Micro-area analysis in SIMS depth profiling by mesa-structure preparation

To improve the depth resolution in secondary ion mass spectrometry (SIMS) depth analysis by reducing the crater-edge effect, samples with mesa-structure projections were prepared by photolithography. The depth profiles of boron implanted into silicon were studied by comparing those for a conventional flat sample and the mesa-structure sample while systematically changing the gate area ratio. The mesa-structure preparation was very useful for eliminating undesired ions originating from the crater edge or surroundings of the analyzed area; it therefore led to remarkable improvement in the depth profiles while keeping a low background level of the order of 10−1 cps and high dynamic range of the order of 105 even at a high gate area ratio of more than 30%. As a result, a good depth profile for a 4 μm × 8 μm sample was successfully achieved by this method.