bluuebunny/crossref_metadata_2025 huggingface dataset:
Mask split algorithm for stencil mask in electron projection lithography
Authors: Yamashita Hiroshi , Takeuchi Kunio , Masaoka Hideki
Published: July 2002

We developed a mask split algorithm, “M-Split,” using some theories of computational geometry. First, we determined which patterns to split based on actual stencil mask fabrication and defined singular patterns. These singular patterns consisted of nonconvex polygons and could be identified by computational geometry. The contoured singular patterns were then split into two complementary masks, balancing the pattern area density. The split resulted in an 80 nm design-rule logic device, showing that the original patterns could be completely split into polygons that could safely fabricate a stencil mask with a pattern area balance of 50.00% between two complementary masks. The ratio of increase of polygons caused by splitting was 4.84. The computational time without contouring and data output for one 1-mm-square sub field on a 4× mask was 14.2 s for the logic device.
Parameter extraction for 193 nm chemically amplified resist from refractive index change
Authors: Sohn Young-Soo , Oh Hye-Keun , An Ilsin
Published: July 2002

Some of the important areas to be improved for lithography simulation are: obtaining correct exposure parameters and determining the change of refractive index. It is known that the real and imaginary refractive indices are changed during exposure. We obtained these refractive index changes during exposure for 193 nm chemically amplified resists. The variations of the transmittance as well as the resist thickness were measured during ArF excimer laser exposure. We found that the refractive index change is directly related to the concentration of the photo acid generator and deprotected resin. It is important to know the exact values of acid concentration from the exposure parameters since a small difference in acid concentration magnifies the variation in the amplified deprotection during postexposure bake. We developed and used a method to extract Dill ABC exposure parameters for 193 nm chemically amplified resist from the refractive index change upon exposure.
Investigation of diamond film deposition on steel without and with ion beam nitriding pretreatment
Authors: Shang N. G. , Lee C. H. , Zhou X. T. , Meng F. Y. , Chan C. Y. , Lee S. T. , Bello I.
Published: July 2002

The surface morphology, film quality, interface structure, growth rate and adhesion of diamond films prepared by hot filament chemical vapor deposition on commercial steel substrates with and without ion beam nitriding pretreatment were investigated by scanning electron microscopy, x-ray diffraction, scanning Auger spectroscopy, a Vickers microindenter, and microRaman spectroscopy. Apart from quite different surface morphologies, both the quality and growth rate of diamond films deposited on the ion beam nitrided steel substrates were higher than those on the unnitrided steel substrates. Similar diamond/steel interface structure were observed on both the nitrided and unnitrided steel. Diamond films were grown on steel substrates via carbide interlayers formed in situ during the diamond deposition rather than via a graphitic soot interlayer. Ion beam nitriding appeared to enhance the diamond growth through thickening of the carbide interlayer. The adhesion of diamond films on the nitrided steel was tested by a Vickers microindenter.
Interplay of current crowding and current self-quenching effects in planar cold cathodes
Authors: Modukuru Y. , Cahay M.
Published: July 2002

In planar cold cathodes making use of semimetallic thin films to achieve low or negative electron affinity, the effects of dc current crowding can be affected by the trapping of electrons being reflected towards the cathode as a result of space-charge effects in the vacuum gap between cathode and anode. A self-consistent solution of the interplay between current crowding and space-charge effects can lead to a nonmonotonic lateral distribution of the anode current density depending on the width of the emission window. This behavior is in sharp contrast with the monotonic decrease of the anode current density from the edges towards the center of the emission window when space-charge effects in the vacuum region are neglected.
Room temperature replication in spin on glass by nanoimprint technology
Authors: Matsui S. , Igaku Y. , Ishigaki H. , Fujita J. , Ishida M. , Ochiai Y. , Komuro M. , Hiroshima H.
Published: July 2002

A compact nanoimprint lithography (NIL) system using the driving power of a stepping motor has been developed. Compared to a conventional NIL system with a hydraulic press, there are some additional features of the NIL system such as compactness and low cost. We propose the use of spin on glass (SOG) instead of PMMA to avoid thermal expansion and demonstrate SOG patterns with 200 nm linewidths at room temperature replications using the NIL system. The SOG patterns were transferred to gold metal using liftoff and to a silicon substrate by reactive ion etching.
Stability improvement at high emission densities for gold thin film photocathodes used in advanced electron beam lithography
Authors: Gosavi Suresh , McCarthy J. M. , House J. L. , Scholte van Mast Bart G. , Janaway G. , Berglund C. N.
Published: July 2002

Multi-electron beam lithography has been proposed as a promising approach to achieve high throughput for mask writing and direct wafer writing. Laser driven photocathodes represent an attractive candidate for multiple beam, high brightness sources. Thin film gold photocathodes that can be handled in air are of particular interest because of their potential for practical sources. In this article we present a study of the degradation mechanisms that change photocurrent yield for thin film gold photocathodes. Two general degradation mechanisms were studied: microstructural changes of the gold thin film and surface reactions. Observed microstructural changes included loss of gold coverage of the sapphire substrate, gold grain growth and an increase in surface roughness. A titanium adhesion layer was shown to stabilize coverage and proved stable to 700 °C by in situ transmission electron microscopy (TEM) experiments on planar sections of the Au/Ti/sapphire thin film stack photocathode. Reactions at the surface included physisorption and chemisorption of species and the subsequent reactions that occur when they diffuse to the laser illumination/electron emission site. X-ray photoelectron spectroscopy detected multiple monolayers of hydrocarbons on the surface of the Au following deposition and exposure to air. A product layer at the illumination sites as thick as 28 nm was detected using scanning electron macroscopy, atomic force microscopy and TEM following long term (1000–1200 min.) photoyield stability tests. Photoyield versus time plots for all the Au/Ti/sapphire cathodes were similar with an initial high photoyield, a drop to a minimum, then a rise to a second maximum followed by a slow 2%/h decay. Desorption of weakly bound physisorbed and chemisorbed species and growth of a reaction product layer within the electron emission zone are proposed as mechanisms to explain the photoyield behavior. Similar photoyield stability behavior was observed when Pt/Ti/sapphire photocathodes were tested. The photoyield degradation mechanisms observed in these tests are likely to be active on all thin film transmissive photocathodes subjected to high intensity illumination and will add to changes which occur when more reactive thin film photocathodes are used such as cesium telluride. Stability was improved to less than 1%/h for 16 h within the region of slow decay following the initial transient by illuminating the emission site on the cathode with high intensity UV light with a high O2 partial pressure. Emission current densities in excess of 6.0 A/cm2 were measured with a Faraday cup. Given these results, this work suggests that higher current densities and stability can be achieved.
Alignment system using voltage contrast images for low-energy electron-beam lithography
Authors: Nakasugi Tetsuro , Ando Atsushi , Sugihara Kazuyoshi , Yamazaki Yuichiro , Miyoshi Motosuke , Okumura Katsuya
Published: July 2002

We have proposed an alignment system for low-energy electron-beam lithography. The proposed alignment system is based on the following unique concepts: (1) an alignment mark is detected using voltage contrast images caused by charging, and (2) to improve the alignment accuracy of global alignment, the alignment accuracy can be inspected before the pattern exposure without any loss of time. In order to verify these concepts, we performed a series of experiments. Using an electron beam of a few keV, we detected a mark buried by thick insulator films; even if direct access to the marks by the primary beam is prevented, the mark detection is possible. Also, we confirmed that the simultaneous observation of exposure patterns and alignment mark is possible using the voltage contrast images caused by charging: the inspection is possible for the exposure status without resist development.
Mark detection in low-energy electron-beam lithography
Authors: Fritz G. S. , Kern D. P.
Published: July 2002

An implementation of the Rau-detector has been investigated with respect to its use for mark detection in low-energy electron-beam lithography. The generation of signals from marks commonly used in electron-beam lithography is discussed. With this detector, images of trenches etched into silicon were obtained with electron energies as low as 1 keV. Signal-to-noise ratio and bandwidth were determined from line scans across sequences of etched trenches. The trench depth has been varied from 40 to 500 nm. The measurements have also been performed with resist coated trenches. It is demonstrated that the Rau-detector is well suited for mark detection in low-energy electron- beam lithography systems. Due to its small size, it leads itself to microcolumn application.
Optimization method of the double exposure technique with alt-PSMs for below a 0.13 μm node
Authors: Kikuchi Koji , Ohnuma Hidetoshi , Kawahira Hiroichi
Published: July 2002

A new method to optimize the structure of alternative phase shifting masks (alt-PSMs) with dual trench type and optical proximity effect correction (OPC) has been developed from the viewpoint of pattern placement error and gate width fluctuation. The pattern placement error and gate width fluctuation have been reduced significantly to meet the requirements of overlay margin and critical dimension (CD) accuracy for the 0.13 μm node devices by this method. The optimum mask structure for reducing a pattern placement error was determined by the simulation that takes account of the mask topography effect. The alt-PSM with a deep trench depth of 570 nm and a phase difference of about 170° between the phase shifted and nonshifted area was optimum to reduce pattern placement error. At the optimum condition, a high contrast was also obtained. For the experiment, we used a set of masks to study dependence of mask cross sectional structure. While the dependence of pattern placement error on focus shift is much larger for the nonoptimized mask, it is small with the mask having the optimized value of our study. With respect to the gate width fluctuation, it can be categorized into three folds. We have developed optimization methods for them, respectively. First one is associated with pattern pitches and shifter lengths. It could be reduced by mask bias OPC of a binary mask. Second one is gate width fluctuation at the end of shifter. Third one is what we call necking shape, which is pattern shrinkage near the end of shifter. For the latter two cases, we have applied OPC of extended shifters with additional patterns. Linewidth fluctuation was reduced by applying these OPC to the pattern.
Nanoscale modification of electronic states of graphite by highly charged Ar-ion irradiation
Authors: Meguro T. , Hida A. , Suzuki M. , Koguchi Y. , Takai H. , Yamamoto Y. , Maeda K. , Aoyagi Y.
Published: July 2002

This article describes a new nanomodification technique of electronic states. This technique involves highly charged ion (HCI) irradiation on the solid surface. The high potential energy of slow HCI, which induces multiple emission of electrons from the surface, provides a strong modification of the electronic states of the local area of surfaces. This unique process, induced by approaching slow HCI, converts metallic highly oriented pyrolytic graphite to a nonconductive structure, indicating the transformation of sp2 graphite to an sp3 nanoscale diamond-like structure.
Subresolution placement using infrared image alignment to the computer-aided design database for backside probing and editing
Authors: Sengupta M. , Sinha M. , Dajee G. , Tsao C. C.
Published: July 2002

As more integrated circuits are packaged in controlled collapse chip connection format, internal debug tools need to image devices through their silicon packaging. Infrared (IR) optical systems make through-silicon imaging possible, but navigation becomes challenging because IR resolution is often lower than positioning accuracy required for design debug. We perform subresolution image alignment between computer-aided design (CAD) and IR images to obtain the required placement accuracy. Our goal is to automate and improve CAD-based IR navigation for silicon-side probing and editing. Using our alignment algorithm, which combines equalization, oversampling, and cross correlation, we demonstrate the ability to achieve 0.1 μm placement accuracy with a 1 μm resolution optical system.
Study of reverse annealing behaviors of p+/n ultrashallow junction formed using solid phase epitaxial annealing
Authors: Jin Jian-Yue , Liu Jinning , Jeong Ukyo , Mehta Sandeep , Jones Kevin
Published: July 2002

Solid phase epitaxial (SPE) annealing at low temperature has the advantage of high dopant activation and very little dopant diffusion. However, due to the low thermal budget engaged in SPE, a large amount of defects can exist in the area beyond the original interface of the crystal and the pre-amorphized layer. These defects may cause severe junction leakage. They may also cause dopant diffusion and deactivation in a following higher temperature process. This work studies the reverse annealing behaviors during a second annealing step for SPE-formed p+/n junction using either 1 keV B+ or 5 keV BF2+ implants. Four-point probe, secondary-ion-mass spectroscopy, and transmission electron microscopy are used in this study. The results show that the boron deactivation after second-step annealing is not only correlated with the transmission electron diffraction (TED), but also correlated with the end of range defect evolution. The results also show that BF2 implanted wafer has slower boron deactivation, less TED and slower defect evolution than the B implanted wafer. In addition, the BF2 implanted wafer shows a much slower SPE regrowth rate at 550 °C than the B implanted wafer.
Heavy ion projection beam system for material modification at high ion energy
Authors: Weidenmüller U. , Meijer J. , Stephan A. , Bukow H. H. , Sossna E. , Volland B. , Rangelow I. W.
Published: July 2002

Ion projection techniques have shown promising prospects to applications in direct high energy, high dose, and high quality material modification. The major advantages are a parallel processing for short implantation times and a mask separated from the target, which allows for implantation with high resolution and high quality even under extreme conditions. A system for high beam power has been developed. The key issues of our high energy ion projection system are the single solenoid lens with low imaging aberrations and the stencil mask which has to provide the necessary high resolution features and to withstand a beam power up to 100 W/cm2. A high aspect ratio stencil mask is used for this purpose. The system has a demagnification factor of 16–22 and showed a resolution of 300 nm so far which is close to the physical limit for MeV ions from lateral straggling in the target. The setup, the mask, and some applications are presented.
Investigation of temperature coefficient of resistance and crystallization of semiconducting YBaCuO thin films using pulsed laser annealing
Authors: Yildiz A. , Çelik-Butler Z. , Butler D. P. , Kim Choong-Un
Published: July 2002

We explored the electrical and dielectric properties of yttrium barium copper oxide (YBa2Cu3O6+x) with different oxygen content. The aim was to perform a study of the annealing conditions using a pulsed laser annealing (PLA) system to obtain optimum temperature coefficient of resistance (TCR) for bolometric structures and low loss tangent for pyroelectric structures without causing a thermal damage to the underlying layers. Oxygen content of samples was changed by annealing with an excimer laser (λ=248 nm) at different power levels and pulse number under high vacuum. X-ray diffraction patterns of these samples were taken to examine the level of crystallization. We observed different crystallization levels for different annealed samples. For bolometric samples, semiconducting YBaCuO thin films were deposited by rf sputtering at room temperature on oxidized Si wafers. The films were amorphous to polycrystalline as deposited. PLA was performed on the samples at varying number of pulses from 100 to 300 at two power levels of 20 and 25 mJ/cm2. The purpose was to decrease the oxygen content of the samples, thus making them more resistive with higher TCR, while simultaneously increasing the long range atomic order and hence crystallinity. For dielectric properties, the samples were fabricated following the model of a capacitor. 2000 Å YBaCuO was sandwiched between two 3000 Å Nb electrodes with an effective area 7.35×10−4 cm2 in contact with the substrate. The annealing was done with 50 pulses at power levels of 25 and 40 mJ/cm2. Our aim was to achieve a small loss tangent through PLA, thus decreasing the amount of power dissipated in the capacitor for pyroelectric detection applications. Capacitance and resistance measurements were done at different temperatures to calculate the loss tangent.
Photocapacitance of deep levels in GaP crystals surface treated by reactive ion etching
Authors: Hashimoto Hideo , Saito Takao , Suto Ken , Nishizawa Jun-ichi
Published: July 2002

Damaged layers of GaP crystals surface treated by reactive ion etching using PCl3 gas are evaluated by capacitance–voltage, secondary ion mass spectroscopy, and photocapacitance (PHCAP) measurements. The reduction of the carrier concentration is observed at the surface region within the depth of 60–70 nm, where Cl atoms injected with high energy are observed. PHCAP measurement reveals that density of the deep levels increases with decreasing gas pressure. The deep levels are thought to be the complexes of shallow donor impurities and intrinsic point defects.
Ab initio molecular orbital characterization of dimethyl group-III azides as sources for photolytic production of free radical beams
Authors: Hayashi Keiji , Kanayama Takuo , Shimizu Toyohiro , Kawamura Yasunori , Kameko Kenji , Kawakita Seiji
Published: July 2002

Use of a beam of biradicaloid such as dialkyl group-III nitrene produced by the method of photodissociation of energetic compound beams (PDECB) is expected to be advantageous to the low-temperature thin-film growth of stoichiometric group-III nitride. Through the clarification of fundamental processes involved in pyrolysis as well as photolysis of dimethylgallium azide [(CH3)2GaN3], dimethylaluminum azide [(CH3)2AlN3], and dimethylboron azide [(CH3)2BN3] based on post-self-consistent field ab initio molecular orbital methods, we discuss the suitability of these possible source compounds for the production of beams of dimethylgalliumnitrene [(CH3)2GaN], dimethylaluminumnitrene [(CH3)2AlN], and dimethylboronnitrene [(CH3)2BN] by the PDECB method. The theoretical results suggested that (CH3)2GaN3 is a promising PDECB source material in that this molecule possesses the nature of unimolecular metastable dye.
Quantitative voltage measurement of high-frequency internal integrated circuit signals by scanning probe microscopy
Authors: Weng Z. , Falkingham C. J. , Bridges G. E. , Thomson D. J.
Published: July 2002

This article describes a scanning probe microscopy technique for quantitative high-speed voltage wave form measurement inside an operating integrated circuit. Internal signals are determined by sensing the local electrostatic force on a noncontacting micromachined probe cantilever that is closely positioned above the circuit test point. Amplitude modulation based downconversion is employed to measure repetitive high-frequency signals which can have a bandwidth much greater than the mechanical response of the probe. A force-nulling technique is used to obtain accurate absolute voltages without the need for complex calibration or precise probe positioning, and enables direct measurement of passivated circuits. A method of eliminating dc offset errors, such as that due to material work function differences, is described. Measurement of signals on the passivated interconnects of a wideband distributed amplifier is presented. The instrument demonstrates a voltage accuracy of <30 mV over a dynamic range of 2.5 V.
Nondestructive, in-line characterization of device performance parameters of shallow junction processes
Authors: Kluth G. Jonathan , En William G. , Borden P. , Bechtler L. , Nijmeijer R.
Published: July 2002

Deep submicron transistor source–drain structures require a challenging combination of ultrashallow depth and low series resistance. Because these factors affect off-state leakage, drive current, and threshold voltage, it is important to maintain tight control of junction depth and depth uniformity over the full wafer diameter. A method for nondestructive, small area, high throughput characterization of ultrashallow junctions, called Carrier Illumination™ (CI) has recently been developed. It offers the potential for in-line monitoring of critical parameters associated with shallow junction processes. The CI method measures the active doping depth of shallow implants such as source/drain extensions on product wafers. Recent results demonstrate the ability of CI measurements to indicate junction depth variation due to implant dose, energy, and annealing temperature and time. This article presents correlation of in-line CI junction depth measurements to end-of-the line electrical properties of n metal–oxide–semiconductor (MOS) and pMOS transistors and test structures. This indicates that it is possible to maintain process control of the effective channel length and threshold voltage at front-end process steps, well before electrical probing is possible.
High-temperature gas sensor using perovskite thin films on a suspended microheater
Authors: Grudin O. , Marinescu R. , Landsberger L. M. , Kahrizi M. , Frolov G. , Cheeke J. D. N. , Chehab S. , Post M. , Tunney J. , Du X. , Yang D. , Segall D.
Published: July 2002

Suspended microstructures consisting of a thin oxide/nitride diaphragm with embedded polysilicon heaters were designed and fabricated using a standard complementary metal–oxide–semiconductor process and simple postprocessing. Thin films of gas sensitive materials based on the SrFeO2.5+x nonstoichiometric perovskite family were deposited onto the diaphragms by room-temperature pulsed excimer laser deposition. Successful chemical sensor functionality was demonstrated. With applied power up to 30 mW, estimated temperatures of the gas sensor film up to 900 °C were reached. When the device was exposed to volatile organic compounds (VOCs) such as acetone and methanol, a reversible ten to 100-fold increase in sensor film resistance was observed, with response times from less than 1 s to a few minutes. Sensor response sensitivity depended on applied power and on the nature of the VOC analyte. This sensor device has the potential for use in multiarray configurations such as in an electronic nose.
Atomic force microscopy study of the early stages of Sn phase separation on Si(111) surfaces
Authors: Hu Qin , Zinke-Allmang Martin
Published: July 2002

Sn clustering on Si(111) samples was studied during deposition at 100 °C and after an additional postdeposition anneal at 200 °C for 5 min. These conditions lead to early stage morphologies for the surface phase separation process of the thin film. We focus in this atomic force microscopy study on (i) the evolution of the partial ordering in the nearest-neighbor distance distributions observed in the late stage of phase separation and (ii) on the role of well-defined substrate defects on the development of the early stage morphology.
Characterization of High Dose Mn, Fe, and Ni implantation into p-GaN
Authors: Pearton S. J. , Overberg M. E. , Thaler G. , Abernathy C. R. , Theodoropoulou N. , Hebard A. F. , Chu S. N. G. , Wilson R. G. , Zavada J. M. , Polyakov A. Y. , Osinsky A. V. , Norris P. E. , Chow P. P. , Wowchack A. M. , Van Hove J. M. , Park Y. D.
Published: July 2002

The magnetization of p-GaN or p-AlGaN/GaN superlattices was measured after implantation with high doses (3–5×1016 cm−2) of Mn, Fe, or Ni and subsequent annealing at 700–1000 °C. The samples showed ferromagnetic contributions below temperatures ranging from 190–250 K for Mn to 45–185 K for Ni and 80–250 K for Fe. The use of superlattices to enhance the hole concentration did not produce any change in ferromagnetic ordering temperature. No secondary phase formation was observed by x-ray diffraction, transmission electron microscopy, or selected area diffraction pattern analysis for the doses we employed.
Morphological evolution and surface and interface structure of aluminum on polyimide
Authors: Lin Xue-Feng , Grove David A. , Wei Lun-Cun , Strossman Greg S. , Lefever-Button Glenn , Kingsley Jeffrey R.
Published: July 2002

Al growth and nucleation on polyimide and the resultant surface morphologies and interfacial structures have been investigated by atomic force microscopy, focused ion beam scanning electron microscopy, Rutherford backscattering spectroscopy, and x-ray photoelectron spectroscopy. Al growth on polyimide proceeds in a two-dimensional-like mode. Initial Al deposition results in the formation of nanoparticles, exhibiting the interface structures arising from the Al interacting with the carbonyl groups of the polyimide. Subsequent Al growth produces a landscape of crystallized islands, and these islands have submicrometer dimensions with different orientations.
Molecular-beam epitaxy growth and properties of BexZn1−xTe alloys for optoelectronic devices
Authors: Maksimov O. , Muñoz Martin , Tamargo M. C. , Lau J. , Neumark G. F.
Published: July 2002

We report the molecular-beam epitaxy growth and characterization of BexZn1−xTe epitaxial layers on (100) InP substrates. BexZn1−xTe layers with x varying from 0 to 0.58 were grown. Good control of the composition is achieved by adjusting either the Be or the Zn cell temperatures. The layers exhibit high-crystalline quality, as established by double crystal x-ray diffraction and etch pit density measurements. Narrow x-ray rocking curves with a linewidth of 72 arcsec and etch pit density of 5×105 cm−2 are obtained for the BexZn1−xTe layers closely lattice matched to the InP substrate. BexZn1−xTe layers under tensile strain, which have higher BeTe content, exhibit slower degradation of the crystalline quality as a function of lattice mismatch than layers under compressive strain. The lattice-hardening properties of BeTe are proposed to be the reason for this behavior.
Single-crystal GaN/Gd2O3/GaN heterostructure
Authors: Hong M. , Kwo J. , Chu S. N. G. , Mannaerts J. P. , Kortan A. R. , Ng H. M. , Cho A. Y. , Anselm K. A. , Lee C. M. , Chyi J. I.
Published: July 2002

Heteroepitaxy of single-crystal Gd2O3 on GaN (with a wurtzite hexagonal close-packed (hcp) structure) and single-crystal GaN on Gd2O3 was achieved. In situ reflection high-energy electron diffraction reveals a sixfold symmetry in the in-plane epitaxy of the rare earth oxide on GaN and also in the overgrowth of GaN on the oxide. Single-crystal x-ray diffraction measurements find that these single-crystal oxide films are indeed the high temperature hexagonal phases of the sesquioxides, stabilized by the GaN substrate epitaxy. Despite a large mismatch in the lattice constant, the fully relaxed oxide films are of excellent structural quality. The x-ray diffraction results revealed that the GaN grown on the rare earth oxide is a single-crystal and has the same crystallographic hcp structure as the underlying GaN. The structures of both layers of GaN were also studied by cross section transmission electron microscopy.
Design of multiplexer in amorphous silicon technology
Authors: Mohan N. , Karim K. S. , Nathan A.
Published: July 2002

The large area capability of amorphous silicon technology finds many active matrix displays and imaging arrays employing the a-Si:H thin film transistors (TFTs) as analog switches. The TFTs are limited to simple switching applications due to the low driving current and metastability issues inherent to a-Si:H technology. The most apparent metastability issue in an a-Si:H TFT is threshold voltage (Vt) shift due to prolonged gate bias. The Vt shift is more pronounced for positive gate biases than for negative gate biases. Moreover, in the presence of a pulse gate bias, the Vt shift depends on the frequency of operation. Considering the large number of gate and data lines in displays and imaging arrays, multiplexer circuits can provide benefits such as reducing the pin count of the array, reducing the number of external chips and hence, overall system cost. In amorphous silicon technology, Pass transistor logic (PTL)-based multiplexers (MUXes) are attractive since they can be designed to have manageable Vt shifts and less transistors than logic gates based MUXes. In this article, we present Vt shift measurements on in-house fabricated a-Si:H TFTs under relevant bias conditions and analyze the performance of a PTL-based MUX circuit in a-Si:H technology.
2.4 GHz voltage control oscillator and power amplifier monolithic microwave integrated circuits based on 0.25 μm complementary metal–oxide–semiconductor technologies
Authors: Hsiao Chao-Chih , Kuo Chin-Wei , Ho Chien-Chih , Chan Yi-Jen
Published: July 2002

In this article, a 0.25 μm monolithic complementary metal–oxide–semiconductor (CMOS) 2.4 GHz voltage-controlled oscillator has been demonstrated to have a tuning efficiency of 390 MHz/V, a phase noise of −94 dBc/Hz at a 100 kHz offset, and an output power of −3.76 dBm. In addition, a one-stage CMOS microwave power amplifier has also been presented. The transducer gain (S21) is 15.3 dB at 2.4 GHz, and the return loss (S11) is greater than 15 dB. This power amplifier could deliver a 16.2 dBm output power, a 15 dB power gain, and a 27% power-added efficiency.
Thermal stability of SiO2/CoSi2/polysilicon multilayer structures improved by cavity formation
Authors: Alberti A. , La Via F. , Ravesi S.
Published: July 2002

The electrical and structural stabilities of SiO2/CoSi2/polysilicon multilayer structures have been improved by 75 °C using 40 keV nitrogen atoms implanted in silicon before silicidation at a dose of 5×1015/cm2. During the reaction process, small cavities have been created within the polysilicon layer and simultaneously pushed ahead by the poly/amorphous silicon interface created by the implant and moving toward the surface. The process has ended up with a band of big cavities located at the silicide/silicon interface. They have an average diameter of 35 nm and are preferentially located at the silicide grain boundaries. Sheet resistance measurements (Rs), Rutherford backscattering spectroscopy and transmission electron microscopy analyses have shown that these interfacial cavities have prevented the agglomeration process to occur up to 1025 °C 30 s annealing process and have reduced the driving force for silicide boundary grooving.
Fabrication of micrometer and nanometer scale structures in silica sol-gel films using electron beam writing methods
Authors: Visovsky Nick J. , Ukrainczyk Ljerka , Dawes Steven B.
Published: July 2002

We have discovered and developed a process where positive relief structures in silica sol-gel films can be made using electron beam writing methods. Electron beam cured sol-gel structures have been made that have lateral and vertical dimensions both on the micron and nanometer scales. The sol-gel structures can be used as etch masks or deposition masks on substrates or can be used directly as positive relief molds for embossing the micro- or nanoscale features into other materials.
Freestanding microheaters in Si with high aspect ratio microstructures
Authors: Tian W.-C. , Pang S. W.
Published: July 2002

Freestanding, high aspect ratio microstructures in Si were micromachined as thick microheaters. These microheaters, combined with adsorbents, can be used as preconcentrators in a micromachined gas chromatography system. Dry etching of Si using etch and passivation cycles has been developed to produce 240 μm thick Si microheaters with 3 μm wide wires, achieving a high aspect ratio of 80:1. This optimized dry etching technology results in high etch rates with vertical profiles for thick Si microheaters up to 535 μm. Microheaters with 40 μm wide wires, 110 μm gaps, 400 μm thick, and an area of 9 mm2 have been fabricated. With the heater on a 140 μm thick Si membrane, it takes 1320 mW to increase the temperature by 290 °C. The power consumption is reduced to 447 mW for the same temperature raise with a freestanding Si microheater. Heating response for freestanding Si microheaters with different thicknesses is also studied. These Si microheaters have fast response times and reach 75% of the final temperature in 5 s. Microheaters consisting of Si wires and posts show similar response time and heating uniformity. In addition, power consumption is reduced by thermal isolation of the microheaters. These thick, freestanding high aspect ratio Si microheaters can provide high power efficiency, large adsorbent capacity, and high mechanical strength.
Growth and evolution of ZnCdSe quantum dots
Authors: Shan C. X. , Fan X. W. , Zhang J. Y. , Zhang Z. Z. , Li B. S. , Lu Y. M. , Liu Y. C. , Shen D. Z. , Kong X. G. , Wang X. H.
Published: July 2002

ZnCdSe quantum dots (QDs) were fabricated successfully under Stranski–Krastanow mode by metalorganic chemical vapor deposition. Prior to growth, the critical thickness was first calculated in terms of strain relaxation and the growth was then performed with the help of the calculation. The evolution of the QDs was also studied by atomic force microscopy and spectroscopy. Two kinds of variations in the QDs appeared over time, the Ostwald ripening process and dot-formation process. Moreover, the shape of the dots changed from pyramidlike to domelike, with the transition explained by the theory of crystal growth. By analyzing photoluminescence spectra, two emission mechanisms were revealed and were thought to be zero-dimensional (0D) and 2D-like excitons. With increasing growth interruptions, the luminescence intensity ratio of the 0D to 2D-like excitons increased, which gave further evidence of the evolution of QDs.
Performance of a New Electrostatic Getter-Ion Pump
Authors: Denison D. R.
Published: July 2002

Performance characteristics of a multicelled, electrostatic, triode, getter-ion pump are described, with data on pumping speeds vs pressure for Ar, N2, O2, and H2, starting characteristics, pressure measurement, ultimate pressure, residual gas composition, and operating life. A 6-in.-diam orifice pump has a baffled N2 pumping speed of over 1700 liter/sec below 5 × 10−7 Torr and pumps argon at 25 liter/sec. Pumping speeds higher than those predicted by the titanium sublimation rate are observed for N2, O2, and H2 at pressures above 10−6 Torr. At 10−3 Torr, the N2 speed is higher by a factor of 38. For N2 and O2, the higher than expected pumping speed is attributed to direct interaction of the gas with the sublimator, which operates at a temperature at which the interaction rate is maximal.
High-Stability Controller for Bayard-Alpert Ionization Gauges
Authors: Spencer C. M. , Stäheli D.
Published: July 2002

A controller, for Bayard-Alpert gauges, which regulates the grid current to better than 0.01%, using readily obtainable components, is described. Grid current ranges from 8 μA to 80 μA have been used successfully at pressures below 10−6 Torr.
Destructive Breakdown in Thin Films of SiO, MgF2, CaF2, CeF3, CeO2 and Teflon
Authors: Budenstein Paul P. , Hayes Paul J. , Smith J. Lynn , Smith Wallace B.
Published: July 2002

Prebreakdown and breakdown electrical properties, and also the light emitted during destructive breakdown, have been studied in thin-film capacitors with the dielectrics SiO, MgF2, CaF2, CeF3, CeO2, and Teflon. Capacitors were formed on glass substrates and had dielectric thicknesses from 900 to 16000 Å. At temperatures between 80 and 380 K, breakdown characteristics are found to be independent of prebreakdown ac and dc conduction. All of the materials studied show a threshold field for the onset of breakdown (on the order of 106 V/cm) that is almost temperature independent and varies with dielectric thickness w approximately as w−1/2. All materials also have a threshold voltage for the cessation of breakdown which is typically between 10 and 20 V. The light emitted during breakdown contains the arc spectra of the dielectric and the two electrodes. Intensity of single wavelengths of light were recorded simultaneously with voltage waveforms and show that all lines are emitted from the very beginning of breakdown conduction. Hence, breakdown conduction is due to the formation of a gaseous arc. This arc, formed in less than 10−8 sec, carries the high current characteristic of breakdown and causes destruction of the dielectric.
Aberrations and tolerances in a double-deflection electron-beam scanning system
Authors: Thomson M. G. R.
Published: July 2002

A magnetic deflection system intended for use in an electron-beam lithography instrument has been analyzed. The electron beam is to be scanned over a 0.3-mm-square field at a working distance of 15 mm and with a final lens convergence semiangle of 0.013 rad. The maximum allowed spot broadening is 0.05% of the side of the square (i.e., 0.15 μm) and the maximum distortion is half of this (0.075 μm). A system is proposed with a performance which substantially exceeds these requirements so some of the excess can be sacrificed in exchange for a larger tolerance of construction and alignment errors. Dynamic correction methods are not necessary. The system is constrained (by the dimensions of a final lens that had already been chosen) to fit within a cylinder 30 mm in diameter and 100 mm long. No magnetic material is used for the core of the deflection coils. A double-deflection system was analyzed theoretically and the geometric and chromatic aberrations were calculated. The azimuthal positions of the conductors that are parallel to the electron-beam axis are critical. To obtain best performance, the angles must be correct to within a degree, but to meet the above requirements an error up to 8° can be tolerated. The tolerance of off-axis misalignment of the whole scanning system was estimated. For best performance the misalignment must not exceed ±0.25 mm, but in this application distances of up to ±2 mm can be tolerated. In the absence of errors, the system can scan over 1/30 rad (0.5 mm) square.
Flatness, contrast, and resolution considerations of cathode projection microfabrication systems
Authors: Wardly G. A.
Published: July 2002

’’Universal’’ edge-resolution curves have been calculated for cathode-projection microfabrication systems (CPS). The results show that submicron lithographic resolution requires photoemission energy spreads less than 100 ppm. This favors cesium iodide photocathodes which have up to a 0.5-V energy spread. Exposure contrast in the CPS is made worse by a broad flood of reimpacting backscatter electrons. Furthermore, submicron edge-resolution and registration capabilities of the CPS are made tenuous without a chucking device to hold the anode workpiece repeatably flat to about ±1 μm. Without flattening, performance can be impaired by image distortion and thermal effects.
Facepiece−to−face leakage evaluation using a helium leak detection method
Authors: Cyr Rob Roy , Watkins Dudley W.
Published: July 2002

Assurance of a proper fit and thus maximum respiratory protection to the user of respiratory protective devices is the subject of increasing emphasis by the government under the Occupational Safety and Health Act. The primary method of assessing protection is to measure the amount of leakage from a challenge atmosphere surrounding a test subject into the breathing zone inside the respiratory protective device being worn. Methods currently in use are either largely subjective, present some hazard to the test subject, or are subject to unpredictable errors. This paper presents a simple method of using physiologically inert helium as a diluant in a respirable mixture of air, and then detecting the amount of helium leaking into the respirator facepiece with a mass spectrometer helium leak detector equipped with a special sampling and calibration system. Data obtained indicate a capability of repeatability assessing leakage rates as low as one standard cubic centimeter per minute, translating roughly into determining protection factors of better than 10000 for full facepiece respirators. Shortcomings of the available equipment and suggestions for improving the accuracy and rapidity of data collection are discussed.
Outgassing coefficient development for improved leaktightness sensitivity in vacuum drift testing
Authors: Schalla Clarence A.
Published: July 2002

The parameters of vacuum outgassing are developed into variable gang coefficients adaptable to all materials, shapes, and conditions. Programmable equations and cascading charts for design and test use are presented. Outgassing data is introduced for rigid foams, honeycomb, and braided cable evacuation and is synthesized into area/volume effect factors applicable to any material. Coefficients for predicting bulk outgassing are shown to provide a rapid and optimized method for improving the leaktightness sensitivity of drift testing so much so as to be used in lieu of leak checking by mass spectrometer. Detectable inleakage rates for the vacuum pressure−rise (drift) method of determining leaktightness are defined for test articles of small volume to large space simulation chambers and underground nuclear effects testbeds. Offered as a test aid adjunct are nomograms developed for direct determination of true pressures from comparative readings of thermocouple and radiation type ionization gauges which are air calibrated but subjected to unknown concentrations of water vapor or helium.
Abstract: Occluder film process monitoring by residual gas analysis
Authors: Provo J. L.
Published: July 2002

In this study, a high−sensitivity residual gas analyzer monitors vacuum system leaks and total environmental conditions prior to, during, and after the deposition and hydriding of erbium occluder films. With the capability of detecting leaks below 1×10−10 STD cm2/sec, the analyzer aids in the identification and detection of gases for improved deposition and hydriding.
A pneumatic logic interface for valve throttling
Authors: Hugenberger Charles E.
Published: July 2002

The control advantages of manual throttling valves can be achieved with air−operated valves without any sacrifice to the inherent advantages of pneumatic control. The interface circuit is placed between system controls and the valve, and requires no modifications to existing equipment, other than the rerouting of air lines and power input to the solenoid valve. All systems controls, whether manual or automatic, remain fully functional. The use of this logic interface permits precise valve positioning resulting in pressure and throughout control necessary for sputtering and other applications.
Abstract: Characterization of multilayer thin films using secondary ion mass spectrometry and improvement of the analytical techniques
Authors: Lewis R. K.
Published: July 2002

Secondary ion mass spectrometry (SIMS) has been shown to be a highly sensitive analytical technique for characterizing thin films. 1 In depth analysis results because of the inherent nature of the sputtering process. With the more sophisticated SIMS instruments an imaging mode is provided which also gives a spatial distribution analysis. When this spatial information is combined with depth analysis a truly three−dimensional characterization results. It has been shown that this combined analysis can prevent confusing variations in spatial distribution with uniform depth gradients in depth profile analysis.

The most important advantage the SIMS technique has over other analytical techniques with good depth profiling capability (e.g.: Auger electron spectroscopy, AES) is that a much higher sensitivity can be achieved with SIMS. In favorable cases where the ion yield is high and large areas (diam ≳ 50 μ) are available this sensitivity has been shown to be 104 to 105 times higher than any other analytical techniques applicable to depth profiling.

The depth profiles described in this paper have been obtained with a specific SIMS instrument. This is the direct imaging mass analyzer developed by Cameca following the original concepts of Slodzian and Castaing. 2,3 This instrument has been shown to be well suited to the depth profile analysis of multilayer thin films. The principal advantages and disadvantages of the SIMS technique are the following: Advantages: (1) A very high gram detection sensitivity (10−15−10−19 g) can be achieved. (2) Rapid depth profiling is possible (up to 500 Å/sec). (3) All elements can be detected (inert gases excepted). (4) A very high detection sensitivity occurs for the very light elements. (5) Surface into bulk analysis can be performed in the same experiment. Disadvantages: (1) Many polyatomic cluster ions are generated by the sputtering process which produce serious mass interferences, particularly at higher masses. (2) Secondary ion yield enhancement effects from the presence of reactive elements seriously interfere with quantitation. (3) Sputtering artifacts can limit depth resolution. (4) The destructive nature of sputtering limits certain types of analysis.

These points are illustrated in the study of a series of multilayer thin films which have undergone various heat treatments producing interdiffusion. The principle limitation of SIMS depth profiling (item 1 above) is mass interference. This problem is considerably minimized when high mass resolution (m/Δm≳3000) is available. Recently an electrostatic analyzer has been integrated into the Cameca IMS 300 design which converts the geometry into a Neir Johnson type configuration. 4 This design allows a mass resolution up to 5000 to be achieved which greatly increases the applicability of the instrument for depth profiling and other microanalytical applications.
Metal–semiconductor cathode structures with enhanced injection efficiency
Authors: Moutou P. C. , Godart J. J. , Montel J.
Published: July 2002

We have shown in a previous paper that the Ni–Ge–Au alloyed contact to GaAs had microprecipitates and current-limiting properties. Here we prove that such contacts have low contact resistance at low bias levels. We describe a structure consisting of an array of Au Schottky diodes of small diameter (1– 6μm) on 1018 cm−3 GaAs and show that there is greatly enhanced injection, much more than a size effect would explain. An edge effect is more likely. But both effects would not explain the low resistance of a real contact. We suggest that microprecipitates containing a high proportion of Ge may give a smaller barrier height.