A nanoanalytical investigation of elemental distributions in high-k dielectric gate stacks on silicon

Two high-k gate stacks with the structure Si/SiO2/HfO2/TiN/poly-Si are characterised using nanoanalytical electron microscopy. The effect of two key changes to the processing steps during the fabrication of the stacks is investigated. Electron energy-loss spectroscopy is used to show that the TiN layer has a very similar composition whether it is deposited by PVD or ALD. Spectrum imaging in the electron microscope was used to profile the distribution of elements across the layers in the stack. It was found that when the anneal after HfO2 deposition is carried out in a NH3 atmosphere instead of an O2 atmosphere, there is diffusion of N into the SiO2 and HfO2 layers. There is also significant intermixing of the layers at the interfaces for both wafers.