bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling vapor deposition of low-K polymers: Parylene and polynaphthalene
Authors: Rogojevic Svetlana , Moore James A. , Gill William N.
Published: July 2002

By using different mechanisms of deposition and growth, new models of Parylene deposition rates have been developed and compared with experimental data over a wide range of conditions. It is shown that the surface adsorption (boundary) condition is a crucial factor in determining how the results of these models behave. Minimal differences in the behavior of the overall rates of deposition are obtained among the Parylene models using the same adsorption condition with either surface or bulk film reactions. However, their basic structures are considerably different. Although both diffusion/reaction and surface reaction models with either Langmuir-type or Flory-type monomer adsorption have attractive features, they fail to represent the data on rates of deposition over the wide range of conditions reported in the literature. In contrast, the models based on Brunauer, Emmett, and Teller multilayer adsorption seem to include the benefits of both Langmuir and Flory adsorption and simulate the data well over a much broader range of temperature. This suggests that multilayer adsorption is an important phenomenon in the low temperature vapor deposition of these polymers. Here we try to clarify the important physical/chemical mechanisms involved as well as the similarities and differences among various approaches to formulation of deposition models. A polynaphthalene deposition model is developed on the basis of both gas phase reactions followed by adsorption on the surface with subsequent reaction to form the film. The model is capable of simulating the data very accurately. However, the data available are limited in range and more experimental data are required to establish the uniqueness of the rate equations proposed.
Effects of rare gas dilution for control of dissociation, ionization, and radical density in fluorocarbon ultrahigh-frequency plasmas
Authors: Samukawa Seiji , Nakano Toshiki
Published: July 2002

The effects of diluting ultrahigh-frequency CxFy plasmas with Xe, Ar, and He are studied by optical emission spectroscopy and Langmuir probe measurement. The Ar and He dilutions are found to shift the electron energy distribution function toward higher energies. Ar and Xe also drastically increase the electron density, whereas He does not change the electron density. As a result, Ar dilution increases the ratio of ion density to CF2 density. It is expected that the Ar dilution changes the balance between the etching and the polymer deposition and significantly affects the SiO2 etching characteristics. He dilution causes a high degree of dissociation and a large increase in the density of F atoms for CxFy gases, in addition to the dilution of CF2 radical density, because of its high threshold energy for ionization. The Xe dilution drastically increases the ne while it maintains a lower electron temperature.
Effect of additive noble gases in chlorine-based inductively coupled plasma etching of GaN, InN, and AlN
Authors: Hahn Y. B. , Hays D. C. , Donovan S. M. , Abernathy C. R. , Han J. , Shul R. J. , Cho H. , Jung K. B. , Pearton S. J.
Published: July 2002

The effects of additive noble gases, He, Ar and Xe to chlorine-based inductively coupled plasmas (ICPs) for etching of GaN, AlN and InN were studied in terms of etch rate and selectivity. The etch rates were greatly affected by the chlorine concentration, rf chuck power and ICP source power. The highest etch rates for InN were obtained with Cl2/Xe, while the highest rates for AlN and GaN were obtained with Cl2/He. It was confirmed that efficient breaking of the III-nitrogen bond is crucial for higher etch rates. The InN etching was dominated by physical sputtering; the GaN and AlN etch rates were limited by initial breaking of the III-nitrogen bond. Maximum selectivities of ∼80 for InN to GaN and InN to AlN were obtained with the Cl2-based discharges.
Reactor-scale models for rf diode sputtering of metal thin films
Authors: Desa S. , Ghosal S. , Kosut R. L. , Ebert J. L. , Abrahamson T. E. , Kozak A. , Zou D. W. , Zhou X. , Groves J. F. , Wadley H. N. G.
Published: July 2002

This article describes the development of an integrated physical model for the rf diode sputtering of metal thin films. The model consists of: (1) a computational fluid dynamic finite element model for the velocity and pressure distribution of the working gas Ar flow in the chamber, (2) a steady-state plasma model for the flux and energy of Ar ions striking the target and the substrate, (3) a molecular dynamics sputtering model for the energy distribution, angle distribution, and yield of the sputtered atoms (Cu) from the target, and (4) a direct simulation Monte Carlo (DSMC) model for the transport of Cu atoms through the low-pressure argon gas to the deposition substrate. The individual models for gas flow, plasma discharge, Cu sputtering, and DSMC-based Cu atom transport are then integrated to create a detailed, steady-state, input–output model capable of predicting thin-film deposition rate and uniformity as a function of the process input variables: power, pressure, gas temperature, and electrode spacing. Deposition rate and uniformity in turn define the characteristics of thin films exploited in applications, for example, the saturation magnetic field for a giant magnetoresistive multilayer. This article also describes the development of an approximate input–output model whose CPU time is several orders-of-magnitude faster than that of the detailed model. Both models were refined and validated against experimental data obtained from rf diode sputtering experiments.
Graded TiAlN layers deposited by electron cyclotron resonance-assisted reactive sputtering
Authors: Raveh A. , Rosen D. Z. , Shneck R. , Weiss M.
Published: July 2002

Graded TiAlN layers were deposited by plasma reactive sputtering assisted by electron cyclotron resonance (ECR). For reactive sputtering, dual cathode radio-frequency magnetron targets, Ti and Al, were used. The layers were deposited using various combinations of variables such as power input, bias substrate voltage, and gas feed composition. The deposition process was monitored by optical emission spectroscopy (OES). The OES results indicate that microwave excitation added to radio-frequency plasma has contrasting effects on the Ti and Al concentration in the gas phase, enhancing titanium and quenching aluminum species reaching the deposited substrate. Thus, by the regulation of the ECR power and the ratio of nitrogen to argon flow, formation of graded layers is possible. The layers formed in this way were characterized with regard to structure, composition, and mechanical properties using an x-ray diffractometer, an Auger electron spectroscopy microscope, and a Vickers microhardness and scratch tester (for adhesion). It was observed that layers deposited at a low ECR power (⩽100 W) yielded an oriented (111) crystalline structure with good adhesion (failure load >70 N). These layers displayed a higher microhardness (∼25 GPa) at substrate bias voltage (∼50 VDC) than that of a grounded substrate (10–15 GPa). However, layers deposited at an ECR power higher than 100 W showed a random or amorphous structure with an intermediate adhesion range (failure load of 30–50 N). The relationship between the processing parameters, the structure, and the properties of the layers formed are presented and discussed.
Preliminary measurements illustrating the effect of desorption and molecular residence times on the molecular drag process
Authors: Chew Andrew D. , Dedman Emma R. , Abreu Raul A. , Creaye Ian
Published: July 2002

In this article we describe preliminary experiments based on a technique originally devised by Holst and Clausing [G. Holst and P. Clausing, Physica (The Hague) 6, 48 (1926)] whereby molecules are beamed onto a disk rotating at high speed and the point of desorption identified. This in principle provides a means for the direct determination of molecular residence times. Preliminary results indicate that the residence times of helium, nitrogen, oxygen, krypton, xenon and Suva (a refrigerant) on oxidized aluminum are not in the range of 0.1 ms–1 s. An experimental facet possibly indicating a residence time for carbon dioxide on oxidized aluminum at 27 °C of 0.62 ms was identified. The possible application of the technique to gas separation is also discussed.
Diamond coated silicon field emitter array
Authors: Albin S. , Fu W. , Varghese A. , Lavarias A. C. , Myneni G. R.
Published: July 2002

Diamond coated silicon tip arrays, with and without a self-aligned gate, were fabricated, and current–voltage characteristics of 400 tips were measured. Diamond films were grown uniformly on Si tips using microwave plasma after nucleation with 10 nm diamond suspension and substrate bias. An emission current of 57 μA was obtained at 5 V from the ungated array tips separated from an anode at 2 μm. In the case of the gated arrays with 1.5 μm aperture, an emission current of 3.4 μA was measured at a gate voltage of 80 V for an anode separation of 200 μm. The turn-on voltages for these two types of devices were 0.2 and 40 V, respectively. Diamond coated Si tip arrays have potential applications in field emission based low voltage vacuum electronic devices and microsensors.
Low damage dry etching of III–V materials for heterojunction bipolar transistor applications using a chlorinated inductively coupled plasma
Authors: Etrillard J. , Bresse J. F. , Daguet C. , Riet M. , Mba J.
Published: July 2002

Etching of InGaAs and InP in inductively coupled plasma (ICP) using SiCl4 was studied for heterojunction bipolar transistor (HBT) applications. Low sample temperature was used to minimize etching isotropy and to reduce group V element desorption. The low ion energy etching process results in a damaged layer thickness of a few Å. Auger electron spectroscopy results on InP demonstrate a very thin layer of nonstoichiometric material. The nature of the etching mask impacts the surface contamination: local contamination effects due to sputtering are observed. For such low ion energy process, the sample preparation before ICP etching is shown to be very important for surface roughness, as observed by atomic force microscopy. Various preparation schemes have been investigated, before ICP etching, for reduction of the surface degradation resulting from ICP etching. It is shown that the best results in terms of roughness and etch-rate are obtained with a silicon nitride mask and surface oxidation by ultraviolet ozonization before a wet desoxidation immediately preceding the ICP etching. An ICP process was used successfully for partly etching the base mesa of HBT structures. No significant difference with wet etching was observed in terms of induced damage and HBT current gain.
W and WSix Ohmic contacts on p- and n-type GaN
Authors: Cao X. A. , Ren F. , Pearton S. J. , Zeitouny A. , Eizenberg M. , Zolper J. C. , Abernathy C. R. , Han J. , Shul R. J. , Lothian J. R.
Published: July 2002

W and WSi Ohmic contacts on both p- and n-type GaN have been annealed at temperatures from 300 to 1000 °C. There is minimal reaction (⩽100 Å broadening of the metal/GaN interface) even at 1000 °C. Specific contact resistances in the 10−5 Ω cm2 range are obtained for WSix on Si-implanted GaN with a peak doping concentration of ∼5×1020 cm−3, after annealing at 950 °C. On p-GaN, leaky Schottky diode behavior is observed for W, WSix and Ni/Au contacts at room temperature, but true Ohmic characteristics are obtained at 250–300 °C, where the specific contact resistances are, typically, in the 10−2 Ω cm2 range. The best contacts for W and WSix are obtained after 700 °C annealing for periods of 30–120 s. The formation of β-W2N interfacial phases appear to be important in determining the contact quality.
Using historical wafermap data for automated yield analysis
Authors: Tobin Kenneth W. , Karnowski Thomas P. , Gleason Shaun S. , Jensen David , Lakhani Fred
Published: July 2002

To be productive and profitable in a modern semiconductor fabrication environment, large amounts of manufacturing data must be collected, analyzed, and maintained. This includes data collected from in- and off-line wafer inspection systems and from the process equipment itself. This data is increasingly being used to design new processes, control and maintain tools, and to provide the information needed for rapid yield learning and prediction. Because of increasing device complexity, the amount of data being generated is outstripping the yield engineer’s ability to effectively monitor and correct unexpected trends and excursions. The 1997 SIA National Technology Roadmap for Semiconductors highlights a need to address these issues through “automated data reduction algorithms to source defects from multiple data sources and to reduce defect sourcing time.” SEMATECH and the Oak Ridge National Laboratory have been developing new strategies and technologies for providing the yield engineer with higher levels of assisted data reduction for the purpose of automated yield analysis. In this article, we will discuss the current state of the art and trends in yield management automation.
Surface cleaning on aluminum for ultrahigh vacuum using supercritical fluid CO2 with H2O and NaCl as additives
Authors: Momose T. , Yoshida H. , Sherverni Z. , Ebina T. , Tatenuma K. , Ikushima Y.
Published: July 2002

Ozone treatments have been shown to reduce the outgassing rates in ultrahigh vacuum for several metals. We have further studied surface cleaning employing supercritical fluid CO2 which has high solubility for hydrocarbons. The sample measured was a half section of an anodic oxidized Swagelok fitting (A2024) 10.8 mm diameter and 8.5 mm in length saw sectioned along the axis. The cut surface was used as the reference surface. The treated and untreated surfaces were analyzed by x-ray photoelectron spectroscopy, evaluating the surface carbon density obtained from the ratio of the convoluted area of Al(2p), O(1s), and C(1s) peaks. Carbon density of the untreated surface is 87%. Following the treatment with supercritical fluid CO2 at 50 °C and 80 atm for 2 h, the carbon was reduced to 65%. Treating at 2 h at 70 °C and 94 atm showed the same 65% carbon. Adding water and increasing the supercritical fluid CO2 pressure to 100 atm showed carbon at 57%. However, adding some salt (NaCl) to the mixture produced a dramatic carbon reduction to as low as 13%. No pressure dependence was observed.
Self-organized Ge quantum wires on Si(111) substrates
Authors: Jin G. , Tang Y. S. , Liu J. L. , Wang K. L.
Published: July 2002

Self-organized Ge quantum wires have been grown on regular atomic steps formed along [1̄10] direction on Si(111) substrates by annealing at 870 °C in vacuum. The samples have been studied by ex situ atomic force microscopy (AFM), Raman scattering and low temperature photoluminescence spectroscopy. The AFM results suggest that the mechanism of the formation of the wires be the evolution of self-organized lined-up quantum dots. Good quality Ge quantum wires have been formed and clear quantum confinement-induced quantization in the wires has been observed.
Adsorption structures of NO/Pt(111) investigated by scanning tunneling microscopy
Authors: Matsumoto M. , Tatsumi N. , Fukutani K. , Okano T. , Yamada T. , Miyake K. , Hate K. , Shigekawa H.
Published: July 2002

The adsorption structure of nitric oxide (NO) on Pt(111) was studied at 10 and 70 K by scanning tunneling microscopy (STM). The island growth modes at both temperatures are similar except for the domain size of the 2×2 structure. In these low temperature region, two phases can coexist at medium coverages. These phases are assigned to the two NO species occurring at different stretching-vibrational frequencies observed in the previous vibrational spectroscopic studies. The relative location of two different species observed by STM and its stretching-vibrational frequencies suggests that the adsorption sites of NO on the Pt(111) surface at low and high coverages correspond to the hollow and the on-top sites, respectively.
Reconstructions of Ag on high-index silicon surfaces
Authors: Blankenship S. R. , Song H. H. , Baski A. A. , Carlisle J. A.
Published: July 2002

Si(5 5 12), a recently discovered, stable high-index surface of silicon, may offer a superior template for the growth of one-dimensional metallic structures. We are using reflection high-energy electron diffraction, scanning tunneling microscopy (STM), and synchrotron radiation photoemission to determine the morphology and electronic structure of Ag on this surface. Si(5 5 12) exhibits a sharp (2×1) reconstruction after flashing to ∼1250 °C. Despite the many different atomic substructures present in this reconstruction, several distinct surface core levels in the Si 2p core, and surface states in the valence band, are observed. The nature of these states is very similar to those on the clean Si(100)-(2×1) surface, which suggest that they are derived from the dimer/tetramer subunits. The growth of Ag is split into two distinct regimes. For growth at low coverages (θ<0.25 ML) and relatively low growth temperatures (T<450 °C), the 1× and 2× diffraction spots gradually fade and then the 1× spots sharpen slightly, as θ and T approach 0.25 ML and 450 °C, respectively. A very weak 3× periodicity is observed along the row direction on these surfaces. STM results show that in this low θ/T regime, Ag forms very long monoatomic chains on top of the tetramer rows on these surfaces. For higher coverages (θ<0.4 ML) and temperatures (450 °C<T<600 °C), the 3× diffraction spots increase greatly in intensity, indicating a stronger 3× periodicity forming along the row direction. Preliminary STM data indicate a variety of 3×-like structures coexisting on these high θ/T surfaces, with some indications of nanofaceting.
Mg clusters on MgO surfaces: Characterization with metastable impact electron spectroscopy, ultraviolet photoelectron spectroscopy (HeI), and temperature programmed desorption
Authors: Günster J. , Stultz J. , Krischok S. , Goodman D. W. , Stracke P. , Kempter V.
Published: July 2002

MgO films (2 nm thick) were grown on Mo and W substrates while metastable impact electron (MIES) and ultraviolet photoelectron spectroscopy (UPS) (HeI) spectra were collected in situ. Apart from the valence band emission no additional spectral features have been detected with electron spectroscopies. After exposing the oxide surface to Mg (substrate temperature between 100 and 300 K) an additional peak not seen with UPS, located within the band gap, shows up in MIES. This band, located at ∼2 eV above the top of the valence band with a full width at half maximum of ∼1 eV at the lowest exposures, can be detected in MIES until its intensity falls below a level of 10−3 of that from the valence band. This additional emission is attributed to the formation of small, nonmetallic Mg clusters. The energetic position of the cluster emission closely matches that of the expected ionization of surface FS+/FS centers. It is proposed that in the initial phase of the Mg exposure, F center-type defects are produced close to extended defects, such as steps, corners, etc. These Mg-induced defects appear to play an important role as nucleation sites for cluster formation. At sufficiently large exposures a densely packed Mg film forms.
Formation of hydronium and methoxonium on Pt(110): Ab initio determination of spectroscopically observed species
Authors: Blowers P. , Chen N. , Masel R. I.
Published: July 2002

Previously, other researchers have examined the coadsorption of water and hydrogen on Pt(111) with electron energy loss spectroscopy (EELS) and have seen the formation of a new species. This new species was originally designated to be a “hydronium” species, where hydronium referred to H3O+ surrounded by water. However, the formation of H3O+ on platinum has not been widely accepted in the literature because the formation of a bare H3O+ not surrounded by water is not a thermodynamically favored process. In this work, we use ab initio calculations at the MP2(full)/6–31g* level to predict the gas phase frequencies for a host of water and water-cluster species. These frequencies are compared to high resolution EELS spectra to identify which species form on Pt(110). We find that H5O2+, H7O3+, and H9O4+ fit the EELS spectra quite well, while H3O, H3O−, and H3O+ do not show the right vibrational modes. We have also done similar calculations for methanol. Methanol has a higher proton affinity than water, so it seems possible that methanol could also form a positively charged species like methoxonium, CH3OH2+. Once again, EELS spectra show a new species forms on Pt(110). Ab initio calculations are compared to a high resolution EELS spectrum of hydrogen coadsorbed with methanol on platinum. The most likely species to form here is methoxonium, possibly in a methanol cluster. This conclusion is supported by additional spectra of deuterated species that show the correct isotopic shifts in frequencies predicted by calculations. The conclusion from our study is that ions can form during coadsorption of hydrogen and water and hydrogen and methanol on Pt(110). The ions are probably hydrated, but the further EELS evidence strongly supports ion formation.
Damage to III–V devices during electron cyclotron resonance chemical vapor deposition
Authors: Lee J. W. , Mackenzie K. D. , Johnson D. , Shul R. J. , Hahn Y. B. , Hays D. C. , Abernathy C. R. , Ren F. , Pearton S. J.
Published: July 2002

GaAs-based metal semiconductor field effect transistors (MESFETs), heterojunction bipolar transistors (HBTs), and high electron mobility transistors (HEMTs) have been exposed to ECR SiH4/NH3 discharges for deposition of SiNx passivating layers. The effect of source power, rf chuck power, pressure, and plasma composition have been investigated. Effects due to both ion damage and hydrogenation of dopants are observed. For both HEMTs and MESFETs there are no conditions where substantial increases in channel sheet resistivity are not observed, due primarily to (Si–H)° complex formation. In HBTs the carbon-doped base layer is the most susceptible layer to hydrogenation. Ion damage in all three devices is minimized at low rf chuck power, moderate ECR source power, and high deposition rates.
Magnetic field induced changes in electron states of a superlattice
Authors: Paranjape V. V.
Published: July 2002

It is known that the difference in the effective mass of the electron in the adjacent layers of a superlattice leads to a coupling between the electron states, which are in the parallel and perpendicular directions to the growth axis. As a consequence of this coupling, the electron band structure of the superlattice is altered. The alterations are shown in this article to be significant when a magnetic field normal to the layers is applied. Expressions for the effective mass of the electron, the width of the first miniband, and the density of states of the electrons as a function of magnetic field are obtained. Numerical results for the effective mass and bandwidth are illustrated in several diagrams.
Residual strain and resultant postrelease deflection of surface micromachined structures
Authors: Hubbard T. , Wylde J.
Published: July 2002

The mechanical behavior of surface micromachined structures is significantly affected by residual strains introduced in the manufacturing process. In this article we develop a relationship among residual strain, structure geometry, material properties and the resultant deflection upon release. Microstructures are more susceptible to the effects of residual strain than macromechanical structures for two reasons: (1) Surface layers are deposited at high temperatures and due to differential thermal expansion are subject to large and variable residual strains. (2) Many microstructures have large aspect ratios. Analytical solutions are presented in which beams are modeled as bilayer structures subject to uniform axial stresses and as monolayer structures with an arbitrary stress distribution. The predicted results compare favorably to experimental measurements of complementary metal–oxide–semiconductor surface micromachined beams.
Compounds of the CdTe–In2Te3 system in CdTe–In film grown by the close-spaced vapor transport technique combined with free evaporation
Authors: Hernández M. P. , Iribarren A. , Zapata Torres M. , Bartolo P. , Sosa V. , Peña J. L.
Published: July 2002

Polycrystalline thin films of CdTe–In were grown by the close-spaced vapor transport technique combined with free evaporation of In. The indium concentration in the samples increased according to the rise in temperature of the In source. X-ray diffraction analysis allowed us to identify the CdTe (α) phase in all samples, together with the CdIn2Te4 (β) phase in the samples grown at the highest temperatures of the In source. Auger electron spectroscopy was used to quantify the chemical composition of the films. The sensitivity factors were calculated assuming that the solid solution (CdTe)1−x(In2Te3)x was formed. For samples of low In concentration, the lattice parameter decreased linearly with the molar percent of In2Te3 in CdTe. This behavior corroborated the presence of the solid solution.
Self-assembled monolayers for polymer and protein cationization with time-of-flight secondary ion mass spectrometry
Authors: Michel Roger , Luginbühl Reto , Graham Daniel J. , Ratner Buddy D.
Published: July 2002

Detection of cationized polymers and proteins with time-of-flight secondary ion mass spectrometry has been achieved using novel substrates consisting of carboxylic acid terminated self-assembled monolayers (SAMs) with silver ion substituted headgroups. However, other metal ions (Na, Cu, Tl, or Li) as SAM headgroups can be used as well. Polymers were deposited on the metal ion derivatized SAMs by spin coating while proteins were adsorbed onto the substrates. Control experiments carried out on nonsubstituted and methyl-terminated SAMs suggest that only metal ions in close proximity to the polymer can cationize the molecules and their fragments. Both cationized fragments and whole molecular species were observed for 1 kD polyethyleneoxide and low molecular weight proteins (<2 kD).
Surface roughness scattering at the Si–SiO2 interface
Authors: Goodnick S. M. , Gann R. G. , Sites J. R. , Ferry D. K. , Wilmsen C. W. , Fathy D. , Krivanek O. L.
Published: July 2002

Scattering of inversion layer electrons at the oxide semiconductor interface is a major source of mobility degradation in MOSFETs. We have studied, on the same sample, high resolution TEM cross sections of the Si–SiO2 interface and detailed temperature dependent electronic and magnetic transport measurements. The expeirmental mobility data are compared to a model containing terms for surface roughness and impurity scattering including carrier screening. The statistical properties of the interface fluctuations appear as parameters which are adjusted to fit the transport data. While the TEM pictures indicated an interfacial boundary which deviated by only one atomic layer, an assumed peak-to-peak deviation of approximately five atomic layers is required to fit the experimental mobility. Thus, while the overall comparison of the surface parameters suggests that roughness scattering is a plausible mechanism, close agreement between the theory and experiment is not obtained.
Submicron pattern replication using a high contrast mask and two-layer resist in x-ray lithography
Authors: Saitoh Yasunao , Yoshihara Hideo , Watanabe Iwao , Nakayama Satoshi
Published: July 2002

The effects of photoelectrons and Auger electrons from the x-ray mask on contrast and resolution were experimentally investigated in the replication of submicron resist patterns in x-ray lithography. A resist thinner than 550 Å was exposed by electrons generated from a Si–N membrane. The effect of electrons from the Au absorber is observed even with a 1 μm thick Au absorber pattern, because of the continuous radiation spectrum generated, producing wavelengths shorter than those of the characteristic radiation. A polymer film coating on the Au absorber pattern increases the contrast of the mask, because electrons from the x-ray mask are absorbed by the polymer film. The unwanted exposure of a resist by electrons from a Si wafer was also studied. On the basis of these results, we proposed a new two-layer resist process. In this way, a submicron resist pattern can easily be realized by using a high contrast mask and a two-layer resist.
Improved energy analyzer for voltage measurement in electron beam probing for LSI diagnosis
Authors: Ito A. , Ookubo K. , Goto Y. , Furukawa Y. , Inagaki T.
Published: July 2002

To reduce the error caused by the local field effect in electron beam voltage measurement, a hemispherical retarding field energy analyzer extraction system for secondary electrons has been investigated. Based on the results of experiments, an improved energy analyzer was devised, which has a planar extraction grid combined with spherical extraction and retarding grids. It can generate a uniform extraction field of about 800 V/mm, keeping the retarding field spherical. Linearization error was reduced to ±0.15 V. Measurement error was also reduced to about one-tenth of our previously developed hemispherical analyzer. Typically error is less than ±0.3 V for electrodes more than 5 μm wide over electrode voltages from 0 to 5 V.
Thin film structure to reduce radiation damage in x-ray lithography
Authors: Maldonado J. R. , Reisman A. , Lezec H. , Bumble B. , Williams C. K. , Iyer S. S.
Published: July 2002

A method to decrease radiation damage to VLSI devices when using x-ray lithography is described. To decrease the x-ray radiation reaching the device SiO2 gates, an x-ray absorbing thin film is interposed between the resist and the device structure. Tungsten has been shown to meet all the requirements for the absorbing layer material. In particular, a RIE technique to obtain straight profiles in tungsten using a conventional CF4/O2 mixture is described in the paper. In addition, the dosimeter film technique utilized to calibrate the x-ray source is described in the appendix.
Printability of defects in optical lithography: Polarity and critical location effects
Authors: Mastromarco Vincent , Neureuther A. R. , Toh Kenny
Published: July 2002

Two-dimensional aerial image simulation and resist development with sample for positive photoresist along critical cross sections have been used to explore and establish models for defect interactions with features. Clear and opaque defects along a line edge give the same linewidth variation versus defect size, such as (ΔL/L)=10% for a 0.23 λ/NA defect. The resist dissolution process for large edge bias (0.14 λ/NA) and low edge bias (0.03 λ/NA) tends to terminate on constant intensity contours of 10% and 25%, respectively. The defect-induced linewidth variation is independent of bias linewidth except for transparent intrusions into narrow resist lines and opaque protrusions into narrow spaces. Here perturbations of adjacent intensity extrema results in large-lateral dissolution effects. Defects between two adjacent minimal sized features at a minimal spacing were used to explore critical location effects. For defects <0.2 λ/NA the results follow the algebraic model for single feature interactions and centered defects are less significant than edge defects. However, for large defects the centered case is more likely to cause openings and bridging. Line edge bias can be introduced to enhance the removal of bridging through the three-dimensional dissolution effects at the expense of increased top loss for transparent defects. A moderate amount of line edge bias is needed to balance polarity effects and sizes up to 1/2 of the minimum feature size of 0.8 λ/NA may be tolerable.
Spot-size measurement in an electron-beam pattern generator.
Authors: Chisholm T.
Published: July 2002

The spot-size measurement method introduced by Rishton et al. has been successfully adapted for use in any Philips Beamwriter. As the spot is scanned across an etched silicon edge mounted on a substrate holder, the current passing the edge is recorded by a waveform analyzer which then computes the spot size. Apart from initial calibration, the measurements are independent of the Beamwriter. Computer simulations show the influence on the final result of response speed, noise, and stage vibration. Good qualitative agreement between the simulations and measurements allows rules for obtaining accurate results to be formulated. Consistent measurements of spots from 21 to 500 nm have been obtained from several Beamwriters at a number of facilities. It is also shown that the Beamwriter’s internal measurements are accurate when allowance is made for the width of the edge of the marker used.
Control of fixturing-induced distortion in x-ray masks
Authors: Wilson A. D. , Lapadula C. , Silverman J. P. , Viswanathan R. , Voelker H. , Fair R.
Published: July 2002

Mask distortion can be one of the major contributions to overlay error in x-ray lithography. Although some overlay errors due to mask patterning errors (limited by the accuracy of the electron-beam writing tool) will always be present, a significant amount of additional overlay error can be attributed to mask distortion caused in part by the way the mask is mechanically held in place. This fixturing-induced distortion can be present not only during the x-ray exposure step, but also during the mask writing itself. It is clearly important to reduce such distortion to a minimum if x-ray lithography is to fulfill its potential. We have developed a kinematic mask holder to effectively eliminate the distortion due to fixturing that has been observed with other mask holders. A description of the fixture is presented, along with experimental results showing the resulting distortion when used in an electron-beam writing tool, a Nikon 2I measuring tool, and an x-ray stepper. The stepper results are also compared to results using a nonkinematic fixture. In all cases, the kinematic fixture results in distortion of less than 0.02 μm (1σ), consistent with the noise of the measurements in all three tools.
An ultra-low stress tungsten absorber for x-ray masks
Authors: Itoh Masamitsu , Hori Masaru
Published: July 2002

A stress compensation technique for a tungsten (W) absorber for an x-ray mask has been developed. Tungsten films with a thickness of 500 nm were deposited using the magnetron dc sputtering method in an argon (Ar) working gas at a power of 1 kW. A high film density (18.0 g/cm3) was obtained at a low working gas pressure. Neon (Ne), Ar, krypton (Kr) and silicon (Si) ion implantations were performed with a projection range (Rp) of 50 nm, at doses of 1014–1015 ions/cm2 to modify the absorber stress. The ion implantation reduced the film stress to less than 5×107 dyn/cm2. Ar and Kr implanted film stress stability was less than 5×107 dyn/cm2. Ne and Si implanted film stresses were not stable.
Correlation of in-plane and out-of-plane distortion in x-ray lithography masks
Authors: Ku Y. C. , Lim Michael H. , Carter J. M. , Mondol M. K. , Moel A. , Smith Henry I.
Published: July 2002

The implementation of x-ray lithography requires that in-plane distortion caused by absorber stress be eliminated (i.e., be made less than ∼10% of minimum feature sizes). As a rule of thumb, for large-area membranes (i.e., ≥30 mm diam) stress-induced distortion is negligible if absorber stress is kept below 108 dynes/cm2 (10 MPa). The most common way of determining absorber stress on membranes is to measure the out-of-plane deflection in a Linnik or Mireau interferometer. Out-of-plane deflection is caused by absorber bending moment. It is possible, in principle, for an absorber to have a stress that varies with depth in such a way that bending moment is zero but net in-plane stress is not. To determine if there is a one-to-one correspondence between out-of-plane and in-plane distortion, and in order to check the validity of Yanof’s model, we have developed two methods of measuring in-plane distortion: a moiré method and a holographic interferometry (HI) method. Both require that one etch or lift-off a grid on one surface of the x-ray mask membrane using holographic lithography and reactive-ion etching. On the opposite surface an x-ray absorber is deposited and patterned. In the moiré method another holographic exposure is performed, at the same spatial period as the grid, but at a small azimuthal rotation. After development, a clear moiré pattern is formed, from which one can calculate the in-plane distortion and corresponding absorber stress. In the HI method, the mask is placed in the standing wave produced by two intersecting laser beams. A fringe pattern can then be seen on a charge coupled device camera. The HI method provides a higher sensitivity to in-plane distortion than the moiré method and should enable one to measure in-plane strain at a level corresponding to in-plane distortion below 1 nm for typical pattern geometries.
Lithographic tolerances based on vector diffraction theory
Authors: Flagello D. G. , Rosenbluth A. E.
Published: July 2002

The classic rules for scaling lithographic resolution derive from scalar models of image formation in air, and must be reexamined as numerical apertures (NAs) increase beyond 0.5. This article describes a vector image code (VIC) based on plane wave decomposition of the radiation that propagates from the exit pupil, and a modified thin film treatment of propagation into the photoresist. Tolerances on resolution, depth-of-focus (DOF), and source polarization can be derived from VIC simulations. The strongest vector diffraction effects arise from polarization in the illumination, producing nonscalar effects in exposure-to-clear curves (‘‘swing curves’’), as well as orientation-dependent asymmetries in printed patterns. Modeling shows that the small asymmetries previously reported [D. Flagello, A. E. Rosenbluth, C. Progler, and J. Armitage, Microcircuit Engineering 1991 (Elsevier, New York, 1991)] at 0.55 NA increase rapidly for NAs beyond 0.7. Resolution increases more slowly than NA−1 at high NA, even with unpolarized illumination and perfect focus control. The contrast loss can largely be ascribed to the in-plane or parallel component of the E field within any image slice; the out-of-plane or perpendicular component actually shows a slight contrast increase. Snell’s law reduces the angular range of E orientations in the resist, so the contrast loss in resist is much less than in air. At high NA, the aerial image loses its relevance as a predictor of lithographic performance. Snell’s law also implies spherical aberration in the refracted field, reducing DOF in thick resist layers. Further, focal tolerances calculated with the traditional ±λ/2 NA2 criterion are shown to be optimistic, since this criterion is derived from the paraxial form for defocus.
Aberration properties of focused ion-beam induced by space charge effect
Authors: Hirohata S. , Kosugi T. , Sawaragi H. , Aihara R. , Gamo K.
Published: July 2002

The ion-beam broadening induced by the space charge effect (SCE) was investigated for conditions relevant to ion beam processes. A Monte Carlo calculation including the effect of lens aberration has been performed. This makes it possible to estimate the beam broadening induced by the SCE following lens aberration changes. Results show that the beam broadening induced by the SCE around the retarding region is less than 8% of the total probe diameter assuming 100 μA/sr of angular current density at the source, 10 eV of energy dispersion, 0.1–10 nA of the probe current, and 0.1–25 keV of landing energy. Results also show that the beam broadening induced by the SCE is more sensitive to angular current density at the source rather than total probe current. The minimum probe diameter at 1 nA of the probe current and 100 eV of landing energy is 0.12 μm at 400 μA/sr of angular current density at the source.
Wet silylation and dry development with the AZ 5214TM photoresist
Authors: Gogolides Evangelos , Tsoi Elizabeth , Nassiopoulos Androula G. , Hatzakis Michael
Published: July 2002

A positive tone surface imaging process using wet silylation and dry development of AZ 5214TM photoresist was developed. The process steps are spinning and prebake of the photoresist, i-line exposure, postexposure bake, wet silylation, and dry development in O2 plasma. The process has been developed using statistically designed experiments, starting with a Placket–Burman screening experimental design for six variables. These experiments showed that the composition of the silylating solution was the most important variable. As a result, a mixture experimental design followed, with the concentrations of the silylating agent and solvents as the only variables. Characterization of the process and process window definition were done with ultraviolet spectroscopy of films made on quartz wafers, and scanning electron microscope photographs.
Spatial correlation of electron-beam mask errors and the implications for integrated circuit yield
Authors: Berglund C. N. , Maluf N. I. , Ye Jun , Owen G. , Browning R. , Pease R. F. W.
Published: July 2002

Specifications for masks are usually based on the assumptions that pattern errors can be adequately described by a stationary Gaussian distribution of independent point processes. Critical dimension and feature position errors across chrome-on-glass photomask plates were measured, and the results show that a description of these errors in terms of a 3-sigma variation about a mean value based on the above description is inadequate and often misleading. Mask dimensional errors exhibit considerable spatial correlation across a plate, and have a spatial power spectrum that has implications for integrated circuit yield because of the different ways that photolithography systems can transfer reticle errors to the wafer. Depending on the spatial correlations of the errors and the specific lithography system the implications could be either positive or negative. As a result any quantitative consideration of the effect of mask errors on device performance and yield must consider mask error spatial correlations specifically.
Simple metrology scheme with nanometer resolution employed to check the accuracy of an electron beam lithography system
Authors: Hübner B. , Koops H. W. P.
Published: July 2002

The ‘‘self-comparison method’’ is used to measure positioning errors, thermal and mechanical instabilities as well as field distortions of a high-resolution electron beam lithography system. For drift measurements, line gratings are overlaid with slightly rotated gratings of the same constant in subsequent exposures. From the position of the moiré patterns we deduce positioning errors with 2.5 nm resolution. Since moiré measurements are equivocal, we use in addition vernier patterns with a resolution of 150 nm to overcome this problem. The measurements are made with an optical microscope but not with a calibrated metrology tool. Distortion measurement is carried out using an image acquisition system with 512×512 pixels together with a video camera and an optical microscope. Images of a point grating filling a full field are taken at various positions in the field. The grating in the center region is taken as a reference for the measurement. Field distortions are measured from differences in the grating constant and rotation between the center region and the outer regions. These are determined by comparing the center of mass of each grating point in the images with the corresponding points in the reference image. Differences in the grating constant down to 0.0003 times the constant and rotations of 0.0003 rad can be measured. These results are then fitted to a polynomial function of fifth order representing the field aberrations. Using this method, the distortions of the image acquisition system have no influence on the result of the evaluations .
Pattern placement metrology precision evaluation
Authors: Nash S. C. , Fecteau T. J. , Cook J. S.
Published: July 2002

Meeting the pattern placement requirement for 0.25-μm groundrule x-ray masks is a key development challenge. The e-beam mask lithography system and process-induced distortions influence pattern placement. To understand and control these tools and processes, and to disposition finished x-ray masks, more precise pattern placement metrology is required. This article presents the results of an evaluation of the Leica LMS 2000 Laser Metrology System for pattern placement metrology on x-ray masks.
Etch masks of semimetallic amorphous carbon thin films produced by electron-beam sublimation of graphitic carbon
Authors: Porkolab G. A. , Wolf E. D.
Published: July 2002

Smoothness of etched facets at all angles is a critical requirement for photonic devices in such materials as AlGaAs/GaAs which are etched at variable angles by directed ion beam/reactive gas etching systems such as chemically assisted ion beam etching (CAIBE). Semimetallic amorphous carbon thin films have been found to produce excellent etched facets that are smoother than those etched with other mask materials. This material also exhibits very low CAIBE etch rates and very low chemical reactivity with substrate materials such as AlGaAs/GaAs or silicon. The semimetallic amorphous carbon was deposited up to 400 nm thick by electron beam sublimation of graphitic carbon onto substrates such as polished wafers of GaAs, Si, Ge, and onto glass. The electron-beam sublimation deposited (EBSD) semimetallic amorphous carbon, EBSD semimetallic a-C, can be patterned directly by SF6 reactive ion etcher via a standard photoresist mask, it can be used as an etch mask in CAIBE systems, and it can be stripped clean in hydrogen or oxygen plasmas. Etch rate selectivities of approximately 30:1 of (AlGaAs):(EBSD semimetallic a-C) were observed in CAIBE experiments. The EBSD semimetallic a-C is being used as the etch mask in a self-aligned four-CAIBE steps process to microfabricate surface-emitting high-power single-mode AlGaAs/GaAs laser arrays.
High-indium modulation doped field effect transistors on GaAs substrates
Authors: Uppal P. N. , Gill D. M. , Svensson S. P. , Tu D-W.
Published: July 2002

We have grown InxGa1−xAs modulation doped field effect transistors (MODFETs) using novel buffer layer schemes on GaAs substrates with x values up to 0.5. The MODFET active layers were grown at substrate temperatures between 500 and 520 °C and characterized by x-ray diffraction, photoluminescence, and Hall effect measurements. MODFET devices with 0.15 μm gate length were fabricated, and dc and rf tested. Our work has indicated that the electron mobility in the MODFETs is a function of the growth mode, i.e., two-dimensional (2D) layer-by-layer versus three-dimensional island growth. MODFET performance, the ability to maintain a streaky reflection high-energy electron diffraction pattern, as well as morphology had a very strong correlation. With these observations in mind we used a buffer layer scheme to give 2D growth fronts for InxGa1−xAs with x values up to 0.5, which is a modification of the buffer scheme described in K. Maezawa and T. Mizutani, IEEE Trans. Electron Devices 37, 1416 (1990). For In0.34Ga0.66As channel MODFETs we observed a room-temperature electron mobility of 6620 cm2/V s with a 2D carrier density of 5.9 × 1012 cm−2 (double-doped channel), a dc transconductance of 800 mS/mm and a rf gain of 13.5 dB at 35 GHz for a 0.15 μm gate length.