bluuebunny/crossref_metadata_2025 huggingface dataset:
Poly(methacrylic anhydride) positive electron beam resist
Authors: Miller Leroy J. , Brault Robert G. , Granger Diana D. , Jensen John E. , Ast Camille I. van , Lewis Margaret M.
Published: July 2002

Poly(methacrylic anhydride) (PMAH) is a positive resist for use in electron beam (e-beam) lithography. It is derived by heating coatings of the precursor polymer, poly(tert-butyl methacrylate) or PtBMA, on the wafer. Crosslinks are introduced during the thermal conversion. The sensitivity and line profiles of PMAH e-beam images are significantly affected by the synthesis route, the pre-exposure processing, and the development method. Development with organic solvents can swell and soften the resist, especially in areas that received some exposure to radiation. This causes the walls of the image to expand or flow into the image cavity, thereby limiting the sensitivity at which high resolution can be achieved. However, the use of a new, nonswelling, basic developer gives PMAH a sensitivity of 2.5 μC/cm2 with better than 0.5 μm resolution.
A wire electronic discharge machine saddle-type deflector for electron beam lithography systems
Authors: Hanying Liu , Wenjian Tang
Published: July 2002

A new type of magnetic deflector [wire electron discharge machine (EDM) deflector] has been constructed for our gaussian round beam exposure system. To optimize the design of conventional saddle-type deflection coils used for electron beam lithography systems (EBLS), one of the most important technical problems lies in the achievement of consistency between the computer aided design (CAD) calculated model and the actual structure of the windings. The present paper investigates the relation between the deflection aberration and winding width as well as winding distribution when the parameters of the deflector are optimized. The calculated results show that with 30° central angle of the winding and larger variance of the winding width the influence of third-order aberration is negligible in micron-EBLS and submicron-EBLS. The design and experimental results are discussed for a new type of saddle coil used in EBLS and fabricated by the wire electron discharge machine (wire EDM) technology, this deflector indicates consistency between the CAD model and the actual structure of the winding. In our μm-order EBLS using the wire EDM deflector, field stitching accuracy of <0.3 μm can be realized. The beam positioning accuracy is ∼0.2 μm.
Relationship of ambient deposition conditions to formation of thermally activated voids in Al/Si interconnects
Authors: Tice W. , Slusser G.
Published: July 2002

The failure of microelectronics chips due to formation of stress−induced voids in Al/Si alloy interconnects is discussed. The propensity for thermal voiding in Al/Si is associated with a particular microstructural and compositional state derived from poor vacuum coditions during deposition.(AIP)
Testing integrated circuit microstructures using charging-induced voltage contrast
Authors: Aton T. J. , Mahant-Shetti S. S. , Gale R. J. , Bennett-Lilley M. H. , Harward M. G. , Pico C. A. , Weaver T. L.
Published: July 2002

We describe recent experiments using a novel method of testing isolation and continuity in microstructures using an electron beam technique. We use the beam of an unmodified scanning electron microscope (SEM) to deposit charge on microstructures typical of advanced integrated circuits. Differences in potential induced by that charging are detected by observing the voltage contrast between microstructure elements. With an unmodified SEM, isolation to about 2×1011 Ω can be verified. Examples are shown of structures for checking patterning capability and measuring defect density in manufacturing.
Aberration due to misalignment in electrostatic lens and deflection systems
Authors: Kurihara Kenji
Published: July 2002

The aberration of electrostatic lens and deflection systems due to misalignment is analyzed for design of microfabrication systems. The potential for a lens and deflector having an electrode axis shift is approximated by introducing a shift function that expresses the electrode shift from the optical axis. On the basis of this approximation, mixed aberrations due to misalignment of lens and deflector electrodes can be analyzed, including the effect of a nonuniform electrode axis shift. Practical third order aberration coefficients are formulated in a compact form by eight integration functions, and are classified into 67 geometrical aberration coefficients and 4 chromatic aberration coefficients.
Growth and characterization of GaAs grown by metalorganic molecular-beam epitaxy using trimethylgallium and arsenic
Authors: Tu C. W. , Liang B. W. , Chin T. P. , Zhang J.
Published: July 2002

We report a study of growth kinetics of metalorganic molecular-beam epitaxy (MOMBE) of GaAs by reflection high-energy electron diffraction (RHEED) intensity oscillation and characterization of these MOMBE-grown GaAs layers by Hall effect measurement and x-ray rocking curve analysis. The growth rate depends not only on the substrate temperature but also on the arsenic pressure. The high p-type doping by carbon, in the high 1019-cm−3 range, results in strain and a smaller lattice constant in the epitaxial layer. Rapid thermal annealing, however, can improve the crystalline quality of the layer without degrading the electrical properties.
Heterostructure acoustic charge transport devices on molecular-beam epitaxy grown GaAs/(Al,Ga)As epitaxial layers
Authors: Tanski W. J. , Sacks R. N. , Merritt S. W. , Cullen D. E. , Branciforte E. J. , Eschrich T. C. , Carroll R. D.
Published: July 2002

Molecular-beam epitaxy (MBE) has been used to grow very high quality layers for the confinement and transport of electrons in heterostructure acoustic charge transport (HACT) devices. In this paper the HACT device concept is reviewed, details of the layer structure and growth techniques are presented, and the performance of transversal filters produced with this material are discussed. It is demonstrated that the MBE growth techniques and epilayer design are adequate to produce charge transport efficiencies in excess of 0.9999 on HACT devices 1 cm (3.3 μs) long with 480 sensing taps. Considerable effort has been made to produce epilayers meeting the extremely demanding requirements of this large area device, and some details of this effort are discussed.
Study of isoelectronic In doping in molecular beam epitaxy grown GaAs thyristors
Authors: Kim H. K. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

Studies have been conducted of isoelectronic In doping in n-GaAs and p-GaAs grown by molecular beam epitaxy. The concentration of most of the electron and hole traps are suppressed by up to three orders of magnitude by introducing 0.2–1 at. % In and increasing growth temperatures from 500 to 550 °C. As a result an improvement in minority carrier lifetime and diffusion length is achieved. This is demonstrated by the comparison of pnp and npn GaAs homojunction transistors grown with and without In doping in base layers. Based on these results, pnpn GaAs homojunction thyristors were designed and fabricated with and without In doping in the middle n and p-GaAs layers. More than a factor of 2 reduction in the trigger current was observed as a result of the In doping.
Merging focused ion beam patterning and optical lithography in device and circuit fabrication
Authors: Murguia James E. , Musil Christian R. , Shepard Mark I. , Lezec Henri , Antoniadis Dimitri A. , Melngailis John
Published: July 2002

Combining optical lithography and focused ion beam (FIB) patterning in direct-write device and circuit fabrication by generating large features optically and small features with the FIB can significantly reduce beam writing time. Our approach to FIB pattern definition is ideally suited for alignment to optically patterned features and takes full advantage of the lithographic and implantation capabilities of the FIB. Optical and FIB patterns are designed simultaneously in the very large scale integrated layout tool magic, [magic, Report No. UCB/CSD 85/225 University of California, Berkley (March 1985)]. We have developed a software package magtofib [James E. Murguia, Christian Musil, Mark Shepard, Sasan Zamani, magtofib, Massachusetts Institute of Technology (1989)] which takes its input from the magic data file and converts it to FIB stage and beam commands. The FIB is aligned by operating in scanning ion microscope mode and finding the centroid of an optically produced die alignment mark. Since the coordinate systems of a typical optical reticle, stepper, and of the FIB are, in general, nonorthogonal and rotated with respect to the wafer, the alignment error increases as one moves away from the alignment point. To place features 1 cm apart to an accuracy of 0.1 μm, calibration must be better than one part in 105. This precision is achieved with a linear transformation calculated from three alignment crosses on the pattern perimeter which transform computer aided design layout coordinates into wafer coordinates. The transformation is calculated once per wafer. The patterning tools have been demonstrated using three types of alignment marks and two resists, on a variety of devices, as well as x-ray masks. The alignment accuracy is ±0.1 μm. In addition, we report a process to combine optical and FIB lithography on the same layer using the same positive UV resist (KTI 820) as a negative FIB resist.
Investigation of process latitude for quality improvement in x-ray lithography mask fabrication
Authors: Trube J. , Chlebek J. , Grimm J. , Huber H.-L. , Löchel B. , Stauch H.
Published: July 2002

Statistical methods are applied to improve the quality of fabrication steps in x-ray mask production. A second-order central composite design was used to optimize the bonding procedure in the mask blank preparation. The computer-controlled bonding process delivers 4-in. mask blanks with a flatness in the range of 2–4 μm. Factorial design as an optimizing method was applied to improve the quality of gold absorber patterns. The dependence of surface roughness of pulse plated structures on switch-on time, duty cycle, and current was investigated. Using optimized parameters, an improvement of lateral homogeneity and a decrease of grain size was achieved.
Experimental determination of the proximity effect from 25 to 100 keV in electron beam patterned x-ray masks
Authors: Umbach C. P. , Broers A. N.
Published: July 2002

Experimentally determined radial exposure distributions at beam voltages of 25, 50, 75, and 100 keV have been used to study the electron beam proximity effect produced by 30 nm Au/5 nm Cr/2.2 μm Si x-ray mask structures. For comparison, additional results were also obtained using bulk Si, 50 nm thick Si3N4 and 30 nm Au/5 nm Cr/50 nm Si3N4 substrates. Above 25 keV, the x-ray mask structures showed a reduced long range backscattering relative to bulk Si due to the loss of electrons out the backside of the masks. The Au/Cr plating base was found to be the major source of backscattering over distances <1.0 μm, and to limit the reduction in the ratio of backscattered to forward scattered exposure which resulted from increasing the beam voltage. The decrease in the proximity effect above 75 keV appears to be minimal. Although additional experiments are required to quantify the magnitude of the plating base enhanced proximity effect on developed resist profiles, it is apparent that simply increasing the beam voltage will not eliminate the lateral backscattering produced by the plating base during the electron beam patterning of x-ray masks.
Electron beam/optical intralevel mix-and-match lithography for deep submicron device fabrication
Authors: Matsuda Tadahito , Iwadate Kazumi , Tanaka Akinobu , Kawai Yoshio , Komatsu Kazuhiko
Published: July 2002

e-beam/optical intralevel mix-and-match lithography using a silicone-based positive photoresist (SPP), a Gaussian e-beam system, and an i-line stepper is described. In this technology, pattern width and placement depend only on the e-beam system to avoid the design rule limitation due to alignment error between the two lithographic tools and the optical resolution limit. A strategy for classifying pattern data into e-beam writing data and optical exposure data is introduced. A marked improvement in throughput and a linewidth accuracy of less than ±25 nm have been achieved by reducing the e-beam writing area.
Precision height measurements of freeze fracture replicas using the scanning tunneling microscope
Authors: Woodward J. T. , Zasadzinski J. A. N. , Hansma P. K.
Published: July 2002

We propose a general model for the interaction between a scanning tunneling microscope tip and a surface being imaged in air. The van der Waals force and a liquid bridge formed from condensation cause a net attraction between the tip and sample. If the sample is flexible or weakly bound to the scanning tunneling microscopy (STM) base our model predicts this attraction can lead to a significant amplification of the height of surface features. STM images of a freeze-fracture replica of a mica surface clearly show the amplification. Freshly made replicas of an atomically smooth mica surface had a standard deviation in their heights of 0.51 nm, but this increased to 0.61 nm after five days in a Petri dish and to 1.64 nm after one day of exposure to air. Methods of further reducing the amplification are discussed.
Scanning tunneling microscope imaging of hoops from the cell sheath of the bacteria methanospirillum hungatei and atomic force microscope imaging of complete sheathes
Authors: Blackford B. L. , Jericho M. H. , Mulhern P. J. , Frame C. , Southam G. , Beveridge T. J.
Published: July 2002

This paper describes techniques used to image the cell sheath of the archaebacterium methanospirillum hungatei. Scanning tunneling microscope (STM) studies were done on hoop-shaped components separated from the cell sheath by chemical treatment. High-quality images were only obtained when the hoops were dispersed on highly oriented pyrolytic graphite and overcoated with a conductor, although hopping scans occasionally could image uncoated sheath fragments. Atomic force microscope (AFM) studies of the entire sheath showed the characteristic surface corrugation that was also seen in STM and in electron microscope images. We suggest that the STM imaging of any large biological structures may be limited principally by low electrical conductivity, although tip-sample interactions and poor adhesion to the substrate also contribute to difficulties in the technique.
A metallic replica/anchoring technique for scanning tunneling microscope or atomic force microscope imaging of large biological structures
Authors: Blackford B. L. , Jericho M. H.
Published: July 2002

We describe and give results for a metallic replica technique in which biological structures are first deposited on a flat graphite substrate and then overcoated with a thick metallic film. The metallic film is then peeled off the graphite, and its underside is imaged by the scanning tunneling microscope (STM), which shows indentation-type replicas. We have used the technique on the cell sheath of the bacterium methanospirillum Hungatei, and find that the surface detail of the replica image is as good as that for a metal-coated sheath. We also find that the biological structures stay in the indentations during the peeling-off process, which gives the possibility of imaging bare structures that would normally be pushed along a flat substrate by the STM or atomic force microscope (AFM) tip.
Observation of individual organic molecules at nitronyl nitroxide single crystal surface by using atomic force microscopy
Authors: Ruan Like , Bai Chunli , Wang Hailiang , Hu Zhongying , Wan Meixiang
Published: July 2002

The surface studies of nonconductive single crystal of the organic ferromagnetic material, 2-(4-nitrophenyl)4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy 3-oxide, have been first carried out by the atomic force microscope (AFM) developed in our laboratory. The individual molecules are clearly resolved in the AFM images and the molecular arrangement is in good agreement with the bulk crystal structure.
The metalorganic chemical vapor deposition growth of HgCdTe on GaAs at 300 °C using diisopropyltelluride
Authors: Korenstein R. , Hallock P. , MacLeod B.
Published: July 2002

HgCdTe was grown by the metalorganic chemical vapor deposition alloy process on (111)B CdTe/GaAs and (111)B CdTe substrates at 300 °C using diisopropyltelluride, dimethlycadmium, and elemental mercury. Excellent surface morphology and compositional uniformity were obtained at this temperature. Hall effect measurements indicate that n-type (111) HgCdTe with carrier concentration below 1015 cm−3 and good mobilities at 77 K can be obtained on GaAs substrates.
Growth and carrier concentration control of Hg1−xCdxTe heterostructures using isothermal vapor phase epitaxy and vapor phase epitaxy techniques
Authors: Lee S. B. , Kim D. , Stevenson D. A.
Published: July 2002

We report on the growth and characterization of mercury cadmium telluride (MCT) heterostructures grown by isothermal vapor phase epitaxy (ISOVPE) and vapor phase epitaxy (VPE). This report consists of the use of both ISOVPE and VPE methods for growing wider band gap MCT on narrow band gap MCT, the compositional and structural characterization of as-grown layers, and the use of two zone Hg ampoules for carrier concentration control. The crystal perfection of some heterostructures is as good as that of the ISOVPE-grown layers. The carrier concentrations and mobilities of the ISOVPE-grown layers are substantially improved by a two zone Hg annealing technique.
Subsurface chemisorption of small atoms on semiconductors: B, C, and N on GaAs
Authors: Menon Madhu , Allen Roland E.
Published: July 2002

Several years ago we predicted that small atoms like B will chemisorb at subsurface sites on III–V semiconductors. Although this conclusion is explained by the open structures of tetrahedrally bonded materials, it was based on detailed simulations of chemisorption via Hellmann–Feynman molecular dynamics. Subsequently, it has been discovered that B occupies a subsurface site on Si(111). Here we report further simulations of the chemisorption of small atoms—namely, B, C, and N on GaAs(110)—and conclude that subsurface chemisorption on semiconductors should be a common phenomenon.
A scanning tunneling microscopy study of the platinum catalysts particles supported on graphite
Authors: Yeung King Lun , Wolf Eduardo E.
Published: July 2002

Scanning tunneling microscopy has been used to image platinum catalyst precursors and reduced platinum catalyst crystallites supported on graphite substrate at ambient condition. The catalysts were prepared by impregnation and ion exchange of precursor salt solutions unto the graphite substrate. Both nonfunctionalized and nitric acid functionalized nuclear grade high purity graphites were used as substrate. The crystallites’ size and distribution, microstructure, morphology, and surface structures are dependent on the substrate functionalization, the choice of precursors and the preparation method. Surface atomic structures of the crystallites deviate from that of single crystal studies but closely approximate the structure of O2 induced surface reconstruction.
Surface structure of thin metallic films on mica as seen by scanning tunneling microscopy, scanning electron microscopy, and low-energy electron diffraction
Authors: Buchholz Stefan , Fuchs Harald , Rabe Jürgen P.
Published: July 2002

Silver, gold, palladium, and chromium films have been evaporated onto mica at substrate temperatures ranging from −150 °C to +400 °C. Scanning tunneling microscopy (STM) images were obtained under ambient conditions. Silver and gold films exhibit an increasing grain size together with a grain flattening as the substrate temperature increases. At 275 and 400 °C for silver and gold, respectively, terraces with dimensions of the order of more than 100 nm are formed. However, also characteristic holes on the scale of a few 10 nm were always present. In addition, the gold films exhibit characteristic holes on the nanometer scale. While the larger holes are also visible on scanning electron microscopy micrographs, the smaller are not. Low-energy electron diffraction patterns prove the (111) orientation of both, silver and gold films; however, the quality of the silver patterns is better, consistent with the more perfect terraces as seen by STM. Palladium, evaporated at temperatures up to 350 °C did not exhibit similarly large and flat terraces. An improvement is achieved if prior to the palladium, silver is evaporated at elevated temperatures. Chromium, contrary to the fcc metals Ag, Au, and Pd crystallizes bcc, and forms a stable surface oxide under ambient conditions. The reproducibility of its STM images under ambient conditions depends on the applied bias and can be attributed to the surface oxide. Films evaporated at 50 °C exhibit a grainy structure. For the 350 °C films areas with a columnar morphology have been observed. In conclusion, epitaxially grown Ag(111) films evaporated at 275 °C onto mica have been shown to exhibit large flat terraces suitable for nanoscale modifications and chemisorption studies with the STM.
Etching of SiO2 film by synchrotron radiation in hydrogen and its application to low-temperature surface cleaning
Authors: Nara Yasuo , Sugita Yoshihiro , Nakayama Noriaki , Ito Takashi
Published: July 2002

Synchrotron radiation-assisted etching of SiO2 in a hydrogen atmosphere and its application to pretreating and cleaning substrates prior to Si film deposition is discussed. Thermally oxidized SiO2 film is etched in irradiation by synchrotron radiation at about 500 °C. Its etch rate increases by a factor of two in a hydrogen atmosphere. SiO2 core electron excitation by such irradiation seems to play an important role in SiO2 film modification and etching. This treatment reduced the interface contaminants such as oxygen and carbon between the deposited film and substrate to levels below the detection limit of secondary ion mass spectroscopy. Our results demonstrate that this new process is effective for low-temperature treatment.
Laser-produced plasmas for soft x-ray projection lithography
Authors: Silfvast W. T. , Richardson M. C. , Bender H. , Hanzo A. , Yanovsky V. , Jin F. , Thorpe J.
Published: July 2002

Laser-produced plasmas are one of the most likely sources to be used for soft x-ray projection lithography. The characteristics of these sources are described in terms of the expected radiation efficiency within the illumination bandwidth of a lithographic system. Measurements of the plasma particulate emission are described and techniques for interdicting this emission before it reaches the illumination optics are discussed. The laser requirements are obtained for a lithographic system producing a wafer rate of 60, 6 in. wafers per hour.
Chemical beam epitaxy growth of high-quality InAlAs using TMAA
Authors: Sherwin M. E. , Munns G. O.
Published: July 2002

InAlAs has been grown by chemical beam epitaxy using trimethylamine alane for use in InAlAs/InGaAs and InAlAs/InP high-electron-mobility transistors (HEMTs). Oxygen levels as low as 6 × 1017 cm−3 have been achieved. Background carrier concentrations are on the order of 2 × 1014 cm−3, with a best 14-K photoluminescence full width at half-maximum of 18.5 meV. InAlAs/InGaAs submicrometer HEMTs exhibit transconductances as high as 890 mS/mm with a corresponding ft of 150 GHz.
Preparation of transmission electron microscopy cross sections using nanofabrication techniques
Authors: Yater J. A. , Thompson Michael O.
Published: July 2002

A method for preparing cross sectional transmission electron microscopy (TEM) specimens using thin film processing techniques is described. Optical lithography is used to pattern lines of photoresist on the sample, followed by shadow evaporation of Al against the resist sidewalls. Removal of the resist leaves free standing, 100 nm wide metal lines on the surface. A selective, anisotropic reactive ion etch into the substrate then produces 1.5 μm tall, 100 μm wide walls, which, when turned on their sides, are sufficiently thin to allow transmission of high energy electrons in the TEM. This technique permits very specific, as well as very large, regions of a sample to be thinned for cross sectional examination. The processing steps are straightforward and may be easily adapted to other materials.
Chemical vapor deposition of amorphous hydrogenated silicon: Chemistry–structure–performance relationships
Authors: Hess Peter
Published: July 2002

Results obtained for deposition of hydrogenated amorphous silicon by infrared lasers and ultraviolet (UV) lasers are compared with plasma deposition data. Mechanistic information is extracted from the results obtained recently by in situ diagnostic techniques and ex situ analysis of the film properties. A similar mechanism is proposed for the first stage of the deposition process including gas phase chemistry and chemisorption of film precursors for soft and energized processing. Characteristic differences are observed in the second dehydrogenation and solidification stage of the deposition process. Compared with CO2 laser processing UV photons induce additional dehydrogenation The plasma environment has the potential to restrict the formation of polyhydrides and leads to the most efficient dehydrogenation.
Dopant profile extraction from spreading resistance measurements
Authors: Mathur Rajiv
Published: July 2002

In the past year, several researchers have reported on methods for extracting the true dopant profile from spreading resistance measurements. This paper reports on some theoretical aspects of the 1D Poisson analysis used in these methods. Linear perturbation analysis is used to show the origin of noise amplification when calculating the dopant profile from the measured carrier profile. Perturbations on model data are used to demonstrate the robustness and accuracy of the general noise reduction method proposed by Mathur and Thurgate, without making any a priori assumptions about the functional form of the dopant profile. This method successfully extracts the surface dopant profile for low-doped ultrashallow junctions for which the on-bevel electrical junction falls outside the sample.
Measurement of ultra-abrupt doping transitions using capacitance versus voltage techniques
Authors: Sadwick L. P. , Hwu R. J. , Streit D. C. , Jones W. L. , Tan K. L. , Velebir J. R. , Yen H. C.
Published: July 2002

In this work we report on methodologies and procedures to obtain the doping profile of semiconductor homo- and heterostructure devices with ultra-abrupt doping transitions at or near the surface of a device or test structure using capacitance–voltage measurement techniques. Novel methods to obtain the complete carrier distribution (or ‘‘spike’’) of structures containing single of multiple planar (also known as delta) doped layers will be addressed. Techniques to measure the true doping profile of abrupt step and staircase doped structures will also be discussed. Extensive numerical models and methods have been developed to accurately extract doping and carrier concentration profiles of traditional and two-dimensional electron (or hole) gas devices. The analysis and acquisition techniques which have been developed are applicable to all group IV and III–V compound semiconductor devices containing p-n homojunctions or heterojunctions, Schottky or Mott barriers, or MOS or MIS barriers. General limitations imposed by Debye screening and specific considerations related to quantum mechanical carrier confinement will be discussed. Strategies to confirm the abruptness of the impurity doping or alloy composition transitions will also be addressed.
Numerical extraction of ultra-shallow one-dimensional metal–oxide–semiconductor doping profiles from capacitance–voltage measurements
Authors: Osse A. L. M. , Krusius J. P.
Published: July 2002

Traditional electrical doping profile extraction techniques fail for ultra-shallow metal–oxide–semiconductor (MOS) doping profiles due to simplifications in the physical models or limitations in the analytical formulas. A method to overcome these problems is presented, based on the numerical extraction of doping profiles from capacitance–voltage (C–V) measurements without limiting approximations. The following steps are involved: measurement of the high and low frequency C–V characteristics of a MOS test structure; definition of an initial parametrized representation of the doping profile using analytical basis functions; determination of the interface trapped charge from the measured C–V characteristics; minimization of the difference between the calculated C–V characteristic, computed from the full one-dimensional solution of Poisson’s equation, and the measured C–V characteristic, by optimizing the doping profile parameters. All computations are performed on an engineering workstation which can also control the C–V measurements and data acquisition. The method is demonstrated for MOS structures with known doping profiles, interface trap densities, and measurement noise. Uniqueness, resolution, and sensitivity issues of the extracted doping profiles are also discussed.
Lateral and in-depth junction delineation of buried Sb-doped layers following silicidation
Authors: Honeycutt J. W. , Rozgonyi G. A.
Published: July 2002

The demarcation of Sb-doped Si buried layer structures has been investigated following silicidation-enhanced diffusion. After Co and Ti silicidation at 700 and 800 °C, respectively, two-dimensional perspectives of the two buried n/p junction interfaces have been obtained by optical microscopy of bevel-polished and etched (or stained) cross sections. Greatly enhanced and asymmetric diffusion of Sb buried layers is observed under silicided regions, as well as at large distances from the edges of silicided stripes. Excellent correlation of micrographs with one-dimensional experimental secondary ion mass spectrometry profiles was obtained. Metrology and shallow junction processing/characterization issues are discussed.
Study of zinc thin films formed using large clusters in the ionized cluster beam deposition technique
Authors: Urban Frank K. , Feng Susan W. , Nainaparampil Josekutty J.
Published: July 2002

Ionized cluster beam (ICB) deposition uses a beam of ionized, accelerated atom clusters to grow thin films. It has been shown that in ICB efforts prior to late 1991, significant numbers of large clusters were not present in depositing beams. Since that time, formation of such large clusters of zinc by homogeneous nucleation has been demonstrated by Gspann using radiation crucible heating and pulsed ionizer time of flight cluster size measurement and in our laboratory using electron bombardment heating and deflected deposition cluster measurement. Crucible pressure was increased from 2 to over 1000 Torr and a converging–diverging nozzle 18 mm long and 0.4 mm in diameter at the throat was used in place of the older 1 mm×1 mm nozzles. Increasing source pressure from 2.8 to 11.3 atm (280–1130 kPa) is accompanied by an increase in peak average cluster size from a few hundred to over 2000 atoms/cluster. Surface roughness of cluster formed films increases with increasing incident cluster energy using a cluster beam peaking at ∼2200 atoms/cluster in average size for cluster energies from thermal to approximately thermal plus 700 eV.
Angle-resolved magneto-tunneling spectroscopy to probe valence band anisotropy in Si/Si1−xGex quantum wells
Authors: Kesan V. P. , Gennser U. , Syphers D. A. , Smith T. P. , Iyer S. S.
Published: July 2002

The resonances of a resonant tunneling structure are probed by a magnetic field applied parallel to the interfaces, which enables us to investigate the local band structure in k space. By rotating the magnetic field in the plane of the interfaces the energy surface at constant k∥ is investigated. Using this technique differently strained Si/Si1−xGex quantum wells were studied, where with a large anisotropy of the energy levels was seen, with the symmetry axes of light holes and heavy holes being rotated 45° with respect to each other. In the case of resonant tunneling diodes with relaxed Si1−xGex quantum wells grown on thick, relaxed Si1−xGex buffer layers, the anisotropy is smaller, and without complete symmetry between different 90° in-plane directions, which may be due to anisotropic strain relaxation in the Si1−xGex buffer layers.
Comparison of a triangular-shape field emitter array and flat surface-emitter vacuum diodes
Authors: Shieh Jyun-Li , Ren Rui-Jun , Shieh Tsay-Jiu , Klemer David P. , Chen Chun-Yao
Published: July 2002

Two types of field emitters were fabricated and characterized. The first type consisted of triangular-shaped metal/vacuum/metal emitter array vacuum diodes formed by a self-aligned evaporation process to achieve a vacuum gap in the submicron range. The second were flat surface-emitter vacuum diodes, which use the silicon surface layer as the emitter and were prepared by standard silicon integrated circuit processing techniques. The vacuum gap is on the order of 0.1 μm, determined by a gate oxidation thickness. Both types of diodes are intended to provide high total emission current. The triangular-shaped emitter array vacuum diodes show a turn-on voltage in the range of 10–50 V and an emission current in the range of 50–500 nA. The flat surface-emitter vacuum diodes, in general, have a lower turn-on voltage of around 10 V and a higher emission current in the microamp range. The flat surface-emitter vacuum diodes, using silicon as the emitter, also have much better stability and reliability. In this article, we present the fabrication process and measurement results.
Design considerations of silicon avalanche cathodes
Authors: Wang M. , Lu Y. , Lalevic B.
Published: July 2002

Silicon avalanche cathodes using ultrashallow p–n junction have been used as a current source in vacuum microelectronics and have shown promising potential for device applications. In this article, device simulation results with a two-dimensional, two-carrier device modeling program which simultaneously solves Poisson’s and both the electron and hole continuity equations are presented. The simulation includes impurity concentration and electric field dependent mobility models, impurity concentration dependent Shockley–Read–Hall and Auger recombination, band gap narrowing, and impact ionization model. Due to the small vertical dimension of the n-type shallow channel, the nonplanar surface structure resulting from subsequent processing steps influences the device performance. The simulation results indicate locations of current crowding in our prototype devices. In order to achieve maximum emission current density, it is very important to obtain a uniform emission across the entire emitter areas. The design considerations are discussed for the improved performance of the silicon avalanche cathodes.
Fabrication of gated silicon field-emission cathodes for vacuum microelectronics and electron-beam applications
Authors: Trujillo Johann T. , Hunt Charles E.
Published: July 2002

Two types of silicon gated field-emission cathodes have been fabricated. The first is fabricated using a phosphosilicate glass insulation layer and a non-self-aligned etched polysilicon gate. The second type is formed by evaporating silicon dioxide and chrome onto a field-emission point capped by its etch mask. The self-aligned gate is then patterned by lifting-off the cap. Cathode current of the etched-gate structure was not measured until 150 V, at which value the device also failed. Current was measured, however, between the gate and the anode of this structure. This gate-anode current is attributed to a nonplanar gate structure and a gate-anode spacing of ∼0.5 μm. Gate-anode currents follow a Fowler–Nordheim characteristic, emitting 0.16 μA/gate at 4 V. Current from the lift-off structure was measured between the cathode and the gate. Currents averaging to 0.2 μA/tip at 23 V on the gate have been measured. These devices are intended for application to vacuum microelectronics, flat-panel displays, and cold-cathode electron-beam instruments.
Molecular-beam epitaxially grown InP/InGaAsP heterostructure for inversion-channel devices
Authors: Kovacic S. J. , Robinson B. J. , Swoger J. H. , Simmons J. G. , Thompson D. A.
Published: July 2002

A heterostructure, based on InP/InGaAsP alloys grown by gas source molecular-beam epitaxy, is presented which can be used to implement the inversion-channel family of devices. The double-heterostructure optoelectronic switch (DOES) is demonstrated for the first time in the InP/InGaAsP materials system and the current density versus voltage characteristics are presented. Numerical simulations are used to demonstrate the tolerances required in materials growth, doping, and layer thickness in order to successfully realize the heterostructure and the associated I–V characteristics of the DOES. In addition, material and interface quality are shown by simulations to affect the I–V characteristics of the InP/InGaAsP-based DOES.
Transport properties of a two-dimensional electron gas closely separated from an underlying n+ GaAs layer: The fabrication of independent ohmic contacts using molecular beam epitaxial regrowth and in situ focused ion beams
Authors: Linfield E. H. , Hamilton A. R. , Iredale N. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

Recently we have described a new method for the fabrication of independent ohmic contacts to a two-dimensional electron gas (2DEG) closely separated from an underlying n+ GaAs layer. This was achieved by using molecular beam epitaxial regrowth on an in situ focused ion implanted epilayer. In this article, we present further transport properties of backgated high electron mobility transistors which indicate the versatility of this fabrication technique. Results are presented for two wafers, both with a separation of ≊1.38 μm between the backgate and 2DEG: one having a high carrier concentration, the other a low carrier concentration. For the high carrier concentration wafer, it is shown that up to −7 V could be applied to the backgate at 1.2 K while maintaining leakage currents of <1 nA. Further, in combination with a surface Schottky gate, the onset of second subband occupation was investigated as the 2DEG confining potential was altered. For the low carrier concentration wafer, it is shown that successful backgating action was maintained even when the temperature was increased to ≊150 K.
Fixed and trapped charges at oxide–nitride–oxide heterostructure interfaces formed by remote plasma enhanced chemical vapor deposition
Authors: Ma Y. , Yasuda T. , Lucovsky G.
Published: July 2002

This article discusses the preparation of device-quality oxide–nitride–oxide (ONO) structures by a sequence of low-temperature plasma-assisted processes. The emphasis is on the relationship between (i) the chemical bonding (a) within the nitride film and (b) at the internal interfaces of a metal–insulator–semiconductor (MIS) structure, and (ii) the electrical properties of these devices with an ONO gate dielectric. In a MIS device, the flatband voltage is shifted from its ideal value by fixed positive charge primarily at the two internal oxide–nitride (O/N) interfaces. The amount of fixed charge is relatively insensitive to the source gas mixture for nitride deposition, and can be reduced by a rapid thermal annealing (RTA) process. Charge trapping at the SiO2/Si interface is increased by N-atom migration to this interface that occurs during the nitride deposition, and is more sensitive to the source gas mixture, but also is decreased by a high-temperature RTA.
Boltzmann–Matano analysis based model for boron diffusion from polysilicon into single crystal silicon
Authors: Sultan Akif , Bhattacharya Surya , Batra Shubneesh , Banerjee Sanjay
Published: July 2002

The diffusion of boron in single crystal silicon has been modeled following a BF2 or boron implant in a polysilicon layer deposited on a single crystal silicon substrate. The effective concentration-dependent diffusivities of boron in single crystal have been extracted using Boltzmann–Matano analysis from the experimental boron diffusion profiles measured using secondary ion mass spectrometry. The effective boron diffusivities are found to be independent of the implant dose. A new analytical model for concentration-dependent boron diffusivities has been implemented in the PEPPER simulation program to accurately model the boron diffusion profiles in single crystal silicon for a polysilicon-on-single-crystal-silicon structure. The model has been verified for a wide range of furnace anneal conditions (800–950 °C, from 30 min to 6 h), and implant conditions (BF2 doses varied from 5×1015 to 2×1016 cm−2 at 70 keV and boron dose of 5×1015 cm−2 at 20 keV).
Solid source diffusion from agglomerating silicide sources. I. Measurement and modeling
Authors: Tsai J. Y. , Canovai C. , Osburn C. M. , Wang Q. F. , Rose J. , Cowen A. , Denker M. S.
Published: July 2002

An optimized secondary ion mass spectrometry (SIMS) technique was used to characterize the solid source diffusion of dopants, i.e., arsenic and boron, from agglomerating cobalt disilicide sources. It was found that interface roughness plays a dominant role in determining the dopant profiles observed by SIMS. Double convolution of a step function with an exponential function, which represents the SIMS cascade mixing, and then again with a Gaussian function, which represents the silicide interface roughening, were performed to fit the SIMS silicon signal in the transition region of the silicide/silicon interface. Experimental profiles were then deconvoluted with the same functions to derive the ‘‘true’’ dopant diffusion. This convolution methodology eliminates the broadening factors provided by the measuring instrument and by the sample itself, and therefore results in a more physically meaningful diffusion profile. The broadening of SIMS silicon signal also provides a very precise characterization of the thermal stability of the thin polycrystalline silicide film. An analytical model was established to relate the SIMS silicon broadening and the sheet resistance of the agglomerated silicide film. This model predicts that while the amplitude of the root-mean-square roughening goes as the square root of time, the increase in sheet resistance varies linearly with time, provided that the amplitude of roughening is considerably smaller than the thickness of the silicide film.
Angle of incidence effects of an oxygen ion beam on the surface chemistry of GaAs
Authors: Solomon J. S. , Grant J. T.
Published: July 2002

This article describes the influence of the angle of incidence of the interaction of oxygen ions with GaAs surfaces and the effects these interactions have on compositional quantification by secondary ion mass spectrometry. Both Auger electron and small spot size x-ray photoelectron spectroscopies were used to study the chemistry of the bombarded surfaces. The oxidation states of gallium and arsenic and the overall gallium-to-arsenic ratios were found to vary in a systematic way with angle of incidence. Changes in gallium and arsenic surface chemistry are correlated with secondary ion yields of dopants or impurity atoms.
Silicon dioxide deposition by electron cyclotron resonance plasma: Kinetic and ellipsometric studies
Authors: Hernandez M. J. , Garrido J. , Piqueras J.
Published: July 2002

Silicon dioxide has been deposited from electron cyclotron resonance silane/oxygen plasmas at temperatures below 150 °C. Deposition rates over 4000 Å/min have been obtained. The refractive indexes in the measuring range of 1.5–4.5 eV were found to be almost insensitive to the different deposition rates and flux ratio regimes except in the near infrared region where small deviations from thermal oxide indexes were observed. Etch rates and refractive indexes were very close to the thermal oxide values for low silane/oxygen flow ratios 0.025, whereas the refractive index decreased and the etch rate increased for the largest flow ratios used (0.20). After a low temperature annealing, 500 °C in nitrogen ambient, the refractive indexes reached the best obtained values and were independent of the conditions under which the layers were deposited.
Pulse-time modulated electron cyclotron resonance plasma etching for highly selective, highly anisotropic, and less-charging polycrystalline silicon patterning
Authors: Samukawa Seiji , Terada Kazuo
Published: July 2002

Highly selective, highly anisotropic, notch-free and charge build-up damage-free polycrystalline silicon etching is achieved using an electron cyclotron resonance plasma modulated at a pulse time in the range of 10–20 μs. In this plasma, the selectivity ratio of the polycrystalline silicon etching rate to the SiO2 etching rate is increased significantly by the same etching rate as that attained using a continuous discharge. Additionally, vertical and notch-free phosphorus-doped polycrystalline silicon etching profiles and suppressing charge build-up damage can be achieved. These results are attained by controlling the ion energy distribution through the duty ratio, maintaining a high ion current density, generating a collimated ion flux, and eliminating surface charge with the pulsed discharge.
Progress toward spin-sensitive scanning tunneling microscopy using optical orientation in GaAs
Authors: Jansen R. , van der Wielen M. C. M. M. , Prins M. W. J. , Abraham D. L. , van Kempen H.
Published: July 2002

Advances toward spin-sensitive scanning tunneling microscopy are reported here, using optically created spin polarized electrons in GaAs. As a first step, tunneling spectroscopy has been performed on GaAs samples with light excitation. Dependence of photoinduced effects on excitation power, tip–sample distance, and doping density are presented. Similar measurements were conducted for a cleaved GaAs tip, showing short circuit currents of several hundred pA upon laser illumination. Results support the feasibility of using such tips as a spin-sensitive local probe.
Comparison of advanced plasma sources for etching applications. II. Langmuir probe studies of a helicon and a multipole electron cyclotron resonance source
Authors: Tepermeister I. , Ibbotson D. E. , Lee J. T. C. , Sawin H. H.
Published: July 2002

Radial profiles of electron temperature, electron density, and ion current density near the wafer surface are presented for a rf-inductively coupled helicon and a multipole electron cyclotron resonance source as a function of applied source power, applied rf-bias power, and reactor pressure. Both sources show similar trends with respect to changing process conditions, with electron densities in the mid 1011 cm−3 range and electron temperatures between 5.5 and 6.5 eV. An increase in applied source power results in an increase in both electron density and ion current density as expected. An increase in applied rf-bias power results in a 10% change in the measured electron density and ion current density; however, the electron temperature shows a much stronger dependence, indicating that ion flux and ion energy are not completely independent. Radial uniformity is similar in both sources, with the helicon exhibiting better uniformity at the conditions explored. Neither applied source power nor rf-bias power significantly affect radial plasma uniformity above the wafer in both sources, but higher reactor pressure does degrade uniformity in the helicon. We attribute this to the 2:1 geometric expansion between the upper antenna section and the lower plasma confinement section where the measurements are taken. The conditions resulting in optimum radial uniformity of electron temperature, electron density, and ion current density are similar to those for the optimum etching rate uniformity measured in previous studies; yet the uniformity obtained from the Langmuir probe diagnostic is not affected by changing process conditions to the degree that etching uniformity is affected. This can be a result of the difference in chemistry between the two studies since hydrogen bromide was used for etching and argon was used for Langmuir probe measurements. It may also indicate that the correlation between plasma uniformity and etching uniformity is relatively weak or second order compared to other variables affecting uniformity such as rf bias of the wafer.