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Jan 2013

Volume 31, Issue 1, Articles (01xxxx)

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J. Vac. Sci. Technol. A 31, 01A103 (2013); http://dx.doi.org/10.1116/1.4750372 (9 pages)

Frank Greer, Erika Hamden, Blake C. Jacquot, Michael E. Hoenk, Todd J. Jones, Matthew R. Dickie, Steve P. Monacos, and Shouleh Nikzad
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Interface layer in hafnia/Si films as a function of ALD cycles

Pierre-Giovanni Mani-Gonzalez, Milton-Oswaldo Vazquez-Lepe, Francisco Espinosa-Magaña, and Alberto Herrera-Gomez

J. Vac. Sci. Technol. A 31, 010601 (2013); http://dx.doi.org/10.1116/1.4747324 (6 pages)

Online Publication Date: 22 August 2012

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A systematic angle resolved x-ray photoelectron spectroscopy study of the structure of hafnia films grown on silicon with atomic layer deposition (ALD) is presented. The hafnium precursor employed was tetrakis dimethyl amino hafnium with water as the oxidant agent. The number of ALD cycles ranged from 3 to 25. The Hf 4f spectrum shows two components 0.47 eV apart, one associated with hafnia (17.6 eV) and the other (18.1 eV) with a hafnium silicate interface layer. The composition of the interface layer, HfxSi1-xOy, evolves continuously from silicon-rich (x = 0.1 for 3 ALD cycles) to hafnium rich (x = 0.75 for 25 ALD cycles). The binding energy difference between the Hf 4f components associated with the silicate and hafnia changes very little with the silicate composition. The binding energy of the Si4+ component, which is associated with the silicate, varies from 3.25 to 2.85 eV (referenced to the Si0+ component) with the number of ALD cycles. The oxygen stoichiometric coefficient of the silicate is close to the expected value of 2 for all the samples. However, the hafnia shows an excess of oxygen for some of the samples.
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79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
68.35.Ct Interface structure and roughness
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Modeling of inductively coupled plasma Ar/Cl2/N2 plasma discharge: Effect of N2 on the plasma properties

Romain Chanson, Ahmed Rhallabi, Marie Claude Fernandez, Christophe Cardinaud, and Jean Pierre Landesman

J. Vac. Sci. Technol. A 31, 011301 (2013); http://dx.doi.org/10.1116/1.4766681 (11 pages)

Online Publication Date: 27 November 2012

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A global kinetic model of Cl2/Ar/N2 plasma discharge has been developed, which allows calculation of the densities and fluxes of all neutral and charged species considered in the reaction scheme, as well as the electron temperature, as a function of the operating conditions. In this work, the results from the global model are first compared to the calculations given by other models. Our simulation results are focused on the effect of nitrogen adding to the Cl2/Ar plasma mixture, which impacts both neutral and charged species transport phenomena. The N2 percentage is varied to the detriment of Cl2 by keeping the total flow rates of Cl2 and N2 constant. In order to better understand the impact of N2 addition to the Cl2/Ar gas mixture, the authors analyzed the output plasma parameters calculated from the model for different N2 flow rate percentages. Indeed, the simulation results show a decrease in electron density and an increase in electron temperature with increasing percentage of N2. Particular attention is paid to the analysis of electronegativity, Cl2 and N2 dissociation, and positive ion to neutral flux ratio evolution by varying percentage of N2. Such parameters have a direct effect on the etching anisotropy of the materials during the etching process.
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52.80.-s Electric discharges
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.65.-y Plasma simulation

Can surface cracks and unipolar arcs explain breakdown and gradient limits?

Zeke Insepov and Jim Norem

J. Vac. Sci. Technol. A 31, 011302 (2013); http://dx.doi.org/10.1116/1.4766929 (10 pages)

Online Publication Date: 27 November 2012

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The authors argue that the physics of unipolar arcs and surface cracks can help understand rf breakdown and vacuum arc data. They outline a model of the basic mechanisms involved in breakdown and explore how the physics of unipolar arcs and cracks can simplify the picture of breakdown and gradient limits in accelerators, tokamaks as well as laser ablation, micrometeorites, and other applications. Cracks are commonly seen in SEM images of arc damage and they are produced as the liquid metal cools. They can produce the required field enhancements to explain field emission data and can produce mechanical failure of the surface that would trigger breakdown events. Unipolar arcs can produce currents sufficient to short out rf structures, and can cause the sort of damage seen in SEM images. They should be unstable, and possibly self-quenching, as seen in optical fluctuations and surface damage. The authors describe some details and consider the predictions of this simple model.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Pi High-frequency and RF discharges
62.10.+s Mechanical properties of liquids
52.25.Gj Fluctuation and chaos phenomena
52.38.Kd Laser-plasma acceleration of electrons and ions
52.55.Fa Tokamaks, spherical tokamaks

Reorganization of graphite surfaces into carbon micro- and nanoparticles under high flux hydrogen plasma bombardment

Kirill Bystrov, Lenze van der Vegt, Gregory De Temmerman, Cécile Arnas, and Laurent Marot

J. Vac. Sci. Technol. A 31, 011303 (2013); http://dx.doi.org/10.1116/1.4769733 (9 pages) | Cited 1 time

Online Publication Date: 7 December 2012

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Fine-grain graphite samples were exposed to high density low temperature (ne ∼ 1020 m−3, Te ∼ 1 eV) hydrogen plasmas in the Pilot-PSI linear plasma generator. Redeposition of eroded carbon is so strong that no external precursor gas injection is necessary for deposits to form on the exposed surface during the bombardment. In fact, up to 90% of carbon is redeposited, most noticeably in the region of the highest particle flux. The redeposits appear in the form of carbon microparticles of various sizes and structures. Discharge parameters influence the efficiency of the redeposition processes and the particle growth rate. Under favorable conditions, the growth rate reaches 0.15 μm/s. The authors used high resolution scanning electron microscopy and transmission electron microscopy to study the particle growth mode. The columnar structure of some of the large particles points toward surface growth, while observation of the spherical carbon nanoparticles indicates growth in the plasma phase. Multiple nanoparticles can agglomerate and form bigger particles. The spherical shape of the agglomerates suggests that nanoparticles coalesce in the gas phase. The erosion and redeposition patterns on the samples are likely determined by the gradients in plasma flux density and surface temperature across the surface.
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81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
52.25.-b Plasma properties
52.77.Dq Plasma-based ion implantation and deposition
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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Low emissivity high-temperature tantalum thin film coatings for silicon devices

Veronika Rinnerbauer, Jay J. Senkevich, John D. Joannopoulos, Marin Soljačić, Ivan Celanovic, Robert R. Harl, and Bridget R. Rogers

J. Vac. Sci. Technol. A 31, 011501 (2013); http://dx.doi.org/10.1116/1.4766295 (5 pages)

Online Publication Date: 7 November 2012

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The authors study the use of thin ( ∼ 230 nm) tantalum (Ta) layers on silicon (Si) as a low emissivity (high reflectivity) coating for high-temperature Si devices. Such coatings are critical to reduce parasitic radiation loss, which is one of the dominant loss mechanisms at high temperatures (above 700 °C). The key factors to achieve such a coating are low emissivity in the near infrared and superior thermal stability at high operating temperatures. The authors investigated the emissivity of Ta coatings deposited on Si with respect to deposition parameters, and annealing conditions, and temperature. The authors found that after annealing at temperatures ≥ 900 °C the emissivity in the near infrared (1−3 μm) was reduced by a factor of 2 as compared to bare Si. In addition, the authors measured thermal emission at temperatures from 700 to 1000 °C, which is stable up to a heater temperature equal to the annealing temperature. Furthermore, Auger electron spectroscopy profiles of the coatings before and after annealing were taken to evaluate thermal stability. A thin (about 70 nm) Ta2O5 layer was found to act as an efficient diffusion barrier between the Si substrate and the Ta layer to prevent Si diffusion.
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68.55.at Other materials
81.15.Dj E-beam and hot filament evaporation deposition
66.30.Fq Self-diffusion in metals, semimetals, and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Er Solid metals and alloys
81.40.Gh Other heat and thermomechanical treatments

Effects of the gas ambient in thermal activation of Mg-doped p-GaN on Hall effect and photoluminescence

Wei Lu, David Aplin, Arthur R. Clawson, and Paul K. L. Yu

J. Vac. Sci. Technol. A 31, 011502 (2013); http://dx.doi.org/10.1116/1.4768174 (5 pages)

Online Publication Date: 27 November 2012

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The effects of thermal annealing in N2, O2, Ar or mixed gas ambient on the electrical and optical properties of metal-organic-chemical-vapor-deposition-grown Mg-doped p-type GaN were investigated by Hall effect and photoluminescence. A systematical study on optimizing annealing gas combination, time, and temperature for achieving high activation efficiency of Mg acceptors was conducted simultaneously. High hole concentration of 9.07 × 1017 cm−3 and low resistivity of 0.622 Ω-cm using the optimized annealing condition were achieved. In agreement with some previous studies, annealing in the mixed gas ambient of N2 and O2 provided significant improvements in activation efficiency of Mg acceptors compared with annealing in pure O2, N2, or Ar. The room- and low-temperature photoluminescence spectra measured from the samples annealed in N2-rich ambient showed significantly higher photoluminescence intensity at both 2.8- and 3.2-eV band transitions. Consistent with the study of others, the experimental results of this study indicated that when annealing in the mixed N2/O2 gas ambient O2 effectively helps activate Mg acceptors by releasing H from Mg-H complexes but also oxidizes GaN; it is likely that the presence of N2 is beneficial in reducing the formation of nitrogen vacancies.
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72.20.My Galvanomagnetic and other magnetotransport effects
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
61.72.jd Vacancies
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing

Influence of inert gases on the reactive high power pulsed magnetron sputtering process of carbon-nitride thin films

Susann Schmidt, Zsolt Czigány, Grzegorz Greczynski, Jens Jensen, and Lars Hultman

J. Vac. Sci. Technol. A 31, 011503 (2013); http://dx.doi.org/10.1116/1.4769725 (13 pages)

Online Publication Date: 7 December 2012

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The influence of inert gases (Ne, Ar, Kr) on the sputter process of carbon and carbon-nitride (CNx) thin films was studied using reactive high power pulsed magnetron sputtering (HiPIMS). Thin solid films were synthesized in an industrial deposition chamber from a graphite target. The peak target current during HiPIMS processing was found to decrease with increasing inert gas mass. Time averaged and time resolved ion mass spectroscopy showed that the addition of nitrogen, as reactive gas, resulted in less energetic ion species for processes employing Ne, whereas the opposite was noticed when Ar or Kr were employed as inert gas. Processes in nonreactive ambient showed generally lower total ion fluxes for the three different inert gases. As soon as N2 was introduced into the process, the deposition rates for Ne and Ar-containing processes increased significantly. The reactive Kr-process, in contrast, showed slightly lower deposition rates than the nonreactive. The resulting thin films were characterized regarding their bonding and microstructure by x-ray photoelectron spectroscopy and transmission electron microscopy. Reactively deposited CNx thin films in Ar and Kr ambient exhibited an ordering toward a fullerene-like structure, whereas carbon and CNx films deposited in Ne atmosphere were found to be amorphous. This is attributed to an elevated amount of highly energetic particles observed during ion mass spectrometry and indicated by high peak target currents in Ne-containing processes. These results are discussed with respect to the current understanding of the structural evolution of a-C and CNx thin films.
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81.15.Cd Deposition by sputtering
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.aj Insulators
78.47.D- Time resolved spectroscopy (>1 psec)

Photoluminescence characterization of polythiophene films incorporated with highly functional molecules such as metallophthalocyanine

Hiroaki Kobe, Kazumasa Ohnaka, Hitoshi Kato, Susumu Takemura, Kazuhiro Shimada, Tomoyasu Hiramatsu, and Kazunori Matsui

J. Vac. Sci. Technol. A 31, 011504 (2013); http://dx.doi.org/10.1116/1.4772946 (11 pages)

Online Publication Date: 20 December 2012

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The photoluminescence (PL) of conducting polymer polythiophene (PT) films incorporated with metallophthalocyanines (PcMs) such as CuPc, MgPc, FePc, Li2Pc, and CoPc was studied by PL and time-correlated single photon counting (TCSPC) measurements. Polymer films were prepared by electrochemical polymerization and PcMs migrated into the polymer films by a diffusion method using acetonitrile or toluene as a solvent to dissolve the PcMs. The wavelength of PL emission peaks changed significantly depending on the solvent used in the doping process. Using acetonitrile, the observed PL emission peaks originated from the Q band, whereas they were assigned to the Soret band in the case of toluene. TCSPC measurements showed that PL emission took place through a ligand–ligand transition process when using acetonitrile because the average lifetimes were comparable and independent of the central metal ions for CoPc-, Li2Pc-, and MgPc-doped polymer films. Conversely, using toluene, it was found that ligand–ligand emission occurred for Li2Pc-, MgPc-, and FePc-doped films. To identify the cause of the drastic change in PL emission pattern, x-ray photoelectron spectroscopy measurements were obtained. A lower binding energy component appeared in the C 1s core-level spectra of acetonitrile-processed PcM-doped PT films, whereas this component shifted to higher energy and overlapped with the main peak for toluene-processed PcM-doped PT films. The lower binding energy component corresponded to photoelectrons due to the C atoms in the benzene rings of the ligand. Lower binding energy components also appeared in the N 1s core-level spectra of acetonitrile-processed PcM-doped PT films, and this component shifted to higher energy for toluene-processed PcM-doped PT films. These lower energy components were assigned to the core-level peaks due to the N atoms at the meso position bridging between pyrrole rings. This suggests that the electron charge at the N sites of the meso positions in toluene-processed films was smaller than in acetonitrile-processed ones. The changes in energy at benzene C sites and meso N sites suggest that the electronic states of the phthalocyanine in the toluene-processed films were porphyrin-like, so the Soret band became dominant in the PL emission spectrum.
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78.66.Qn Polymers; organic compounds
79.60.Fr Polymers; organic compounds
82.35.-x Polymers: properties; reactions; polymerization
82.45.-h Electrochemistry and electrophoresis
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
78.55.Kz Solid organic materials
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Direct comparison of spectroscopic data with cluster calculations of plutonium dioxide and uranium dioxide

J. G. Tobin, S.-W. Yu, B. W. Chung, M. V. Ryzhkov, and A. Mirmelstein

J. Vac. Sci. Technol. A 31, 013001 (2013); http://dx.doi.org/10.1116/1.4772959 (3 pages) | Cited 1 time

Online Publication Date: 20 December 2012

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The density of states predicted by cluster calculations of PuO2 and UO2 is directly compared to the results from soft x-ray spectroscopy. Remarkably good agreement between the experimentally measured spectroscopic peaks and the calculated density of states of the central part of the cluster is observed.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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Magnetically coupled ultrahigh vacuum manipulator with a sample grabber

Seong Heon Kim and Alex de Lozanne

J. Vac. Sci. Technol. A 31, 013201 (2013); http://dx.doi.org/10.1116/1.4769127 (4 pages)

Online Publication Date: 29 November 2012

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The authors present a simple design for a magnetically coupled manipulator capable of grabbing small samples in an ultrahigh vacuum environment. The opening and closing of the sample grabber is accomplished by the relative rotation of independent rings of magnets. This manipulator provides high values of axial force (30 lb) and azimuthal torque (23 in. lb).
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07.07.Tw Servo and control equipment; robots
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Aluminum-doped zinc oxide formed by atomic layer deposition for use as anodes in organic light emitting diodes

Su Cheol Gong, Yong-June Choi, Hyuncheol Kim, Chang-Sun Park, Hyung-Ho Park, Ji Geun Jang, Ho Jung Chang, and Geun Young Yeom

J. Vac. Sci. Technol. A 31, 01A101 (2013); http://dx.doi.org/10.1116/1.4738749 (6 pages) | Cited 1 time

Online Publication Date: 26 July 2012

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Aluminum-doped zinc oxide films produced by atomic layer deposition were investigated for use as anodes in organic light emitting diode (OLED) devices. Al-doped ZnO (AZO) films (∼200 nm thick) were deposited at temperatures of 200, 230, and 260 °C and the AZO film deposited at 260 °C demonstrated carrier mobility, carrier concentration, resistivity, and transmittance values of 16.2 cm2 V−1 s−1, 5.18 × 1020 cm−3, 7.34 × 10−4 Ω cm, and 90%, respectively. OLED devices with a DNTPD/TAPC/Bebq2:10% doped RP-411/Bphen/LiF/Al structure on a glass substrate fabricated using an AZO anode formed at 260 °C showed turn-on voltage, maximum luminance, and current efficiency values of 5.3 V, 16680 cd/m2, and 4.8 cd/A, respectively.
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81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.60.Jb Light-emitting devices
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors

Atomic layer deposition of Ti-HfO2 dielectrics

Matthew Werner, Peter J. King, Sarah Hindley, Simon Romani, Sean Mather, Paul R. Chalker, Paul A. Williams, and Jakob A. van den Berg

J. Vac. Sci. Technol. A 31, 01A102 (2013); http://dx.doi.org/10.1116/1.4748570 (7 pages)

Online Publication Date: 24 August 2012

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Titanium-doped hafnium oxide films, TixHf1−xO2−δ, have been deposited with a Ti content of x = 0.1 and x = 0.5, by atomic layer deposition. The TixHf1−xO2−δ growth rate is lower compared with the growth rates of the individual binary oxides; however, the composition of the films is unaffected by the reduced growth rate. An 850  °C spike anneal and a 500  °C 30 min furnace anneal were performed, and the resulting film composition and structure was determined using medium energy ion scattering, x-ray diffraction, and transmission electron microscopy. The Ti0.1Hf0.9O2−δ films readily crystallize into a monoclinic phase during both types of annealing. By contrast, the Ti0.5Hf0.5O2−δ films remain amorphous during both annealing processes. Electrical characterization of the as-deposited Ti0.1Hf0.9O2−δ films yielded a dielectric constant of 20, which is slightly higher than undoped HfO2 films. The as-deposited Ti0.5Hf0.5O2−δ films showed a significant increase in dielectric constant up to 35. After a 500  °C 30 min anneal, the dielectric constant reduced slightly to 27. The leakage current density of the amorphous film remains relatively unaffected at 8.7×10−7 A/cm2 at −1 MV/cm, suggesting this composition/heat treatment is a candidate for future device dielectrics.
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68.55.aj Insulators
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Atomically precise surface engineering of silicon CCDs for enhanced UV quantum efficiency

Frank Greer, Erika Hamden, Blake C. Jacquot, Michael E. Hoenk, Todd J. Jones, Matthew R. Dickie, Steve P. Monacos, and Shouleh Nikzad

J. Vac. Sci. Technol. A 31, 01A103 (2013); http://dx.doi.org/10.1116/1.4750372 (9 pages)

Online Publication Date: 13 September 2012

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The authors report here on a new technique, combining the atomic precision of molecular beam epitaxy and atomic layer deposition, to fabricate back illuminated silicon CCD detectors that demonstrate world record detector quantum efficiency (>50%) in the near and far ultraviolet (155–300 nm). This report describes in detail the unique surface engineering approaches used and demonstrates the robustness of detector performance that is obtained by achieving atomic level precision at key steps in the fabrication process. The characterization, materials, and devices produced in this effort will be presented along with comparison to other approaches.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
85.60.Gz Photodetectors (including infrared and CCD detectors)

Height distribution of atomic force microscopy images as a tool for atomic layer deposition characterization

Krzysztof Kolanek, Massimo Tallarida, and Dieter Schmeisser

J. Vac. Sci. Technol. A 31, 01A104 (2013); http://dx.doi.org/10.1116/1.4754557 (9 pages)

Online Publication Date: 2 October 2012

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The authors propose the analysis of surface height histograms as a tool for the atomic layer deposition (ALD) growth characterization in the initial stage of the process. ALD of HfO2 on a Si(100)/SiO2 substrate was investigated in situ by ultra high vacuum atomic force microscope working in noncontact mode. The ALD cycles, made by using tetrakis-di-methyl-amido-Hf and H2O as precursors, were performed at 230 °C. After each ALD cycle, the relation between the film growth and the root mean square surface roughness was studied. Parameters equivalent to HfO2 layer thickness, coverage, and surface roughness of the substrate and deposited material can be calculated in the proposed routine.
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68.55.aj Insulators
68.55.jd Thickness
68.37.Ps Atomic force microscopy (AFM)
68.35.bg Semiconductors

X-ray photoelectron spectroscopy study on the chemistry involved in tin oxide film growth during chemical vapor deposition processes

Gilbère J. A. Mannie, Gijsbert Gerritsen, Hendrikus C. L. Abbenhuis, Joop van Deelen, J. W. (Hans) Niemantsverdriet, and Peter C. Thüne

J. Vac. Sci. Technol. A 31, 01A105 (2013); http://dx.doi.org/10.1116/1.4756898 (6 pages)

Online Publication Date: 4 October 2012

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The chemistry of atmospheric pressure chemical vapor deposition (APCVD) processes is believed to be complex, and detailed reports on reaction mechanisms are scarce. Here, the authors investigated the reaction mechanism of monobutyl tinchloride (MBTC) and water during SnO2 thin film growth using x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). XPS results indicate an acid–base hydrolysis reaction mechanism, which is tested with multilayer experiments, demonstrating self-terminating growth. In-house developed TEM wafers are used to visualize nucleation during these multilayer experiments, and results are compared with TEM results of APCVD samples. Results show almost identical nucleation behavior implying that their growth mechanism is identical. Our experiments suggest that in APCVD, when using MBTC and water, SnO2 film growth occurs via a heterolytic bond splitting of the Sn-Cl bonds without the need to invoke gas-phase radical or coordination chemistry of the MBTC precursor.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.A- Nucleation and growth
68.55.at Other materials
68.43.Mn Adsorption kinetics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Substrate-biasing during plasma-assisted atomic layer deposition to tailor metal-oxide thin film growth

H. B. Profijt, M. C. M. van de Sanden, and W. M. M. Kessels

J. Vac. Sci. Technol. A 31, 01A106 (2013); http://dx.doi.org/10.1116/1.4756906 (9 pages) | Cited 1 time

Online Publication Date: 4 October 2012

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Two substrate-biasing techniques, i.e., substrate-tuned biasing and RF biasing, have been implemented in a remote plasma configuration, enabling control of the ion energy during plasma-assisted atomic layer deposition (ALD). With both techniques, substrate bias voltages up to −200 V have been reached, which allowed for ion energies up to 272 eV. Besides the bias voltage, the ion energy and the ion flux, also the electron temperature, the electron density, and the optical emission of the plasma have been measured. The effects of substrate biasing during plasma-assisted ALD have been investigated for Al2O3, Co3O4, and TiO2 thin films. The growth per cycle, the mass density, and the crystallinity have been investigated, and it was found that these process and material properties can be tailored using substrate biasing. Additionally, the residual stress in substrates coated with Al2O3 films varied with the substrate bias voltage. The results reported in this article demonstrate that substrate biasing is a promising technique to tailor the material properties of thin films synthesized by plasma-assisted ALD.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.77.-j Plasma applications

Ion conduction in nanoscale yttria-stabilized zirconia fabricated by atomic layer deposition with various doping rates

Kyung Sik Son, Kiho Bae, Jun Woo Kim, Jeong Suk Ha, and Joon Hyung Shim

J. Vac. Sci. Technol. A 31, 01A107 (2013); http://dx.doi.org/10.1116/1.4755921 (4 pages)

Online Publication Date: 8 October 2012

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The ion conduction of yttria-stabilized zirconia (YSZ) was studied by varying the doping ratios during atomic layer deposition (ALD). The ALD cycle ratio for the yttria and zirconia depositions was varied from 1:1 to 1:6, which corresponded to the doping ratios from 28.8% to 4.3%. The in-plane conductivity of ALD YSZ was enhanced by up to 2 orders of magnitude; the optimal ALD doping ratio (10.4%) was found to differ from that of bulk YSZ (8%). This different relationship between the doping ratio and the ion conduction for ALD YSZ versus bulk YSZ is due to the inhomogeneous doping in the vertical direction of the ALD YSZ films, as opposed to the homogenous doping of bulk YSZ.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.up Other materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.55.aj Insulators

On the kinetics of spatial atomic layer deposition

Paul Poodt, Joep van Lieshout, Andrea Illiberi, Raymond Knaapen, Fred Roozeboom, and Almie van Asten

J. Vac. Sci. Technol. A 31, 01A108 (2013); http://dx.doi.org/10.1116/1.4756692 (7 pages)

Online Publication Date: 10 October 2012

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Spatial atomic layer deposition (ALD) is a promising technology for high deposition rate and high-throughput ALD that can be used for roll-to-roll and large-area applications. In an ideal spatial ALD reactor, the design of the injector should be tuned to the deposition kinetics of the ALD reaction, requiring an in-depth knowledge of the dependencies of the growth per cycle (GPC) on the main kinetic parameters. The authors have investigated the deposition kinetics of spatial ALD of alumina from trimethylaluminum and H2O at atmospheric pressure. A kinetic model was developed, which describes the growth per cycle as a function of the main kinetic parameters. The observation of a √t time dependency in the GPC indicates that precursor diffusion to substrate is rate limiting. Next to a fundamental insight into the kinetics of atmospheric pressure spatial ALD, this model can be used for design optimization of new spatial ALD reactors. Furthermore, the model shows that the maximum alumina deposition rates obtainable with spatial ALD are in the order of several nm/s.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.Fx Diffusion; interface formation

Atomic layer deposition of Al-doped ZnO thin films

Tommi Tynell, Hisao Yamauchi, Maarit Karppinen, Ryuji Okazaki, and Ichiro Terasaki

J. Vac. Sci. Technol. A 31, 01A109 (2013); http://dx.doi.org/10.1116/1.4757764 (4 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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Atomic layer deposition has been used to fabricate thin films of aluminum-doped ZnO by depositing interspersed layers of ZnO and Al2O3 on borosilicate glass substrates. The growth characteristics of the films have been investigated through x-ray diffraction, x-ray reflection, and x-ray fluorescence measurements, and the efficacy of the Al doping has been evaluated through optical reflectivity and Seebeck coefficient measurements. The Al doping is found to affect the carrier density of ZnO up to a nominal Al dopant content of 5 at. %. At nominal Al doping levels of 10 at. % and higher, the structure of the films is found to be strongly affected by the Al2O3 phase and no further carrier doping of ZnO is observed.
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68.55.ag Semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.61.Ga II-VI semiconductors
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.uj III-V and II-VI semiconductors

Low temperature deposition of Ga2O3 thin films using trimethylgallium and oxygen plasma

Inci Donmez, Cagla Ozgit-Akgun, and Necmi Biyikli

J. Vac. Sci. Technol. A 31, 01A110 (2013); http://dx.doi.org/10.1116/1.4758782 (4 pages)

Online Publication Date: 12 October 2012

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Gallium oxide (Ga2O3) thin films were deposited by plasma-enhanced atomic layer deposition (ALD) using trimethylgallium as the gallium precursor and oxygen plasma as the oxidant. A wide ALD temperature window was observed from 100 to 400 °C, where deposition rate was constant at ∼0.53 Å/cycle. X-ray photoelectron spectroscopy survey scans indicated the presence of gallium, oxygen, and carbon elements with concentrations of ∼36, ∼51.8, and ∼12.2 at. %, respectively. As-deposited films were amorphous; upon annealing at 900 °C under N2 atmosphere for 30 min, polycrystalline β-Ga2O3 phase with a monoclinic crystal structure was obtained. Refractive index and root mean square roughness of the annealed Ga2O3 film were higher than those of the as-deposited due to crystallization.
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68.55.aj Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.66.Fn Inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators

Excitation of radiative polaritons by polarized broadband infrared radiation in thin oxide films deposited by atomic layer deposition

Anita J. Vincent-Johnson, Andrew E. Masters, Xiaofeng Hu, and Giovanna Scarel

J. Vac. Sci. Technol. A 31, 01A111 (2013); http://dx.doi.org/10.1116/1.4759442 (4 pages)

Online Publication Date: 16 October 2012

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This work contributes to the understanding of infrared radiation interaction with matter and its absorption for energy harvesting purposes. By exciting radiative polaritons in thin oxide films with polarized infrared radiation, a further evidence is collected that a link exists between radiative polaritons and the heat recovery mechanism hypothesized in previous research. In the voltage transient occurring when the infrared radiation is turned on, the observed time necessary to reach the maximum voltage and the voltage intensity versus angle of incidence exhibit a mismatch when generated by polarized and nonpolarized infrared radiation. The existence of collective charge oscillation modes in the semiconductor-based elements of the thermoelectric power generators supporting the heat recovery mechanism is suggested as the main source of the discrepancy.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Hv Other nonmetallic inorganics
84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
68.55.A- Nucleation and growth

Chemistry of Cu(acac)2 on Ni(110) and Cu(110) surfaces: Implications for atomic layer deposition processes

Qiang Ma and Francisco Zaera

J. Vac. Sci. Technol. A 31, 01A112 (2013); http://dx.doi.org/10.1116/1.4763358 (10 pages) | Cited 1 time

Online Publication Date: 25 October 2012

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The thermal chemistry of copper(II)acetylacetonate, Cu(acac)2, on Ni(110) and Cu(110) single-crystal surfaces was probed under vacuum by using x-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Some data for acetylacetone (Hacac, CH3COCH2COCH3) adsorbed on Ni(110) are also reported as reference. Chemical transformations were identified in several steps covering a temperature range from 150 K to at least 630 K. The desorption of Hacac and a 3-oxobutanal (CH3COCH2CHO) byproduct was observed first at 150 and 180 K on Ni(110) and at 160 and 185 K on Cu(110), respectively. Partial loss of the acetylacetonate (acac) ligands and a likely change in adsorption geometry are seen next, with the possible production of HCu(acac), which desorbs at 200 and 235 K from the nickel and copper surfaces, respectively. Molecular Cu(acac)2 desorption is observed on both surfaces at approximately 300 K, probably from recombination of Cu(acac) and acac surface species. The remaining copper atoms on the surface lose their remaining acac ligands to the substrate and become reduced directly to metallic copper. At the same time, the organic ligands follow a series of subsequent surface reactions, probably involving several C–C bond-scissions, to produce other fragments, additional Hacac and HCu(acac) in the gas phase in the case of the copper surface, and acetone on nickel. A significant amount of acac must nevertheless survive on the surface to high temperatures, because Hacac peaks are seen in the TPD at about 515 and 590 K and the C 1s XPS split associated with acac is seen up to close to 500 K. In terms of atomic layer deposition processes, this suggests that cycles could be design to run at such temperatures as long as an effective hydrogenation agent is used as the second reactant to remove the surface acac as Hacac. Only a small fraction of carbon is left behind on Ni after heating to 800 K, whereas more carbon and additional oxygen remains on the surface in the case of Cu.
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68.43.Mn Adsorption kinetics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.43.Vx Thermal desorption

Combining dynamic and static depth profiling in low energy ion scattering

Rik ter Veen, Michael Fartmann, Reinhard Kersting, and Birgit Hagenhoff

J. Vac. Sci. Technol. A 31, 01A113 (2013); http://dx.doi.org/10.1116/1.4764111 (3 pages)

Online Publication Date: 26 October 2012

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The advantages of combining dynamic and static depth profiling in low energy ion scattering are demonstrated for an Si/SiOx/W/Al2O3 ALD stack. Dynamic depth profiling can be used to calibrate static depth profiling. Energy losses of 152 and 215 eV/nm were found for 3 keV 4He+ and 5 keV 4He+ primary ions, respectively, for the experimental configuration used. This is in good agreement with the values used in the field. Static depth profiling can be used to recognize sputter artifacts in dynamic depth profiles.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Crystal AlN deposited at low temperature by magnetic field enhanced plasma assisted atomic layer deposition

Wenwen Lei and Qiang Chen

J. Vac. Sci. Technol. A 31, 01A114 (2013); http://dx.doi.org/10.1116/1.4764112 (7 pages)

Online Publication Date: 26 October 2012

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In this paper, AlN films prepared at low temperature by magnetic field enhanced plasma assisted atomic layer deposition (PA-ALD) using trimethyl aluminum and the mixture gas of nitrogen and hydrogen were investigated. Two discharge modes were employed for PA-ALD AlN, i.e., radio-frequency (RF) discharge mode and microwave electron cyclotron resonance (ECR) mode. The structure of the film, compositions, crystallinity, surface roughness, and properties of refractive index as well as photoluminescence were studied by Fourier transform infrared spectroscope, x-ray photoelectron spectroscope, x-ray diffraction, atomic force microscope, spectroscopic ellipsometry, and photoluminescence spectrometer, respectively. Comparison of the as-deposited films prepared in two discharge modes, the authors result that temperature played an important role in in ECR mode, AlN films deposited in ECR mode at 250 °C is crystalline except a little bit of aluminum rich with the contamination of carbon and oxygen; whereas in RF discharge mode, the direct interaction of plasma, the all process parameters affect the properties of the AlN films, like the strength of magnetic field, deposition temperature. The intense emission band measured through photoluminescence spectrum of the as-deposited AlN suggests that there may be potential applications in electronic and optoelectronic nanodevices.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

HfxZr1−xO2 compositional control using co-injection atomic layer deposition

Steven Consiglio, Kandabara Tapily, Robert D. Clark, Genji Nakamura, Cory S. Wajda, and Gert J. Leusink

J. Vac. Sci. Technol. A 31, 01A115 (2013); http://dx.doi.org/10.1116/1.4764473 (5 pages)

Online Publication Date: 30 October 2012

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As a replacement for SiO2 based gate dielectrics, HfO2 with an admixture of ZrO2 has the potential to provide a higher dielectric constant than pure HfO2 by means of stabilization of higher-k phases. Accordingly, in this study the authors have pursued a means to control composition of HfxZr1−xO2 films grown by atomic layer deposition by simultaneously flowing Hf and Zr metal precursors during the precursor exposure step and varying the molar flow ratio. Using the tetrakis(ethylmethylamino) Hf and Zr precursors, TEMAH and TEMAZ, with either H2O or O3 co-reactants, the co-injection approach for HfxZr1−xO2 was compared with alternating HfO2 and ZrO2 growth cycles and was observed to allow uniform and tunable composition control. For the co-injection process, deviation from the cycle ratio trendline suggests more efficient chemisorption of TEMAZ compared to TEMAH. The authors have also evaluated these films in metal–oxide–semiconductor capacitor structures and verified the electrical equivalence and similar within-wafer distributions of Hf0.2Zr0.8O2 obtained from both processing schemes.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Atomic layer deposition of anatase TiO2 on porous electrodes for dye-sensitized solar cells

Ingo Dirnstorfer, Hannes Mähne, Thomas Mikolajick, Martin Knaut, Matthias Albert, and Kristina Dubnack

J. Vac. Sci. Technol. A 31, 01A116 (2013); http://dx.doi.org/10.1116/1.4764889 (5 pages)

Online Publication Date: 30 October 2012

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Thin TiO2 films were grown by atomic layer deposition on planar and porous substrates and characterized by Raman spectroscopy, x-ray diffraction, high resolution transmission electron microscopy, and spectroscopic ellipsometry. The growth conditions of anatase TiO2 are investigated, motivated by the application in dye-sensitized solar cells, where best results are achieved with electrodes based on anatase TiO2. To enforce an anatase TiO2 growth on substrates stimulating rutile growth, a symmetry breaking ultra thin buffer layer of five cycles Al2O3 was introduced. With this buffer layer anatase TiO2 deposition was demonstrated on planar rutile TiO2 substrates. However, it was found that the necessity of the buffer layer depends on the substrate structure. On porous TiO2 electrodes containing a mixture of anatase and rutile TiO2 domains, a direct anatase TiO2 growth was possible even without a buffer layer.
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81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
88.40.jr Organic photovoltaics
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors

Effect of the amido Ti precursors on the atomic layer deposition of TiN with NH3

Gihee Cho and Shi-Woo Rhee

J. Vac. Sci. Technol. A 31, 01A117 (2013); http://dx.doi.org/10.1116/1.4764898 (5 pages) | Cited 1 time

Online Publication Date: 30 October 2012

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The effect of the amide Ti precursors, tetrakis dimethyl amido titanium (TDMAT), tetrakis ethylmethyl amido titanium (TEMAT), and tetrakis diethyl amido titanium (TDEAT) on the atomic layer deposition of TiN film with ammonia was studied. Surface decomposition mechanism of each precursor was studied with in-situ Fourier transform infrared spectroscopy. It was confirmed that ethyl ligand in the precursor was more stable than methyl and the surface decomposition temperature of TDMAT, TEMAT, and TDEAT was 175, 200, and 250 °C on the SiO2 surface, respectively. The resistivity of the film was decreased with the increase in the substrate temperature due to the film crystallization. The TiN film deposited with TDMAT gave the lowest resistivity even though the atomic layer deposition temperature window was lowest due to the largest amount of carbon incorporation. It was confirmed that carbon incorporation leads to TiC formation and suppressed the postdeposition oxygen uptake possibly due to the elimination of vacancy in the film.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.jd Vacancies
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Atomic layer deposition of epitaxial TiO2 II on c-sapphire

Aivar Tarre, Kristel Möldre, Ahti Niilisk, Hugo Mändar, Jaan Aarik, and Arnold Rosental

J. Vac. Sci. Technol. A 31, 01A118 (2013); http://dx.doi.org/10.1116/1.4764892 (5 pages)

Online Publication Date: 7 November 2012

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Using atomic layer deposition technique, epitaxial titania polymorph TiO2 II was grown on α-Al2O3(0 0 1) (c-sapphire) substrates. TiCl4 and H2O served as precursors. The growth temperature ranged from 350 to 680 °C. Raman scattering and high-resolution x-ray diffraction and reflection measurements were applied to characterize the films. It appeared that the films contained, in addition to TiO2 II, anatase and/or rutile phase. The dependence of the film properties on the growth temperature and the film thickness was explored. The growth of the TiO2 II phase was shown to be controlled by the α-Al2O3 substrate orientation. This phase did not grow when the substrate was (0 1 2) oriented (r-sapphire). The epitaxial relationship was determined to be (1 0 0)[0 math 0]TiO2 II ∥ (0 0 1)[1 2 0]sapphire, (1 0 0)[0 0 1]TiO2 II ∥ (0 0 1)[1 0 0]sapphire.
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68.55.aj Insulators
78.66.Nk Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Structural properties of as deposited and annealed ZrO2 influenced by atomic layer deposition, substrate, and doping

Wenke Weinreich, Lutz Wilde, Johannes Müller, Jonas Sundqvist, Elke Erben, Johannes Heitmann, Martin Lemberger, and Anton J. Bauer

J. Vac. Sci. Technol. A 31, 01A119 (2013); http://dx.doi.org/10.1116/1.4765047 (9 pages) | Cited 2 times

Online Publication Date: 7 November 2012

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Thin ZrO2 films are of high interest as high-k material in dynamic random access memory (DRAM), embedded dynamic random access memory, and resistive random access memory as well as for gate oxides. Actually, ZrO2 is predicted to be the key material in future DRAM generations below 20 nm. Profound knowledge of pure and doped ZrO2 thin films, especially of the structural properties, is essential in order to meet the requirements of future devices. This paper gives a detailed overview about the structural properties of ZrO2 films in dependence of various process parameters. The study of atomic layer deposition (ALD) growth mechanisms of ZrO2 on a TiN-substrate in comparison to a Si-substrate covered with native oxide exhibits significant differences. Furthermore, the structural properties crystallinity, surface roughness, and film stress are studied after the ALD deposition in dependence of the process parameters deposition temperature, layer thickness, and underlying substrate. Remarkable dependencies of the ZrO2 crystallization temperatures on the substrates are figured out. The structural properties after various annealing steps are monitored as well. The influence of doping by SiO2 and Al2O3 is studied, which is primarily used to keep the thin films amorphous during deposition.
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68.55.A- Nucleation and growth
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Cc Kinetics of defect formation and annealing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.U- Doping and impurity implantation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Atomic layer deposition of Ga-doped ZnO transparent conducting oxide substrates for CdTe-based photovoltaics

Paul R. Chalker, Paul A. Marshall, Simon Romani, Joseph W. Roberts, Stuart J. C. Irvine, Daniel A. Lamb, Andrew J. Clayton, and Paul A. Williams

J. Vac. Sci. Technol. A 31, 01A120 (2013); http://dx.doi.org/10.1116/1.4765642 (5 pages)

Online Publication Date: 7 November 2012

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The atomic layer deposition of gallium doped zinc oxide films is investigated as a method of fabricating transparent conducting oxide substrates for cadmium telluride based photovoltaic cells. The growth parameters and properties of gallium-doped ZnO were established for a range of dopant concentrations. 1 at. % gallium-doped films exhibited the lowest electrical sheet resistances and were selected as substrates to deposit Cd1−xZnxS/CdTe photovoltaic cells. The average current density–voltage characteristics of 16 cells under AM1.5 illumination yielded a conversion efficiency of 10.8% and a fill-factor of 65%.
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88.40.hj Efficiency and performance of solar cells
88.40.jm Thin film III-V and II-VI based solar cells
73.61.Ga II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors

Copper deposition on TiO2 from copper(II)hexafluoroacetylacetonate

David G. Rayner, James S. Mulley, and Roger A. Bennett

J. Vac. Sci. Technol. A 31, 01A121 (2013); http://dx.doi.org/10.1116/1.4765644 (5 pages)

Online Publication Date: 7 November 2012

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The authors have studied the adsorption of CuII(hfac)2 on the surface of a model oxide system, TiO2(110), and probed the molecular stability with respect to thermal cycling, using atomic scale imaging by scanning tunneling microscopy supported by x-ray photoemission spectroscopy. They find that at 473 K, the adsorbed metal-organic molecules begin to dissociate and release Cu atoms which aggregate and form Cu nanoparticles. These Cu nanoparticles ripen over time and the size (height) distribution develops into a bimodal distribution. Unlike other organometallic systems, which show a bimodal distribution due to enhanced nucleation or growth at surface step edges, the nanoparticles do not preferentially form at steps. The reduced mobility of the Cu islands may be related to the co-adsorbed ligands that remain in very small clusters on the surface.
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68.43.Mn Adsorption kinetics
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Evaluating Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition techniques

Jacob A. Bertrand and Steven M. George

J. Vac. Sci. Technol. A 31, 01A122 (2013); http://dx.doi.org/10.1116/1.4763360 (8 pages) | Cited 1 time

Online Publication Date: 8 November 2012

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Al2O3 gas diffusion barriers grown directly on Ca films using atomic layer deposition (ALD) techniques were evaluated using several methods based on Ca oxidation. The Al2O3 ALD films were grown on Ca films at 120 °C using trimethylaluminum and H2O as the reactants. The oxidation of the Ca films was then monitored versus time at 70 °C and ∼28% relative humidity either by measuring the electrical conductance of the Ca film or by recording the photographic image of the Ca film. In the photographic images, the Ca films revealed that the Al2O3 ALD films have a small number of pinhole defects that lead to Ca film oxidation areas that grow radially around the pinhole defect versus time. A burst of new oxidation areas also appeared suddenly at later times and grew radially versus time. This rapid “blooming” may be related to another type of defect caused by water corrosion of the Al2O3 ALD films. In the electrical conductance measurements, the conductance of the Ca film initially showed little change versus time. The conductance then dropped rapidly when the oxidation area in the photographic image was a noticeable fraction of the Ca film area. The conductance measurements yielded a water vapor transmission rate (WVTR) value of ∼2 × 10−2 g/(m2 day) prior to the rapid reduction of the conductance. The photographic images of the Ca film were also analyzed to obtain a WVTR value assuming radial oxidation of the Ca film around defects. The WVTR values obtained from the electrical conductance and the photographic images were in approximate agreement and increased versus Ca film oxidation until the rapid blooming of new circular oxidation areas. The WVTR values are larger than previous measurements and may indicate that Al2O3 ALD films grown directly on Ca are less stable and degraded by Ca film oxidation. This study reveals that a range of WVTR values can be obtained from different variations of the Ca test depending on the extent of Ca film oxidation.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.65.Mq Oxidation
81.65.-b Surface treatments
82.45.Bb Corrosion and passivation
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

TEMAZ/O3 atomic layer deposition process with doubled growth rate and optimized interface properties in metal–insulator–metal capacitors

Wenke Weinreich, Tina Tauchnitz, Patrick Polakowski, Maximilian Drescher, Stefan Riedel, Jonas Sundqvist, Konrad Seidel, Mahdi Shirazi, Simon D. Elliott, Susanne Ohsiek, Elke Erben, and Bernhard Trui

J. Vac. Sci. Technol. A 31, 01A123 (2013); http://dx.doi.org/10.1116/1.4766281 (11 pages) | Cited 2 times

Online Publication Date: 27 November 2012

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ZrO2 is of very high interest for various applications in semiconductor industry especially as high-k dielectric in metal–insulator–metal (MIM) capacitor devices. Further improvement of deposition processes, of material properties, and of integration schemes is essential in order to meet the strict requirements of future devices. In this paper, the authors describe a solution to solve one of the key challenges by reducing the process time of the bottle neck high-k atomic layer deposition (ALD). The authors extensively optimized the most common ALD process used for the ZrO2 deposition (TEMAZ/O3) resulting now in a doubled growth rate compared to the published growth rates of maximum 1 Å/cycle. Chemical reactions explaining the origin of the high growth rate are proposed by theoretical process modelling. At the same time, the outstanding electrical properties of ZrO2 thin films could be preserved. Finally, the integration of the ZrO2 process in MIM capacitor devices with TiN electrodes was evaluated. Thereby, the known effect of TiN bottom electrode oxidation by the O3 process was analyzed and significantly reduced by different integration approaches including wet chemical treatments and ALD process variations. The resulting MIM capacitors show low leakage current and high polarity symmetry.
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84.32.Tt Capacitors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Effect of in situ hydrogen plasma treatment on zinc oxide grown using low temperature atomic layer deposition

Tae-Hoon Jung, Jin-Seong Park, Dong-Ho Kim, Yongsoo Jeong, Sung-Gyu Park, and Jung-Dae Kwon

J. Vac. Sci. Technol. A 31, 01A124 (2013); http://dx.doi.org/10.1116/1.4767813 (4 pages)

Online Publication Date: 27 November 2012

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Zinc oxide (ZnO) films under in situ hydrogen plasma were deposited via atomic layer deposition (ALD) at an extremely low temperature (100 °C). Diethyl zinc ((C2H5)2Zn) and deionized water were used as the zinc and oxygen source, respectively. The growth rate of the ZnO films decreased to 1.26 and 1.06 Å/cycle due to changes in the hydrogen plasma treatment power and exposure time, respectively. The resistivity of the ZnO films decreased to 7.6 × 10−4 Ω cm, even at 100 °C, with a very high carrier concentration (1.4 × 1021 cm−3) due to the increasing oxygen deficiencies in the ZnO films. The carrier mobility was decreased slightly to 8.6 cm2/Vs via grain boundary scattering due to the enhanced polycrystallization. Based on the x-ray diffraction and x-ray photoelectron spectroscopy, the carrier concentration and mobility were strongly correlated to the oxygen deficiency and crystallinity, respectively. In addition, the in situ hydrogen plasma in the ZnO ALD had an important role in sequentially generating oxygen deficiencies and enhancing polycrystal growth.
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68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
61.72.Mm Grain and twin boundaries
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Atomic layer deposition of aluminum-doped zinc oxide films for the light harvesting enhancement of a nanostructured silicon solar cell

Sheng-Hui Chen, Shih-Hao Chan, Chun-Ko Chen, Shao-Ze Tseng, Chieh-Hsiang Hsu, and Wen-Hao Cho

J. Vac. Sci. Technol. A 31, 01A125 (2013); http://dx.doi.org/10.1116/1.4767837 (5 pages)

Online Publication Date: 27 November 2012

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Anodic-aluminum-oxide (AAO) template lithography and atomic layer deposition (ALD) antireflection coating techniques have often been applied for the fabrication of wide-angle antireflection structures on silicon solar cells. In this study, an AAO template was fabricated as a mask to block the high density plasma dry etching from the crystalline silicon to form nanostructures on the surface of the crystalline silicon wafer. Then, a 55-nm-thick aluminum-doped zinc oxide (AZO) film was deposited on the silicon nanostructures using the ALD method. The results show that the application of a nanostructured AZO film can decrease the average reflectivity of the crystalline silicon to 0.83% in the wavelength range from 400 to 850 nm for an incident angle of 8°. The conversion efficiency of the nanostructured silicon solar cell can be enhanced from 6.93% to 8.37%.
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88.40.jj Silicon solar cells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
88.40.hj Efficiency and performance of solar cells

Probing the properties of atomic layer deposited ZrO2 films on p-Germanium substrates

Ariadne P. Kerasidou, Martha A. Botzakaki, Nikolaos Xanthopoulos, Stella Kennou, Spyridon Ladas, Stavroula N. Georga, and Christoforos A. Krontiras

J. Vac. Sci. Technol. A 31, 01A126 (2013); http://dx.doi.org/10.1116/1.4768166 (5 pages) | Cited 1 time

Online Publication Date: 27 November 2012

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Zirconium oxide (ZrO2) thin films of 5 and 25 nm thickness were deposited by atomic layer deposition at 250 °C on p-type Ge substrates. The stoichiometry, thickness, and valence band electronic structure of the ZrO2 films were investigated by x-ray and ultraviolet photoelectron spectroscopies. For the electrical characterization, metal-oxide-semiconductor (MOS) capacitive structures (Pt/ZrO2/p-Ge) have been fabricated. Capacitance–voltage and conductance–voltage (C–V, G–V) measurements performed by ac impedance spectroscopy in the temperature range from 153 to 313 K reveal a typical MOS behaviour with moderate frequency dispersion at the accumulation region attributed to leakage currents. For the determination of the leakage currents conduction mechanisms, current density–voltage (J–V) measurements were carried out in the whole temperature range.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.20.At Surface states, band structure, electron density of states
71.20.-b Electron density of states and band structure of crystalline solids
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Electrical characterization of atomic-layer-deposited hafnium oxide films from hafnium tetrakis(dimethylamide) and water/ozone: Effects of growth temperature, oxygen source, and postdeposition annealing

Hector García, Helena Castán, Salvador Dueñas, Luis Bailón, Francesca Campabadal, Oihane Beldarrain, Miguel Zabala, Mireia Bargallo González, and Joan Marc Rafí

J. Vac. Sci. Technol. A 31, 01A127 (2013); http://dx.doi.org/10.1116/1.4768167 (7 pages)

Online Publication Date: 27 November 2012

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The electrical properties of HfO2-based metal–insulator–semiconductor capacitors have been systematically investigated by means of I–V and C–V characteristics, admittance spectroscopy, deep level transient spectroscopy, conductance transient, and flat band voltage transient techniques. Attention is also given to the study of the temperature dependence of the leakage current. HfO2 films were grown on p-type silicon substrates by atomic layer deposition using hafnium tetrakis(dimethylamide) as hafnium precursor, and ozone or water as oxygen precursors. The growth temperature ranged from 150 to 350 °C. Low growth temperatures prevent decomposition and high growth rate, as well as high contamination levels. As a result, the leakage current is lower for lower deposition temperatures. Some of the deposited samples were submitted to a postdeposition annealing at 650 °C in N2 atmosphere, showing a decrease in the leakage current and an increase in the equivalent oxide thickness (EOT), whereas interfacial state density increases and defect density inside the dielectric bulk decreases. Regarding dielectric reliability, in our experimental conditions, HfO2 layers grown at 150 °C exhibit the largest EOT and breakdown voltage. The electrical behaviour is clearly linked with structural properties, and especially with the formation of an interfacial layer between the HfO2 layer and the silicon substrate, as well as with the presence of several impurities.
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73.61.Ng Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.32.Tt Capacitors
85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.20.At Surface states, band structure, electron density of states

Blistering of atomic layer deposition Al2O3 layers grown on silicon and its effect on metal–insulator–semiconductor structures

Oihane Beldarrain, Marta Duch, Miguel Zabala, Joan Marc Rafí, Mireia Bargalló González, and Francesca Campabadal

J. Vac. Sci. Technol. A 31, 01A128 (2013); http://dx.doi.org/10.1116/1.4768170 (6 pages)

Online Publication Date: 27 November 2012

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In this work, a study of the influence of the processing conditions on the blistering of Al2O3 layers grown by atomic layer deposition (ALD) on silicon substrates is presented. The phenomenon occurs when the as-deposited layers are annealed at high temperature in a N2 atmosphere. The characterization of the blistering in terms of density and dimensions indicates that the higher the annealing temperature the higher the density but also the smaller the blister diameter, while the thicker the oxide the larger the blisters. The processing of the blistered layers to obtain Al-Al2O3-Si structures enhances the blistering phenomenon and at the same time affects the silicon surface underneath the blister. This has been evidenced by chemical etching of the deposited layers that have revealed in circular silicon voids of the size of the blister. The influence of the oxygen precursor used in the ALD process has also been investigated, showing that the blister size is reduced when using O3 instead of H2O. Finally, the use of a thin thermally grown SiO2 layer is shown to avoid blistering of Al2O3 films.
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61.72.Cc Kinetics of defect formation and annealing
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Cf Surface cleaning, etching, patterning

Low-temperature atomic layer deposition of Al2O3 on blown polyethylene films with plasma-treated surfaces

Gyeong Beom Lee, Kyung Sik Son, Suk Won Park, Joon Hyung Shim, and Byoung-Ho Choi

J. Vac. Sci. Technol. A 31, 01A129 (2013); http://dx.doi.org/10.1116/1.4768171 (8 pages)

Online Publication Date: 27 November 2012

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In this study, a layer of Al2O3 was deposited on blown polyethylene films by atomic layer deposition (ALD) at low temperatures, and the surface characteristics of these Al2O3-coated blown polyethylene films were analyzed. In order to examine the effects of the plasma treatment of the surfaces of the blown polyethylene films on the properties of the films, both untreated and plasma-treated film samples were prepared under various processing conditions. The surface characteristics of the samples were determined by x-ray photoelectron spectroscopy, as well as by measuring their surface contact angles. It was confirmed that the surfaces of the plasma-treated samples contained a hydroxyl group, which helped the precursor and the polyethylene substrate to bind. ALD of Al2O3 was performed through sequential exposures to trimethylaluminum and H2O at 60 °C. The surface morphologies of the Al2O3-coated blown polyethylene films were observed using atomic force microscopy and scanning electron microscopy/energy-dispersive x-ray spectroscopy. Further, it was confirmed that after ALD, the surface of the plasma-treated film was covered with alumina grains more uniformly than was the case for the surface of the untreated polymer film. It was also confirmed via the focused ion beam technique that the layer Al2O3 conformed to the surface of the blown polyethylene film.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.41.+e Polymers, elastomers, and plastics
68.55.am Polymers and organics
68.03.Cd Surface tension and related phenomena
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

New approach toward transparent and conductive ZnO by atomic layer deposition: Hydrogen plasma doping

Matthew A. Thomas, Johnathan C. Armstrong, and Jingbiao Cui

J. Vac. Sci. Technol. A 31, 01A130 (2013); http://dx.doi.org/10.1116/1.4768172 (6 pages)

Online Publication Date: 27 November 2012

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A hydrogen plasma doping process was combined with the traditional atomic layer deposition (ALD) technique in order to enhance the transparency and conductivity of ZnO films. The hydrogen plasma was included in situ during each ALD cycle and was found to be more effective at producing highly conductive ZnO when used before the H2O vapor pulse that is standard to thermal-ALD processes. Through the hydrogen plasma doping process, the resistivity and carrier concentration of the ALD ZnO films are improved to levels suitable for transparent conductive oxide applications. These favorable electrical properties, combined with improved transparency, make such H-doped ZnO films comparable to some of the best Al-doped ZnO materials achieved with ALD processes in the literature. At thicknesses well below 200 nm, the H-doped ALD ZnO films maintain optimal resistivities near 7 × 10−4 Ω cm along with average transmittance values of ∼92% from 400 to 1000 nm.
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81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors

Atomic layer deposition of zinc indium sulfide films: Mechanistic studies and evidence of surface exchange reactions and diffusion processes

Pascal Genevée, Frédérique Donsanti, Nathanaelle Schneider, and Daniel Lincot

J. Vac. Sci. Technol. A 31, 01A131 (2013); http://dx.doi.org/10.1116/1.4768919 (6 pages)

Online Publication Date: 29 November 2012

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The authors present the elaboration of zinc indium sulfide (ZnInxSy) thin films in the context of a cadmium-free buffer layer development for copper indium gallium diselenide photovoltaic solar cells. The films were deposited by atomic layer deposition (ALD) from ZnEt2 (DEZ), In(acac)3 (acac = acetylacetonate), and H2S at 200 °C. In situ growth kinetics studies were performed with the quartz crystal microbalance technique to determine the respective mass gain per cycle of ZnS and In2S3 layers, allowing determination of the atomic compositions of the ZnInxSy thin films to be expected if the deposition strictly follows the rule of mixtures. As the experimental atomic compositions of the ZnInxSy films differ significantly from this rule, a comprehensive study of the growth mechanism was performed to determine the nature of the side reactions. First, an exchange reaction between In2S3 and the Zn precursor was identified, though this process is not sufficient to account for the experimental data, and therefore, a second process which corresponds to the diffusion of species within the film was also found to take place. Ultimately, the atomic compositions of the ZnInxSy films can be explained by a rate-limited exchange reaction at the surface between DEZ and the In2S3 layer, combined with diffusion of the species in the whole film. More generally, such side reactions should be considered in ALD of multinary compounds, even at low temperature.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
88.40.jn Thin film Cu-based I-III-VI2 solar cells
68.35.Fx Diffusion; interface formation

Physical and electrical characteristics of atomic-layer deposition-HfO2 films deposited on Si substrates having different silanol Si-OH densities

Joel Molina, Carlos Zuniga, Wilfrido Calleja, Pedro Rosales, Alfonso Torres, and Alberto Herrera-Gomez

J. Vac. Sci. Technol. A 31, 01A132 (2013); http://dx.doi.org/10.1116/1.4769206 (6 pages)

Online Publication Date: 29 November 2012

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In this work, ultrathin HfO2 films, less than 6 nm in thickness, are deposited by atomic-layer deposition (ALD) on Si substrates that have a variable density of silanol (Si-OH) chemical bonds after oxidizing the Si surface using hot H2O2. Given the surface chemistry needed for proper ALD growth of HfO2, OH-last surfaces are needed in order to react with the Hf-based precursor during half-cycle of this reaction. The later is important for proper nucleation and uniform growth of ultrathin HfO2 by ALD. Depending on the immersion time of an initially HF-last Si surface in hot H2O2, ultrathin and nonstoichiometric chemical oxides SiOx are formed presenting a variable density of Si-OH bonds which are measured after Fourier-transform infra red spectroscopy. Following SiOx formation, HfO2 is directly deposited on these surfaces by ALD using water (H2O) and tetrakis-dimethylamino-hafnium as precursors. Metal–insulator–semiconductor (MIS) capacitors are then formed using both HfO2/Si and HfO2/SiOx/Si stacked structures and their electrical characteristics are evaluated. It is found that a variable density of Si-OH chemical bonds have an impact on the physical and electrical characteristics of these MIS structures by reducing their atomic surface roughness (Rrms) and gate leakage current density (Jg), and at the same time, increasing their flat band voltage (Vfb) for the same immersion times in H2O2. Obtaining the lowest Rrms, Jg, and Vfb are possible by using intermediate H2O2 immersion times between 4 and 8 min, which is also directly related to an intermediate Si-OH bond density.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.32.Tt Capacitors

Preparation and phase structures of Zn–Ti–O ternary compounds by atomic layer deposition

Xu Qian, Mo-Yun Gao, Yan-Qiang Cao, Bing-Lei Guo, and Ai-Dong Li

J. Vac. Sci. Technol. A 31, 01A133 (2013); http://dx.doi.org/10.1116/1.4769451 (6 pages)

Online Publication Date: 30 November 2012

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Zn–Ti–O (ZTO) ternary films with various Zn/Ti cycle ratios were deposited on Si substrates using diethylzinc and titanium isopropoxide as Zn and Ti sources by atomic layer deposition (ALD). The effect of Zn/Ti cycle ratio and postannealing temperature on the growth rate, composition, phase structure, and morphology of ZTO films were investigated by a series of analytical tools. It is found that for ALD ZTO films, the growth per cycle (GPC) of TiO2 deposited on ZnO-terminated surface is faster than that of pure TiO2, while the GPC of ZnO deposited on TiO2-terminated surface becomes slower than that of pure ZnO. This makes the Zn/Ti cycle ratio effect on the film composition become weak. The postannealing temperature and ALD sequence play important roles in facilitating the ZTO phase evolution. Pure Zn2TiO4 phase can be obtained in the (1:2)-ZTO films with 40.3 mol. % Ti content postannealed at 900 °C. For (2:5)-ZTO samples with 48.8 mol. % Ti content, pure h-ZnTiO3 phase can be formed at 700 °C. At 700 °C and above, the rutile TiO2 phase appears for (1:3)-ZTO samples with 52.1 mol. % Ti content. The scanning electron microscopy images confirm with increasing the postannealing temperature; the grain size becomes large with the inhomogenous morphologic change due to the h-ZnTiO3 phase decomposition into Zn2TiO4 and rutile TiO2 phases.
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68.55.aj Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Characterization of atomic layer deposition HfO2, Al2O3, and plasma-enhanced chemical vapor deposition Si3N4 as metal–insulator–metal capacitor dielectric for GaAs HBT technology

Jiro Yota, Hong Shen, and Ravi Ramanathan

J. Vac. Sci. Technol. A 31, 01A134 (2013); http://dx.doi.org/10.1116/1.4769207 (9 pages)

Online Publication Date: 6 December 2012

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Characterization was performed on the application of atomic layer deposition (ALD) of hafnium dioxide (HfO2) and aluminum oxide (Al2O3), and plasma-enhanced chemical vapor deposition (PECVD) of silicon nitride (Si3N4) as metal–insulator–metal (MIM) capacitor dielectric for GaAs heterojunction bipolar transistor (HBT) technology. The results show that the MIM capacitor with 62 nm of ALD HfO2 resulted in the highest capacitance density (2.67 fF/μm2), followed by capacitor with 59 nm of ALD Al2O3 (1.55 fF/μm2) and 63 nm of PECVD Si3N4 (0.92 fF/μm2). The breakdown voltage of the PECVD Si3N4 was measured to be 73 V, as compared to 34 V for ALD HfO2 and 41 V for Al2O3. The capacitor with Si3N4 dielectric was observed to have lower leakage current than both with Al2O3 and HfO2. As the temperature was increased from 25 to 150 °C, the breakdown voltage decreased and the leakage current increased for all three films, while the capacitance increased for the Al2O3 and HfO2. Additionally, the capacitance of the ALD Al2O3 and HfO2 films was observed to change, when the applied voltage was varied from −5 to +5 V, while no significant change was observed on the capacitance of the PECVD Si3N4. Furhermore, no significant change in capacitance was seen for these silicon nitride, aluminum oxide, and hafnium dioxide films, as the frequency was increased from 1 kHz to 1 MHz. These results show that the ALD films of Al2O3 and HfO2 have good electrical characteristics and can be used to fabricate high density capacitor. As a result, these ALD Al2O3 and HfO2 films, in addition to PECVD Si3N4, are suitable as MIM capacitor dielectric for GaAs HBT technology, depending on the specific electrical characteristics requirements and application of the GaAs devices.
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85.30.Pq Bipolar transistors
85.30.Tv Field effect devices
85.40.Sz Deposition technology

Atomic layer deposition of Al2O3 and AlxTi1−xOy thin films on N2O plasma pretreated carbon materials

Andrey M. Markeev, Anna G. Chernikova, Anastasya A. Chouprik, Sergey A. Zaitsev, Dmitry V. Ovchinnikov, Holger Althues, and Susanne Dörfler

J. Vac. Sci. Technol. A 31, 01A135 (2013); http://dx.doi.org/10.1116/1.4769793 (5 pages)

Online Publication Date: 6 December 2012

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A mild N2O plasma treatment technique (low power and low substrate temperature) for carbon materials' (including graphite and carbon nanotubes) functionalization followed by subsequent high-k dielectric atomic layer deposition (ALD) was developed. It was shown that N2O plasma carbon functionalization leads to the formation of epoxide and carboxylic groups on the carbon surface which act as active centers for ALD and, as a result, conformal and uniform Al2O3 and TixAl1−xOy films' growth occurred on the carbon surfaces. It was shown that the electrical properties of multinary TixAl1−xOy oxides are more promising in comparison to single Al2O3 oxide. Some electrical properties of the TixAl1−xOy films observed were a high dielectric constant ∼19, low leakage current density (<3 × 10−5 A/cm2 at 1 MV/cm), and high breakdown field (∼5.5 MV/cm).
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77.55.F- High-permittivity capacitive films
52.77.Dq Plasma-based ion implantation and deposition
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Epitaxial strontium titanate films grown by atomic layer deposition on SrTiO3-buffered Si(001) substrates

Martin D. McDaniel, Agham Posadas, Thong Q. Ngo, Ajit Dhamdhere, David J. Smith, Alexander A. Demkov, and John G. Ekerdt

J. Vac. Sci. Technol. A 31, 01A136 (2013); http://dx.doi.org/10.1116/1.4770291 (9 pages)

Online Publication Date: 6 December 2012

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Epitaxial strontium titanate (STO) films have been grown by atomic layer deposition (ALD) on Si(001) substrates with a thin STO buffer layer grown by molecular beam epitaxy (MBE). Four unit cells of STO grown by MBE serve as the surface template for ALD growth. The STO films grown by ALD are crystalline as-deposited with minimal, if any, amorphous SiOx layer at the STO-Si interface. The growth of STO was achieved using bis(triisopropylcyclopentadienyl)-strontium, titanium tetraisopropoxide, and water as the coreactants at a substrate temperature of 250 °C. In situ x-ray photoelectron spectroscopy (XPS) analysis revealed that the ALD process did not induce additional Si–O bonding at the STO-Si interface. Postdeposition XPS analysis also revealed sporadic carbon incorporation in the as-deposited films. However, annealing at a temperature of 250 °C for 30 min in moderate to high vacuum (10−6–10−9 Torr) removed the carbon species. Higher annealing temperatures (>275 °C) gave rise to a small increase in Si–O bonding, as indicated by XPS, but no reduced Ti species were observed. X-ray diffraction revealed that the as-deposited STO films were c-axis oriented and fully crystalline. A rocking curve around the STO(002) reflection gave a full width at half maximum of 0.30° ± 0.06° for film thicknesses ranging from 5 to 25 nm. Cross-sectional transmission electron microscopy revealed that the STO films were continuous with conformal growth to the substrate and smooth interfaces between the ALD- and MBE-grown STO. Overall, the results indicate that thick, crystalline STO can be grown on Si(001) substrates by ALD with minimal formation of an amorphous SiOx layer using a four-unit-cell STO buffer layer grown by MBE to serve as the surface template.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.60.Dp Adsorbed layers and thin films
81.40.Gh Other heat and thermomechanical treatments
68.55.aj Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Low-temperature (≤200 °C) plasma enhanced atomic layer deposition of dense titanium nitride thin films

Nigamananda Samal, Hui Du, Russell Luberoff, Krishna Chetry, Randhir Bubber, Alan Hayes, and Adrian Devasahayam

J. Vac. Sci. Technol. A 31, 01A137 (2013); http://dx.doi.org/10.1116/1.4769204 (8 pages)

Online Publication Date: 10 December 2012

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Titanium nitride (TiN) has been widely used in the semiconductor industry for its diffusion barrier and seed layer properties. However, it has seen limited adoption in other industries in which low temperature (<200 °C) deposition is a requirement. Examples of applications which require low temperature deposition are seed layers for magnetic materials in the data storage (DS) industry and seed and diffusion barrier layers for through-silicon-vias (TSV) in the MEMS industry. This paper describes a low temperature TiN process with appropriate electrical, chemical, and structural properties based on plasma enhanced atomic layer deposition method that is suitable for the DS and MEMS industries. It uses tetrakis-(dimethylamino)-titanium as an organometallic precursor and hydrogen (H2) as co-reactant. This process was developed in a Veeco NEXUS™ chemical vapor deposition tool. The tool uses a substrate rf-biased configuration with a grounded gas shower head. In this paper, the complimentary and self-limiting character of this process is demonstrated. The effects of key processing parameters including temperature, pulse time, and plasma power are investigated in terms of growth rate, stress, crystal morphology, chemical, electrical, and optical properties. Stoichiometric thin films with growth rates of 0.4–0.5 Å/cycle were achieved. Low electrical resistivity (<300 μΩ cm), high mass density (>4 g/cm3), low stress (<250 MPa), and >85% step coverage for aspect ratio of 10:1 were realized. Wet chemical etch data show robust chemical stability of the film. The properties of the film have been optimized to satisfy industrial viability as a Ruthenium (Ru) preseed liner in potential data storage and TSV applications.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
68.55.J- Morphology of films
52.77.Dq Plasma-based ion implantation and deposition
61.66.Bi Elemental solids
61.66.Dk Alloys
73.61.Ng Insulators

Atomic layer deposition of zinc sulfide with Zn(TMHD)2

Andrew Short, Leila Jewell, Sage Doshay, Carena Church, Trevor Keiber, Frank Bridges, Sue Carter, and Glenn Alers

J. Vac. Sci. Technol. A 31, 01A138 (2013); http://dx.doi.org/10.1116/1.4769862 (5 pages)

Online Publication Date: 10 December 2012

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The atomic layer deposition (ALD) of ZnS films with Zn(TMHD)2 and in situ generated H2S as precursors was investigated, over a temperature range of 150–375 °C. ALD behavior was confirmed by investigation of growth behavior and saturation curves. The properties of the films were studied with atomic force microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, ultraviolet–visible–infrared spectroscopy, and extended x-ray absorption fine structure. The results demonstrate a film that can penetrate a porous matrix, with a local Zn structure of bulk ZnS, and a band gap between 3.5 and 3.6 eV. The ZnS film was used as a buffer layer in nanostructured PbS quantum dot solar cell devices.
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81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
88.40.J- Types of solar cells
71.20.Nr Semiconductor compounds
78.70.Dm X-ray absorption spectra

Atomic layer deposition onto carbon fiber: From single layer deposition via multilayer structure to metal oxide microtubes

Stefan Knohl, Amit Kumar Roy, Werner A. Goedel, Steffen Schulze, and Michael Hietschold

J. Vac. Sci. Technol. A 31, 01A139 (2013); http://dx.doi.org/10.1116/1.4768917 (7 pages)

Online Publication Date: 11 December 2012

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Layers of alumina, titania and double layers of alumina/titania (and reverse) were deposited onto bundles of carbon fibers in an atomic layer deposition process. Scanning electron microscopy (SEM) images of the coated carbon fibers revealed that each fiber of a bundle was coated homogenously and separately and that no bridges were formed between the fibers. Transmission electron microscopy and SEM images showed that the coating was conformal, uniform, had a good adhesion to the fiber surface and that the morphology of the coating surface was similar to that of fiber surface. In case of double layers, the average deposition rate of coatings did not depend on the sequence of layer deposition. After coating, the carbon fibers were selectively removed by thermal oxidation in air at temperatures of 550 °C and 900 °C, leading to metal oxide microtubes.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.bt Other materials
68.35.Np Adhesion

Gallium nitride MIS-HEMT using atomic layer deposited Al2O3 as gate dielectric

Richard Lossy, Hassan Gargouri, Michael Arens, and Joachim Würfl

J. Vac. Sci. Technol. A 31, 01A140 (2013); http://dx.doi.org/10.1116/1.4771655 (5 pages) | Cited 1 time

Online Publication Date: 12 December 2012

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Metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) were fabricated with an AlGaN/GaN heterostructure. The ALD-deposited Al2O3 layer served as gate dielectric under the gate electrode and as passivation layer in the access region. Different processing routes were tested and confirm that choosing the optimum order of processing steps is required to take full advantage of MIS-HEMT capabilities. Gate leakage currents as low as 2 × 10−10 A/mm at VGS = −20 V were measured. They are 4 orders of magnitude lower compared to the Schottky reference. Also, drain leakage went down to 10−8 A/mm and thus reduced by 3½ decades compared to the Schottky-type. The corresponding on/off-ratio rates 108. The subthreshold swing improved considerably from 180 mV/dec for the Schottky type to 90 mV/dec for the MIS-HEMT. Breakdown voltage is >200 V for a gate-drain distance >4 μm. From S-parameter measurements ft = 18 GHz and fmax = 72 GHz were extrapolated.
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85.30.Tv Field effect devices
81.65.Rv Passivation

Comprehensive comparison of structural, electrical, and reliability characteristics of HfO2 gate dielectric with H2O or O3 oxidant

Yi-Lung Cheng, You-Ling Chang, Cheng-Yang Hsieh, and Jian-Run Lin

J. Vac. Sci. Technol. A 31, 01A141 (2013); http://dx.doi.org/10.1116/1.4771664 (6 pages)

Online Publication Date: 13 December 2012

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The growth, composition, electrical characteristics, and reliability performance of high-k HfO2 dielectric films that were deposited by an atomic layer deposition technique are studied. The films were grown using tetrakis(ethylmethylamino)hafnium precursor and either H2O or ozone (O3) as the oxidant. When H2O was the oxidant, the resulting HfO2 film had a thinner interfacial layer than that obtained using the O3 oxidant, but the bulk HfO2 layer was of a poorer quality. Of the annealed HfO2 films with a comparable equivalent oxide thickness, the O3 oxidant-based HfO2 films had better electrical properties and reliability. The oxide charge density, the hysteresis, the leakage current, the breakdown electrical field, and the time to dielectric breakdown of the HfO2 film that was deposited with O3 oxidant were all better those of the film that was deposited with H2O oxidant. Additionally, the dynamic stress, including unipolar and bipolar stresses, increases the times to dielectric breakdown for both HfO2 films. However, the increase under bipolar stress was greater for the HfO2 films that were grown using the H2O oxidant because more detrapping occurred.
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77.55.D- High-permittivity gate dielectric films
73.61.Ng Insulators
77.22.Jp Dielectric breakdown and space-charge effects
77.80.Dj Domain structure; hysteresis
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.at Other materials

Comparison between ZnO films grown by plasma-assisted atomic layer deposition using H2O plasma and O2 plasma as oxidant

Yumi Kawamura, Nozomu Hattori, Naomasa Miyatake, and Yukiharu Uraoka

J. Vac. Sci. Technol. A 31, 01A142 (2013); http://dx.doi.org/10.1116/1.4771666 (5 pages) | Cited 1 time

Online Publication Date: 13 December 2012

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Zinc oxide (ZnO) thin films have attracted significant attention for application in thin film transistors (TFTs) due to their specific characteristics, such as high mobility and transparency. In this paper, the authors fabricated TFTs with ZnO thin films as channel layers deposited by plasma-assisted atomic layer deposition (PAALD) at 100 °C using two different plasma sources, water (H2O-plasma) and oxygen gas (O2-plasma), as oxidants, and investigated the effects of the plasma sources on TFT performances. The TFT with ZnO channel layer deposited with H2O-plasma indicated higher performances such as a field effect mobility (μ) of 1.1 cm2/Vs. Analysis of the ZnO films revealed that the residual carbon in the film deposited with H2O-plasma was lower than that of O2-plasma. In addition, the c-axis preferred orientation was obtained in the case of the ZnO film deposited with H2O-plasma. These results suggest that it is possible to fabricate high-performance ZnO TFTs at low temperatures by PAALD with H2O-plasma.
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68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Tv Field effect devices

Interfacial chemistry of hydrofluoric acid-treated In0.53Ga0.47As(100) during atomic layer deposition of aluminum oxide

Bernal Granados-Alpizar, Fee Li Lie, and Anthony J. Muscat

J. Vac. Sci. Technol. A 31, 01A143 (2013); http://dx.doi.org/10.1116/1.4770288 (9 pages)

Online Publication Date: 19 December 2012

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Atomic layer deposition (ALD) of aluminum oxide on In0.53Ga0.47As(100) prepared with aqueous or gas phase hydrofluoric acid (HF) was followed using x-ray photoelectron spectroscopy after each pulse of trimethylaluminum (TMA, Al(CH3)3) and water at 170°C up to three cycles. On the surface prepared using aqueous HF, the primary oxide was As2O3, which was removed by the first TMA pulse depositing about two layers of AlOx and leaving residual As+1 oxide at the interface that persisted even after three complete ALD cycles. The aluminum oxide AlOx film was O deficient but was closed off, trapping the As+1 oxide at the interface. The C and O coverages were modulated by TMA and water pulses supporting the expected near 1 Å per cycle growth during the second and third ALD cycles. The larger absolute change in the C than the O coverage suggests that the reaction of TMA with O–H groups is more facile than the reaction of water with Al−CH3 moieties, explaining the less than monolayer growth per cycle intrinsic to ALD processes. On the surface prepared using gas phase HF, the fluorides and oxides of all substrate atoms were removed after one complete ALD cycle and a second TMA pulse, which also deposited about two layers of AlOx. Yet, the surface was passivated by the residual F left from the gas phase HF process and by the large increase in C deposited in the first TMA pulse. There is clear evidence for Al–F bonding, and the locations of the Al 2p peaks combined with the large peak widths indicate that the Al atoms deposited in a variety of local bonding environments. The film was not closed off by the first ALD cycle because F and C capped reaction sites, inhibiting further growth of aluminum oxide up to three ALD cycles.
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68.55.aj Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.60.Dp Adsorbed layers and thin films
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Atomic layer deposition of ZnO on Cu-nanoclusters for methanol synthesis

Ziyu Zhang, Matthew Patterson, Maoming Ren, Ying Wang, John C. Flake, Phillip T. Sprunger, and Richard L. Kurtz

J. Vac. Sci. Technol. A 31, 01A144 (2013); http://dx.doi.org/10.1116/1.4772460 (6 pages)

Online Publication Date: 19 December 2012

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The properties of ALD-grown ZnO thin films on Cu clusters supported on ZnO(10math0) have been studied with scanning tunneling and scanning electron microscopy in combination with angle-resolved x-ray photoelectron spectroscopy. Deposition at room temperature of two monolayers of Cu on ZnO(10math0) results in metallic Cu0 clusters ∼8 nm wide by 1.4 nm high. Higher coverages of 15 ML results in a similar morphology, with slightly larger cluster sizes. Following air-exposure and ALD-growth of two cycles of ZnO, the Cu exhibits Cu+ species characteristic of Cu2O and the thin ZnO coating is hydroxylated. Electrochemical studies of ALD ZnO coatings on Cu suggest that they are more active for CO2 reduction.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.45.-h Electrochemistry and electrophoresis
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.ag Semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Atomic layer deposition of cobalt oxide thin films using cyclopentadienylcobalt dicarbonyl and ozone at low temperatures

Byeol Han, Kyu Ha Choi, Jae Min Park, Jung Woo Park, Jongwan Jung, and Won-Jun Lee

J. Vac. Sci. Technol. A 31, 01A145 (2013); http://dx.doi.org/10.1116/1.4772461 (4 pages)

Online Publication Date: 19 December 2012

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The authors report the atomic layer deposition (ALD) of cobalt oxide thin films at 50–150 °C using alternating exposures to cyclopentadienylcobalt dicarbony [CpCo(CO)2] and ozone. The growth rates were 0.08–0.11 nm/cycle and the ALD cobalt oxide films showed excellent step coverage. With increasing substrate temperature to 200 °C, however, the growth rate sharply increased and cobalt-rich film was deposited owing to thermal decomposition of the cobalt precursor. The reaction of the cobalt precursor molecule with the growing film surface was investigated by in situ quartz crystal microbalance (QCM), and the QCM result also indicates that CpCo(CO)2 thermally decomposes to cobalt on the growth surface at 200 °C.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Electrical conductivity and photoresistance of atomic layer deposited Al-doped ZnO films

Rajeh M. Mundle, Hampton S. Terry, Kevin Santiago, Dante Shaw, Messaoud Bahoura, Aswini K. Pradhan, Kiran Dasari, and Ratnakar Palai