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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 5 • Date Sep 2011

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Displaying Results 1 - 25 of 29
  • Hydrogen effects in hydrofluorocarbon plasma etching of silicon nitride: Beam study with CF+, CF2+, CHF2+, and CH2F+ ions

    Page(s): 050601 - 050601-4
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    Hydrogen in hydrofluorocarbon plasmas plays an important role in silicon nitride (Si3N4) reactive ion etching. This study focuses on the elementary reactions of energetic CHF2+ and CH2F+ ions with Si3N4 surfaces. In the experiments, Si3N4 surfaces were irradiated by monoenergetic (500–1500 eV) beams of CHF2+ and CH2F+ ions as well as hydrogen-free CF2+ and CF+ ions generated by a mass-selected ion beam system and their etching yields and surface properties were examined. It has been found that, when etching takes place, the etching rates of Si3N4 by hydrofluorocarbon ions, i.e., CHF2+ and CH2F+, are higher than those by the corresponding fluorocarbon ions, i.e., CF2+ and CF+, respectively. When carbon film deposition takes place, it has been found that hydrogen of incident hydrofluorocarbon ions tends to scavenge fluorine of the deposited film, reducing its fluorine content. View full abstract»

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  • Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges

    Page(s): 050801 - 050801-26
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    Plasma-assisted atomic layer deposition (ALD) is an energy-enhanced method for the synthesis of ultra-thin films with Å-level resolution in which a plasma is employed during one step of the cyclic deposition process. The use of plasma species as reactants allows for more freedom in processing conditions and for a wider range of material properties compared with the conventional thermally-driven ALD method. Due to the continuous miniaturization in the microelectronics industry and the increasing relevance of ultra-thin films in many other applications, the deposition method has rapidly gained popularity in recent years, as is apparent from the increased number of articles published on the topic and plasma-assisted ALD reactors installed. To address the main differences between plasma-assisted ALD and thermal ALD, some basic aspects related to processing plasmas are presented in this review article. The plasma species and their role in the surface chemistry are addressed and different equipment configurations, including radical-enhanced ALD, direct plasma ALD, and remote plasma ALD, are described. The benefits and challenges provided by the use of a plasma step are presented and it is shown that the use of a plasma leads to a wider choice in material properties, substrate temperature, choice of precursors, and processing conditions, but that the processing can also be compromised by reduced film conformality and plasma damage. Finally, several reported emerging applications of plasma-assisted ALD are reviewed. It is expected that the merits offered by plasma-assisted ALD will further increase the interest of equipment manufacturers for developing industrial-scale deposition configurations such that the method will find its use in several manufacturing applications. View full abstract»

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  • Kelvin probe force microscopy-based characterization techniques applied for electrostatic MEMS/NEMS devices and bare dielectric films to investigate the dielectric and substrate charging phenomena

    Page(s): 051101 - 051101-17
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    In this study, two different characterization techniques based on Kelvin probe force microscopy (KPFM) have been used to investigate the dielectric and substrate charging in electrostatic micro- and nano-electromechanical systems (MEMS and NEMS). The first technique (KPFM-MEMS) has been employed to study the discharging process on a microscopic scale in a charged MEMS dielectric film. This has been performed by monitoring the surface potential decay with time of charged PECVD silicon nitride films implemented in electrostatic capacitive MEMS switches. The second methodology, KPFM-thin films (KPFM-TF), has been applied to investigate the charging/discharging processes in bare SiNx films as well as the substrate charging phenomenon. It makes use of the atomic force microscope tip to simulate charge injection through a single asperity, and then measure the induced surface potential. The influence of the SiNx film thickness and deposition conditions has been studied. Moreover, the impact of bias amplitude and bias polarity applied during charge injection has been explored. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy material characterization techniques have been used to determine the chemical bonds and compositions, respectively, of the SiNx films being investigated. The nanoscale KPFM results obtained in this study reveal an accurate understanding of both the dielectric charging and the substrate charging that take place in electrostatic MEMS/NEMS devices. View full abstract»

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  • Incorporation of hydrogen in CuInSe2: Improvements of the structure

    Page(s): 051201 - 051201-5
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    CuInSe2 single crystals were ion implanted with a dose of 3 × 1016 cm-2 by 2.5 keV H+ at 150 and 250 °C. Before and after the implantation the crystals were analyzed by Rutherford backscattering/channeling (RBS/C) along the <112> axis using 2 MeV He+. The RBS/C spectra indicate that the implantation at 150 °C introduces a layer of radiation damage, whereas after the implantation at 250 °C no structural deterioration of the lattice can be seen. Quite the contrary, the RBS/C spectra reveal a considerable decrease in the dechanneling parameters suggesting improvements in the lattice structural quality attributed to the incorporation of hydrogen. View full abstract»

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  • Photovoltaic characteristics of a-Si/β-FeSi2/c-Si double heterojunction fabricated by magnetron sputtering

    Page(s): 051202 - 051202-4
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    A novel β-FeSi2 solar cell with amorphous-Si/β-FeSi2/crystalline-Si (a-Si/β-FeSi2/c-Si) double heterojunction structure was investigated. The c-Si (100) wafers were used as substrate materials. Polycrystalline β-FeSi2 thin film and a-Si thin film were grown by magnetron sputtering. In dark condition, the a-Si/β-FeSi2/c-Si heterojunction showed a better rectifying property than that of the β-FeSi2/crystalline-Si (β-FeSi2/c-Si) heterojunction. Under air mass 1.5 illumination, the measured conversion efficiency of a-Si/β-FeSi2/c-Si heterojunction increased by 59.7% compared with that of β-FeSi2/c-Si heterojunction. The effective enhancement of photovoltaic performance was ascribed to the extended built-in electric field distribution and the increased built-in potential. These results illustrated an attractive way to improve the conversion efficiency of β-FeSi2 solar cells by using the double heterojunction. View full abstract»

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  • Imaging and phase identification of Cu2ZnSnS4 thin films using confocal Raman spectroscopy

    Page(s): 051203 - 051203-11
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    Copper zinc tin sulfide (Cu2ZnSnS4 or CZTS) is a potential candidate for next generation thin film solar cells because it contains abundant and nontoxic elements and exhibits high light absorption. Thin films of CZTS are typically synthesized by sulfidizing a stack of zinc, copper, and tin films. In addition to CZTS, a variety of binary and ternary metal sulfides can form and distinguishing among phases with similar crystal structure can be difficult. Herein, the authors show that confocal Raman spectroscopy and imaging can distinguish between CZTS and the other binary and ternary sulfides. Specifically, Raman spectroscopy was used to detect and distinguish between CZTS (338 cm-1), Cu2SnS3 (298 cm-1), and Cu4SnS4 (318 cm-1) phases through their characteristic scattering peaks. Confocal Raman spectroscopy was then used to image the distribution of coexisting phases and is demonstrated to be a useful tool for examining the heterogeneity of CZTS films. The authors show that, during sulfidation of a zinc/copper/tin film stack, ternary sulfides of copper and tin, such as Cu2SnS3 form first and are then converted to CZTS. The reason for formation of Cu2SnS3 as an intermediary to CZTS is the strong tendency of copper and tin to form intermetallic alloys upon evaporation. These alloys sulfidize and form copper tin sulfides first, and then eventually convert to CZTS in the presence of zinc. As a consequence, films sulfidized for 8 h at 400 °C contain both CZTS and Cu2SnS3, whereas films sulfidized at 500 °C contain nearly phase-pure CZTS. In addition, using Cu Kα radiation, the authors identify three CZTS X-ray diffraction peaks at 37.1° [(202)], 38° [(211)], and 44.9° [(105) and (213)], which are absent in ZnS and very weak in Cu2SnS3. View full abstract»

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  • Effects of temperature and near-substrate plasma density on the structural and electrical properties of dc sputtered germanium thin films

    Page(s): 051301 - 051301-13
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    Germanium thin films were deposited by dc reactive magnetron sputtering as a function of substrate temperature and ion flux using an unbalanced magnetron with an external magnetic field. The ion flux and energy distribution were measured using a retarding field energy analyzer (RFEA), a flat probe with a guard ring, and cylindrical Langmuir probes. The RFEA ion flux, the flat probe saturation currents, and the ion densities inferred from the cylindrical probe data are in very good agreement over a wide range of plasma densities, which were varied both by the external coil current and discharge power. The RFEA ion energy distributions are in good agreement with the plasma potentials inferred from the cylindrical probes, and suggest that the nonuniformity of the plasma in the vicinity of the substrate holder should be considered in the interpretation of probe results in these systems. The deposited films were characterized by x-ray diffraction, Raman spectroscopy, optical transmission, resistivity, and Hall effect measurements. Under low ion bombardment conditions, an abrupt onset of the crystalline phase with respect to temperature is observed in the Raman and x-ray diffraction measurements, and the crystal quality increases with increasing temperature above the transition temperature. The transition is also accompanied by a sharp decrease in film resistivity. The microcrystalline films have a strong preferential orientation in the (220) direction, and are p type with carrier densities in the range 1018 cm-3 and mobilities in the range 15–30 cm2/V-s. The structural and electronic properties of the films are sensitive to the ion flux. Near the transition temperature the effects of increasing ion flux can be attributed to the small temperature rise that accompanies the higher plasma density. At higher temperatures the increased ion flux results in a more random crystallographic orientation, with significantly lower carrier conce- - ntrations and only slightly lower carrier mobilities, implying either a reduction in acceptor defect density and/or the creation of compensating n-type defects. View full abstract»

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  • Inductively coupled plasma etching of graded-refractive-index layers of TiO2 and SiO2 using an ITO hard mask

    Page(s): 051302 - 051302-6
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    Transparent dielectric layers with varying compositions of TiO2 and SiO2, and ITO are deposited on sapphire and Si substrates by using an RF sputter system. Inductively coupled plasma (ICP) reactive ion etching (RIE) of the ITO hard mask is examined under H2, CH4, and Cl2 chemical environments. The slope of the sidewall and the etch residue on the sidewall of the ITO hard mask are controlled by the flow rates of H2, CH4, and Cl2. ICP-RIE dry etch of TiO2 and SiO2 is investigated under fluorinated environments. Comparable etch rates of TiO2 and SiO2 (ratio ≈ 2:1) and high selectivity ≫ 1 over ITO are found. Graded-refractive-index (GRIN) layers, made up of multiple dielectric layers of TiO2 and SiO2, are patterned to form cylindrical pillars by ICP etching using the ITO hard mask. Fluorine containing residues are identified on the TiO2 and SiO2 surfaces. Various etch chemistries are investigated to obtain smooth, vertical, and residue-free sidewalls of the GRIN pillars. View full abstract»

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  • Formation of tetragonal or monoclinic ZrO2 coatings by oxygen plasma treatment of Zr74.7Cu19.7Nb5.6 glassy thin films

    Page(s): 051303 - 051303-6
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    The authors report on the production of stable nanostructured tetragonal and/or monoclinic ZrO2 nanopillars achieved by means of oxygen plasma treatment of ternary Zr74.7Cu19.7Nb5.6 glassy films. The Zr-based metallic glass thin films were successfully deposited by magnetron sputtering and subsequently subjected to oxygen plasma for various exposure times. The compositions of the oxidized films were determined by Auger electron spectroscopy and X-Ray photoelectron spectroscopy depth profiling while the surface morphology was evaluated by means of atomic force microscopy and scanning electron microscopy. X-Ray diffraction was used for the structural analysis. Our results show that, depending on the length of time of oxygen plasma treatment, tetragonal and/or monoclinic ZrO2 films can be formed, the surface morphology of which exhibit nanopillar structures with an increased effective surface. These findings provide an easy and efficient way for growing ZrO2 coatings with a predefined structure suitable for protective and possibly for catalytic applications. View full abstract»

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  • Modelling of fluorine based high density plasma for the etching of silica glasses

    Page(s): 051304 - 051304-9
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    An etching simulator has been developed to study the etching of commercial silica glass (Pyrex®, D263®, AF45®, and Vycor®) in a SF6/Ar inductively coupled plasma (ICP) discharge. The etching model is based on the development of the plasma kinetic model coupled to a two dimensional (2D) Monte Carlo cellular surface model to predict the etched surface morphology as a function of the operating conditions. The SF6/Ar plasma model allows us to predict the neutral and ion species fluxes, as well as the density and the temperature of electrons, as a function of the reactor operating conditions. Such output parameters are used as input parameters in both the sheath and etching models. The 2D Monte Carlo cellular model is based on the representation of both the substrate and the mask by uniform cells, which each represents a real number of sites. The preferential redeposition mechanism of the etched products on the metallic sites seems to play an important role on the formation and the propagation of the etched surface roughness. The results obtained by the model are compared with the experimental results for etching rate and roughness. A satisfactory agreement between the experimental results and the model concerning the etching rate and the etched surface morphology has been obtained for different glasses. View full abstract»

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  • Mechanisms for sealing of porous low-k SiOCH by combined He and NH3 plasma treatment

    Page(s): 051305 - 051305-8
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    Porous dielectric materials, such as SiOCH, are used as the insulator in interconnect wiring in microelectronics devices to lower the dielectric constant and so decrease the RC time delay. Sealing of the pores (up to a few nm in diameter) is necessary to prevent degradation of the low-k properties during subsequent processing steps by diffusion of reactants through the pores into the material. Sequential treatment of porous SiOCH by He and NH3 plasmas is potentially a means of sealing pores while maintaining the low-k of the dielectric. The He plasma activates surface sites to accelerate the reactions responsible for pore sealing. NH3 plasma treatment completes the sealing through one of two mechanisms resulting from the adsorption of NHx radicals — catalyzing the formation of a densified surface layer or formation of Si-N, C-N and N-N bonds to bridge over the pore. In this paper, we discuss mechanisms for pore sealing bridging bonds based on results from an integrated computational investigation of the etching, cleaning, activation and sealing of porous SiOCH in sequential Ar/C4F8/O2, Ar/O2, He and Ar/NH3 plasmas. The authors found that pores in excess of 1 nm in radius are difficult to seal due to the inability of N-bonding to bridge the pore opening. Factors affecting the sealing efficiency, such as treatment time, average pore radius and aspect ratio are discussed. View full abstract»

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  • Modeling of implantation and mixing damage during etching of SiO2 over Si in fluorocarbon plasmas

    Page(s): 051306 - 051306-12
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    Energetic ion bombardment during plasma etching of microelectronics devices is necessary to activate chemical process and define features through the ions’ anisotropic trajectories. These energetic fluxes can also cause damage and mixing of the constituents of crystalline lattices. These properties are likely best modeled using molecular dynamics (MD) simulations. The computational expense of these techniques makes feature scale simulations difficult, and so motivates development of approximate methods that can be used to model full features. In this regard, an implantation and mixing model has been developed and implemented into a Monte Carlo feature profile model to simulate the mixing and damage to the underlying Si during high aspect ratio (HAR) etching of SiO2 trenches. Fluxes to the surface were provided by a reactor scale model. The feature scale model was validated by comparison to the mixing produced by Ar+ bombardment of Si with and without F and CF fluxes as predicted by MD simulations. Scaling of mixing damage of underlying Si during HAR of SiO2 etching in Ar/C4F8/O2 plasmas for rf bias powers of 1–4 kW was investigated. The authors found that mixing damage at the bottom of HAR features, though increasing in magnitude with increasing ion energy, does not scale as dramatically as on flat surfaces. This is due to the reflection of ions off of sidewalls which moderate the ion energies. View full abstract»

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  • Size control of nanopores formed on SiO2 glass by swift-heavy-ion irradiation and its application to highly sensitive biomolecular detection

    Page(s): 051402 - 051402-6
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    Swift-heavy-ion irradiation creates latent tracks in SiO2 glass and nanopores with a high aspect ratio can be formed along these ion paths by selective etching of the latent tracks using hydrogen fluoride (HF) vapor. Here we report that the size of nanopores can easily be controlled by simply changing the temperature of the HF solution generating the vapor and/or that of the SiO2 glass exposed to the vapor. Furthermore, this method of size control was used to produce SiO2 glass sheets with nanopores of different sizes and number densities for use as the waveguide layer in the sensing plates for a waveguide-mode sensor. In comparison with nonperforated plates, the increased surface area due to the formation of nanopores was found to create up to a tenfold increase in sensitivity. View full abstract»

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  • Anisotropic etching induced by surface energy driven agglomeration

    Page(s): 051403 - 051403-5
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    The authors report on a previously unobserved anisotropic etching method in which a eutectic droplet created by heating a multilayer Au/Ge film is driven to form negative pits on the crystalline semiconductor surface. The etching process involves surface diffusion, evaporation, and pit formation. The shape of the pit is controlled by the underlying substrate symmetry. The surface morphology, crystal structure, and interfacial composition of the substrate (Si and Ge) were studied as a function of the thickness of the Au and Ge bilayer using scanning electron microscopy. The placement and size of the negative pits can be controlled by prepatterning the film. View full abstract»

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  • Optimized growth of Ge nanorod arrays on Si patterns

    Page(s): 051501 - 051501-5
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    Self-assembly of polystyrene nanospheres and reactive ion etching have been used to seed Si substrates on which Ge nanorods could be grown by glancing angle deposition (GLAD). This method enables production of large area planar-closed-packed arrays of Ge-GLAD nanostructures on Si seed patterns. A strong column competition on a broad seed width (ws) and a narrow interseed separation distance (Rs) causes the growth of closely bunched multiple structures on the Si seeds. Nanorod growth optimization is realized through the systematic variation of Si seed widths (ws) and the interseed separation distance (Rs), which enable the growth of singular nanorods on each Si seed. View full abstract»

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  • Ultrathin TiSiN overcoat protection layer for magnetic media

    Page(s): 051502 - 051502-11
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    TiSiN ultrathin films (10–50 Å) deposited by reactive magnetron sputtering from TixSiy targets were used as anticorrosion overcoats to protect Co-containing recording media. Films’ growth, structure, composition, resistance against hydrolysis, and anticorrosion performances were studied by spectroscopy (x-ray reflectivity and diffraction, ellipsometry, x-ray photoelectron spectroscopy, Fourier transform infrared reflection–absorption spectroscopy) and simulated by molecular dynamics (using modified Tersoff-type interatomic interactions). TiSiN ultrathin overcoats were found to be dense amorphous oxynitrides containing Ti–O–Si linkages. The conversion of SiNx into SiOx by hydrolysis was prevented by introducing less than 20 at. % of Ti in the films. Thanks to the formation of Ti–O–Si linkages which densify the films and reduce oxygen diffusion, good corrosion protection of the magnetic media was achieved down to 28 Å TiSiN overcoat thickness. View full abstract»

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  • Pulsed chemical vapor deposition of Cu2S into a porous TiO2 matrix

    Page(s): 051505 - 051505-5
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    Chalcocite (Cu2S) has been deposited via pulsed chemical vapor deposition (PCVD) into a porous TiO2 matrix using hydrogen sulfide and a metal-organic precursor. The precursor used is similar to the more common Cu(hfac)(tmvs) precursor, but it is fluorine free and exhibits increased thermal stability. The simultaneous exposure of the substrate to the copper precursor and hydrogen sulfide resulted in nonuniform Cu2S films with a temperature independent deposition rate implying gas phase reaction kinetics. The exposure of mesoporous TiO2 and planar ZnO to alternating cycles of the copper precursor and hydrogen sulfide resulted in a PCVD film that penetrated fully into the porous TiO2 layer with a constant deposition rate of 0.08 nm/cycle over a temperature range of 150–400 °C. The chalcocite (Cu2S) stoichiometry was confirmed with extended x-ray absorption fine structure measurements (EXAFS) and x-ray photoelectron spectroscopy. Calculations of the EXAFS spectrum for different CuxS phases show that EXAFS is sensitive to the different phase stoichiometries. Optical absorption measurements of CVD thin films using photothermal deflection spectroscopy show the presence of a metallic copper-poor phase for gas phase nucleated films less than 100 nm thick and a copper-rich semiconducting phase for thicknesses greater than 100 nm with a direct band gap of 1.8 eV and an indirect bandgap of 1.2 eV. View full abstract»

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  • Effect of substrate temperature on the properties of transparent conductive ZnO:Al thin films prepared by RF sputtering

    Page(s): 051506 - 051506-4
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    Transparent conductive ZnO:Al thin films were successfully deposited on glass substrates via radio frequency sputtering with a ceramic target in ambient argon. X-ray diffraction, profilometry, Hall-effect measurement, and spectrophotometry were employed to investigate the structural, electrical, and optical properties of films. The electrical and optical properties were found to be strongly dependent on the crystalline quality, grain size, and thickness of the films. X-ray diffraction spectra indicated that the crystalline quality of the films improved and grains became larger with increasing substrate temperature. Transmission spectra revealed that films possessed a higher transmittance in the visible range with an increase of the substrate temperature, but the band gap did not broaden obviously. Films with a resistivity of about 2.66 × 10-4 Ω cm and an average transmittance above 90% in the visible range were obtained at the optimum temperature of 450 °C. View full abstract»

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  • Dependence of film texture on substrate and growth conditions for CdTe films deposited by close-spaced sublimation

    Page(s): 051507 - 051507-6
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    The texture of CdTe films deposited via close-spaced sublimation (CSS) was studied. Different substrates were used, including Si(100), fluorine-doped SnO2 (FTO), and CdS, and different growth conditions were applied. The texture behaviors of each sample were evaluated based on its XRD spectrum and are found to be dependent on both the substrate and the growth conditions. The texture strength is found to be, in order, Si(100) > FTO > CdS at a substrate temperature of 763 K under 100 Pa Ar, which is the opposite of the order of the surface roughness of the substrates. The textures of the films on FTO and chemical bath deposition (CBD)-CdS substrates, especially on CBD-CdS, are very sensitive to the growth conditions, whereas those on Si(100) are not. It is found that the texture is strengthened at elevated temperatures and suppressed under decreased ambient pressure. It is also found that the textured films are composed of both (111) and (511) texture components, which is believed to be the result of the twinning in (111) oriented grains. View full abstract»

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  • Silicon nanoparticle synthesis by short-period thermal anneals at atmospheric pressure in argon

    Page(s): 051508 - 051508-6
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    Silicon nanoparticles have been studied for a wide variety of applications including nanoelectronic, photovoltaic, and optoelectronic devices. In this work, silicon nanoparticles were synthesized by short-period annealing of silicon-on-insulator substrates to temperatures ranging between 600 and 900 °C in argon gas at atmospheric pressure. Two different top silicon layers were deposited by ion-beam sputtering onto oxidized substrates. The thinner 6 nm top layer samples were annealed to temperatures for 30 s periods while thicker 15 nm top layer samples were annealed for 60 s periods. For both sets of samples, nanoparticles were observed to form at all the anneal temperatures through imaging by AFM. One long-period UHV anneal study, with 30-min anneal times, observed nanoparticle formation at temperatures similar to the current work while another similar long-period UHV anneal reported nanoparticle formation only above well-defined formation temperatures that depended upon the starting top layer thickness. In the current work, the average nanoparticle radius was found to increase both with the final anneal temperature and anneal period. For the highest anneal temperatures of the 6 nm top layer samples, a changing surface topography indicated that the thinner Si source layer was becoming depleted and the nanoparticle formation process was nearing completion. No such changes were observed for the thicker 15 nm samples at the same temperatures. View full abstract»

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  • Impact of parasitic reactions on wafer-scale uniformity in water-based and ozone-based atomic layer deposition

    Page(s): 051509 - 051509-8
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    The exceptional thickness control and conformality of atomic layer deposition (ALD) has made it the process of choice for numerous applications from microelectronics to nanotechnology. Its benefits derive from the self-limiting character of surface chemical processes (adsorption and chemical reaction) that occur upon saturation of the active sites present on the surface. However, identifying a suitable process window in which ALD benefits are realized at the wafer scale can be a challenge, even in favorable cases. The authors explore here the prototypical case of ALD Al2O3 obtained from trimethyl aluminum (TMA), using a cross-flow ALD reactor design chosen to highlight deviations from expectations for true ALD behavior. Cross-wafer uniformity at the wafer scale (100 mm diameter) is investigated for both water and ozone used as oxidants, as a function of precursor dose and nitrogen purge conditions outside as well as inside the parameter space where ALD’s process benefits are realized. While nonuniformities lower than 1% were achievable for both oxidants, the ozone-based process offers significant benefits over the water-based process, namely, a broader process window and 3 × lower TMA dosages. The growth per cycle and uniformity are essentially unchanged with overexposures of either TMA or ozone. However, for overdosing of water growth rates are considerably higher than the nominal 0.95 Å/cycle and as well as degraded uniformity are observed. While underdosing of all precursor results in depletion of film growth in the flow direction across the wafer surface, these nonuniformities are more dramatic for water than ozone. These observations suggest the use of water as oxidant, if in excess dose condition, can introduce parasitic reactions in addition to the fundamental half-reactions for ALD Al2O3. Such reactions, e.g., associated with excess hydrogen-bonded water, lead to enhanced growth - - rates and degradation of uniformity. View full abstract»

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  • Polymer wires with quantum dots grown by molecular layer deposition of three source molecules for sensitized photovoltaics

    Page(s): 051510 - 051510-6
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    Molecular layer deposition (MLD) can be used to grow organic tailored materials, where different molecules are sequentially connected in designated arrangements. Using MLD, polymer wires containing quantum dots (QDs) of lengths ∼0.8, ∼2, and ∼3 nm were grown by connecting three source molecules in monomolecular steps. The peak energy of the QD absorption shifted to higher energy with decreasing QD length, due to the quantum confinement effect. Consequently, the polymer wires exhibited a widening of their absorption spectra from ∼480 to ∼300 nm. This was attributed to the superposition of individual absorption bands of different QDs. A sensitization model for ZnO in photovoltaic devices is proposed, in which polymer wires with QDs as the sensitizing layer reduce the heat energy loss during absorption. View full abstract»

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  • Growth temperature control of the epitaxy, magnetism, and transport in SrTiO3(001)/La0.5Sr0.5CoO3 thin films

    Page(s): 051511 - 051511-9
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    The authors report a detailed study of the influence of deposition temperature on the microstructure, phase purity, nanoscale chemical homogeneity, stoichiometry, and magnetic and electronic properties of epitaxial La0.5Sr0.5CoO3 thin films grown on SrTiO3(001) substrates via reactive dc magnetron sputtering. The results are interpreted in terms of the temperature-dependent interplay between crystallization, strain relaxation, and cation mobility (which improve with increasing deposition temperature), and oxygenation (which deteriorates at the highest deposition temperatures). In addition to the established approach to epitaxial sputter deposition based on high temperature deposition combined with subsequent ex situ annealing in O2, our results also identify a narrow deposition temperature window ∼600–625 °C, where single phase, highly crystalline, low surface roughness epitaxial films can be obtained with close to ideal stoichiometry without postdeposition annealing. Electronic and magnetic properties similar to bulk single crystals can be obtained in this region. View full abstract»

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  • Phase, grain structure, stress, and resistivity of sputter-deposited tungsten films

    Page(s): 051512 - 051512-8
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    Sputter-deposited W films with nominal thicknesses between 5 and 180 nm were prepared by varying the base pressure prior to film deposition and by including or not including sputtered SiO2 encapsulation layers. X-ray and electron diffraction studies showed that single phase, polycrystalline α-W could be achieved in as-deposited films as thin as 5 nm. The stress state in the as-deposited films was found to be inhomogeneous. Annealing resulted in stress relaxation and reduction of resistivity for all films, except the thinnest, unencapsulated film, which agglomerated. In-plane film grain sizes measured for a subset of the annealed films with thicknesses between 5 and 180 nm surprisingly showed a near constant value (101–116 nm), independent of film thickness. Thick-film (≥120 nm) resistivity values as low as 8.6 μΩ cm at 301 K were obtained after annealing at 850 °C for 2 h. Film resistivities were found to increase with decreasing film thicknesses below 120 nm, even for films which are fully A2 α-W with no metastable, A15 β-W evident. View full abstract»

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  • Vibrational spectroscopy of low-k/ultra-low-k dielectric materials on patterned wafers

    Page(s): 051513 - 051513-6
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    Comparing with much valuable research on vibrational spectroscopy on low-k dielectrics in different substrates, this paper investigates the vibrational spectroscopy of low-k and ultra-low-k dielectric materials on patterned wafers. It is found that both Raman and FTIR spectroscopy are necessary as complement to characterize low-k and ultra-low-k dielectric materials on patterned wafers. Significant differences in the Raman and FTIR spectra between low-k and ultra-low-k dielectric materials are also observed. Moreover, Raman spectroscopy has an advantage in analyzing the mixed structure of low-k/ultra-low-k and Cu at nanometer-scaled sizes. The results in this paper show that Raman combined with FTIR spectroscopy is an effective tool to characterize dielectric thin film properties on patterned wafers. View full abstract»

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The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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G. Lucovsky
North Carolina State University