Applications of microfocussed ion beams in surface and thin film analysis

Abstract

The use of microfocussed ion beams from liquid metal ion sources has allowed new standards of spatial resolution to be obtained in secondary ion mass spectrometry (SIMS). The combination of high spatial resolution with high sensitivity makes SIMS imaging a powerful technique for materials characterization and production problem-solving. In this paper a SIMS instrument is described which provides 500 Å spatial resolution using a gallium liquid metal ion source. This is used in combination with a high transmission quadrupole mass filter to produce chemical maps with both positive and negative secondary ions up to 1200 amu. Physical images containing topographical information are also possible by detection of secondary electrons or the total ion signal. A computer framestore facility allows ion and electron images to be stored digitally and subsequently overlaid in different colours. Images may be analysed retrospectively and processing facilities available include the addition, subtraction and ratioing of images, retrospective line-scan analysis, image rotation and zoom. In particular, the acquisition of a set of mass-selected images may be stored sequentially as a multi-element three-dimensional array. These data may be software-reconstructed to form an image of any plane through the original matrix. Examples of high resolution SIMS and the new techniques of data processing are given on a variety of samples including thin films and semiconductors.