Page 185 - Inorganic Mass Spectrometry - Fundamentals and Applications

l 72 Cristy

MAGNET
Mass Analysis ELECTROSTATIC A~ALYZE~
\ Ener~,A~lysis

PRIMARY COL^^^
Primary Probe Beam

SOURCE CHAMBER
Secondary Beam

I
COLLECTOR
Secondary Bern ~~tect~on SAMPLE
Sensitive ~gh-resolution ion micro probe S ~ H) Phigh-mass-resolution,
(
~gh-sensitivity instrument designed for isotopic geochronology, dimensions in millimeters.

ment, based on an original design by G. Slodzian, features 50-nm resolution with
a CS source (Fig. 4.14). The design incorporates normal incident primary ions and
normal extraction of secondary ions (coaxial) to optimize objective lens perforrn-
ance and ion collection. This requires that primary and secondary ions be of op-
posite polarity. Thus, CS+ primary is used to produce negative secondary ions, and
0- primary is used to produce positive secondary ions. The analyzer is based on
the Mattauch-Herzog geometry and includes five movable detectors for parallel
ion detection and simultaneous secondary electron imaging.
In response to the necessity for SMS to provide profiling with resolutions
approaching or exceeding 1 nm, Dowsett al. developed an ultralow-energy float-
et
ing ion gun (FX,IG) [62] for semiconductor processing. This gun was designed to
maintain high profiling currents with energies between 200 eV and 5 keV (Fig.
4.15). Depth resolution of 1 nm and currents >l pA at 1 keV and >200 nA at 250
eV on spot sizes of 100 pm were reported; a 30-pm probe size was achieved.
Some good books, reviews, and historical perspectives of the field of sec-
sec on^^^ Ion se ss
ondary ion mass spectrometry have been published, including
at
S~ectro~et~, proceedings of a workshop held the National Bureau of Standards
in Gaithersburg, Maryland, September 16"18,1974 [63]. The proceedings include