Surface charge compensation for a highly charged Ion emission microscope

LBNL-52429.doc 10:04 A M Surface Charge Compensation for a Highly Charged Ion Emission Microscope J. W. McDonald, A. V. Hamza, M . W. Newman, J. P. Holder, and D. H. G. Schneider Lawrence Livermore National Laboratory T. Schenkel E. O. Lawrence Berkeley National Laboratory A surface charge compensation electron flood gun has been added to the Lawrence Livermore National Laboratory (LLNL) highly charged ion (HCI) emission microscope. HCI surface interaction results in a significant charge residue being left on the surface of insulators and semiconductors. This residual charge causes undesirable aberrations in the microscope images and a reduction of the Time-Of-Flight (TOF) mass resolution when studying the surfaces of insulators and semiconductors. The benefits and problems associated with HCI microscopy and recent results of the electron flood gun enhanced HCI microscope are discussed. INTRODUCTION In the last few years increasing demands of the semiconductor industry for materials characterization at high spatial resolution have driven the instrument development field. To meet the increasing demands of the semiconductor industry for materials characterization at very high spatial resolution an impressive array of instruments have been developed (transmission electron microscopy, scanning tunneling electron microscopy, etc.). There is an equally impressive array of instruments and techniques available to determine material composition (secondary ion mass spectroscopy, Auger electron spectroscopy, photoelectron spectroscopy, etc.). The LLNL HCI driven emission microscope provides both high spatial resolution and very sensitive compositional analysis simultaneously it has been described in detail by Hamza et al. . Emission microscopes are a special class of electron microscopes that accelerate and image low energy electrons and other charged particles from a planar surface. The history of emission microscopes began more than 100 years ago (see reference ). The HCI emission microscope described here is a combination of two emission microscopes developed in the 1960s. The first an Ar+ ion beam induced electron emission microscope where the kinetic emission of electrons forms an image. The second a secondary ion emission microscope where an ion beam is used to sputter secondary ions, which are imaged. In the present instrument electrons and secondary ions are imaged and the mass of the secondary ions is determined by time of flight. Thus, a variety of contrast imaging modes are available. The emission microscope described here uses HCIs as the excitation source. The highly charged ions bring four crucial advantages, a large secondary electron yield, high secondary ion yields, high ionization probability of the secondary emission, and high molecular yields.