML）测试样品，展示了在透射软X射线显微镜的全场范围内进行MTF校准和分辨率表征。我们表明，除了直接测量显微镜的MTF外，使用BPRML样品进行的测试还可用于微调仪器的焦距。我们的结果证实了该方法的通用性，使其适用于空间波长带宽从几纳米到数百毫米的多种计量仪器。
