Ion microsource integrated with scanning electron microscope for sample preparation

Abstract

The authors developed the Ar+ ion microsource, which can generate a filamentary ion beam of a few tens of µm at its half-power diameter with a target current up to 50 µA at − 4 kV extracting voltage. This comprises a ceramic discharge capillary of 1 mm in inner diameter and 10 mm long with a very small copper anode and a cathode outlet aperture of 0.5 mm in diameter at its ends. The arrangement has been examined in three alternative designs equipped with cathodes of different shapes and materials and two extraction voltage supply schemes, i.e., with the negatively biased sample and the earthed cathode or the earthed sample and the cathode at a floating positive potential (recommended solution). Numerous other factors were considered that can affect the standard SEM operation, such as excessive working gas leakage and jamming with discharge interferences, e.g., streamers. The microsource makes a compact structure that can be positioned above the sample inside a standard SEM without any changes to its original structure and collisions with standard modes of the SEM operation. Such a tool enables the removal of target microvolumes in chosen places, so it can be used for some technological purposes, such as making small apertures. However, its main goal is to uncover the bulk internal structure of the specimen, imaging it in a 3D form. Therefore, the microsource is placed on the movable arm and coupled with the semiconductor four-quadrant backscattered electron (BSE) detector, which enables 3D imaging of the uncovered structure with the multidetector method. This implies taking in one scan a set of images from four or five directions, using both material- and topography-sensitive channels of information (BSE and secondary electron SE), which facilitates their interpretation.