Showing papers in "Journal of Vacuum Science and Technology in 2008"

Survey on measurement of tangential momentum accommodation coefficient

Abstract: The value of tangential momentum accommodation coefficient (TMAC) is required while prescribing the boundary condition for flow of gases in the slip and transition flow regimes. The precise determination of its value is important for several other applications as well. This article reviews the experimental techniques employed by researchers over the decades to measure this coefficient and the values reported in the literature, with relevance to calculation of the slip velocity. The review shows that the value of TMAC is dependent on a number of parameters including nature of the gas, pressure of the gas, material of the surface, surface cleanliness and roughness, and surface temperature. For monatomic gases, the TMAC at about 0.93 is almost constant with respect to the Knudsen number, and this value can be employed for most commonly available surface materials. However, for nonmonatomic gases, TMAC decreases with an increase in Knudsen number; a correlation of TMAC with Knudsen number for this class of ga...

Main determinants for III–V metal-oxide-semiconductor field-effect transistors (invited)

Abstract: Lacking a suitable gate insulator, practical GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) have remained all but a dream for more than four decades. The physics and chemistry of III–V compound semiconductor surfaces or interfaces are problems so complex that our understanding is still limited even after enormous research efforts. Most research is focused on surface pretreatments, oxide formation, and dielectric materials; less attention is paid to the III–V substrate itself. The purpose of this article is to show that device physics more related to III–V substrates is as important as surface chemistry for realizing high-performance III–V MOSFETs. The history and present status of III–V MOSFET research are briefly reviewed. A model based on the charge neutrality level is proposed to explain all experimental work he performed on III–V MOSFETs using ex situ atomic-layer-deposited high-k dielectrics. This model can also explain all reported experimental observations on III–V MOSFETs using ...

Atomic layer deposition of tin oxide films using tetrakis(dimethylamino) tin

Abstract: The authors present a new method for preparing thin films of SnO2 by atomic layer deposition (ALD) using alternating exposures to tetrakis(dimethylamino) tin and hydrogen peroxide. This method avoids problems of corrosion and agglomeration associated with the halogenated compound, SnCl4. Tin oxide films were successfully deposited on a variety of substrates using deposition temperatures of 50–300°C at an average growth rate of 1.2A∕cycle. They use in situ quartz crystal microbalance and quadrupole mass spectrometry measurements to explore the mechanism for SnO2 ALD. Scanning electron microscopy of SnO2 films deposited on Si(100) show that the SnO2 films are smooth, conformal, and nearly featureless, while atomic force microscopy yields a surface roughness of only 0.84nm for a film with a thickness of 92nm. X-ray diffraction reveals that the SnO2 films are amorphous. Films deposited on glass yielded a resistivity of ∼0.3Ωcm and an optical transmission of 94% for a film thickness of 140nm. X-ray photoelectr...

Exotic shapes of gold nanoparticles synthesized using plasma in aqueous solution

Abstract: Gold nanoparticles with exotic shapes, such as triangle, pentagon, and hexagon, have been synthesized by glow discharge in aqueous solutions. A pulsed power supply was used to generate discharges in the aqueous solutions. Pulse width and frequency were 2 μs and 15 kHz, respectively. Discharges were generated at applied voltages of 1600 and 3200 V. The shapes of the gold nanoparticles and electron diffraction patterns were observed by transmission electron microscopy. The nanoparticles obtained were about 20 nm in diameter. In particular, at the higher voltage of 3200 V, nanoparticles with anisotropic shapes were synthesized. In the initial stages of synthesis, diameter decreased with discharge time as the nanoparticles redissolved in the solution. After discharge for 25 min, nanoparticles with anisotropic shapes appeared. This discharge led to the generation of H2O2 and a decrease in pH as a result of the consumption of OH radicals during the generation of H2O2 and electron donation of H radicals to the s...

Rarefied gas flow through short tubes into vacuum

Abstract: A rarefied gas flow into vacuum through a tube of finite length is investigated over the whole range of gas rarefaction by the direct simulation Monte Carlo method. The nonequilibrium effects at the inlet and outlet of the tube have been considered by including in the computational domain large volumes of the upstream and downstream reservoirs. Results for the dimensionless flow rate and for the flow field are presented for a wide range of the gas rarefaction and for various values of the length to radius ratio in the range from 0 to 10. The influence of the gas-surface interaction model, as well as the effect of the intermolecular potential model on the gas flow, is examined. A good agreement has been obtained between the present numerical results and the corresponding experimental ones available in the literature.

Role of hydrogen bonding environment in a-Si:H films for c-Si surface passivation

Abstract: The search for an ideal surface passivation layer of crystalline silicon (c-Si) to be employed in a silicon heterojunction photovoltaic device has garnered much attention. The leading candidate is a few nanometers of intrinsic amorphous silicon ((i)a-Si:H) film. Reported dependencies of film surface passivation quality on substrate preparation, orientation, and deposition temperature have been extended in this work to include H2 to SiH4 dilution ratio and postdeposition annealing. Simple avoidance of the deposition regimes that lead to epitaxial growth of Si on the c-Si substrate produces decent lifetimes on the order of 500μs. Subsequent low temperature annealings cause an important restructuring of Si–H bonding at the a-Si:H∕c-Si interface increasing the amount of monohydride at the c-Si surface. This restructuring would reduce the c-Si surface defect density and cause an improvement of surface passivation as confirmed by effective lifetime measurements. Final effective carrier lifetimes up to 2550μs ar...

Growth and characterization of vanadium dioxide thin films prepared by reactive-biased target ion beam deposition

Abstract: Using a novel growth technique called reactive bias target ion beam deposition, the authors have prepared highly oriented VO2 thin films on Al2O3 (0001) substrates at various growth temperatures ranging from 250to550°C. The influence of the growth parameters on the microstructure and transport properties of VO2 thin films was systematically investigated. A change in electrical conductivity of 103 was measured at 341K associated with the well known metal-insulator transition (MIT). It was observed that the MIT temperature can be tuned to higher temperatures by mixing VO2 and other vanadium oxide phases. In addition, a current/electric-field induced MIT was observed at room temperature with a drop in electrical conductivity by a factor of 8. The current densities required to induce the MIT in VO2 are about 3×104A∕cm2. The switching time of the MIT, as measured by voltage pulsed measurements, was determined to be no more than 10ns.

Surface patterns from block copolymer self-assembly

Abstract: It is widely recognized that further extension of optical lithography to even smaller dimensions will be accompanied by rapid increasing cost and difficulty. There is growing interest in devising alternative patterning methods that will support the evolution of microelectronics to the 10nm length scale. Block copolymer lithography, which uses self-assembled microdomains of block copolymers in thin films, can provide arrays of periodic patterns of 10–50nm length scales with a simple process and low cost. While this capability is attractive, the periodic nature of the microdomain patterns places significant restrictions on how block copolymer lithography can be practically implemented. In this review, the authors survey materials and methods for carrying out the controlled assembly of block copolymers in thin films for surface patterning applications. After a brief introduction to block copolymers and their phase behavior, the authors discuss ordering of block copolymer in thin films based on four different...

Plasma-assisted molecular beam epitaxy and characterization of SnO2 (101) on r-plane sapphire

Abstract: Plasma-assisted molecular beam epitaxy has been shown to be a viable and practical method for producing high quality tin oxide, SnO2. Phase-pure epitaxial single crystalline SnO2 (101) thin films of 1μm in thickness were reproducibly grown on r-plane sapphire Al2O3 (101¯2) substrates. The SnO2 epitaxy progressed in the Volmer–Weber growth mode. A minimum on-axis ω-scan full width at half maximum of 0.22° for the SnO2 (101) peak was measured indicating relatively low film mosaic. An epitaxial relationship of [010]SnO2∥[1¯21¯0]sapphire and [1¯01]SnO2∥[1¯011]sapphire was determined between the film and substrate. A SnO2 film tilt of 1.3° around the [010]SnO2 toward [0001]sapphire was measured. A dislocation density of 8×109cm−2 was measured. Hall effect measurements quantified an unintentionally doped electron concentration for different samples in a range (0.3–3.0)×1017cm−3 with a corresponding electron mobility range of 20–100cm2∕Vs. The SnO2 growth behavior was determined to be in one of the two distinct ...

Deposition of nanoscale multilayer CrN/NbN physical vapor deposition coatings by high power impulse magnetron sputtering

Abstract: Nanoscale multilayer CrN/NbN physical vapor deposition (PVD) coatings are gaining reputation for their high corrosion and wear resistance. However, the CrN/NbN films deposited by ABS™ (arc bond sputtering) technology have some limitations such as macrodroplets, porosity, and less dense structures. The novel HIPIMS (high power impulse magnetron sputtering) technique produces macroparticle-free, highly ionized metal plasma, which brings advantages in both surface pretreatment and coating deposition stages of the PVD process. In this study, nanoscale multilayer CrN/NbN PVD coatings were pretreated and deposited with HIPIMS technology and compared with those deposited by HIPIMS-UBM (unbalanced magnetron) and by the ABS™ technique. In all cases Cr+ etching was utilized to enhance adhesion by low energy ion implantation. The coatings were deposited at 400 °C with substrate biased (Ub) at −75 V. During coating deposition, HIPIMS produced significantly high activation of nitrogen compared to the UBM as observed w...

Role of oxygen impurities in etching of silicon by atomic hydrogen

Abstract: In a pure-hydrogen glow discharge plasma, the etch rate of silicon increases with increasing temperature up to about ≥1100 A/s at 60–80 °C and, upon a further increase of the temperature, etch rate strongly decreases, showing Arrhenius-like dependence with negative apparent activation energy of −1.5 kcal/mol. When the Si sample is at the floating potential, oxygen impurities of ≥10 at. ppm strongly decrease the etch rate. At more than 70 ppm of oxygen, the etching stops. Oxygen adsorbed on the Si surface can be removed by ion bombardment when negative potential is applied to the Si sample and the Si is then etched chemically by H atoms. The etching by atomic hydrogen is isotropic in an oxygen-free system. A controllable addition of a few ppm of oxygen in combination with negative bias of the Si sample results in highly anisotropic etching with thin oxide acting as side-wall passivation.

Lithium phosphorous oxynitride films synthesized by a plasma-assisted directed vapor deposition approach

Abstract: A plasma-assisted directed vapor deposition approach has been explored for the synthesis of lithium phosphorous oxynitride (Lipon) thin films. A Li3PO4 source was first evaporated using a high voltage electron beam and the resulting vapor entrained in a nitrogen-doped supersonic helium gas jet and deposited on a substrate at ambient temperature. This approach failed to incorporate significant concentrations of nitrogen in the films. A hollow cathode technique was then used to create an argon plasma that enabled partial ionization of both the Li3PO4 vapor and nitrogen gas just above the substrate surface. The plasma-enhanced deposition process greatly increased the gas phase and surface reactivity of the system and facilitated the synthesis and high rate deposition of amorphous Lipon films with the N∕P ratios between 0.39 and 1.49. Manipulation of the plasma-enhanced process conditions also enabled control of the pore morphology and significantly affected the ionic transport properties of these films. This...

Optical second-harmonic generation in thin film systems

Abstract: The surface and interface sensitive nonlinear optical technique of second-harmonic generation (SHG) is a very useful diagnostic in studying surface and interface properties in thin film systems and can provide relevant information during thin film processing. An important aspect when applying SHG is the interpretation of the SHG response. In order to utilize the full potential of SHG during materials processing it is necessary to have a good understanding of both the macroscopic and the microscopic origin of the SHG response, particularly in thin film or multilayer systems where the propagation of radiation is another important aspect that should be considered carefully. A brief theoretical overview on the origin of the SHG response and a description of the propagation of radiation will be given. Furthermore, several methods will be discussed that might reveal the possible macroscopic and microscopic origins of the SHG response in thin film systems. The different approaches will be illustrated by examples...

Seasoning of plasma etching reactors: Ion energy distributions to walls and real-time and run-to-run control strategies

Abstract: Wafer-to-wafer process reproducibility during plasma etching often depends on the conditioning of the inside surfaces of the reactor. Passivation of reactor surfaces by plasma generated species, often called seasoning, can change the reactive sticking coefficients of radicals, thereby changing the composition of the radical and ion fluxes to the wafer. Ion bombardment of the walls may influence these processes through activation of surface sites or sputtering, and so the spatial variation of ion energies on the walls is important. These seasoning processes may occur during a single etching process or on a wafer-to-wafer basis. The seasoning of plasma etching reactors will be discussed using results from a computational investigation of p-Si etching in chlorine plasmas. The transport of etch products, passivation of walls, and sputtered products from walls are accounted for, as well as differentiating the ion energy distributions to different surfaces. A real-time, closed-loop control of etch rate to counter the effects of seasoning was achieved using the bias voltage as an actuator.

Silicate formation and thermal stability of ternary rare earth oxides as high-k dielectrics

Abstract: Hf-based dielectrics are currently being introduced into complementary metal oxide semiconductor transistors as replacement for SiON to limit gate leakage current densities. Alternative materials such as rare earth based dielectrics are of interest to obtain proper threshold voltages as well as to engineer a material with a high thermal stability. The authors have studied rare earth based dielectrics such as Dy2O3, DyHfOx, DyScOx, La2O3, HfLaOx, and LaAlOx by means of ellipsometry, time of flight secondary ion mass spectroscopy x-ray diffraction, and x-ray photoelectron spectroscopy. The authors show that ellipsometry is an easy and powerful tool to study silicate formation. For ternary rare earth oxides, this behavior is heavily dependent on the composition of the deposited layer and demonstrates a nonlinear dependence. The system evolves to a stable composition that is controlled by the thermal budget and the rare earth content of the layer. It is shown that silicate formation can lead to a severe overe...

Thermal stability and thermo-mechanical properties of magnetron sputtered Cr-Al-Y-N coatings

Abstract: Cr1−xAlxN coatings are promising candidates for advanced machining and high temperature applications due to their good mechanical and thermal properties. Recently the authors have shown that reactive magnetron sputtering using Cr-Al targets with Al/Cr ratios of 1.5 and Y contents of 0, 2, 4, and 8 at % results in the formation of stoichiometric (Cr1−xAlx)1−yYyN films with Al/Cr ratios of ∼1.2 and YN mole fractions of 0%, 2%, 4%, and 8%, respectively. Here, the impact of Y on thermal stability, structural evolution, and thermo-mechanical properties is investigated in detail. Based on in situ stress measurements, thermal analyzing, x-ray diffraction, and transmission electron microscopy studies the authors conclude that Y effectively retards diffusional processes such as recovery, precipitation of hcp-AlN and fcc-YN, grain growth, and decomposition induced N2 release. Hence, the onset temperature of the latter shifts from ∼1010 to 1125 °C and the hardness after annealing at Ta=1100 °C increases from ∼32 to ...

Methods of producing plasma enhanced chemical vapor deposition silicon nitride thin films with high compressive and tensile stress

Abstract: Various methods of generating high stress in thin plasma enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) films are reported. Besides the mainstream variation of plasma power and other process parameters, novel techniques such as creation of high density layers in multilayer PECVD structures or exposure of SiN films to ultraviolet radiation are shown to increase intrinsic film stress. Thin PECVD SiN films have been analyzed by a variety of analytical techniques including Fourier transform infrared spectroscopy, x-ray reflectivity (XRR), time of flight secondary ion mass spectrometry, and transmission electron microscopy to collect data on bonding, density, chemical composition, and film thickness. The level of bonded hydrogen as well as film density has been found to correlate with film stress. Creation of multilayer structures and high density layers help to build up more stress compared to a standard single layer film deposition. Both the density and number of layers in a film, character...

Classical size effect in oxide-encapsulated Cu thin films: Impact of grain boundaries versus surfaces on resistivity

Abstract: A methodology is developed to independently evaluate surface and grain boundary scattering in silicon dioxide-encapsulated, polycrystalline Cu thin films. The room-temperature film resistivity for samples with film thicknesses in the range of 27 to 1 65 nm and different grain sizes (determined from approximately 400 to 1500 grains per sample) is compared to existing and empirical models of surface and grain boundary scattering. For the combined effects of surface and grain boundary scattering, the surface specularity parameter p is 0.6±0.2 and the grain boundary reflectivity coefficient R is 0.45±0.03. It is thereby shown that the resistivity contribution from grain boundary scattering is significantly greater than that of surface scattering for Cu thin films having Cu∕SiO2 surfaces and grain sizes similar to film thickness.

Physical vapor deposition synthesis of tungsten monocarbide (WC) thin films on different carbon substrates

Abstract: The synthesis of tungsten monocarbide (WC) thin films has been performed by physical vapor deposition on various substrates including glassy carbon, carbon fiber sheet, carbon foam, and carbon cloth. The WC and W2C phase contents of these films have been evaluated with bulk and surface analysis techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. These characterization techniques were also used to determine the effects of synthesis by nonreactive and reactive sputtering. The synthesis of WC particles supported on the carbon fiber substrate has also been accomplished using the temperature programmed reaction method. Overall, the results demonstrate that the phase purity of tungsten carbides can be controlled by the deposition environment and annealing temperatures.

Stress evolution and defect diffusion in Cu during low energy ion irradiation: Experiments and modeling

Abstract: Measurements of stress generation in Cu during low energy ion irradiation show that the induced stress depends on temperature and ion flux. A steady-state compressive stress is observed during irradiation, which turns into tensile stress after the irradiation is stopped. The results cannot be explained by the incorporation of gas ions alone, and point defects generated by the ions must be considered. In this work, the authors develop a continuum model that includes ion implantation, sputtering, and defect diffusion to explain the experimental data. The authors show that the experimental results can be reproduced primarily by considering a difference in diffusivity between interstitials and vacancies.

Oxidation of silicon nanowires for top-gated field effect transistors

Abstract: The oxidation of unintentionally doped p-type silicon nanowires grown by the vapor-liquid-solid (VLS) method and their integration into top-gated field effect transistors is reported. Dry thermal oxidation of as-grown silicon nanowires with diameters ranging from 20to400nm was carried out at 700 and 900°C with or without the addition of a chlorinated gas source. The oxidation rate was strongly dependent on the as-grown nanowire diameter, with the large-diameter nanowires oxidizing up to five times faster than the smallest nanowires at 900°C. At each diameter, the addition of trichloroethane (TCA) enhanced the rate compared to oxidation in pure O2. Top-gated field effect transistors fabricated from nanowires oxidized at 700°C had significantly less hysteresis in their subthreshold properties when TCA was added, but oxidation at 900°C with or without TCA provided hysteresis-free devices with improved subthreshold slope. Such enhancements in the electrical properties are expected based on advances in planar ...

Effect of negative bias voltage on CrN films deposited by arc ion plating. II. Film composition, structure, and properties

Abstract: Chromium nitride (CrN) films were deposited on Si wafers by arc ion plating at various negative bias voltages and several groups of N2∕Ar gas flux ratios and chamber gas pressures. The authors systematically investigated the influence of negative bias voltage on the synthesis, composition, microstructure, and properties of the arc ion plating (AIP) CrN films. In this article, the authors investigated the influence of negative bias voltage on the chemical composition, structure, and mechanical properties of the CrN films. The results showed that the chemical composition and phase structure of the AIP CrN films were greatly altered by application of negative bias voltage. Due to the selective resputtering effect, substoichiometric CrN films were obtained. With increase in bias voltages, the main phases in the films transformed from Cr+CrN to Cr2N at low N2∕Ar flow ratios, whereas the films at high N2∕Ar flow ratios retained the CrN phase structure. The CrN films experienced texture transformation from CrN (...

Effect of negative bias voltage on CrN films deposited by arc ion plating. I. Macroparticles filtration and film-growth characteristics

Abstract: [Wang, Qi Min; Kim, Kwang Ho] Pusan Natl Univ, Natl Core Res Ctr Hybrid Mat Solut, Pusan 609735, South Korea. [Wang, Qi Min] Inst Met Sci & Technol, Div Surface Engn Mat, Shenyang 110016, Peoples R China.;Kim, KH (reprint author), Pusan Natl Univ, Natl Core Res Ctr Hybrid Mat Solut, Pusan 609735, South Korea;kwhokim@pusan.ac.kr

Reduction in hydrogen outgassing from stainless steels by a medium-temperature heat treatment

Abstract: The authors carried out heat treatments, in-vacuum or in-air at 400 °C, to reduce the hydrogen outgassing rate from stainless steels. An outgassing rate as low as 2×10−14 Torr l s−1 cm−2 was routinely achieved by a medium-temperature bakeout, but it took much longer time than reported to perform intensive thermal treatment. The result shows that the diffusion process governs degassing only at the early stage of degassing while the recombination limits outgassing at low concentrations. Air baked chambers had somewhat lower outgassing rates than in-vacuum baked chambers, suggesting that the surface oxide acts as a further barrier for H2 outgassing. However, the main effect may be attributed to the removal of mobile hydrogen through diffusion. The results showed that the ultralow outgassing rate can be reproducibly achieved for stainless steel chambers with the established heat treatment procedure. The study also showed that the ultralow outgassing property of a treated chamber can be restored by a low temperature (>150 °C) postbakeout, after exposure to ambient air.

Atomic-scale investigation of graphene formation on 6H-SiC(0001)

Abstract: The growth of graphene on the silicon-terminated face of 6H-SiC(0001) was investigated by scanning tunneling microscopy (STM) measurements. The initial stages of ultrahigh vacuum graphitization resulted in the growth of individual graphene sheets on random SiC terraces. These initial graphene sheets contained few defects, and the regions of clean SiC were free of contamination, exhibiting a 63×63R30° surface reconstruction. However, graphitization to multilayer thickness resulted in multiple defects, as observed with the STM. A high density of defects was observed, which may be attributed to the initial treatment of the SiC wafer. We characterize these defects, showing that they are located predominantly below the first layer of graphene.

Test particle simulation of the role of ballistic electrons in hybrid dc/rf capacitively coupled plasmas in argon

Abstract: Hybrid dc/rf plasma sources are an emerging equipment technology in plasma etching for semiconductor manufacturing. In this work, test particle simulations are used to describe the nature and role of the ballistic electrons, which originate as secondary electrons on a dc/rf (i.e., VHF, 60MHz) biased upper electrode and are then accelerated in the sheath toward the opposite non-dc biased lower electrode. This opposite electrode, on which a wafer is placed, may have rf bias power applied to it at low frequencies. 2MHz is typical. While a hybrid dc/rf plasma source is sustained by the VHF power source, simulations reveal ballistic electrons assist in the production of a plasma characterized by a relatively high ionization rate constant, especially in the dc sheath. The dc source helps to provide a source of high energy electrons that may reach the wafer. However, when the rf bias is applied on the lower electrode, ballistic electrons are confined in the potential well formed between electrodes and easily the...

Growth and interface of HfO2 films on H-terminated Si from a TDMAH and H2O atomic layer deposition process

Abstract: HfO2 thin films have been deposited by an atomic layer deposition (ALD) process using alternating pulses of tetrakis(dimethyl)amino hafnium and H2O precursors at a substrate temperature of 200–325°C. The initial stage of film growth on OH- and H-terminated Si(100) surfaces is investigated using Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). The authors observe an initial growth barrier on the Si–H surface for the first approximately four process cycles, where film growth is more efficient on the OH-terminated surface. Both starting surfaces require about 15cycles to reach a steady growth rate per cycle, with the OH-terminated surface displaying a slightly higher growth rate of 2.7×1014Hf∕cm2 compared to 2.4×1014Hf∕cm2 for Si–H. Combining the RBS and SE data we conclude that the films deposited on the OH-terminated surface are denser than those deposited on the Si–H surface. Angle-resolved XPS measurements reveal the formation of a...

Self-limiting deposition of aluminum oxide thin films by pulsed plasma-enhanced chemical vapor deposition

Abstract: Self-limiting deposition of aluminum oxide (Al2O3) thin films was accomplished by pulsed plasma-enhanced chemical vapor deposition using a continuous delivery of trimethyl aluminum (TMA) and O2. Film characterization included spectroscopic ellipsometry and Fourier transform infrared (FTIR) spectroscopy. Deposition rates scaled with TMA exposure and could be controlled over a large range of 1–20A∕pulse. For fixed conditions, digital control over film thickness is demonstrated. Deposition rates initially decreased with substrate temperature before becoming constant for Ts>100°C. Higher growth rates at low temperature are attributed to the thermal reaction between H2O, produced during the plasma on step, with TMA during the plasma off step. Gas-phase analysis confirms the coexistence of these species, and their degree of overlap is a strong function of the chamber wall temperature. With both the substrate and chamber wall temperature elevated, impurities related to carbon and hydroxyl groups are attenuated b...

Temperature effect on the glancing angle deposition of Si sculptured thin films

Abstract: Si sculptured thin films consisting of spiral-, screw-, and columnlike-shaped nanostructures were grown by ion beam-induced glancing angle deposition of Si on rotating bare Si[001] substrates at different substrate rotational speeds and substrate temperatures ranging from room temperature to (360±10)°C. For rotational speeds leading to the growth of nanoscrews at room temperature, morphology changes are observed with increasing temperature, such as an increase of the critical height at which single spiral fibers start merging to screws, thus giving the possibility to grow separated nanospirals with diameters of about 30 nm over a large thickness range. A decrease of the overall film thickness, indicating a change in the film density, is also observed with increasing the substrate temperature. For deposition conditions leading to the growth of vertical columns at room temperature, the substrate temperature influences the total number of columns, the column diameter, and the total structure height. The temp...

In situ ultrahigh vacuum residual gas analyzer “calibration”

Abstract: Knowing the residual gas spectrum is essential for many applications and research in ultrahigh vacuum (UHV). Residual gas analyzers (RGAs) are used for both qualitative and quantitative gas analyses, where the quadrupole mass analyzers are now the most popular. It was found that RGAs supplied by different manufacturers are not necessarily well calibrated for quantitative gas analysis. A procedure applied for in situ RGA “calibration” against a calibrated UHV total pressure gauge is described in this article. It was found that special attention should be paid to H2 calibration, as RGAs are usually much more sensitive to H2 than ionization gauges. The calibration coefficients are quite reproducible in Faraday cup mode, however, using the secondary electron multiplier requires frequent checks of the calibration coefficients. The coefficients obtained for the RGA allow the use of the RGA as an accurate device for gas spectrum analysis.