bluuebunny/crossref_metadata_2025 huggingface dataset:
Single shot laser damage in ultraviolet mirrors with a stepwise reflectivity profile
Authors: Diso Daniela , Perrone Maria Rita , Piegari Angela , Protopapa Maria Lucia , Scaglione Salvatore
Published: July 2002

The photoacoustic and photothermal beam deflection techniques and microscopic inspection have been used to measure the laser damage threshold of mirrors with a stepwise reflectivity profile designed for KrF excimer lasers (248 nm). Laser damage resistance studies on the low and high reflectivity regions of the mirrors, as well as on the border between the high and low reflectivity regions, have been performed with a KrF laser delivering pulses of 25 ns duration. It is shown that the presence of a sharp step in the coating thickness, and consequently, in the mirror reflectivity profile does not significantly affect the damage threshold. Indeed, the damage threshold fluence of 1.8 J/cm2 in the high reflectivity area reduces to 1.1 J/cm2 in the low reflectivity region as it would for two independent high and low reflectivity coatings. The damage threshold in the border region is 1.4 J/cm2.
Hermetic indium metal-to-glass-tube seal
Authors: Lenzen M. , Collins R. E.
Published: July 2002

A hermetic seal was achieved between a modified stainless-steel 1/2 in. SWAGELOK fitting and a 1/2 in.×1.5 mm soda-lime glass tube. The seal was made at room temperature by compressing indium wire, sheet, or pellets into a space between the outer wall of the glass tube and the conical sealing surface of the fitting. Using a helium leak detector, the leak rate between room temperature and 150 °C was determined to be less than 10−9 Torr L s−1.
Light absorption in a resistive-gate GaAs charge-coupled device
Authors: Hu S. , Cresswell J. V. , Bryman D. A. , Kwok H. L.
Published: July 2002

A 128 pixel uniphase resistive-gate GaAs charge-coupled device was fabricated at the TRI University Meson Facility to study its optical absorption properties under monochromatic illumination in the visible and infrared range. It was found that when the incident light energy exceeded that of the band gap, there was a progressive reduction in the charge collection efficiency. This was attributed to a carrier recombination effect at the cermet–GaAs interface. A simple recombination model was proposed to explain the observation. A comparison between theory and measurement suggested a match between the two would require a minority carrier lifetime on the order of nanoseconds and an interface recombination velocity in the neighborhood of 107−8 cm/s. Such a high recombination velocity suggested a surface state density as high as the density of the surface atoms. Extrinsic absorption measurement indicated the presence of additional carrier generation in the wavelength range between 1.3 and 2.0 μm.
Si/Si
1−x
Ge
x
photodetectors using three-dimensional growth modes to enhance photoresponse at λ=1550 nm
Authors: Janz S. , Baribeau J.-M. , Lockwood D. J. , McCaffrey J. P. , Moisa S. , Rowell N. L. , Xu D.-X. , Lafontaine H. , Pearson M. R. T.
Published: July 2002

This article explores the use of Si1−xGex quantum-well layers with a coherent-wave or island-growth morphology in Si1−xGex based telecommunications photodetectors. The structural properties of such heterostructures have been determined by transmission electron microscopy, atomic force microscopy, x-ray diffraction, and Raman scattering. Photoluminescence and photocurrent spectroscopy measurements establish that strained, dislocation free Si0.5Ge0.5/Si superlattices were produced with band gaps as low as 0.745 eV, corresponding to an absorption edge near λ=1650 nm. These anomalously low band gaps result from a combination of reduced quantum confinement and higher local Ge concentration at the quantum-well thickness maxima. Waveguide photodetectors based on a coherent-wave Si/Si0.50Ge0.50 superlattice have achieved a photoresponse of 0.16 A/W at 1550 nm.
Comparison of plasma chemistries for dry etching of Ta2O5
Authors: Lee K. P. , Jung K. B. , Singh R. K. , Pearton S. J. , Hobbs C. , Tobin P.
Published: July 2002

Inductively coupled plasma etching of Ta2O5 was performed in a variety of different chemistries, including SF6 with additions of O2, Ar, CH4 or H2; Cl2/Ar; N2/Ar; and CH4/H2/Ar. Etch rates up to ∼1200 Å min−1 were achieved with either SF6- or Cl2-based chemistries. Under these conditions the etch rates for Si were approximately four to seven times faster, although equirate etching was achieved at low source powers and low halogen gas percentages in the plasma chemistry. The etched Ta2O5 surfaces were smooth (root mean square roughness ⩽0.5 nm) over a broad range of conditions of source power, chuck power, and process pressure. The etch rates with N2/Ar and CH4/H2/Ar were an order of magnitude lower than with SF6 or Cl2. There was no effect of postdeposition annealing on the Ta2O5 etch rates, at least up to 800 °C.
Advanced selective dry etching of GaAs/AlGaAs in high density inductively coupled plasmas
Authors: Lee J. W. , Devre M. W. , Reelfs B. H. , Johnson D. , Sasserath J. N. , Clayton F. , Hays D. , Pearton S. J.
Published: July 2002

We report a breakthrough for selective etching of GaAs over AlxGa1−xAs, x=0.2, layer with a high density plasma source. This result is particularly important for III–V devices such as heterojunction bipolar transistors (HBTs) or high electron mobility transistors (HEMTs). For example, fabrication of HBTs requires a process for selective etching of a GaAs contact layer while stopping on AlGaAs layer. Inductively coupled plasma (ICP) etching with BCl3/SF6/N2/He chemistries showed extremely high selectivity of GaAs over AlGaAs (>200:1) and a photoresist (>10:1). This process also produced excellent sidewall passivation on GaAs with reasonably high rate (>1500 Å /min.). Both scanning electron microscope and atomic force microscope data showed AlGaAs etch stop layer was quite smooth after processing. We found that He played a key role in enhancing selectivity and obtaining smooth AlGaAs surfaces. When used with resist masks, addition of N2 into BCl3/SF6 plasma helped formation of passivation on the sidewall and maintained high anisotropy. An optimized condition with BCl3/SF6/N2/He ICP plasmas showed excellent pattern transfer into GaAs with high rate, anisotropy, and selectivity.
Growth of ultrathin Co/Cu/Si(110) films
Authors: Maat S. , Liu C. , Eads W. , Umlor M. T. , Mankey G. J.
Published: July 2002

We report the results of a study of the structural properties of Co films deposited on Cu/H–Si(110). A Cu(111) buffer layer is formed by evaporation or ultrahigh vacuum sputter deposition on the H-terminated Si(110) surface. From consideration of bulk lattice constants, the Cu films undergo a 6% expansion along the [1, −1, 0] direction and a 13% compression along the [1, 1, −2] direction. The structure and annealing behavior of the Cu buffer layer was determined with a combination of low-energy electron diffraction (LEED) and Auger electron spectroscopy. The LEED patterns of Co films evaporated on this buffer layer are compared to Co films grown on a Cu(111) single crystal.
Cyclic voltammetry, x-ray photoelectron spectroscopy, secondary-ion-mass spectrometry, and ion-scattering spectrometry examination of zirconium passive film breakdown in the presence of sulfate
Authors: Schennach R. , Mamun A. , Kunamneni N. , Cocke D. L.
Published: July 2002

Passive films on zirconia were prepared by potentiodynamic polarization in the presence of a range of anions and at various pH values. With sulfate and chloride anions in the electrolyte we found unique transpassive peaks in the cyclic voltammograms that appear to be associated with an amorphous-to-crystalline transition and subsequent enhanced species transport along the resulting grain boundaries. X-ray photoelectron spectroscopy, secondary-ion-mass spectrometry, and ion-scattering spectrometry have been used to characterize the films before and after the passive film breakdown. The passive film breakdown can be qualitatively described by Enp=Ec+η+Φ+Einh. Where Enp is the pitting potential, Ec the corrosion potential in acidified solution, η the polarization necessary to obtain a current density high enough to maintain acidity inside the pit, Φ the potential drop inside of the pit, and Einh the contribution to the pitting potential resulting from inhibitors present. The results of these surface studies along with the variation in the cyclic voltammetry scans have been used to describe the process and to present a model that involves chemically bound water oxidation and local oxygen evolution. The effects of either Ohmic drop and/or local acidification are presented as well.
Reactions of acetic acid on UO2(111) single crystal surfaces
Authors: Chong S. V. , Idriss H.
Published: July 2002

The reactions of acetic acid have been investigated on the (111) surface of uranium dioxide single crystals, which was characterized by low energy electron diffraction and Auger electron spectroscopy. Temperature programmed desorption (TPD) of this molecule displays a rich chemistry on both the stoichiometric and electron beam sputtered surfaces. Acetic acid-TPD on a stoichiometric surface yields ketene (dehydration) as the main product, plus acetaldehyde as the minor product. On an electron beam sputtered surface, two additional association products were observed—butene and crotonaldehyde. The carbon yield of ketene on the stoichiometric surface was comparable to that of CeO2(111) and TiO2(001), higher than that of ZnO(0001) and Cu2O(100), but lower than that of MgO(100). This investigation has shown the ability of UO2(111) surfaces to dehydrate, reduce, and reductively couple organic molecules.
Substrate rotation-induced compositional oscillation in molecular beam epitaxy (MBE)
Authors: Alavi K. , Petroff P. M. , Wagner W. R. , Cho A. Y.
Published: July 2002

Small amplitude periodic compositional variations in the growth direction have been observed in GaxIn1−x As and AlxIn1−x As layers grown by MBE with a rotating substrate holder in transmission electron microscopy (TEM) studies. The period of these compositional oscillations has been correlated with the substrate rotation frequency. These oscillations have been attributed to the small variations in the flux profile of the group III elements over the substrate area. Sharp peaks obtained in x-ray diffraction studies indicate the absence of compositional grading in the growth direction, despite these oscillations.
A precision wide-range optical gap measurement technique
Authors: Flanders D. C. , Lyszczarz T. M.
Published: July 2002

This paper describes a new optical interferometric technique for measuring the gap between a mask and a substrate in proximity printing lithography systems. A uniform-intensity, collimated He–Ne laser beam is focused onto the mask. Light reflected from the mask interferes with the light reflected from the substrate to form a characteristic pattern. To first order, the spatial frequency of this pattern is linearly dependent upon the mask-to-substrate gap. A linear array is used to observe the interference pattern. The resulting signal is processed using correlation techniques to determine the gap. Highly accurate, absolute measurements can be made using this scheme which is quite distinct from the well known interferometric methods which can only measure relative motion. The achievable accuracy and range are functions of illumination, system geometry, signal detection, and processing. An experimental measurement system has demonstrated ±0.25% accuracy over a 25 to 120 μm range.
I
n s
i
t
u infrared spectroelectrochemistry
Authors: Korzeniewski Carol , Pons Stanley
Published: July 2002

The vibrational spectrum of molecules at or near an electrode surface can be obtained using subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) and electromodulated infrared spectroscopy (EMIRS). The large electric field existing at the electrode/solution interface is sufficient to induce dipole moments in highly polarizable molecules. The magnitude of the induced dipole moment is proportional to the electric field strength. As a result of this interaction some totally symmetric normal vibrations are made infrared active, and other bands appear in violation of the surface selection rule. This effect is known as the electrochemical Stark effect. Calculation of the expected absorption coefficients for the totally symmetric modes of adsorbed species gives values which are close to those observed experimentally. Experimental evidence of Ag mode activation of adsorbed pyrene is presented. The electric field dependence of the integrated absorption coefficient is demonstrated for acrylonitrile adsorbed on a gold electrode.
An experimental variable shaped electron beam lithography system
Authors: He Fu-min , Lin Chun-lan , Fang Guan-rong , Wang Li-ming
Published: July 2002

An experimental variable shaped electron beam lithography system has been built to verify the theoretical design considerations and fundamental control method. The electron beam column consists of four magnetic lenses, two square apertures, two aligners, an angular aperture, a set of blanking plates, and a position deflection yoke. The size of the beam spot is varied by a set of electrostatic deflection plates. In order to maintain the current density in the spot constant, as the size of the beam spot varies, the center of the shaped deflection plates is placed to coincide with the image of the gun crossover, and the shaped deflection plates position can be electrically adjusted. The acceleration voltage is 20 kV. The field size is 2.5 mm square. The maximum spot size is 10 μm2. The maximum current density is 1 A/cm2. The system is controlled by an EG 3003 computer. The beam blanking switching time is 50 nS.
A line electron lens
Authors: Levi Mark W.
Published: July 2002

An electron lens, designed for simultaneous exposure of the entire length of a line, has been developed. Two versions have been built and tested. The focal properties of the lenses for both paraxial and far-off-axis trajectories have been computed with a short (two page) fortran program. It is expected that a more carefully made version of this lens should be capable of producing lines less than 0.025  μm wide, and as smooth as the capability of the resist which will be exposed. Furthermore, it is expected that the lines can be made straight to substantially better than 0.025  μm. It is also expected that it will be possible to position lines parallel to one another to an accuracy commensurate with their straightness. The lens is electrostatic, and focal conditions can be adjusted so that the lens is afocal to first order with respect to changes in the lens-to-workpiece spacing. It is also possible to mask segments of the line, although the axial resolution will probably be good only to a few micrometers. The structure and mathematics which permit its characteristics to be so easily obtained are described.
Derivation of the condition for onset of instabilities of a conducting fluid surface under electrostatic stress: Application to liquid metal ion sources
Authors: Miskovsky N. M. , Cutler P. H. , Kazes E.
Published: July 2002

In this paper we have used a virtual-work energy analysis to derive a new set of equations which determine both the static equilibrium shape of an electrostatically stressed conducting fluid maintained at a constant potential and the condition for the onset of instabilities. From the equilibrium equation we make the important observation that, unlike the Taylor equilibrium analysis, the new derivation explicitly includes the work associated with the deformation of the fluid surface held at fixed potential by an external power source. Furthermore, in interpreting the equations for instability, it is found that any initiation of breakdown need not occur uniformly over the fluid surface. This is to be contrasted with the implication of the Taylor stress condition for the conical model which predicts breakdown of the entire fluid surface at the same voltage. Moreover, it is demonstrated that the critical voltage for emission or breakdown is a function of the local curvature and depends in a point-to-point fashion upon the shape of the entire surface.
X-ray laser fabrication by anisotropic etching of silicon
Authors: Hawryluk A. M. , Ciarlo D. R. , Rambach G. D.
Published: July 2002

Microfabrication technology has previously been used to produce UV and soft x-ray optics and diagnostics. We report on a microfabrication technique which, under appropriate conditions, should produce soft, monochromatic and collimated x rays (an x-ray laser). Thislaser cavity requires the capability of producing a ‘‘knife-edge’’ structure with high dimensional accuracy over several centimeters, and the fabrication of vacuum windows transmissive to soft rays. We have been able to achieve these goals using anisotropic etching of thinned (100) silicon wafers.
Chain scissioning yields and dry etch durabilities of polymers based on itaconic acid derivatives
Authors: Anderson C. C. , Rodriguez F.
Published: July 2002

The effect of the side group substituent on the chain scissioning yield (Gs) and reactive-ion etch (RIE) durability in a CF4/O2 plasma for polymers based on itaconic acid derivatives has been studied. Gs and RIE etch rates were found to decrease with increasing size of the ester group for mono- and dialkyl itaconate polymers. Halogen substitution on the ester group increased both Gs and RIE etch rates dramatically. Monoalkyl itaconate polymers are more susceptible to degradation under radiation than the corresponding dialkyl itaconate but their RIE etch rates are identical. Improved dry etch durabilities were found for polymers of aromatic esters and amides of itaconic acid, but they have very poor Gs values, typically 0.25–0.75 times that of poly(methylmethacrylate), PMMA. The highest RIE durabilities (4× improvement over PMMA) were obtained by treating copolymers of itaconic acid and methyl methacrylate (coated on silicon wafers) with a metal hydroxide.
RBS analysis with a 1 μ beam
Authors: Morris W. G. , Katz W. , Bakhru H. , Haberl A. W.
Published: July 2002

Rutherford backscattering spectrometry (RBS) has been performed on microelectronic circuits with a spatial resolution of approximately 1.5 μm. A beam of 2 MeV He+ ions is apertured to 10 μm, and then demagnified to 1 μm by a quadrupole doublet lens. The beam current striking the sample is about 0.3 nA. An electrostatic scanning system is used to form a secondary electron image of the surface in order to locate features of interest. Analysis is performed in frame, line, or spot modes.
Computer-aided analysis of electron beam induced heating, melting, and resolidification of metals and semiconductors
Authors: Bhattacharyya Manoj K. , Tuma David T. , Cendes Zoltan J.
Published: July 2002

The problem of heating, melting, and resolidification of solid targets by collimated electron beams is discussed. The transient multiphase moving boundary problem has been solved by the finite element method using an enthalpy formulation. The effect of electron beam penetration and material properties variation with temperature have been taken into consideration. Results are presented for the extent of melting for copper and silicon. The velocity of resolidification for copper is 10–20 m/s, whereas for silicon it is about 1–3 m/s. The results agree very well with published experimental measurements.
A high-speed, high-precision electron beam lithography system (electron optics)
Authors: Saitou N. , Okumura M. , Matsuoka G. , Matsuzaka T. , Komoda T. , Sakitani Y.
Published: July 2002

A variably shaped electron beam exposure system HL-600 has been developed for both direct wafer writing and mask making. It was designed as a high-throughput tool to cover lithography requirements down to a 0.5 μm linewidth. To achieve this high-throughput capability, many newly developed techniques were adopted in the electron optics and in the control electronic circuits. The simplified electron beam column consists of only four magnetic lenses. The magnetic deflection for main field scanning was enlarged so as to reach up to 6.5 mm sq in order to reduce the overhead time associated with work stage movement. In addition, the design of an objective lens system with a small aberration, and an algorithm for deflection aberration correction were developed. Automatic measurement of defocusing and astigmatism aberrations at a number of sample points were performed by taking through focusing, and the third order polynomial correction function of deflection was determined. As a result, the edge resolution for the 2 μm sq beam was less than 0.2 μm over a 6.5 mm sq field. The column uses a flat-top-type LaB6 electron gun with high brightness and large emittance. Although the maximum beam size and current density were limited by Coulomb blurring, the gun realizes a 6.4 μm sq size and 10 A/cm2 density at the same time. It typically has a 5000 h lifetime. This HL-600 is capable of writing more than ten 4 in. wafers per hour on the average. In addition to a summary of the HL-600 system, this paper describes details concerning the novel techniques in optics and some exposure results.
Sub-100-nm-wide, deep trenches defined by reactive ion etching
Authors: Pang S. W. , Randall J. N. , Geis M. W.
Published: July 2002

In this study, reactive ion etching (RIE) has been used to define vertical trenches with dimensions considerably smaller than the lithographically defined width. Gratings with 320 nm period were defined using a masked ion beam exposure of PMMA, followed by lift-off of a Ni mask. For shallow etching, tapered profiles were obtained. For more deeply etched structures, the tapered walls converged and formed sub-100-nm-wide, highly anisotropic trenches. The trench formation is not a crystal orientation dependent effect and has been obtained in GaAs, SiO2, and nonstoichiometric silicon nitride (SiNx). The etched profiles and the final trench widths depend on the RIE conditions and the substrate materials. Ion divergence in the RIE reactor was measured using nitrocellulose and was found to increase with chamber pressure. The measured half-angle of ion divergence was 0.7° at 2 mTorr and increased to 1.2° at 20 mTorr during RIE in CF4 at 500 V self-induced dc bias voltage. The ion distribution inside these trenches was calculated using a model based on the Monte Carlo method. The result indicated that ion flux decreased at the bottom of the trenches, but increased near the top of the trenches due to ion scattering from the tapered sidewalls. These ion scattering effects contribute to the formation of trenches ranging from 20 to 60 nm in width and as deep as 1 μm.
Critical Koehler illumination for shaped beam lithography
Authors: Essig Manfred , Pfeiffer H. C.
Published: July 2002

The crossover of a thermionic electron gun acts as the virtual source in conventional electron beam lithography systems employing critical illumination as well as those employing Koehler illumination [Broers, SEM (IIT Research Institute, Chicago, 1979)]. The concept of critical Koehler illumination [Essig, IBM Tech. Discl. Bull. 27, 1224 (1985)] combines critical illumination and Koehler illumination to image the cathode surface as the real source of the electrons into the probe shaping aperture and finally onto the target plane (window ray trace). Further on, the crossover as the virtual exit pupil of the gun lens is imaged into the entrance pupil of the final lens (pupil ray trace). Thus, in critical Koehler illumination, the linked beam concept consequently correlates conjugate planes of a probe forming system to those of the electron gun. The implementation of critical Koehler illumination in shaped beam lithography systems requires a special imaging mode of the electron gun. A typical triode gun can provide imaging of the emitter surface. Critical Koehler illumination has a high current efficiency, and the cathode supplies only the number of electrons needed in the target plane, so that maximum cathode lifetime and minimum electron–electron interaction in the beam result. Beam stability and spot image quality are substantially improved.
A 1 : 1 electron stepper
Authors: Ward R. , Franklin A. R. , Lewin I. H. , Gould P. A. , Plummer M. J.
Published: July 2002

A new approach to electron projection is described which is suited to the design of an electron stepper. Electrons are emitted from the clear areas of a Cr mask by the interaction of short wavelength UV radiation with a CsI photocathode. A grid separates mask from wafer, creating a field-free region into which conventional electron backscatter detectors may be placed to provide alignment signals. The system employs uniform electric and magnetic fields and the image size is limited only by the physical size of the grid. We calculate the distortion at the grid apertures and show that high resolution may be achieved by positioning the grid at the first magnetic focus and the wafer at the second. Experiments have been carried out in which submicron resolution is demonstrated and alignment signals are generated.
A theoretical performance comparison of six electrostatic e-beam deflectors
Authors: Schaefer Christoph H.
Published: July 2002

The following electrostatic e-beam deflectors are simulated numerically and compared: (1) Box deflector; (2) modified box deflector; (3) dokekapole deflector; (4) simplified octupole deflector; (5) 20-pole deflector; (6) conventional octupole deflector. Two types of aberrations arise in the deflection of an electron-image of negligible size: raster distortion and spot blurring. For each deflector, these aberrations are computed and plotted as functions of deflection amplitude. The present computations make no use of perturbational aberration theory but rely on the method of ray tracing in 3D fields. The full effect of fringe fields due to finite gap widths and finite lengths of electrodes is accounted for. The surface-charge density method has been utilized for the accurate numerical calculation of the fields.
Excited-atom production by electron and ion bombardment of alkali halides
Authors: Walkup R. E. , Avouris Ph. , Ghosh A. P.
Published: July 2002

We present experimental results on the production of excited atoms by electron and ion bombardment of alkali halides. For the case of electron bombardment, Doppler shift measurements show that the electronically excited atoms have a thermal velocity distribution in equilibrium with the surface temperature. Measurements of the absolute yield of excited atoms, the distribution of population among the excited states, and the systematic dependence on incident electron current and sample temperature support a model in which the excited atoms are produced by gas-phase collisions between desorbed ground-state atoms and secondary electrons. In contrast, for the case of ion bombardment, the excited atoms are directly sputtered from the surface, with velocity distributions characteristic of a collision cascade, and with typical energies of ∼10 eV.
Progress in self-developing metal fluoride resists
Authors: Kratschmer E. , Isaacson M.
Published: July 2002

Thin films of metal fluorides such as AlF3, FeF2, CrF2, CsF, LaF3, BaF2, and SrF2 have been used as electron beam sensitive resists. When exposed in an ultrahigh vacuum system by a high intensity electron beam at line doses of 0.5 to 400 μC/cm at 100 keV on a thin membrane substrate, the films act as positive resists. At line doses of typically an order of magnitude less than in the case of the positive resist mode, the films also act as negative resists requiring the use of an appropriate developer. The exposure properties for these metal fluoride resists are discussed along with their film properties, sensitivity, and etching characteristics.
Effects of photoelectrons ejected from the substrate on patterning characteristics in x-ray lithography
Authors: Deguchi Kimiyoshi , Namatsu Hideo , Komatsu Kazuhiko , Yoshikawa Akira
Published: July 2002

The effects of photoelectrons and Auger electrons ejected from the substrate on the resist pattern profile and the minimum x-ray exposure dose (sensitivity) are investigated for various substrate materials. It is found that patterning controllability becomes more severe due to pattern undercutting, although the minimum x-ray exposure dose for single-layer resist on the Mo substrate is 32% smaller than that for the three-layer resist. These effects are quantitatively estimated by the Grün range of photoelectrons in the resist and by the photoionization cross section of the substrate materials. These calcuated values coincide with the experimental results. By using the three-layer resist system with a low photoionization cross section, accurate 0.5 μm very large-scale integrated patterns are replicated on the Mo substrate with a large exposure dose margin of ±20%.
Use of a pi-phase shifting x-ray mask to increase the intensity slope at feature edges
Authors: Ku Y.-C. , Anderson Erik H. , Schattenburg Mark L. , Smith Henry I.
Published: July 2002

In x-ray lithography at deep submicron and sub-100-nm linewidths, the effects of diffraction are not negligible. We have investigated the possibility of improving the slope of the irradiance profile at feature edges by using an absorber that produces a pi-phase shift in addition to about 10 dB attenuation. Both numerical simulation and experimental modeling at a longer wavelength (365 nm) were used. These show that the irradiance profile at the edge of features is steeper when using a pi-phase shifting mask. For gold, the condition of pi-phase shift and 10 dB attenuation occurs when the wavelength is 1.15 nm and the thickness is 290 nm; and for tungsten at a wavelength of 1.3 nm and a thickness of 275 nm. X-ray masks made with the proper phase-shift and attenuation yield an increased slope at feature edges which should result in improved process latitude. The phase-shifting scheme introduced here differs from those previously described, and applies to patterns of arbitrary geometry, including isolated lines and spaces.
Reduction in x-ray mask distortion using amorphous WNx absorber stress compensated with ion bombardment
Authors: Kanayama Toshihiko , Sugawara Minoru , Itoh Junji
Published: July 2002

In order to reduce distortion and to obtain good pattern-placement accuracy in x-ray masks, a stress-compensation technique in x-ray absorber layers has been developed using ion bombardment. The absorber material selected is amorphous WNx (x=0.1) deposited with rf sputtering because its compressive stress of 1010 dyn/cm2 can be completely compensated with the present technique, although it is effective in all the metals attempted with both compressive and tensile stresses. It is shown that ion bombardment at an elevated temperature enables precise stress control together with excellent thermal stability in stress. In-plane distortion caused by opening of 3×3-mm2 patterns in the WNx absorber was measured in masks with 2-μm-thick SiNx supporting membranes. The 0.4-μm-thick WNx layers used were stress compensated by bombardment with 400-keV N+ ions at 300 °C to a dose of 4 to 6×1014 ions/cm2. The distortion has been reduced to less than 5×10−6 relative to the pattern size. The mechanism of the stress compensation is also discussed.
Applications of a variable energy focused ion beam system
Authors: Narum D. H. , Pease R. F. W.
Published: July 2002

A novel ion focused beam system has recently been designed and constructed that employs retarding field, electrostatic optics such that beams of Ga+ ions with energies as low as 25 eV can be focused into a submicron diameter spot. In this paper we review the ion-optical performance of this system and then describe the interactions of the beam with the target. In the conventional mode (30-keV landing energy) the system has been used to sputter etch tracks in gold (on a silicon substrate) of width 0.16 μm. However, as the landing energy is reduced below 200 eV, the action of sputter etching gives way to deposition and tracks of gallium 1.5 to 3 μ wide have been laid down in this manner. That the tracks were indeed gallium was confirmed by x-ray microanalysis. The appearance of the tracks suggested that the interface between the gallium and the substrate affects the morphology of the track. Two obvious and prosaic applications include the repair of both clear and opaque mask defects, and making and breaking integrated circuit electrical interconnections. More ambitious applications include combining the system with molecular-beam epitaxy to build true three-dimensional, sub-0.1-μm device structures.
Active electronic compensation of ambient magnetic fields for electron optical columns
Authors: Golladay S. D.
Published: July 2002

In order to reduce ac magnetic field interference with electron beam instruments, a relatively simple and inexpensive electronic field compensation system has been built. The system has a bandwidth extending from ∼8–200 Hz and reduces field strength at the sensor by a factor of about 50 (60 Hz). Because of inhomogeneities in the noise field, the compensated field strength increases with distance from the sensor, but is typically reduced by a factor between 10 and 50 at a distance of 10 cm for the case of a nonmagnetic environment. System performance in a magnetic environment, as in the application to an electron beam instrument, depends on sensor position. Fields within a simulated column consisting of a mu-metal cylinder are reduced by a factor of 5 or more with sensor position optimized. ac magnetic field interference with an electron beam instrument was reduced by a similar factor.
Application of synchrotron x-ray lithography to fabricate fully scaled 0.5 μm complementary metal–oxide semiconductor devices and circuits
Authors: Wang L. K. , Silverman J. , Seeger D. , Petrillo E. , DiMilia V. , Katcoff D. , Kwietniak K. , Acosta R. , Petrillo K. , Brodsky S. , Babich I. , Vladimirsky O. , Voelker H. , Viswanathan R. , Warlaumont J. , Wilson A. , Devenuto R. , Hill B. , Hsia L. C. , Rippstein R. , Wasik C.
Published: July 2002

High performance fully scaled 0.5 μm complementary metal–oxide semiconductors very large scale integrated (CMOS VLSI) circuits have been fabricated using synchrotron x-ray lithography technology. X-ray lithography is employed at all levels to attain a minimum feature size of 0.5 μm. The wafer exposures are done at the VUV storage ring from the National Synchrotron Light Source, Brookhaven National Laboratory. A stepper built at IBM Yorktown Heights is used at the beamline to perform the wafer exposures. All the lithography levels are aligned to the prefabricated 0.5 μm deep silicon trench zero level with an overlay less than 0.1 μm (1σ) between levels. Single level resists (both positive and negative) are used throughout the entire CMOS process. Linewidth control better than 0.01 μm and alignment tolerance less than 0.10 μm are accomplished. The patterning of this x-ray lithography mask is accomplished through a vector scan electron beam direct writing system. Masks made of boron doped silicon membranes with electroplated gold are used as the absorber. An average linewidth variation less than 0.2 μm can be attained for the (25 mm)2 field size masks. A retrograded N well 0.5 μm CMOS process is used to exercise the fabrication of x-ray lithography VLSIs. In the (25 mm)2 testsite, CMOS devices, ring oscillators and fully scaled 0.5 μm CMOS SRAM (static random access memory) are densely populated to exercise this technology. In this experiment CMOS devices and ring oscillators are successfully fabricated. The device characteristics are essentially the same as those fabricated using other lithography methods. A fully scaled 0.5 μm 61 stage inverter ring oscillator was measured at a delay of 95 ps/stage when operating at a 3.5 volts power supply. Radiation effects on the fabricated CMOS devices are studied. With the final 400 °C hydrogen ambient annealing, there is no apparent difference on the device characteristics in comparison to the same devices fabricated using optical lithography.
A reflection high-energy electron diffraction study of (100) GaAs vicinal surfaces
Authors: Chalmers S. A. , Gossard A. C. , Petroff P. M. , Gaines J. M. , Kroemer H.
Published: July 2002

The RHEED specular beam profiles produced by GaAs vicinal surfaces are examined and correlated with the surface topography. It is found that the shape of split peaks produced with the incident beam normal to step edges is a measure of surface orientation over lengths on the order of terrace widths, but is not sensitive to short range roughness on the terraces themselves. The profile produced with the incident beam parallel to step edges is sensitive to terrace roughness and can be correlated with RHEED intensity oscillation behavior. It is also found that reconstruction disorder can influence the specular beamwidth.
Surface and in-depth analysis of hydrogenated carbon layers on silicon and germanium by mass and electron spectroscopy
Authors: Sander P. , Altebockwinkel M. , Storm W. , Wiedmann L. , Benninghoven A.
Published: July 2002

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.
Application of a low-pressure radio frequency discharge source to polysilicon gate etching
Authors: Cook J. M. , Ibbotson D. E. , Flamm D. L.
Published: July 2002

We have shown that a discharge can be sustained at low pressure (≲10−3 Torr) in a single-wafer reactor using experimental quarter-wave helical resonator structures operated at radio frequencies. These discharge sources have been used to etch submicron-wide polysilicon gates with chlorine and chlorine/oxygen mixtures. Selectivities for undoped polysilicon over oxide and hard baked trilevel photoresist were 70:1 and 2.8:1, respectively, in a 75 W discharge operated at 0.1 mTorr with a Cl2/1% O2 feed gas mixture. Anisotropic profiles of 0.25 μm lines were obtained across 100 mm wafers with negligible linewidth loss. These preliminary experiments show that rf resonator discharges may offer an alternative to low-pressure microwave discharges such as those based on electron cyclotron resonance.
Ion beam assisted etching and deposition
Authors: Gamo Kenji , Namba Susumu
Published: July 2002

I n situ vacuum processing technology is becoming increasingly important with the increasing scale of integration and continuing shrinkage of device dimensions. Ion beams induce various chemical effects which are very promising for applications such as in situ processing technology, with the promise of improved high processing rates and low process-induced damage. The present paper is intended to review various etching and deposition techniques which utilize ion beam induced chemical effects. The effect of damage and importance of a low energy beam will also be described.
Reactive ion etching of TiSi2/n+ polysilicon polycide structure for very large scale integrated application
Authors: Qiuxia Xu , Soujing Zhou , Yuyin Zhao , Shuming Feng
Published: July 2002

TiSi2 has the lowest resistivity among various refractory metal silicides and a low forming temperature also. It is considered that TiSi2 would be an important material for the scale above 4M dynamic random access memory integration, it has given rise to universal attention. In this paper, reactive ion etching characteristics of TiSi2/n+ polysilicon polycide structure are investigated in detail, and the probable mechanisms are discussed. The mixture of SF6–Cl2 is chosen as etch gases for TiSi2 polycide patterning. The experimental analysis indicates that the etch rates are dependent on various etching process parameters, such as gas composition, radio frequency power, and gas pressure, the etching profiles are dependent on gas composition. Strict anisotropic etching of TiSi2/n+ polysilicon double layer structure with 0.6 μm linewidth has been achieved by a single-step process. The etch rate ratio of n+ polysilicon to TiSi2 is equal to 1.03 and that of n+ polysilicon to SiO2 is equal to 18. The integrity of resist mask is good. The reproducibility of the process is satisfactory.
Development of centrally controlled synchrotron radiation lithography beamline system
Authors: Nishino J. , Kawakami M. , Yanagisawa T. , Okada K.
Published: July 2002

The centrally controlled beamline system for synchrotron radiation lithography has been investigated using the SORTEC storage ring(l GeV). From a practical standpoint, the recently built beamlines aim at attaining a centrally controlled beamline system, which is also serially interfaced with the storage ring. In operating the beamlines, not only local control, but also a central control notion is adopted. The central beamline control system comprises a beamline main computer and a programmable sequence controller (PSC) link. The local beamline control system consists of a PSC, a control panel, and a personal computer. The beamline main computer collects each beamline status datum through the PSC link, receiving the storage ring data from the main computer of the 1 GeV synchrotron radiation (SR) source. A novel oscillating mirror mechanism is proposed, in which the mirror chamber, driven by a combination of a cam mechanism and pulse motor installed in air, is oscillated to scan the mirror, thus producing high reliability and compact design. In addition, a practical beamline structure is offered which fulfills system vacuum protection and protects operators from radiation exposure.
Polysilyne thin films as resists for deep ultraviolet lithography
Authors: Kunz R. R. , Horn M. W. , Goodman R. B. , Bianconi P. A. , Smith D. A. , Freed C. A.
Published: July 2002

A new class of organosilane polymers, the polysilynes, have been examined as resist materials for deep ultraviolet lithography. These polymers have the formula [SiR]n, and polymers with R=n-propyl, n-butyl, isobutyl, amyl, cyclohexyl, and phenyl have been examined. Photolysis of polysilyne films with 193, 215, or 254 nm light results in the formation of an organosiloxane. Latent images of this oxidized material can be selectively developed yielding a negative tone image either by wet development in toluene or dry development in a Cl2 or HBr plasma. The best sensitivities at 193 nm were 20 mJ/cm2 for wet developed poly(n-butylsilyne) and 200 mJ/cm2 for dry developed poly(phenylsilyne). Positive tone wet development in polar solvents, such as acetone, is incomplete and yields a thin, insoluble residue layer.
Characterization of oxide film on titanium by scanning tunneling microscopy/spectroscopy: Influence of the tip composition
Authors: Jobin M. , Emch R. , Zenhausern F. , Steinemann S. , Descouts P.
Published: July 2002

Atomic level structural and electronic analysis of titanium passivated by an oxide film is crucial for understanding the biocompatible properties of this transition metal. Scanning tunneling microscope (STM) images of electropolished titanium samples show a rather smooth surface in the nanometer range with structure attributed to surface defects induced by the electropolishing technique. I–V spectra were performed with the STM using W, PtIr, and Au tips. These spectra completed by normalized conductivities spectra are compared and discussed in order to determine surface electronic properties of the oxide film and to estimate the influence of the STM tip. The surface band gap of this amorphous thin film mainly composed of TiO2 is shifted to positive tip voltage and is similar to the one of an n-type semiconductor with band bending bringing the valence band closer to the Fermi level. The surface band gap extends from −0.5 to +0.8 eV for a Au tip and from −0.1 to 0.7 eV for a W tip, which shows that W induces states in the band gap. Reproducible peaks in the local density of states of our Ti oxide surface appear both for Au and W tips at the same energies and are clearly apparent in the normalized conductivity curves.
Angle-resolved tunneling spectroscopy of the charge density wave density of states in 1T-TaS2
Authors: Enomoto H. , Ozaki H. , Suzuki M. , Fujii T. , Yamaguchi M.
Published: July 2002

We report the first observation of the anisotropic nature of the gap structure in 1T-TaS2 associated with the charge density waves (CDW). The rotating angle dependence of the tunneling current between two parallel planar crystals, probe crystal and sample crystal, was measured by rotating the former over the latter. By virtue of the conservation of the perpendicular component of the electron wave vector in the direct tunneling, together with the parallelopiped shape of the band structure in the two-dimensional materials, the tunneling current between two layered materials manifests the angle dependence with the rotational symmetry of the energy band structure around the axis normal to the layers. The energy gap and other parameters of the CDW density of states are observed in the dI/dV-V characteristics. They show 60° periodicity, reflecting the symmetry of the CDW associated electronic structure in 1T-TaS2.
X-ray irradiation effects on a microwave-plasma chemical vapor deposition diamond membrane
Authors: Suzuki K. , Kumar R. , Windischmann H. , Sano H. , Iimura Y. , Miyashita H. , Watanabe N.
Published: July 2002

Diamond membrane masks, fabricated using microwave-plasma chemical vapor deposition, have been evaluated for their dimensional stability as well as other principal characteristics, during 15-MJ/cm3 x-ray irradiation within a vacuum. After x-ray irradiation, intensity of the diamond Raman band at 1332 cm−1 increased to 150% of that unirradiated membrane. Spin density in the diamond increased up to 1.5×1019 spins/g; two times higher than that before irradiation. Despite these effects, in-plane distortion due to x-ray irradiation of the diamond membrane on a half-area of 25-mm square was extremely small (<0.08 μm). Optical transparency of the membrane increased by 4.5%–6.1% at 633 nm due to x-ray irradiation.
Two-mirror telecentric optics for soft x-ray reduction lithography
Authors: Kurihara Kenji , Kinoshita Hiroo , Mizota Tsutomu , Haga Tsuneyuki , Torii Yasuhiro
Published: July 2002

A two-mirror telecentric optic has been designed for soft x-ray reduction lithography with high throughput using synchrotron radiation. A resolution of 0.1 μm is achieved at a wavelength of 130 Å with a 15-mm ring field. In the design, aberrations, including distortion, are reduced using aspherical concave and convex mirrors with an ellipsoid surface at a numerical aperture of 0.07. Telecentric imaging is obtained by illuminating a reflection mask using focusing toroidal mirrors. The designed optics achieves a modulation transfer function (MTF) value of over 40% at a spatial frequency of 5000 lines/mm capable of resolving 0.1-μm lines and spaces. The depth of focus is ±1 μm. The distortion is <0.01 μm in the image field. The imaging field is a 12.5-mm radius ring field which enables a 15×15-mm field exposure by the ring-field scanning method. The reduction ratio is 1/5.