Trap Reduction through O₃ Post‐Deposition Treatment of Y₂O₃ Thin Films Grown by Atomic Layer Deposition on Ge Substrates

Abstract

For Ge‐based metal‐oxide‐semiconductor field‐effect transistor application, high‐k Y2O3 thin films are deposited on Ge single‐crystal substrate using atomic layer deposition. The primary drawbacks of a metal‐oxide‐semiconductor capacitor with pristine Y2O3 are large hysteresis and high leakage current. Through forming gas annealing (FGA), the leakage current can be reduced by approximately three orders of magnitude, along with the reduction of interface trap density. However, there is still a large hysteresis in the capacitance–voltage curves. O3 post‐deposition annealing (OPA) is used to solve the problem. The formation of the YGeOx interfacial layer through OPA and the reduction of the defect level of the Y2O3 thin film effectively decrease the hysteresis, which also decreases the leakage current. Additionally, the hysteresis is 690 mV when only FGA is performed. However, it is further reduced to 260 mV through OPA. Moreover, the remote oxygen scavenging effect using TiN/Pt electrodes prevents an unintentional increase in equivalent oxide thickness (EOT). The 4.7 nm thick Y2O3 film results in an EOT of 1.77 nm and leakage current density of 2.1 × 10−7 A cm−2 (at flat band voltage—1 V) after the OPA.

Comparison of high-k Y2O3/TiO2 bilayer and Y-doped TiO2 thin films on Ge substrate

“…The authors recently reported that the as-deposited amorphous Y 2 O 3 film had a highly defective property if no additional O 3 treatment was performed. Therefore, GeO diffusion appears larger in the amorphous Y 2 O 3 layer compared to the relatively stable TiO 2 layer [27].…”

“…The high ∆N st was due to ∆N st present in the Y 2 O 3 and YTO thin film layers, not due to the diffusion of Y and Ti into the Ge/GeO 2−x interface or GeO 2−x layer, as discussed later. When the thickness ratio of Y 2 O 3 :TiO 2 was 3:4, the ideal dielectric constant was calculated as ∼22.9 from the dielectric constants of Y 2 O 3 and TiO 2 of ∼15.6 and ∼35.4 in the previous reports, respectively [19,27]. The k-value of the bilayer thin film was calculated from the C-V curve of figure 6(a) as ∼17.8.…”