bluuebunny/crossref_metadata_2025 huggingface dataset:
Space-charge effects in projection electron-beam lithography: Results from the SCALPEL proof-of-lithography system
Authors: Liddle J. A. , Blakey M. I. , Bolan K. , Farrow R. C. , Gallatin G. M. , Kasica R. , Katsap V. , Knurek C. S. , Li J. , Mkrtchyan M. , Novembre A. E. , Ocola L. , Orphanos P. A. , Peabody M. L. , Stanton S. T. , Teffeau K. , Waskiewicz W. K. , Munro E.
Published: July 2002

In projection electron-beam systems resolution and throughput are linked through electron–electron interactions collectively referred to as space-charge effects. Hence, a detailed understanding of these effects is essential to optimizing the lithographic performance of a projection electron-beam lithography system. Although many models have been developed to describe one or more of the various aspects of the Coulomb interactions that occur in the beam, there is minimal experimental data available. We have performed a series of experimental measurements in the scattering with angular limitation projection electron-beam lithography (SCALPEL) proof-of-lithography system to characterize the space-charge effects for such an optical configuration. The results of those measurements have been compared to a combination of computer simulations and analytical models. The agreement between the models and experiments was good, within the limits of experimental error. We determined the exponent in the dependence of blur on beam current to be 1.029±0.16 (1σ), consistent with more recent models. Additionally, we comment on the use of blur modeling for system optimization.
Nitrided thermal SiO2 for use as top and bottom gate insulators in self-aligned double gate silicon-on-insulator metal–oxide–semiconductor field effect transistor
Authors: Ahmed Shibly S. , Denton John P. , Neudeck Gerold W.
Published: July 2002

Nitrided thermal oxide was used to reduce the degradation of top and bottom gate insulators of self-aligned double gate metal–oxide–semiconductor field effect transistors that use a form of selective epitaxial growth of silicon (SEG) called tunnel epitaxy. The degradation of thermal oxide was due to the exposure of gate insulator to the epi-growth ambient gases during the epitaxial growth. Both thermal oxide and thermally nitrided oxide samples were exposed to the epi-reactor gases and then the electrical characteristics were measured. Nitrided oxide showed significantly higher breakdown field, lower leakage current, and lower interface states than the thermal oxide after exposure to the selective epi-growth environment. For a 30 min stress in epi-reactor ambient, thermal oxide showed average breakdown fields of less than 1 MV/cm due to the formation of pinholes, while nitrided oxide samples showed average breakdown fields of 15.6 MV/cm for same stress condition. Interface state density (Dit) of nitrided oxide improved after exposure to epitaxial growth ambient. The average Dit reduced from ∼3.5×1010/cm2 eV to ∼1.5×1010/cm2 eV for a 30 min SEG/epitaxial lateral overgrowth stress for nitrided oxides.
Theoretical sputtering yields of Al and Mg targets in physical vapor deposition processes
Authors: Bordes J. M. , Bordes Ch. , Ehret E. , Gschwind R. , Bauer Ph.
Published: July 2002

Calculations of sputtering yields are performed for aluminum and magnesium target materials with the use of a homemade software based on the analytical expression of Garcia-Rosalès. The theoretical yield of magnesium is about twice the value related to aluminum in accordance with the experimental ratio of the Mg/Al deposition rates. We show that the deposits of the same materials must be subjected to densification followed by resputtering phenomena when a bias voltage is set to the substrates. These predictions are confirmed by atomic force microscopy observations, especially for magnesium deposits owing to their texture and the high sputtering yield of this material.
Effects of post-treatment of MgO on the discharge characteristics of an alternating current plasma display panel
Authors: Kim Joong-Kyun , Moon Kyung-Sup , Whang Ki-Woong , Lee Ji-Hwa
Published: July 2002

The decrease in operation voltages, such as firing and sustain voltages, and their instability has been observed frequently and is believed to be typical of the initial operation of an alternating current plasma display panel (ac PDP). To explain this decrease, we investigated the surface morphology, preferred crystal orientation, chemical species, and outgassing impurities of protecting MgO thin films, along with ac PDP manufacturing steps, using scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and a quadrupole mass spectrometer (QMS). Even though no significant changes were observed in the surface morphology, a drastic reduction in carbon impurity, as well as the initial high carbon concentration in the film, was observed. Furthermore, localization of the contaminants in the vicinity of the surface was observed during the heat treatment. With regard to the carbon contaminant, the QMS experiments showed consistent results. In the experiment measuring the secondary electron emission coefficient, the measured value of the MgO film increased and saturated when heated in a vacuum. From these observations, it is thought that the degree of carbon contamination of the MgO surface, along with the secondary electron emission characteristics, is the dominating factor that causes the decrease in the operation voltages and their instability.
Secondary-ion-mass spectrometry and high-resolution x-ray diffraction analyses of GaSb–AlGaSb heterostructures grown by molecular beam epitaxy
Authors: Gerardi C. , Giannini C. , De Caro L. , Tapfer L. , Rouillard Y. , Jenichen B. , Däweritz L. , Ploog K. H.
Published: July 2002

Secondary-ion-mass spectrometry and high-resolution x-ray diffraction are used to investigate AlxGa1−xSb/GaSb heterostructures (0.2<x<1) grown by molecular beam epitaxy. We show that the AlCs+ and GaCs+ intensities, obtained by using caesium cluster secondary-ion-mass spectrometry mode, vary linearly with the relative concentrations, and therefore, allows us to evaluate quantitatively the aluminum and gallium contents in the epitaxial layers. Intermixing of Ga/Al species at the GaSb/AlSb interfaces could be clearly detected by secondary-ion-mass spectrometry and is also confirmed by high-resolution x-ray diffraction. The intermixing is the result of a particular mechanism in order to minimize the strain energy, and occurs prior to the lattice relaxation, which generates structural defects taking place. The analyses also give evidence of a constant arsenic contamination (∼0.5%) both in the GaSb buffer and in the AlxGa1−xSb layers. In fact, As contamination occurs if the molecular beam epitaxy chamber has been used previously for the growth of As-compound materials. We show that the signal obtained by using the caesium cluster secondary-ion-mass spectrometry mode AsCs+ is nearly unaffected by the changes of the Al content throughout the total structure (matrix effects) contrary to what occurs for single As ions.
Electrical properties of molecular beam epitaxially grown AlxGa1−xSbyAs1−y and its application in InP-based high electron mobility transistors
Authors: Cai W. Z. , Moshegov N. T. , Mayer T. S. , Miller D. L.
Published: July 2002

We have investigated the use of lattice-matched AlxGa1−xSbAs quaternary alloys in InP-based microelectronic devices. The band alignment for AlxGa1−xSbAs/InGaAs is calculated across the entire compositional range of x using van de Walle and Martin’s model solid theory, and the theoretical predictions agree with previously published values within 0.1–0.3 eV. Temperature-dependent current–voltage measurements are carried out on Au/Cr/AlxGa1−xSbAs Schottky diodes grown by molecular beam epitaxy. From an Arrhenius analysis, an effective barrier height of 0.67–0.79 eV is obtained, which decreases as the x increases in the range of 0.5⩽x⩽0.9. For the first time, InAlAs/InGaAs high electron mobility transistors are fabricated with an AlxGa1−xSbAs barrier enhancement layer. A reduced gate leakage and delay of gate forward turn-on are attributed to the incorporation of AlxGa1−xSbAs. The effectiveness of AlxGa1−xSbAs is more pronounced for x=0.5 and 0.7 than for x=0.9.
Etch characteristics of CeO2 thin films as a buffer layer for the application of ferroelectric random access memory
Authors: Oh Chang-Seok , Kim Chang-Il , Kwon Kwang-Ho
Published: July 2002

Cerium oxide (CeO2) thin film has been proposed as a buffer layer between the ferroelectric film and the Si substrate in metal–ferroelectric–insulator–silicon structures for ferroelectric random access memory applications. In this study, CeO2 thin films were etched with a Cl2/Ar gas combination in an inductively coupled plasma. The etch properties were measured for different gas mixing ratios of Cl2/(Cl2+Ar) while the other process conditions were fixed at rf power (600 W), dc bias voltage (−200 V), and chamber pressure (15 mTorr). The highest etch rate of the CeO2 thin film was 230 Å/min and the selectivity of CeO2 to YMnO3 was 1.83 at a Cl2/(Cl2+Ar) gas mixing ratio of 0.2. The surface reaction of the etched CeO2 thin films was investigated using x-ray photoelectron spectroscopy (XPS) analysis. There is a Ce–Cl bonding by chemical reaction between Ce and Cl. The results of secondary ion mass spectrometer analysis were compared with the results of XPS analysis and the Ce–Cl bonding was discovered at 176.15 (amu). These results confirm that the Ce atoms of the CeO2 thin films react with chlorine and a compound such as CeCl remains on the surface of the etched CeO2 thin films. These products can be removed by Ar-ion bombardment.
Focusing of low energy electrons by submicrometer patterned structures in low energy electron microscopy
Authors: Kan H.-C. , Phaneuf R. J.
Published: July 2002

We report the observation of focusing of low energy electrons by submicrometer pits patterned onto a silicon crystal surface. Images of an array of pits obtained with a low energy electron microscope consist of an array of bright spots whose diameters depend strongly on the energy of the incident electrons. Our electron-optical simulation shows that each pit acts like an electrostatic lens, focusing the electrons along its optical axis, with a focal position which indeed depends strongly on the incident energy.
Characterization of iodoheptafluoropropane as a dielectric etchant. II. Wafer surface analysis
Authors: Karecki Simon , Chatterjee Ritwik , Pruette Laura , Reif Rafael , Vartanian Victor , Sparks Terry , Lee J. J. , Beu Laurie , Miller Charles
Published: July 2002

This article forms the second part of a three-part series which presents a systematic characterization of iodoheptafluoropropane (C3F7I) based oxide etch processes in an inductively coupled high density plasma etch tool. Parts I and III of the article discuss etch process behavior and effluent composition, respectively. The focus of this article is on the characterization of films deposited by 1-iodoheptafluoropropane (CF2I–CF2–CF3) processes using two techniques: X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. A significant result obtained in this study is that, while iodoheptafluoropropane has a greater tendency to polymerize than its perfluorinated counterpart, C3F8, because of its lower F:C ratio, the C3F7I etch process is driven, in large part, by physical mechanisms stemming from bombardment of the wafer surface by massive iodine ions. The mechanisms discussed in this article provide a consistent explanation that reconciles the highly polymerizing behavior of iodoheptafluoropropane with its relatively low mask and stop layer selectivity, as compared to a C3F8 based process in the same inductively coupled etch tool.
Selective plasma nitridation and contrast reversed etching of silicon
Authors: Sharma Shashank , Sunkara Mahendra K. , Crain Mark M. , Lyuksyutov Sergei F. , Harfenist Steven A. , Walsh Kevin M. , Cohn Robert W.
Published: July 2002

A new method of selectively patterning a silicon substrate with silicon dioxide and silicon nitride is demonstrated. An oxide patterned silicon substrate is directly nitrided using a microwave generated nitrogen plasma. Upon subsequent selective wet chemical etching using KOH, the oxide is removed and etching proceeds into the silicon, revealing a contrast reversed pattern of the oxide. The etch resistance of the nitrided surface is maximized by increasing the microwave power, pressure, and nitridation duration. The etch rate of silicon dioxide is negligibly affected and its etch rate is nearly the same as before nitridation. Compositional analysis of the nitride and the nitrided oxide using x-ray photoelectron spectroscopy confirms that microwave plasma nitridation produces Si–N covalent bonds.
Electron beam writing methods of x-ray masks for eliminating thermal image placement errors
Authors: Kise Koji , Aya Sunao , Yabe Hideki , Ami Shigeto , Marumoto Kenji , Satoh Shin-ichi , Watanabe Hiroshi
Published: July 2002

In this article we describe electron beam writing methods to suppress image placement errors due to the thermal distortion and drift of x-ray masks. Parts of device patterns are written outside of the writing area of a mask before the device pattern writing step to stabilize the temperature of the mask (preparatory writing method). The seesaw writing method, which divides a pattern into many slit parts that are written reciprocally, is used to compensate for the nonuniformity of the heating rate of the mask according to the mask’s position on the stage. The absorber fiducial mark is formed on the mask instead of the cassette or the stage to prevent the drift of the mask, and furthermore, to reduce mask-to-mask overlay errors. The writing is performed by referring to the absorber coordination marks on the mask after the registrations of the marks are measured with an image placement (IP) measurement system (mark-on-the-mask method). The effectiveness of these methods is evaluated through the fabrication of a full-chip mask of a 64 Mbit dynamic random access memory, and an IP accuracy close to 20 nm is obtained.
Focusing field emission arrays constructed by self-aligned photolithography
Authors: Li Dejie , Zhang Jinchi
Published: July 2002

In this article, fabrication and characterization data for a focusing Mo field emission array (FEA) are presented. This FEA is made by a technique of self-aligned photolithography. The final structure is referred to as a double-gate field emission array, with the gates acting as extraction and focusing electrodes. With this technique of self-aligned photolithography, the extraction gate aperture and the focusing gate aperture are both kept absolutely coaxial with their corresponding tips, and the ratio between diameters of the extraction aperture and the focusing aperture is kept controllable. A scanning electron microscope image of the completed microstructure shows the diameter of the extraction aperture to be as small as 1.2 μm, and the ratio of the focusing aperture diameter to that of the extraction aperture to be approximately 2:1.
Enhancement of electron field emission from amorphous carbon films by plasma treatments
Authors: Lee Kuei-Yi , Ryu Jeong-Tak , Fujimoto Keiichi , Honda Shin-ichi , Katayama Mitsuhiro , Hirao Takashi , Oura Kenjiro
Published: July 2002

The electron field emission properties of amorphous carbon (a-C) films deposited using a rf magnetron sputtering system have been improved by introducing a simple method of argon and nitrogen plasma treatments at room temperature. Surface morphologies of the a-C films were investigated by scanning electron microscopy, and the nitrogen contents were measured by x-ray photoelectron spectroscopy (XPS). XPS study revealed that nitrogen was incorporated into a-C films of the samples treated with nitrogen plasma. A maximum nitrogen content of 7.7 at. % was achieved with a 45 min plasma treatment. The emission properties improved with the plasma treatment in both argon and nitrogen plasma.
Experimental conditions for a highly ordered monolayer of gold nanoparticles fabricated by the Langmuir–Blodgett method
Authors: Huang Shujuan , Tsutsui Gen , Sakaue Hiroyuki , Shingubara Shoso , Takahagi Takayuki
Published: July 2002

A highly ordered monolayer film of alkanethiol-encapsulated gold nanoparticles was fabricated on a silicon substrate by using the Langmuir–Blodgett (LB) method. The effects on the particle order, of the particle concentration and the type of solvent of the LB spreading suspension of encapsulated gold particles, were studied. We found that a low particle concentration of 0.06–0.3 mg/mL in chloroform is optimal for the fabrication of high quality gold particle monolayers. Since the proposed method is not restricted to gold particles, it is believed to be a practical process for fabricating quantum dot structures of various particle sizes and compositions.
In situ submicron patterning with silicon nitride evaporation masks
Authors: Purbach U. , de Lozanne A.
Published: July 2002

We describe a technique for ultra-high-vacuum compatible deposition of structures on flat substrates. This technique allows one to form micrometer and even submicron-sized structures on a flat surface with minimal contamination. It also has the advantage of producing a smooth edge profile similar to those achieved using a two-layered resist.
Lithographically induced self-assembly of microstructures with a liquid-filled gap between the mask and polymer surface
Authors: Deshpande Paru , Chou Stephen Y.
Published: July 2002

We have observed that a featureless polymer thin film on a flat plate that is separated from another flat plate by a liquid filled gap can self-assemble into a periodic micropillar array. Moreover, we have observed that if there is a pattern on one of the plates, the boundary of the pillar array will align with the boundary of the pattern resulting in single domain arrays. The phenomenon is believed to be due to the unstable growth of surface waves in the polymer system caused by an attractive Coulombic interaction between the top plate and polymer. A transition temperature has been found below which ordered patterns are not observed in the bilayer system. This self-assembled phenomenon suggests a novel way of controlling flow in microfluidic devices.
Investigation of fluorine in dry ultrathin silicon oxides
Authors: Vereecke G. , Röhr E. , Carter R. J. , Conard T. , De Witte H. , Heyns M. M.
Published: July 2002

The origins of fluorine in dry ultrathin silicon oxides (<1 nm) were investigated as the incorporation of fluorine in these layers may improve their reliability and interface quality. Oxides were grown at room temperature (RT) by UV/O2 in an integrated tool combining vapor HF surface preparation and oxide growth in a single chamber. The chemical composition and thickness of the layers were characterized by x-ray photoelectron spectroscopy. It is shown that incorporation of fluorine in these oxides originated mainly from the contamination of the tool (dead spaces and surface adsorption) and from the fluorine left at the wafer surface by the in situ HF process. The levels of these sources of fluorine were about two orders of magnitude higher than from a wet HF dip. No evidence was found for the existence of subsurface fluorine [Kasi et al., Appl. Phys. Lett. 58, 2975 (1991)] as oxides grown in a separate noncontaminated cell (UV/O2, 1 atm O2, RT to 200 °C) did not show any significant increase in fluorine content as a function of oxide thickness. Hence the amount of fluorine incorporated into oxides grown in cluster tools under similar conditions will depend not only on the method selected for surface preparation but also on whether surface preparation and oxidation are performed in the same chamber or not. The possible benefits of determined fluorine levels are discussed.
Global pattern density effects on aluminum alloy etching for sub-0.25 μm technology logic devices
Authors: Baek Kye Hyun , Kim Kil Ho , Hwang Chung Ho , Lee Dae Hoon
Published: July 2002

Global pattern density effects on aluminum alloy etching were quantitatively analyzed for sub-0.25 μm technology logic devices. We found that etching the metal layer with one pattern density while applying the plasma activation parameters optimized for the other pattern density often results in inferior performance, even if the minimum design rules of both layers are the same. Additional studies show that the aluminum etch rate has an almost linear relationship to the pattern density of the etched metal layer when all the activation parameters are fixed. This evokes the necessity that the plasma activation parameters be optimized properly with the pattern density of each metal layer as well as with the minimum design rule. We speculate that these pattern density effects are caused by the variation of etching environment that is solely determined by effective etchants density and their effective residence time. Thus it may be possible to alleviate the global pattern density effects by controlling the plasma activation parameters in such a way that these two effective values are independent of the pattern density. Based on the aforementioned speculation we controlled total pressure and feed gas flow rate and were able to achieve stable etching performance independent of the global pattern density.
Ion-assisted etching of W film by an Ar+ beam in XeF2 with the addition of H2, N2, or O2
Authors: Ichinose Hideo
Published: July 2002

W etching is carried out by an Ar+ beam in XeF2 with the addition of H2, N2 or O2. The energy of the beam is 400 eV and the current is 0.2 μA. The spontaneous etching rate in XeF2 with the addition of N2 or O2 decreases by about 0.6 times compared with that in XeF2 (2×10−6 Torr), for which the total pressure of the mixed gas is 2×10−5 Torr. The nitrogen or oxygen atoms attached on the W surface disturb the attachment between W and fluoride atoms. The ion-assisted etching rate increases by about 1.5 times in XeF2 by adding N2 or O2 compared with that in XeF2 (2×10−6 Torr), for which the total pressure of the mixed gas is 2×10−5 Torr. It is speculated that the addition of N2 or O2 gas to fluorinated gas acts upon the surface reaction to suppress the sidewall etching rate when the mask patterned W gate line is plasma etched by the same kind of gas mixture. The mixing layer is thought to be formed by W and nitrogen or by an oxygen atom by ion-assisted etching. The W–W bond in the mixing layer is thought to be weaker than that in W film both physically and chemically, which makes the etching increase. The thickness of the mixing layer is estimated to be about 10 Å. But the spontaneous ion-assisted etching rate did not change in the case of H2 addition.
Titanium atom densities in reactive rf magnetron sputtering for TiO2 deposition
Authors: Nakamura Tadashi , Okimura Kunio
Published: July 2002

Titanium (Ti) atom densities on the radial and axial directions in Ar–O2 reactive rf (13.56 MHz) magnetron sputtering were investigated by an atomic absorption method for the conditions where crystalline TiO2 films grow. Ti atom densities in pure Ar discharge were also measured for comparison with those in the Ar–O2 mixture discharge. At a total pressure of 3.5 Pa and rf power of 200 W, the Ti atom densities in the Ar–O2 discharge were (0.2–3.1)×109 cm−3, two orders smaller than those [(0.2–2.2)×1011 cm−3] in pure Ar discharge in the measured region. On the other hand, the Ti atom densities in the Ar–O2 discharge at a total pressure of 0.35 Pa were (0.2–2.9)×109 cm−3, while those were (0.1–1.0)×1010 cm−3 in the pure Ar discharge at 0.35 Pa. Radial profiles of the Ti atom density with a peak structure in Ar–O2 and pure Ar were interpreted based on the plasma parameters and self-bias voltage.
Confinement effects on the spatial extent of the reaction front in ultrathin chemically amplified photoresists
Authors: Goldfarb Darı́o L. , Angelopoulos Marie , Lin Eric K. , Jones Ronald L. , Soles Christopher L. , Lenhart Joseph L. , Wu Wen-li
Published: July 2002

Sub-100 nm lithography poses strict requirements on photoresist material properties and processing conditions to achieve necessary critical dimension control of patterned structures. As resist thickness and feature linewidth decrease, fundamental materials properties of the confined resist polymer can deviate from bulk values and impact important processing parameters such as the postexposure bake (PEB) temperature. The effects of these confinement-induced deviations on image or linewidth spread have not been explored. In this work, we characterize the resist thickness dependence of the spatial extent of the reaction-diffusion process in a chemically amplified photoresist system under varying processing conditions. Bilayer samples are prepared with a lower layer of a protected polymer (p-tert-butoxycarboxystyrene) and a top layer of a de-protected polymer [poly(4-hydroxystyrene)] loaded with a photoacid generator. After flood exposure, PEB, and development, changes in the thickness of the protected polymer provide a measure of the spatial extent of the reaction front between the polymer layers. The velocity of the reaction front is significantly reduced with decreasing thickness of the protected polymer layer under identical processing conditions.
Backside sputter depth profiling of phosphorus diffusion from a polysilicon source
Authors: Ronsheim P. , Chidambarrao D. , Jagannathan B. , Hunt D.
Published: July 2002

Sputtered depth profile resolution on some samples can be improved by sputtering from the backside of the wafer; utilizing the lower profile broadening of a leading edge measurement, as opposed to the trailing edge. This work develops a technique for simple and accurate backside thinning using a silicon-on-insulator substrate. A combination of backside grinding and selective wet etching results in a planar and smooth surface for accurate measurements. Using 800 eV oxygen sputtering, the measured slope due to the sputter broadening is 1.6 nm/decade of concentration for a phosphorus distribution. The technique is used to evaluate shallow phosphorus diffusion from doped polysilicon to provide calibration for diffusion modeling.
Ion beam proximity lithography on spherical substrates with continuously scanned, self-complementary masks
Authors: Ruchhoeft Paul , Wolfe J. C. , Bass Robert
Published: July 2002

This article demonstrates, for the first time, the formation of 1 μm Manhattan geometries on a 3 mm deep spherical substrate subtending a 60° angle. The approach uses ion beam proximity lithography to achieve the large depth-of-field and a self-complementary mask strategy to enable each wafer level to be defined by a single, dimensionally stable mask. This demonstration is a first step toward validating a more general approach that modeling suggests will be capable of patterning 7.5 mm deep substrates with twice the subtended angle.
Properties of porous HSQ-based films capped by plasma enhanced chemical vapor deposition dielectric layers
Authors: Iacopi F. , Baklanov M. R. , Sleeckx E. , Conard T. , Bender H. , Meynen H. , Maex K.
Published: July 2002

This article presents a study on Dow Corning® XLK™, an inorganic porous material with about 50% porosity and a dielectric constant of 2.0. It focuses on matters linked to sealing the porous film by depositing a plasma enhanced chemical vapor deposition (PECVD) dielectric cap layer. The study shows that the material can be modified during cap deposition due to the fast diffusion of reactants and radicals through the porous network, and acquire totally new properties which can be either beneficial or detrimental, depending on the chosen process. In particular, it is found that cap deposition processes on XLK in an oxidizing ambient, as used for SiO2 deposition, should be avoided. On the other hand, a beneficial modification of the dielectric film has been observed after SiC:H capping. It is also shown that there exists a critical thickness of capping material below which the cap layer reveals the presence of pinholes. The critical thickness value for a PECVD SiC:H cap layer on top of an XLK film is around 25 nm.
Deuterium and fluorine radical reaction kinetics on photoresist
Authors: Greer Frank , Coburn J. W. , Graves David B.
Published: July 2002

The etching of two photoresists (PR) was investigated using beams of Ar+ ions and neutral fluorine and deuterium atoms. Large increases in the PR etch yields were observed as the flux ratio of the fluorine atom to the Ar+ ion beam was increased. However, there was no observed effect of deuterium on the PR etch yield despite the detectable formation of DF during the etching process. To explain this observation, the following abstraction and recombination probabilities from the PR surface were measured using modulated beam mass spectrometry: F atoms abstracting adsorbed D atoms (γFD=0.19), D atoms abstracting adsorbed F atoms (γDF<0.05), and D atoms recombining with adsorbed D atoms (γDD=0.06). These measurements were insufficient by themselves to make any conclusive statements about the observed independence of the etch yield on D atom flux, so a phenomenological model of the PR etching process was developed to explain the observed phenomena. When these measured quantities were used as parameters in this model, it was possible to predict the observed lack of effect of D atoms on the PR etch yield. During the course of these experiments, the etching probability of a D atom was also measured (1.5×10−4) and found to be in good agreement with previously published values.
Growth of ultrathin cobalt films on Fe(001) studied by reflection high-energy electron diffraction and x-ray diffraction
Authors: Blomqvist P. , Wäppling R.
Published: July 2002

Thin layers of the body-centered-cubic (bcc) cobalt (Co) phase with (001) orientation have been grown on single-crystalline Fe(001). Reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD) have been used to investigate the surface and the bulk crystal structure of the deposited Co films. The RHEED investigation shows that the bcc Co structure can be stabilized up to about 8 atomic monolayers (at. ML) and that the bcc Co surface is more atomically rough as compared to Fe but improves with increased growth temperature. RHEED patterns from thicker Co films indicate a transformation from the bcc structure to a hexagonal close packed (hcp). The XRD investigation shows that this hcp phase is textured and that the films contain a small amount of Co with a face-centered-cubic stacking sequence.
Detection of chamber conditioning by CF4 plasmas in an inductively coupled plasma reactor
Authors: Cruden Brett A. , Rao M. V. V. S. , Sharma Surendra P. , Meyyappan M.
Published: July 2002

During oxide etch processes, buildup of fluorocarbon residues on reactor sidewalls can cause run-to-run drift and will necessitate time for conditioning and cleaning of the reactor. Various measurements in CF4 and Ar plasmas are made in an attempt to identify a metric useable to indicate the chamber condition. Mass spectrometry and Langmuir probe data show that the buildup of fluorocarbon films on the reactor surface causes a decrease in plasma floating potential, plasma potential, and ion energy in argon plasmas. This change in floating potential is also observed in CF4 plasma operation, and occurs primarily during the first hour and a half of plasma operation. A slight rise in electron density is also observed in the argon plasmas. Because the change is seen in an argon plasma, it is indicative of altered physical, not chemical, plasma-surface interactions. Specifically, the insulating films deposited on metal surfaces alter the electromagnetic fields seen by the plasma, affecting various parameters including the floating potential and electron density. An impedance probe placed on the inductive coil shows a slight reduction in plasma impedance due to this rising electron density. The optical emission of several species, including CF, C2, Si, and C, is also monitored for changes in density resulting from the buildup of film on the chamber wall. Changes in the optical emission spectrum are comparable to the noise levels in these measurements.
Sputter-etching characteristics of barium–strontium–titanate and bismuth–strontium–tantalate using a surface-wave high-density plasma reactor
Authors: Stafford L. , Margot J. , Delprat S. , Chaker M. , Queney D.
Published: July 2002

The etching of barium–strontium–titanate (BST) and bismuth–strontium–tantalate (SBT) deposited using a pulsed laser deposition technique has been investigated using a nonreactive (argon) surface-wave high-density plasma source. The etch rate of the rf-biased thin films was determined as a function of the self-bias voltage, of the magnetic field intensity and of the gas pressure. It was found that high etch rates with a good selectivity over resist can be achieved without any plasma chemistry, provided the plasma is operated in the very low pressure regime (i.e., below 1 mTorr). For SBT, etch rates as high as 3000 Å/min with a selectivity of 0.2 over HPR-504 photoresist were obtained with self-bias voltages lower than 150 V. It is also found that even though BST and SBT present similar sputter-etching characteristics, SBT is etched about two times faster than BST as a result of the difference in the atomic density of each material.
Use of reflective and amorphous materials for dark field stepper alignment on silicon carbide substrates
Authors: Mancini David P. , Resnick Douglas J. , Tompkins Harland , Moore Karen E.
Published: July 2002

A method of performing fine alignment for stepper lithography using a dark field alignment system (DFAS) has been developed for low reflectivity substrates. This patented process is useful for substrates such as silicon carbide (SiC), which do not provide adequate reflected light in DFAS systems for alignment mark detection. The method involves forming alignment mark structures from thin films of materials that have the following two characteristics: adequate reflectance to broadband illumination typical of DFAS systems and a fine-grained or amorphous morphology. Alignment mark materials must also be resistant to grain growth during high temperature (950 °C) anneals common to SiC processing to avoid any increase in surface roughness which can lower mark contrast. This study includes modeling of the reflectivity of several candidate materials and characterization of film surfaces using atomic force microscopy.
Diamondlike carbon deposition on plastic films by plasma source ion implantation
Authors: Tanaka T. , Yoshida M. , Shinohara M. , Takagi T.
Published: July 2002

Application of pulsed high negative voltage (∼10 μs pulse width, 300–900 pulses per second) to a substrate is found to induce discharge, thereby increasing ion current with an inductively coupled plasma source. This plasma source ion beam implantation (PSII) technique is investigated for the pretreatment and deposition of diamond-like carbon (DLC) thin layer on polyethylene terepthalate (PET) film. Pretreatment of PET with N2 and Ar plasma is expected to provide added barrier effects when coupled with DLC deposition, with possible application to fabrication of PET beverage bottles. PSII treatment using N2 and Ar in separate stages is found to change the color of the PET film, effectively increasing near-ultraviolet absorption. The effects of this pretreatment on the chemical bonding of C, H, and O are examined by x-ray photoelectron spectroscopy (XPS). DLC thin film was successfully deposited on the PET film. The surface of the DLC thin layer is observed to be smooth by scanning electron microscopy, and its structure characteristics are examined by XPS and laser Raman spectroscopy. Subsequent processing using acetylene or acetylene and Ar (20%) produced thin carbon layers that are confirmed to be graphite-dominated DLC. Also, this PSII method is employed in order to deposit the DLC layer on the inside surface of the PET bottle and to reduce oxygen permeation rate by 40%.
Characterization of gate oxynitrides by means of time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy. Quantification of nitrogen
Authors: Ferrari S. , Perego M. , Fanciulli M.
Published: July 2002

We present a methodology for the quantitative estimation of nitrogen in ultrathin oxynitrides by means of time of flight secondary ion mass spectrometry (TOF-SIMS) and x-ray photoelectron spectroscopy (XPS). We consider an innovative approach to TOF-SIMS depth profiling, by elemental distribution of single species as sum of peaks containing such species. This approach is very efficient in overcoming matrix effect arising when quantifying elements were distributed in silicon and silicon oxide. We use XPS to calibrate TOF-SIMS and to obtain quantitative information on nitrogen distribution in oxynitride thin layers. In the method we propose we process TOF-SIMS and XPS data simultaneously to obtain a quantitative depth profile.
High-resolution in situ electron beam patterning using Ti(OC3H7)4 as a negative-type resist
Authors: Mitchell William J. , Hu Evelyn L.
Published: July 2002

Our previous studies on the electron beam resist properties of inorganic titanium isopropoxide films condensed on semiconductor surfaces addressed mainly the electron sensitivity of this negative-type resist, i.e., the contrast curve behavior. In order to determine its resolution capabilities, we have used scanning electron microscopy to analyze the pixel sizes and shapes that result after exposing condensed titanium isopropoxide films of various thicknesses (from as low as the 10’s of Å range to as high as 10 000 Å) to a scanning electron beam for different times. We have found that resolution is strongly dependent on initial film thickness and electron beam exposure. While occurring at the lowest electron exposure, the smallest, well-defined pixels were observed with films on the order of 100 Å; thinner films (in the 10’s of Å range) resulted in pixels with poor definition. For films with sufficient thickness, dual pixel behavior was observed above a critical electron exposure, in which a narrow pixel with height approximating the initial film thickness would appear at the center of a thin, a broader area pixel that was observed for all exposures. Moreover, the broad area pixel’s height was relatively insensitive to initial thickness and exposure. By qualitative comparison with standard electron-resist scattering models in the literature, we argue that the thin, a broad area pixel is an artifact of the backscattered electron component generated from the interaction of the electron beam with the substrate, whereas the narrow and thick central pixel that appears after sufficiently high exposures, is representative of the forward-scattered electron distribution of the incident beam within the resist film.
Intraband and interband photocurrent spectroscopy and induced dipole moments of InAs/GaAs(001) quantum dots in n–i–n photodetector structures
Authors: Chen Zhonghui , Kim Eui-Tae , Madhukar Anupam
Published: July 2002

We have investigated normal-incidence intra- and interband spectra of self-assembled steep InAs/GaAs(001) quantum dots (QDs) with an average height of ∼8.0 nm and average base width of ∼21 nm placed in n–i(QDs)–n photodetector structures. The ground state occupation of the QDs in the n–i(QDs)–n configuration is examined and used to assign observed intraband transitions. A photovoltaic effect in intraband photocurrent is observed and shown to arise from induced dipole moments. Stark shift in interband photocurrent spectroscopy reveals the presence and direction of interband transition induced dipoles, making this study the first to determine both intra- and interband dipoles in the same ensemble of QDs.
Design of high speed Si/SiGe heterojunction complementary metal–oxide–semiconductor field effect transistors with reduced short-channel effects
Authors: Li P. W. , Liao W. M.
Published: July 2002

By taking advantages of higher carrier mobility and bandgap engineering in the Si/SiGe system, we explore the channel and source/drain (S/D) designs for Si/SiGe heterojunction complementary metal–oxide–semiconductor field effect transistors (CMOSFETs). A planar CMOS structure is proposed in which a strained SiGe layer (the hole channel) and a strained Si layer (the electron channel) grown on relaxed SiGe wells are designed for p- and n-MOSFETs, respectively, to provide better current drive capability. On the other hand, a strained-SiGe S/D heterojunction is also included in the CMOSFET device structure in that the band offset between S/D and the channel is found to be very effective in suppressing short-channel effects such as drain-induced barrier lowering/bulk punchthrough and drain leakage. With proper structure design, the near symmetrical n-MOS/p-MOS VT, enhanced current-drive capability and reduced short channel effects are achievable within the proposed planar structure.
Structure and Annealing Behavior of Metal Films Deposited on Substrates near 80 °K. II. Gold Films on Glass
Authors: Vook R. W. , Witt F.
Published: July 2002

An in situ x-ray investigation of gold films has been carried out. Films were deposited on glass near 80 °K in high vacuum. Measurements were made on the as-deposited films as well as after annealing at temperatures up to 370 °C. In the as-deposited films the following results were obtained: (1) The lattice parameter perpendicular to the film surface was a few tenths of a percent less than the bulk value. (2) The films contained large numbers of intrinsic stacking faults and twins. (3) Nonuniform strains of the order of a few percent were also present. (4) The true crystallite sizes were estimated to be between several hundred and one thousand angstroms, where the estimate depended mainly on how the twin fault density was measured. (5) These films were (111) oriented with the strongest texture occurring in the thinnest film. When the films were annealed, changes in integrated x-ray intensity and line shapes were observed to occur near −15 °C. After room-temperature anneals, the imperfection densities had annealed out to such an extent that no contributions to line broadening and peak shifts could be detected. Grain growth occurred also upon annealing the films. A tendency towards the formation of a (100) texture was observed. The relative amount of growth occurring in the various (hkl) oriented crystallites was explained qualitatively in terms of surface and strain energies, the latter resulting from the difference in thermal expansion coefficients between film and substrate.
An Absolute Micromanometer Using Diamagnetic Levitation
Authors: Evrard R. , Boutry G.-A.
Published: July 2002

A friction-free suspension in vacuo is provided for a graphite disk by magnetic induction. The disk rotates round a vertical line of force inside a properly designed stator; when the stator is cooled, a thermomolecular torque is developed and the acceleration thus given to the disk is measured by an automatic device. It is shown that this acceleration depends only on the geometrical design of the manometer and on the pressure, to which it is proportional. The manometer unit is passive, very small, and insensitive to vibrations and shocks affecting the vacuum setup. The lower limit of its range of measurement is less than 10−10 Torr. When stator cooling is removed, the disk is influenced only by a (smaller) molecular damping torque. This depends on the composition of the residual atmosphere; provided this is known, the magnitude of the damping can be computed a priori with good precision so that the instrument becomes a useful standard manometer for calibration in the 10−3 to 10−7 Torr range.
New deflected-beam gauge for pressures below 10−12 Torr
Authors: Blechschmidt D.
Published: July 2002

Design and performance of a new hot-filament ionization gauge, specially developed for total pressure measurements down to 10−14 Torr, are described. The gauge features an electrostatically deflected ion beam which is directed at the funnel cathode of a small channel electron multiplier (CEM). The spurious signal due to electronic desorption of ions from the anode is extremely small, because these ions are typically of higher initial total energy than those from the residual gas, and may, therefore, be evicted from the high-energy side of the ion beam that is energetically dispersed by the deflecting electric field. The x-ray background corresponds to a pressure in the 10−14 Torr range, and since it can be measured just by inverting the deflector potential, it may easily be zeroed out electronically. Almost none of the secondary particles, released by x rays or ions from the deflecting electrodes, is counted, because the CEM cathode is operated at high negative potential and because most positive secondary ions are collected at the negative deflecting electrode, due to their small kinetic energy. The gauge’s sensitivity for nitrogen is about 1017 counts/s⋅Torr⋅A, corresponding to 105/Torr for a CEM gain of 107. It is mounted on a 113.5-mm metal flange with ceramic feedthroughs and may be baked up to about 300 °C.
Electron-beam fabrication of chromium master masks
Authors: Ballantyne J. P.
Published: July 2002

Conventional photolithographic methods of mask manufacture in the semiconductor industry have limitations which can be overcome using electron lithography. This paper describes application of the electron-beam exposure system (EBES) to the fabrication of chromium master masks using the negative electron resist poly(glycidyl methacrylate-co-ethyl acrylate). Lithographic characterization methods developed specifically for this application include the variation of feature size and develped resist thickness with exposure and have led to the choice of correct operating conditions for EBES. Writing time for a typical 2.5-in. (6.35-cm) mask is 30–60 min, and processing time is about 70 min (excluding inspection and handling). Linewidth control is better than ±0.5 μm and chip yields typically exceed 90% per mask level for LSI circuits. Masks with chip sizes up to 20×16 mm have been processed. One-micrometer feature sizes are obtained routinely.
Distortion measurements in an electron image projector
Authors: Scott J. P.
Published: July 2002

Distortion measurements in an electron image projector for integrated-circuit fabrication are described. It is shown that the major cause of distortion which varies from exposure to exposure is due to slice bowing, and that this distortion is approximately 1/30 the height of the bow. This figure can be reduced by increasing the operating magnetic field strength.
Abstract: Mass microanalyzer using electron-beam guiding ion source
Authors: Takagi T. , Yamada I. , Kishi T.
Published: July 2002

A new apparatus which performs microanalysis by analyzing ions evaporated from a specimen by the impact of a focused, scanned electron beam from an electron-optical column which includes a ring cathode and electrostatic lenses is described. A model is developed that involves four steps:

(1) Material is locally evaporated from a specimen by bombardment with electrons of energy about 10 keV.

(2) The evaporated atoms are ionized by inelastic collisions with both primary and secondary electrons near the point of impact of the electron beam.

(3) The ions are trapped in the potential well (∠0.1–1 eV) formed by the electron beam.

(4) The ions are accelerated through the electron-optical column toward the entrance slit of the mass spectrometer and are mass analyzed.

The model predicts that for a primary electron current Ie, the collected ion current Ii is equal to (2m/M) Ie or 4×10−8 A for N2 ions and Ie=1 mA. For high beam currents (1 mA), the spatial resolution of the system was demonstrated to be less than 1 mm. The ultimate spatial resolution of the system is estimated to be 1 μm with the removal of 44 atom layers from the specimen; this estimate is based on a minimum detectable ion current of 10−16 A and a collection angle of 10−2 rad.

Experimental results were obtained from a specimen of evaporated NaCl on stainless steel. The preliminary experiments demonstrate the possible use of this instrument for surface analysis and the theory indicates the technique could provide micron spatial resolution.