Sang Woon Lee

Enhanced electrical properties of SrTiO3 thin films grown by atomic layer deposition at high temperature for dynamic random access memory applications

SrTiO3 (STO) thin films were deposited at 370°C by atomic layer deposition using H2O as the oxidant, and Ti(O–iPr)2(thd)2 and Sr(thd)2 as Ti, and Sr precursors, respectively. Denser STO films were produced at this deposition temperature. The saturated growth rate was 0.15A∕cycle. The adoption of a thin crystallized seed layer resulted in crystallized perovskite STO films at the as-deposited state without higher temperature post-annealing. A tox of 0.72nm (dielectric constant of 108) and a low leakage current density (∼10−7A∕cm2 at 0.8V) were obtained from a planar capacitor structure consisting of Pt∕20-nm-thick STO/Ru (bottom).

Atomic Layer Deposition of Ru Thin Films Using 2,4-(Dimethylpentadienyl)(ethylcyclopentadienyl)Ru by a Liquid Injection System

Ru thin films were grown on Si, SiO 2 , TiO 2 , and TiN substrates by atomic-layer deposition using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru and O 2 as Ru precursor and reactant, respectively, at temperatures ranging from 230 to 280°C. A saturated growth rate of 0.04 nm/cycle and a low oxygen concentration (below the detection limit of Auger electron spectroscopy) were obtained at 250°C. The Ru film showed a negligible incubation period on all the different types of substrates, and an active nucleation behavior which resulted in a very smooth film surface morphology. The dimethylpentadienyl ligand enhanced the active nucleation of Ru and retarded the oxidation of the grown Ru layer. Good step coverage (>90%) was obtained from the Ru film grown on a capacitor hole with an aspect ratio of 17 and an opening diameter of 150 nm by a proper control of the Ar carrier gas flow rate.

Growth Characteristics of Atomic Layer Deposited TiO2 Thin Films on Ru and Si Electrodes for Memory Capacitor Applications

TiO 2 thin films were grown by an atomic-layer-deposition process at growth temperatures ranging from 200 to 300°C on Ru and Si substrates using Ti[OCH(CH 3 ) 2 ] 4 and H 2 O as metal precursor and oxygen source, respectively, for metal-insulator-metal capacitor application in dynamic random access memories. The saturated film growth rate on Ru and Si substrates was 0.034 and 0.046 nm/cycle, respectively. The TiO 2 film growth on a Ru substrate showed a rather long incubation period and the incubation period decreased with increasing Ti[OCH(CH 3 ) 2 ] 4 pulse time, whereas the H 2 O pulse time had almost no influence on the incubation period. A growth rate transition, from low to high values, (thickness 7-8 nm) was observed when the films were grown at temperatures >250°C, whereas the films grown at lower temperatures did not show the transition. The transition was due to the structural change of the film from an amorphous/nanocrystalline to the well-crystallized polycrystalline anatase phase. The TiO 2 films grown at temperatures >250°C showed a dielectric constant of ∼35. A 14-nm-thick TiO 2 film showed an equivalent oxide thickness of 1.7 nm and a leakage current density of 5 X 10 - 6 A/cm 2 at 1 V.

Atomic Layer Deposition and Electrical Properties of SrTiO3 Thin Films Grown Using Sr ( C11H19O2 ) 2, Ti ( Oi-C3H7 ) 4, and H2O

Atomic layer deposited SrTiO 3 (STO) thin films were grown using Sr(C 11 H 19 O 2 ) 2 and Ti(Oi-C 3 H 7 ) 4 with a remote plasma activated or thermal H 2 O vapor as oxidant at growth temperatures ranging from 190 to 270°C. The as-grown films were amorphous and showed a low effective dielectric constant of -20 with a low leakage current density (< 10 -7 A/cm 2 at 1 V). The chemical binding status of the Sr ions varied with the degree of crystallization of the STO film. A reasonable film growth rate and stoichiometric cation composition were obtained when the vaporization temperature of Sr-precursor was <200°C with the thermal H 2 O vapor. The low density of the as-grown film induced a large shrinkage in the film thickness which caused microcracking of the crystallized films during postannealing, even with the increased H 2 O supply. Adoption of thin (∼5 nm) crystallized seed layer before the main layer STO growth improved the microstructure after the crystallization and the leakage current performance. As a result of the process optimization, the best electrical properties of an STO film grown on a Ru electrode were 0.45 nm for the equivalent oxide thickness and 1 X 10 -3 A/cm 2 for the leakage current density at 1 V.

Improvement in the leakage current characteristic of metal-insulator-metal capacitor by adopting RuO2 film as bottom electrode

The dielectric constant, equivalent oxide thickness (tox), and leakage current properties of Pt/(Al-doped)TiO2/RuO2 capacitors were examined in comparison with Pt/(Al-doped)TiO2/Ru capacitors. The Al-doped TiO2 and undoped TiO2 films grown on RuO2 showed high dielectric constants of 60 and 102, respectively. The minimum tox of these films were 0.46 nm and 0.56 nm, respectively, while still satisfying the dynamic random access memory leakage current density specification (< 1 × 10−7 Acm−2 at capacitor voltage of 0.8 V). These excellent electrical properties of (Al-doped) TiO2 on RuO2 were attributed to the high work function and the reduced interfacial effect on RuO2.

Influences of a Crystalline Seed Layer during Atomic Layer Deposition of SrTiO3 Thin Films Using Ti ( O-iPr ) 2 ( thd ) 2, Sr ( thd ) 2, and H2O

In situ crystallized ∼20 nm thick SrTiO 3 (STO) thin films were deposited by atomic layer deposition at a growth temperature of 370°C using a 3 or 5 nm thick crystalline STO seed layer before depositing the main layer. The influences of the annealing temperature used to crystallize the seed layer on the structure and electrical properties of the entire STO film were investigated. There was an optimum annealing temperature (650-700°C) for achieving the optimum electrical performance. When the annealing temperature was 750°C induced adverse chemical interactions between the seed STO and Ru electrode, which inhibited in situ crystallization of the main layer when the seed-layer thickness was 3 nm. A slightly thicker seed layer (5 nm) was necessary for achieving a well-crystallized STO film when the seed annealing temperature was 750°C.

Substrate Dependent Growth Rate of Plasma-Enhanced Atomic Layer Deposition of Titanium Oxide Using N2O Gas

TiO 2 thin films were grown on Ru, Pt, Al 2 O 3 -passivated Ru, and Si substrates by plasma-enhanced atomic layer deposition at 280°C. The Ru-substrate-enhanced growth (∼3 times higher than that on Si at <100 cycles) was attributed to the electron donation and the diffusion of previously contained oxygen from Ru onto the growing surface. When the Al 2 O 3 layer was interposed between the Ru substrate and TiO 2 film, even as thin as 0.4 nm, the electron donation was largely suppressed. Above 16―20 nm, the growth rates of rutile TiO 2 (on Ru) and anatase TiO 2 (on Si) were 0.055 and 0.04 nm/cycle, respectively.

Electronic Conduction Mechanism of SrTiO3 Thin Film Grown on Ru Electrode by Atomic Layer Deposition

In situ crystallized 20 nm thick SrTiO 3 (STO) thin films were grown on a Ru substrate by atomic layer deposition. The leakage current-voltage characteristics of the film were examined from 313 to 403 K under electron injection conditions from the Ru electrode. The leakage current was dominated by Schottky emission in the low electric field ( 0.3 MV/cm) region. The estimated effective mass of the tunneling electron was ~0.1m 0 .

Controlling the initial growth behavior of SrTiO3 films by interposing Al2O3 layers between the film and the Ru substrate

The effects of thin Al2O3 layers interposed between atomic layer deposited SrTiO3 (STO) films and Ru substrates on the growth and properties of STO films were examined. Although a 3–4 nm thick TiO2 barrier layer was necessary to completely suppress the oxygen diffusion from the underlying Ru(O) layer, which could result in uncontrolled excessive Sr incorporation into the film, a 2–3 nm thick Al2O3 barrier layer was sufficient to achieve the saturated oxygen blocking effect. Therefore, only a 0.4 nm thick Al2O3 layer could effectively suppress uncontrollable initial excessive incorporation of Sr, and a 1 nm thick Al2O3 layer had a blocking effect that was equivalent to that of a 3 nm thick TiO2 layer. STO films were crystallized in situ by the assistance of crystallized 2–3 nm thick STO seed layers that were pre-deposited and annealed. The bulk dielectric constant of STO calculated by the slope of equivalent oxide thickness vs. physical thickness was 173 on the 1 nm thick Al2O3/Ru substrate. However, further research is necessary to reduce the adverse contribution of the interfacial layers to achieve a scaling of the equivalent oxide thickness to ≪0.5 nm.

Effects of Annealing Environment on Interfacial Reactions and Electrical Properties of Ultrathin SrTiO3 on Si

SrTiO 3 films were grown by radio-frequency magnetron sputtering and postdeposition annealing (PDA) in N 2 , O 2 , or NH 3 atmospheres. A Sr silicate layer formed at the interface between the SrTiO 3 film and Si substrate due to Si diffusion into the films during deposition. This resulted in an inhomogeneous composition of SrTiO 3 films along the vertical direction, which was enhanced by PDA. While the thick SrTiO 3 film was crystallized after PDA and the permittivity increased (>220), the thin SrTiO 3 films remained amorphous even after PDA due to the diffused Si. TiO x in the amorphous SrTiO 3 layer was easily nitrided after PDA in an NH 3 atmosphere but TiO x in the crystalline SrTiO 3 layer was barely nitrided. The electrical properties of the SrTiO 3 films were improved by PDA.