bluuebunny/crossref_metadata_2025 huggingface dataset:
Passivation and performance analysis of thin film Peltier heat pumps
Authors: Shafai C. , Brett M. J. , Broughton J. N.
Published: July 2002

SiO 2 passivation of thin film Au–Bi2Te3 based Peltier devices was investigated. SiO2 deposited by plasma enhanced chemical vapor deposition at 350 °C was found to adversely affect the Au–Bi2Te3 devices, while SiO2 thin films deposited in a reactive asymmetric bipolar pulsed dc sputtering process passivated the Au–Bi2Te3 devices with minimal change in device resistivity. Replacing the chrome adhesion film with a Mo–W film to adhere the gold metal to SiO2 was found to further optimize the performance of the thin film Peltier device. Thermal modeling showed that two-arm Au–Bi2Te3 based Peltier devices are realistically capable of a maximum temperature differential of approximately 18 °C, with a thermal response time close to 2 ms/°C.
Photoemission studies of K-promoted oxidation of the GaAs(110) surface
Authors: Lin G. , Zhao T. X. , Liu H. T. , Yang H. W. , Ji M. R.
Published: July 2002

Core-level and valence-band photoemission have been used to investigate oxidation at the K/GaAs(100) interface. The results show that potassium deposited on the top of a substrate forms a polarized layer. The K-promoted oxidation mainly involves As. The initial bonds between an alkali metal and a semiconductor have less of a relation with the amount of adsorbed oxygen, but the disruption of K–As bonds restores a large density of As dangling bonds, and the adsorbed oxygen coupling of these dangling bonds leads to the out-of-proportional function of the As oxide.
Structural determination of wear debris generated from sliding wear tests on ceramic coatings using Raman microscopy
Authors: Constable C. P. , Yarwood J. , Hovsepian P. , Donohue L. A. , Lewis D. B. , Münz W.-D.
Published: July 2002

In order to address the important interest in wear debris and associated wear mechanisms, we have studied a series of physical-vapor deposition ceramic hard coatings (CrN/NbN, CrN, NbN, TiAlN/VN, and TiCN) using a ball-on-disk sliding configuration against corundum. The debris generated were characterized using Raman microscopy to identify compounds, especially oxides, generated during the wear process to gain a better understanding of tribochemical reactions. The high spatial resolution (2 μm), sensitivity to structural changes, and nondestructive nature make this technique ideal for the study of such small amounts of wear debris. This article examines binary, multicomponent, multilayered, and superlattice coatings. Under dry sliding conditions of 5 N normal load and 10 cm/s speed, titanium-based alloy coatings were found to provide TiO2 (rutile) debris. However, the addition of thin layers of VN to the TiAlN system provided a lower friction coefficient, and much less debris through the possible formation of a lubricious surface oxide. CrN- and NbN-based coatings were also found to produce debris with Raman bands corresponding to oxides. Contact temperatures were also estimated by comparison of the tribochemical products generated during sliding wear with the formation temperatures of oxides detected from static oxidation.
Interaction of indium on Si surface in Si molecular beam epitaxy (MBE)
Authors: Yang H. T. , Berry W. S.
Published: July 2002

To investigate the feasibility of using indium to replace Ga as an agent for silicon surface cleaning at lower substrate temperature in ultrahigh vacuum, we have examined the in-diffusion of indium and the surface defects introduced into silicon for various indium desorption processes. For the dynamic desorption case, which simulated the actual cleaning procedure, no significant surface defects were identified, nor was there any indium at the near surface region of the silicon substrate.
A theoretical study of the epitaxial growth of metal overlayers on semiconductor surfaces
Authors: Batra Inder P. , Ciraci S.
Published: July 2002

We report on the energetics for the epitaxial growth of metals on semiconductors and obtain optimal interplanar distances using the self-consistent pseudopotential method. A prototype system for which the lattice mismatch is not too severe has been considered so that the lattice can strain elastically to achieve coherency. An example of such a system is Al(001)–Ge(001) in an epitaxial relation (001)[100]Al∥(001)[110]Ge where the [100]Al axis has been rotated 45° with respect to the Ge [100] axis. We have investigated the pseudomorphic growth of Al from submonolayer to multilayers (in various registry patterns) on the rigid unreconstructed Ge(001) substrate. One significant result of our calculation is that the A1–Ge bond length relaxes as one goes from submonolayer to multilayer coverages of metal indicating a transition from directional covalent to more metallic type of bonding. Another important conclusion is that at monolayer coverages, aluminum at bridging positions in the first layer is more stable (∼1 eV) than at on top positions. This suggests that Frank–van der Merwe growth sequence is likely to initiate at the bridging sites. Furthermore, the energy lost due to an overall strain in pseudomorphically growing many layers is estimated to be well below the energy benefit due to interfacial bonding in bridging sites. We also report that the calculated interfacial bonding energy and the interplanar separation reaches limiting values at about one monolayer coverage, but other properties show slow convergence. The implications of these results for the electronic structure of interfaces and Fermi-level pinning are briefly investigated.
Dry etching of through substrate via holes for GaAs MMIC’s
Authors: Hipwood L. G. , Wood P. N.
Published: July 2002

Through substrate via’s are essential in many GaAs monolithic microwave integrated circuits (MMIC’s). They allow for increased circuit complexity and provide low inductance grounding. A dry etch process is described which has been used for etching vias through 0.2 mm thick GaAs substrates. Freon 12 (CCl2F2) is used at high pressure in a RIE mode at 13.6 MHz. Polymer formation has been identified to be the key to controlling the hole profile.
Silicon doping effects in reactive plasma etching
Authors: Lee Young H. , Chen Mao-Min
Published: July 2002

Silicon etch rates in CF4/O2 plasma have been studied in a diode reactor which allows both reactive ion etching (RIE) and plasma etching. A fluorine population was also measured from the intensity of optical emission in conjunction with argon actinometry, in order to separate etch rates contributed by the ion enhanced etching and the spontaneous chemical etching. A heavily doped n-type silicon etches faster than undoped silicon, while a heavily doped p-type silicon etches slower than undoped silicon. Although this doping effect is present in both ion enhanced etching and chemical etching, it is a more severe influence in the isotropic chemical etching. The thermal activation energy for the chemical etching was measured to be 0.10 eV, independent of the chemical and electrical properties of dopants. The Coulomb attraction between uncompensated donors (As+) and chemisorbed halogens (F−) enhances etch rates in a heavily doped n-type silicon, whereas the Coulomb repulsion between uncompensated acceptors (B−) and chemisorbed halogens (F−) inhibits etch rates in a heavily doped p-type silicon.
Optical characterization of molecular beam epitaxial GaAs/AlxGa1−xAs multi-quantum-well structures using a very low power, narrow band, tunable pulsed dye laser
Authors: Naganuma M. , Song J. J. , Chao C. H. , Kim Y. B. , Masselink W. T. , Morkoç H.
Published: July 2002

High-resolution pulsed laser-induced photoluminescence (PL) and PL excitation spectroscopy have been carried out in MBE grown GaAs/AlxGa1−xAs multi-quantum-well structures at 5 K. At very low laser power levels, fine structures are observed both in the heavy-hole and the light-hole excitonic regions. By combining a selective detection method with PL excitation spectroscopy, energy states buried under a broad spectrum can be separated.
Plasma assisted chemical vapor deposited thin films for microelectronic applications
Authors: Nguyen S. V.
Published: July 2002

This paper reviews some aspects of and recent advances in plasma assisted deposition of thin films for microelectronic applications. The plasma deposition process and some properties of deposited films relative to integrated circuit fabrication will be briefly discussed. Possible trends in future research and development of plasma deposition for microelectronic applications will also be presented.
New optical transitions in Ge–Si ordered atomic-layer structures
Authors: Pearsall T. P. , Bevk J. , Feldman L. C. , Bonar J. M. , Mannaerts J. P. , Ourmazd A.
Published: July 2002

We have observed new optical transitions at 0.76, 1.25, and 2.31 eV in an ordered Si–Ge superlattice. The superlattice structure consists of a sequence of four monolayers (ML) of Ge and 4 ML of Si repeated five times in the (001) crystal orientation. The strained-layer structure of 50 Å total thickness was produced by molecular-beam epitaxy on a Si substrate. Electroreflectance spectroscopy was used to measure seven band-to-band transitions in this structure, while only five transitions are expected for a Ge–Si random alloy. Analysis of our measurements indicate that a new electronic band structure is created for the layered structure as a consequence of its tetragonal unit cell.
Evaluation of the proximity effect and GHOST correction technique for submicron electron beam lithography at 50 and 20 kV
Authors: Kostelak R. L. , Kung E. H. , Thomson M. G. R. , Vaidya S.
Published: July 2002

The magnitude of proximity effect for submicron electron beam lithography has been experimentally quantified using an electrical proximity effect tester (PET). The PET was delineated in MP 2400-17 resist in a trilevel stack on aluminum, using an AT&T electron beam exposure system. At 50 kV the proximity exposure on a 0.5-μm coded feature under the extreme layout conditions in the PET resulted in linewidth variation >0.25 μm. The effective range of the backscattered electrons was measured to be >10 μm. The GHOST proximity correction technique was used to reduce the magnitude of the linewidth variation. Using a 19-μm defocused beam and a correction dose of 30% of the incident, the magnitude of the linewidth deviation on a 0.5-μm feature was reduced to ±0.05 μm. However, the smallest feature that could be successfully GHOSTed was 0.375 μm at 50 kV. This was attributed to uncorrected electron scatter associated with the forward traveling electrons. Resolution of finer geometries was unpredictable. At 20 kV the resolution limit for successful proximity correction with GHOSTing was 0.5 μm. In conjunction with the experimental results, a computer model was used to confirm the limitations of the GHOSTing technique, as well as to establish the tolerances on the GHOST parameters, correction dose, and defocused beam size. At 50 kV the correction dose can vary from 27% to 33%, and the defocused beam diameter can vary from 15 to 26 μm with only a ±0.05-μm linewidth variation on a 0.5-μm feature.
Application of water-soluble contrast enhancing material to g-line lithography
Authors: Endo M. , Sasago M. , Hirai Y. , Ogawa K. , Ishihara T.
Published: July 2002

In this paper, we report the application of contrast enhanced lithography to g-line (436 nm) lithography using our new water-soluble contrast enhancing material, named WSP (water-soluble photopolymer). It has been found that the WSP is effectively utilized about resist pattern profile, resolution, and pattern width control for exposure energy, depth of focus, mask linearity. By use of WSP, submicron lithography has been successfully attained without decrease of throughput and complexity.
Optical properties of ultrathin silicon–germanium superlattices
Authors: Wong K. B. , Morrison I. , Jaros M.
Published: July 2002

We have carried out pseudopotential calculations of the electronic structure of a Si4Ge4(001) superlattice grown on a Si substrate. We show that a model in which the microscopic potential and the bond lengths in the Ge layer are bulklike can account for the transition energies and oscillator strengths of the optical spectra reported for this structure in the literature. This is achieved without invoking a breakdown of the translational symmetry and indirect transitions.
Focused ion beam lithography using Al2O3 as a resist for fabrication of x-ray masks
Authors: Ohta Tsuneaki , Kanayama Toshihiko , Tanoue Hisao , Komuro Masanori
Published: July 2002

Ion bombardment has been found to enhance the etch rate of amorphous rf-sputtered Al2O3 in hot H3PO4 so that this material works as a dry-etch-durable ion beam resist. It is shown that the resist properties depend on the substrate temperature and the magnetic field strength near the target surface during the sputter deposition. The optimized Al2O3 deposited at 380 °C and 9 mT is insoluble in 80 °C H3PO4 when unbombarded, and has a sensitivity of 1×1014 cm−2 and a contrast (γ) of 1.5 for 50-keV Ga+ ions. Density measurement and x-ray diffraction revealed that the optimized Al2O3 has higher density and a more ordered structure. X-ray masks were fabricated by defining 200-nm-wide grooves in 500-nm-thick WNx x-ray absorber layers using the Al2O3 patterned with focused 50-keV Ga+ beams, as a durable mask for electron cyclotron resonance type of plasma etching with SF6; the etch-rate ratio of WNx to Al2O3 was 30. Pattern transfer into poly(methylmethacrylate) from the fabricated mask was successfully carried out with synchrotron radiation.
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u stress measurements during thermal oxidation of silicon
Authors: Kobeda E. , Irene E. A.
Published: July 2002

A two-beam laser reflection technique was used to measure SiO2 film stress during Si oxidation, i.e., in situ at the growth temperature. Results show a higher compressive intrinsic film stress near the Si–SiO2 interface and a lower stress in the bulk of the SiO2 film. Thermal stress is also measured by monitoring the SiO2 film covered Si substrate curvature changes during temperature excursions. Our new results are in general agreement with previous ex situ stress measurements and may indicate that film stress, being highest at the interface, influences the interface reaction in Si oxidation.
Structural and optical properties of III–V quantum wells grown on Si
Authors: Woodbridge K. , Gowers J. P. , Fewster P. F. , Dawson P. , Moore K. J. , Roberts C.
Published: July 2002

We have studied the structural and optical properties of GaAs/AlGaAs multiple quantum well structures (MQW’s) grown on Si for a range of different types of buffer layer with special reference to the effects of strained layer superlattices and thermal annealing on material quality. Layers were analyzed by in situ reflection high-energy electron diffraction and ex situ transmission electron microscopy, x-ray diffraction (XRD), and photoluminescence. Considerable improvement in structural quality of MQW layers was found when (001) substrates tilted towards [110] were used and this appears to be due entirely to elimination of antiphase domains since threading dislocation densities are still quite high. GaAs/InAs strained layer superlattices seem to have a considerable effect on the line direction of threading dislocations presumably due to the strong strain field associated with this structure. XRD diffraction profiles of GaAs/AlGaAs MQW samples show large numbers of satellite peaks indicating good uniformity and periodicity similar to that obtained with MQW’s on GaAs. Using a combination of strained layer superlattice buffers and annealing in these samples, we have obtained 300-K photoluminescence efficiencies comparable to high quality MQW samples grown on GaAs. We have been able to use the photoluminescence decay technique to measure minority carrier lifetimes on some of these samples and values of ∼3 ns have currently been obtained. These results are discussed in relation to the improvement in structural quality observed.
Effect of post-etch treatment on chlorine concentration of AlSi and Ti-capped AlSi films
Authors: Maa Jer-shen , Gossenberger Herman , Paff Richard J.
Published: July 2002

Ti-capped Al–Si films are more susceptible to post-etch corrosion than uncapped Al–Si films. The extent of corrosion of Ti-capped films is related to post-etch treatment. Various post-etch treatments to reduce chlorine concentration are evaluated by x-ray fluorescence analysis. Results of single- and multiple-step treatment, such as baking, partial resist stripping in oxygen plasma in the exit chamber, water rinse, and resist partial stripping followed by wet stripping are presented. A method to estimate the surface concentration of chlorine in atoms/cm2 is described; the chlorine concentration in most cases is less than 5×1015 atoms/cm2.
Growth of Ca0.43Sr0.57F2 molecular beam epitaxy films on GaAs(100) at 560 °C studied by photoemission spectroscopy
Authors: Stair Kathleen , Zajac G. , Chambers F. , Engelhardt M. A. , Höchst H.
Published: July 2002

We report on the MBE growth of thin Ca0.43Sr0.57F2 films deposited on GaAs(100). The interface has been studied using surface sensitive synchrotron radiation photoemission spectroscopy. The fluoride deposition was performed in situ on As terminated 2×4 reconstructed GaAs(100) surfaces at substrate temperatures up to 560 °C. Quantitative analysis of the line shapes and intensity attenuation of the As 3d and Ga 3d substrate emission as well as the evolution of overlayer features from the Ca 3p, Sr 4p, and F 2p spectra indicates a sharp but compositionally graded interface. At 560 °C the fluoride overlayer grows initially in a two-dimensional mode which is then followed by a three-dimensional growth mode (Stranski–Krastanov). Even though the initial layer of ∼15–20 Å grows layer-by-layer, quantitative core spectroscopy of the fluoride layer indicates a severe shortage of fluorine in the interface region. Stoichiometric fluoride films are obtained after a film thickness of ∼500 Å. Films which initially were stoichiometric lose fluorine in vacuum. Concomitant with a decrease in the total fluorine concentration we observe additional emission features in the Ca 3p and Sr 4p spectra. Exposing fluoride films to the UV part of the synchrotron radiation caused severe defect formation which was associated with the loss of fluorine at the surface.
The effect of strain on the valence band structure of InAs(100)
Authors: Williams M. D. , Chiu T. H.
Published: July 2002

Thin pseudomorphic layers of InAs were grown on selected III–V (100) substrates to ascertain the effect of the variation of the in-plane biaxial stress on its valence band density of states. The range over which the stress varies is 6.7% compression to 7% tension. The layers were grown by molecular beam epitaxy using the migration enhanced epitaxy technique. Surface sensitive ultraviolet photoemission spectroscopy showed a strong modification of the valence band (VB) over the chosen stress range. Strain induced shifts in the energy separation of the VB maximum and the spectral feature related to contributions from the X3 and L1 Brillouin zone critical points were observed to be nonmonotonic as a function of biaxial stress.
Thermal stability of ohmic contacts to n-GaAs formed by scanned electron beam processing
Authors: Prasad K. , Faraone L. , Nassibian A. G.
Published: July 2002

Alloyed Au–Ge/Ni and sintered Au/Pd/Ge and Au/Pd/Ni/Ge ohmic contacts were formed on n-GaAs using scanned electron beam processing. Thermal aging studies at elevated temperatures in the range 150–500 °C reveal that sintered ohmic contacts have a much higher resistance to thermal degradation than conventionally alloyed Au–Ge/Ni contacts. Activation energy plots of failure time as a function of aging temperature indicate that sintered Au/Pd/Ni/Ge ohmic contacts have much longer operating life (∼106 h for an eightfold increase in ρc at 300 K) than both alloyed Au–Ge/Ni and sintered Au/Pd/Ge ohmic contacts. Studies on the effects of polyimide and rf sputtered SiO2 passivation layers on the stability of ohmic contacts reveal that polyimide surface passivated contacts exhibit better stability than those passivated with SiO2 . From Arrhenius activation energy analysis, there is strong evidence to suggest that a single degradation mechanism is responsible for ohmic contact failure over the full range of aging temperatures from 150 to 500 °C.
Reduced-confinement GaAlAs tapered-waveguide antenna grown by molecular-beam epitaxy
Authors: Goodhue W. D. , Bossi D. E. , Finn M. C. , Bales J. W. , Rediker R. H.
Published: July 2002

A reduced-confinement GaAlAs tapered-waveguide antenna has been demonstrated. This device, produced by means of a novel growth technique using molecular-beam epitaxy, employs a longitudinal variation in the refractive index and thickness of the waveguide film to achieve reduced-mode confinement near the sample endface. In initial experiments this antenna has produced far-field beam divergences as narrow as 8.2° full width at half-maximum (FWHM).
Preliminary evaluation of a laser-based proximity x-ray stepper
Authors: Frackoviak J. , Celler G. K. , Freeman R. R. , Jurgensen C. W. , Kola R. R. , Novembre A. E. , Tai W. W. , Thompson L. F. , Trimble L. E. , Tomes D. N.
Published: July 2002

This paper reports on the initial lithographic evaluation of a commercial 1:1 proximity stepper that uses a laser-based plasma x-ray source. Our preliminary tests have shown that 0.4- and 0.5-μm lines and spaces can be printed consistently on Si wafers using a positive resist, which has a sensitivity of 6–10 mJ/cm2. Features smaller than 0.4 μm can be obtained, but the overlay accuracy of this system is targeted at 0.5-μm design rules. The 3σ spread in linewidth is greater than 0.05 μm, however, the stepper contribution must be separated from the resist processing issues, reticle critical dimension variations, and scanning electron micrograph measurement precision.
Fabrication of a 1 Mbit dynamic random access memory with four levels using x-ray lithography
Authors: Hoffman S. , Nash S. , Ritter R. , Smith W.
Published: July 2002

A 1 Mbit dynamic random access memory (DRAM) was recently fabricated with all critical levels exposed using synchrotron x rays. Lithography for the critical levels (isolation, transfer gate, contacts, and metal) was performed at the Brookhaven National Laboratory—National Synchrotron Light Source (vacuum ultraviolet ring) on an IBM beamline using a Karl Suss XRS-200 x-ray stepper. The remaining levels were exposed with standard step-and-repeat optical tools. Most nonlithographic processing was performed in a mature 1 Mbit production line. Bit yields of up to 50% were found on several 256 K input–output (I/O) segments. An optical control lot processed through equivalent nonstandard steps produced a comparable yield. Considering the extensive off-line processing required for this experiment, this yield exceeded expectations.
X-ray mask process-induced distortion study
Authors: Nash S. C. , Faure T. B.
Published: July 2002

X-ray masks for fabrication of 0.25 μm ultralarge-scale-integration devices have to meet very tight pattern placement requirements. Because of the nature of x-ray mask substrates, control of the distortion caused by the processing of the mask after e-beam lithography is important. The pattern placement distortions that occur during the processing of an x-ray mask are examined, and the effect of gold absorber electroplating, e-beam-resist strip, and plating-base strip processes are studied. It has been found that x-ray mask process-induced distortion is very sensitive to the amount of gold coverage and the connectivity of the gold pattern.
Novolak resin-based positive electron-beam resist system utilizing acid-sensitive polymeric dissolution inhibitor with solubility reversal reactivity
Authors: Shiraishi Hiroshi , Hayashi Nobuaki , Ueno Takumi , Sakamizu Toshio , Murai Fumio
Published: July 2002

This paper deals with a novel novolak resin-based positive resist system designed for practical direct electron-beam fabrication. The novel positive resist system, which has a solubility reversal mechanism, consists of an acid-sensitive polymeric dissolution inhibitor, an acid generator, and a novolak matrix resin. Various kinds of polymers, which can be converted to dissolution promoters by acid-catalyzed reaction, are investigated as the dissolution inhibitor of the system. A tetrahydropyranyl-protected poly(p-vinylphenol) (THP-M) is selected as the polymeric dissolution inhibitor. THP-M is insoluble in aqueous base solutions and compatible with novolak resins. The acid-catalyzed deprotection of THP-M results in poly(p-vinylphenol), which is soluble in aqueous base solutions and can be a dissolution promotor in the system. It is found that a methanesulfonic acid ester is the most effective acid generator for this resist system. Aryl onium salts, well-known acid generators, are not effective because of their strong dissolution-inhibition behavior results in negative tone patterns. High-resolution patterns (0.4-μm lines and spaces) are achieved with high sensitivity (2.5 μC/cm2 at 30 kV).
Reliability enhancements for the direct wafer exposure electron beam system EB60
Authors: Watanabe Takashi , Morosawa Tetsuo , Shimazu Nobuo , Morita Hirofumi , Yamauchi Hironori , Iwata Atsushi
Published: July 2002

Based on the exposure architecture of ‘‘EB60,’’ intensive effort has been made to achieve an integrated system that is both reliable and easy to adjust. First, the central processing unit (CPU) and network structure have been modified to exploit an open system environment and to tighten communication between the e-beam and computer aided design (CAD) systems. Exposure data are transferred over a high-speed optical cable directly from the remotely located CAD resident host CPU. Five custom larger scale integrated circuits (LSIs) have been designed and implemented. A complimentary metal–oxide semiconductor LSI (22 Kgates) that performs general linear matrix functions in 60 ns has been applied to minor-field-deflector, shaping-deflector, shot-time, stage movement, and overlay coordinate corrections. A shot control super self-aligned transistor (SST) LSI (2.5 Kgates), which covers all functions operating at 400 MHz, has eliminated the tedious adjustment of emitter coupled logic (ECL) circuits. Taken together, these LSIs have substantially reduced the space occupied by on-board logic circuits. A digital calculation method has been introduced in major-field-deflector amplifiers. All these improvements have markedly enhanced the reliability and maintainability of EB60, while at the same time making the system more user-friendly and comprehensive.
Substrate-epitaxial layer interface effects on AlGaAs/GaAs heterostructure device properties
Authors: Gray M. L. , Yoder J. D. , Brotman A. D. , Chandra A. , Parsey J. M.
Published: July 2002

Device characteristics of AlGaAs/GaAs heterostructure field effect transistors fabricated by molecular-beam epitaxial growth are related to the condition of the substrate-epitaxial layer interface. The presence of carbon on the GaAs wafer surface prior to growth has been found to produce a p-type, conducting interfacial region. We demonstrate that the concentration of carbon on the wafer surface can be significantly reduced by exposing the wafers to ultraviolet radiation. Depletion- and enhancement-mode device transfer characteristics and transconductance curves have been obtained on heterostructure wafers that were subjected to an ultraviolet-ozone surface preparation. A comparison of these results with the device properties of wafers receiving a standard cleaning procedure is presented. A model describing the interaction between the interfacial p-type region and the two-dimensional electron gas channel is also included.
Characteristics of silicon strip doping sources for molecular beam epitaxy
Authors: King W. D. , Griffiths G. J. , Giugni Stephen
Published: July 2002

The use of a filament doping source for Si doping of molecular beam epitaxy (MBE) grown III–V semiconductors provides many benefits in the areas of cleanliness, simplicity of construction, and source lifetime. This work details the thermal and doping characteristics associated with such sources. Expressions are developed for the flux, temperature, and power relations, and for the heating and cooling characteristics. We show that the thermal response allows the doping to be varied by at least two orders of magnitude during the time taken to grow one monolayer at normal growth rates (1 μm/h), and for most applications this obviates the need for a shutter. The source is clean (largely because it is only the strip itself which is at an elevated temperature), repeatable, reliable, has a lifetime comparable with that of the system, and can achieve doping levels of 1019 cm−3 in GaAs with mobilities of 1300 cm2 V−1 s−1 at room temperature.
Surface related core level shifts for the Si(111)√3×√3: Al system
Authors: Andersen J. N. , Wigren C. , Karlsson U. O.
Published: July 2002

The Si(111)√3×√3:Al reconstruction has been studied by surface sensitive high resolution core level spectroscopy. It is shown that three components are needed to fit the Si 2p spectra. The Al 2p emission is found to consist of more than one component and it is argued that this is related to defects in the overlayer.
Density of states of quantum-well systems with interface roughness and point defects
Authors: Li Z. Q. , Pötz W.
Published: July 2002

We present selected results from a theoretical study of the local density of states of imperfect quantum-well structures. At the example of GaAs–AlGaAs, we investigate the validity of the virtual crystal approximation (VCA) for ternary alloys, show how quantum confinement can be evidenced in the local density of states (LDOS), discuss antisite defect levels in quantum wells, and finally, analyze the effects of interface roughness on the local density of states.
Si doping of AlGaAs using Si2H6 grown by gas-source molecular-beam epitaxy using trimethylamine alane, triethylgallium, and AsH3
Authors: Fujii Toshio , Okamoto Naoya , Sandhu Adarsh , Ando Hideyasu , Kataoka Yuji
Published: July 2002

We investigated Si doping characteristics and background oxygen and carbon impurity incorporation in gas-source molecular-beam epitaxy grown n-AlGaAs as a function of the AlAs mole fraction, x, using uncracked Si2H6 as the cold gaseous dopant source and trimethylamine alane, triethylgallium, and AsH3 as host constituent sources. The carrier concentration of n-AlGaAs showed a linear dependence on the Si atomic concentration in the x range from 0 (GaAs) to 0.40. The activation efficiency of Si in the n-AlGaAs films was more than 60% in the carrier concentration range of 1.5 × 1017–3 × 1018 cm−3. The oxygen concentration was in the range of 3–4 × 1017 cm−3 which is insensitive to x, and the carbon concentration increased gradually from 4 to 7 × 1016 cm−3 with increasing x in the range of 0.09–0.40.
Effect of dislocations on the electrical and optical properties of long-wavelength infrared HgCdTe photovoltaic detectors
Authors: Johnson S. M. , Rhiger D. R. , Rosbeck J. P. , Peterson J. M. , Taylor S. M. , Boyd M. E.
Published: July 2002

The quantitative effects of dislocations on the electrical and optical properties of long-wavelength infrared (LWIR) HgCdTe photovoltaic detectors was determined by deliberately introducing dislocations into localized regions of two high-performance arrays having cutoff wavelengths of 9.5 and 10.3 μm at T=78 K. Results show that dislocations can have a dramatic effect on detector R0A product, particularly at temperatures below 78 K. For large dislocation densities, R0A decreases as the square of the dislocation density; the onset of the square dependence occurs at progressively lower dislocation densities as the temperature decreases. A phenomenological model was developed which describes the dependence of the detector R0A product with dislocation density, based on the conductances of individual and interacting dislocations which shunt the p–n junction. Spectral response and quantum efficiency are only weakly affected, as is the diffusion component of the leakage current. The 1/f noise current was found to increase approximately linearly with dislocation density and also tracks with the magnitude of the leakage current similar to a data trendline established for undamaged HgCdTe detectors. These results can be used to understand the performance limitations of LWIR HgCdTe arrays fabricated on heteroepitaxial substrates.
Digital scan model for focused ion beam induced gas etching
Authors: Harriott L. R.
Published: July 2002

Focused ion beam (FIB), assisted, gas etching has several advantages over physical sputtering in many FIB applications. Advantages include etch rate enhancements of 1–2 orders of magnitude, dramatically reduced redeposition of etched material on sidewalls in high-aspect ratio structures, and reduced implantation of the primary ion species in the sample. Applications which benefit from FIB gas etching include photomask and x-ray mask defect repair, integrated circuit modification for failure analysis, and sample preparation for scanning electron microscope and transmission electron microscope analysis. In this article, a simple model is presented which takes into account the ion beam and scanning parameters, gas flux, and basic material constants. Approximate formulas are given in terms of these parameters and compared to experimental results.
Layer structure evaluation of multilayer x-ray mirror by combination of focused ion beam etching and transmission electron microscopy
Authors: Nakajima Kunio , Sudo Shuzo , Yakushiji Makoto , Ishii Takayuki , Aoki Sadao
Published: July 2002

Cross-sectional transmission electron microscopy (TEM) specimens were fabricated by a focused ion beam etching for the purpose of investigating the layer structure of multilayer coated x-ray mirror. Uniform samples 0.1 μm wide, 4 μm tall, and 10 μm long were prepared. The structure of a Ni–C multilayer film was observed over a large area. Good agreement between the multilayer periods obtained by TEM and diffraction analysis was found.
Silicon dioxide trench filling process in a radio-frequency hollow cathode reactor
Authors: Gross M. , Horwitz C. M.
Published: July 2002

A process is described for void-free silicon dioxide filling of trenches using a hollow cathode reactor. The process is carried out in a modified hollow cathode of a type similar to those used in previous studies. Silane gas is fed in through the top target of the hollow cathode which supports a low frequency (1 MHz), low pressure (∼0.2 Pa) oxygen and xenon discharge. The combination of low gas pressure, low excitation frequency, and silane feed position combine to produce high ion bombardment and a low rate of gas phase reaction. This produces what is believed to be an ion induced reaction with surface adsorbates, leading to directional oxide film growth. The faceting caused by ion-bombardment etching also serves to locally planarize the deposit. So far, trenches with 1 μm openings and aspect ratios up to 2.5:1 have been successfully filled at rates over 400 Å/min. Refractive index measurements of the deposited oxides have given results similar to thermally grown silicon dioxide.
Dry etching of CdTe/GaAs epilayers using CH4/H2 gas mixtures
Authors: Neswal M. , Gresslehner K. H. , Lischka K. , Lübke K.
Published: July 2002

A CH4/H2 gas mixture has been used for the dry etching of (100) and (111) oriented CdTe epilayers in a barrel reactor. The effects of various process parameters on etch rate and surface morphology were studied with special attention paid to the gas composition and the total chamber pressure as well as the crystallographic orientation of the sample. Clear evidence is found for both isotropic and preferential etching along crystallographic planes depending on the set of etch parameters used.
Optimization of electrostatic deflectors
Authors: Szilagyi M. , Cho H.
Published: July 2002

Optimization of electrostatic lenses was successfully achieved by using the cubic spline method or the a priori given multielectrode approach. In this article we propose optimization of electrostatic deflectors by using the cubic spline method for the purpose of attaining the minimum beam spot size. We propose the reconstruction of the electrodes of electrostatic spline deflectors in terms of the optimized first harmonic field distribution functions. Our calculations show that geometrical deflection aberrations can be reduced by 2–3 orders of magnitude.
Distributed Bragg grating integrated-optical filters: Synthesis and fabrication
Authors: Wong V. V. , Ferrera J. , Damask J. N. , Murphy T. E. , Smith Henry I. , Haus H. A.
Published: July 2002

The design, fabrication, and measurement of planar, passive Bragg grating-based transmission filters is presented. We combine interferometric lithography, spatial-phase-locked electron-beam lithography, x-ray nanolithography, and optical lithography with silica-on-silicon waveguiding substrates to define rib waveguides and grating patterns that have multiple quarter-wave shifts along the grating length. Transmission filters such as Gaussian, Butterworth, and Chebyshev can be designed and fabricated with these technologies.
Gap fill dependence of fluorinated polyimide films on solid content, adhesion promoter, spin dwell time, and solvent spray
Authors: Wang Shi-Qing , Zhao Bin
Published: July 2002

Cross sectional scanning electron microscopy was used to study the dependence of gap fill capabilities in 0.25–2.0 μm wide Al–Cu metal gaps of DuPont fluorinated polyimide films on solid content, adhesion promoter, spin dwell time, and solvent spray. It was found that reduced solid content, application of adhesion promoter and solvent spray improve gap fill capabilities. However, these improvements are insignificant. Spin dwell time has little effect on gap fill.
X-ray photoelectron spectroscopy study on native oxidation of As-implanted Si (100)
Authors: Yano Fumiko , Hiraoka Akiko , Itoga Toshihiko , Matsubara Atsuko , Kojima Hisao , Kanehori Keiichi , Mitsui Yasuhiro
Published: July 2002

The native oxidation of As-implanted Si surfaces used in actual ultralarge scale integrated processes are investigated. Quantitative analysis of oxidation is made possible by x-ray photoelectron spectroscopy spectral decomposition of Si 2p into Si4+, Six+, and Si0+, and by calculation of SiO2 and SiOx thicknesses using the decomposition results. Here, the sensitivity is such that less than 1 Å change is detectable. The native oxidation of As-implanted (1×1015–1×1016/cm2, at 25 kV) Si(100) is compared to that of Si(100) without implantation. The results show that the oxidation rate of As-implanted Si is faster than that of Si without implantation, that the native oxide on As-implanted Si includes more suboxide than that on Si without implantation, and that As is oxidized in deeper regions than Si. These results indicate that As implantation changes the Si native oxidation mechanism itself. We propose an oxidation model of As-implanted Si to explain our observations, and discuss the validity of this model.
Monitoring of deposition and dry etching of Si/SiGe multiple stacks
Authors: Tillack B. , Richter H. H. , Ritter G. , Wolff A. , Morgenstern G. , Eggs C.
Published: July 2002

Deposition and patterning of Si/SiGe multiple stacks have been investigated by in situ monitoring techniques. Reflection supported interferometry has been applied to evaluate the thickness and optical parameters of each of the films during the deposition of the stacks by rapid thermal chemical vapor deposition. During patterning by reactive ion etching of these stacks, the nonselectivity of the etch process has been eluded by monitoring of the 265.1 nm Ge line using optical emission spectroscopy. In this way an etch stop can be achieved within any of the thin films of the stack. The results demonstrate an opportunity for in situ control, including end point detection of deposition and patterning of Si/SiGe multiple stacks.
Hydrogen bonding molecules and their effect on scanning tunneling microscope image contrast of covalently immobilized protein molecules
Authors: Parker Marie-Claire , Davies Martyn C. , Tendler Saul J. B.
Published: July 2002

The enzyme catalase has been covalently bound to a self-assembled monolayer adsorbed to a gold substrate using an organic solvent-based attachment method. The enzyme was shown to remain catalytically active after immobilization to the surface. Methanol was adsorbed to the protein surface under conditions of controlled vapor pressure. The effects on the scanning tunneling microscope (STM) image contrast of covalently immobilized catalase were recorded under varying conditions of partial pressure; from the dry state to a 100% methanol saturation level. A significant increase in image contrast was observed as the amount of methanol bound to the protein increased. The data obtained in this study have been compared to contrast changes observed upon protein hydration, which like methanol, also increases protonic surface conduction through surface hydrogen bonding. The method described here can be used for the rapid and facile identification of adsorbed biological material that may not be immediately discernible under ambient STM imaging conditions.
Nanolithography with neutral chromium and helium atoms
Authors: Brezger B. , Schulze Th. , Drodofsky U. , Stuhler J. , Nowak S. , Pfau T. , Mlynek J.
Published: July 2002

We describe two experiments that use neutral atomic beam techniques to write nanostructures. In the chromium experiment, we have used neutral chromium atoms to write one- and two-dimensional periodic nanometer-scale structures in a direct way. The periodic structure is given to the atomic beam by a laser light mask. In a second experiment, we have used a self-assembling monolayer as a resist for metastable helium atoms in a proximity printing experiment.
Metal-based single electron transistors
Authors: Chen W. , Ahmed H.
Published: July 2002

Metal-based single electron transistors operating at liquid nitrogen temperature were fabricated. Multiple tunnel junctions with metal particles of about 3 nm in diameter were used to construct the transistors. In these transistors the gates are placed directly underneath the islands and separated only by a 10-nm-thick dielectric. The capacitance of the islands is less than 1 aF. Clear oscillations induced by gate bias voltage are observed in the current–voltage characteristics at 77 K.
Dry etching of germanium in magnetron enhanced SF6 plasmas
Authors: McLane G. F. , Dubey M. , Wood M. C. , Lynch K. E.
Published: July 2002

Magnetron enhanced reactive ion etching of germanium was investigated in SF6 plasmas. Ge etch rates were determined as a function of cathode power density (0.1–0.5 W/cm2), pressure (2–8 mTorr), and SF6 flow rate (2–11.5 sccm). Etch rate increased as pressure and flow rate were increased, but exhibited the unusual characteristic of decreasing as cathode power was increased. Auger electron spectroscopy measurements showed the presence of a sulfur residue (<1 at. %) upon etching, while scanning electron microscopy revealed that smooth etched surfaces were attained in SF6 magnetron enhanced plasmas.
Detection and control of ferroelectric domains by an electrostatic force microscope
Authors: Hong J. W. , Kahng D. S. , Shin J. C. , Kim H. J. , Khim Z. G.
Published: July 2002

An electrostatic force microscopy (EFM) method has been used for the detection and control of the microdomain in ferroelectric single crystal [triglycine sulfate (TGS)] and thin film piezoelectric transducer (PZT). In this method, EFM is operated in a dynamic contact mode that allows a simultaneous measurement of the topographic and domain contrast images. Through the analysis of the force between the tip and ferroelectric surface, the surface charge density of TGS single crystal is obtained. Polarization charge density of TGS obtained in this method is 2.7 μC/cm2 at room temperature. A complex pattern was written on a PZT film by the polarization reversal. The line shape or the intensity of the reoriented domain does not show any noticeable dependence on the writing speed. The threshold bias for writing on a PZT film studied in this work was 4 V.
Processing of diamondlike carbon using plasma immersion ion deposition
Authors: Lee D. H. , Walter K. C. , Nastasi M.
Published: July 2002

Plasma immersion ion deposition (PIID) has been used to synthesize hard amorphous hydrogenated carbon or diamondlike carbon (DLC) thin films on Si substrates with rf inductive plasmas of various Ar and C2H2 gas mixtures. The surface hardness and stress of the films were highly dependent on the magnitude of the total rf power and the pulse-bias duty factor. The ratios of the ion flux and the film deposition flux, Ji/Jd, were estimated and correlated with DLC film stress, hardness, and the amount of argon and hydrogen content retained. The DLC properties (hardness and film stress) were maximal when the Ji/Jd value ranged between 0.6 and 0.8. The balance between ion-energy transfer and relaxation in the surface and subsurface carbon atoms may explain the DLC growth in this work. The role of ion-current flux in the PIID process was found to be as important as it is in conventional ion beam assisted deposition processing.
Plasma enhanced chemically vapor deposited thin films for microelectromechanical systems applications with tailored optical, thermal, and mechanical properties
Authors: Horn M. W. , Goodman R. B. , Rothschild M.
Published: July 2002

Microbridge materials optimized for room temperature infrared microbolometers have been fabricated using plasma enhanced chemical vapor deposition (PECVD). Thin films were deposited from tetramethyldisiloxane (TMDS) and oxygen. They have a 4× lower thermal conductivity than that of Si3N4 and an inherent absorption coefficient (8–12 μm range) approximately half that of nitride. The PECVD films deposited from TMDS are compatible with current complementary metal–oxide–semiconductor processing and have been shown to have adequate mechanical strength for use as microbolometer membranes.
Gas assisted etching of copper with focused ion beams
Authors: Edinger K.
Published: July 2002

With the implementation of copper instead of aluminum as the metallization layer in high performance integrated circuits, the use of gas assisted etching of copper for focused ion beam (FIB) based failure analysis and circuit rewiring becomes important. In the present study the effects of exposing a copper substrate with a mixture of chlorine (Cl2) and anhydrous ammonia (NH3) during ion bombardment have been investigated. The exposure of the copper surface to Cl2 or to NH3/Cl2 mixtures leads to the formation of a reaction layer. The thickness of this layer and its texture depends on the FIB parameters such as ion beam dwell time, Cl2 pressure, and the NH3 to Cl2 flux ratio. In addition, the experiments indicate that the formation of the reaction layer is enhanced in areas that have been previously exposed (i.e., damaged) with the ion beam. The etch yield shows a strong dependence on the ion beam dwell time and the gas flux. For short dwell times and low NH3 and Cl2 flux a 12-fold increase over physical sputtering could be achieved. With increasing Cl2 flux the etch rate decreased and the maximum in the etch yield shifted to longer dwell times, indicating a change in the rate limiting step of the ion induced reaction sequence.