荷電ビーム用多段四極子補正レンズの高精度アライメント技術

Abstract

In charged particle optics, high-precision alignment of multistage multipole lens is essential for the realization of a non-rotationally symmetrical correction-lens system. A six-stage self-aligned quadrupole correction-lens system consisting of six quadrupoles and four aperture electrodes was designed and constructed. Machining accuracy and high-precision alignment techniques for the multistage correction-lens elements are reported in this article. The correction-lens system is assembled using cylindrical components, which can be machined with high accuracy. To overcome the problem of azimuthal error in the multistage quadrupole lens, the correction-lens system consists of two lens-casing cylinders of the same shape and size. To suppress azimuthal error among three quadrupoles in a lens-casing cylinder, four long positioning shafts and eight ceramic insulating shafts are inscribed in this cylinder. Cylindricity of the positioning shafts is less than 0.2μm over a length of 65 mm. Quadrupole electrodes are mounted on four pairs of ceramic insulating shafts using a Z-axis positioning jig. All sets of quadrupole electrodes are finished with varying diameters and lengths less than 0.15μm. The constructed multistage quadrupole correction lens is installed as an objective lens in a focused ion beam system, and azimuthal error between two lens-casing cylinders are corrected by using scanning ion microscope images.