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

Issue 4 • Date Jul 2003

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Displaying Results 1 - 25 of 142
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Large blueshift in InGaAs/InGaAsP laser structure using inductively coupled argon plasma-enhanced quantum well intermixing

    Page(s): L1 - L4
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    An inductively coupled plasma-enhanced quantum well intermixing technique has been developed to induce a shift in the band gap in quantum well structures using argon plasma. The emission of the InGaAs/InGaAsP laser structure was blueshifted as much as 104 nm with linewidth broadening of only 10.6 nm using 5 min plasma exposure and subsequent rapid thermal annealing. This large shift is attributed to inductively coupled plasma at high ion current density (with 100’s of eV ion impact energy) that promotes desirable point defects near the surface of the samples. The result has demonstrated an effective approach for large band gap tuning of InGaAs/InGaAsP laser structures. © 2003 American Vacuum Society. View full abstract»

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  • High-resolution pattern generation using the epoxy novolak SU-8 2000 resist by electron beam lithography

    Page(s): L5 - L7
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    We report the fabrication of high-resolution sub 50 nm patterns by electron beam lithography using the epoxy novolak SU-8 2000 resist formulation. The minimum linewidth achieved is on the order of 30 nm and corresponds to a threefold reduction in minimum linewidth over previous reports describing similar resist chemistries. Our results also show that it is possible to fabricate dense linear grating elements without proximity correction. The dry etch resistance of native SU-8 2000 was found to be nearly twice that of poly(methylmethacrylate), making it ideal for applications that require pattern transfer. These studies are intended to explore the feasibility of SU-8 2000 as an electron beam resist for pattern generation on length scales below 50 nm. © 2003 American Vacuum Society. View full abstract»

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  • Gas-induced current decay of molybdenum field emitter arrays

    Page(s): 1187 - 1202
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    Field emission displays can be seriously limited by current degradation of Mo field emitter arrays, primarily due to inadequate vacuum conditions inside their thin vacuum packages. Most lifetime studies describe the deleterious effects of short exposures to oxygenic gases on device performance. Here, we review experimental results on the emission characteristics of molybdenum field emitter arrays in a variety of gas ambients for extended periods. We find that even in inert gas, the emission current degrades rapidly, comparable to that observed in oxygenic gas ambients. Surprisingly, after exposure when the device is again operated under high vacuum conditions, various levels of current recovery can be observed. No evidence for ion sputter damage is observed. Existing degradation models do not provide an adequate explanation for this behavior. Rather, we suggest that these results point toward a model common for all gaseous ambients based on shallow implantation of ions into the field emitter tips. This creates a near surface layer that modifies the tunneling barrier, and thus subsequently the emission current. Support for this mechanism comes from several experimental observations. The implant degradation model is also consistent with devices that incorporate a field emitter ion pump process as a means to reduce pressure in the sealed vacuum package. © 2003 American Vacuum Society. View full abstract»

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  • Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. II. Effects of source power and bias voltage in a CF4 plasma

    Page(s): 1203 - 1209
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    Variations in the properties of sidewalls due to the redeposition of etch products emitted from the bottom during SiO2 etching in a CF4 plasma were studied under different conditions of source power and bias voltage, in the range of 100 and 500 V, and 0 and 400 W, respectively. A Faraday cage and a step-shaped SiO2 pattern located in a transformer coupled plasma etcher permitted the control of the incident angle of ions, thus permitting the redeposition phenomenon to be observed on a macroscopic scale. Under all process conditions, the deposition rate on sidewall (A), affected by the redeposition of particles emitted from the bottom, was larger than that on sidewall (B), which was unaffected by the redeposition, because particle redeposition induced the formation of a sidewall passivation layer on sidewall (A). It was indirectly confirmed that the amount and the kinetic energy of particles sputtered from the bottom were closely related to the formation of the sidewall passivation layer. The redop-effect, which indicates the extent to which the redeposition contributes to the deposition rate on the sidewall, increased with bias voltage and source power. The extent of etching of the SiO2 underlayer of sidewall (B) increased with both the source power and bias voltage, in contrast to the case of sidewall (A). On sidewall (A), the extent of SiO2 etching increased continuously with source power, but only increased with bias voltage when the latter was under 300 V. The etching decreased at higher bias voltages. © 2003 American Vacuum Society. View full abstract»

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  • Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. III. Effects of O2 addition to CF4 plasma

    Page(s): 1210 - 1215
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    The effect of added O2 on the etching of SiO2 sidewalls in a CF4 plasma was examined using a transformer-coupled plasma etcher, for two cases when the sidewall was either affected or unaffected by particles emitted from the bottom SiO2 surface. The deposition rate on the sidewall decreased in proportion to the amount of added O2. This occurred because the increased amount of F radicals enhanced the re-etching of SiO2, which is present beneath the surface polymer layer, and of etch products, which are redeposited from the bottom. The surface polymer layer on the sidewall, affected by particles emitted from the bottom, became thin and smooth as a result of the reaction with O radicals. The chemical etch rate of the sidewall, unaffected by energetic ions and bottom-emitted particles, and the bottom etch rates were the highest for oxygen concentrations of 10% and 20%, respectively. These concentrations were lower than an O2 concentration of 30%, which yields the maximum concentration of F radicals. The mismatch in the O2 concentrations arises because the O2 concentration required to obtain the maximum etch rate on the sidewall or bottom surface is determined by competitive reactions among F, CF2, O radicals, and incident ions. © 2003 American Vacuum Society. View full abstract»

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  • Electron emission from nanotips of amorphous diamond

    Page(s): 1216 - 1223
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    Amorphous diamond can be deposited with a high-density (4×1010 emitters/cm2) of nano-sized emitters. The turn on applied field strength was reduced by increasing aspect ratio of amorphous diamond nanotips. Moreover, the field emission was highly sensitive to the aspect ratio of tips, and relatively inert to the sp3/(sp3+sp2) ratio. The lowest turn on applied field strengths was 4.6 V/μm at the current density of 10 μA/cm2; and 11 V/μm at the current density of 10 mA/cm2. High reproducibility of field emission was also observed in this study. © 2003 American Vacuum Society. View full abstract»

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  • Effect of substrate on the step coverage of plasma-enhanced chemical-vapor deposited tetraethylorthosilicate films

    Page(s): 1224 - 1229
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    Plasma-enhanced chemical-vapor deposition tetraethylorthosilicate (TEOS) films are extensively used as the interlayer dielectric films in multilevel interconnection processes. When TEOS oxide films were deposited on metal patterns three different substrates, titanium nitride (TiN), aluminum (Al), and oxide (SiO2), were used. This study examines the dependence of these substrates on TEOS step coverage. The deposition rates of TEOS oxide revealed that the SiO2 substrate lead to highest TEOS deposition rate during the initial deposition period of 5 s. Then, the TEOS deposition rate of the substrates was nearly the same. The TiN substrate exhibited the highest sidewall step coverage but the sidewall step coverage of the Al substrate deteriorated due to its granular surface. Additionally, different substrates exhibited different coverage of the bottom step. Moreover, the bottom step coverage exceeded the sidewall coverage for all substrates. © 2003 American Vacuum Society. View full abstract»

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  • Enhanced field emission from chemically etched and electropolished broad-area niobium

    Page(s): 1230 - 1239
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    Electron field emission from broad-area metal surfaces is known to occur at a much lower electric field than predicted by the Fowler–Nordheim law. This enhanced field emission (EFE) presents a major impediment to high electric field operation in a variety of applications, e.g., in superconducting niobium radio-frequency cavities for particle accelerators, klystrons, and a wide range of high-voltage vacuum devices. Therefore, EFE has widely been the subject of fundamental research for years. Although micron or submicron particles are often observed at such EFE sites, the strength and number of emitting sites and the causes of EFE depend strongly on surface preparation and handling. Furthermore, the physical mechanism of EFE remains unknown. To systematically investigate the sources of this emission and to evaluate the best available surface preparation techniques with respect to the resulting field emission, a dc scanning field emission microscope (SFEM) was built at the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). Broad-area samples can be moved laterally in a raster pattern (2.5 μm step resolution) under a high-voltage microtip for EFE detection and localization in the SFEM. The emitting sites can then be characterized by scanning electron microscopy and energy dispersive x-ray spectrometry without breaking ultrahigh vacuum. After preparation by chemical etching and electropolishing combined with ultrasonic deionized water rinse, EFE sources from planar Nb have been studied. Emitters have been identified and analyzed, and based on scan results the preparation process has been refined and improved. With the improved preparation process, field-emission-free or near-field-emission-free surfaces at ∼140 MV/m have been achieved consistently on a number of samples. © 2003 American Vacuum Society. View full abstract»

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  • Fabrication of controlled sidewall angles in thin films using isotropic etches

    Page(s): 1240 - 1247
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    Angular structures in thin films have applications in microelectronics and optoelectronics. In this study we analyze isotropic etching of a two-layer system for the fabrication of angular sidewalls. Such a process is attractive because of its bulk processing capability. The isotropic etch process is demonstrated to provide good control of the sidewall angle. Theoretical analysis along with numerical simulation of the slope etching process is used to understand profile evolution. The numerical simulations showed that to obtain a flat angular sidewall face, reaction controlled etching is needed. Angular sidewalls are fabricated in plasma enhanced chemical vapor deposition (PECVD) silicon oxide with PECVD silicon nitride as the sacrificial layer using an isotropic, buffered hydrofluoric acid based, wet chemical etch. PECVD silicon nitride is shown to be a good material for use as the sacrificial layer because of its etch rate controllability through deposition conditions. Controlled angles ranging from 5° to 50° are demonstrated using this isotropic etch technique. Penetration of the etchant between the photoresist and the sacrificial silicon nitride layers is determined to be the cause of the limited range of the angles that could be etched. The rms roughness of the etched faces ranged from 79 to 389 Å. © 2003 American Vacuum Society. View full abstract»

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  • Plasma molding over deep trenches and the resulting ion and energetic neutral distributions

    Page(s): 1248 - 1253
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    A two-dimensional fluid/Monte Carlo simulation was developed to study plasma molding over deep trenches and the resulting ion and energetic (fast) neutral distributions, with emphasis on neutral beam sources. Plasma molding occurs when the sheath thickness is comparable to or smaller than the trench width. Using the electric field profiles predicted by the self-consistent fluid simulation, ions and energetic neutrals (resulting mainly by ion neutralization on the sidewall) were followed by the Monte Carlo simulation. The dominant energetic species at the bottom of a high aspect ratio trench were neutrals. A thin sheath (compared to the trench width), favored a larger energetic neutral flux at the bottom, at the expense of neutral energy and directionality. A relatively thick sheath produced neutrals of higher directionality at the expense of neutral flux. Neutral energy and directionality both increased by increasing the sheath potential. © 2003 American Vacuum Society. View full abstract»

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  • Conductance imaging of thermally desorbed silicon oxide

    Page(s): 1254 - 1257
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    We report on the use of scanning tunneling microscopy-conductance mapping to image voids in a thermally decomposed wet-chemical silicon oxide. Prominent contrast is observed between regions of remaining oxide and atomically clean silicon surface regions due to the difference in the local density of electronically active surface states. Differences in measured tunneling spectra within the voids, and in the surrounding oxidized regions, confirm that the origin of the contrast is mainly due to surface Fermi-level pinning at the clean Si(100) surface and metal–insulator–semiconductor junction behavior at the oxidized region. The maps show little sensitivity to pure topographical features, such as steps, and allow selective probing of electronic variations across a device structure with a resolution of 2 nm or better. © 2003 American Vacuum Society. View full abstract»

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  • Temperature-dependent inelastic response of passivated copper films: Experiments, analyses, and implications

    Page(s): 1258 - 1264
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    The temperature-dependent mechanical behavior of passivated copper films is studied. Stresses in copper films of thickness ranging from 40 to 1000 nm, deposited on quartz or silicon substrates and passivated with silicon oxide were measured by using the substrate curvature method. The thermal cycling spans a temperature range from -196 to 600 °C. It was observed that the passivated films do not exhibit a significant stress relaxation at high temperatures that is typically found in unpassivated films. The measured mechanical behavior was found to be rate insensitive within the heating/cooling rate range of 5–25 °C/min. Furthermore, a significant strain hardening during the course of thermal cycling was noted. Analyses employing continuum plasticity show that the experimentally measured stress–temperature response can only be rationalized with a kinematic hardening model. Analytical procedures for extracting the constitutive properties of the films that were developed on the basis of such model are presented. To emphasize the importance of the appropriate choice of constitutive model, results of finite element modeling for predicting thermal stresses in copper interconnects are presented. The modeling assumed parallel copper lines embedded within the combined low k/oxide dielectric materials. It was found that ignoring plastic strain hardening of copper can lead to significant errors in the stress and strain developed in the interconnect. © 2003 American Vacuum Society. View full abstract»

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  • High-resolution scanning tunneling microscopy imaging of Escherichia coli lysine transfer ribonucleic acid

    Page(s): 1265 - 1267
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    We have obtained high-resolution scanning tunneling microscopy (STM) images of Escherichia coli lysine transfer ribonucleic acid (tRNA) adsorbed onto Cu(111) substrates using a pulse injection method. One of the two arms of the L-shaped structure of the observed tRNA is longer than the other. Because hydrogen bonds that maintain the unique three-dimensional structure of tRNAs exist in the hinge region and in one arm of L-shaped structures that include the anticodon stem, we concluded that the longer arm in the L-shaped structure includes the anticodon stem, and the shorter arm includes the acceptor stem. This work supports the view that STM is a powerful tool for obtaining high-resolution images of biomolecules that are too difficult to crystallize. © 2003 American Vacuum Society. View full abstract»

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  • Etch mechanism and etch-induced effects in the inductively coupled plasma etching of GaN

    Page(s): 1268 - 1272
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    The inductively coupled plasma (ICP) processing of gallium nitride (GaN) using SF6/N2 and Cl2/Ar gas mixtures has been compared. ICP processing of GaN using SF6 and N2 mixture of 1:1 produces an optimized etch rate of 67 nm/min while five times higher etch rate of 314 nm/min is achieved using Cl2 and Ar mixture of 1:3. Etch mechanism studies indicate an ion-induced, coupled with a large chemical enhancement component for both SF6/N2 and Cl2/Ar inductively coupled plasma etching. From electrical diode characterization, an increase in electrical degradation with increasing dc bias in Cl2/Ar plasma is observed, while an improvement of diode characteristics is evident after etching in SF6/N2 plasma. X-ray photoelectron spectroscopy results indicate the presence of a significantly Ga deficient surface after etching GaN in Cl2 and Cl2/Ar plasmas. Correlation between etch mechanism and etch-induced damage results strongly indicates the existence of ion-induced chemical damage in the ICP etching of GaN in Cl2 and Cl2/Ar plasmas. © 2003 American Vacuum Society. View full abstract»

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  • Inductively coupled plasma reactive ion etching of ZnO using BCl3-based plasmas

    Page(s): 1273 - 1277
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    Etching characteristics of ZnO are investigated by means of inductively coupled plasma (ICP) reactive ion etching in BCl3-based plasmas. Etch rates are studied as a function of BCl3/Cl2/Ar chemistries, substrate temperature, ICP coil power, rf power, and working pressure. Surface profilometer, scanning electron microscopy, and atomic force microscopy are used to characterize etch rates, etch profiles, and the surface morphologies of etched samples. It is shown that the etch rate is determined by the BCl3 content in the plasma. Auger electron spectroscopy results demonstrate that the BCl3-based etching process produces negligible changes in the surface stoichiometry of ZnO. © 2003 American Vacuum Society. View full abstract»

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  • Transition from sub-Poissonian to super-Poissonian shot noise in planar cold cathodes

    Page(s): 1278 - 1285
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    In recently investigated cold cathodes, the energy distribution of the injected electron beam into vacuum is quite different from the hemi-Maxwellian distribution typical of thermionic cathodes. We use an ensemble Monte Carlo technique to study shot noise in planar cold cathodes in which the emission into vacuum is characterized by an average injection energy far in excess of the thermal energy typical of thermionic cathodes. For a sufficiently large voltage across the vacuum gap, the low frequency shot noise power spectrum of the anode current is found to agree with the Schottky classical result at low value of the cathode emission current. At the onset of current self-quenching due to space-charge effects, there is first a shot-noise reduction followed by a shot-noise enhancement in the anode current fluctuations for emission current densities far into the saturation regime. It is shown that this shot noise enhancement is due to large fluctuations in both energy and space of the maximum of the energy potential hump in front of the cathode. © 2003 American Vacuum Society. View full abstract»

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  • Lithographic characterization of the printability of programmed extreme ultraviolet substrate defects

    Page(s): 1286 - 1290
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    Extreme ultraviolet lithography, the leading next-generation lithography candidate, has now entered the commercialization phase. One of the most daunting challenges to the commercial viability of this technology is the issue of defect-free multilayer-coated reflection masks. Of great potential interest are multilayer deposition processes that can effectively reduce the printability of substrate defects, thereby relaxing substrate particle cleanliness requirements and facilitating the precoating substrate-inspection task. In particular, ion-beam deposition with additional ion-assisted polishing has been shown to drastically reduce defect sizes as seen after multilayer coating. Here we report on tests performed to lithographically characterize the effectiveness of defect smoothing and to verify defect printability models. The results show that normally printable 50 nm substrate defects are rendered nonprintable through the smoothing process. Moreover, a programmed defect fabrication method enabling controlled proximity printing tests is presented. © 2003 American Vacuum Society. View full abstract»

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  • Field emission electroluminescence on diamond and carbon nanotube films

    Page(s): 1291 - 1296
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    Field emission electroluminescence (FEEL), observed during field emission from polycrystalline diamond films for the first time, is initiated at field emission currents above 1 μA. The electroluminescence spectra exhibit the main luminescence peak at 482 nm. Typically, the luminescence intensity increases with the emission current. Although the FEEL observed in diamond and carbon nanotube films is poorly understood, it seems to be related to certain types of defects in the films. © 2003 American Vacuum Society. View full abstract»

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  • Scanning tunneling microscopy and spectroscopy studies of the oxide nanofilms on the stainless steel surface

    Page(s): 1297 - 1300
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    We have performed the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy measurements of the oxide nanofilms formed on stainless steel at 450 °C in oxygen partial pressures (p) of 1×10-7 and 1×10-9Torr. The STM observations reveal that the films grown at p of 10-7Torr consist of grains varying from 40 to 120 Å in size, while the films grown at p of 10-9Torr consist of grains of about 400 Å. We also show that the native oxide layers of stainless steel surfaces exhibit subgrain structures with grains of size in the range 30–60 Å. The current–voltage characteristics allow us to identify iron oxides, in the films grown at p of 10-7Torr, Fe3O4, and Fe2O3, whereas the films grown at p of 10-9Torr are pure Cr2O3. We thus conclude that oxidation at p of 10-9Torr develops complete Cr2O3 films with large grains, while oxidation at p of 10-7Torr develops iron-rich oxide films with small grains. © 2003 American Vacuum Society. View full abstract»

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  • Rectifying characteristics of sputter-deposited SiGe diodes

    Page(s): 1301 - 1305
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    Schottky and pn junction diodes with good rectifying characteristics have been prepared based on the polycrystalline SiGe (poly-SiGe) thin film deposited by the ion-beam-sputtering (IBS) technique. Boron and phosphorus diffusion techniques have been used to dope and crystallize as-deposited amorphous SiGe film. Rectification ratios as high as 4000 and 1800 have been achieved in Pt/n-poly-SiGe and Ti/p-poly-SiGe Schottky diodes, respectively, while rectification ratio higher than 1500 and breakdown voltage higher than 200 V have been achieved in poly-SiGe pn junction diodes. Schottky barrier height has been determined to be 0.62 and 0.59 eV for Pt/n-poly-Si0.81Ge0.19 and Ti/p-poly-Si0.81Ge0.19 contacts, respectively, which indicates that the band alignment of poly-SiGe may be substantially different from that of epitaxial SiGe. © 2003 American Vacuum Society. View full abstract»

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  • Rapid thermal annealing effects on the electrical behavior of plasma oxidized silicon/silicon nitride stacks gate insulators

    Page(s): 1306 - 1313
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    We present a comparative study of the electrical and structural characteristics of metal–insulator–semiconductor (MIS) devices using SiN1.55:H or SiN1.55:H/SiOx stacks as gate dielectrics, with the aim of improving the thermal stability of the SiN1.55:H/Si interface. The dielectrics were grown on Si by the electron cyclotron resonance plasma method. The stacks were produced by plasma oxidation of the Si surface, resulting in a thin layer of SiOx (PO–SiOx), followed by deposition of the SiN1.55:H layer. Afterwards, the samples were rapid thermally annealed (RTA) at temperatures ranging from 300 to 1000 °C. Some representative samples were studied by Fourier transform infrared spectroscopy to characterize the bonding structure of the SiN1.55:H/PO–SiOx stack and its evolution with the annealing temperature. The results were in good agreement with the well known model for suboxide evolution with the temperature: the formation of highly defective nanocrystalline Si clusters inside a high quality SiO2 matrix. This process takes place for RTA temperatures higher than 700 °C. This model also explains the results derived from C–V measurements, which show improvement of the PO–SiOx/Si interface as a result of the formation of the high quality SiO2 matrix. Additionally, the thermal stability improved with respect to the SiN1.55:H/Si interface, which suffers significant degradation when annealed above 600 °C, while devices made with the stacks are able to hold annealing temperatures up to 900 °C. On the other hand, the formation of nc-Si results in degradation of the reliability of the MIS devices. © 2003 American Vacuum Society. View full abstract»

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  • Modeling of vacancy flux due to stress-induced migration

    Page(s): 1314 - 1317
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    The stress-induced migration phenomenon is one of the problems related to the reliability of metal interconnections on semiconductor devices. The phenomenon causes voids and fractures to occur in the interconnections when the semiconductor devices are maintained at a high temperature for long periods. The purpose of this study is to theoretically clarify the temperature characteristics of the phenomenon. First, the residual thermal stress and the vacancy concentration in the interconnection with a slitlike void were calculated based on fundamental discussions on the residual thermal stress and the vacancy concentration in the interconnection without voids. Next, the vacancy flux to the slitlike void was considered at various temperatures. The theoretical results reveal that the temperature characteristic of the vacancy flux has a peak at a certain temperature which changes due to stress relaxation. Therefore, the temperature facilitating easy void formation shifts to a lower value with void expansion. Finally, the results of the theoretical analyses were compared with the results of high-temperature storage tests of samples. The theoretical results qualitatively agree with the results of the tests. © 2003 American Vacuum Society. View full abstract»

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  • Embossing of polymers using a thermosetting polymer mold made by soft lithography

    Page(s): 1318 - 1322
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    In this article we present a mechanical pattern transfer process where a thermosetting polymer mold instead of a metal, dielectric, ceramic, or semiconductor master made by conventional lithography was used as the master to pattern thermoplastic polymers in hot embossing lithography. The thermosetting polymer mold was fabricated by a soft lithography strategy, microtransfer molding. For comparison, the thermosetting polymer mold and the silicon wafer master were both used to imprint the thermoplastic polymer, polymethylmethacrylate. Replication of the thermosetting polymer mold and the silicon wafer master was of the same quality. This indicates that the thermosetting polymer mold could be used for thermoplastic polymer patterning in hot embossing lithography with high fidelity. © 2003 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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Meet Our Editors

Editor
Gary E. McGuire
International Technology Center