Page 290 - Inorganic Mass Spectrometry - Fundamentals and Applications

276 Marcus

costs, potential contamination, and a realm of additional considerations, as de-
scribed in the previous sections. The use of radio frequency (rf) powering of the
glow discharge plasma circumvents many of these challenges, providing a single
methodology and apparatus for the analysis of both conductive and nonconductive
sample types. As will be described, rf GD-MS has as its genesis the use of mass
spectrometry to monitor and study plasma etchin~/deposition. It is interesting to
rf
of
note that although “analytical” GD-MS has been an active area work over the
of
last l0 years, the number of publications in this area easily outnumber all those
the other CD-MS methods for nonconductor analysis combined.

tals of Radio Fr~~~e~cy
Glow

The use of rf potentials (typically 13.56 MHz) to sustain low-pressure plasmas
(p~icularly at nonconducting electrodes) is not new, as they have been used for
over 30 years as sputter etching/deposition devices in the electronics industry [57].
A large number of detailed reports describe the underlying principles of analyti-
cal rf GD source operation as they are high interest for applications in both the
of
atomic emission and mass spectrometric sampling modes. The operation of the
of
plasmas is easily understood when one considers a scenario applying a high volt-
7.6 for the case of a *l-kV square
age to an insulating surface as depicted in Fig.
wave potential. At time zero, a large negative potential applied to the cathode sur-
face causes breakdown of the discharge gas such that positive ions are accelerated
to the electrode surface. This of course causes the negative potential to be neutral-

Response of an insulating electrode immersed in a low-pressure atmosphere to
the application of a high-frequency square wave potential.