Calibration of a scanning electron microscope from two coordinates

Abstract

Methods for the calibration of a scanning electron microscope (SEM) operating in the secondary slow electron collection mode from two coordinates, using a single certified size, are described. Calibration is performed with a new test object made of silicon with pitch structures consisting of grooves and cross-shaped protrusions. All relief elements have trapezoidal profiles with large inclination angles of the side walls. The planes of the side walls coincide with the crystallographic planes {111} of silicon, and the planes of the top of the protrusions and bottom of the grooves coincide with the crystallographic planes {100}. The certified parameter is the pitch of the pitch structure, equal to 2000 nm. Two methods of SEM calibration are described. The first one employs for calibration the end parts of the pitch structures. It enables one to determine the pixel size from two coordinates; the electron-beam size (effective diameter), from two coordinates; and the nonorthogonality of the beam to the test object plane, from one coordinate. The second method employs for calibration a cross-shaped protrusion. It enables one to determine the pixel size from two coordinates; the electron beam size, from two coordinates; and the nonorthogonality of the beam to the test object plane, from two coordinates. The methods of SEM calibration are tested using an S4800 SEM. The asymmetry (1.5%) of the image, caused by the difference in the pixel sizes in two coordinates, and the asymmetry of the SEM electron beam (about 30%), caused by beam defocusing, are found. The nonorthogonality of the electron beam is less than 1° in both coordinates.