Development of a triplasmatron ion source for the generation of SF5+ and F- primary ion beams on an ion microscope secondary ion mass spectrometry instrument

A hot filament duoplasmatron ion source operating with argon has been modified by the addition of an enclosed expansion cup mounted to the extraction side of the duoplasmatron anode. Using sulfur hexafluoride (SF6) as a feed gas, this triplasmatron ion source has been used to generate SF5+ and F- primary ion beams for secondary ion mass spectrometry (SIMS). For positive primary ions, the current extracted from the source is composed of a series of SFx+ cluster ions (x = 1-5) with the SF5+ ion being the most intense. SF5+ currents of similar to 10-20 nA with a maximum of 40 nA are obtained at an extraction voltage of 10 kV. By applying a positive bias to the expansion cup, a localized secondary are discharge is initiated giving 200 nA-300 nA of SF5+ with a current density of 0.5 mA/cm(2). Depending on the operating parameters of the source, lifetimes of greater than 70 h have been achieved. For negative primary ions (with the cup removed), the current extracted from the source is primarily composed of F- ions with a maximum current of 3 mu A. The source can be briefly dosed with SF6 and will generate F- beams for 1-2 days without any additional gas being added. Evaluation of the SF5+ and F- ion beams for common SIMS applications demonstrates that these novel primary beams offer significant advantages for depth profiling, organic surface characterization and imaging. (C) 1999 American Vacuum Society. [S0734-2101(99)01003-9].