Paper AS+BI-TuA10
TOF SIMS Analyses of Ga Concentration as a Function of Distance from FIB Milled Features

Tuesday, October 30, 2012, 5:00 pm, Room 20

Focused ion beams are routinely used for site-specific specimen preparation, nanopatterning, and analysis. It is important to know whether the primary ion beam is present outside the region targeted for ion beam modification. A previous report showed that > 1E12 atoms/cm² of Ga was detected up to several millimeters away from a focused ion beam (FIB) milled feature [1]. In this work, we reproduce this earlier report using a blind study of 2 different state-of-the-art Ga-FIB columns. Each column was used to FIB mill a 100 μm x 100 μm square into a (100) Si wafer at 30 keV with a nominal beam current of 20 nA at constant dose. Time of flight secondary ion mass spectrometry (TOF SIMS) was used to measure Ga depth profiles and Ga surface concentration at a distance up to 6.5 mm from the FIB milled square. In column “A,” > 1E12 atoms/cm² of Ga was detected up to ~ 5 mm from the FIB milled square. Column “B” showed considerably less Ga with > 1E12 atoms/cm² detected within ~ 250 μm from the FIB milled square. The depth profiles show that the Ga concentration was fairly uniform to a depth of ~ 2 nm from the surface for column “A” and ~ 1 nm into the surface for column “B”. Using SRIM [2] simulations we determine that these implantation depths correspond to an ion energy < 500 eV. The consequences of the presence of Ga at long distances from desired FIB milled features will be discussed.

[1] U. Muehle, R. Gaertner, J. Steinhoff, W. Zahn, “Characterisation of Ga-distribution on a silicon wafer

after inline FIB-preparation using inline ToFSIMS,” M. Luysberg, K. Tillmann, T. Weirich (Eds.): EMC 2008, Vol. 1: Instrumentation and Methods, pp. 749–750, DOI: 10.1007/978-3-540-85156-1_375, © Springer-Verlag Berlin Heidelberg 2008

[2] www.srim.org