Page 189 - Inorganic Mass Spectrometry - Fundamentals and Applications

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E (ION ENERGY)
Comparisons of gold sputter yields as a function of mass of bomb~ding ion
with calculations of Rol's collision model. (From Ref. 73.)

The depth of penetration of the primary ion and the width of the damage zone
in
in the solid increase with the energy of the primary ion. Thus, profiling, in which
depth resolution is important, lower-energy ion beams are used to keep the dam-
age zone as narrow as practicable. Figure 4.19 shows the effect of primary ion en-
ergy on profile resolution [75]. Depth resolution also depends on the angle of im-
pact. Impact angles are normally quoted as degrees off noma1 incidence. Ion
beams striking at larger angles penetrate to shallower depths and, thus, provide
greater depth resolution.
A number of efTects lead to loss of profile depth resolution. The effect of
crystallite orientation on sputtering rate is shown in Fig. 4.20, in which l0 keV &+
ions at 50" incidence were used to sputter polyc~stal~ne iron 1761, This ion etch-
ing may be useful to bring out grain structure but leads to loss of depth resolution