Using electron cyclotron resonance sputtering in the deposition of ultrathin Al2O3 gate dielectrics

Abstract

The gate-dielectric characteristics of an ultrathin ${\mathrm{Al}}_2{\mathrm{O}}_3$ film deposited by electron cyclotron resonance sputtering are investigated. The sputtering process is classified as operating in either of two deposition modes: a metal mode and an oxide mode. Characteristics of the deposited films, such as their surface morphology, uniformity of thickness, and degrees of interlayer-oxide formation, are presented for both modes. The electrical characteristics of metal-mode ${\mathrm{Al}}_2{\mathrm{O}}_3$ films after annealing in a high vacuum (around ${10}^{\text{−4}}\hspace{0.17em}\mathrm{Pa})$ are looked at in detail. The metal-mode condition and high-vacuum annealing prevents the formation of interlayer oxide and reduces the flat-band voltage ${\mathrm{(V}}_{\mathrm{FB}})$ shift but also produces a rather large capacitance–voltage $\mathrm{(C–V)}$ hysteresis loop. A small equivalent oxide thickness of 1 nm, low values for leakage current of around ${\text{2×10}}^{\text{−3}}\hspace{0.17em}{\mathrm{A/cm}}^2,$ and a fixed negative-charge density of ${\text{7×10}}^{10}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}$ are demonstrated for the metal-mode films. The large $\mathrm{C–V}$ hysteresis loop is reducible by oxidation.