Microstructure Edge Measurement With Nanometer Lateral Resolution Based on Astigmatism

In microstructure geometry measurement, the lateral resolution of optical methods is limited by diffraction, which is generally in the micrometer and submicrometer levels. To achieve the measurement with nanometer resolution required for ultraprecision manufacturing, this article innovatively extends the astigmatism method to lateral measurement. By analyzing the morphological changes of the astigmatic spot when the edge passing through the beam, a model is developed that relates focus error signal (FES) to edge position. Based on this model, a lateral measurement method with nanometer resolution is proposed. Performance tests show that the probe based on this method can achieve a lateral resolution of 2 nm in the X- and Y-directions, with repeatability of 15 and 20 nm, respectively. In microstructure measurement experiments, high-precision measurement for microslit width and edge angle on single crystal silicon wafers is achieved in the developed experimental system.