A simple secondary ion mass spectrometry (SIMS) apparatus has been constructed. A Superior Electronics, 3K/5U, electron gun has been converted to an ion gun capable of producing a 1 mm diam, 2 keV, 1 μA beam. To achieve wide dynamic range at high resolution in the mass analysis of the secondary ions using a quadrupole mass spectrometer (QMS), the ion injection energy must be ≲4 eV. Ions sputtered from the target with these low energies are selected with a simple cylindrical mirror analyzer placed in front of the QMS. Single monolayers are easily analyzed using a beam density of 10−7 A/cm2; bulk profile analysis is performed while sputtering with higher beam densities. Signal-to-background ratios in excess of 106 are acheved. Positive SIMS of clean and cesiated GaAs single crystals have been obtained and are discussed. A composition versus depth profile of a GaAs–AlxGa1−x As sandwich structure is also presented.
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Schubert et al. (1973) studied this question.
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