Depth profiling in secondary ion mass spectrometry for ultra-thin layer with nanometer order thickness by mesa-structure fabrication

摘要

We attempted to make an accurate depth profiling in secondary ion mass spectrometry (SIMS) including backside SIMS for ultra-thin nanometer order layer. The depth profiles for HfO _2 layers that were 3 and 5 nm thick in a-Si/HfO _2/Si were measured using quadrupole and magnetic sector type SIMS instruments. The depth profiling for an ultra-thin layer with a high depth resolution strongly depends on how the crater-edge and knock-on effects can be properly reduced. Therefore, it is important to control the analyzing conditions, such as the primary ion energy, the beam focusing size, the incidence angle, the rastered area, and detected area to reduce these effects. The crater-edge effect was significantly reduced by fabricating the sample into a mesa-shaped structure using a photolithography technique. The knock-on effect will be serious when the depth of the layer of interest from the surface is located within the depth of the ion mixing region due to the penetration of the primary ions. Finally, we were able to separately assign the origin of the distortion to the crater-edge effect and knock-on effect.