Surface analysis, gate leakage currents and electrical characteristics of Mn ions incorporated into ZrO2 gate dielectric layer in silicon MOS capacitors

Abstract

The metal oxide semiconductor capacitors containing Mn doped ZrO2 high-κ films acted as active oxide layer were fabricated on Si (100) wafer by electron beam evaporation. Structural analysis by GIXRD revealed a complete tetragonal phase stabilization in ZrO2 thin films when doped with 5 and 8 mol% Mn and annealed at 500 °C. Film thickness of 40–80 nm was confirmed by XRR and cross-sectional FESEM analysis. Composition analysis by XPS showed that the ZrO2 thin films were stoichiometric and the Mn ions have existed in +2 oxidation state. The film surfaces were obtained to be smooth and crack free when analyzed by FESEM and AFM where the RMS roughness was found to be in the range from 0.43 to 0.82 nm. All the MOS capacitors have shown good capacitance-voltage characteristics with equivalent oxide thicknesses varying from 7.2 to 9.7 nm. The highest dielectric constant of 39.2 was observed in ZrO2 layer with 8 mol% Mn and the dielectric constant was increasing with Mn concentration. Leakage current in the MOS capacitors was found reduced by an order of magnitude due to Mn stabilized tetragonal ZrO2 layer. Among the MOS capacitors the leakage current density of as low as 1.28 × 10−6 A/cm2 was recorded at −1 V with 5 mol% Mn concentration in ZrO2 layer. The complex leakage currents across the dielectric layer in the MOS capacitors were explained based on several current conduction mechanisms. Leakage current in these devices was predominantly covered by space charge limited conduction mechanism. At lower voltages (less than −5 V), Poole-Frenkel and Schottky emission were found dominant whereas Trap-assisted tunneling and Fowler-Nordheim tunneling had contributed to the leakage current conduction at voltages greater than −10 V.