Quantitative Depth Profiling of Argon in Tungsten Films by Secondary Ion Mass Spectrometry.

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Abstract
Depth profiling of Ar in Ar-implanted tungsten (W) films with an excellent detection limit was investigated by secondary ion mass spectrometry (SIMS). Depth profiles of Ar with the detection of Ar+ and ArCs+ secondary ions, which were produced by O2+ and Cs+ primary ions, respectively, were compared in view of the detection limit and the depth resolution. The detection limit of Ar monitoring Ar+ was limited by the carbon- and oxygen-containing molecular ion (C2O+) in the sample as well as in the SIMS instrument. It was observed that some of the Ar+ ions were produced in the vacuum above the sample surfaces, whereas the ionization of almost all C2O+ occurred at the samples. By using different energy spectra between Ar+ and C2O+, we showed that the energy-filtering technique is advantageous for suppressing C2O+ ion detection. It is also confirmed that the ArCs+ secondary ion is only slighting by the C2OCs+ mass-interference ion. A detection limit of 4 x 10(18) cm(-3) for monitoring Ar+ and 3 x 10(16) cm(-3) for monitoring ArCs+ was achieved under a primary-ion current density of 0.16 mA/cm2. The detection of ArCs+ ion rather than Ar+ was found to be superior in the detection limit and the depth resolution. We conclude that SIMS is useful for the determination of the Ar depth distribution in W films.

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