Effect of the Annealing Temperature of the Seed Layer on the Following Main Layer in Atomic‐Layer‐Deposited SrTiO₃ Thin Films

Abstract

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.

Improving the Properties of SrRuO3 Electrode Films Grown by Atomic Layer-Deposited SrO and Pulsed Chemical Vapor-Deposited RuO2 Using Al2O3 Capping Layers

“…(a) EOT as a function of POT of the STO dielectric layer and (b) leakage current density ( J ) as a function of EOT of the MIM capacitors at 0.8 V. Data for the STO/Ru case are reproduced with permission from refs , (Copyright [2019] WILEY-VCH Verlag GmbH & Co.).…”

“…Details of the ALD STO process were reported elsewhere. 5 TE was deposited by DC reactive sputtering using a shadow mask with a 300 μm diameter. After the TE deposition, postmetallization annealing (PMA) was conducted at 400 °C for 30 min under an air atmosphere.…”

“…H 2 O and O 3 gases were used as the reactant gases of SrO and TiO 2 sublayers, respectively. Details of the ALD STO process were reported elsewhere . TE was deposited by DC reactive sputtering using a shadow mask with a 300 μm diameter.…”

“…The perovskite SrRuO 3 (SRO) is a conductive oxide that has been studied extensively as a bottom electrode material for dielectric or ferroelectric materials with perovskite structures. , Among the functional perovskite materials, SrTiO 3 (STO) is gaining attention as a dielectric material for the next-generation dynamic random access memory (DRAM) capacitor because of its vast dielectric constant ( k ) value of ∼300 at room temperature . However, the crystallization of the STO film grown by the atomic layer deposition (ALD) process required complicated processing steps, such as two-step growth, limiting its practical application in DRAM. − In contrast, the SRO bottom electrode enables in situ crystallization of STO through heteroepitaxial growth, as SRO has almost the same lattice parameter as STO ( a SRO = 0.3923 nm for the pseudocubic structure, a STO = 0.3905 nm for the cubic structure) . While the well-crystallized SRO could be grown by physical vapor deposition, such as pulsed laser deposition, at high temperatures (≥650 °C), its limited compatibility with the DRAM process requires that ALD should also deposit it. , Nonetheless, feasible ALD of the SRO film has limited success, as described below.…”

Enhancing the Crystallization and Properties of the SrRuO3 Electrode Film Grown by Atomic-Layer-Deposited SrO and Pulsed-Chemical Vapor-Deposited RuO2 through Al Substitution

“…During ex situ crystallization, capacitor properties are degraded by densification (thickness shrinkage) of the STO film that forms microcracks and deterioration of the interface of the bottom electrode/dielectric layer. Therefore, an in situ crystallization process was attempted using the two-step process, where the thin (∼3–5 nm) STO seed layer was deposited and crystallized first by rapid thermal annealing (RTA). − The main STO layer (7–8 nm) was subsequently deposited on the crystallized seed layer, which had the in situ crystallized structure. However, such a two-step process rendered the capacitor fabrication process complicated.…”