Page 194 - Inorganic Mass Spectrometry - Fundamentals and Applications

Surface topography on 20 keV 0,' bombarded surfaces: a (above), silicon
(high
(high B,,); b (above), ge~~ium B,,); a (below), tin (low B,,); b (below), alu-
minum (low B,,). Doses -1 X loi9 ions/cm2. (From Ref. 78.)

Ge at 8.3 and 6.8 eV, respectively, the ion-bombarded area was quite uniform, but
as B,, decreased, more surface topography developed. Their §EM images of Si,
Ge, Sn, and A1 after sputtering with 20 keV O,+ are shown in Fig. 4.22. Rotation
of the sample (sometimes called alar rotatio~) [79] is commonly used with off
normal incidence sputtering to minimize the formation of sputter-induced topog-
raphy,
Surface roughness, primary beam current density uniformity, and primary
cu~e~t stability are extrinsic factors that affect the flatness the advancing crater
of
bottom and thus depth resolution. Usually electronic or mechanical aperturing is
used to limit collection of secondary ions to the central, flattest portion
of the sput-
ter crater, thereby reducing edge effects and maxi~zi~g depth resolution, Elec-
tronic aperturing is used with microprobe inst~ments in which the primary beam
is deflected in a raster pattern, The electronic aperture allows counting to take place