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

Issue 5 • Date Sep 2009

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Displaying Results 1 - 25 of 44
  • Effect of sidewall passivation in BCl3/N2 inductively coupled plasma etching of two-dimensional GaAs photonic crystals

    Page(s): L21 - L24
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    The effect of surface passivation in BCl3/N2 inductively coupled plasma reactive-ion etching of GaAs-based photonic crystals (PhCs) was investigated. It is shown that sidewall passivation is crucial for achieving cylindrical, vertical PhC holes, where the exact shape of the hole is controlled via the N2 content in the plasma composition. The achieved quality of PhC membrane cavities was established by optical characterization of such cavities incorporating site-controlled quantum wires as integrated light source. View full abstract»

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  • Effects of Ga+ milling on InGaAsP quantum well laser with mirrors milled by focused ion beam

    Page(s): L25 - L27
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    InGaAsP/InP quantum well ridge waveguide lasers were fabricated for the evaluation of Ga+ focused ion beam milling of mirrors. Electrical and optical properties were investigated. A 7% increment in the threshold current, a 17% reduction in the external quantum efficiency, and a 15 nm blueshift in the emission spectrum were observed after milling as compared to the as-cleaved facet result. Annealing in inert atmosphere partially reverts these effects, resulting in a 4% increment in the threshold current, an 11% reduction in the external efficiency, and a 13 nm blueshift with the as-cleaved result. The current-voltage behavior after milling and annealing shows a very small increase in leakage current, indicating that optical damage is the main effect of the milling process. View full abstract»

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  • Analysis of dielectric constant of a self-forming barrier layer with Cu–Mn alloy on TEOS-SiO2

    Page(s): L28 - L31
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    A Cu–Mn alloy film was deposited on SiO2 to self-form a diffusion barrier layer of MnOx at their interface. Transmission electron microscopy revealed that the barrier layer was formed not on the Cu alloy side but on the SiO2 side. Capacitance-voltage measurement revealed the decrease in the dielectric constant of the barrier layer from 11.4 to 5.1 with increasing annealing temperature. The obtained results indicated that the self-forming barrier layer with Cu–Mn is an excellent barrier layer without posing any negative influences on the interconnect line resistance and on the insulator capacitance. View full abstract»

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  • Impact of in situ SiNx layer grown with metal organic vapor phase epitaxy on the electrical and optical properties of AlN/GaN metal insulator semiconductor field effect transistor structures

    Page(s): 2079 - 2083
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    AlN/GaN metal insulator semiconductor field effect transistor structures (MISFETs) with and without in situ SiNx were investigated. The in situ SiNx passivation layer was deposited using silane and ammonia immediately after the AlN/GaN heterostructure growth by metal organic vapor phase epitaxy. Superior Ohmic quality and improvement of the dc and rf characteristics were obtained with devices made on passivated layers in comparison with unpassivated devices. This enhancement of electrical characteristics is attributed to the fact that the in situ SiNx suppresses the depletion of the two-dimensional electron gas (2DEG) and air exposure while processing. The studies of the in situ SiNx quality and its implication to the 2DEG conducted with Hall, transmission line measurements, capacitance-voltage (C-V) measurements, and photoluminescence measurements showed that the electrical and optical characteristics of AlN MISFET structures were substantially degraded or changed after SF6 plasma treatment. View full abstract»

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  • Analysis of thermally activated kinetics and uniformity of photoresist ashing process on 300 mm wafers

    Page(s): 2084 - 2090
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    Ashing rate and nonuniformity are the usual parameters used for the evaluation of industrial ashers. A detailed study of the wafer temperature and of its effect on the two contributions to the diminution of photoresist thickness, namely, shrinkage and chemical reactions, gives a solid ground for understanding the variations of ashing rate with process conditions. It is in particular shown how variations of shrink with temperature affect the measured ashing rate. This analysis serves as a basis for proposing tests that could be used as “standards” and ease the objective comparison of industrial ashers, based on real performances. They include a determination of ashing rate on hard-baked wafers for characterization of radical density, a demonstration of the ion-free nature of the process, and a determination of wafer heat-up rate. Due to the very reproducible nature of the distribution of ashing rates over a wafer, it is argued that the “range” parameter should be used over standard deviation for the measurement of nonuniformity within a wafer. View full abstract»

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  • Effects of exposure time on defects and demolding force in soft ultraviolet nanoimprint lithography

    Page(s): 2091 - 2096
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    Based on a contact process, the ultraviolet (UV) nanoimprint process can overcome the linewidth limit of conventional photolithography caused by the diffraction effect. However, the contact between the mold and resist may introduce various defects to the two components. Some researchers have investigated the defects that emerge in the imprint process, such as particle contamination and curing shrinkage of the resist. However, the curing process of the resist itself should be studied because the curable resist is the carrier of the pattern transfer and the replication is accomplished by its shape remodeling. In this article, the authors focus on the effects of exposure time on the defects and demolding force in the soft UV imprint process. The replications are made by a soft polydimethylsiloxane mold under the same process parameters except that the curing time is different. Moreover, the curing degree of the resist and the value of the demolding force under various curing doses are measured. A mechanical model is established to analyze the behavior of the resist, which transitions from a liquid to solid stage by stage, and will help the authors to understand the above effects. By analyzing the relationships among the model of the resist, curing degree, demolding force, and resultant defects in the experiments, they propose a curing window, within which the curing time in the imprint process helps to remove defects in the shaped patterns and soft mold. Finally, using the optimized curing time, the best replicated patterns with 100 nm features are obtained. View full abstract»

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  • Inductively coupled plasma reactive ion etching of bulk ZnO single crystal and molecular beam epitaxy grown ZnO films

    Page(s): 2097 - 2101
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    Dry etching processes for bulk-single crystal zinc oxide (ZnO) and molecular beam epitaxy (MBE) grown ZnO have been investigated using inductively coupled plasma (ICP) of CH4 and SiCl4 based plasma chemistry. The CH4-based chemistry showed a higher etch rate than the SiCl4 based chemistry, presumably due to the formation of highly volatile metal organic zinc compound. The influence of base pressure, radio frequency table power, and ICP power on etch rate was studied. Auger electron spectroscopy has been employed to examine the surface stoichiometry of etched ZnO using both plasma chemistries. Furthermore, with optimized process parameters, the effect of plasma etching on the optical properties of MBE grown ZnO film is studied. An enhancement of the band edge luminescence along with almost complete suppression of defect level luminescence in hydrogen-containing plasma treated ZnO film has been observed. View full abstract»

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  • Enhancement of operation temperature of InAs/GaAs quantum-dot infrared photodetectors with hydrogen-plasma treatment

    Page(s): 2102 - 2105
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    Postprocess hydrogen treatment is performed over fabricated ten-period InAs/GaAs quantum-dot infrared photodetectors. While keeping similar spectral responses at the same applied voltage, a reduced dark current is observed for the H-plasma-treated device, which is attributed to the suppression of surface leakage-current induced by surface damage during device processing. The significant reduction in dark current also enhanced the operation temperature of the device up to 100 K. Also observed are the smoothed-out mesa edges after the H-plasma treatment, which results in trapezoidal mesa edges. In this case, a longer propagation length in the device of the reflected incident light at the mesa edge would enhance the normal-incident absorption ratio of the H-plasma-treated device. View full abstract»

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  • Growth scaling of metal oxide columnar thin films deposited by glancing angle depositions

    Page(s): 2106 - 2111
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    The self-similar growth scaling of TiO2, SiO2, and Al2O3 vertical post-glancing-angle deposited films has been characterized. Films were deposited using three deposition systems and four different deposition conditions. For a given film, good agreement was found with a self-similar growth model w(h)=w0hp. For the materials studied here, p was found to increase with deposition angle, in contrast to some previous literature reports. Values of 0.017±0.005, 0.011±0.005, and 0.014±0.005 deg-1 were found for TiO2, SiO2, and Al2O3, respectively. View full abstract»

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  • Effect of Ta buffer layer and thickness on the structural and magnetic properties of Co thin films

    Page(s): 2112 - 2116
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    Single Co and Ta/Co bilayers were grown on Si(100) substrates in a magnetron sputtering system. The effect of Ta buffer layer and the thickness of Co layer on the structural and magnetic properties of the Co layers has been studied. A single Co layer shows a textured structure above thickness of 40 nm according to the x-ray diffraction (XRD) pattern. The magnetic properties of Co layers depend significantly on the thickness of the films. Ta grows as highly textured β-Ta (tetragonal) phase on Si with a smooth surface. The XRD and atomic force microscopy results show that the Ta buffer layer improves the structural properties dramatically, resulting in a strongly textured and smoother surface morphology. The Ta layer also affects the magnetic properties of Co layers to a large extent, especially inducing an in-plane anisotropy in thin Co films. View full abstract»

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  • Mechanism of reducing line edge roughness in ArF photoresist by using CF3I plasma

    Page(s): 2117 - 2123
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    The roughening mechanism of ArF photoresist during etching was investigated to find out why CF3I gas reduces the line edge roughness (LER) in the photoresist pattern better than CF4 gas. Since the plasma of reactive ion etching (RIE) consists of ultraviolet (UV) photons, radicals, and ions, the authors used a UV lamp and a neutral beam source for evaluating the effect of different plasma compositions on the photoresist roughness. The roughness was found not to increase only by UV photons or F radicals, but increase under the CF4 RIE plasma which has both UV photons and F radicals. A C–F modified layer was generated on the resist surface because the UV damaged CO bonds reacted with F radicals and the resist surface became softer and shrank. Since CF3I plasma has a lower UV intensity and fewer F radicals compared with CF4 plasma, the shrinkage on the sidewall of the photoresist was suppressed and resulted in a smaller LER when this plasma was used. View full abstract»

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  • Structural and electrical properties of metal contacts on n-type ZnO thin film deposited by vacuum coating technique

    Page(s): 2124 - 2127
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    The authors report on fabrication and characterization of Al and Pt metal contacts on ZnO thin films grown on ITO coated glass substrates using thermal evaporation technique. The structural and surface properties of ZnO thin film were studied by using x-ray diffraction and atomic force microscopy techniques. Atomic force micrographs revealed that ZnO microparticles have perfect pyramidal shape with small surface roughness (average rms value of 3 nm). The current voltage characteristics of Pt/ZnO and Al/ZnO contacts were studied by scanning tunneling microscopy. The Pt contact on ZnO thin films behaves as a rectifying contact with a barrier height of 0.72 eV, while Al contact on ZnO thin film turns out to be Ohmic in nature. The band gap of ZnO thin film was estimated to be 3.10 eV from absorption spectroscopic measurements. View full abstract»

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  • Transparent dual-gate InGaZnO thin film transistors: OR gate operation

    Page(s): 2128 - 2131
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    Transparent dual-gate (DG) InGaZnO4 thin film transistors for OR logic operation were fabricated on a glass substrate. A 100-nm-thick SiO2 layer used as both top and bottom gate dielectrics was deposited by plasma enhance chemical vapor deposition at 200 °C. Compared to bottom gate, top gate thin film transistors (TFTs) exhibited better device performance with higher saturation mobility, drain current on-to-off ratio, lower threshold voltage, and subthreshold gate-voltage swing. This improved performance was mainly attributed to low process-induced damage or low parasitic capacitance between gate and source/drain and low parasitic resistance between channel and source/drain in top-contact TFT configuration (coplanar type). DG-mode TFTs showed saturation mobility of ∼16.9 cm2 V-1 s-1, drain current on-to-off ratio of ∼1×106, subthreshold gate-voltage swing of ∼0.33 V decade-1, and threshold voltage of ∼1.25 V. The results demonstrate that DG InGaZnO4 TFTs are effective in improving the device performance because the channel layer is modulated independently by a top or, bottom gate signal and are well suited for OR gate operation. View full abstract»

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  • Plasma treatment methods to improve indium bump bonding via indium oxide removal

    Page(s): 2132 - 2137
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    Flip chip hybridization, also known as bump bonding, is a packaging technique for microelectronic devices which directly connects an active element or a detector to a substrate readout face down, eliminating the need for wire bonding. Indium bump technology has been a part of hybridization for many years and has been extensively employed in the infrared imager industry. However, obtaining a reliable, high yield process for high density patterns of bumps can be quite difficult in part due to the tendency of the indium bumps to oxidize during exposure to air. In this study, plasma, thermal, and wet chemical methods were screened to determine their ability to remove indium oxide from indium bumps. A novel two-step plasma process using methane, argon, and hydrogen was developed that removes indium oxide from indium bumps after prolonged air exposure while maintaining a low sample temperature. This method was tested by fabricating a fully hybridized scientific grade visible complementary metal oxide semiconductor detector and imaging a standard test pattern. View full abstract»

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  • Highly sensitive positive-working molecular resist based on new molecule

    Page(s): 2138 - 2144
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    A highly sensitive positive-working molecular resist based on a new molecule, 1,3,5-tris[p-(p-hydroxyphenyl)-phenyl]benzene (THTPPB), was designed and synthesized. THTPPB showed a high glass transition temperature (Tg) of 145 °C. Some acid-leaving groups were attached to THTPPB to realize positive-working performance developed by an alkaline aqueous developer. 70 nm line-and-space (1:1) positive tone pattern was fabricated with high sensitivity (≪1 μC/cm2) by the exposure to a low-energy electron beam (5 keV). View full abstract»

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  • Pd/Ru/Au Ohmic contacts to InAlSb/InAs heterostructures for high electron mobility transistors

    Page(s): 2145 - 2152
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    The authors describe a Pd/Ru/Au Ohmic contact with enhanced thermal stability over the more commonly used Pd/Pt/Au Ohmic contact for InAlSb/InAs high electron mobility transistors. Transmission electron microscopy shows that reaction between Pd and the semiconductor begins in samples even before they are annealed. Decreases in contact resistance are correlated with increasing reaction between Pd and the semiconductor for annealing and aging at 175–225 °C for 3 h or 1 week. Small voids form in severely aged samples but do not increase the contact resistance. The Ru diffusion barrier is never observed to react with any other materials in either the contact or the semiconductor, and Au remains isolated from the Pd-bearing reaction products and semiconductor. View full abstract»

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  • Controlled etching and regrowth of tunnel oxide for antenna-coupled metal-oxide-metal diodes

    Page(s): 2153 - 2160
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    The authors have designed a new procedure for fabrication of infrared (IR) sensors. These sensors consist of a dipole antenna coupled with a metal-oxide-metal (MOM) (AlAlOxPt) diode. The surface of electron beam evaporated Al, serving as one of the electrodes, is cleaned using an Ar plasma, followed by in situ controlled growth of the tunneling oxide, AlOx. The antenna, its leads, and the overlap of the Al and Pt electrodes that defines the MOM overlap area are all defined using electron beam lithography. The MOM overlap area of these devices is as small as 50×80 nm2. Features of our process include the use of dissimilar metals for the formation of the MOM diode, small MOM diode size, and controlled etching and regrowth of the tunneling oxide. A CO2 laser at 10.6 μm was used for the IR characterization of these sensors. Current-voltage and IR measurements are presented. The normalized detectivity (D*) for these devices was found to be 2.13×106 cmHz1/2W-1. View full abstract»

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  • Nonlinear large deflection of nanopillars fabricated by focused ion-beam induced chemical vapor deposition using double-cantilever testing

    Page(s): 2161 - 2165
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    Nanopillars with nanosized diameter and microsized length can be constructed by chemical vapor deposition using a focused ion beam. For a pillar consisting of an outer amorphous carbon ring and an inner gallium core, we performed the bending tests using the unique double-cantilever specimen joining two pillars together by an electron-beam deposition technique in a scanning electron microscope. The precise load-deflection curves indicate that the pillars have a nonlinear softening region after the linear response as the diameter increases. However, pillars finally become extremely hardened at the large deformation. Thus, the pillar intrinsically possesses much more flexibility and stable deflection for bending than expected, in contrast to tensile deformation. The bending rigidity obtained by the infinitesimal deflection corresponds well to that by the resonance vibration tests reported so far. It also certifies that the proposed double-cantilever bending method can maintain high accuracy for the nanoscaled materials testing. View full abstract»

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  • Cu-plated through-wafer vias for AlGaN/GaN high electron mobility transistors on Si

    Page(s): 2166 - 2169
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    A robust method for creating Cu-plated through-wafer vias for AlGaN/GaN high electron mobility transistors on Si is reported. The initial 70 μm deep vias with diameters of 50 μm are created by deep Si reactive ion etching, followed by pulsed Cu electroplating and mechanical polishing to planarize the metal. This is an attractive approach for increasing the effective thermal conductivity of the composite substrate for very high power device applications. View full abstract»

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  • Fabrication and optical properties of Ti-doped W18O49 nanorods using a modified plasma-arc gas-condensation technique

    Page(s): 2170 - 2174
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    In this study, Ti-doped W18O49 nanorods were prepared without any templates or catalysts using a modified plasma-arc gas-condensation technique. Structure investigations were conducted and the optical properties of the as-prepared nanorods were characterized by field emission gun scanning electron microscope, high-resolution transmission electron microscope, x-ray diffractometer, x-ray photoelectron spectroscope, micro-Raman, and ultraviolet (UV)-visible spectrometers. The experimental results showed that the diameter and the length of the as-prepared nanorods were approximately 20 nm and 3 μm, respectively. The as-prepared nanorods exhibited W18O49 structures and characteristic Raman peaks could be observed. UV-visible absorption investigations revealed that Ti-doped W18O49 nanorods exhibited a redshift phenomenon when compared with the pure TiO2 and WO3. View full abstract»

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  • Effects of Si interlayer on resistance switching of Pt/Si/TiO2/Pt structures

    Page(s): 2175 - 2181
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    In order to improve the resistive switching reliability of devices made using TiO2 grown by atomic layer deposition at 130 °C, a thin Si layer was inserted between the Pt top electrode and the TiO2 thin films. The annealing of the Pt/Si(O)/TiO2/Pt structures at 300 °C in N2 ambient produced Pt/Pt3Si/PtSi particle-embedded SiO2/Ti-silicate/TiO2/Pt multistructures, as confirmed by x-ray diffraction, x-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. The as-annealed multistructures showed enhanced adhesion properties and significantly improved resistive switching performances, especially in terms of the number of the switching cycles and device yield. Based on the analyses, the authors proposed that the interfacial formation of Pt3Si and Ti silicate is responsible for the enhanced adhesion and the improved resistive switching reliability of TiO2 devices result from the enhanced mechanical stability as well as the presence of Ti silicate, which acts as source and sink for defects. View full abstract»

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  • Novel heterostructure of CdS nanoparticle/WO3 nanowhisker: Synthesis and photocatalytic properties

    Page(s): 2182 - 2186
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    A novel heterostructure of CdS nanoparticles/WO3 nanowhiskers was synthesized using a simple two-step process; thermal evaporation and chemical bath deposition. First, WO3 nanowhiskers (NWs) were grown on a tungsten substrate by thermal evaporation of WO3 powder in a tube furnace at 1050 °C. Sequentially, CdS nanoparticles (NPs) were deposited on WO3 nanowhiskers by chemical bath deposition. CdS nanoparticles modified WO3 nanowhiskers showed enhanced visible light absorption compared to bare WO3 nanowhiskers. The photocatalytic activity was studied by the photodegradation of methylene blue. CdS NP/WO3 NW heterostructures showed remarkably enhanced photodecomposition efficiencies compared to bare WO3 nanowhiskers. View full abstract»

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  • Evolution of surface morphology of dry-etched ZnO with Cl2/Ar plasma

    Page(s): 2187 - 2191
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    This work elucidates the surface morphologies of dry-etched ZnO films formed by reactive ion etching using a Cl2/Ar mixture. The root-mean-square (rms) roughness and etching rate were obtained by varying the gas flow ratio, the radio-frequency (rf) plasma power, and the chamber pressure. Atomic force microscopy results and surface topographies are discussed. The rms roughness is highest, 24.20 nm, at a Cl2/Ar flow rate of 150/10 SCCM (SCCM denotes cubic centimeter per minute at STP), a working pressure of 190 mTorr, and a rf power of 300 W. Such films are suitable for use as roughened transparent contact layers in light-emitting diodes. Bearing ratio analysis reveals that under the aforementioned condition, the nanorods covered 25.4% of the total surface area and their maximum height was approximately 150.83 nm. Moreover, high and low etching rates of 300 and 16 Å/min were obtained at rf powers of 300 and 50 W, respectively, supporting the ZnO-based devices and the gate-recess process. View full abstract»

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  • Effect of liquid dispensing on flow field for immersion lithography

    Page(s): 2192 - 2199
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    Immersion lithography has been proposed as a method for improving optical lithography resolution to 50 nm and below. The premise behind the concept is to increase the refraction index in the space between the lens and the wafer by insertion of a high refractive index liquid in place of the low refractive index air that currently fills the gap. During the scanning and exposure process, immersion liquid is injected into the space between the wafer and the lens with certain inlet pressure and angle. Because the liquid will act as a lens component during the lithographic process, it must maintain high uniform optical quality. One source of optical degradation may be due to liquid contamination by chemical products or impurities during exposure period. Immersion liquid renovation is probably the best solution. Refreshing cycle time and flow field velocity distribution were investigated by experimental and simulation methods. An empirical formula of velocity distribution was proposed in this article. The other source of optical degradation may be due to lens distortion caused by the pressure distribution nonuniformity in the flow field of the immersion liquid. Consequently, any deviations of pressure distribution on the flow field boundary in direct contact with lens may damage the uniform optical path. Three-dimensional computational fluid dynamics models were built to assess the pressure distribution characteristics relevant to flow rates and injecting angles of the immersion liquid. Compared with experimental results, the numerical simulation results were presented and discussed, featuring flow field stream patterns, lens normal and shear pressure, and injection flow, considering fluid injecting velocity, dispense ports quantity, and direction angles. View full abstract»

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  • The effect of acid on superconformal filling in 100 nm trenches

    Page(s): 2200 - 2205
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    A study is undertaken to determine the effect of low (10 g/L) and high (100 g/L) acid conditions on superconformal copper electroplating. The suppressor used is the surfactant P-104 at 200 ppm, with the accelerator bis(3-sulfopropyl)-disulfide (SPS) at a concentration of 5–35 ppm. High acid open circuit potential and polarization curves are shifted approximately -30 mV from low acid, both with and without P-104; Tafel slopes are the same at ∼100 mV/decade. P-104 displays the same suppression strength in both electrolytes. Patterned 100 nm trenches show that the rate of high and low acid filling is essentially the same at low SPS concentration (5 ppm). As SPS increases, high acid filling is improved; the effect in low acid is inverse, albeit not as strong. As suppression strength is the same in high and low acids, the dependence on SPS during filling is attributed to acceleration, which involves an interaction between suppressor and accelerator molecules. 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