Oh Seong Kwon

Chemically Conformal ALD of SrTiO3 Thin Films Using Conventional Metallorganic Precursors

SrTiO 3 (STO) thin films were grown on Si wafer, Pt- and Ru-coated Si wafers, respectively, by an atomic layer deposition (ALD) technique using conventional metallorganic precursors, Sr(C 1 1 H 1 9 O 2 ) 2 (Sr(thd) 2 ) and Ti(Oi-C 3 H 7 ) 4 (TTIP) as Sr- and Ti-precursors, respectively, with a remote-plasma activated H 2 O vapor as the oxidant at a wafer temperature of 250°C. Patterned Si wafers with contact holes having a diameter of 0.13 and 1 μm depth (aspect ratio of 8) was used in order to test the film-thickness and cation-composition conformalities over the contact hole surface. The ALD behavior of the STO film was critically dependent on the Sr(thd) 2 source heating temperature. When the Sr source temperature was ∼200°C. This difficulty resulted in a nonuniform cation composition ratio along the contact hole.

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.

Protection of SrBi2Ta2O9 ferroelectric capacitors from hydrogen damage by optimized metallization for memory applications

The degradation behavior of integrated Pt/SrBi2Ta2O9/Pt capacitors by hydrogen impregnation during the intermetal dielectric deposition and passivation is investigated. The hydrogen ions generated as a reaction byproduct from the SiH4-based deposition processes of the dielectric films induce reduction in the remanent polarization (Pr) as well as the imprint behavior of the small size capacitors (2×2 μm2). The degree of degradation is quite dependent on the size of the individual capacitors. The smaller capacitors underwent more serious degradation implying that the hydrogen ions impregnate into the SBT layer mainly along the etched side area of the capacitors not through the top Pt electrode. Metallization adopting TiN/Al/TiN/Ti multilayer is very effective in suppressing the hydrogen impregnation. In particular, the Ti layer appears to block the hydrogen penetration. Therefore, the optimized metallization scheme, wider metal lines than the top electrode area by 1 μm, successfully protects the integrated ...

Degradation behavior in the remnant polarization of SrBi2Ta2O9 thin films by hydrogen annealing and its recovery by postannealing

The degradation behavior in the remnant polarization (Pr) of sol–gel-derived SrBi2Ta2O9 (SBT) thin films, with Pt top and bottom electrodes, by annealing under a 5% H2/95% N2 atmosphere is investigated. The hydrogen annealing is performed at temperatures ranging from 250 to 480 °C. By annealing, the Pr drops to almost zero for all temperatures. Postannealing at temperatures higher than 700 °C under an air atmosphere recovers the Pr. Interestingly, the recovery is most ineffective for the sample annealed at the Curie temperature of the SBT films. A phenomenological model that explains this anomalous recovery behavior is presented.

Polarity-dependent rejuvenation of ferroelectric properties of integrated SrBi2Ta2O9 capacitors by electrical stressing

The electric-field-induced rejuvenation behavior of the degraded ferroelectric properties of integrated Pt/SrBi2Ti2O9/Pt capacitors was investigated. Integration processes, especially plasma-enhanced chemical vapor deposition of the passivation layers, generate hydrogen ions and electrons which act as domain pinning centers and a source of a negative internal electric field. Domain pinning was found to reduce the remanent polarization (Pr) and internal field that induces an imprint to the positive bias direction. Alternating current cyclings with peak voltages of +/−6 V rejuvenated the degraded ferroelectric performance of the capacitors. Cycling with a negative bias was more effective in fixing the damage than was a positive bias. Baking at 125 °C again degraded the rejuvenated ferroelectric performance. The degree of re-degradation was also dependent on the polarity of the rejuvenating bias. The polarity-dependent behavior of rejuvenation was explained on the basis of a negative-internal-field model due...

Stress effects of the inter-level dielectric layer on the ferroelectric performance of integrated SrBi2Ta2O9 capacitors

The thermal stress effects of the inter-level dielectric (ILD) layer on the ferroelectric performance of integrated Pt/SrBi2Ta2O9(SBT)/Pt capacitors were investigated. Two different thin film materials, pure SiO2 grown at 650 °C and B- and P-doped SiO2 grown at 400 °C by chemical vapor deposition techniques, were tested as an ILD layer. The ILD layer encapsulated the SBT capacitor array. During high temperature thermal cycling (up to 800 °C) after ILD deposition, which is used for both densifying the ILD and curing of the various damage imposed on the SBT capacitors, a large thermal stress occurred in the bottom Pt layer due to the thermal expansion mismatch between the various layers. In particular, the pure SiO2 ILD layer between the capacitors did not allow thermal expansion of the Pt layers, which led to a large accumulation of compressive stress in the layer. This resulted in hillock formation in the bottom Pt layer and eventual capacitor failure. However, the B- and P-doped SiO2 ILD layer contracted...

Evaluation of Novel Sr Precursors for Atomic Layer Deposition of SrO Thin Film

Atomic layer deposition (ALD) process to deposit SrO film using novel Sr precursor – Sr (Methoxy-TetramethylHeptadiene)2 was estimated. Fig.1 showed the chemical structure of the synthesized Sr(MTHD)2. Fig. 2 showed thermal gravimetric analysis results of Sr(MTHD)2 and commercially used Sr (Tetra-Methyl Hetadiene)2. 50 % precursor evaporation temperature (T50) of Sr (MTHD)2 was 330 C, which was 30 C lower than that of Sr(TMHD)2. Liquid delivery system with flash evaporator was used to transport the precursors to substrate. The precursors were dissolved in Tetra Hydro Furan (THF) to prevent clogging during the delivery process. Ozone was used as a reactant to deposit SrO. It was found that thickness uniformity range of SrO film on Si wafer was less than 2 %. The deposition rate of SrO film using new Sr precursor was 0.4 A/cycle, which was almost same regardless of substrate temperatures up to 400 C. High vapor pressure and good thermal stability of new Sr precursor make it promising candidates for ALD precursors to deposit SrTiO3, aSrTiO3. Fig.1. Chemical structure of Sr(MTHD)2