Experimental Investigation of Ultrathin Al₂O₃ Ex-Situ Interfacial Doping Strategy on Laminated HKMG Stacks via ALD

Abstract

In this work, a p-type high-<inline-formula> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> metal gate (HKMG) with 3-nm interfacial Al₂O₃ doping HfO₂ laminated dielectric is presented to achieve the required gate electrode effective work function (EWF). Through the ex-situ interfacial doping strategy with various Al₂O₃ thickness, the electrical and interface characteristics of p-type HKMG MOSCAP are investigated. The results show that these parameters are strongly dependent on the thickness of the Al₂O₃. By increasing the Al₂O₃ thickness, the flat-band voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{\text {FB}}$ </tex-math></inline-formula>) positive shift is elevated by 360 mV, and the trap/detrap electrons density (<inline-formula> <tex-math notation="LaTeX">${N}_{\text {ot}}$ </tex-math></inline-formula>) is significantly suppressed by an order of magnitude. In addition, the interface charge density (<inline-formula> <tex-math notation="LaTeX">${N}_{\text {SS}}$ </tex-math></inline-formula>) is significantly reduced, and interface trap density (<inline-formula> <tex-math notation="LaTeX">${D}_{\text {it}}$ </tex-math></inline-formula>), time-dependent dielectric breakdown (TDDB), and positive bias stress (PBS) is obviously improved. Finally, EWF modulation was increased from 4.976 to 5.206 eV (over the valence band edge of 5.17 eV). The results reveal that it is possible to tailor dielectric and electrical properties of high-<inline-formula> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> layers by adding a proper amount of interfacial Al₂O₃ doping into HfO₂, meeting the criteria required for gate electrode p-type EWF. These results and discussion provide an effective method for the integration of the HKMG stack in the MOSFETs and also useful for design of CMOS integration.