Low-frequency noise assessment of border traps in Al₂O₃ capped DRAM peripheral MOSFETs

Low-frequency noise has been used to study the impact of an Al₂O₃ work-function-engineering cap layer on the gate oxide quality of SiO₂/HfO₂ DRAM peripheral n- and pMOSFETs. It is shown that from the 1/f-like spectra a border trap density profile can be extracted, which depends on whether the cap is deposited below or above the HfO₂ layer. In general, the presence of Al in the high-κ material leads to a higher trap density, with a maximum concentration close to or at the SiO₂/HfO₂ interface, where a dipole layer is expected to form. When removing the cap layer from the SiO₂ interfacial layer, excess generation-recombination-like noise is introduced for the n-channel devices, indicating the presence of dry-etching damage at the SiO₂/HfO₂ interface. (paper)