Suppressed Thermally Induced Flatband Voltage Instabilities with Binary Noble Metal Gated Metal--Oxide--Semiconductor Capacitors

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We investigated thermally induced flatband voltage (V_{\text{FB}}) instabilities with single noble metals (Pt, Ir, Pd), their binary metal (IrPt) and control TiN used for gate electrodes in metal oxide semiconductor devices with atomic layer deposited HfO2 gate dielectric. As-deposited e-beam evaporated noble metals and sputtered TiN gated devices show near band-edge p-type metal--oxide--semiconductor (pMOS) characteristics and higher V_{\text{FB}} than midgap value, respectively. After 450 °C at 30 min forming gas anneal, V_{\text{FB}} of devices with e-beam evaporated single metals and sputtered TiN is substantially shifted toward mid-gap position, indicating thermally induced V_{\text{FB}} instability. However, device with binary metal alloy gate shows suppressed V_{\text{FB}} shifts and work-function as high as 4.95 eV is attained with 450 °C at 30 min FGA. It can be explained by oxygen diffusion within gate stack structure into interfacial layer (IL) between Si and HfO2 during anneal, leading to thicker IL and vacancy generation in dielectric.
2012-02-25