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

Issue 1 • Date Jan 1989

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

    Page(s): toc1
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    Freely Available from IEEE
  • Oxygen plasma etching for resist stripping and multilayer lithography

    Page(s): 1 - 13
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    Oxygen‐based plasmas commonly used in resist stripping and multilayer resist patterning are contrasted to highlight the differences involved in these applications. Mechanisms for polymer etching are reviewed, with particular emphasis on silicon‐containing resists proposed for bilayer lithography. While silicon‐containing materials offer a simpler process than trilayer schemes for improving lithographic resolution, considerable differences in etch behavior among these materials have been observed. Further characterization and fundamental understanding are required before widespread acceptance of silicon‐containing resists is achieved. View full abstract»

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  • Polymer deposition and etching mechanisms in C2F6 radio‐frequency plasma as studied by laser‐induced fluorescence

    Page(s): 14 - 18
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    Spatial profiles of CF2 concentration in C2 F6 rf plasma are measured by the laser‐induced fluorescence method. The observed profiles are explained by the generation and recombination reaction mechanisms of CF2 . It is found that the deposition rate of fluorocarbon polymer on SiO2 film is proportional to [CF2]n ; n=2.5–3.0, whereas the etch rate of SiO2 is proportional to [CF2]. Both the etching and the deposition reactions proceed at the same time. Based on these observations, reaction mechanisms for fluorocarbon polymer deposition and SiO2 etching are analyzed. View full abstract»

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  • Ion beam assisted chemical etching of Si by SF6

    Page(s): 19 - 23
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    Ar+ ions of 0.5 to 2 keV from a broad‐beam Kaufman ion source have been used to induce chemical etching of Si by SF6 effusing from a gas dispensing ring placed near the Si surface. Etch rates have been measured as a function of sample temperature, SF6 flux, and ion energy. As the Si temperature is reduced below 120 K the Si yield per Ar+ ion rises to reach a maximum enhancement of about 8–10 just below 100 K, compared to pure physical sputtering. The results suggest that the dominant effect of the sample temperature is to control the fluorine supply via the evaporation rate of physisorbed SF6 molecules. This etching process has been applied to produce micron‐sized, blazed gratings in Si, using Al as a hard mask. Blaze angles up to 70° have been produced by tilting the sample with respect to the ion beam. View full abstract»

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  • Examination of fluorocarbon‐based plasmas used in the selective and uniform etching of silicon dioxide by response‐surface methodology: Effects of helium addition

    Page(s): 24 - 34
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    The process parameter space for fluorocarbon plasmas (C2F6/CHF3 and CF4/CHF3, with and without He) which are used to etch SiO2 has been examined with a Lam Research Autoetch 580 parallel plate, single‐wafer etching system by response‐surface methodology. The response or behavior of the plasmas differs very significantly with reactor pressure, etch gas mixture, and He addition. In particular, substantially higher SiO2 etch rates are obtained with C2F6/CHF3 plasmas than with CF4/CHF3 plasmas at an equivalent radio frequency power density for similar gas flow rates at significantly different reactor pressures: ∼2500 Å/min at ∼400 mTorr with C2F6/CHF3 mixtures and ∼750 Å/min at ∼1500 mTorr with CF4/CHF3 mixtures. Upon addition of He to the plasmas, the SiO2 etch rate maximum for the C2F6‐based plasma shifts to ∼800 mTorr and declines to ∼2000 Å/min, while that for the CF4‐based plasma remains near 1400 mTorr and increases to ∼1000 Å/min. Whereas the addition of He sharply degrades the etching uniformity with C2F6/CHF3 mixtures, it has no apparent effect on the etching uniformity with CF4/CHF3 mixtures, which is high with or without the addition of He over the parameter space which was explored. For the C2F6/CHF3 plasma, the etch selectivity to silicon is highest at 700–1100 mTorr, while for the CF4/CHF3 plasma the selectivity is highest at 1100–1500 mTorr. Although addition of He substantially improves the selectivity with the CF4/CHF3 plasmas, it has no effect on selectivity with the C2F6/CHF3 plasma. These detailed characterizations of process parameter space have led to a uniform and selective SiO2 sidewall spacer etching process which may be readily extended to other SiO2 etching processes with this equipment and these gas mixtures. View full abstract»

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  • Detection of dry etching product species with in situ Fourier transform infrared spectroscopy

    Page(s): 35 - 40
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    In situ Fourier transform infrared (FTIR) spectroscopy has been utilized to detect gas‐phase product species resulting from the dry etching of aluminum and heavily doped n‐type polycrystalline silicon (n+ poly‐Si) in Cl2 . The products of aluminum etching in Cl2 were investigated in the presence and absence of a plasma. With the plasma off, Al2 Cl6 was the only infrared‐active etch product detected at both low (50 °C) and high (≫120 °C) sample temperatures. With the discharge on, the spectrum was more complex, indicating partial fragmentation of the dimer etch product in the plasma forming AlCl3 and, perhaps, AlCl. Silicon tetrachloride was the only infrared‐absorbing product detected during the Cl2 plasma etching of n+ poly‐Si. Unsaturated silicon chlorides (SiClx , x=1–3) were not present at detectable levels. These results are compared with those of ultrahigh vacuum (UHV) beam studies; in comparing UHV results with those obtained in a processing plasma, allowances must be made for the considerable difference in pressure, and therefore, in species’ fluxes in these two experimental environments. Unlike UHV studies, in situ FTIR measurements permit detection of etch products under typical processing conditions. When interpreting the results, however, the possibility that the products leaving the sample surface react further upon entering the plasma must be considered. View full abstract»

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  • Reactive ion etching of GaAs and AlGaAs in a BCl3–Ar discharge

    Page(s): 41 - 46
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    Reactive ion etching of GaAs and AlGaAs has been performed in a BCl3 –Ar discharge. Etching properties have been studied as functions of BCl3 percentage (0%–100%), total pressure (2.5–30.0 mTorr), and power density (0.06–0.22 W/cm2 ). At low pressures (2.5–12.5 mTorr) and intermediate BCl3 percentages (25%–75%), profiles exhibiting a high degree of anisotropy are achieved. Under anisotropic conditions, etch rates are about 0.05–0.1 μm/min (at power density of 0.22 W/cm2 ), somewhat lower than for other chlorine‐containing gases. Conditions for etching GaAs and AlGaAs at equal rates have been determined. There is a small lag time between ignition of the glow discharge and the start of etching. The relative concentration of Cl atoms in the plasma, as measured by optical emission actinometry, correlates well with the etch rate for various operating parameters. View full abstract»

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  • Replicated resist pattern resolution with synchrotron orbital radiation

    Page(s): 47 - 54
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    For investigating the fundamental characteristics and resolution limit of patterns replicated with synchrotron orbital radiation (SOR), a computer simulation program, synchrotron orbital radiation lithography simulation system (sorsis) has been developed and resulting resist pattern profiles have been analyzed in detail. In sorsis, Fresnel integrals are performed by a new model based on introducing the SOR wavelength distribution, mask contrast, and phase difference into calculations. Positive‐type resist replication pattern profiles are calculated to evaluate pattern characteristics and are compared with experimental results. These results derive a resolution limit evaluation method, representing the equation W=ϵ(Gλp /2)1/2.3 , where W is the minimum linewidth, G the proximity gap, λp the wavelength peak, and ϵ the parameter mainly determined by resist characteristics and x‐ray mask absorber thickness. In this way, optimum conditions for precise pattern replication and accurate pattern profile control can be realized easily. View full abstract»

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  • Two‐layer resist fabrication by new portable conformable masking i‐line lithography

    Page(s): 55 - 58
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    A new technique for submicron optical lithography is reported. Water‐soluble contrast enhancing material for i‐line exposure prevented the undercut profile of negative photoresist and attained high‐aspect‐ratio rectangular patterns. New portable conformable masking i‐line lithography using the water‐soluble contrast enhancing material could successfully fabricate a two‐layer resist composed of negative photoresist RU‐1100N as a top layer and positive deep ultraviolet resist poly(dimethylglutarimide) as a bottom layer. View full abstract»

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  • Microwave plasma etching of Si and SiO2 in halogen mixtures: Interpretation of etching mechanisms

    Page(s): 59 - 67
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    An experimental study of the etching of Si with SF6 /halogen and halogen mixtures has been performed in a multipolar electron cyclotron resonance plasma with independent rf biasing. At constant total pressures and at a constant ion energy (75 eV), the anisotropy and the etch rate of silicon have been measured as a function of halogen percentages in the mixtures. The results are explained in terms of a recently developed diffusion model for plasma etching. Fluorine, chlorine, and bromine mixtures, contrary to iodine, etch Si, and SiO2. The bromine and chlorine adsorption on silicon appears to be monolayerlike, whereas fluorine adsorption is clearly of the multilayer type. Experimental results on etching anisotropy and selectivity with respect to SiO2 are also analyzed with emphasis on the peculiar behavior of bromine. View full abstract»

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  • Poly(methacrylic anhydride) positive electron beam resist

    Page(s): 68 - 72
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    Poly(methacrylic anhydride) (PMAH) is a positive resist for use in electron beam (e‐beam) lithography. It is derived by heating coatings of the precursor polymer, poly(tert‐butyl methacrylate) or PtBMA, on the wafer. Crosslinks are introduced during the thermal conversion. The sensitivity and line profiles of PMAH e‐beam images are significantly affected by the synthesis route, the pre‐exposure processing, and the development method. Development with organic solvents can swell and soften the resist, especially in areas that received some exposure to radiation. This causes the walls of the image to expand or flow into the image cavity, thereby limiting the sensitivity at which high resolution can be achieved. However, the use of a new, nonswelling, basic developer gives PMAH a sensitivity of 2.5 μC/cm2 with better than 0.5 μm resolution. View full abstract»

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  • A study of electron beam metrology using computer simulation

    Page(s): 73 - 78
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    For studying the technology of the critical dimension measurement using an electron beam (EB), a computer simulation based on the Monte Carlo and the surface charge methods is carried out, and a wave form of backscattered electrons (BE’s), which hardly suffer from the charging phenomenon, is precisely analyzed using this simulation. First, line widths obtained individually by threshold, maximum slope, and linear approximation methods are examined about various incident‐EB conditions such as an accelerating voltage and a beam diameter. The dependencies of pattern structures, such as dimension, side‐wall angle, and materials of the patterns, on measured line width are evaluated next. As a result of these calculations, it is found that the variation of the incident‐EB conditions doesn’t affect practically the results of the line‐width measurement in BE‐detection systems, while secondary‐electron signals are easily deformed by the charging phenomenon. Although the measured width much depends on the pattern structure, the linear approximation method is comparatively suitable for the purpose of obtaining the width of bottom edges in BE‐detection systems. View full abstract»

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  • Optical system for a low‐energy focused ion beam

    Page(s): 79 - 82
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    A low‐energy focused ion beam (FIB) would be a very useful tool for shallow doping with low damage density to the substrate. For a low‐energy FIB, an optical system using a retarding field is advantageous because of a low chromatic aberration coefficient which could not be reduced with a conventional column. Some evaluations were made for an optical column with a retarding electrode for practical use. The secondary electron trajectories within the equipotential space were calculated by the surface‐charge method, and some secondary‐electron images were observed with an experimental column having a retarding electrode. View full abstract»

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  • Deflection for scanning ion beam systems

    Page(s): 83 - 85
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    Three achromatic deflectors intended for ion lithography are proposed, in which the beam is incident perpendicular to the target. One of these deflectors uses mixed electrostatic and magnetostatic fields, thereby exhibiting mass dependent deflection. Although this is not favorable for a deflector, this setup works well as an achromatic mass filter. Best performance is obtained using a pre‐lens deflector using one lens as a corrector. A two lens corrector has theoretically even better performance, but mechanical and electrical tolerances will probably inhibit good performance. View full abstract»

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  • A wire electronic discharge machine saddle‐type deflector for electron beam lithography systems

    Page(s): 86 - 88
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    A new type of magnetic deflector [wire electron discharge machine (EDM) deflector] has been constructed for our gaussian round beam exposure system. To optimize the design of conventional saddle‐type deflection coils used for electron beam lithography systems (EBLS), one of the most important technical problems lies in the achievement of consistency between the computer aided design (CAD) calculated model and the actual structure of the windings. The present paper investigates the relation between the deflection aberration and winding width as well as winding distribution when the parameters of the deflector are optimized. The calculated results show that with 30° central angle of the winding and larger variance of the winding width the influence of third‐order aberration is negligible in micron‐EBLS and submicron‐EBLS. The design and experimental results are discussed for a new type of saddle coil used in EBLS and fabricated by the wire electron discharge machine (wire EDM) technology, this deflector indicates consistency between the CAD model and the actual structure of the winding. In our μm‐order EBLS using the wire EDM deflector, field stitching accuracy of ≪0.3 μm can be realized. The beam positioning accuracy is ∼0.2 μm. View full abstract»

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  • Focused ion beam lithography using Al2O3 as a resist for fabrication of x‐ray masks

    Page(s): 89 - 92
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    Ion bombardment has been found to enhance the etch rate of amorphous rf‐sputtered Al2O3 in hot H3PO4 so that this material works as a dry‐etch‐durable ion beam resist. It is shown that the resist properties depend on the substrate temperature and the magnetic field strength near the target surface during the sputter deposition. The optimized Al2O3 deposited at 380 °C and 9 mT is insoluble in 80 °C H3PO4 when unbombarded, and has a sensitivity of 1×1014 cm-2 and a contrast (γ) of 1.5 for 50‐keV Ga+ ions. Density measurement and x‐ray diffraction revealed that the optimized Al2O3 has higher density and a more ordered structure. X‐ray masks were fabricated by defining 200‐nm‐wide grooves in 500‐nm‐thick WNx x‐ray absorber layers using the Al2O3 patterned with focused 50‐keV Ga+ beams, as a durable mask for electron cyclotron resonance type of plasma etching with SF6; the etch‐rate ratio of WNx to Al2O3 was 30. Pattern transfer into poly(methylmethacrylate) from the fabricated mask was successfully carried out with synchrotron radiation. View full abstract»

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  • The effect of LaB6 cathode shape on its performance in a JBX 5DII electron beam lithography system

    Page(s): 93 - 97
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    The focused beam size and current for a JBX 5DII electron beam lithography system was measured for various shaped, (100) single‐crystal LaB6 cathodes at 50‐kV beam voltage. The performance of a 90° full angle, conically shaped cathode with a 15‐μm spherical apex radius was compared with a similar cathode, but with a variable diameter flat at the cathode apex. As the flat size varied from 15 to 30 μm, the minimum beam size (for 50 pA of beam current) varied from 11 to 37 nm for a cathode temperature of 1830 K. The performance of the 15‐μm truncated compared favorably with the 15‐μm spherical shaped cathode. For larger beam diameters, the beam current for the truncated cathode exceeded that of the 15‐μm spherical shaped emitter. The truncated cathode was operated in excess of 3100 h with no performance degradation. View full abstract»

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  • Electron optical performance of electron beam lithography columns predicted by a simple model

    Page(s): 98 - 103
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    A simple model is presented which predicts the maximum attainable current density and associated optimum brightness and semi‐angle in a variable shaped spot (VSS) and a Gaussian spot (GS) electron beam lithography system for a given resolution (edge width). For a GS the optimum source demagnification factor is also predicted. The contribution of the forward scattering in the resist is taken into consideration. The model allows the assessment of the sensitivity of the attainable current density to various design and operation parameters. The model is based on the quadratic sum of uncorrelated and uncorrectable aberrations and solves the expression for the sum for the current density using the reduced brightness as variable. VSS systems are characterized by an optimum brightness and a high sensitivity to stochastic trajectory displacement due to electron–electron interaction. The acceleration potential has a paramount effect on the attainable current density, still enhanced when forward scattering due to the resist is included. In GS systems the chromatic and geometrical aberrations limit the attainable density. The brightness attainable with Lanthanum–hexaboride emitters is satisfactory for VSS systems but GS systems require very high brightness guns (e.g., TFE) to exploit the potential for achieving a high current density. View full abstract»

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  • On the gate capacitance of metal–oxide semiconductor structures in N‐channel inversion layers on ternary chalcopyrite semiconductors

    Page(s): 104 - 110
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    An attempt is made to derive model expressions of the gate capacitance of metal–oxide semiconductor structures in n‐channel inversion layers on ternary chalcopyrite semiconductors at low temperatures, taking n‐channel inversion layers on CdGeAs2 as examples, under both the weak and strong electric field limits, respectively. It is found, on the basis of newly derived two‐dimensional electron energy spectra within the frame work of k↘∙p↘ formalism for both the limits by considering the anisotropies of the band parameters, that the gate capacitances increase with increasing surface electric field in an oscillatory manner and the crystal‐field splitting parameter enhances the numerical values of the gate capacitance for both the limits. In addition, the corresponding well‐known results for n‐channel inversion layers on parabolic energy bands are also obtained from the generalized expressions. View full abstract»

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  • Influence of substrate temperature and InAs mole fraction on the incorporation of indium during molecular‐beam epitaxial growth of InGaAs single quantum wells on GaAs

    Page(s): 111 - 115
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    The influence of substrate temperature and InAs mole fraction on the incorporation of indium during molecular‐beam epitaxial growth of lattice mismatched InGaAs single quantum wells on GaAs have been investigated. For growth of In0.25Ga0.75As at temperatures ≪570 °C, a transition from two‐dimensional to three‐dimensional growth is observed at a certain thickness of InGaAs. This thickness appears to be related to the thickness at which misfit dislocations are generated since it depends upon the substrate temperature during growth. The thickness is largest for quantum wells grown at lower temperature and decreases as the substrate temperature increases. This transition from two‐dimensional to three‐dimensional growth is not observed at high temperatures (≫570 °C) where an indium‐induced (4×2) surface reconstruction exists. For growth at 590 °C, Auger electron spectroscopy measurements indicate that the indium atoms reside on the surface of the as‐grown layer. However, the growth front of InGaAs remains planar even though indium adatoms do not incorporate into an In0.25Ga0.75As square quantum well. This type of indium surface segregation during growth does eventually degrade the macroscopic morphology of the surface, but only after a capping layer is deposited on top of the InGaAs. Some surface degradation in capped structures is also observed for In0.15Ga0.85As and In0.07Ga0.93As single quantum wells when grown at high temperature (≫570 °C), although it is less severe for these lower indium concentrations. View full abstract»

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  • Embedded growth of gallium arsenide in silicon recesses for a coplanar GaAs on Si technology

    Page(s): 116 - 119
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    A GaAs on Si coplanar technology by molecular‐beam epitaxy, that is suitable to combine GaAs and Si circuits on chip is reported. Coplanarity is obtained after the GaAs is grown embedded in masked wells in the Si substrate, which were formed by wet chemical etching with a controlled solution of HF:HNO3. Scanning electron microscope and profiling studies show the extreme flatness and the intentional misorientation of several degrees of the recessed surfaces. A possible process is proposed to realize a coplanar surface by lifting off polycrystalline GaAs with the masking dielectric. The GaAs surface step height remaining after liftoff is ≪0.6 μm for a 2‐μm‐thick deposit. Metallization without loss of continuity is performed over the GaAs to Si border with evaporated metal lines, 150 nm thick and 1.25 μm wide, indicating the feasibility of interconnecting side by side integrated devices in both semiconductor materials. View full abstract»

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  • Boron diffusion within TaSi2 /poly‐Si gates

    Page(s): 120 - 126
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    The redistribution of boron implanted into TaSi2 /poly‐Si gates after high temperature anneals has been investigated as a function of the implantation dose and energy as well as the implantation scheme, i.e., boron implantation either into the silicide or into the poly‐Si prior to TaSi2 deposition. Implantation and diffusion profiles were obtained by means of secondary ion mass spectrometry whereas the electrical characterization of the resulting structures was performed using high‐frequency capacitance–voltage measurements. The results indicate that boron can easily diffuse from TaSi2 into poly‐Si and vice versa at 900 °C. Independent of the implantation scheme, the boron concentration within poly‐Si was found to saturate at ∼1×1019 at/cm3 for boron doses ≫5×1014 at/cm2. The excess of boron always accumulates within the silicide. The solubility limit of boron within TaSi2 was estimated to be ≫3.5×1020 at/cm3. Boron concentrations of ∼1×1019 at/cm3 within poly‐Si were found to be sufficient to realize p+ ‐polycide gates with stable and reproducible threshold voltages similar to p+ ‐poly‐Si gates. The observed boron redistribution behavior within the polycide is discussed in terms of combined lattice and grain boundary diffusion as well as grain boundary segregation. View full abstract»

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  • Via hole filling with gold melting by KrF excimer laser irradiation

    Page(s): 127 - 128
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    One pulse of a KrF excimer laser emitting radiation at a wavelength of 248 nm was used to completely fill via holes in silicon dioxide (diameter: 2 μm, depth: 1 μm) by melting a 600‐nm‐thick gold layer on a 100‐nm‐thick Cr adhesion layer. The pulse width was 23 ns full width at half‐maximum (FWHM) and the pulse energy was 160 mJ, yielding a laser fluence at sample surface of ∼0.6 J/cm2. The result is a nearly planar structure. 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