bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray mask fogging by electrons backscattered beneath the membrane*
Authors: Christenson K. K. , Viswanathan R. G. , Hohn F. J.
Published: July 2002

Proximity effects can be reduced when exposing x-ray mask membranes by increasing the electron-beam accelerating voltage. Forward scattering in the resist is reduced and exposure due to backscattered electrons is also reduced since the more energetic electrons are able to pass through the electroplating base and thin mask membrane. However, electrons that pass through the mask can strike an object down stream from the mask, backscatter, and produce a broad background exposure or ‘‘fogging’’ in the resist. Under some conditions, fogging can cause >40% dose variations over the mask, degrading the line width control severely. We investigated this fogging effect for different electron trap materials at various electron energies. Our results indicate that dose variation from fogging can be reduced to <3% by placing a carbon mat downstream from the membrane. The effect of fogging has been further attenuated to <1% by using a textured, low Z material (Aluminium Honeycomb) to trap (absorb) the electrons that are transmitted through the mask. This paper will discuss the magnitude and distribution of backscatter fogging as a function of the absorber’s composition, texture, and distance from the membrane.
Methods for proximity effect correction in electron lithography
Authors: Owen Geraint
Published: July 2002

A convenient and unambiguous way of characterizing the proximity effect is by use of the modulation transfer function. Six types of correction scheme are compared in this way, these being the use of high beam energies (>20 keV), of low beam energies (<20 keV), the use of multilayer resists, exact dose correction, ‘‘self-consistent’’ dose correction, and the application of correction exposures. The main conclusions drawn are that the use of high beam energies reduces the proximity effect significantly; that exact dose correction, in addition to performing better than the ‘‘self-consistent’’ technique, is computationally superior; and that correction exposures are effective, particularly in combination with other correction techniques.
High resolution atomic force microscopy potentiometry
Authors: Weaver J. M. R. , Abraham David W.
Published: July 2002

A method is presented for performing attractive-mode force potentiometry with submillivolt accuracy and a typical spatial resolution of order 50 nm. The technique permits measurements to be made in air on specimens which may be passivated or oxidized, conducting or semiconducting, with virtually no sensitivity to oxide thickness or character. An initial demonstration is presented showing voltage measurements on a commercial operational amplifier.
Atomic images and defect structures of the epitaxially precipitated carbon layers on Ni(111) surface
Authors: Yamazaki S. , Tanaka M. , Tanaka S. , Fuginami M. , Uemori R. , Fujita D. , Homma T. , Ono M.
Published: July 2002

The structure of carbon layers precipitated on Ni(111) surface by surface segregation was investigated using scanning tunneling microscopy (STM). As a result of STM observations, it was clarified that the atomic arrangement and electronic structure of the carbon layers were essentially the same as those of the highly oriented pyrolytic graphite (HOPG). And some defect structures which run along 〈11̄00〉 directions were observed.
Electron optics for high throughput electron beam lithography system
Authors: Sohda Yasunari , Nakayama Yoshinori , Saitou Norio , Itoh Hiroyuki , Todokoro Hideo
Published: July 2002

A new electron optical column has been designed for cell projection method involving 0.2 μm large scale integration fabrication. Assuming a resist sensitivity of 1 μC/cm2 and a deflection settling time of 100 nsec, the maximum shot length is optimized to 5 μm. The objective lens system has two magnetic lenses and one magnetic deflector, and the lens system size enlargement effect has been investigated to deflect the beam up to 5 mm square field. As a result, beam edge resolution under 0.07 μm and shaped beam distortion under 0.01 μm have been achieved. In order to reduce the practical settling time, a three stage deflection system has been adopted.
A method for calculating the current density of charged particle beams and the effect of finite source size and spherical and chromatic aberrations on the focusing characteristics
Authors: Sato M. , Orloff J.
Published: July 2002

A method for calculating current density of a focusing system including the effects of finite source size, spherical, and chromatic aberrations is presented. Current density at the target plane can be determined by calculating the origin of trajectories at the object plane, for each target point. The relation between object and image points is calculated by numerical integration of the ray equation and using the analytical results from geometrical aberration theory. The focusing characteristics for current density distributions are also investigated. A focusing position which gives the maximum axial current density does not give a good beam current profile (measured by a knife edge) in the case of large aberrations, because the aberrations cause the current distribution to have a long tail.
Synchrotron x-ray standing-wave study of Sb on GaAs(110) and InP(110)
Authors: Kendelewicz T. , Woicik J. C. , Miyano K. E. , Cowan P. L. , Karlin B. A. , Bouldin C. E. , Pianetta P. , Spicer W. E.
Published: July 2002

The soft x-ray standing-wave technique has been used to study ordered monolayers of Sb on GaAs(110) and InP(110). Using the back-reflection diffraction geometry from (220) planes, we determine the perpendicular distances of Sb atoms to the substrate and compare these with theoretical calculations and elastic low-energy electron diffraction determinations. The various models of Sb chemisorption are evaluated on the basis of our data.
Electron beam induced metalization of palladium acetate
Authors: Stark T. J. , Mayer T. M. , Griffis D. P. , Russell P. E.
Published: July 2002

Films of palladium acetate Pd(OOCH3)2 0.1 and 0.3 μm thick have been stoichiometrically altered through exposure to electron beams of 1–30 keV. The lowest required doses for alteration, 1000 and 2500 μC/cm2, were obtained using beam energies of 4 and 5 keV, respectively. These results have been related to Monte Carlo simulations of energy absorbed within a thin surface film. The minimum line widths of features produced was less than 100 nanometers with estimated Pd/C ratio of 1 and measured resistivities as low as 100 μΩ cm.
Fast proximity effect correction method using a pattern area density map
Authors: Murai Fumio , Yoda Haruo , Okazaki Shinji , Saitou Norio , Sakitani Yoshio
Published: July 2002

This article proposes a new method for proximity effect correction that utilizes newly developed hardware. The correction algorithm modifies the exposure dose for each exposure point by referring to a pattern area density map. The only additional process in this method is virtual exposure to make the map. The virtual exposure is carried out once at the first use of the large-scale integration circuit pattern and can be processed in only 30 s. The pattern area density map makes it possible to correct the proximity effect from the lower-level patterns by the new map calculated from the two maps of lower level and exposing level. The usefulness of this method is verified by experiments using model patterns.
Comparison between etching in Cl2 and BCl3 for compound semiconductors using a multipolar electron cyclotron resonance source
Authors: Pang S. W. , Ko K. K.
Published: July 2002

Controllable dry etching of GaAs and InP using a multipolar electron cyclotron resonance (ECR) source and a radio frequency (rf)-powered electrode was investigated. The etch characteristics were studied as a function of microwave power, rf power, distance from the ECR source, pressure, and temperature. Etch rate is found to increase with microwave power initially, then decrease at higher microwave power due to reduction in ion energy. Surface morphology becomes rougher and etch profile is more undercut at higher microwave power, but can be improved using higher rf power or by Ar addition. As the ECR source distance increases, the concentration of ions and neutral species decrease, but the ion energy increases. Therefore, when etching is limited by the arrival rate of reactive radicals, etch rate decreases with source distance. When the process is limited by the ion-enhanced reaction or removal rates, etch rate increases with source distance. Etch rate and self-induced dc bias voltage (‖Vdc‖) typically increase with pressure. The increase in ‖Vdc‖ is believed to be caused by the lower ion flux at higher pressure. However, when the reactive species concentrations and the ion energy are low, etch rate decreases with pressure. Low pressure was observed to favor smooth surface morphology and vertical etch profile. Etch rates for both GaAs and InP increase with temperature, with InP etch rate exceeding GaAs at 380 °C. Using a Cl2/Ar mixture with 10% Cl2, 70 W rf power and 25 W microwave power at 0.5 mTorr, 0.1 μm wide features that are 1 μm deep have been fabricated in GaAs with vertical profile and smooth surface morphology.
Fabrication of sub-20 nm trenches in silicon nitride using CHF3/O2 reactive ion etching and oblique metallization
Authors: Wong T. K. S. , Ingram S. G.
Published: July 2002

A direct process for fabricating nanometer size trenches in Si3N4 using high voltage electron beam lithography and CHF3/O2 reactive ion etching has been developed and characterized. The process can be used on both bulk and thin membrane substrates and has demonstrated a feature resolution of better than 20 nm. An extension of this process allows 15 nm wide slots to be fabricated in a metal film without performing any metal etching.
Ion transport anisotropy in low pressure, high density plasmas
Authors: Gottscho Richard A.
Published: July 2002

Controlling ion transport is critical for controlling line profiles during the plasma etching of submicron structures for ultra-large-scale integrated circuits. Fortunately, the newest generation of plasma reactors are operated at low enough pressures that the sheath region separating the plasma from the wafer becomes collisionless. Under these circumstances, the ion angular distribution function at the wafer surface can be calculated from the sheath voltage and the ion velocity distribution function at the sheath edge. In this work, several limiting cases for the ion angular distribution function are considered. A good approximation for the angular distribution at the wafer surface is derived by assuming that the perpendicular velocity distribution is Gaussian, in agreement with experiment, while the parallel velocity distribution is a delta function with the magnitude of the parallel velocity simply given by the magnitude of the sheath voltage. Parallel velocity distributions with finite width at the sheath edge are shown to have only a small effect on the ion angular distribution function at the wafer surface. With these simple assumptions, the ion angular distribution function at the wafer surface is a function of only one parameter: the ratio of the sheath voltage to the perpendicular ion temperature.
Development of positive electron-beam resist for 50 kV electron-beam direct-writing lithography
Authors: Sakamizu Toshio , Yamaguchi Hidenori , Shiraishi Hiroshi , Murai Fumio , Ueno Takumi
Published: July 2002

A positive chemical amplification resist system has been developed for 50 kV electron-beam direct-writing lithography. This resist consists of a meta-cresol/para-cresol novolak resin, tetrahydropyranyl-protected polyvinylphenol (THP-M) as a polymeric dissolution inhibitor, and tri(methanesulfonyloxy)benzene (MeSB) as an acid generator. Radiation-induced hydrolysis of MeSB in the novolak resin matrix was confirmed to yield methanesulfonic acid and phenol derivatives by using gel-permeation and high-performance liquid chromatography. The catalytic chain length of THP-M deprotection was estimated to be approximately 300 in the matrix. It was found that the compatibility of a polymeric dissolution inhibitor with a novolak matrix relates to their polarity characteristics, and that the increase of para-cresol ratio in the novolak matrix can enhance the compatibility with THP-M and dissolution-inhibition capability of the composition. The optimized composition and process of the resist system achieved high aspect ratio patterns (0.3-μm contact holes/1.6-μm thickness) with high sensitivity (3.5 μC/cm2 at 50 kV).
Angular and energy distributions of ions emitted from a GaIn liquid alloy ion source
Authors: Medvedev V. K. , Chernyi V. I. , Popovich N. N.
Published: July 2002

Angular distributions of Ga+, In+, and Cu+ ions from a GaIn liquid alloy ion source are very different. With the source at room temperature, In+ ions appear to be emitted into a narrow angular ring at the edge of the Ga+ emission cone, and Cu+ ions are emitted into the central part of that cone. Energy distributions of Ga+ and In+ ions vary strongly as the source temperature increases, and at high temperatures depend on the angle from the axis of the emission cone. A mechanism of space separation of ions due to the difference of their evaporation fields is proposed. The possible influence of charged droplet emission on the angular and energy distributions of ions is discussed. A mechanism for the optical radiation from a liquid metal ion source, due to charge-exchange processes, is proposed.
Low-damage electron-beam-assisted dry etching of GaAs and AlGaAs using electron cyclotron resonance plasma electron source
Authors: Watanabe Heiji , Matsui Shinji
Published: July 2002

Low-damage etching using an electron-beam (EB)-induced surface reaction (EB-assisted dry etching) is studied. Low-energy and high-current density EB is obtained from argon (Ar) initiated electron-cyclotron-resonance (ECR) plasma. The rate of EB-assisted dry etching, showering 120 eV EB onto a GaAs substrate in a 1×10−4 Torr chlorine gas (Cl2) atmosphere, is more than ten times larger than that for Cl2 gas etching. A 0.4 μm linewidth fine structure in GaAs was transferred. Etching of AlGaAs in Cl2 and the selective etching of GaAs from AlGaAs through the addion of SF6 gas into Ar-ECR plasma have been performed. The degree of damage induced by EB-assisted dry etching is optically and electrically characterized using a GaAs/AlGaAs quantum well (QW) structure and a two-dimensional electron gas (2DEG) heterostructure samples, respectively. The results were compared with those of samples prepared by ion-beam-assisted etching (IBAE). It is shown that EB-assisted dry etching does not degrade these properties, whereas for IBAE, reduction of both PL intensity from a QW and hall mobility in a 2DEG are observed.
Twenty years of semiconductor surface and interface structure determination and prediction: The role of the annual conferences on the physics and chemistry of semiconductor interfaces
Authors: Duke C. B.
Published: July 2002

During the two decades 1974–93, semiconductor surface structure determination has evolved into a routine tool. This rapid evolution resulted from the confluence of three factors: the development of new techniques (e.g., scanning tunneling microscopy) and the improvement of old ones (e.g., low-energy electron diffraction), greatly increased reliability of vacuum equipment and electronics, and orders of magnitude enhancement in the speed and cost effectiveness of digital computers. A critical role of the annual conferences on the physics and chemistry of semiconductor interfaces (PCSI) in this evolution was to focus the attention of researchers on surface and interface structure as the key measurable intermediary between electronic materials processing and the performance of the resulting devices. Studies of several important systems, e.g., the (110) cleavage faces and (100) molecular-beam epitaxy growth faces of zinc blende structure compound semiconductors, were driven by events reported at PCSI conferences. These conferences were instrumental in stimulating the development of theoretical models which could extrapolate between vacuum surfaces, for which structural data have become readily available, and semiconductor heterostructures, for which comparable data are only now beginning to appear. Because of this development, the insight developed for vacuum surfaces is currently being applied to the prediction of interface specific electronic properties of semiconductor heterostructures (e.g., band offsets in heterojunctions and Schottky barrier heights in epitaxical metal–semiconductor junctions). In this way the PCSI conferences have forged a link between the surface science of semiconductors and the fabrication of microelectronic devices so that both evolve faster than either one would have otherwise. This article documents some specific examples of the nature and consequences of this process.
Microstructure and light emission in stain-etched Si1−xGex alloys
Authors: Pike W. T. , Ksendzov A. , Fathauer R. W. , George T.
Published: July 2002

The microstructure of stain-etched porous Si1−xGex layers has been studied using transmission electron microscopy (TEM) and chemical microanalysis and the results correlated with photoluminescence (PL) from the porous regions. High-resolution TEM imaging and diffraction indicate that the porous layers are mostly composed of amorphous material with some crystallites at the porous-substrate interface. Energy dispersive x-ray and electron energy-loss spectroscopies have been used to chemically profile cross sections of the layers and obtain porosity measurements at the nanometer level. All the layers have a porosity of between 70% and 80% and are substantially Ge rich compared to the unetched material. The PL from the porous layers drops off sharply with increasing Ge content of the stain-etched alloy and the redshift expected in the quantum-confinement model of light emission is absent. However the data is consistent with a simple model which assumes that the light-emitting species in the porous layers contains only a few atoms of Si.
Measurement of Si wafer and SiO2 layer microroughness by large sample atomic force microscope
Authors: Yasutake M. , Wakiyama S. , Kato Y.
Published: July 2002

Microroughness, which accompanies the miniaturization of device dimensions, is essential to the reliability of the device. The atomic force microscope (AFM) is available as a Si microroughness evaluation apparatus but most models cannot measure large size wafers in an environment with a lot of disturbance, such as a clean room. The AFM used for the measurement is a lever scan type in which a small scale optical lever defection detector and cantilever are installed at the top of a tube piezoscanner, and is linked to an optical microscope. It can accurately position within 4 μm on up to an 8 in. sample. The performance of this system includes a lateral resolution of approximately 5 Å and a Z direction resolution of about 0.5 Å. The CZ P-type (100) size 4 in. wafer used in the measurement is oxidized after three types of washing, and the relationship between the roughness of the bare wafer and the roughness of the oxidized wafer is measured.
Electron beam sublimation deposited and lifted-off carbon mask for InP reactive ion etching
Authors: Hur Katerina Y. , McKenna Thomas P. , Kazior Thomas E.
Published: July 2002

Carbon thin films produced by electron beam sublimation deposition and solvent liftoff have been used as reactive ion etch masks for etching deep trenches on InP. Using a Cl2:HBr:BCl3:Ar-based plasma in a reactive ion etcher, 15-μm-wide trenches were etched to a depth of 18 μm. The etch rate selectivity between InP and the carbon mask is better than 100:1. The resulting sidewall profiles are highly anisotropic due to the low sputter rate of carbon.
Crystallization process of Langmuir–Blodgett films of octadecylthiobenzoquinone
Authors: Garnaes J. , Bjo/rnholm T. , Jo/rgensen M. , Zasadzinski J. A.
Published: July 2002

Atomic force microscopy images of the electron acceptor 2-octadecylthio-1,4-benzoquinone prepared as 2–4 Y-type Langmuir–Blodgett films revealed the formation of nanoscale crystals one week after deposition. The crystals have a layered structure with a total height from 3 to 15 nm and they each covered an area of <1 μm2 on the substrate. In the plane of a layer, the molecules formed a two molecular rectangular unit cell with sides of 0.51±0.01 nm and 1.35±0.03 nm. The measured step height of a layer was 3.6±0.2 nm and gives a tilt of the alkyl chains of 54±3° relative to the normal to the interface between layers. The packing density of 0.34±0.1 nm2 per molecules in the plane of a layer is significantly different from the packing density on the water subphase during deposition and the packing density found on the flat Langmuir–Blodgett bilayer of about 0.26 nm2. This means that a transition from a two-dimensional packing to a three-dimensional bulk crystal has taken place. This transition is more easily induced on a hydrophobic silicon substrate than on a bilayer of hydrophobic fatty acid. Six months after preparation, the crystal had grown in size, and now covered a typical area of ≊15 μm2. The mobility of molecules necessary for this growth is discussed.
Sixteen-megabit dynamic random access memory trench depth characterization using two-dimensional diffraction analysis
Authors: Hatab Ziad R. , McNeil John R. , Sohail H. Naqvi S.
Published: July 2002

Advances in memory IC technology for dynamic random access memory (DRAM) devices have come about from a reduction in individual cell thickness with a corresponding increase in cell depth in order to maintain the same stored capacitance value. As the memory size on DRAM devices rises, memory cells must get deeper making the process of measuring depth more difficult. In this article we describe a novel, nondestructive, noncontact metrology technique which utilizes both two-dimensional diffraction analysis and multivariate statistical methods to measure deep trench depth in the 6–9 μm range. We applied this technique to two DRAM product wafers and obtained a successful prediction of trench depth for both wafers with an accuracy of ±0.04 μm, or ±0.56% variation relative to scanning electron microscope measurements of the same samples.
Reactive ion etching lag on high rate oxide etching using high density plasma
Authors: Akimoto Takeshi , Nanbu Hidetaka , Ikawa Eiji
Published: July 2002

In this article, reactive ion etching (RIE) lag effect dependence on total gas flow in contact hole etching is first investigated at a high oxide etch rate using high density plasma. We used surface wave coupled plasma apparatus, which achieves a high density of over 1011 cm−3 and a high oxide etch rate of over 1 μm/min. In the high gas flow etching process, a strong RIE lag is observed. However, the low gas flow etching process suppresses the RIE lag. Total gas flow dominates the RIE-lag effect, and the oxygen of the etching product plays an important role for reducing the RIE-lag effect.
Low-energy focused ion beam system and direct deposition of Au and Si
Authors: Yanagisawa Junichi , Kito Kuniyoshi , Monden Kentaro , Gamo Kenji
Published: July 2002

A low-energy focused ion beam system which is combined with molecular beam epitaxy apparatus was developed. Focusing characteristics were estimated by secondary electron and transmitted ion images. Using this system, the direct deposition of Au and Si was performed, which is important for in situ contact formation. Film purity was measured by Auger electron spectroscopy. Results show that the amount of impurities inside the film depends both on the deposition rate and on the chemical property of the deposition material.
Observation of 1.5 μm quantum confined Stark effect in InGaAs/AlGaAs multiple quantum wells on GaAs substrates
Authors: Kim Sam-Dong , Trezza John A. , Harris James S.
Published: July 2002

We demonstrate the quantum confined Stark effect near 1.5 μm in the InGaAs/AlGaAs quantum wells grown on GaAs. This is achieved through the successful growth of very highly mismatched InGaAs/AlGaAs multiple quantum wells (MQWs) on GaAs substrates by molecular beam epitaxy. In these devices, linearly graded InGaAs buffer layers are grown beneath the MQWs to minimize threading dislocations. Furthermore, to improve the material quality and interface smoothness of the MQWs, a very low growth temperature (280 °C) is used in addition to a one monolayer deposition of GaAs and growth interruptions on both sides of quantum wells. These devices clearly exhibit the quantum confined Stark effect as measured by electroabsorption at 300 K.
Highly sensitive positive resist based on vinyl ether chemistry
Authors: Taguchi T. , Yamashita Y. , Suzuki T. , Yamaoka T.
Published: July 2002

A new positive resist composed of a bifunctional vinyl ether monomer as crosslinker and a photoacid generator and an acidic base resin was investigated. This resist system utilizes the unique reaction of the vinyl ether monomer; the vinyl ether forms crosslinks of base resins by prebaking and the crosslinks are decoupled by acidolytic reaction via generation of an acid upon exposure. In order to investigate the lithographic properties for x-ray lithography, effects of crosslinker concentration and process conditions on the resist were evaluated. The resist has a high sensitivity of 35 mJ/cm2 and a high gamma value of 10. A good profile for 0.3 μm lines and spaces patterns is obtained. Furthermore, it is found that this resist system has high thermal resistance up to 180 °C against both pattern deformation and resist thickness loss.
Thick film positive photoresist: Development and resolution enhancement technique
Authors: McKean Dennis R. , Russell Thomas P. , Hinsberg William D. , Hofer Don , Renaldo Alfred F. , Willson C. Grant
Published: July 2002

The development of a positive, thick film photoresist consisting of a diazonaphthoquinone sensitizer and a novolac resin is described which has the capability of meeting a wide range of thick film requirements necessary for magnetic recording head fabrication. This photoresist system can coat 4–15-μm-thick films over various types of topography on a variety of different metal and dielectric surfaces (copper, Permalloy, and alumina). Moreover, this resist is compatible with copper, permalloy, and gold plating baths as well as different metal etchants. The photoresist can be used to produce images with wall profiles greater than 80° with a resolution capability approaching 2 μm lines and spaces in a 7.5-μm-thick film. Process latitude is demonstrated over a wide range of exposure doses and focus positions. Enhancement of thick film photoresist resolution has been achieved using a method which involves the treatment of photoresist films with dilute surfactant solutions. A number of factors have been found to effect the outcome of this method including the surfactant structure and concentration, the method and period of application, and the order of processing steps. Under proper conditions significant enhancement of photoresist contrast is observed which is accompanied by improvement of photoresist image profile and resolution. The method is particularly useful in electroplating applications.
Electron emission enhancement by overcoating molybdenum field-emitter arrays with titanium, zirconium, and hafnium
Authors: Schwoebel P. R. , Spindt C. A. , Brodie I.
Published: July 2002

Overcoating Spindt-type field-emitter-array cathodes with several monolayers of Ti, Zr, or Hf leads to a decrease in the voltage for the same emission current by 30 to 40%. This change is entirely ascribable to a 1 eV decrease in surface work function and an increase by a factor of 10 to 100 in the pre-exponential term of the Fowler–Nordheim relation. The postdeposition current voltage characteristics have been observed to remain essentially unchanged for periods of greater than 100 hours at current levels of 10 μA/tip. Field-emission micrographs indicate that the increase in pre-exponential term cannot be attributed to an increase in the emitting area. A plausible explanation is that the electron supply function for these overcoatings is larger than that of the as-fabricated emitter.
Pb/Si(111) investigation at the ultralow-coverage range
Authors: Gómez-Rodríguez J. M. , Veuillen J.-Y. , Cinti R. C.
Published: July 2002

The very early stages of Pb deposition on Si(111)7×7 surfaces have been studied by means of scanning tunneling microscopy. Variable temperature measurements combined with unusually long periods of imaging time have made it possible to analyze the dynamics of Pb atom pairs. The observations show that the pairs are actually mobile at room temperature within the half (7×7) unit cells where they are adsorbed. An activation energy of 0.40±0.04 eV has been measured for this thermally activated process.
Island, trimer, and chain formation on the Sb-terminated GaAs(111)B surface
Authors: Moriarty P. , Beton P. H. , Henini M. , Woolf D. A.
Published: July 2002

The surface structures resulting from the deposition of various coverages of Sb on the GaAs(111)B-(2×2) surface at room temperature, followed by annealing in the 100–375 °C temperature range, have been investigated using scanning tunneling microscopy. At low annealing temperatures Sb islands are observed displaying no ordered atomic structure, between which the As trimer based (2×2) reconstruction of the clean GaAs surface is visible. Annealing above 250 °C causes the formation of Sb trimers which are distinguishable from the remaining As trimers via contrast differences in filled- and empty-state images. Annealing at still higher temperatures leads to the creation of Sb chain pairs oriented along the substrate 〈110〉 directions, coexisting with regions of Sb trimer based reconstruction between the chain pairs. The local periodicity of the patterns of Sb trimers between the chain pairs is dependent on the separation between chain pairs.
Measurement of the backscatter coefficient using resist response curves for 20–100 keV electron beam lithography on Si
Authors: Watson G. Patrick , Fu Diana , Berger Steven D. , Tennant Donald , Fetter Linus , Novembre Anthony , Biddick Christopher
Published: July 2002

The effective backscatter coefficient η is a quantity that must be known with precision so that the proximity effect can be adequately compensated to minimize feature size variations in electron beam lithography. A unique technique to measure η that does not require the precise form of the backscatter dose distribution was employed. This method simply compares the resist response near the center of printed features that are much smaller and much larger than the characteristic range of the long range scatter. This technique was already employed to estimate the backscatter coefficient on Si at 100 keV beam energies. We have extended this measurement to determine η at lower beam energies. Results show that η on Si is 0.38, 0.50, 0.55, and 0.46 for 100, 50, 40, and 20 keV beam energies, respectively. Monte Carlo simulations indicate a trend of decreasing η with increasing beam energy, consistent with the experimental results except at 20 keV.
Defect properties of Si-, O-, N-, and H-atoms at Si—SiO2 interfaces
Authors: Lucovsky G. , Jing Z. , Lee D. R.
Published: July 2002

A chemical bonding model for defects and defect precursors at Si—SiO2 interfaces is presented. Bonding geometries of neutral and charged Si-, O-, N-, and H-atoms are described in terms of the valence shell electron pair repulsion model, thereby identifying a qualitative distinction between charged (a) Si-atoms, and charged (b) O-, N-, or H-atoms. Threefold coordinated Si- atoms are stable in three charge states (+, 0, and −), and can be active as trapping and/or recombination centers depending on their charge state. In contrast, there is a direct relationship between charge state and bonding coordination for O-, N-, and H-atoms, and as such their roles in defect generation processes are qualitatively different. Reaction mechanisms based on these differences in local bonding are (i) discussed for the generation of defects comprised of threefold coordinated Si-atoms, and/or positively charged H-, O-, and N-atoms, with coordinations of two, three, and four, respectively, and (ii) compared with experiments.
Nanofabrication using neutral atomic beams
Authors: Thywissen J. H. , Johnson K. S. , Younkin R. , Dekker N. H. , Berggren K. K. , Chu A. P. , Prentiss M. , Lee S. A.
Published: July 2002

We present a survey of neutral atom lithography. The combination of nm-scale features, large-area parallel deposition, and effective resists demonstrates the promise of atoms as a lithographic element. We demonstrate the transfer of 70-nm-wide features from a neutral atomic beam into a substrate using several resists, including self-assembled monolayers of alkanethiolates on Au and of alkylsiloxanes on SiO2, and “contamination” resists deposited from vapor. Unlike photons and electrons, noble gas atoms in energetic metastable states have an internal state structure that is easily manipulable, introducing the possibility of novel lithographic schemes based on the optical quenching of internal energy.
Integrated Fabry–Pérot distance control for atomic force microscopy
Authors: Ruf A. , Abraham M. , Diebel J. , Ehrfeld W. , Güthner P. , Lacher M. , Mayr K. , Reinhardt J.
Published: July 2002

This article reports on the first “standalone” optical atomic force microscope (AFM) based on an integrated Fabry–Pérot AFM sensor. The new AFM consists of two components: a cantilever with an integrated tip and a Fabry–Pérot cavity and an optical system for supply and detection of the light. A batch process for the reproducible production of the new Fabry–Pérot cantilever by thin film technology is described. The tip diameters achievable are below 10 nm. The Fabry–Pérot gap of approximately 7 μm realized reduces thermal drift and phase noise. The optical system is produced by high precision mechanics. It consists of one part that is fixed to the piezo tube and another part that can be exchanged. The advantage of the new AFM is the high resolution of the integrated optical detection system combined with an easy handling system for cantilever exchange without any adjustment. This makes the approach very attractive as a standard tool for inspection in semiconductor industry, surface manipulation on a nanometer scale, or surface studies in ultrahigh vacuum.
IC1 plasma etching of III–V semiconductors
Authors: Lee J. W. , Hong J. , Lambers E. S. , Pearton S. J.
Published: July 2002

Etch rates in excess of 1.5 μm/min for InP and InSb, 1.2 μm/min for GaAs and 0.7 μm/min for GaSb at room temperature were obtained in electron cyclotron resonance IC1/Ar plasmas at low additional rf power (150 W). There was little dependence of etch rate on microwave power over the range 400–1000 W for InP, and selectivities of 6–10 over mask materials such as SiO2, SiNx, and W were typical. Smooth surface morphologies were obtained over a wide range of plasma parameters for GaAs and GaSb, while preferential loss of P led to rough morphologies for InP at high rf powers. IC1-based plasmas appear to be promising universal etchants for Ga- and In-based III–V semiconductors.
InAs room temperature infrared photoconductive detectors grown by molecular-beam epitaxy
Authors: Liu Biing-Der , Lin Ray-Ming , Lee Si-Chen , Sun Tai-Ping
Published: July 2002

Despite the large lattice mismatch of 7.2% with respect to GaAs, the InAs photoconductor has been successfully fabricated on the GaAs substrate by molecular-beam epitaxy. Both the responsivity and the detectivity of the detector depend on the bias voltage across the device. When tested under an 800 K blackbody source, the highest achieved responsivity at 77 K is 34.5 A/W. The maximum specific detectivity is 1.3×1011 cm Hz1/2/W at 77 K. At 300 K, the highest responsivity and detectivity are 0.7 A/W and 2.1×108 cm Hz1/2/W, respectively.
Features of InGaAlAs/InP heterostructures
Authors: Ramam A. , Chua S. J.
Published: July 2002

InGaAlAs epilayers lattice matched to an InP substrate are grown by molecular beam epitaxy with band gap energies varying in the range 0.8–1.42 eV. The I–V/C–V characteristics of the Schottky diodes fabricated on InGaAlAs/InP heterostructures are investigated in the temperature range 80–300 K to study the variation of barrier heights with the Al mole fraction in the alloy. It is noted that at room temperature due to the dominance of thermionic emission the Schottky characteristics are not observable on low Al fraction structures, primarily because of the low metal–semiconductor barrier and low heterostructure barrier potentials. However, at 80 K the potentials are high enough to provide measurable characteristics. For an Al mole fraction of 0.23, the band lineup of the InGaAlAs/InP heterostructure changes from type I to staggered type II. Also, for the band gap engineered InGaAlAs alloys, the variations of mobility and doping concentration in the temperature range 80–400 K are presented as a function of the Al mole fraction in the alloy.
Deep, vertical etching of flame hydrolysis deposited hi-silica glass films for optoelectronic and bioelectronic applications
Authors: McLaughlin A. J. , Bonar J. R. , Jubber M. G. , Marques P. V. S. , Hicks S. E. , Wilkinson C. D. W. , Aitchison J. S.
Published: July 2002

We report on the use of CHF3, C2F6, and SF6 as etch gases for deep reactive ion etch processing of germano-boro-silicate glass films prepared by flame hydrolysis deposition (FHD). The glass film under study had a composition of 83 wt % SiO2, 12 wt % GeO2, and 5 wt % B2O3. The scope of the study was to identify the benefits and drawbacks of each gas for fabrication of deep structures (>10 μm) and to develop an etch process in each gas system. The etch rate, etch profile, and surface roughness of the FHD glass films were investigated for each gas. Etch rates and surface roughness were measured using a surface profiler and etch profiles were assessed using a scanning electron microscope. It was found that SF6 had the highest FHD glass etch rate and nichrome mask selectivity (>100:1) however, it had the lowest photoresist mask selectivity (<1:2) and highest lateral erosion. CHF3 had the lowest FHD glass etch rate but high selectivity over both nichrome (>80:1) and photoresist (>10:1) and the etch profile was found to be smooth and vertical. C2F6 had a similar etch profile to that of CHF3, but the selectivity over both mask materials was lower than in CHF3. Fused silica was used as a reference material where it was found the percentage drop in etch rate in C2F6, SF6, and CHF3 was −12%, −15%, and −37%, respectively. From the results presented here CHF3 proved to be the most versatile etch process as either photoresist or nichrome masks could be used to attain depths of 20 μm, or more.
SiGe/Si heterostructures produced by double-energy Si+ and Ge+, and Ge+ and Ge2+ ion implantations
Authors: Xia Zheng , Ristolainen Eero O. , Holloway Paul H.
Published: July 2002

Si 1−x Ge x / Si heterostructures were formed on Si(100) wafers by using single-energy Ge+ implantation, double Si+ and Ge+ implantations, or double Ge+ and Ge2+ implantations. Both near surface (hairpin dislocations) and end-of-range (EOR) damage (dislocation loops) were found. At high doses, EOR damage was found beyond the original amorphous/crystalline (a/c) interfaces after annealing. The double implantation processes using low energy and high dose Ge+ implantation to form a compositionally graded SiGe alloy layer, or using a high energy and low dose Si+ or Ge2+ implantation to form a deep amorphous layer, caused a spatial separation between the Ge maximum and a/c interface. Subsequent solid phase epitaxy anneals localized the EOR beyond the peak Ge positions. Rutherford backscattering spectroscopy channeling measurements confirm that the double-energy Ge+/Ge2+ method led to the fewest residual defects.
Rigorous simulation of mask corner effects in extreme ultraviolet lithography
Authors: Pistor Thomas V. , Adam Konstantinos , Neureuther Andrew
Published: July 2002

A windowing and multilayer acceleration methodology for rigorous electromagnetic analysis of extreme ultraviolet masks in three dimension is introduced and used to explore strong feature asymmetries associated with off-axis illumination. Specifically synthesizing large features from smaller simulation domains and replacement of the multilayer substrate by upward radiating equivalent sources are used and allow mask corner effects to be analyzed in about 10 h on a 200 MHz workstation. Windowing synthesizes the fields for a large mask feature from simulation of smaller domains such as corners. With off-axis illumination at angles of even a few degrees, hot spots in the near field occur at edges of the mask which face the illumination. This effect is associated with diffraction of the upward reflected light and its propagation in the presence of the side wall of the mask edge profile.
Molecular beam epitaxy growth of boron-containing nitrides
Authors: Gupta V. K. , Wamsley C. C. , Koch M. W. , Wicks G. W.
Published: July 2002

Layers of BN, BGaN and BAlN were grown by molecular beam epitaxy using ammonia on (0001) sapphire substrates. The crystal structure and material quality of these layers were assessed by reflection high energy electron diffraction, x-ray diffraction, Fourier transform infrared reflectance, and photoluminescence spectroscopy. These measurements reveal that while BN layers grow as polycrystalline films, BGaN and BAlN layers grow as single crystals with boron composition up to 2% and 6%, respectively. A monotonic increase in the band gap energy and a decrease in c-lattice constant were observed with increasing boron concentrations in BGaN samples. Yellow-band emission and increased surface roughening were also observed in samples with higher boron compositions.
Selective area chemical vapor deposition of titanium oxide films: Characterization of Ti(OC3H7)4 as an electron beam resist
Authors: Mitchell William J. , Hu Evelyn L.
Published: July 2002

We have shown that condensed multilayer films of titanium isopropoxide [Ti(−OC3H7)4] on cold GaAs(001) substrates are easily converted to nonvolatile titanium oxide deposits by exposure to a 10 keV electron beam. Using spatially resolved Auger electron spectroscopy, we have measured the initial kinetics of this electron beam induced decomposition reaction and have found it to be zeroth order (in precursor concentration) with an extremely high zeroth-order reaction cross section of (1.5±0.6)×10−14 cm2/electron. Consequently, exposures as low as 23 μC/cm2 result in titanium oxide films with thicknesses on the order of 5 Å. Moreover, the remaining unexposed precursor simply desorbs upon annealing to room temperature, ensuring selective area oxide deposition. The etch resistance of these titanium oxide patterns were characterized by etching in Cl2 at a substrate temperature of 250 °C. We found that exposures above 23 μC/cm2 produce robust, etch resistant oxide films which result in efficient pattern transfer to the underlying GaAs(001) substrate by etching. Moreover, clear undercut- and V-etch profiles were observed in the orthogonal 〈011〉 and 〈011̄〉 directions, respectively, characteristic of a crystallographic etch mechanism on the GaAs(001) surface.
Interferometry for end point prediction during plasma etching of various structures in complementary metal–oxide–semiconductor device fabrication
Authors: Layadi N. , Molloy S. J. , Esry T. C. , Lill T. , Trevor J. , Grimbergen M. N. , Chinn J.
Published: July 2002

We present results of an interferometric end point prediction technique for use in plasma etching of various gate and localized oxidation of silicon (LOCOS) structures in advanced complementary metal–oxide–semiconductor device fabrication. Etch experiments were carried out in a production high-density plasma source (decoupled plasma source) reactor made by Applied Materials. The end point prediction technique has been applied successfully to many samples and types of structures commonly found in integrated circuit manufacturing. These include: doped and undoped polysilicon material; patterned and unpatterned wafers; flat and topographic surfaces; resist and hard-mask patterned wafers with oxide underlayers of various thicknesses; and product wafers with varied pattern density. The ability to predict endpoint and avoid breakthrough of gate oxides as thin as 19 Å has been investigated. The end point detection system has also been shown to be effective in other etch processes including LOCOS etch, where the end point of the Si3N4 etch on the underlying SiO2 must be triggered as early as possible to avoid excessive oxide loss or etching of the Si substrate. The flexibility of the end point algorithm together with the external trigger controller are demonstrated to be crucial for successful end point prediction.
Fabrication of two-dimensional photonic crystal waveguides for 1.5 μm in silicon by deep anisotropic dry etching
Authors: Zijlstra T. , van der Drift E. , de Dood M. J. A. , Snoeks E. , Polman A.
Published: July 2002

Fabrication process for sharp waveguide bends in a two-dimensional photonic band gap structure in silicon is developed. The waveguide bend is defined by removing a row of pillars in a two-dimensional photonic crystal of 5 μm long, 205 nm diameter pillars placed on a square lattice with a pitch of 570 nm. To meet the severe nanotolerance requirements in such a device the SF6/O2 electron cyclotron resonance plasma process at reduced temperature is tailored to extreme profile control. The impact of main plasma parameters—i.e., temperature, oxygen/fluorine content, and ion energy—on the sidewall passivation process is unraveled in detail. Crystallographic orientation preference in the etch rate is observed.
EB-X3: New electron-beam x-ray mask writer
Authors: Morosawa Tetsuo , Saito Kenichi , Takeda Yuji , Kunioka Tatsuya , Shimizu Akira , Kato Junichi , Matsuda Tadahito , Kuriyama Youichi , Nakayama Yoshinori , Matsui Yasuji
Published: July 2002

The EB-X3 is an electron-beam mask writer designed to pattern x-ray masks with minimum feature sizes of 100 nm and below with good beam placement accuracy. The target patterning resolution is 50 nm, and a beam acceleration voltage of 100 kV is used to achieve it. This resolution has already been demonstrated using the previous version of the writer, the EB-X2 (developed last year), which also employs an acceleration voltage of 100 kV. On the other hand, the target placement accuracy for the EB-X3 is less than 10 nm, which is more than three times smaller than that for the EB-X2. To improve the placement accuracy, the resolution of the laser measurement system was changed from λ/128 (=5 nm) to λ/1024 (=0.6 nm), and the address unit was set to 1 nm, which yields a reproducibility of mark detection of 4 nm (3σ) and a calibration accuracy for deflection distortion of 5 nm(|mean|+3σ). In addition, the laser measurement system monitors five axes (X, Y, yaw, and pitch [X,Y]) and the results are fed back to position the beam. Furthermore, the signal fluctuations of the deflection, lens, and aligner circuits were reduced, so that beam fluctuations are kept under 2 nm. The EB-X3 was delivered to the ASET Super-fine SR Lithography Laboratory in March 1999, and is now being evaluated for use in x-ray mask fabrication. The prospects are good for achievement of a placement accuracy of 10 nm (3σ) in the near future.