Search

This study examines the influences of the Al2O3 and Y2O3 insertion layers (ILs) on the structural and electrical features of ZrO2 thin films for their application to dynamic random access memory capacitors. The ultra‐thin Al2O3 IL (0.1–0.2 nm) dissolves into the ZrO2 layers, which causes the top and bottom portions of the ZrO2 film to merge and have smaller lattice parameters. However, the thicker Al2O3 IL (>≈0.4 nm) forms a continuous layer and separates the top and bottom portions of the ZrO2 film. Interestingly, the diffusion of Al does not occur in this case. Overall, the dielectric constant (κ) of the ZrO2/Al2O3/ZrO2 film is lower than that of the undoped ZrO2 film due to the involvement of the low‐κ Al2O3 IL. In contrast, the Y2O3 IL does not interfere with the grain growth of ZrO2, rendering the continuous ZrO2 grain formation throughout the entire film thickness despite the presence of the continuous region with a higher Y‐concentration. The most crucial finding is that the Y‐doping significantly decreases the leakage current without sacrificing the dielectric constant. This leakage current decrease can be ascribed to the p‐type doping effect of Y ions in the n‐type ZrO2. [ABSTRACT FROM AUTHOR]

Y2O3/TiO2 bilayer thin films and Y-doped TiO2 (YTO) thin films were deposited on a Ge substrate by atomic layer deposition at a substrate temperature of 250 °C. They were used as gate insulators to examine the electrical properties of Pt/TiN/TiO2/Y2O3/p-Ge and Pt/TiN/YTO/p-Ge metal–oxide–semiconductor capacitors. A 7 nm thick bilayer thin film showed a lower leakage current density by more than one order of magnitude compared to a YTO thin film with the same thickness due to the high conduction band offset between the Y2O3 layer and Ge substrate. However, the bilayer thin film showed a large hysteresis of 950 mV. On the other hand, the YTO thin film showed significantly reduced hysteresis of 120 mV due to the smaller slow trap density. The voltage acceleration factors of the bilayer thin film and YTO thin film were 1.12 and 1.25, respectively, higher in the YTO thin film. The interfacial trap density of the 7 nm thick bilayer and YTO thin films were 3.5 × 1011 cm−2 eV−1 and 2.7 × 1011cm−2 eV−1, respectively. The equivalent oxide thickness of the YTO film could be scaled down to 0.9 nm, and a leakage current density of 1.4 × 10−4A cm−2 at flat band voltage −1 V was achieved. This study confirmed that the YTO film can be used as a promising ternary high-k oxide for a Ge-based field-effect-transistor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Al is doped to a SrTiO3 (STO) thin film grown by atomic layer deposition (ALD) to decrease the leakage current. One ALD cycle of Al2O3 is processed either at the top or at the bottom of the STO films, and the electrical properties are compared with those of the undoped STO films. The ≈3.5 nm‐thick seed layer is first deposited and crystallized through rapid thermal annealing, and from 5 to 20 nm‐thick main layers are subsequently grown for in situ crystallization of the main layer. When an Al2O3 deposition cycle is inserted below the first seed layer, the crystallization of the STO films is disturbed, and the bulk dielectric constant degrades from 149 (undoped STO) to 71. When the Al2O3 deposition cycle is performed after the STO main layer growth, however, the dielectric constant degradation is minimized (120). In both cases, the leakage current decreases 20 times compared with the undoped STO case because of the conduction band offset increase. Consequently, the equivalent oxide thickness and physical oxide thickness decrease from 0.71 to 0.63 nm and from 10.3 to 8.6 nm, respectively, through Al doping on the top of the STO films with a sufficiently low leakage current (<10−7 A cm−2). [ABSTRACT FROM AUTHOR]

SrTiO3 (STO) films are grown via atomic layer deposition at 370 °C with a two‐step growth method. A 5‐nm‐thick seed layer is first deposited and annealed via rapid thermal annealing (RTA) at temperatures ranging from 450 to 650 °C, and the main layer is subsequently grown on the annealed seed layer for in situ crystallization. When the RTA temperature is 500 °C or lower, the seed layer remains amorphous, and the main layer is also grown in the amorphous phase. At the 550 °C seed annealing temperature, the STO film is partially crystallized, and at the higher annealing temperature, the STO main layer is fully crystallized. The oxygen diffuses through the vertically aligned grain‐boundaries during the crystallized film growth, which induces the oxidation–reduction reaction of the underlying Ru substrate. This reaction causes a higher growth rate in the crystalline phase. The large growth rate difference between the amorphous and crystalline regions induces a severe roughening of the main layer. When RTA is done at 600 °C, the film is mostly crystallized, and the main layer becomes smooth again. Consequently, a 0.52 nm equivalent oxide thickness is achieved with the low leakage current of 2.5 × 10−8 A cm−2 at the 0.8 V applied bias. [ABSTRACT FROM AUTHOR]

The electrical characteristics of metal–insulator–metal (MIM) capacitors consisting of a ZrO2/Al2O3/ZrO2 (ZAZ) dielectric film, a TiN bottom electrode (BE), and two different top electrodes (TEs; TiN and Ru) are examined. The enhanced property in the leakage current density versus equivalent oxide thickness (J–tox) plot is observed in the MIM structure with the Ru TE for the ZAZ film with specific film thickness of ≈4.6 nm. Especially, the J due to the electron injection from the TiN BE was significantly decreased for the Ru TE case compared to the TiN TE sample at 1–2 MV cm−1 electric field region. These extraordinary behaviors are found to have originated the change in the oxygen vacancy density in the ZAZ film, which induces Poole–Frenkel emission through the reaction with the active oxygen during the Ru TE fabrication process. The difference in nonlinearity of the capacitance–voltage (C–V) curve also indicates a different trap density at the interface of ZAZ and the TiN BE, suggesting a change in the oxygen vacancy density in the ZAZ film. Two different materials, sputter‐grown TiN and atomic layer deposition (ALD)‐grown Ru, are prepared for the top electrode (TE) material of ZrO2/Al2O3/ZrO2 (ZAZ)‐based capacitors for DRAM application. The electrical characteristics are investigated, and the capacitor with a Ru TE shows a much lower J value than the TiN TE at an oxide thickness (tox) value of about 1.0 nm. [ABSTRACT FROM AUTHOR]