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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Issue 1 • Date Jan 1999

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Displaying Results 1 - 25 of 47
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Scanning tunneling microscopy studies of formation of 8×5 reconstructed structure of Ga on the Si(001) surface

    Page(s): 1 - 6
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    The behavior of Ga on the Si(001) 2×1 surface has been studied for Ga coverage of 0.8 monolayers and annealing temperatures in the range 623–863 K by means of scanning tunneling microscopy. Annealing at the lowest annealing temperature Ta leads to the formation of the Ga 2×2 phase, which is a result of self-arrangement of Ga dimers, as well as irregular Ga clusters. An increase in Ta to 673 K results in the formation of a partially ordered metastable Ga 5×2 phase, whereas further increase in Ta leads to the transformation of the 5×2 structure into 8×n (n=4,5) structure, the degree of order of which gradually increases with an increase in the annealing temperature. At Ta=833 K the surface is uniformly covered by the periodically aligned arrays of 8×5 units, this 8×5 structure is believed to consist of the ordered double-layered Ga clusters having 24–26 Ga atoms in the first layer and four Ga atoms in the second layer. The 8×5 units are out of registry with the underlying Si surface in one direction, this uncoupling from the surface is believed to be caused by Ga–Ga interactions. Further increase in Ta up to 863 K results in the evaporation of the Ga atoms from the surface giving rise to the redimerization of the Si and Ga atoms and reappearance of the Ga 2×2 phase. © 1999 American Vacuum Society. View full abstract»

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  • Scanning tunneling microscopy study of the adsorption of toluene on Si(001)

    Page(s): 7 - 11
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    Scanning tunneling microscopy is used to investigate the adsorption of toluene on the Si(001)-2×1 surface. At room temperature, adsorption occurs exclusively on top of dimer rows and results in several binding geometries. A metastable and weakly bound state is observed initially upon adsorption. This state converts to a more stable geometry. Conversions between the dominant adsorbed states are observed and can be induced by the scanning tunneling microscopy (STM) tip. These states closely resemble those of benzene on Si(001). Evidence that toluene interacts with more surface dimers than benzene is found in the bias dependence of the adsorbed states in STM images. Toluene decomposes upon annealing, leaving carbon on the surface. © 1999 American Vacuum Society. View full abstract»

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  • Evidence for liquid indium nanoparticles on Ge(001) at room temperature

    Page(s): 12 - 21
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    Indium films up to 6 ML thick on the Ge(001) surface in ultrahigh vacuum have been both deposited at and investigated at room temperature. The investigation techniques used were scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and low energy electron diffraction. Correlated AES and STM observations strongly suggest In–Ge intermixing, while XPS rules out compound formation. For a film 5 ML thick, nanoparticles approximately 15 nm high and 60 nm across with a pronounced faceted shape were observed in STM using a Pt–Ir tip scanning as far from the surface as possible. For smaller tip-sample distances, a dynamic tip-sample interaction was observed which resulted in sawtooth topographic data inconsistent with the topography observed at larger tip-sample separations. The evidence is that the epitaxial film is in the liquid phase at room temperature, in spite of the In bulk melting point at atmospheric pressure being 430 K. The liquid phase hypothesis is supported by a thermodynamic calculation which considers the impact of heteroepitaxial stress on the melting point. © 1999 American Vacuum Society. View full abstract»

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  • Optical system for tunneling-electron luminescence spectro/microscopes with conductive-transparent tips in ultrahigh vacuums

    Page(s): 22 - 28
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    A unique optical system has been developed for a tunneling-electron luminescence (TL) spectro/microscope with conductive-transparent (CT) tips operable and changeable in an ultrahigh vacuum (UHV). The optical system consists of two essential elements. The first element is fiber-optics, which effectively guides the luminescence from the CT tips to optical detectors without the need for optical alignment. The fiber-optics features (1) a mechanism to automatically reproduce optical coupling between the CT tip and the fiber every time the tip is changed, (2) a fiber set in a vacuum chamber to prevent steep fiber bending, and (3) a compact fiber-optic vacuum seal that maintains high transmittance and limits low gas leakage to ultimate pressures below 10-10 Torr. The second element is optical detection and processing, which reduce the influence of fluctuations in TL intensities, which is a serious problem in TL measurements. The main structures of this element are a whole spectral detector for spectroscopy and a tip-scan-synchronized photon counter for microscopy. The optical system was characterized through TL measurements on semiconductor nanostructures at low temperatures in an UHV. A TL spectro/microscope with the optical system achieved satisfactory performance. © 1999 American Vacuum Society. View full abstract»

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  • Scanning tunneling microscope-induced luminescence of GaN at threading dislocations

    Page(s): 29 - 32
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    We have studied the scanning tunneling microscope-induced luminescence of GaN at low temperature. The emitted photons are investigated using bias spectroscopy techniques. Near band edge emission is detected at low temperature at tip biases exceeding Vt=3.25 V. Corresponding luminescence images reveal a correlation between threading dislocations and nonradiative recombination. A hole diffusion length of LD=30–55 nm is evaluated from the extent of the nonluminescent areas. Preliminary assessment of luminescence morphology is performed with standard cathodoluminescence. © 1999 American Vacuum Society. View full abstract»

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  • Area evaluation of microscopically rough surfaces

    Page(s): 33 - 39
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    In this article, a novel roughness function is developed which enables the assessment of the area of a microscopically rough surface measured by atomic force microscopy (AFM). A reliable area of a surface with microscopic roughness has proven to be difficult to compute due to the small vertical and large spatial differences which cause significant round off error in the computation. Instead of the usual procedure of computing the area of a surface directly from the data set, we utilized the fact that surface area increases with roughness. Two roughness parameters, root mean square (rms) and fractal dimension (DF) yielding vertical and horizontal information, respectively, are employed to provide a reasonably complete description of surface roughness. We show that the area of a microscopically rough surface is exponentially related to DF and quadratically to rms, and these relationships are the basis of a novel roughness function. This function is shown to be both sensitive to the changes in surface topography, and reliable in providing the area of a surface with microscopic roughness. © 1999 American Vacuum Society. View full abstract»

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  • Application of advanced micromachining techniques for the characterization and debug of high performance microprocessors

    Page(s): 40 - 43
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    Micromachining techniques such as focused ion beam milling have become an integral part of the design debug cycle at many companies for providing fast verification of bug fixes in silicon. With flip chip packaging becoming more prevalent for future high performance processors, it is necessary to perform circuit edits and bug fixes on the silicon while the chip is packaged in the flip chip package. With this technology, however, conventional frontside probing and traditional circuit rewiring of packaged devices are not practical. We have developed a combination of new micromachining techniques for directly accessing metal signals from the backside of the chip. Here we will describe this new process, the technologies used, and some basic applications. © 1999 American Vacuum Society. View full abstract»

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  • Nitrogen influence on dangling-bond configuration in silicon-rich SiOx:N,H thin films

    Page(s): 44 - 48
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    Paramagnetic centers were studied in different SiOx:N,H films deposited by plasma-enhanced chemical vapor deposition in a wide composition range. The total dangling-bond concentration is detected to be proportional to the oxygen content. Moreover, sample irradiation by ultraviolet light revealed also that nitrogen impurities play some role. In particular, the presence of N–H bonds induces a release of the film stress, which seems to be related to the concentration of dangling bonds. It is also shown that both weak Si–Si and Si–H bonds may serve as precursors for the dangling-bond formation. © 1999 American Vacuum Society. View full abstract»

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  • Interface charge and nonradiative carrier recombination in Ga2O3–GaAs interface structures

    Page(s): 49 - 52
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    We have investigated the dual role of interfacial defects in creating both nonradiative interface recombination and interface charge. Our studies are based on Ga2O3–GaAs interface structures with their unique properties such as low interface state density and radiative GaAs band-to-band recombination. The self-consistent analysis of the steady-state dependence of the spontaneous GaAs emission on excitation density provides all critical characteristics of interfacial defects simultaneously: the density of interface states, their capture cross sections, the interface recombination velocities, and the oxide charge. © 1999 American Vacuum Society. View full abstract»

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  • A study of the relationship between Si/SiO2 between interface charges and roughness

    Page(s): 53 - 59
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    This study examines the correlation between interface roughness and charges. Atomic force microscopy (AFM) and a newly developed area roughness function which couples two roughness parameters, root-mean-square (rms) and fractal dimension (DF), are used to reliably and accurately characterize surface roughness. Interface charges (Dit and Qf) are measured using high frequency and quasistatic capacitance–voltage methods. This study is divided into three parts where smooth, purposely roughened, and purposely smoothened Si substrates are used to make metal–oxide–semiconductor capacitors for measurements. Purposely roughened substrates are obtained using a chemical acid etch solution. Purposely smoothened substrates are initially roughened with the chemical acid etch solution and smoothened through thermal oxidation. We report that the increases of Dit and Qf with Si roughness are due entirely to the area increase and orientation changes the result from roughness. © 1999 American Vacuum Society. View full abstract»

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  • Deep levels in low temperature GaAs probed by field effect deep level transient spectroscopy

    Page(s): 60 - 67
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    Low temperature (LT) GaAs grown on semi-insulating GaAs by molecular beam epitaxy has been investigated by field effect deep level transient spectroscopy at several reverse bias fields ranging from -1×105 to -4×105V/cm. The activation energy, capture cross section, and electron–phonon coupling parameter all have been found to be modulated by the applied field. The theories of the Schottky effect and the electron–phonon coupling effect have been considered to interpret the electron conduction mechanisms in LT GaAs. © 1999 American Vacuum Society. View full abstract»

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  • Numerical modeling of electron transport in a cylindrical cell

    Page(s): 68 - 72
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    A physical and mathematical model is developed for the numerical simulation of electron transport in a multielectrode microcell with a circular emitter. Two circular grid electrodes are included in the model to control the electron beam. A target plate face electrode is considered as a secondary electron source. Electron beam transport in a self-consistent electric field is simulated using a cylindrical particle mesh code. Some typical examples are calculated to demonstrate the effectiveness of the proposed technique for optimization of beam control. The influence of a magnetic field on the static and dynamic characteristics of the microcell is also studied. Split anode difference current is predicted in a magnetic field and thus the microvacuum cell may be used as a magnetosensitive element. © 1999 American Vacuum Society. View full abstract»

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  • Effect of light exposure on 1/f noise in a-Si:H

    Page(s): 73 - 76
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    We measure the changes induced in the 1/fα conductance fluctuation power spectrum of n-type a-Si:H in the dark after illumination by band-gap light of intensity 0.17 W/cm2. Initially the relative noise power decreases by a factor of 5 over the first 100 min of exposure. For longer exposures, the noise recovers but preferentially at higher frequencies causing α to decrease from 1.1 in the annealed state to between 0.8 and 0.9 after 60 h of illumination. Also after long exposures, the spectrum does not fit a simple power law but has additional weight at higher frequencies. Other aspects are typical of 1/f noise, a linear dependence on applied current and Gaussian statistics, in both the annealed and light soaked states, which are in disagreement with other reports on similar material. Some of the increase in noise beyond the 100 min exposure is attributed to carriers interacting with localized states that become emptied as the Fermi level drops. © 1999 American Vacuum Society. View full abstract»

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  • Fabrication technology of ultrafine SiO2 masks and Si nanowires using oxidation of vertical sidewalls of a poly-Si layer

    Page(s): 77 - 81
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    A fabrication technology of the vertical ultrafine SiO2 wall masks using oxidation of sidewalls of a polycrystalline silicon (poly-Si) layer and Si nanowires utilizing the SiO2 wall masks have been developed. To obtain the vertical SiO2 wall mask, an optimum electron cyclotron resonance (ECR) plasma etching and a suitable wet etching of the poly-Si layer after the sidewall oxidation has been achieved. The vertical ultrafine SiO2 wall masks 10 nm wide and 90 nm high with 33 nm in space have been successfully fabricated for the first time. The dimensions of width and space become essentially smaller than the size of an electron beam resist pattern. The height is sufficient for ECR plasma etching. Si nanowires 10 nm wide and 18 nm thick have been precisely obtained by the ECR plasma etching of the thinned silicon-on-insulator layer using the vertical ultrafine SiO2 wall masks. The fabrication technology using the vertical ultrafine SiO2 wall masks has remarkable merits of fineness, scalability, and wide applicability. It can be utilized for fabricating various designed nanostructures. © 1999 American Vacuum Society. View full abstract»

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  • Tandem accel lens advantageous in producing a small spot focused ion beam

    Page(s): 82 - 85
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    This article presents a novel electrostatic lens which is particularly advantageous in producing a smaller spot focused ion beam (FIB). The lens has a tandem structure made up of conventional einzel lenses operated in the acceleration (accel) mode. The structure allows the lens to work under significantly lower excitation voltages compared with conventional accel lenses, making it possible to converge high energy FIB at short focal lengths to minimize aberrations. The minimum spot size obtainable for a 30 keV FIB with 1 pA current has been calculated for various objective lens applications under a restriction where the excitation voltage should be below the beam voltage (30 kV). Spot sizes are 7.3, 6.6, and 4.8 nm for the conventional accel, decel, and tandem accel lenses discussed in this article, respectively. © 1999 American Vacuum Society. View full abstract»

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  • Nanolithography using a 100 kV electron beam lithography system with a Schottky emitter

    Page(s): 86 - 89
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    We present lithography results with a new electron beam lithography system using a W/ZrO Schottky emitter operating at 100 kV acceleration voltage. The wide range of available beam currents between 100 pA and 50 nA allows both high resolution nanolithography and large area patterning. Resolution tests with line and dot arrays patterned by lift off using a poly(methyl/methacrylate) resist showed a minimum linewidth of 12 nm for 36 nm line pitch written with a beam current of 1.1 nA, 15 nm for 50 nm pitch written with 3 nA and 30 nm for 100 nm pitch written at 12 nA. The smallest spacing between features at 1.1 nA current was 36 nm for lines and 32 nm for dot arrays. The high current density of the beam at very small spot sizes makes the system a promising tool for nanofabrication using both conventional resist as well as high resolution but low sensitivity inorganic resist. © 1999 American Vacuum Society. View full abstract»

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  • Vapor deposition polymerization of 4-fluorostyrene and pentafluorostyrene

    Page(s): 90 - 94
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    Solventless deposition of thin, uniform dielectric films is of considerable interest and importance in the microelectronics industry due to environmental concerns and increasing wafer sizes. This work demonstrates a solvent-free method for atmospheric pressure chemical vapor deposition polymerization of thin films on a variety of substrates, including silicon, molybdenum, platinum and copper. Polymerization of 4-fluorostyrene (4FS) and pentafluorostyrene (PFS) is used as a model system. Depth profiling is performed using x-ray photoelectron spectroscopy, ellipsometry, and step profilometry. Film growth is found to be independent of substrate, and proceeds with activation energies of 14±1 and 15±1 kcal/mol, respectively, for 4FS and PFS deposition between 425 and 550 K. Films are shown by gel permeation chromatography to consist of low molecular weight polymer and oligimer species (between 3 and 140 repeat units). Atomic force microscopy analysis of films grown by this method indicates that the root mean square thickness variation along the surface is about 2.5%. View full abstract»

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  • Observations on the formation and ashing of giant folds in high dose ion-implanted resists

    Page(s): 95 - 100
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    A kinetics of surface transformations and ashing of high energy high dose As+ implanted resists was studied. Continuous bulk polymer structures, having minimum cross-sectional dimensions 10–30 times larger than the initial resist thickness, were found. These structures, named as giant folds, are formed as a result of heating and melting of the normal polymer resist sublayer and its interaction with a mechanically deformed implanted resist layer. The giant folds are responsible for the most difficult to remove surface remaining features of ion implanted resists processed in downstream gas discharge ashers. It is shown that the main problem of dry ashing of ion implanted resists of this type is the flow patterns of the normal resist sublayer, not the hard implanted surface layer itself. © 1999 American Vacuum Society. View full abstract»

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  • Environmental stability of 193 nm single layer chemically amplified resists

    Page(s): 101 - 108
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    The principle of chemical amplification was introduced to develop fast and high resolution resist materials, primarily for deep-ultraviolet (UV) lithography. Excellent sensitivity in CA resists emanates from the utilization of a photogenerated species, typically an acid, to cause several catalytic crosslinking or deblocking events during a postexposure bake (PEB) reaction. Deactivation of the photoacid by airborne basic contaminants or other pathways typically changed the feature width and/or the profile as a function of the delay between exposure and the PEB. Decreasing the photoacid strength, use of low activation energy protecting groups, a decrease in the catalytic turnover rates or a combination of these has helped alleviate this. Today, deep-UV resists that show several hours of postexposure stability are available. We have examined the postexposure delay stability of several 193 nm resists that varied in matrix polymer, photoacid generator, and protecting group chemistry as a function of different concentrations of ammonia and N-methyl pyrrolidone (NMP) at three different relative humidity conditions. In this article we will discuss the experimental setup and describe the environmental contamination stability of these different resists as well as describe in detail the design methodology employed in formulating the resist that showed no significant variation in its linewidth of 0.16 μm line/space pairs with 13 ppb of ammonia or 14 ppb of NMP. © 1999 American Vacuum Society. View full abstract»

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  • High-resolution resist etching for quartermicron lithography using O2/N2 supermagnetron plasma

    Page(s): 109 - 112
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    For quartermicron lithography, fine pattern etching of bilayer resist was investigated using O2/N2 supermagnetron plasma. The maximum etch rate was obtained at a radio frequency (rf) phase difference of 150°–180° which was observed between two rf powers of the same frequency supplied to two parallel electrodes. The side etchings of resist walls were reduced by lowering the electrode (wafer) temperature to -30 °C. By the increment of N2 concentration from 0% to 60%, the etch rate decreased little, and the side etchings of resist walls became only ±0.015 μm at a self-bias voltage Vdc of -140 to -180 V. Microloading effect was greatly improved by lowering a wafer temperature to -30 °C and by increasing Vdc to -180 V. © 1999 American Vacuum Society. View full abstract»

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  • Use of polymethylmethacrylate as an initial pattern transfer layer in fluorine- and chlorine-based reactive-ion etching

    Page(s): 113 - 117
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    The properties of polymethylmethacrylate (PMMA) as a pattern transfer mask in commonly used fluorine- and chlorine-based reactive-ion etching processes have been studied. A reduction in the PMMA etch rate in CHF3 and SiCl4 has been observed for a machine with a lower oxygen background level and an optimum selectivity of silicon nitride to PMMA in CHF3 reactive-ion etching (RIE) was obtained also. The machine with the lower base pressure does not exhibit high RIE lag and this allows better transfer of submicron patterns from PMMA to dielectric layers. This improved selectivity has led to a better intermediate mask for the fabrication of photonic band gap structures in AlGaAs. © 1999 American Vacuum Society. View full abstract»

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  • Parametric study of the etching of SiO2 in SF6 plasmas: Modeling of the etching kinetics and validation

    Page(s): 118 - 126
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    The uniform distributed electron cyclotron resonance plasma of SF6, excited at either 2.45 or 5.85 GHz, has been applied to study the etching of SiO2 by F atoms as a function of the three relevant plasma parameters: neutral F-atom flux, ion flux, and ion energy. Three saturation effects are observed. At constant ion current density, the etch rate at first increases linearly with F-atom flux, but then it reaches a plateau, which rises when one raises the ion current density. Second, at constant F-atom flux, initially the etch rate also climbs linearly with ion current density, and again, levels out at larger ion current density, and is higher at larger F-atom flux; however, the initial increase is independent of the F-atom flux. Third, the etch rate evolves similarly as a function of bias voltage for constant F-atom flux and ion current density. These results are first interpreted by a simple mechanism of F-atom adsorption on the SiO2 surface, followed by SiF4 formation at, and desorption from the surface, and by assuming a constant density of adsorption sites for fluorine on the SiO2 surface. However, although this model provides the general trends of the etching kinetics of SiO2 as a function of each plasma parameter, it nevertheless fails explaining many details of the observed etch rates. In fact, ion induced desorption of oxygen from the SiO2 surface is mandatory prior to F-atom adsorption on the Si overlayer thus built up on SiO2. The model resulting from this hypothesis is in complete agre- - ement with the experimental results obtained on the etching kinetics of SiO2 in SF6 plasmas. © 1999 American Vacuum Society. View full abstract»

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  • Kinetics of etch products and reaction process in electron cyclotron resonance plasma etching of Si

    Page(s): 127 - 137
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    The effect of etch products on the Si etching characteristics in electron cyclotron resonance plasmas with Cl2 was investigated by using both plasma diagnostics and a numerical simulation. The etch products both in the gas phase and on the etched surface were observed by in situ Fourier transform infrared (FTIR) absorption spectroscopy. The concentration range of silicon tetrachloride SiCl4 detected as the gas-phase etch product during Si etching was about 1012 molecules/cm3 within the pressure range of 0.1–10 mTorr, while that of silicon oxide was 1010–1012 molecules/cm3. On the etched surface, unsaturated silicon chlorides SiClx (x=1–3) as well as SiCl4 were observed. Moreover, the effect of the etch products was numerically investigated by using a kinetic etching model. The calculated etch rate showed good agreement with the measured one within the pressure range of 0.1–10 mTorr even though the sticking coefficient of silicon oxide was varied from 0.001 to 0.5. The coverage of the SiClx layer saturated about one monolayer beyond pressure of 1 mTorr. The bare Si surface area and the actual coverage of the oxide layer decreased by increasing the gas pressure. However, the actual coverage of oxide layer at ≪1 mTorr varied according to the sticking coefficient of silicon oxide. The calculated concentration of the etch products was the same order of magnitude as the concentration obtained by in situ FTIR diagnostics. It is expected that the effect of etch products on the etching characteristic,- - especially etched profiles, becomes more and more important at pressure of less than 1 mTorr. © 1999 American Vacuum Society. View full abstract»

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  • Smooth and anisotropic reactive ion etching of GaAs slot via holes for monolithic microwave integrated circuits using Cl2/BCl3/Ar plasmas

    Page(s): 138 - 144
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    A process to produce very smooth and highly anisotropic through-the-wafer slot via holes using reactive ion etching in Cl2/BCl3/Ar mixtures has been developed. In this study, we have extensively investigated the GaAs etch rate and resultant etch profiles as functions of bias voltage, gas ratio, flow rate, chamber pressure, aspect ratio, and etch time. An optimum via hole etching process using a Plasma Therm 790 reactive ion etching system was determined to be 300 V bias voltage, gas flow ratio of Cl2:BCl3:Ar=4:3:10, and chamber pressure of 15 mTorr. The average etch time for 20 μm wide ×60 μm long vias on a 50 μm thick 3 in. diam wafer is 180 min using a total flow rate of 50 sccm, which corresponds to an average etch rate of 0.3 μm/min. This process has been successfully implemented on two-stage Ka-band monolithic microwave integrated circuit driver amplifiers fabricated by TRW. Under a pulsed bias with Vds=5.0 V and an input power of 15 dBm, the average power added efficiency was greater than 40% with a 13–14 dB gain between 32 and 36 GHz. A peak power added efficiency of 44% was achieved at 35 GHz. © 1999 American Vacuum Society. View full abstract»

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Aims & Scope

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

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Editor
Gary E. McGuire
International Technology Center