NUCLEAR MICROPROBE ANALYSIS AND IMAGING - CURRENT STATE-OF-THE-ART PERFORMANCES

The current state-of-the-art performances claimed for nuclear microbea m spatial resolutions are: (a) 400 nm spot sizes for high current (100 pA) proton beams, (b) 400 nm for high current alpha particle beams, ( c) 100 nm for low proton current (<0.1 pA) applications such as Scanni ng Transmission Ion Microscopy (STIM) and Ion Beam Induced Charge (IBI C) and (d) 50 nm for low current alpha particles, These claims, howeve r, have been undermined not only by the lack of a common and generally accepted resolution standard, but also by the lack of a consistent ap proach between groups regarding a recognised method of beam spot measu rement. The lack of a definitive method for assessing spatial resoluti on is hindering the future development of nuclear microprobes to highe r spatial resolutions. We require the manufacture of resolution standa rds specifically tailored for nuclear microprobe spot size measurement s, for both high and low current operations. Until such resolution sta ndards are available, one commercially available standard which has hi gh potential for high current proton beam resolution tests is the Ebea m test chip manufactured for the characterisation of electron beam tes ters. This chip has patterns as small as 0.5 mu m in size produced in 0.5 mu m thick aluminium by direct electron beam writing. Using both a nalytical Particle Induced X-ray Emission (PIXE) imaging and PIXE line scans, the nuclear microscope facility at the National University of Singapore has demonstrated spatial resolutions of less than 400 nm for a 100 pA beam of 2 MeV protons. Low current resolution standards have more stringent requirements. One potential standard tested in Singapo re is a prototype self-supporting X-ray mask used in X-ray lithography . This test standard, however, is not commercially available at the mo ment, is fragile and therefore difficult to handle and easily fracture d. Using off-axis STIM imaging and line scanning over this mask, the N US nuclear microscope facility has demonstrated beam spot sizes less t han 130 nm for a 1 pA 2 MeV proton beam. (C) 1998 Elsevier Science B.V .