ALD-type Growth Research Articles

In situ XPS study of low temperature atomic layer deposition of B2O3 films on Si using BCl3 and H2O precursors

In this study, atomic layer deposition (ALD) of nanoscale boron oxide (B2O3) films on Si using BCl3/H2O precursors at room temperature was investigated using in situ x-ray photoelectron spectroscopy (XPS). B2O3 thin films are of considerable interest in ultra-shallow Si doping applications, including high aspect ratio FinFET structures, where film conformality and precise thickness control are crucial. ALD is therefore of particular interest for such applications. XPS data demonstrate that initial BCl3 exposures on Si at room temperature are self-limiting and are accompanied by partial B-Cl dissociation and Cl-Si formation. H2O exposures >1.7 × 108 Langmuir at room temperature removed Cl from B sites, but failed to remove Cl from the Cl-Si species. ALD-type growth of B2O3 was observed with an average growth rate of ∼2.5 Å/cycle and without further increase in the Cl content. The initial Cl contamination was due to Cl-Si bond formation at the interface, without Cl incorporation into the oxide film. The role of Cl in the inhibition of oxide film growth was further investigated by the reactions of BCl3/O2 on SiO2 at room temperature and 650 K. BCl3/O2 precursors exhibit negligible B2O3 growth at room temperature. At 650 K, B2O3 growth was observed with a decreasing growth rate per BCl3/O2 cycle, corresponding to an increase in the Cl:B atomic ratio. These data indicate that room temperature ALD using BCl3/H2O precursors is a potential route toward the formation of uniform B2O3 films for shallow Si doping applications, but that Cl-Si formation significantly impacts initial oxide nucleation and growth.

Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition

New complexes MoO2(tBuAMD)2 (1) and WO2(tBuAMD)2 (2) (AMD = acetamidinato) are synthesized and fully characterized as precursors for atomic layer deposition (ALD). They contain metal-oxo functionalities not previously utilized in ALD-type growth processes and are fully characterized by 1H and 13C NMR, X-ray diffraction (XRD), Fourier transform infrared, thermogravimetric analysis, single-crystal XRD, and elemental analysis. Guided by quartz-crystal microbalance studies, ALD growth methodologies for both complexes have been developed. Remarkably, these isostructural compounds exhibit dramatic differences in ALD properties. Using 1 and O3, amorphous, ultrathin molybdenum oxynitride (MoON) films are grown on Si(100) wafers. Using 2 and H2O yields amorphous WO3 films on Si(100) wafers that crystallize as WO3 nanowires upon annealing. Although 1/H2O and 2/O3 growth was attempted, effective ALD growth could only be obtained with 1/O3 and 2/H2O, underscoring reactivity differences in these precursors. Film thick...

Atomic/Molecular Layer Deposition of Lithium Terephthalate Thin Films as High Rate Capability Li-Ion Battery Anodes

We demonstrate the fabrication of high-quality electrochemically active organic lithium electrode thin films by the currently strongly emerging combined atomic/molecular layer deposition (ALD/MLD) technique using lithium terephthalate, a recently found anode material for lithium-ion battery (LIB), as a proof-of-the-concept material. Our deposition process for Li-terephthalate is shown to well comply with the basic principles of ALD-type growth including the sequential self-saturated surface reactions, a necessity when aiming at micro-LIB devices with three-dimensional architectures. The as-deposited films are found crystalline across the deposition temperature range of 200-280 °C, which is a trait highly desired for an electrode material but rather unusual for hybrid inorganic-organic thin films. Excellent rate capability is ascertained for the Li-terephthalate films with no conductive additives required. The electrode performance can be further enhanced by depositing a thin protective LiPON solid-state electrolyte layer on top of Li-terephthalate; this yields highly stable structures with capacity retention of over 97% after 200 charge/discharge cycles at 3.2 C.

Use of B2O3 films grown by plasma-assisted atomic layer deposition for shallow boron doping in silicon

Plasma-assisted atomic layer deposition (PALD) was carried for growing thin boron oxide films onto silicon aiming at the formation of dopant sources for shallow boron doping of silicon by rapid thermal annealing (RTA). A remote capacitively coupled plasma source powered by GaN microwave oscillators was used for generating oxygen plasma in the PALD process with tris(dimethylamido)borane as boron containing precursor. ALD type growth was obtained; growth per cycle was highest with 0.13 nm at room temperature and decreased with higher temperature. The as-deposited films were highly unstable in ambient air and could be protected by capping with in-situ PALD grown antimony oxide films. After 16 weeks of storage in air, degradation of the film stack was observed in an electron microscope. The instability of the boron oxide, caused by moisture uptake, suggests the application of this film for testing moisture barrier properties of capping materials particularly for those grown by ALD. Boron doping of silicon was demonstrated using the uncapped PALD B2O3 films for RTA processes without exposing them to air. The boron concentration in the silicon could be varied depending on the source layer thickness for very thin films, which favors the application of ALD for semiconductor doping processes.

Growth of Bi2O3 Ultrathin Films by Atomic Layer Deposition

Bismuth trioxide (Bi2O3) ultrathin films were successfully synthesized on silicon substrates by means of atomic layer deposition (ALD) using Bi(thd)3 (thd: 2,2,6,6-tetramethyl-3,5-heptanedionato) and H2O as precursors. The optimum ALD window was about 270–300 °C, and an ALD-type growth mechanism via surface saturation reaction was identified; the growth rate was about 0.1 Å/cycle. The X-ray diffraction and high-resolution transmission electron microscopy investigation revealed that Bi2O3 films crystallized into a predominant alpha phase above 250 °C. The resistivity at room temperature was about 1.2 × 106 Ω·cm, which is also proof of the α-phase of as-deposited Bi2O3 films. In addition, a new method to obtain γ-Bi2O3 film was discovered. The α-Bi2O3 films (synthesized by ALD) transformed into metastable γ-Bi2O3 with preferred orientation (222) after annealing above 512 °C, and γ-phase could persist at room temperature.

Atomic Layer Deposition of Hexagonal and Orthorhombic YMnO3 Thin Films

Thin films of both the hexagonal and orthorhombic forms of YMnO3 have been fabricated through atomic layer deposition (ALD) and subsequent heat treatment. ALD-type growth of essentially cation-stoichiometric YMnO3 films was achieved in a reproducible manner in a temperature interval of 250−300 °C using Y(thd)3, Mn(thd)3, and ozone as precursors. The as-deposited films were amorphous, but a postdeposition heat treatment carried out in a temperature range of 750−900 °C depending on the substrate/polymorph yielded highly crystalline films. On Si(100) substrate, the product was the hexagonal phase of YMnO3, whereas on LaAlO3(100) and SrTiO3(100) substrates, the metastable orthorhombic YMnO3 phase was formed. On the perovskite substrates, the films were highly oriented, the direction of the orientation moreover depending on the choice of the substrate crystal.

Novel mixed alkylamido-cyclopentadienyl precursors for ALD of ZrO2 thin films

Mixed alkylamido-cyclopentadienyl compounds of zirconium, (RCp)Zr(NMe2)3 (R = H, Me or Et) are introduced as precursors for atomic layer deposition (ALD) of high permittivity zirconium oxide thin films. Ozone was used as the oxygen source. Only slight differences were observed in the ALD growth characteristics between the three liquid precursors. The ALD-type growth mode was verified at 300 °C with a growth rate of about 0.9 A cycle−1. Good film conformality was observed, as step coverages of 80–90% were measured for films deposited onto high aspect ratio (60 : 1) trenches. As compared to the commonly used Zr(NEtMe)4 precursor, these novel precursors showed comparative volatility and growth rate but higher thermal stability, as well as lower impurity content in the deposited stoichiometric ZrO2 films. The films deposited by the (RCp)Zr(NMe2)3/O3 processes tended to crystallize in the high temperature cubic form even when the film thickness exceeded 50 nm, while the Zr(NEtMe)4/O3 process resulted in films with mixed phases. The cubic phase ensures high permittivity and thus the capacitance equivalent thickness remained extremely low, even below 0.8 nm, with low leakage current density of 10−7 A cm−2 at 1 V when a 6.4 nm ZrO2 film was deposited on TiN.

Growth of iron cobaltoxides by atomic layer deposition

Thin films of iron cobalt oxides with spinel-type structure are made by the atomic layer deposition (ALD) technique using Fe(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione), Co(thd)2, and ozone as precursors. Pulse parameters for ALD-type growth are established and such growth can be achieved at deposition temperatures between 185 and 310 degrees C. Films have been deposited on amorphous soda-lime glass and single-crystalline substrates of Si(100), MgO(100), and alpha-Al2O3(001) which all provide crystalline films, but with various orientations and crystallite sizes. Application of an external magnetic field during the film growth does not influence film growth characteristics (growth rate, crystallinity, topography etc.). Magnetization data are reported for phase-pure films of spinel-type structure with composition Fe2CoO4.

Atomic Layer Deposition of HfO2 Thin Films Exploiting Novel Cyclopentadienyl Precursors at High Temperatures

Atomic layer deposition (ALD) of HfO2 thin films was studied using four novel cyclopentadienyl precursors, namely, (CpMe)2HfMe2, Cp2Hf(OMe)2, (CpMe)2Hf(OMe)Me, and (CpMe)2Hf(OMe)2. Ozone was used as the oxygen source. Among the cyclopentadienyl precursors, (CpMe)2HfMe2 and (CpMe)2Hf(OMe)Me were the most promising, showing ALD-type growth characteristics at high temperatures as the self-limiting growth mode was confirmed at 400 °C. ALD-type growth was verified also on 60:1 aspect ratio trench structures even at 450 °C, where perfect conformality was obtained. The growth rate stayed nearly constant at around 0.5 Å/cycle at substrate temperatures between 350 and 500 °C. When Cp2Hf(OMe)2 and (CpMe)2Hf(OMe)2 were applied, slight decomposition of the precursor was detected at 350−400 °C, and thus a self-limiting growth mode was not achieved. Time-of-flight elastic recoil detection analyses demonstrated stoichiometric HfO2 films, where impurity concentrations were below 0.1 at % for C, H, and N in films deposited from each of the four Hf precursors. In addition, thin HfO2 films showed good dielectric properties such as low hysteresis, nearly ideal flatband voltage, and effective permittivity values similar to previously reported HfO2 films obtained by the alkylamide-based processes.

Growth of thin films of Co 3O 4 by atomic layer deposition

Thin films of cobalt oxide were made by atomic layer deposition (ALD), using Co(thd) 2 (Hthd = 2,2,6,6-tetramethylheptan-3,5-dione) and ozone as precursors. Films were deposited on soda–lime glass and single crystals of Si(100). Pulse and purge parameters for ALD-type growth were established and such growth was found to occur for depositions within the temperature range of 114–307 °C. A preferred (100)-orientation was observed at the low end of the temperature range for films deposited on soda–lime glass and Si(100). At the high end of the temperature range, films deposited on Si(100) showed (111)-oriented growth, while films deposited on soda–lime glass substrates were unoriented. The electrical resistivity of as-deposited films on soda–lime glass were in the range of 0.13–4.48 Ω cm and showed a non-monotonic dependence on film thickness, with a minimum for films with a large proportion of grain boundaries.

High Growth Rate of Erbium Oxide Thin Films in Atomic Layer Deposition from (CpMe)3Er and Water Precursors

Organometallic tris(methylcyclopentadienyl)erbium and water were successfully exploited as precursors for the atomic layer deposition (ALD) of Er 2 O 3 thin films. Deposition studies were carried out in the temperature range 175-450 °C, where Si(100) and soda-lime glass were used as substrates. ALD-type growth mechanism could be verified at relatively low deposition temperatures of 250 °C and 300 °C, where a high growth rate (1.5 A per cycle) for an ALD process was obtained. The deposited Er 2 O 3 films were smooth and very uniform, and contained only low concentrations of carbon and hydrogen as impurities. The films were crystalline with the (111) orientation of the cubic phase dominating. The effective permittivity of the Er 2 O 3 /native SiO 2 insulator stack was approximately 10.

Growth of manganese oxide thin films by atomic layer deposition

Thin films of manganese oxide are made by the ALD (atomic layer deposition) technique using Mn(thd) 3 (Hthd=2,2,6,6-tetramethylheptan-3,5-dione) and ozone as precursors. Pulse parameters for ALD-type growth are established and such growth can be achieved at deposition temperatures between 138 and 210 °C. Films have been deposited on both soda-lime glass and Si(100) single crystals. The electrical resistivities of as-deposited films grown on soda-lime glass are measured to be 0.3–3.2 Ω cm (linear four-point-probe measurements).