Investigation of the analysis parameters and background subtraction for high-k materials with atom probe tomography

In this paper we present depth profiles of a high-k layer consisting of HfO2 with an embedded sub-nm thick ZrO2 layer obtained with atom probe tomography (APT). In order to determine suitable measurement parameters for reliable, reproducible, and quantitative analysis, we have investigated the influence of the laser energy and the specimen temperature on the resulting elemental composition. In addition we devise a procedure for local background subtraction both for the composition and the depth scale that is crucial for gaining reproducible results. We find that the composition of the high-k material remains unaffected even for extreme laser energies and base temperatures, while higher laser energies lead to an accumulation of silicon at the upper interface of the high-k layer. Furthermore we show that APT is capable of providing sub-nm depth resolution for high-k materials with high reproducibility, good compositional accuracy, and high measurement yield.

Research highlights
► HfO2 gate oxides were analyzed by atom probe tomography.
► Sub-nm depth resolution and excellent reproducibility were obtained.
► We describe measurement artifacts and how to avoid them.
► Background events have to be removed for best reproducibility.
► Measurement yield of about 90% was achieved.