bluuebunny/crossref_metadata_2025 huggingface dataset:
Hollow cathode etching with CF4 gas mixtures
Authors: Horwitz Chris M.
Published: July 2002

Earlier papers have shown that high etch rates and controlled profiles can be obtained with the rf hollow cathode configuration. The etch selectivity of SiO2 with respect to Si was of the order 5 to 1 with a CF4 etch gas, and this paper investigates the effect of H2 and O2 gas additions on the etch selectivity in a symmetrical hollow cathode system. CF4/O2 mixtures cause the SiO2/Si etch rate ratio to vary between 0.75 and 1.5. CF4/H2 mixtures have to date yielded a SiO2/Si etch ratio of 16. The etched angle in CF4/H2 mixtures is controlled as in CF4 hollow cathode etching, and it is shown that this control is caused by the competitive coating process.
Simulation of mask scattering effects in masked ion beam lithography
Authors: Atkinson Gary M. , Neureuther Andrew R.
Published: July 2002

A new simulation program has been developed for modeling masked ion beam lithography and has been used to study the impact of mask scattering on resist profile shape. The model uses analytical calculations to find the energy deposition in the resist. The program output is the development contour in the resist for any specified time, mask, resist, or beam parameters. The program has been applied to a study of the mask membranes and absorber patterns used in masked ion beam lithography. The applications are to membrane support scattering, absorber layer scattering, tapered absorbers, and technological evaluation. The membrane scattering of the beam is found to have a minimum divergence of ≊0.3°. It is also possible to achieve inverse contrast in the ion beam mask, for thin absorbers. This same effect causes the effective bias of a tapered absorber to be approximately 75% of the taper width. Also, relatively high angled tapers can be tolerated for heavy absorbers within certain limitations. Finally, using optimistic assumptions, the channeling approach to masked ion beam lithography appears limited to a minimum feature size of about 0.25 μm.
Digital image processing for micrometrology
Authors: Frosien J.
Published: July 2002

The production of high-performance micro- and optoelectronic circuits with constant physical properties requires not only qualitative control but also quantitative determination of the microstructures which they contain. Such investigations are not limited to completed circuits. The aim is to apply them to every single process step in order to detect and correct errors and exceeded tolerances at an early stage. The low-voltage scanning electron microscope is the ideal instrument for these metrological investigations. By combining it with a digital image processing system, structural measurements can be obtained automatically from surface images. The image evaluation programs developed allow objective determination of structural widths and angles of slope as well as grating constants of periodic objects. A measuring accuracy of 0.05 μm can be attained. The time required for image evaluation lies between a few seconds and one minute depending upon the procedure used.
The flip-and-shift signal enhancement application for a predictive electron-beam pattern registration model
Authors: King D. C. , Steckl A. J. , Morgenstern J. L. , McDonald J. F. , Bourgeois M. A. , Yemc D. J. , Elminyawi I.
Published: July 2002

A simple physical model based on an absorption-like mechanism has been developed for the backscattering of electrons from registration marks used in e-beam lithography pattern alignment. The model uses a signal with an exponential dependence on the traversed material path length. This model produces simulated registration signals in close agreement with experiments for marks with a variety of topological features. Error between data and simulation is less than 5%. The model has been used in investigations of novel registration signal manipulation schemes. Signal power resulting from the use of one such scheme, ‘‘flip-and-shift,’’ is shown to be significantly greater than from simply summing individual detector signals.
An optical alignment microscope for x-ray lithography
Authors: Bobroff N. , Tibbetts R. , Wilczynski J. , Wilson A.
Published: July 2002

An alignment system suitable for x-ray proximity printing has been developed. The imaging system is based on a dual focus, dark field microscope. A detailed discussion of the optical system and its laboratory performance is presented.
Fabrication of bipolar transistors by maskless ion implantation
Authors: Reuss Robert H. , Morgan Damon , Goldenetz Ann , Clark William M. , Rensch David B. , Utlaut Mark
Published: July 2002

The first focused ion beam (FIB) arsenic ion implants are reported. A shallow junction, vertical npn bipolar transistor fabricated by maskless implantation of B and As is described. For comparison, devices on the same wafer were also processed with conventional, broad-beam B and/or As implants. Good transistor performance is obtained for each type of implanted transistor. Device characteristics for FIB and conventional implants are generally the same. However, initial results indicate that diode quality and junction leakage appear somewhat degraded (excess generation–recombination) for FIB arsenic implanted devices. Characteristics of FIB boron implanted devices obtained over an extended period have been measured. These data indicate that wafer-to-wafer dose uniformity and quality (diode ideality and leakage currents) is equal to that for conventional implants (standard deviations <10%). Device-to-device quality on a single wafer is also equal for the two techniques, while the device reproducibility is somewhat less for FIB, indicating some minor fluctuations in beam current (dose).
Focused ion beam etching of resist materials
Authors: Harakawa K. , Yasuoka Y. , Gamo K. , Namba S.
Published: July 2002

The self-developing and processing properties of nitrocellulose were investigated in comparison with the resists such as PMMA (polymethylmethacrylate) and PBS (polybutene-1-sulfone). Then self-developed submicron patterns were drawn in nitrocellulose with focused ion beam irradiation. A 200 nm thick, 370 nm wide aluminum line pattern was obtained by using a 520 nm thick nitrocellulose layer.
Polyimide as a negative electron resist and its application in crossovers and metal on polymer mask fabrication
Authors: Patrick W. , Mackie W. S. , Beaumont S. P. , Wilkinson C. D. W.
Published: July 2002

Polyimide is characterized as a negative electron resist with an average contrast of 2.1. Crossovers in which continuous metallic lines are deposited over polyimide bridges (patterned by e-beam lithography) have been fabricated. The leakage current through the polymer is negligible for potentials as high as 70 V applied between the crossovers and underlying contacts. A process for fabricating metal on polymer (MOP) ion implantation masks, using only organic solvents, is described. These masks are shown to be more reliable than those fabricated using oxygen plasma etching, as they are easier to remove completely after ion implantation.
Optimization of solvent development in radiation induced graft lithography of poly(methylmethacrylate)
Authors: Kim S. Y. , Choi J. , Pulver D. , Moore J. A. , Corelli J. C. , Steckl A. J. , Randall J. N.
Published: July 2002

Irradiation of poly(methylmethacrylate) film, PMMA, with e-beam, H+, x ray, and deep UV creates reactive centers which combine with acrylic acid vapor to form graft and/or block copolymers with solubilities different from that of PMMA. Dissolution rate studies of modified PMMA using a variety of solvents have revealed that while toluene forms good negative-tone images, it develops too slowly, and that a mixture of methylisobutylketone and isopropanol is not selective enough to give images with good contrast. Consideration of the solubility parameters of pure PMMA and pure poly(acrylic acid) (PAA) indicates that organic esters such as methylformate (MF), ethylacetate (EA), and a commercially available mixture (Dupont Co.) of dimethylsuccinate, dimethylglutarate, and dimethyladipate (DBE) could be useful development solvents for the samples under discussion. The data obtained reveal that toluene gives the best image, but also reveal that the dissolution rates decrease as the development fronts proceed into the body of the film.
New techniques for modeling focused ion beams
Authors: Narum D. H. , Pease R. F. W.
Published: July 2002

Monte Carlo computer simulations of e-beam systems have proven quite successful in determining the contribution of mutual particle repulsion to critical beam parameters such as spot size and energy spread. For similar simulations on ion beams, the small charge-to-mass ratio of ions results in significant numerical problems which do not occur in the simulation of electron beams. New techniques are introduced which extend the application of this Monte Carlo technique to higher perveance beams. These techniques include the use of a periodic boundary condition on the simulation charge packet, a dynamic sphere of influence which reduces the number of interactions to be evaluated, and a dynamic time step which accounts for varying ion densities and random ion collisions. The resulting program is used to simulate a focused 50 kV Ga+ beam, with a source divergence angle of 2 mrad and currents of up to 1 μA. Significant beam broadening was observed at currents in excess of 10 nA and the broadening was observed to increase with the application of a retarding field. Finally, arrival time distributions at the target plane were analyzed and no reduction in the statistical noise was observed as a result of space charge smoothing.
The mechanism of overhang formation in diazide/novolak photoresist film by chlorobenzene soak process
Authors: Mimura Yoshiaki
Published: July 2002

The mechanism of overhang formation in a diazide/novolak photoresist film by the chlorobenzene soak process for lift-off stencil fabrication is investigated by gel permeation chromatography. The experimental results show that overhang profile formation is controlled mainly by the removal of photoactive compounds (PAC’s) from a resist film. The amount of PAC loss within the modified region in a resist film must be precisely controlled to form a desired overhang profile. The amount of PAC loss depends mainly upon the molecular weight of the PAC’s and the kind of soaking solvent used.
Transform based proximity corrections: Experimental results and comparisons
Authors: Haslam M. E. , McDonald J. F.
Published: July 2002

This paper presents a comparison between the transform based proximity correction method and the GHOST background equalization method. Both methods are presented and evaluated in general as well as for a specific test structure. Emphasis is placed upon the frequency domain characteristics of each approach. It is shown that the GHOST method, by itself, while successfully equalizing the background exposure without the use of extensive computation, lacks good high frequency characteristics. This limits the fidelity of the corrections for features in the range of 0.50–0.20 μm. The transform or Fourier precompensation method can handle such features but it requires some degree of computation and data compaction. Experimental results are presented along with corresponding computer generated simulations. It is found that a very accurate measurement of the e-beam point spread function is essential to make the transform method perform properly. A technique is presented to achieve such a measurement.
Lead calcium telluride grown by molecular beam epitaxy
Authors: Partin D. L. , Clemens B. M. , Swets D. E. , Thrush C. M.
Published: July 2002

PbCaTe has been grown for the first time using the technique of molecular beam epitaxy. Source ovens containing Ca, Te, PbTe, Tl2Te (p dopant) and Bi2Te3 (n dopant) were used to grow films on (111) oriented BaF2 substrates or on (100) oriented PbTe substrates. Auger electron spectroscopy studies of Pb1−xCaxTe films have shown that the incorporation of calcium is independent of substrate growth temperature in the range 300–400 °C, despite the relatively high vapor pressure of elemental calcium in this temperature range. The diffusion coefficient of Ca in PbTe is ≲3×10−17 cm2/s at 370 °C. The energy band gap increases as dEg/dx=2.5 eV for small x, as determined by infrared transmission studies at room temperature. For x=0.15, the energy gap is 0.65 eV. The index of refraction decreases with increasing calcium concentration up to x∼0.15, but increases anomalously for x=0.26. The electron and hole mobilities at 80 K are comparable and decrease to a few hundred cm2/V s for x=0.15. From x-ray diffraction studies, the crystal lattice constant is almost independent of x for x<0.15. These results suggest that PbCaTe may be a useful material for long wavelength (λ>2 μm) diode lasers.
A Mott mixer diode
Authors: Nagle J. P. , Hing L. A. , Kerr T. M. , Summers J. G.
Published: July 2002

The success of millimeter wave systems depends on the realization of high performance mixer diodes with minimal device parasitics. A Mott diode structure has been fabricated which gives a constant capacitance over a wide voltage range. A consequence of this is that the variation in noise figure as a function of local oscillator power is significantly less than for a conventional Schottky diode structure. The Mott structure requires a thin lightly doped epilayer, 0.15 μm thickness with carrier concentration of 5×1016 cm−3, on a thick heavily doped layer, 3 μm thickness with carrier concentration 2×1018 cm−3 on a semi-insulating substrate. The requirement of sharp interfaces between the n/n+ and n+ semi-insulating substrate regions necessitates the use of molecular beam epitaxy (MBE) grown material. The diodes fabricated on these layers exhibit excellent dc characteristics having a typical breakdown voltage of 8 V, series resistance of 4 Ω, turn-on voltage of 0.7 V, and total capacitance of 50 fF. These devices are rugged, economical, and have been fabricated using integrated circuit compatible technology. As a result of this the diode is being used as the basic building block in the design of monolithic millimeter wave integrated circuits.
Lattice-mismatched heteroepitaxial interface of GaAsySb1−y on GaAs substrates
Authors: Cheng H. , Koyanagi T. , Milnes A. G.
Published: July 2002

Specular GaAsySb1-y films with Sb content less than 30% have been grown heteroepitaxially on GaAs buffer layers by controlling the atomic flux ratio of Sb to Ga with the supply of excess arsenic flux to maintain a slight group V stabilized surface condition. The incorporation coefficient of antimony atoms is about 0.5 at a growth temperature of 520 °C. Free carrier concentration profiles of specimens with GaAsySb1-y/GaAs interfaces measured by electrolytic C–V profiling show dips in the interface regions, probably caused by interface energy states within the band gap due to the misfit structure. The total number of missing carriers in the interface region is on the order of 3×1011 cm−2 and is two orders of magnitude lower than that expected from dangling bond lattice-mismatch considerations.
Unique resist profiles with Be and Si focused ion beam lithography
Authors: Morimoto Hiroaki , Onoda Hiroshi , Kato Takaaki , Sasaki Yoshinobu , Saitoh Kazunori , Kato Tadao
Published: July 2002

The delineation of resist patterns has been investigated for two kinds of ions, Be and Si. Patterns consisting of 0.2 μm lines and spaces were fabricated in 0.7 μm thick resist with good repeatability and accuracy. This shows that the influence of proximity effects can be disregarded. The broadening of patterns was observed for Si exposure because of the more significant influence of recoil atoms. As a special application of focused ion beam lithography, a new process for fabricating a mushroom gate electrode for a GaAs microwave field-effect transistor (FET) was demonstrated utilizing the particular exposure characteristics of the different ion species.
Shot noise limits to measurement accuracy and bandwidth in electron-beam testing
Authors: Spicer D. F. , Sackett J. N.
Published: July 2002

Theoretical calculations of the limits due to shot noise in e-beam waveform measuring systems are presented. A theoretical equation for the secondary electron energy distribution is used to derive the limits to attainable measurement bandwidth, voltage resolution, and measurement time. Real time, averaged real time, and stroboscopic measurement methods are considered. The results (which depend almost entirely on the parameters of the electron beam) are presented as a set of simple equations and a set of graphs. It is concluded that shot noise significantly limits the performance of practical e-beam testing systems.
Influence of absorber stress on the precision of x-ray masks
Authors: Müller K.-H. , Tischer P. , Windbracke W.
Published: July 2002

The membrane of an x-ray mask is only a few microns thick in order to achieve a high x-ray transmission in the areas without absorber patterns. Stress within the absorber material can lead to distortion of such a thin membrane and, consequently, also of the placement of the absorber pattern. The acceptable relative edge distortion ε of an absorber pattern on a mask decreases with the increasing number of functions within the chip area (ε is defined as the ratio between the displacement and the length of the chip). The next generation of megabit memories needs distortions of ε≤6×10−6. To estimate the requirements for the maximum allowable stress within the absorber material, we calculated the pattern distortion of an x-ray mask using a simple one-dimensional model. The results show the influence of thickness and Young’s moduli of the membrane and of the absorber material on the edge distortion of a pattern. The most important conclusion from these calculations is that the stress of the gold absorber material should be less than 107 N/m2 in order to achieve ε≤6×10−6. We compared the results of the calculations with experimental results. We measured the stress of the electroplated gold layers before and after annealing. In parallel we determined the resulting distortions on the thin x-ray masks using light-optical methods. Good agreement between calculations and experimental results was found.
Zero step coverage using a nozzle jet expansion deposition technique
Authors: Ramanarayanan R. , Wong J. , Lu T-M. , Skelly D.
Published: July 2002

A completely nonconformal Al step coverage was observed on via structures with almost vertical sidewalls using a nozzle jet expansion deposition technique. For vias of dimensions 0.8 and 1 μ, deposition of Al by this technique resulted in a uniform layer of Al at the bottom of the vias with no sidewall coating. Possible use in several very large scale integrated (VLSI) metallization applications is suggested.
Al on GaAs(110) revisited: Kinetic considerations
Authors: Williams M. D. , Chin K. K. , McCants C. E. , Mahowald P. H. , Spicer W. E.
Published: July 2002

The effects of surface and interface kinetics on the formation of the Schottky barriers are presented. The results were obtained from photoemission spectroscopic studies of the Al/GaAs(110) system. Al clusters when it is deposited by evaporation onto the room temperature GaAs substrate. We have kinetically limited this process by cooling the substrate (≤−50 °C). A comparison of the interfaces in this regime and at room temperature shows a significant variation in the Fermi level pinning behavior with overlayer coverage. The pinning is significantly delayed from reaching completion (0.7 eV below the conduction band minimum for n-type GaAs) for the cold substrate. In fact, it is only 0.5 eV at 3 ML. Once the substrate is warmed to room temperature, however, the pinning goes to completion. The pinning for the cold substrate also goes gradually to completion for coverages between 1.4 and 8 ML. To first order, this work supports the model of Zunger which suggests that the pinning is due to defects induced by the formation of metal clusters.
Chemical reaction at the In on GaAs(110) interface
Authors: Chin K. K. , Kendelewicz T. , Newman N. , Lindau I. , Spicer W. E.
Published: July 2002

The annealing of In on the GaAs(110) interface has been studied by photoemission electron spectroscopy (PES). It is found that the metallic In overlayer (10 ML) evaporated on the substrate at room temperature starts to disperse at 120 °C (the melting point of bulk In is 157 °C). Upon annealing above 160 °C, the In 4d core level displays a chemical shift of 0.8 eV which is a typical binding energy difference between the In 4d of metallic In and that of covalently bonded In. This is interpreted as one of the spectroscopic evidences that the chemical reaction cIn+GaAs→InxGa1−xAs+Inc−xGay +(x−y)Ga may occur at the interface. The correlation of the interfacial chemical reaction, the kinetic effect, and the bulk thermodynamic prediction is explored. It is argued that, since the reaction is kinetic or interdiffusion limited, the interface (not in equilibrium) of 10 ML In on GaAs upon annealing can be treated as a very In-rich ternary system in thermodynamic equilibrium. Thus, it is possible that the observed interfacial reaction can be explained by the bulk thermodynamic predictions.
Kinetics and energetics studies at surfaces and interfaces
Authors: Kobayashi A. , Paik S.-M. , Das Sarma S.
Published: July 2002

The diffusion coefficient on a surface and the strain at a lattice-mismatched interface are obtained employing a molecular dynamics simulation and an atomistic energetics calculation, respectively. It is found that (i) the diffusion coefficient exhibits a nonlinear Arrhenius behavior, (ii) the coverage dependence of the diffusion coefficient is independent of temperature and can be cast into a simple exponential form, (iii) the strain developed at the interface depends on the size of adsorbate clusters, and (iv) the critical size for the onset of pseudomorphism depends linearly on the relative strength between the adsorbate–adsorbate and adsorbate–substrate interactions.
Low resistance polysilicon interconnects with self-aligned metal
Authors: Mitchell N. S. J. , Armstrong B. M. , Gamble H. S. , Wakefield J.
Published: July 2002

A technique for enhancing the conductivity of polysilicon interconnects by self-aligned layers of platinum has been developed. A sheet resistance of approximately 1 Ω/⧠ was achieved for an interconnect height of 270 nm. Very thin layers of platinum have also been used to provide self-alignment of other metals such as nickel, titanium, and aluminum. Nickel and titanium required prolonged ultrasonic processing to achieve self-alignment to the polysilicon, as their specific stiffness coefficients were less favorable than that of platinum. Aluminum self-alignment was only achieved after overlaying with films of nickel and platinum, and subsequently removing the latter layers by dissolving the nickel in fuming nitric acid. Polysilicon interconnects enhanced with a layer of self-aligned aluminum yielded a sheet resistance of 1.2 Ω/⧠ for a total interconnect height of 120 nm. Metal-oxide semiconductor (MOS) transistors and ring oscillators manufactured with metal enhanced interconnects showed no degradation effects when compared to those manufactured by the standard MOS process. Therefore, the process offers the advantages of self-aligned source and drain regions and high yields associated with polysilicon gate technology together with those of a highly conducting metal gate.
Distortion correction and overlay accuracies achieved by the registration method using two-stage standard mark system
Authors: Takamoto Kiichi , Okubo Tsuneo , Matsuda Tadahito
Published: July 2002

A registration method using the two-stage standard mark system is developed for high accuracy overlaying of patterns on a deformed wafer in an electron beam lithographic system used for direct wafer writing of 0.5 μm very large-scale integrated (VLSI) patterns. Deflection distortions are corrected according to height z of a pattern writing field on a wafer. In this paper, deflection distortion correction and overlay accuracies are examined experimentally. Main field (2.6×2.6 mm) distortions are corrected using the third-order power function of the main field coordinates (X, Y). Correction coefficients related to shift, deflection gain, and deflection rotation are shown to be a linear function of z, in spite of varying the beam focusing level with z. Each distortion expressed in terms up to the third-order power of (X, Y) can be corrected with an accuracy within 0.02 μm. Overlay accuracies within 0.12 μm (3σ) are yielded when two-layer test patterns are exposed on a wafer deformed about 75 μm in the Z direction.
Archival information storage by selective electron beam melting of structured targets
Authors: Oro James A. , Wolfe J. C.
Published: July 2002

We demonstrate archival information storage by electron beam melting of selected elements within a two dimensional array of gold columns. The individual columns were 60 nm in diameter, 270 nm in height, and spaced on 130 nm centers. These columns could be selectively melted with a 40 nm diam, 175 nA, 7 kV electron beam in times less than 60 ns. Upon melting, the columns become spherical droplets with 120 nm diameter. The encoding is binary; partial melting does not occur.
Effects of ambient gases on ion emission stability of liquid-metal ion sources
Authors: Arimoto Hiroshi , Miyauchi Eizo , Hashimoto Hisao
Published: July 2002

Effects of ambient gases on ion emission stability of Au–Si–Be and Pd–Ni–Si–Be–B liquid-metal (LM) ion sources have been studied. Water vapor and oxygen gas have significant effects on ion emission stability. These effects are thought to be due to oxidation of the liquid-metal surface, especially the Be atoms. A higher operating temperature enhances these effects, while it reduces the effects for Ga-ion sources. Vapor pressures of resultant oxides are discussed to explain these results. We have obtained positionally stable ion beams (fluctuation <0.08 μm) with a constant ion current (fluctuation <0.02%) and a constant beam diameter (fluctuation<0.03 μm at beam diameter of 0.2 μm) by operating the sources under a vacuum pressure of 2×10−7 Torr in a 100 kV FIBI (focused-ion-beam implanter).
The importance of the short-circuit failure mode in aluminum electromigration
Authors: Towner Janet M.
Published: July 2002

Electromigration was studied in a number of Al-based metallizations. For pure Al and Al–Cu alloys, open circuits were the dominant failure mode. In other systems, including layered conductors and homogeneous Al–Ti, Al–Cr, and Al–V alloys, interlevel short-circuit failure was greatly favored. Short circuits were usually detected prior to a significant increase in the conductor resistance.
Sum-frequency generation on dye-coated surfaces using collinear and noncollinear excitation geometries
Authors: Muenchausen R. E. , Nguyen D. C. , Keller R. A. , Nogar N. S.
Published: July 2002

Resonantly enhanced surface second-harmonic generation and sum-frequency generation has been demonstrated on rhodamine 6G coated glass substrates using different excitation geometries. The collinearly excited, doubly-resonant sum-frequency signal is enhanced by more than two orders of magnitude relative to resonantly enhanced second-harmonic generation. For noncollinear excitation, the relative efficiency of nonlinear generation as a function of the angular dependence of the input beams is calculated and compared with experiment.
Tunneling spectroscopy study of aniline adsorbed on aluminum oxide
Authors: Graves R. J. , Wallace C. B. , Ellialtioglu R. , White H. W.
Published: July 2002

Aniline has been studied using tunneling spectroscopy. Detailed comparisons of the spectrum with infrared data of aniline adsorbed on iron oxide, other tunneling data, and infrared and Raman spectra of aniline in the gas, liquid, and solid phases are presented. Large shifts (>100 cm−1) to lower frequencies were seen for the two aniline N–H stretching bands, the NH2 deformation mode, and the C–N stretching mode. Smaller shifts were also seen in the aromatic ring stretching mode frequencies. Comparisons of a′ with a″ vibrational modes and of out of the benzene plane with in-plane bending modes indicated that the a″ modes and the in-plane bending modes had lower intensities and appeared less frequently than did the a′ and the out-of-plane modes in the spectrum. The shifts in N–H frequencies and the dominance of the a′ and the out-of-plane modes indicated that the orientation of aniline on aluminum oxide is one in which aniline is bonded to the surface via the N atom with the benzene group primarily parallel to the surface, though slightly tilted away from the surface, and the NH2 H atoms undergo some degree of hydrogen bonding with surface O atoms or hydroxyls. This orientation is consistent with the results of Busca et al. as discussed in the text.
Characteristics of Nb-based tunnel junctions fabricated by selective trilayer ion-beam etching process
Authors: Tsuge H.
Published: July 2002

Characteristics of Nb/Nb oxide/Pb-alloy junctions fabricated by selective trilayer ion-beam etching process have been studied with respect to junction quality, reproducibility, uniformity, and thermal stability. The key steps in the process comprise in situ junction trilayer formation involving thermal oxidation, junction area definition by deep ultraviolet photolithography, and highly selective Pb-alloy layer patterning by ion-beam etching in an Ar–O2 atmosphere. Especially, the junctions fabricated in this process have exhibited excellent uniformity and reproducibility with PbAuIn and PbIn counterelectrodes. Standard deviations in critical current for 100 series-connected junctions with 4×4 and 2×2 μm areas are 0.8% and 2.4%, respectively. The junctions with critical currents of about 80% of Bardeen–Cooper–Schrieffer values and without any knee structure in I–V curves are obtained reproducibly over a wide critical current range from 102 to 104 A/cm2. Annealing tests have indicated that these junctions have sufficient thermal stability for integrated circuits.
Reactive ion-etching-induced damage in silicon using SF6 gas mixtures
Authors: Arora B. M. , Pinto R. , Sachidananda Babu R.
Published: July 2002

Damage introduced in silicon during reactive-ion etching (RIE) in SI6 gas containing 10 Vol % of H2, He, N2, O2, or Ar has been investigated using Schottky barrier measurements and Rutherford backscattering. RIE was performed at 0.1 Watt cm−2 power density with the radio frequancy (rf) cathode covered with a quartz plate. The annealing effect on damage was studied at various temperatures up to 800 °C in dry N2. The results indicate that the damage has two components namely, a shallow near-surface region with lattice damage and a deep layer containing discrete defect centers which act as donors. The extent of the deep damage layer is the net balance between two competing processes: (a) the etch rate, and (b) the rate of damage migration into silicon. However, the damage has been found to reach a saturation level after RIE for 1 min in all the gas mixtures studied. The results also suggest that RIE in SF6+10% H2 gas mixture causes a deep damage layer which could, however, be annealed at 150 °C aided significantly by the passivation of defect centers by hydrogen permeated during RIE. On the other hand, the damage induced in SF6+10% Ar-etched samples has been found to anneal at 800 °C indicating there by a higher level of lattice damage or amorphization of the near-surface layer of silicon. Therefore, the mass of the bombarding ion significantly affects the nature of the damage layers.
Cleavage-related electronic states of Al–InP(110) interfaces
Authors: Viturro R. E. , Shaw J. L. , Brillson L. J.
Published: July 2002

Cathodoluminescence spectroscopy studies of III–V compound semiconductor surfaces and their metal interfaces show that the optical emission of deep-level surface and interface states depend on semiconductor-surface morphology. Spatially resolved measurements reveal metal-induced interface states at cleavage steps whose optical emission properties depend on electron-beam injection level. The density and spatial distribution of such metal-cleavage-related states may account for variation in electronic measurements reported for clean III–V compound semiconductor/metal interfaces.
Hydrogen implanted polycrystalline silicon: Resistivity and grain boundary chemistry
Authors: Puppin E.
Published: July 2002

Low-pressure chemical vapor deposition polysilicon samples doped with B, P, and As were implanted with H+2 and subsequently annealed at different temperatures in the range from 100 to 1000 °C. The observed evolution of resistivity suggests that hydrogen ionizes the dopant atoms which have segregated to grain boundaries and reactivates them from the electrical viewpoint.
Fast Monte Carlo simulation of charged particle beams
Authors: Jansen G. H.
Published: July 2002

A fast algorithm for the ray tracing of an ensemble of interacting charged particles in drift space has been developed for a fast Monte Carlo simulation program. It is based on a decomposition of the full interaction into a sum of two particle effects, which are estimated by means of analytical results. It is demonstrated that the reduction to two particle dynamics is allowed for practical beams used in lithography and microscopy, without decreasing the accuracy of the simulation. The new algorithm is up to two orders of magnitude faster (depending on the specific beam considered) than the algorithm using third order numerical integration with a variable time step. The program can be used on a fast microcomputer keeping the run time within practical limits.
Optimization of the magnetic deflection system by the method of orthogonal design
Authors: Zhi-xing Xie , Da-quan Huang , Qing-gai Shen
Published: July 2002

By using the expressions of the field parameters and with the aid of the Orthogonal Design Method, we optimized the design of the saddle deflection yoke with a ferromagnetic shield. The results obtained agree with the practical model. It is pointed out that the end ear and the distribution of the field parameter B0(z) have important effects on the deflection aberrations. An example is given that compares the electron optical properties of the deflection coils with the cosine distribution and finite length with that of a distributed winding.
Design of an electrostatic optical system for ion beam lithography
Authors: Tang T. T. , Sheng C. Y.
Published: July 2002

An electrostatic optical system has been designed to produce a submicron ion beam probe. The main task is to design a low spherical and low chromatic aberration accelerating–focusing lens for the ion gun and to design a combined focusing–deflection system with low deflection aberrations. The gun lens aberrations are minimized by using a parameter optimization method. Very low chromatic aberration coefficients of 3.1 or 6.9 mm are obtained for a working distance of 3 or 6 mm and for an acceleration ratio of 10. An analysis is made of the combined electrostatic focusing–deflection system using MOL concept. A practical electrostatic MOL system was developed which gives good overall deflection aberration performances. It has a theoretical resolution of 73 nm for a beam half-angle of 5 mrad over a 0.8×0.8 mm scanning area and the resolution can be upward to 20 nm after dynamic correction of the deflection aberrations.
Fabrication of ultrasmall devices on thin active GaAs membranes
Authors: Lee K. Y. , Frost J. , Stanley C. , Patrick W. , Mackie W. S. , Beaumont S. P. , Wilkinson C. D. W.
Published: July 2002

We report here a method for fabricating metal–semiconductor field effect transistors (MESFET’s) with very short gates on 50 nm thick n-doped GaAs membranes. Membrane devices can be compared to conventional devices on solid substrates in order to study the effect of a substrate on device operation. We also present a technique for making extremely fine pitch interdigital gratings. A metal grating with 24 nm center-to-center spacing has been fabricated on a silicon nitride membrane, the smallest pitch reported so far. Finally, we propose a lateral superlattice structure by using such a grating on a GaAs membrane.
A study of anisotropic trench etching of Si with NF3–halocarbon
Authors: Sellamuthu R. , Barkanic J. , Jaccodine R.
Published: July 2002

Plasma etching of Si was carried out with a parallel plate, radial flow, 13.56 MHz plasma etcher. The formation of a polymer film has been promoted by adding a controlled amount of halocarbon to NF3. The polymer film acts as a sidewall barrier film. As a result, the undercutting usually observed in the etch profile has been eliminated or minimized. The deposition of the polymer film depends on the chemistry and concentration of halocarbon. Etch rates ranging from 0.4 to 0.6 μm/min have been obtained.
Enhanced plasma etch resistance of acrylic acid–calcium acetate modified poly(methylmethacrylate)
Authors: Choi J. O. , Kim S. Y. , Moore J. A. , Corelli J. C. , Steckl A. J.
Published: July 2002

Enhanced dry etch resistance of acrylic acid–calcium acetate modified poly(methylmeth- acrylate) was demonstrated. Selective pattern formation in the irradiated (DUV and e-beam) areas was accomplished using PMMA as a base film and acrylic acid as a modifying monomer. After the acrylic acid modified PMMA has imbibed calcium ion, a latent image was developed by exposure to an oxygen plasma. An involatile calcium oxide layer which had resistance against CHF3 reactive ion etching was generated. The images of modified PMMA were transferred into the silicon dioxide layer.
Comparison of proximity effects in contrast enhancement layer and bilayer resist processes
Authors: Ong Edith , Singh Bhanwar , Ferguson Richard A. , Neureuther Andrew R.
Published: July 2002

Both contrast enhancement layer (CEL) and bilayer resist (PCM) processes, when compared to single layer resist process, promise to extend the useful resolution capability of optical projection printers. Using experimental results and sample simulation, the performances of the CEL and the PCM processes are compared in terms of linewidth control and proximity effects as a function of feature size, dose, and focus. The performances of the PCM and the CEL processes are almost equivalent on polysilicon substrates both experimentally and in simulation. On an aluminum substrate, the CEL process suffers from a large proximity effect which is not seen in the simulation. The PCM process, however, is unaffected by the substrate reflectivity because of the high absorption in the planarization layer. The observed results for the CEL may be caused by lateral scattering of energy from the unmasked areas into the masked areas from the rough aluminum surface. Another possibility is an increase of flare because of high substrate reflection, but simulation shows that this increase would have to be more than 6%.
The EBES4 electron-beam column
Authors: Thomson M. G. R. , Liu R. , Collier R. J. , Carroll H. T. , Doherty E. T. , Murray R. G.
Published: July 2002

The electron-beam column for AT&T Bell Laboratories’ EBES4 electron lithographic system forms a writing spot less than 125 nm in diameter (FWHM) with a current in excess of 250 nA at a fixed beam energy of 20 keV. A thermal-field-emission gun uses a long life zirconium–tungsten cathode operated at 1750–1800 K. The optical system contains three magnetic lenses and produces one intermediate crossover adjacent to a knife-edge. The beam can be blanked in less than 500 ps by deflecting it so that it is interrupted by the knife-edge. The beam current is changed by varying the strengths of the first and second lenses. Fast, accurate deflections are provided by three deflection systems: A telecentric magnetic deflection system covers a 0.28 mm square field and settles in 5 μs. Two electrostatic deflection systems cover 32 and 4 μm square fields with settling times of 100 and 1 ns respectively. The electron-beam column has excellent mechanical stability and reliability, and requires very little maintenance.
A high dose and high accuracy variable shaped electron beam exposure system for quartermicron device fabrication
Authors: Yoshikawa R. , Wada H. , Goto M. , Kusakabe H. , Ikenaga O. , Tamamushi S. , Ninomiya M. , Takigawa T.
Published: July 2002

An electron beam exposure system, EX-7, has been developed for advanced device technology development of quartermicron VLSI ICs such as a 64M bit dynamic RAM. The EX-7 utilizes the variable shaped beam, continuously moving stage and vector scanning concept.1,2 For the quartermicron PMMA (polymethyl-methacrylate) resist pattern formation, the system can write patterns with a 50 kV acceleration voltage and a 50 μC/cm2 dosage. Double electrostatic octopole deflectors have been developed to assure beam positioning accuracy. Deflection distortion can be reduced to 0.01 μm by an automatic calibration method. The beam edge resolution is 0.125 μm at 1 μm-square beam size and 200 A/cm2 current density. A newly developed hierarchical pattern definition method has greatly improved data compaction capability and reduced the conversion time from CAD LSI data to EX-7 data. The data conversion is accomplished by a large scale computer within 15 min for 108 flash/chip VLSI IC pattern data. The throughput of the EX-7 is 5 wafers/h at 109 flashes/wafer and 50 μC/cm2.
Electron-beam programming and testing of complementary metal-oxide semiconductor systems
Authors: Lyszczarz T. M. , Oliver S. , Fried J.
Published: July 2002

This paper describes the application of a scanning electron beam lithography system (SEBL) to the programming and testing of digital CMOS systems via the direct injection of charge into the integrated circuits. E-beam programmable interconnect structures, using floating-gate FETs, implement customization and fault avoidance techniques. E-beam controlled stimulus/response testing circuits, using substrate diodes, provide access to internal circuit nodes and thereby permit efficient testing procedures for large systems. Two system-level applications are presented—a digital multiplier and a crosspoint switch. In both cases, redundant circuit components and programmable interconnect are used to achieve fault tolerance and yield enhancement. An analysis of a wafer-scale crosspoint switch design indicates that e-beam restructuring techniques could be used to implement an 80×75 element array on a 4-in. wafer with 99% yield. The e-beam programming and testing circuits are shown to be compatible with commercial CMOS foundry services. The precision, speed, and automation of the SEBL system make these techniques practical for large-scale digital systems.
Evaluation of chlorinated polymethylstyrene as an x-ray negative resist
Authors: Yoshioka Nobuyuki , Suzuki Yoshiki , Ishio Noriaki , Yamazaki Teruhiko
Published: July 2002

Lithographic performance of chlorinated polymethylstyrene (CPMS) as an x-ray negative resist was investigated. The dependence of sensitivity on polymeric characteristics such as molecular weight and chlorine content was determined for Pd Lα, Al Kα, and Mo Lα radiation. Sensitivity of CPMS increased with increasing molecular weight in accord with the gel formation theory. Resolution requirements limit the molecular weight to below 5×105. The resolution limit was 0.75 μm at the residual resist thickness of 1 μm. Sensitivity of CPMS also depends on the chlorine content being a maximum at 10–18 wt. % for Al Kα and Mo Lα radiation, and at 20–32 wt. % for Pd  Lα radiation. The optimum sensitivity (D0.5g) of CPMS (∼(Mw)=5×105) for Al Kα, Mo Lα, and Pd Lα radiation was 8.4, 23, and 20 mJ/cm2, respectively. The contrast of CPMS for optimum sensitivity was 1.4 to 1.6. The dry etch resistance of the CPMS was 1.5 times higher than that of AZ-type photoresist in CF4+O2 (5%) gas plasma.
Stitching accuracy in a variable-shaped electron-beam exposure system
Authors: Takamoto Kiichi , Matsuda Tadahito , Omata Fujio , Okubo Tsuneo
Published: July 2002

Strategies for stitching rectangular electron beams or deflection fields, and measurement results of field stitching accuracy are described. A beam shaping aperture is newly developed to stitch rectangular beams with high accuracy. The aperture edges are defined by fine gold wires under tensile stress. Rectangular beams projected using this aperture are estimated to have an edge roughness within 0.01 μm and an orthogonality within 1 mrad. An x-y table system is fabricated so as to reduce each of the beam positioning errors due to table movement to 0.02 μm or less. Deflection distortion is measured, using a two-stage standard mark system mounted on the x-y table, and corrected. A test pattern is then written and field stitching accuracy evaluated. About 90% of the measured stitching accuracies are below 0.05 μm for a 1.5×1.5 mm field and about 50% for a 2.5×2.5 mm field.
Deposition of planarized dielectric layers by biased sputter deposition
Authors: Singh B. , Mesker O. , Devlin D.
Published: July 2002

Techniques for depositing planarized P-doped SiO2 layers on 1-μm-deep Al–1% Si, vertically etched, metal steps are described. The techniques, which consist of rf sputter deposition of P–SiO2 films onto rf biased substrates are a single-step process, which employs a single setting of the system parameters to achieve layer planarization and a two-step process, where a second etch-back mode is used to yield thinner planarized films in a shorter time. Scanning electron microscope data showing detailed quasidynamic evolution of the depositing layer profiles are presented. Measurements of dielectric and optical properties and film stress are also presented. The planarized films are found to have characteristics that are comparable to plasma-enhanced chemical vapor deposition SiO2 and thermal SiO2 films.
Sensitization of optical photoresists for electron-beam exposure of submicron patterns
Authors: Goncher G. M. , Lyngdal J. W. , Lamer G. L.
Published: July 2002

A major concern in using electron-beam exposure for defining patterns by direct write on wafers is throughput, given the high cost of an electron-beam lithography tool capable of writing and registering submicron features. Certain optical photoresists have electron-beam sensitivities more than an order of magnitude greater than the polymethylmethacrylate resists typically used for submicron pattern definition. It is desirable, however, to have resist sensitivity several times greater than this (on the order of 10−6 C/cm2) for efficient exposure of complex patterns over large areas of a wafer. Sensitization of optical resists with certain nitrogen heterocycles has been found to produce an increase in sensitivity to electron-beam exposure by up to a factor of 3. We have studied resist sensitization using several optical resists and sensitizers, with resulting electron-beam sensitivities as high as 1.4×10−6 C/cm2. Evidence for reaction between the resist and sensitizer prior to electron-beam exposure has been observed in certain cases. This reaction does not involve the diazo group of the photoactive compound, but produces substantial effects on resist sensitometry. Resolution of the resist is affected both by the type and concentration of sensitizer used; however, patterns as small as 0.25 μ have been defined.