Atomic Layer Deposition Chamber Research Articles

Growth of epitaxial oxides on silicon using atomic layer deposition: Crystallization and annealing of TiO2 on SrTiO3-buffered Si(001)

Epitaxial anatase titanium dioxide (TiO2) films have been grown by atomic layer deposition (ALD) on Si(001) substrates using a strontium titanate (STO) buffer layer without any amorphous SiOx layer at the STO–Si interface. Four unit cells of STO grown by molecular beam epitaxy (MBE) serve as the surface template for ALD growth. To preserve the quality of the MBE-grown STO, the samples were transferred in situ from the MBE chamber to the ALD chamber. The growth of TiO2 was achieved using titanium isopropoxide and water as the coreactants at a substrate temperature of 250 °C. In situ x-ray photoelectron spectroscopy analysis revealed that the ALD process did not induce Si–O bonding at the STO–Si interface. Slight improvement in crystallinity of the TiO2 film was achieved through in situ annealing under vacuum (10−9 Torr) at 450–600 °C. However, the amount of Si–O bonding increased following annealing at temperatures greater than 250 °C. X-ray diffraction revealed that TiO2 films annealed at a temperature of 250 °C in vacuum (10−9 Torr) for 1 h were the anatase phase and well crystallized. The results indicate that careful consideration of growth temperature and annealing conditions may allow epitaxial oxide films to be grown by ALD on STO-buffered Si(001) substrates without formation of an amorphous SiOx layer.

Investigation of interfacial oxidation control using sacrificial metallic Al and La passivation layers on InGaAs

The ability of metallic Al and La interlayers to control the oxidation of InGaAs substrates is examined by monochromatic x-ray photoelectron spectroscopy (XPS) and compared to the interfacial chemistry of atomic layer deposition (ALD) of Al2O3 directly on InGaAs surfaces. Al and La layers were deposited by electron-beam and effusion cell evaporators, respectively, on In0.53Ga0.47As samples with and without native oxides present. It was found that both metals are extremely efficient at scavenging oxygen from III–V native oxides, which are removed below XPS detection limits prior to ALD growth. However, metallic Ga/In/As species are simultaneously observed to form at the semiconductor–metal interface. Upon introduction of the samples to the ALD chamber, these metal bonds are seen to oxidize, leading to Ga/In–O bond growth that cannot be controlled by subsequent trimethyl-aluminum (TMA) exposures. Deposition on an oxide-free InGaAs surface results in both La and Al atoms displacing group III atoms near the surface of the semiconductor. The displaced substrate atoms tend to partially oxidize and leave both metallic and III–V oxide species trapped below the interlayers where they cannot be “cleaned-up” by TMA. For both Al and La layers the level of Ga–O bonding detected at the interface appears larger then that seen following ALD directly on a clean surface.

Growth and characterization of epitaxial anatase TiO2(001) on SrTiO3-buffered Si(001) using atomic layer deposition

Epitaxial anatase titanium dioxide (TiO2) films have been grown by atomic layer deposition (ALD) on Si(001) substrates using a strontium titanate (STO) buffer layer grown by molecular beam epitaxy (MBE) to serve as a surface template. The growth of TiO2 was achieved using titanium isopropoxide and water as the co-reactants at a substrate temperature of 225–250°C. To preserve the quality of the MBE-grown STO, the samples were transferred in-situ from the MBE chamber to the ALD chamber. After ALD growth, the samples were annealed in-situ at 600°C in vacuum (10−7Pa) for 1–2h. Reflection high-energy electron diffraction was performed during the MBE growth of STO on Si(001), as well as after deposition of TiO2 by ALD. The ALD films were shown to be highly ordered with the substrate. At least four unit cells of STO must be present to create a stable template on the Si(001) substrate for epitaxial anatase TiO2 growth. X-ray diffraction revealed that the TiO2 films were anatase with only the (004) reflection present at 2θ=38.2°, indicating that the c-axis is slightly reduced from that of anatase powder (2θ=37.9°). Anatase TiO2 films up to 100nm thick have been grown that remain highly ordered in the (001) direction on STO-buffered Si(001) substrates.

In-Situ Synchrotron X-Ray Scattering Study of Thin Film Growth by Atomic Layer Deposition

We report an atomic layer deposition chamber for in-situ synchrotron X-ray scattering study of thin film growth. The chamber was designed for combined synchrotron X-ray reflectivity and two-dimensional grazing-incidence X-ray diffraction measurement to do a in-situ monitoring of ALD growth. We demonstrate ruthenium thermal ALD growth for the performance of the chamber. 10, 20, 30, 50, 70, 100, 150 and 250-cycled states are measured by X-ray scattering methods during ALD growth process. Growth rate is calculated from thickness values and the surface roughness of each state is estimated by X-ray reflectivity analysis. The crystal structure of initial growth state is observed by Grazing-incidence X-ray diffraction. These results indicate that in-situ X-ray scattering method is a promising analysis technique to investigate the initial physical morphology of ALD films.

(Invited) In Situ XPS in Atomic Layer Deposition of Oxides on Ge (100)

Atomic layer deposition (ALD) is a film growth method that offers unprecedented control of film thickness, uniformity of deposition and low temperature processing on substrates with complex topography. Because ALD occurs by a series of self-limiting surface reactions of vapor phase precursors, there is great interest in understanding the mechanisms of precursor adsorption and how they affect the structure and properties of ALD-grown films and their interfaces with technologically-relevant substrates. In this paper, we describe experiments in which a differentially-pumped x-ray source and photoelectron spectrometer installed in an ALD chamber is used to probe ALD growth of metal oxide films. This in situ XPS system is capable of collecting data within 10's of seconds of an ALD precursor pulse, without moving the substrate or changing its temperature. An application of this system to oxidant treatment of the initial surface of Ge (100) substrates prior to alumina ALD is also discussed.

Control of interface between HfO2 and air‐exposed InGaAs by ultrathin Si interface control layer

AbstractThis paper attempts to control the interface between the air‐exposed InGaAs wafer and a high‐k dielectric by the Si interface control layer (ICL) technique. As the high‐k insulator, HfO2 film was formed by atomic layer deposition (ALD). Prior to a molecular beam epitaxy (MBE) growth of the Si ICL, efforts were made to minimize native oxide components from the InGaAs surface by various wet surface treatment. After the growth of the Si ICL, an ultrathin SiNx layer was formed by in‐situ partial nitridation of the Si ICL to prevent a subcutaneous oxidation during the sample transfer in air to the ALD chamber. Surface/interface properties were characterized by in‐situ X‐ray photoelectron spectroscopy (XPS) at each step of interface formation. By using HF‐based cleaning, interface bonding configurations similar to those obtained by in‐situ UHV process was realized with no trace of native oxide components. As compared with the ALD HfO2/InGaAs metal‐insulator‐semiconductor (MIS) structure which showed existence of strong Fermi level pinning, insertion of the Si ICL achieved large reduction of interface state density, Dit, giving a minimum value of 2x1011 eV‐1cm‐2. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of the “clean-up” of the oxidized Ge(100) surface by atomic layer deposition

While the “clean-up” effect on III-V substrates has recently been well documented interfacial reactions during atomic layer deposition (ALD) on Ge substrates are not fully explored. The “clean-up” of Ge oxides is studied by interrupting the ALD process following individual precursor pulses for in situ monochromatic x-ray photoelectron spectroscopy analysis. Germanium oxides are found to be reduced by TMA and water, while an interfacial GeON layer is only affected by the initial TMA pulse. Oxide free germanium surfaces behave analogously to a surface with initial native oxides since they are oxidized measurably prior to the first TMA pulse due to residual oxidants in a commercial ALD chamber.

Rapid Vapor-Phase Fabrication of Organic−Inorganic Hybrid Superlattices with Monolayer Precision

We report a new layer-by-layer growth method of self-assembled organic multilayer thin films based on gas-phase reactions. In the present molecular layer deposition (MLD) process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and titanium hydroxide. The MLD method is a self- limiting layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good thermal and mechanical stability, and various unique electrical properties. The MLD method, combined with ALD, was applied to the preparation of organic-inorganic hybrid nanolaminate films in the ALD chamber. The organic-inorganic hybrid superlattices were then used as active mediums for two-terminal electrical bistable devices. The advantages of the MLD method with ALD include accurate control of film thickness, large-scale uniformity, highly conformal layering, sharp interfaces, and a vast library of possible materials. The MLD method with ALD is an ideal fabrication technique for various organic-inorganic hybrid superlattices.