bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of electromigration-induced failures in high-temperature sputtered Al-alloy metallization
Authors: Onoda Hiroshi , Hashimoto Keiichi , Touchi Kenshin
Published: July 2002

Electromigration-induced failures in high-temperature sputtered Al-alloy metallization have been studied in terms of Al-alloy microstructure, Si nodules, and reaction products between the Al alloy and the underlayer material. Highly reliable interconnects can be realized by high-temperature sputtered Al–Si–Cu-alloy metallization utilizing a Ti underlayer. The interfacial reaction between the growing Al–Si–Cu film and the Ti underlayer during high-temperature sputtering produces an Al3Ti-alloy layer having a resistivity of about 40 μΩ cm, and Si in Al alloy is absorbed in the Al3Ti layer without forming Si nodules. As the result, a bilayer structure of Al alloy/Al–Ti–Si alloy is formed. The electromigration resistance of the resultant TiN/Al alloy/Al–Ti–Si/TiN structure is drastically improved. It is speculated from the experimental results that this is because of the high quality of the Al-alloy film microstructure, i.e., an increase in (111) orientation, a decrease in the standard deviation of the grain distribution, and the superior current bypass effect through the Al–Ti–Si alloy and underlying TiN layer. In particular, an electrical current easily flows through the Al–Ti–Si alloy and TiN layer before a void completely crosses the upper Al alloy part of the metal line because the formation of the AlN high-resistance layer is suppressed by laying the Ti film between the Al–Si–Cu film and the underlying TiN film. Accordingly, the local temperature increase in the vicinity of the void is not essential to the subsequent void growth due to the lower resistivity of the Al–Ti–Si-alloy layer, resulting in the low void growth rate.
High-brightness light-emitting diodes grown by molecular beam epitaxy on ZnSe substrates
Authors: Eason D. B. , Yu Z. , Hughes W. C. , Boney C. , Cook J. W. , Schetzina J. F. , Black D. R. , Cantwell Gene , Harsch William C.
Published: July 2002

High-brightness blue and green light-emitting diodes (LEDs) operating at peak wavelengths in the range 489–514 nm have been successfully synthesized, processed, and tested. The high-brightness LEDs are II-VI heterostructures grown by molecular beam epitaxy at North Carolina State University using (100) ZnSe substrates produced at Eagle-Picher Laboratory by the seeded physical vapor transport process. The blue LEDs (489 nm) produce 327 μW at 10 mA drive current with an external quantum efficiency of 1.3%. In terms of photometric units, the luminous performance of the ZnCdSe blue LEDs is 1.7 lm/W at 10 mA. The brightest ZnTeSe green LEDs tested to date produce 1.3 mW at 10 mA peaked at 512 nm with an external quantum efficiency of 5.3%. The luminous performance of the green LEDs is 18 lm/W at 10 mA. Using recently-developed n-type conducting ZnSe substrates, green LEDs having external quantum efficiencies of 2.7% have also been demonstrated.
Nanofabrication of subwavelength, binary, high-efficiency diffractive optical elements in GaAs
Authors: Wendt J. R. , Vawter G. A. , Smith R. E. , Warren M. E.
Published: July 2002

A single-etch-step process for the fabrication of high-efficiency diffractive optical elements is presented. The technique uses subwavelength surface relief structures to create a material with an effective index of refraction determined by the fill factor of the binary pattern. Fabrication is performed using electron beam lithography and reactive-ion-beam etching on bulk GaAs, but the process is applicable to any material for which well-controlled etches exist. In this work, we designed and fabricated a blazed transmission grating for operation at 975 nm. The blazed grating exhibits a diffraction efficiency into the first order of 85% of the transmitted power.
Experimental study of field emission properties of the Spindt-type field emitter
Authors: Itoh Shigeo , Watanabe Teruo , Ohtsu Kazuyoshi , Taniguchi Masateru , Uzawa Satoshi , Nishimura Norio
Published: July 2002

This article reports experiments conducted to review several factors closely related to emission quality required for flat panel displays. Using the measurement of the emission of fabricated Spindt-type emitters, the dependence of current density on the distance from the tip of an emitter cone to the upper surface of the gate was investigated. It was also confirmed that the shape of the emitter cone was largely affected by the gate hole diameter and material of cone. The maximum half-angle of emission on anode from a tip was compared between the simulated electron beam spread and actual measurements made for emitter arrays.
Dry photochemical selective etching of InGaAs/InAlAs in HBr gas using a 172 nm excimer lamp
Authors: Habibi Soheil , Totsuka Masahiro , Tanaka Jun , Kinoshita Takeshi , Matsumoto Satoru , Iida S.
Published: July 2002

A new dry photochemical etching process using HBr gas to selectively remove InGaAs layer over an InAlAs layer has been developed. A 172 nm Excimer lamp was used as the photon source for this experiment. The intensity of the 172 nm light on the surface of the samples was 3 mW/cm2. Etch rates of 62 Å/min and 0.61 Å/min are obtained for InGaAs and InAlAs, respectively, at a chamber pressure of 120 mTorr, sample temperature of 80 °C and HBr flow rate of 10 sccm. These rates translate into a selectivity of over 100 for this material system. Scanning electron microscopy pictures and visual inspection reveal that this process is almost damage free, compared to reactive ion etching. This is due to lack of ion bombardment in the photochemical process. X-ray photoelectron spectroscopy analysis suggests that the etch selectivity mechanism is due to the formation of nonvolatile  Al2O3 on the surface of the InAlAs layer. This etching system should be very useful for fabrication of electrical as well as optical devices based on InGaAs/InAlAs heterojunction.
Low-energy electron detection in microcolumns
Authors: Fresser H. S. , Prins F. E. , Kern D. P.
Published: July 2002

Metal–semiconductor–metal (MSM) structures for the application as detectors for low-energy backscattered electrons in electron-beam microcolumns have been investigated. Realized Ti–Si–Ti MSM devices showed current gains of up to 200 for 1 keV electrons. An unsatisfying signal/dark current ratio made the reduction of the dark current necessary. Two different approaches to reduce the dark current were examined: varying the used contact metal and investigating MSM structures with two different contact metals for cathode and anode (asymmetric MSM structures). The accomplished reduction of more than two orders of magnitude demonstrated the possibility to achieve a signal/dark current ratio of 0.4.
Effect of wafer temperature during plasma exposure on charging damage
Authors: Ma Shawming , McVittie James P.
Published: July 2002

Plasma charging induced damage is thought to mainly result from traps generated from charging induced tunneling currents through the thin oxide. Theoretically, any parameters that increase the trap generation rate will increase the charging damage. One such parameter is temperature. While the exact mechanism by which temperature increases the interaction between tunneling electrons and the oxide lattice is not well understood, a number of researchers have reported a decrease in the charge to breakdown Qbd at higher temperatures up to 150 °C. To test the effect of temperature on Qbd an O2 asher was operated in a known charging damage mode with test wafers at different temperatures. Using antenna capacitors with two different peak wafer temperatures (145 and 340 °C) during charging, damage was measured by Qbd and leakage methods after plasma exposure. At 145 °C, it was found that the plasma had only weakly decreased Qbd and increased leakage for the largest antenna area with little effect on the smallest antenna area. However, as the temperature was increased, the larger antenna capacitors showed a significant decrease in Qbd and leakage after plasma exposure. These results are in agreement with a tunneling current damage mechanism for charging, and experimentally suggest that elevated temperature plasma processes, such as plasma-enhanced chemical-vapor deposition, can be expected to be more susceptible to charging damage than etching processes.
Anisotropy in resistivity of MoNx films at 4.2 K
Authors: Kominami Shin’ya , Mita Reiko , Nishino Toshikazu
Published: July 2002

Resistance uniformity of MoNx film resistors is necessary for stable operation of Josephson large scale integrated circuits. Electrical and crystallographic characteristics of MoNx films deposited by the sputtering method have been studied. We have found the resistivity of a MoNx film at 4.2 K depends on the current direction in the film plane. Scanning electron microscopy observations show crystal grains are elongated in the film plane. The shape of the Mo target and the configuration of the substrate influence longitudinal axes of most grains which tend to orient in the same direction. The resistivity of the MoNx film for a current parallel to the longitudinal directions of most grains is lower than that for a current perpendicular to the longitudinal directions. Therefore, the resistivity anisotropy of the MoNx films is mainly due to the anisotropy of the grain boundaries.
Polysilicon gate etching in high density plasmas. II. X-ray photoelectron spectroscopy investigation of silicon trenches etched using a chlorine-based chemistry
Authors: Bell F. H. , Joubert O. , Vallier L.
Published: July 2002

We have used x-ray photoelectron spectroscopy (XPS) to study the chemical constituents present on the surfaces after etching of poly-Si features masked with photoresist. Poly-Si etch rates were determined using in situ HeNe laser ellipsometry. The wafers were etched in a low pressure, high density plasma, helicon source using a chlorine/helium gas mixture. The XPS analysis chamber is connected to the reactor chamber via an ultrahigh vacuum chamber allowing quasi in situ analysis of the etched samples. Electrostatic charging of insulating surfaces and geometric shadowing of photoelectrons by adjacent photoresist lines have been used to differentiate photoemission signals from the tops, sidewalls, and bottoms of the features. Blanket and photoresist masked poly-Si samples were etched without biasing the substrate. The poly-Si etch rate decreased as a function of etching time and finally stopped due to the deposition of an oxide film. When biasing the sample, etching occurred and anisotropic etching profiles could be obtained. A thin oxide film was found on the sidewalls of the photoresist and poly-Si after etching. The thickness of the oxide film increased with etching time. No silicon was found on top of the photoresist. The silicon oxide film deposited on the surfaces resulted from the sputtering of the quartz tube located in the plasma generation region. Substantial amounts of chlorine were found on the tops, sidewalls and bottoms of the features. The chlorine concentrations on the sidewalls of the features etched at high bias power were comparable to those found on the horizontal surfaces when a low bias power was applied. The chlorine concentrations on the tops and bottoms of the features increased with increasing bias power. A low coverage of oxygen was found on all surfaces. The oxygen concentration on the sidewalls of the features also increased with etching time. Less oxygen was found on the bottom of the poly-Si trenches. Small amounts of carbon were detected on the bottoms of the features. A substantial coverage of carbon was present on the poly-Si sidewalls and was about half that found on the tops and sidewalls of the photoresist. These results indicate that the etching of the photoresist and the erosion of the quartz tube may enhance anisotropic etching.
Conductive dots, wires, and supertips for field electron emitters produced by electron-beam induced deposition on samples having increased temperature
Authors: Koops H. W. P. , Schössler C. , Kaya A. , Weber M.
Published: July 2002

The procedure for three-dimensional additive lithography with electron-beam induced deposition is applied in a scanning electron microscope equipped with an image processor beam control system for lithography. Employing organometallic materials, which contain gold or platinum, quantum dots, resistors, and field emitter tips are deposited. Changing the current, the properties of the deposited nanocrystalline compound materials can be selected to be insulating or conducting. High resolution and high aspect ratio structures are grown with this technique. To find the mechanism responsible for conductivity in the deposited material, resistors are characterized at temperatures ranging from −150 °C to +180 °C. Measurements are performed in a high-vacuum chamber equipped with a gas cooling system cooled with liquid nitrogen and a resistive heater. Poole–Frenkel plots show that field electron emission and hopping of electrons is the dominant mechanism of conduction. The metal content of the deposits is increased with rising sample temperatures ranging from room temperature to 100 °C. The deposited material features zero-dimensional electron gas in the nanocrystals of the material. Conductive tips with very small tip radius are routinely deposited as supertips on top of etched tungsten tips at elevated temperatures. The tips are investigated in an ultrahigh vacuum field electron microscope. Working supertips have a confined emission and therefore enhanced brightness is obtained routinely. The increase in brightness is at least ninefold for an emission from one site having a confined emission angle of ±7.2°. The emission current may be as large as 10 μA at extraction voltages below 800 V. No single crystalline tip material is needed to generate these supertips. Beam confinement to one emission site is demonstrated the first time for a deposited supertip.
One step electron-beam lithography for multipurpose diffractive optical elements with 200 nm resolution
Authors: Di Fabrizio E. , Grella L. , Baciocchi M. , Gentili M. , Peschiaroli D. , Mastrogiacomo L. , Maggiora R.
Published: July 2002

Electron-beam lithography allows three-dimensional shaping of polymethylmethacrylate (PMMA) structures with minimum feature size of 200 nm for diffractive optical element fabrication. The key step in fabrication of continuous PMMA profile is the resist process: contrast curve measurement at 40 and 50 kV as well as substrate thickness influence studies (bulk substrates and thin membrane) on resist slope profile were also carried out to determine the best process conditions. Examples of fabricated three-dimensional resist structures include: eight-level blazed PMMA profiles for x-ray focusing elements and a beam shaper for applications at a wavelength of λ=0.633 μm. The intrinsic flexibility and accuracy of the developed process, by which the wide range of diffractive optical elements were fabricated, is a direct consequence of the specifically developed and implemented three-dimensional proximity correction algorithm. A detailed description of such an algorithm will also be given.
Characterization of large-area arrays of nanoscale Si tips fabricated using thermal oxidation and wet etching of Si pillars
Authors: Umbach C. C. , Weselak B. W. , Blakely J. M. , Shen Q.
Published: July 2002

Two-dimensional periodic arrays containing 108 Si pillars with heights of 600–700 nm, widths of 100 nm, and repeat spacings of 300 nm have been fabricated using electron beam lithography on Si(001) substrates. These pillars have subsequently undergone wet oxidation at 800 °C and etching in hydrofluoric acid to produce an array of sharp tips with a height of ∼4000 Å. The x-ray diffraction from this array appears to be dominated by scattering from the bases of the tips. Correlated variations in tip shape, observed with scanning electron microscopy, produce a modulated diffuse background in the diffracted x-ray intensity. These observations demonstrate the feasibility of using high-resolution x-ray diffraction for studying defects in large-area arrays of periodic structures.
Real-time simultaneous optical-based flux monitoring of Al, Ga, and In using atomic absorption for molecular beam epitaxy
Authors: Pinsukanjana Paul , Jackson Andrew , Tofte Jan , Maranowski Kevin , Campbell Scott , English John , Chalmers Scott , Coldren Larry , Gossard Arthur
Published: July 2002

We have developed a multichannel atomic absorption measurement system for real-time simultaneous monitoring of Al, Ga, and In molecular beam fluxes. In our configuration, distinct atomic emission lines from three hollow cathode lamps are combined into one beam, thus requiring only one pair of through view ports for the optical probe beam. Based on the dual beam optical configuration, the reference arm compensates for intensity drift of the light sources. In this work, we demonstrate the use of reflection high energy electron diffraction oscillations for calibrating the absorption signal.
II–VI blue/green laser diodes on ZnSe substrates
Authors: Boney C. , Yu Z. , Rowland W. H. , Hughes W. C. , Cook J. W. , Schetzina J. F. , Cantwell Gene , Harsch William C.
Published: July 2002

This article reports the first blue/green laser diodes grown on ZnSe substrates. The laser structure employed is a p-on-n separate confinement heterostructure consisting of 0.8-μm-thick ZnMgSSe cladding layers lattice-matched to ZnSe, 0.1-μm-thick ZnSe light guiding layers, and a single 60–200-Å-thick ZnCdSe quantum well. Green laser emission (507–517 nm; 2.443–2.394 eV) was observed at temperatures from 77–220 K using cw excitation at 77 K and pulsed excitation (50 ns; 10−1–10−4 duty cycle) at higher temperatures. Blue laser diodes with outputs at 485 nm (2.553 eV) at 77 K have also been fabricated and tested.
Modification of field emitter array tip shape by focused ion-beam irradiation
Authors: Takai M. , Kishimoto T. , Yamashita M. , Morimoto H. , Yura S. , Hosono A. , Okuda S. , Lipp S. , Frey L. , Ryssel H.
Published: July 2002

Tip shapes of Si field emitter arrays, fabricated by a conventional dry etching process, have been modified by focused ion-beam (FIB) irradiation to obtain a sharp cone shape. Flat-topped Si tips could be sharpened by localized sputtering using FIBs for a short time. Tip shape inspections and repairs were also performed using a FIB system combined with an electron-beam column to remove metal residues and melted emitters.
A new structure of field emitter arrays
Authors: Itoh Shigeo , Niiyama Takahiro , Taniguchi Masateru , Watanabe Teruo
Published: July 2002

The evaluation of a new structure of field emitter arrays which was made to obtain high current density in a stable condition is reported. For improving the stability of emitters by means of the resistive layer, conductive island patterns were formed beneath emitter arrays in each mesh cathode line. In the structure above, resistance from mesh cathode lines to each emitter is expected to be uniform. As a result of discussions to make the resistance from mesh cathode lines to each emitter uniform, the new structure was made by forming 21×21 Spindt-type emitter arrays in a mesh cathode with an emitter pitch of 5 μm and with a gate hole diameter of 1.3 μm. Using a specimen of this structure, a current density of 1.54 A/cm2 was achieved at a gate voltage of 170 V, which is about 10 times higher than that of the mesh structure with the same resistance and the same number of emitters, 0.13 A/cm2.
Gold oxide as precursor to gold/silica nanocomposites
Authors: Maya L. , Paranthaman M. , Thundat T. , Bauer M. L.
Published: July 2002

Gold oxide films were prepared by reactive sputtering of pure gold in an oxygen plasma. These films were characterized by chemical and physical means to better understand the behavior of this metastable compound. Gold oxide, Au2O3, decomposes into the elements at 350 °C. It does not react with dry carbon dioxide but does form a metastable bicarbonate in the presence of moisture and CO2, releasing oxygen and eventually reverting to elemental gold. Gold oxide was generated by reactive sputtering along with silica in an oxygen plasma from Au–Si solidified alloys. Gold oxide decomposed upon pyrolysis to produce composites showing different characteristics depending on the gold content. Composites containing about 95 wt % gold produced reflective, conductive, and adherent films. Composites derived from an alloy containing 5 at. % gold produced a nanostructured material with gold clusters of about 5 nm in diameter dispersed in a silica matrix. This nanocomposite showed high resistivity, and capacitance with a dielectric constant of 400.
Strain relaxation in compositionally graded epitaxial layers
Authors: Kim Sam-Dong , Lord Susan M. , Harris James S.
Published: July 2002

A model for strain relaxation in linear compositionally graded epitaxial layers is derived. Equilibrium dynamics for misfit dislocation generation is used in each compositional segment of the graded layers through the film thickness. A local relaxation thicknesses in the compositionally graded layers is calculated as a function of film thickness. The calculated critical thicknesses show good correspondence with the depth of dislocation-free regions which are observed at the top of graded layers with different grading rates. From analysis of the model, we explain the origin of dislocation structures and minimized threading dislocation density in the compositionally graded layers. The compositional grading produces a large equilibrium dislocation spacing compared to that of highly mismatched conventional stepwise growths, and thus enables misfit dislocations to glide freely without dislocation–dislocation interactions. At successive local relaxation thicknesses, lateral dislocations pile up horizontally by continuous dislocation generation and expansion. The analysis with calculated results coincides with dislocation structures observed by transmission electron microscopy in InGaAs graded layers on GaAs.
Microwave plasma nitridation of Si(100), Ge(100), and Si1−xGex surfaces: A comparative study
Authors: Mukhopadhyay M. , Ray S. K. , Maiti C. K.
Published: July 2002

Nitridation studies of Si(100), Ge(100), and epitaxial strained Si1−xGex surfaces in microwave ammonia plasma have been carried out by x-ray photoelectron spectroscopy. A single crystalline Ge(100) surface is found to be totally inert in ammonia plasma, while Si(100) surface undergoes a nitridation reaction. In the case of a SiGe film, only selective nitridation of Si is observed. The selectivity in plasma nitridation has been discussed and the electrical properties of nitrided films have been studied by the characterization of metal–insulator–semiconductor capacitors fabricated using the grown films.
Real-time, noninvasive temperature control of wafer processing based on diffusive reflectance spectroscopy
Authors: Wang Zhongze , Kwan Siu L. , Pearsall T. P. , Booth J. L. , Beard B. T. , Johnson S. R.
Published: July 2002

We demonstrate real-time semiconductor processing temperature control based on direct, noninvasive, in situ measurement of wafer temperature by diffuse reflectance spectroscopy. The precision of the controlled temperature was maintained within ±0.5 °C with an update time of 2 s over a temperature range from 25 to 600 °C for semi-insulating GaAs wafers. Direct control of the wafer temperature using diffuse reflectance spectroscopy is compared to the usual situation where the wafer heater temperature is controlled. The direct control of wafer temperature using diffuse reflectance spectroscopy is shown to be a significant improvement over conventional heater control technology in accuracy, stability, repeatability and response rate, for dynamic control of wafer temperature in the range of 25–600 °C. Our technology can also be applied to Si and other semiconductor wafers following appropriate calibration.
Characterization of novel powder and thin film RGB phosphors for field emission display application
Authors: Chakhovskoi A. G. , Hunt C. E. , Malinowski M. E. , Felter T. E. , Talin A. A.
Published: July 2002

The spectral response, brightness, and outgassing characteristics of new, low-voltage phosphors for application in field emission flat panel displays, are presented. The tested phosphor materials include combustion synthesized powders and thin films prepared by rf diode or magnetron sputtering, laser ablation, and molecular beam epitaxy. These cathodoluminescent materials are tested with e-beam excitation at currents up to 50 μA within the 200–2000 V (e.g., “low-voltage”) and 3–8 kV (e.g., “medium-voltage”) ranges. The spectral coordinates are compared to commercial low-voltage phosphors. Phosphor outgassing, as a function of time, is measured with a residual gas analyzer at fixed 50 μA beam current in the low-voltage range. We find that levels of outgassing stabilize to low values after the first few hours of excitation. The desorption rates measured for powder phosphor layers with different thicknesses are compared to desorption from thin films.
Development of 4 in. field-emission displays
Authors: Gorfinkel Boris , Kim Jong Min
Published: July 2002

This article describes experimental results on the fabrication of monochrome 4 in. field-emission displays (FEDs) on soda–lime glass substrates for practical use in manufacturing display. By fabrication of the Spindt-type field emitters without utilizing conventional resistive layers, several parameters closely related to these emitter arrays are discussed. In addition, analytical studies on the process environments of microtip fabrication and their related processes for FED mass production are significantly focused in this article. The characteristics of the field-emission quality is improved using unique gas and electrical aging effects on the microtip.
Hot electron and quasiballistic transport of nonequilibrium electrons in diamond thin films
Authors: Lerner P. , Cutler P. H. , Miskovsky N.
Published: July 2002

A molecular dynamics simulation of conduction-band transport in diamond has been carried out that combines classical propagation of electrons with choice of scattering events determined by a Monte Carlo algorithm using quantum mechanical rates. The high-field regime is dominated by hot optical phonon scattering for n⩽1019 cm−3 and by electron–plasmon emission for higher electron concentrations. Electron–electron and electron–hole binary processes do not significantly influence the transport characteristics but extend the high-energy tail and asymmetry of the electron distribution, making it more “Maxwellian.” The results demonstrate the possibility of achieving quasiballistic transport in thin diamond films with a significant portion of the field energy imparted to the electrons at high fields (F≈102 V/μm) and electron concentrations up to n≈1018 cm−3.
Generation of subquarter-micron resist structures using optical interference lithography and image reversal
Authors: Decker J. Y. , Fernandez A. , Sweeney D. W.
Published: July 2002

We show that by using interference lithography coupled with image reversal techniques we can generate resist structures ranging from one-dimensional gratings to two-dimensional arrays of posts and holes. These resist structures have high aspect ratios and nearly vertical sidewalls. The structure dimensions are accurately controlled by varying the exposure dose. These structures play critical roles in the generation of subwavelength structured surfaces for optical applications.
Process design and emission properties of gated n+ polycrystalline silicon field emitter arrays for flat-panel display applications
Authors: Uh Hyung Soo , Kwon Sang Jik , Lee Jong Duk
Published: July 2002

The gated n+ polycrystalline silicon (poly-Si) field emitter arrays (FEAs) have been designed and successfully fabricated on an oxidized silicon wafer for large display applications. The proposed structure of the FEAs eliminates the difficulty of having the cathode electrode (n+ diffusion layer)-to-cathode electrode isolation, which is common to crystalline silicon (c-Si) field emitter arrays. Compared with c-Si field emitters, poly-Si emitters showed poor uniformity in device structure such as emitter shape and gate hole, which was thought to be due to the variation of the grain size of poly-Si and the oxide thickness associated with grain boundaries of poly-Si in the sharpening oxidation step. The anode current of 0.1 μA/tip was measured at the gate bias of 82 V from poly-Si emitters with gate hole diameter of 1.2 μm under the vacuum pressure of 3×10−9 Torr. The same anode current was obtained at 80 V from c-Si emitters with the gate hole diameter of 1.6 μm. The gate leakage current for both the c-Si FEA and the poly-Si FEA was much less than 1% of the anode current. Long-term fluctuation characteristics in emission current of the poly-Si FEA are also studied under different sample treatments. In spite of much room for improvement, the emission characteristics of poly-Si FEAs are outstanding in terms of emission current and gate leakage current, compared with those of previously reported poly-Si FEAs.
Field emission displays based on linear horizontal field emission cathodes
Authors: Kuo Huei Pei , Burriesci S. F. , Lin J. , Miller D. J.
Published: July 2002

We have developed a linear horizontal wedge field emission cathode for field emission displays. The cathode consists of a horizontal wedge with a diameter of curvature ∼10 nm. A self-aligned sloping gate is positioned at a distance of ∼10 nm above the wedge. Computer simulation shows that the wedge cathode can operate at a gate voltage of ⩽15 V to allow the use of complementary metal–oxide semiconductor drivers to modulate the electron emission. Coplanar focusing electrodes are incorporated without additional processing steps to collimate the electron beam to a dimension of ∼50 μm onto a high voltage phosphor screen ∼1 mm away. We have fabricated wedge cathodes operating at a gate voltage of ∼60 V with a relatively uniform emission from an area of ∼5 mm×5 mm. The wedge cathode was developed to be fabricated with mainstream large-area equipment for flat panel displays.
Subwavelength, binary lenses at infrared wavelengths
Authors: Wendt J. R. , Vawter G. A. , Smith R. E. , Warren M. E.
Published: July 2002

We describe the nanofabrication of subwavelength, binary lenses in GaAs for operation in the infrared. Subwavelength surface relief structures create an artificial material with an effective index of refraction determined by the fill factor of the binary pattern and can be designed to yield high-efficiency diffractive optical elements. In this work, we designed and fabricated a circular-aperture, off-axis lens with a deflection angle of 20°, focal length of 110 μm, and diameter of 80 μm, for operation at 975 nm. The off-axis lens design has a theoretical efficiency of 92% and the fabricated lens exhibits a diffraction efficiency into the first order of 72% and 59% of the transmitted power for TE and TM polarization, respectively. A significant advantage of these subwavelength structures is that fabrication requires only a single-lithography-and-etch-step process, in this case, electron-beam lithography and reactive-ion-beam etching.
Scanning tunneling microscopy atomic resolution images of sulfur overlayers on Fe(111)
Authors: Cabibil H. , Lin J.-S. , Kelber J. A.
Published: July 2002

We report the first atomic resolution scanning tunneling microscopy (STM) images of S overlayers on the Fe(111) surface. S overlayers were obtained by annealing the Fe(111) crystal to elevated temperatures to induce the segregation of S from the bulk. STM images of the (1×1)-S structure are consistent with the proposed model of one “geometric” monolayer of S atoms occupying on-top three-fold hollow sites of the Fe(111) surface. The STM data also revealed the presence of nanoscopic triangular pits on the (1×1)-S surface. These pits are only one atom deep. Increased segregation of S results in the formation of a (2√3 ×1)R30° structure and an increase in the size and depth of the triangular pits. This new structure corresponds to S coverage corresponding to more than one “geometric” monolayer of S based on one geometric monolayer coverage for the (1×1)-S structure. STM images obtained within large pits reveal a periodic “staircase” topography consisting of terraces with (111) orientation. These terraces are made up of five atomic rows (14 Å) separated by monatomic steps. Images obtained on flat areas in between large pits reveal surface buckling. Two different packing arrangements of surface buckling were observed both consisting of vertically displaced atomic rows with a 14 Å periodicity, identical to the terrace widths of the staircase surface found inside large triangular pits. We propose that additional segregation of S to the (1×1)-S phase to form the (2√3 ×1)R30° structure involves the segregation of S to the subsurface three-fold hollow sites on the Fe(111) surface. The close proximity of S atoms located at on-top and subsurface three-fold hollow sites can result in strong S–S repulsive interactions which consequently drives the surface to undergo structural changes, similar to other reported adsorbate-induced faceting of bcc(111) surfaces.
Molecular beam epitaxial growth of HgCdTe midwave infrared multispectral detectors
Authors: de Lyon T. J. , Vigil J. A. , Jensen J. E. , Wu O. K. , Johnson J. L. , Patten E. A. , Kosai K. , Venzor G. , Lee V. , Johnson S. M.
Published: July 2002

Molecular beam epitaxy (MBE) has been utilized to fabricate high performance HgCdTe infrared detectors with sensitivity to midwave infrared radiation in adjacent spectral bands for two-color thermal imaging applications. Growth of a multilayer HgCdTe device structure by MBE enables the use of an n-p-n device architecture that facilitates pixel-level registration of images in two separate spectral bands. Device structures were grown on CdZnTe(211)(B) substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve detection of infrared radiation in adjacent spectral bands in the 3.5–4.5 μm wavelength range. As-grown device structures were characterized with x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. Mesa type devices were patterned using reactive ion etching and ohmic contacts were made to the two n-type layers for operation of the detectors in a sequential detection mode. The spectral response characteristics of the devices are highly uniform across a 64×64 element array, with standard deviation in cutoff wavelength less than 0.01 μm and external quantum efficiencies greater than 70% in both bands. Sharp detector cutoffs enable spectral crosstalk less than 1% to be obtained for spectral bands with as little as 0.6 μm separation. Junction reverse-breakdown voltages in excess of 500 mV and 80 K dynamic resistance-area products for each component diode in excess of 1×106 Ω cm2 at ±100 mV operating bias have been demonstrated.
Dry-etching development characteristics of Se75Ge25 resist for focused-ion-beam lithography
Authors: Lee Hyun-Young , Chung Hong-Bay
Published: July 2002

We have investigated the focused-ion-beam (FIB) lithographic mechanism of Se75Ge25 resist exhibiting dual-type resist characteristics according to development methods. That is the Ga-FIB exposed Se75Ge25 films act as positive and negative type resists for wet-etching development using a solution of HNO3:HCl:H2O (1:1:3) and dry development by CF4 reactive-ion etching (RIE), respectively. With increasing incident energy, both sensitivity S and contrast Υ are enhanced in the case of wet development, while both are deteriorated in the case of dry development. Considering the deposited energy density and implanted ion-concentration distributions obtained by our Monte Carlo simulation, FIB lithography for wet development depends primarily on the deposited energy and for dry development is dominated by the implanted ions themselves. For a 580 Å thick Se75Ge25 resist exposed by 30 keV Ga+ FIB and developed by CF4 RIE for 5 s under the gas pressure of 200 mTorr, S and Υ are about 1.7×1015 ions/cm2 and 4.44, respectively. In this case the ion concentration exceeds approximately 3.7×1020 ions/cm3, Ga-exposed region is estimated to have a resistance against CF4-reactive gas. A 0.125 μm line pattern, with very small proximity effect, has been successfully fabricated by RIE development after 40 keV FIB exposure with a diameter of 0.120 μm.
Ion beam synthesis of cobalt disilicide using focused ion beam implantation
Authors: Teichert J. , Bischoff L. , Hausmann S.
Published: July 2002

Cobalt disilicide layers were formed by cobalt focused ion beam implantation into silicon. It was found that the CoSi2 layer formation strongly depends on the pixel dwell time. In order to obtain continuous layers, short dwell times of a few μs are needed. Rutherford backscattering and channeling measurements were carried out to understand this effect. The results suggest that the accumulated irradiation damage is larger for longer dwell times. The sputtering yield of cobalt ions was measured and the formation of CoSi2 in noncrystalline silicon investigated.
In situ determination of in-plane strain anisotropy in ZnSe(001)/GaAs layers using reflectance difference spectroscopy
Authors: Hingerl K. , Yasuda T. , Hanada T. , Miwa S. , Kimura K. , Ohtake A. , Yao T.
Published: July 2002

In this article we show in situ and ex situ experimental reflectance difference spectroscopy (RDS) data of ZnSe(001) grown on GaAs, where special attention is focused on the resonancelike structure at the band gap of ZnSe. This feature was reported previously and interpreted as either the transition from the valence band of ZnSe to a quantum well state at the ZnSe/GaAs interface or it was attributed to interface states. We report a new interpretation of this spectral feature which considers anisotropic strain in the ZnSe/GaAs heterostructures. By straining the ZnSe(001) epilayers mechanically, it was observed that the resonance feature changed sign and magnitude, proving that the height of this in-plane anisotropy feature is a measure for the in-plane strain. In-plane strain induces a splitting and shift in energy of the light and heavy hole valence bands. The transition between the light hole valence band and the conduction band is not polarization dependent, however the transition between the heavy hole valence band and the conduction band, as well as the transition between the spin split-off band and the conduction band shows polarization dependence. This difference between the reflectances parallel and perpendicular to the in-plane strain direction can be measured ex situ and in situ with RDS.
Microelectromechanical tunneling sensor fabrication and post-processing characterization using focused ion beams
Authors: Stratton F. P. , Kubena R. L. , McNulty H. H. , Joyce R. J. , Vajo J.
Published: July 2002

Focused ion beams (FIBs) have been previously used as tools for such diverse tasks as high-resolution lithography, where their sub-10 nm spot sizes enable the patterning of diverse nanostructures, and surface compositional analysis, where their ability to sputter material in a localized area allows discrete components of a device or circuit to be characterized. Recently, the authors have capitalized on the FIB’s versatility by using it for microelectromechanical sensor fabrication as well as post-processing device characterization. The HRL FIB nanoprobe system has been used in the fabrication of high-performance surface-micromachined accelerometers operating on the principle of tunneling between a cantilevered beam and a sub-0.1-μm-diam tip lying beneath it on a Si substrate. The 8-nm-diam FIB has been used to pattern small dots in a bilevel negative-positive resist layer which are then transferred into a Au layer to form pyramid-shaped tunneling tip structures whose narrow dimensions are essential to high device performance and stability. High-purity, contamination-free Au on both the tunneling tip and cantilever underside is also critical to high-sensitivity tunneling devices. Because the undersides of the beams cannot be viewed with a scanning electron microscopy, even at high mechanical tilt angles, the cantilevers must be physically peeled back in order to expose their bottom surfaces and analyze them for cleanliness. Depending on the material used for fabricating the cantilevers, the rigidity of the structures can render them difficult to bend. We have used a commercial FIB milling system to cut through a portion of the cantilever width, thus creating a hinge, which facilitates the subsequent peeling back of the structure. Comparison of Auger spectroscopy data on peeled-back beams with and without a FIB-milled hinge shows similar surface contamination levels, indicating that redeposited material due to ion milling is localized enough to not affect the compositional analysis of the tunneling region.
Multipurpose nanobeam source with supertip emitter
Authors: Kalbitzer S. , Knoblauch A.
Published: July 2002

Protrusions of 1 nm dimensions have been grown on single-crystal tips of tungsten and iridium of about 100 nm size. With positive bias the tip can be operated as an intense ion source and with reversed bias intense electron beams can be obtained. In both cases, specific brightness values of up to 1 TA/cm2 srd eV have been recorded under optimized conditions. As for gases, tungsten can be used only for less reactive species, such as hydrogen and rare gases, whereas iridium is also useful for aggressive gasses, such as oxygen. Both metals are excellent electron emitters. Thus, a powerful multipurpose source is realized with supertips of tungsten and iridium, as will be demonstrated by a variety of experimental results on their relevant properties.
Focused ion beam technology applied to microstructure fabrication
Authors: Vasile Michael J. , Nassar Raja , Xie Jushan
Published: July 2002

Focused ion beams (FIBs) have found a place in several research thrusts for the manufacture of mini or micro mechanical objects. This article reports the use of FIB in three distinct applications in microfabrication: prototype structures, micron-sized machine tools and microsurgical manipulators, and ion milling of three dimensional features. Examples of each of these applications are given with the FIB component identified as the enabling or critical component in the technology. The possibility of using FIB milling as part of a production method for micron-sized machine tools is discussed, and the mass production consequences of molds fabricated by three dimensional ion beam milling is also considered. The mathematical procedure and programming steps needed to accurately control FIB three dimensional milling are outlined.
Electronic desorption of alkyl monolayers from silicon by very highly charged ions
Authors: Schenkel T. , Schneider M. , Hattass M. , Newman M. W. , Barnes A. V. , Hamza A. V. , Schneider D. H. , Cicero R. L. , Chidsey C. E. D.
Published: July 2002

Self-assembled alkyl monolayers on Si (111) were exposed to low doses of slow (v≈6.6×105 m/s≈0.3vBohr), highly charged ions, like Xe41+ and Th73+. Atomic force microscope images show craters from single ion impacts with diameters of 50–63 nm. Emission of secondary ions by highly charged projectiles was monitored by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS data give insights into the dependence of electronic desorption effects on the projectile charge state. We discuss the potential of highly charged projectiles as tools for materials modification on a nanometer scale.
Demonstration of a functional quantum-dot cellular automata cell
Authors: Amlani Islamshah , Orlov Alexei O. , Snider Gregory L. , Lent Craig S. , Bernstein Gary H.
Published: July 2002

We report an experimental demonstration of a functional cell for quantum-dot cellular automata (QCA), a transistorless approach to implement logic functions. The four-dot QCA cell is defined by a pair of series-connected, capacitively coupled input and output double dots. We demonstrate that, at low temperature, an electron switch in the input double dot induces an opposite electron switch in the output double dot, resulting in a complete polarization change of the QCA cell. Switching is verified by electrometer signals which are coupled to the output double dot. Experimental results suggest that electron motion in the coupled double dots is strongly correlated and can support high operating frequencies. Agreement between theoretical predictions and experimentally measured values of the dot potentials is excellent.
Nanolithography of metal films using scanning force microscope patterned carbon masks
Authors: Mühl T. , Brückl H. , Kraut D. , Kretz J. , Mönch I. , Reiss G.
Published: July 2002

Recently, we have shown that small trenches in amorphous carbon films can be produced by a field induced local oxidation with a voltage biased cantilever tip in a scanning force microscope. The depth of the holes and the trenches corresponds to the total thickness of the carbon film while the width was found to be as small as 30 nm. Amorphous carbon films as resist masks for lithography show some advantageous properties, e.g., the stability against halogen plasma etching, negligible chemical reactivity with most substrates and the possibility of removing the mask by oxygen reactive ion etching. In this article, we demonstrate the transfer of the carbon patterns into metal films by argon ion beam etching. By this new method, we produced 10-nm-wide trenches in thin AuPd films. Furthermore, we made small gaps in narrow AuPd lines which have been predefined by conventional e-beam lithography. In order to control and minimize the width of the gaps, the resistance of the conducting lines was controlled in situ during ion beam etching.
Nanolithography using wet etched silicon nitride phase masks
Authors: Alkaisi M. M. , Blaikie R. J. , McNab S. J.
Published: July 2002

A new technique for performing chromeless phase shift optical nanolithography is presented. Phase masks have been wet etched into silicon nitride membranes, using either hot H3PO4 or HF. Contact exposure through these masks results in developed photoresist features as small as 90 nm, even for masks with shallow sidewall slopes. The observed effect is attributed to the presence of an abrupt phase step at some point on the wet etch profile, although this does not need to correspond to a π phase shift in order to obtain good contrast exposures. Simulations have been performed for typical wet-etching profiles, and it is found that good contrast is expected for a very wide range of etch depths. In addition, the width of the null in the near-field intensity profile varies with etch depth, indicating that control of feature size is possible. This technique is simple and inexpensive, making it an attractive candidate for nanopatterning a wide variety of substrates.
Fabrication of metallic point contacts: A new approach for devices with a multilayer or a heterointerface
Authors: Gribov N. N. , Theeuwen S. J. C. H. , Caro J. , van der Drift E. , Tichelaar F. D. , de Kruijff T. R. , Hickey B. J.
Published: July 2002

Thin silicon membranes on silicon on insulator substrates are used to fabricate point contacts with a well-defined interface in the nanoconstriction between the two metal electrodes. Transmission electron microscope images of heterointerfaces in conjunction with energy dispersive x-ray analysis of the interfacial region show the capabilities of the process and its limitations. The latter involve material-specific phenomena on a nanoscale, such as an interfacial reaction between a metal film and SiO2 and metal diffusion across the heterointerface. These adverse effects can be avoided by a proper choice of the metals and the deposition temperature, as demonstrated with results of electrical measurements on a Au/Cu heterocontact.