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

Issue 3 • Date May 1989

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Displaying Results 1 - 25 of 26
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • ArF excimer laser processing of plasma enhanced chemical vapor deposition silicon oxynitride thin films: Changes in deep ultraviolet transparency and composition

    Page(s): 429 - 436
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    A series of silicon oxynitride thin films prepared by plasma enhanced chemical vapor deposition was characterized by Fourier transform infrared (FTIR), wavelength dispersive x ray, and ultraviolet/visible spectroscopies. Changes in deep‐UV transparency and in composition of these and similar films on silicon, sapphire, and quartz wafers were then studied as a function of exposure to the output at 193 nm of an ArF excimer laser. Single‐pulse and high‐repetition‐rate exposures at different average pulse energies were performed. No changes were observed in the single‐pulse experiments, while the films increased in UV transparency and decreased in hydrogen content in the high‐repetition‐rate experiments. The effects observed were greater for films on quartz and sapphire, than for films on silicon. While not precluding a UV photon assisted mechanism, these results suggest that the changes in transparency and composition occur via local heating of the film. On the basis of a 10‐μm film, the laser exposure of the film on quartz increased its transparency at 200 nm from 1% T before irradiation to 10% T, a contrast of 10, while the film on sapphire increased from 10% T before irradiation to 25% T, a contrast of 2.5. The primary effect of the irradiation upon composition was to reduce both the NH and SiH contents; however, these results, when compared with data on unirradiated samples with a variety of compositions, indicate that it was the change in SiH content that most directly affected the UV transparency. Thus the photomodifiable, UV absorbing defect is associated with SiH bonds in the glass. Changes in other features of the FTIR spectra were also observed. Overall, the local modification of the UV transparency of silicon oxynitride thin films was readily achieved by current excimer laser technology. While the effect occurred for films on silicon, the results show that the greatest contrast at the low- - est laser fiuence would be achieved in heavily hydrogenated films on quartz. View full abstract»

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  • Window cleaning and fluorine incorporation by XeF2 in photochemical vapor deposition

    Page(s): 437 - 442
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    A new method of maintaining window transparency in photochemical vapor deposition (photo‐CVD) has been developed in which the window is continuously etched clean during the deposition process. This technique is demonstrated in the deposition of a‐Si:H(F) by direct photo‐CVD of Si2H6 using XeF2 as an etchant. XeF2 is also used to clean the chamber between runs. Fluorine may be incorporated in the films via either gas phase or surface reactions with XeF2. The optoelectronic quality of a‐Si:H:F decreases with F incorporation, which suggests that this technique may be particularly suited to the deposition of μc‐Si:H(F) and a‐SiGe :H(F) and a‐SiC :H(F) alloys wherein fluorinated process gases are preferentially employed. View full abstract»

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  • Silicon deposition in diode and hollow‐cathode systems

    Page(s): 443 - 449
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    Deposition of silicon from silane discharges is studied in diode and hollow‐cathode systems. Using the single‐target (‘‘diode’’) configuration as a reference, it is shown that discharge confinement results in substantial increases in deposition rate and efficiency. The ‘‘target‐confined hollow cathode’’ exhibits the best performance; in comparison with a diode discharge at 2‐Pa silane pressure, rates are 20–50× higher at fixed applied rf voltage and 5× higher at fixed input power density. Alternatively, for a fixed deposition rate this new configuration allows the applied rf voltage to be reduced by ∼10 and the power density to be reduced by ∼20, again at a 2‐Pa pressure. Planarizing films are obtained at low pressures and/or low gas flows, while high pressures yield more directional deposition over surface steps. Good agreement with this profile study, and with our deposition rate data, is given by a model wherein ion bombardment is the dominant film forming and etching mechanism at low pressures, and wherein trapping of both excited neutrals and of electrons may contribute to the high efficiencies and rates observed. View full abstract»

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  • Manganese oxide microswitch for electronic memory based on neural networks

    Page(s): 450 - 454
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    High‐density, nonvolatile, associative electronic memories based on neural network models require large arrays of highly uniform, small area, resistive connections (synapses). Such passive, two terminal resistors (very weak connections, 105 to 106 Ω for a 1000×1000 matrix) are uncommon in the current very large scale integration (VLSI) technology. We report on a solid‐state, resistance tailorable, programmable‐once, binary, nonvolatile memory switch based on manganese oxide (MnOx) thin films. MnOx exhibits irreversible memory switching from a conducting (on) to an insulating (off) state, with the off to on resistance ratio of greater than 104. The switching mechanism is current triggered chemical transformation of a conductive MnO2-Δ to an insulating Mn2O3 state. The energy required for the ‘‘switching’’ is of the order of 4 to 20 nJ/μm2. Apart from the high density information storage in such MnOx microswitch arrays as programmable read only memory (PROM), the ‘‘tailorable MnOx fusible links’’ may also be suited for post‐fabrication, ‘‘function‐specific programming’’ of microcircuit architectures. View full abstract»

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  • Thermal oxidation of silicon nitride and silicon oxynitride films

    Page(s): 455 - 465
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    The oxidation behavior of low‐pressure chemical vapor deposition silicon oxynitrides was investigated for layer compositions ranging from that of pure nitride to oxynitride with an atomic ratio of O/N=1. Oxidations were performed at 850–1000 °C in ambients having different H2O/O2 flow ratios. Rutherford backscattering spectrometry and elastic recoil detection were employed to quantify the increase in oxygen content of the films upon oxidation. Hydrogen profiles in oxidized samples were measured using nuclear reaction analysis and elastic recoil detection. We observed that the oxidation rate for either oxynitride composition is nearly two orders of magnitude smaller than that of silicon. Linear oxidation kinetics were measured for the conditions applied in this study, which are indicative of a reaction‐controlled process. The activation energy of this process was determined to be 2 eV for silicon nitride and appeared to decrease with growing oxygen content in oxynitrides. The hydrogen profiles measured in oxidized samples showed a peak at the oxide/oxynitride interface. The size of this peak varies with oxidation conditions and film composition. A reaction mechanism for the oxidation of (oxy)‐nitride is proposed that relates the observed hydrogen accumulation to Si–NH and Si–OH groups at the oxidizing interface. The measured acceleration of the oxidation rate induced by adding small amounts of HCl to the ambient is interpreted in terms of enhanced transport of NH species to the surface. This effect is greatest for pure nitride and diminishes with increasing oxygen content in oxynitride material. View full abstract»

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  • Lateral confinement of microchemical surface reactions: Effects on mass diffusion and kinetics

    Page(s): 466 - 480
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    This paper investigates the effects of lateral confinement on the chemical kinetics of surface reactions that involve diffusive mass transport in the phase above the surface. The phenomena to be expected are illustrated by a theoretical treatment of the reaction types A+D⇄2C or B⇄A+2C, where A is a surface species, and B and C are both gaseous species. The case explored is one in which the back reaction due to the product species C is important. It is assumed that species B is the major constituent of the vapor, and remains so throughout the course of the reaction. The spatial profiles of A and C as a function of time are found by the use of a Green’s function formalism and evaluated numerically for illustrative cases. The results of the calculations provide a possible explanation of the drastic rate enhancement produced in some cases by lateral confinement resulting from the use of focused energy beams. The possibility of dramatic lateral variation of chemical kinetics due to strong concentration gradients of the product species is demonstrated. The results could have application to a broad class of transportlimited surface processing reactions confined by focused beams or by lithographic masking. View full abstract»

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  • Photoemission study on initial stage of GaAs growth on Si

    Page(s): 481 - 486
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    Initial stages of GaAs growth on Si by molecular‐beam epitaxy were investigated by in situ photoemission spectroscopy. The obtained results suggest that the first layer on Si is the As layer, and that the electronic structure of the Si surface exposed to As4 depends on the exposure temperature. The interface structure between GaAs epilayers and Si substrates is discussed in terms of the initial process of the growth. View full abstract»

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  • Monte Carlo calculations of the beam flux distribution from molecular‐beam epitaxy sources

    Page(s): 487 - 490
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    Flux distributions from Knudsen cell sources used in molecular‐beam epitaxy have been determined using Monte Carlo techniques. The increased beaming effect as the cell empties, which produces an increase in film thickness variation across the substrate, is found to be less pronounced than the widely used analytic theory of Clausing predicts. Tilting a full cell is shown to produce flux distributions which are asymmetric about the cell axis, but the effect decreases as the tilted cell empties. View full abstract»

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  • Defect generation by Schottky contacts on n‐GaAs

    Page(s): 491 - 496
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    We studied the influence of different fabrication techniques on the electrical properties of n‐GaAs Schottky contacts. In comparison to the conventional technology for Schottky metallizations represented by wet chemical etching and thermal evaporation the pretreatment of the semiconductor surface was performed either by wet chemical or Ar+ etching and the metallization step by evaporating, sputtering or by ion beam contacting. Diodes prepared by such procedures show very different electrical gehavior but no monotonic dependence of the barrier height from preparation parameters, especially from the ion energy. Whereas ion cleaning at 500 V results in barrier heights of ∼0.3 eV, cleaning at 1000 V gives a barrier of 0.4 eV. The implantation of the contact metal results in a barrier of 0.65 eV. DLTS measurements reveal a tendency of relationships between the barrier height and the dominating deep levels, thus supporting the model of Fermi levels pinning by defect states. DLTS further indicates a sensitive reaction of the EL 2 center on the metallization procedure. View full abstract»

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  • Electrical characterization of in situ fabricated n+‐Si/GaAs interfaces

    Page(s): 497 - 501
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    A very low Schottky barrier height of 0.1 eV for an in situ fabricated n+‐Si/GaAs interface is verified by C–V measurement. The height is approximately equal to the conduction‐band discontinuity of the interface, in spite of a high density of misfit dislocations (lattice mismatch: 4%). Thermal stability of the interface is assured for annealing temperatures up to 850 °C. As an example application, an AlGaAs/GaAs metal–insulator semiconductor‐like heterostructure field effect transistor using n+‐Si for gate material is successfully fabricated. View full abstract»

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  • The addition of Ni in AuZn gate Ohmic contacts for InP junction field effect transistors

    Page(s): 502 - 504
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    The fabrication and characteristics of AuZn/Ni/Cr/Au and AuZn/Ni/TiW/Au gate Ohmic contacts for InP junction field effect transistors (JFET’s) are reported. Auger electron spectroscopy sputter‐depth profiles reveal substantial Ni interdiffusion at the metal–InP interface after heat treatment at 410 °C. The addition of a Ni layer significantly improves the adhesion of the contacts and a TiW barrier layer effectively maintains the conductivity of the gate metallizations after heat treatment. The specific contact resistance of the JFET gate structures is measured to be as low as 2×10-5 Ω cm2, which is the lowest value reported to date for contacts to p‐type InP. InP JFET gate‐drain diodes fabricated with the AuZn/Ni/TiW/Au gate contact exhibit a leakage current of ∼40 nA at -8 V for a 1μm×150 μm gate and a reverse breakdown voltage of 17.5 V at 25 μA. The contacts are shallow, as evidenced by the quality of the p+/n junctions fabricated, and thus are suitable for use in InP JFET structures where thin p+ regions are utilized. View full abstract»

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  • Film redeposition on vertical surfaces during reactive ion etching

    Page(s): 505 - 511
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    During reactive ion etching of tantalum silicide and polysilicon layers in a chlorine based chemistry it is observed that a film (15–20 nm) is deposited on vertical surfaces of etched structures. This film is even present after common resist strip processes. This film is analyzed by Auger electron spectroscopy and transmission electron spectroscopy, and the formation mechanism is investigated. It is shown it is composed of silicon dioxide sputtered from dielectric layers lying under the etched silicide and poly Si layers. Variables influencing the formation of the residual sidewall film are analyzed. It is demonstrated that the observed residual films are not involved in the anisotropic etch characteristics before the silicide or poly Si layer are etched through. It is further demonstrated that a carbon based polymer film or inhibition layer must be responsible for the anisotropic etch profile of the tantalum silicide layer. This second carbon based film is formed only with a sufficient amount of photoresist in the etching chamber. View full abstract»

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  • Analysis of surface contaminants on gallium arsenide and silicon by high‐resolution time‐of‐flight secondary ion mass spectrometry

    Page(s): 512 - 516
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    High‐performance time‐of‐flight secondary ion mass spectrometry (TOF SIMS); characterized by high mass resolution, extremely high sensitivity, and high dynamic range, has been applied to surface analysis of GaAs and Si wafers. Mass separation of metal and hydrocarbon ions of identical nominal masses allows the unambiguous detection of metal contaminants, even in the presence of heavy surface contamination by hydrocarbons. In favorable cases surface sensitivities in the ppm range are achieved. Quantitative element analysis and detection of molecular surface contaminants are possible. View full abstract»

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  • Surface and in‐depth analysis of hydrogenated carbon layers on silicon and germanium by mass and electron spectroscopy

    Page(s): 517 - 528
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    Hydrogenated amorphous carbon layers (a‐C:H) formed by plasma deposition on silicon and germanium substrates have been depth profiled by 5‐keV Ar+ sputtering and analyzed with Auger and photoelectron spectroscopy, secondary ion and secondary neutral mass spectroscopy. Reference data have been established for quantitative analysis, compound identification and the exclusion of the experimental artifact of ion‐bombardment induced carbide formation. The composition, binding state and some structural parameters of a‐C:H layers on Si and Ge substrates have been investigated for various deposition parameters. In each case, a carbidic phase is found in the interface to the substrate. The adhesion of the layers depends mainly on the overlap of this interfacial carbide with the adjacent regions, whereas the hardness of the layers can be characterized by the structure and composition of the layer itself. Changes caused by tempering of the layers are also discussed. View full abstract»

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  • In situ ellipsometry during plasma etching of SiO2 films on Si

    Page(s): 529 - 533
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    The etching of SiO2 films on a Si substrate in an rf plasma in CF4 has been studied with in situ ellipsometry. The etch rate was measured as a function of flow, rf power and pressure. An accurate analysis of the experimental data using numerical simulations based on multilayer models has yielded information both on the refractive index of the etched SiO2 film and on the existence of a top layer. It could be established that a layer is present on top of the SiO2 during etching, which is probably caused by roughening of the SiO2 layer. Furthermore at high pressures (≫8 Pa) it was demonstrated that after the complete removal of the SiO2 film a polymer layer starts growing on the Si substrate. View full abstract»

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  • Modeling of sloped sidewalls formed by simultaneous etching and deposition

    Page(s): 534 - 541
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    Dry etching of microstructures in various materials has sometimes resulted in sidewalls which slope away from the mask edge. In this paper we model this phenomenon using a process of simultaneous isotropic deposition and anisotropic etching which has been shown by others to give good qualitative agreement with observed etched profiles. A simple analytical relationship between the etch and deposition rates of the deposited material is given and used to deduce a number of features of sloped sidewall etching. We compare these predictions with some experimental results gained using metal based compounds as the deposit material. We provide evidence suggesting that this metal compound deposition can explain a number of previous observations of sloped sidewalls. View full abstract»

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  • Magnetron ion etching with CF4 based plasmas: Effects of magnetic field on plasma chemistry

    Page(s): 542 - 546
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    Etching plasmas based on CF4 have been studied in a magnetron ion etching (MIE) system. Optical emission and mass spectra were measured as a function of applied power, pressure, and gas composition. Electrical probes were used to measure the plasma floating potential and the dc self‐bias of the rf electrode. The magnetic field has an effect not only on the physics of the plasma (ion density, plasma impedance, etc.) but also on the chemistry. Two regimes of operation are found to exist. Under typical high‐power MIE operating conditions, the species present in the plasma tend to be more highly dissociated than in a conventional reactive ion etching (RIE) plasma. As a consequence, the tendency for C–F polymer to form on etched Si surfaces is suppressed and selective etching of SiO2 over Si does not occur. At lower powers, the plasma characteristics and etching response revert back to RIE‐like behavior as the degree of dissociation decreases. The implications for etching processes are discussed. View full abstract»

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  • Generation of low‐energy neutral beams and radiation damage of SiO2/Si by neutral bombardment

    Page(s): 547 - 550
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    In order to apply to neutral beam etching, several hundred eV neutral beams have been generated by charge exchange reaction using a magneto‐microwave plasma ion source. The charge exchange cross sections for Ar+ and Kr+ are unexpectedly small, whereas the cross section for Ne+ of 300 eV is 1.7×10-15 cm2 in good agreement with published results. The small cross sections for Ar+ and Kr+ in the present experiments are explained in terms of a nonresonant charge exchange scheme. The capacitance–voltage (C–V) measurements show that the radiation damage to SiO2/Si by Ne0 neutral beam bombardment is much less than those by Ne+ ion beam and by vacuum ultraviolet photons. Consequently, the neutral beam process is a promising method for charge‐free and low‐damage surface processes. View full abstract»

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  • Polycide reactive ion etch: Enhanced circuit performance through profile modification

    Page(s): 551 - 555
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    A three step, ‘‘profile flexible’’ polycide etch was developed which allowed polycide profiles ranging from vertical to controlled undercut. A pressure controlled HCl+CF4 overetch was achieved which enabled profile adjustment as desired. Vertical and undercut (0.25 μ per side) polycide profiles were fabricated and speed comparisons accomplished. The majority of devices with undercut profiles exhibited an increase in speed from 20.8 to 23.8 MHz as compared to those devices with vertical profiles. View full abstract»

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  • Dry etch induced damage in GaAs investigated using Raman scattering spectroscopy

    Page(s): 556 - 560
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    Raman scattering spectroscopy is used to probe the surface electrical properties (surface depletion width) of GaAs after dry etching in either a reactive ion etching (RIE) system or a remote plasma system. A variety of etch gases (argon, helium, Freon 12, HCl) and biases (-80 to -350 V) are used to examine physically and chemically induced damage. Through the use of wet etches, the dry etch induced damage was observed to be within ∼300 Å of the surface. In the RIE system, etching with argon and helium causes the depletion width to widen, with helium inducing a greater effect. A remote plasma does not cause a change in the depletion width, indicating an absence of energetically damaging species. In contrast to inert gases, etching with reactive gases in both systems reduces the effective surface charge. View full abstract»

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  • Dependence of the dissolution characteristics of As2S3 as a photoresist on the condensation rate and evaporation temperature

    Page(s): 561 - 564
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    The conditions of evaporation and condensation of thin layers of arsenous sulfide (As2S3) are described. The difference in the selective dissolution of the illuminated and nonilluminated areas found reveals a possibility for the successful application of As2S3 as an evaporated photoresist for microphotolithographic purposes. In this connection the influence of the condensation rate (Vc) and evaporation temperature (tevp) on the selective dissolution is studied. It is shown that the selective dissolution is negligibly influenced by the condensation rate but strongly affected by the temperature of As2S3 evaporation. View full abstract»

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  • Characterization of diazonaphthoquinone–novolac resin‐type positive photoresist for g‐line and i‐line exposure using water‐soluble contrast enhancement materials

    Page(s): 565 - 568
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    We describe the characterization of conventional diazonaphthoguinone–novolac resin‐type positive photoresist for g‐line (436‐nm) and i‐line (365‐nm) exposure using water‐soluble contrast enhancement materials. In the experiments, the Rayleigh’s theoretical resolution and contrast enhancement capability of the water‐soluble contrast enhancement materials were set to be equal between the each wavelength exposure. As a result, the pattern profiles of the resist were better, however, the latitude of depth of focus was worse for g‐line exposure than for i‐line exposure. Mask linearity had no difference between them. It was found that the improvement of the pattern profiles for i‐line exposure was achieved by using a higher photobleachable photoresist at i‐line. View full abstract»

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  • Observation of internal structure of a positive photoresist image using cross‐sectional exposure method

    Page(s): 569 - 571
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    The internal structure of a novolak/quinonediazide type positive photoresist image was observed using a cross‐sectional exposure method. On the surface of a photoresist image, a photochemically inert layer was detected which does not return to diazo and phenolic compounds with acid treatment. This shows that this layer does not consist of the azoxy compounds. Fourier transform infrared spectrum indicates that this layer includes azocoupling reaction products. It was also found that the formation of the photochemically inert layer and the dissolution of the layer takes place simultaneously at the development front and a resist image is formed during the competition between these two reactions. View full abstract»

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  • Resolution characteristics of a novel silicone‐based positive photoresist

    Page(s): 572 - 575
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    A novel silicone‐based positive photoresist (SPP) is developed for a two‐layer resist system. SPP is composed of an alkali‐soluble silicone polymer (APSQ) and a diazonaphthoquinone compound as a sensitizer. APSQ is newly synthesized by means of acetylation of polyphenylsilsesquioxane (PSQ). A fine SPP pattern below 0.5 μm can be fabricated with a g‐line stepper (NA=0.6) using a two‐layer resist system. Moreover, a 0.4 μm line/space pattern is successfully fabricated at a defocus of ±0.4 μm. The high oxygen reactive ion etching (O2RIE) resistance of SPP makes possible the fabrication of a submicron pattern with a high aspect ratio in a two‐layer system. Pattern width loss can be negligible during O2RIE of a 2 μm thick bottom resist when a 0.6 μm thick SPP is used as the top imaging layer. 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