Moonju Cho

Chemical interaction between atomic-layer-deposited HfO2 thin films and the Si substrate

HfO2 thin films were deposited on Si wafers using an atomic layer deposition technique at temperatures ranging from 200 to 400 °C with HfCl4 as the precursor and H2O as the oxidant. The time-dependent interfacial-layer growth behavior was dependent on the deposition temperature. The interfacial layer grew with increasing deposition time at 200 °C. However, the film thicknesses decreased with increasing deposition time after reaching a certain maximum value at 300 and 400 °C due to the enhanced dissolution of SiOx into the growing films at these temperatures. Post-annealing at 800 °C under a N2 atmosphere resulted in the precipitation of a Si-rich interfacial layer even for the initially interfacial layer free films. This had the effect of reducing the capacitance density of the films.

Interfacial reaction between chemically vapor-deposited HfO2 thin films and a HF-cleaned Si substrate during film growth and postannealing

Interfacial reactions between HfO2 thin films and a Si substrate during thin-film growth and postannealing under a N2 atmosphere were investigated by high-resolution transmission electron microscopy, Auger electron spectroscopy, and electrical measurements of metal–insulator–semiconductor capacitors. HfO2 thin films were deposited on HF-cleaned Si wafers by a chemical-vapor-deposition technique at a wafer temperature of 200 °C using a carbon-free precursor [Hf(NO3)4]. The film thicknesses ranged from 1.5 to 5.6 nm. During the initial stage of film growth, the Si surface oxidized to form a Si-rich hafnium silicate film. With increasing deposition time, Hf-rich hafnium silicate films grew. Postannealing resulted in a double-layered film structure with upper and interfacial layers having dielectric constants of approximately 9.3 and 5.6, respectively. The results were compared with the results from HfO2 films grown on SiO2-passivated Si wafers.

Comparison of HfO2 films grown by atomic layer deposition using HfCl4 and H2O or O3 as the oxidant

HfO2 gate dielectric thin-films were deposited on Si wafers using an atomic-layer deposition (ALD) technique with HfCl4 and either H2O or O3 as the precursor and oxidant, respectively. Although the ALD reactions using either H2O or O3 were successfully confirmed at a deposition temperature of 300 °C, the structural and electrical properties of the HfO2 films grown using the two oxidants were quite different. The stronger oxidation power of the O3 compared to H2O increased the oxygen concentration in the HfO2 film and the rate of interfacial SiO2 formation even at the as-deposited state. Because of the larger oxygen concentration, the decrease in the capacitance density of the film grown with O3 after rapid thermal annealing at 750 °C under N2 atmosphere was slightly larger than that of the HfO2 film grown with H2O. Apart from this weakness, all the other electrical properties, including the fixed charge density, the interface trap density, the leakage current density and the hysteresis in the capacitance–...

Thermal annealing effects on the structural and electrical properties of HfO2/Al2O3 gate dielectric stacks grown by atomic layer deposition on Si substrates

HfO2/Al2O3 gate dielectric thin film stacks were deposited on Si wafers using the atomic layer deposition technique. A 3.3-nm-thick Al2O3 interlayer was grown at 400 °C using Al(CH3)3 and O3, and 2.5–3.5-nm-thick HfO2 films were grown at either 300 or 400 °C using HfCl4 and H2O. Thermal annealing of the dielectric film stack at temperatures ranging from 400 to 1000 °C under pure N2 atmosphere resulted in variation of the equivalent oxide thicknesses. The equivalent oxide thickness of the dielectric film stack showed a minimum after annealing at 650 °C irrespective of the HfO2 film growth temperature. High temperature (>800 °C) annealing induced the formation of SiO2 and intermixing between the HfO2 and Al2O3 layers, which resulted in an increase in the equivalent oxide thickness of the film stack. The structural changes in the stacked films as a function of the annealing temperature were compared with those of HfO2 and Al2O3 single layers. The film stack showed minimal hysteresis (<15 mV) behavior in the ...

Chemical structure of the interface in ultrathin HfO2/Si films

The chemical states of the HfO2/Si (100) interface were investigated using transmission electron microscopy and high-resolution x-ray photoelectron spectroscopy. The depth distributions of Hf chemical states showed that the Hf 4f binding energy remains unchanged with the depth and there is no signature of more than one Hf-O state. These facts strongly suggest that the chemical state of the interfacial layer is not Hf-silicate, as previously believed. Instead, the compositions are mainly Si2O3 and SiO2, judging from the deconvolution of Si 2p spectra. The dielectric constant κ=4.8 of the interfacial layer is also consistent with the above conclusions.

Comparison between atomic-layer-deposited HfO2 films using O3 or H2O oxidant and Hf[N(CH3)2]4 precursor

The dielectric properties of HfO2 thin films, which were deposited on Si wafers by an atomic layer deposition (ALD) technique at a wafer temperature of 300 °C using a N-containing, tetrakis dimethylamido hafnium precursor (Hf[N(CH3)2]4), were highly improved by adopting O3 as the oxidant during the ALD instead of H2O. The films contained a much smaller carbon impurity concentration and were of more amorphous nature compared to the films grown using H2O as oxidant. Temperature-dependent leakage current analysis showed that the films grown using O3 as oxidant had a higher interfacial potential barrier for tunneling and the leakage current densities of the as-deposited film were three orders of magnitude smaller than that of the films grown using H2O. The dielectric constant of the HfO2 film was 24.4 and the leakage current density was 1.6×10−7A∕cm2 when the capacitance equivalent thickness was 1.49 nm.

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.

Chemical Vapor Deposition of HfO2 Thin Films Using a Novel Carbon-Free Precursor: Characterization of the Interface with the Silicon Substrate

HfO 2 thin films were deposited on Si wafers by a chemical vapor deposition (CVD) technique at temperatures ranging from 200 to 400°C using a new carbon-free precursor [Hf(NO 3 ) 4 ]. The growth behavior was under a steady state when the interfacial oxide layer was excluded in film thickness estimation by ellipsometry. The as-grown interfacial layer formed at 200°C was apparently composed of Hf, Si, and O. Postannealing under a N 2 atmosphere at temperatures >500°C resulted in a decrease in interfacial layer thickness by decomposition of the Hf-Si-O layer to SiO 2 and HfO 2 The HfO 2 film showed a crystalline microstructrue even in the as-deposited state when the film thickness was 170 A. However, the films were amorphous when the film thickness was <70 A. The dielectric constant of the as-deposited and postannealed HfO 2 thin films were approximately 18 and 22, respectively.

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.

High-k properties of atomic-layer-deposited HfO2 films using a nitrogen-containing Hf[N(CH3)2]4 precursor and H2O oxidant

HfO2 thin films were deposited on HF-dipped Si wafers at 300 °C using an atomic-layer-deposition technique with N-containing Hf[N(CH3)2]4 and H2O as the precursor and oxidant, respectively. A thin interfacial SiNx layer was spontaneously formed at the HfO2/Si interface during film growth. This interfacial SiNx layer prevented substrate Si diffusion into the HfO2 film. Therefore, the reduction in the capacitance density as a result of post-annealing at 800 °C was minimized. The leakage current density was also reduced due to the more amorphous-like structure of the film. Furthermore, the interfacial trap density (Dit) of <5×1010 cm−2 eV−1 near the midgap energy states was obtained from an as-deposited film that has a capacitance equivalent thickness of 1.8 nm. This Dit value was comparable to that of the well-grown SiO2/Si interface. However, the Dit slightly increased after post-annealing as a result of the increased N concentration at the interface, but it was still <1×1011 cm−2 eV−1.