bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma-enhanced chemical vapor deposition of intrinsic microcrystalline silicon from chlorine-containing source gas
Authors: Platz R. , Wagner S.
Published: July 2002

Microcrystalline silicon (μc-Si:H) of truly intrinsic character can be deposited by plasma-enhanced chemical vapor deposition when dichlorosilane (SiH2Cl2) is added to the SiH4–H2 source gas. A dark conductivity of 5×10−8 S/cm, activation energy of 0.62 eV, and photoconductivity of 1×10−5 S/cm are obtained. The optical band gap for this material is approximately 1.1 eV. No special gas purification or microdoping is required. SiH2Cl2 added in small amounts has the additional effects of enhancing the crystallinity, and of reducing the oxygen incorporation by over a factor of 2. Sub-band gap absorption spectroscopy indicates a low defect density. Very high frequency deposition yields material with lower defect density and higher photoconductivity than material deposited using dc plasma excitation. Transition from amorphous to microcrystalline growth occurs during the first 100–150 nm of film growth. The oxygen content increases as the crystallinity increases. A first p-i-n solar cell with a 1.8 μm thick μc-Si:H(:Cl) i layer exhibits Voc=0.35 V, Isc=4.14 mA/cm2, and FF=55%, demonstrating device-quality material.
Experimental investigation of the respective roles of oxygen atoms and electrons in the deposition of SiO2 in O2/TEOS helicon plasmas
Authors: Granier A. , Vallée C. , Goullet A. , Aumaille K. , Turban G.
Published: July 2002

The respective roles of electrons and oxygen atoms in the plasma enhanced chemical vapor deposition of SiO2-like films are investigated in a low-pressure radio-frequency helicon oxygen/tetraethoxysilane (TEOS) plasma. The plasma and film growth are monitored by optical emission spectroscopy and in situ spectroscopic ellipsometry, respectively. The variations of the atomic oxygen density [O] (measured by actinometry) and the deposition rate are studied as a function of the organosilicon fraction in the O2/TEOS plasma. First, on the basis of these measurements and the data available in the literature, it is established that electrons have the key role in TEOS fragmentation while the contribution of O is shown to be very weak. Second, it is shown that organosilicon films deposited in a TEOS rich plasma are etched by O atoms when exposed to a pure oxygen plasma. The etching rate is proportional to [O] and is of the same order of magnitude than the deposition rate, which demonstrates that deposition and etching really compete in O2/TEOS plasma.
Mask charging and profile evolution during chlorine plasma etching of silicon
Authors: Bogart K. H. A. , Klemens F. P. , Malyshev M. V. , Colonell J. I. , Donnelly V. M. , Lee J. T. C. , Lane J. M.
Published: July 2002

Nonideal feature profile anomalies such as undercut, tapered, or bowed sidewalls and microtrenches at the base of trench sidewalls are often observed after etching masked silicon (Si) in chlorine (Cl2) plasmas. Off-normal impact with subsequent scattering and/or focusing of ions is believed to be the primary cause of these anomalies. Localized buildup of negative charge on the insulating mask sidewalls is one possible source of the ion deflection. Here we show that nearly identically shaped sidewalls and microtrenches were formed when Si features were etched in several Cl2 plasmas (the rf source and substrate bias powers and pressure were varied) regardless of whether the mask was insulating (SiO2) or conducting (Si or tungsten). Therefore, differential charging of the insulating mask material is not the fundamental cause of these profile characteristics. Ion angular distributions for each experimental plasma condition were estimated and the angle through which an ion would be deflected by a charged mask sidewall was calculated using simulated charged-mask field strengths reported in the literature.
Experimental and theoretical results of room-temperature single-electron transistor formed by the atomic force microscope nano-oxidation process
Authors: Gotoh Y. , Matsumoto K. , Maeda T. , Cooper E. B. , Manalis S. R. , Fang H. , Minne S. C. , Hunt T. , Dai H. , Harris J. , Quate C. F.
Published: July 2002

The single-walled carbon-nanotube (SWNT) was grown directly onto the top of the conventional Si atomic force microscopy (AFM) cantilever. This SWNT AFM cantilever was introduced into the AFM nano-oxidation process, which oxidized the titanium (Ti) metal film on the atomically flat α-Al2O3 substrate and formed the ultranarrow oxidized titanium (TiOx) line of 5 nm width. This TiOx line was used as the tunnel junction of the single-electron transistor (SET), and the SET fabricated by this process showed room-temperature Coulomb oscillation with periods of 1 V. It was determined by three-dimensional simulation that the tunnel-junction capacitance shows only weak dependence on the tunnel-junction width.
Early stages of silicide formation on W, Ni, and Pt surfaces, an atom probe, and field ion microscope study
Authors: Tsong T. T. , Wang S. C. , Liu F. H. , Cheng H. , Ahmad M.
Published: July 2002

The atomic structures and composition of silicide layers grown on W, Ni, and Pt surfaces have been studied in the atom probe and the field ion microscope. Four stages of silicide growth on W surfaces have been identified. On the W{112} plane, the atomic image structure of the top surface layer in the first stage, and the first three atomic layers in the second stage of silicide formation do not correlate well with the atomic image structures of WSi2. The W{110} plane does not react with Si atoms during the first two stages. In the third stage, the growth of thin WSi2 films proceeds nearly epitaxially from the W{001} planes to cover the entire W substrate, forming mismatches of silicide lattices along the [110] zone lines of the W. In the final stage, thick layers of polycrystalline silicides are formed. Their orientations are no longer well correlated to the W substrate. Atom-probe analyses show the stoichiometry of these atomically perfect polycrystallines to be WSi2. Identifications of crystal planes of WSi2 can be best done by comparing the image structures with the atomic arrangements of W in the silicide surface planes since the majority of Si atoms are not imaged in the field ion microscope. A pure Si atomic layer on top of the WSi2 (112) plane gives a faint image of ∼1% the regular image intensity of a W layer. FIM images show the W–WSi2 phase boundary to be very sharp. Thick layers of silicide of platinum and nickel have also been analyzed in the atom probe. The platinum silicide layers near the Pt interface have the composition of Pt2Si. Beyond the relatively sharp interface, a few Si atoms can still be found tens of atomic layers inside the platinum matrix. The composition of nickel silicide varies from one region to another. No sharp boundaries seem to exist between different phases. We also find the thick tungsten silicide films to be resistive to oxidation.
Surface potential measurements on floating targets with a parallel beam technique
Authors: Brunner M. , Menzel E.
Published: July 2002

Inspection of uncoated insulating samples in a scanning electron microscope (SEM) is possible by using low beam voltages in order to minimize charging effects. In this paper, the principal parameters affecting the target potential under bombardment by electrons are considered. The influence of primary beam energy and the detector (collector) potential have been investigated. Surface potentials were measured by evaluating the deflection of a ‘‘measuring’’ electron beam which passes parallel above the target surface. The dependence of the surface potential on the incident beam energy and the collector potential has been measured on several materials. Curves obtained for ceramic, glass, copper, and gold are presented. Crossover energies (emission ratio equal to unity) have been determined by these measurements on Au, Cu, Mo, C, Si, GaAs, Sapphire, SiO2, glass, ceramic, and polyimide.
The geometric structures of the GaAs(111) and (110) surfaces
Authors: Tong S. Y. , Mei W. N. , Xu G.
Published: July 2002

We present results of a reconstruction model proposed for the (2×2) GaAs(111) surface, together with a reexamination of the (1×1) GaAs(110) surface structure. Our model indicates that the reconstruction mechanisms on the (111) and (110) surfaces are similar to one another. In both cases, surface electronic energies are lowered via orbital rehybridization between nearest neighbor Ga and As atoms with dangling bonds. Reexamination of the GaAs(110) surface structure confirms our previous result of a tilt angle of ω=27°±2° and rejects a recently proposed value of ω=7°.
Reactive ion etching of GaAs using BCl3
Authors: Sonek G. J. , Ballantyne J. M.
Published: July 2002

The reactive ion etching of GaAs has been investigated in BCl3 plasma discharges. Etching rates have been characterized as functions of pressure (10–25 mTorr), power density (∼0.05–0.5W/cm2), and Cl2/BCl3 gas compositions. Rates of ∼12–20 nm/min have been obtained, and are significantly lower than for other chlorinated plasmas. Etching profiles exhibit a high degree of anisotropy and smooth surface morphologies.
Electrical properties of ideal metal contacts to GaAs: Schottky-barrier height
Authors: Waldrop J. R.
Published: July 2002

The electrical properties, with emphasis on Schottky-barrier height φB, of ideal (no interfacial oxide) contacts to GaAs have been measured for a diverse group of 14 metals by using current-voltage and capacitance–voltage methods. The contact interfaces were formed under controlled ultrahigh vacuum conditions by metal evaporation onto clean (100) surfaces of both n-type and p-type GaAs. The range of φB for n-type contacts is 0.96 to 0.62 eV in the decreasing order: Cu, Pd, Ag, Au, Al, Ti, Mn, Pb, Bi, Ni, Cr, Co, Fe, and Mg. For p-type contacts, the φB range is 0.45 to 0.62 eV. No simple correlation is apparent between φB and contact metal work function nor between φB and the metal–GaAs interface chemistry.
Oxygen ion beam etching for pattern transfer
Authors: Gokan H. , Itoh M. , Esho S.
Published: July 2002

Oxygen ion beam etching for resist materials has been studied. Etch rates of resists depend on oxygen pressure and on acceleration ion energy. The oxygen pressure dependence of etch rates is attributed to the effect of ion assisted neutral oxygen molecules. The neutral oxygen contribution leads to high etch selectivity for resist materials over metals; a selectivity more than 50 is obtained for AZ1350J over Au at 100 eV acceleration energy condition. The oxygen ion beam etching is applied to the pattern transfer for the multilevel resist technique. Hard baked AZ1350J, titanium, and PMMA are applied for a bottom layer, a middle layer, and a top imaging resist layer material, respectively. Under low acceleration energy conditions, an undercut profile is observed in the transferred patterns due to large ion beam divergence. At 500 eV, patterns having square cross sections are obtained. However, with the increase in gap aspect ratio (etch depth over gap width), a slight widening of etched channels at their midpoint (barrel shaped channel) is observed.
Excitation and ionization at surfaces: CO on metals
Authors: Avouris Ph. , Bagus P. S. , Rossi A. R.
Published: July 2002

We discuss the energetics, electronic structure, and stability of neutral excited and ionic states of adsorbates on metals using CO as a prototype. By ab initio cluster calculations we show that two types of negative ion states, bonding and antibonding, exist. We then show that the valence 4σ, 5σ→2π* excitations of chemisorbed CO are essentially unshifted from their free CO positions, while a charge-transfer excitation appears at ∼5–7 eV. Intra-adsorbate polarization effects are shown to be responsible for the spectral shifts of the corresponding core (C1s, O1s→2π*) excitations. The relation between screened positive ion states and neutral excited states is discussed. Finally, the connection between the above spectroscopic results and photon- or electron-stimulated desorption is examined.
Doppler shift laser fluorescence spectroscopy of sputtered and evaporated atoms under Ar+ bombardment
Authors: Husinsky W. , Girgis I. , Betz G.
Published: July 2002

The temperature dependence of the sputtering yield and velocity distribution of sputtered neutral Ca and Cr atoms has been studied by Doppler shift laser fluorescence spectroscopy (DSLFS) for 15-keV-Ar+ ion bombardment.These investigations have been performed in the search for thermal spike effects and radiation-enhanced sublimation in sputtering at elevated temperatures. Ca targets have been studied up to about 270 °C and Cr targets up to 750 °C. The shapes of the velocity distributions do not change in the respective temperature ranges for both target materials. Furthermore, the absolute yield of sputtered neutral ground state atoms does not increase with temperature.This indicates that no radiation-enhanced thermal contribution is of relevant importance. Moreover, we can explain the velocity distributions in both cases by the linear cascade theory of sputtering. The thermal contribution due to thermal evaporation increases drastically above 230 °C for Ca and 550 °C for Cr. In both cases the corresponding velocity distribution can be fitted by a Boltzmann distribution.
Formation of metal–semiconductor interfaces: From the submonolayer regime to the real Schottky barrier
Authors: Schäffler F. , Abstreiter G.
Published: July 2002

Schottky barrier formation with Ag and Au on n-GaAs (110) surfaces is studied by means of electric-field-induced Raman scattering (EFIRS). This technique allows to probe the potential barrier at the interface independently of interdiffusion processes and up to metal film thicknesses exceeding 100 Å. It is found that the Schottky barrier is partly established in the submonolayer range, but is subject to large changes (more than 40%) in the range of 6–30 Å average film thickness. This behavior is assumed to show the influence of bulk-metal properties on the Schottky barrier formation process.
Optical and photochemical factors which influence etching of polymers by ablative photodecomposition
Authors: Braren Bodil , Srinivasan R.
Published: July 2002

Two effects are observed in the etching of films of PMMA or polycarbonate by laser radiation of 193 or 249 nm wavelength, when the aspect ratio of the etched hole exceeds unity. The first is an optical effect which results in the edges of the etched area being ablated more slowly than the center. The second effect causes the etch depth per pulse to decrease with increasing depth. This effect is attributed to the partial absorption of the later part of the laser beam by material ablated from the surface.
A negative photoresist (TAS) for a bi-layer resist system
Authors: Saigo K. , Ohnishi Y. , Suzuki M. , Gokan H.
Published: July 2002

A new negative photoresist TAS for a bilayer resist system has been developed. TAS is composed of poly(triallylphenylsilane), PTASi, and bisazide. PTASi is prepared by the cyclopolymerization of triallylphenylsilane with benzoylperoxide (BPO) in refluxing benzene. PTASi has a five-membered ring and a six-membered ring in a main chain with an allyl group as a side chain. The cyclized structure gives a high softening point, 127–130 °C (Mw is 47 000). The allyl group and bisazide are highly sensitive to UV irradiation forming mainly an aziridine ring. The sensitivity (Dig) for TAS (Mw of PTASi is 49 000) is 0.8 s in a nitrogen atmosphere, while a suitable exposure time for Shipley photoresist MP-1300 is 7–10 s. TAS shows a high O2–RIE resistance. The thickness reduction of TAS under O2–RIE is only 1500 A compared to a 1.6 μm layer of Shipley photoresist MP-1300. Thus, TAS is suitable for use as the top layer in a bilayer resist system. Submicron patterns with steep profile are obtained.
Vertical n
p
n transistors by maskless boron implantation
Authors: Reuss Robert H. , Morgan Damon , Greeneich Edwin W. , Clark William M. , Rensch David B.
Published: July 2002

The use of a focused ion beam (FIB) system with a 0.2 μm beam diameter to fabricate npn bipolar transistors by maskless implantation of B (75 keV, 30 mA/cm2) is described. Devices with a conventional boron implant are fabricated on the same wafer. The material (SIMS profile, Rs) and electrical properties (transistor I–V characteristics) of the FIB implants are comparable to those for conventional implants. Initial evaluation suggests that the lateral spread of the implanted area is <0.1 μm. The similarity in results between the two implant processes demonstrates that the FIB system is functioning as designed (no serious problems with beam pointing stability, target current fluctuations, or introduction of impurities, etc.) and that no significant differences in beam target interactions (dopant distribution, percent activation, residual defects, etc.) occur. Application of an FIB lateral base implant to prevent emitter current crowding is discussed and the fabrication of transistors with lateral profiles demonstrated.
High resolution structuring of emitter tips for the gaseous field ionization source
Authors: Kubby Joel A. , Siegel Benjamin M.
Published: July 2002

Extraction of a stable, high brightness ion beam from an apertured field ion emitter surface requires microfabrication procedures to sculpture the surface topography on both microscopic (100 –1000 nm) and near atomic (10 –100 nm) length scales. Structuring on a near atomic scale is required to confine and stabilize the ion beam by local enhancement of the surface electrostatic field and to orient that emission on the optical axis. Control of the emitter contour on a microscopic scale is required for manipulating the supply of neutral molecules to the ionization site and also affects beam stability. We have developed a method using ion milling for configuring surface contour on microscopic and near atomic length scales which utilizes the morphological changes occurring at ion bombarded surfaces as a result of erosion by sputtering. A SEM study of the microscopic emitter topographical development is compared to computer simulations of the kinematical wave equation which depicts the erosion process. In this way, prediction of configuration on a length scale large compared to the ion penetration depth has been established. TEM observations show the surface development on the length scale of ion penetration depth. Preliminary results using this microfabricated emitter in a gaseous field ion source to produce a hydrogen ion beam with high angular beam confinement are given. Requirements for surface topography that are essential to obtain stable high brightness ion beams are discussed.
Current density distribution in a chromatically limited electron microprobe
Authors: Tuggle D. W. , Swanson L. W. , Gesley M. A.
Published: July 2002

Chromatically limited electron-microprobe systems are quite common in low-voltage scanning microscopy. The non-Gaussian blur disk and the asymmetric focal properties of the system are explained by considering the relation between source electron energy distributions and the spatial distribution of the current density in the vicinity of the image plane.
Very low resistance Au/Ge/Ni/Ag based Ohmic contact formation to Al0.25/Ga0.75As/GaAs and Al0.48In0.52As/Ga0.47In0.53As heterostructures: A behavioral comparison
Authors: Zwicknagl P. , Mukherjee S. D. , Capani P. M. , Lee H. , Griem H. T. , Rathbun L. , Berry J. D. , Jones W. L. , Eastman L. F.
Published: July 2002

High quality Ohmic contacts having specific transfer resistances in the range 0.06≲ ρt≲0.2 Ω mm have been fabricated using Au/Ge/Ni/Ag based metallizations on AlGaAs/GaAs and AlInAs/GaInAs heterostructures. For AlGaAs/GaAs the metallization consisting of 100 Å Ni/800 Å 80 at. % Au–20 at. % Ge/1000 Å Ag/800 Å Au accomplishes this at alloy cycles with maximum sample temperatures 540≤Tmax≤600 °C. The corresponding results for Al0.48In0.52As/Ga0.47In0.53As were achieved with 100 Å Ni/450 Å Ge/800 Å Au/200 Å Ag/800 Å Au, and with alloy cycles having 430 °C≤Tmax≤490 °C. The two semiconductor systems have been studied electrically using the transmission line model and analytically with the help of sputter Auger depth analysis, optical and scanning electron microscopy, and energy dispersive x-ray analysis. In this paper we shall discuss the differences in temperature dependence of metallurgical interactions between the two systems and the corresponding electrical behavior.
Effects of stress on the stability of x-ray masks
Authors: Karnezos M.
Published: July 2002

Accurate reproduction and overlay of submicron features with x-ray lithography puts very stringent requirements on the mask. The stability, flatness, and durability of the mask depend on, among other factors, the stress of the blank membrane and the total stress of the overlaying films. Stress is monitored using three different techniques. Metal absorber stress σm=0.1×109 dyn/cm2 or less with membrane stress σBN∼10 σm is needed for masks with distortion less than 5 ppm. Long-term stability of a boron nitride (BN) mask has been measured to be better than ±0.03 μm (1σ). Mask blanks with flatness <0.2 μm are routinely fabricated with high stress BN and flat glass. High durability membranes (E/1−ν=2.4×1012 dyn/cm2) with low defect counts (<1/cm2) make feasible direct metal deposition on BN and eliminate the use of polyimide.
Resolution limits in x-ray lithography calculated by means of x-ray lithography simulator X
M
A
S
Authors: Betz H. , Heinrich K. , Heuberger A. , Huber H. , Oertel H.
Published: July 2002

Resolution in x-ray lithography is influenced mainly by the exposure geometry, the resist’s behavior, and by the Fresnel diffraction as well. The range of photoelectrons created by the soft x rays, which can also effect the resolution, has been investigated theoretically and experimentally. The effective range remains below 20 nm depending on the resist material and on the exposure wavelength. As the photoelectrons do not limit the resolution in synchrotron lithography under practical conditions (proximity gap≥20 μm), this effect is not considered explicitly in the x-ray lithography simulator xmas which enables the three-dimensional simulation of resist profiles. The application of xmas to synchrotron lithography and the related one-layer resist systems reveals a Fresnel-limited resolution somewhere between 0.1 and 0.2 μm, depending on the actual resist parameters.
Rare gas ion-enhanced etching of InP by Cl2
Authors: McNevin S. C.
Published: July 2002

This paper presents a study of the ion-enhanced etching of InP by Cl2 using a modulated ion beam technique, in which pulses of rare gas ions impinge on an InP surface with coincident Cl2 and the resultant products are detected with a mass spectrometer. The stoichiometry of these products and the dependence of the ion enhanced etching on InP temperature and chlorine pressure are compared to the thermodynamically predicted chemical etching of InP by Cl2. The dependence of the ion-enhanced etching on ion current, ion energy, and ion mass are compared to the dependence on these parameters observed in the physical sputtering of InP. The experimental results are discussed in relation to a model in which the incident ion creates a transient thermal pulse (∼100 ° K) which causes the desorption of the relatively volatile indium chlorides from the surface. Of particular technological importance is the fact that large chemical enhancements over physical sputtering (>100/1) are possible with such a mechanism.
A mechanistic study of SF6/O2 reactive ion etching of molybdenum
Authors: Park Seong-ju , Sun Chung-ping , Purtell R. J.
Published: July 2002

In this work, the reactive ion etching of Mo by SF6 and O2 has been investigated by studying the etching mec hanism. The etching species, etch products, and Mo surface analysis by x− ray photoemission spectroscopy (XPS or ESCA) and electron energy−loss spectroscopy (EELS) have been analyzed to b etter understand the etching mechanism. (AIP)
The Schottky barrier at the InSb(110)–Sn interface
Authors: Förster A. , Tulke A. , Lüth H.
Published: July 2002

Ultraviolet photoemission (UPS) and electron-energy loss spectroscopy (HREELS) are used to study the Schottky barrier of InSb(110)–Sn. Sn deposition in coverages higher than 0.2 monolayers (ML) leads to pinning of the Fermi level near 100 meV above the conduction-band minimum. Since the Sn overlayers are in a polycrystalline or amorphous α-Sn modification the results are discussed within the model of a semiconductor heterojunction.
The etching of silicon in diluted SF6 plasmas: Correlation between the flux of incident species and the etching kinetics
Authors: Mahi B. , Arnal Y. , Pomot C.
Published: July 2002

Etching experiments of silicon in low pressure SF6/Ar and SF6/Kr plasmas under low energy bombardment are conducted using microwave multipolar plasmas. Experimental results using Langmuir probe, emission spectroscopy, and etch profile analysis show the evolution of the etch rate and anisotropy as a function of the density of the reactive species, the ion flux, and ion energy. A correlation between the flux of incident species and etching kinetics has been found. Evolution of the vertical etch yield per incident fluorine atom (result of the interaction process at the plasma–surface interface) as a function of the ratio of ion flux to fluorine atom flux (representative of the ion and fluorine atom generation in the plasma) implicitly allows the influence of certain external parameters such as pressure, excitation power, carrier gas to be taken into account. These results are compared with the current etching models, i.e., damage and sputter desorption models. A transition to perfect anisotropy is observed below a threshold of fluorine atom flux. This critical flux of reactive species itself is a function of the ion flux. The ratio of ion flux to fluorine flux for which lateral etching appears, decreases when the ion energy is increased. These results are analyzed in the light of a new diffusion model developed elsewhere.
Anisotropy of low-energy ion etching via electron cyclotron resonance plasma
Authors: Tobinaga Y. , Hayashi N. , Araki H. , Nakayama S. , Kudoh H.
Published: July 2002

Low-energy reactive ion etching is desirable as a method to fabricate devices, because it does not damage the sample surface. However, anisotropical properties are difficult to obtain with low energy ions. Thus, anisotropical properties with an electron cyclotron resonance (ECR) plasma etcher, with which it is easy to obtain a directional low energy (≤20 eV) ion flux, were examined. The conditions under which a clear enough anisotropical cross section figure was produced, were found and applied to sub-half-micron patterns. An ECR plasma etcher is used here with a standing wave cavity TE113 storing 2.45 GHz microwaves and with a sample chamber separate from the cavity. This kind of etcher does not permit control of an ion’s energy apart from the radicals. However, it is possible to control ionic performance by reducing the gas pressure to ∼1.0 mTorr and obtaining a satisfactory anisotropical etching mode. However, ion and molecule collision appear in the ion flux at that gas pressure. The collision makes disanisotropy; the collisional angle changed from about 15–25 deg for gas pressures from 0.2 mTorr to 1.0 mTorr. According to a simple theoretical calculation, the angle is about 30 deg on the assumption of a one time collision, about twice the value of the experimental result. At last, we obtained the high aspect ratio up to 10 at a gas pressure of 0.1–0.2 mTorr. It follows that it was possible to etch the sample well anisotropically with a low-energy ion flux without causing damage by using an Ion-Flux Type ECR etcher and controlling the gas pressure, and further without spoiling its undamaged nature.
Characterization of a reactive broad beam radio-frequency ion source
Authors: Lossy R. , Engemann J.
Published: July 2002

To overcome the problems of reactive gases on the lifetime of dc-ion sources for etching and deposition applications a capacitively coupled radio frequency (rf)-ion source has been developed. Details on the source characteristics will be given. The excitation of the ion-source plasma is achieved by an electrical rf field at 27.12 MHz. Different rf–electrode configurations are used. The plasma density is enhanced by a multipolar magnetic field. The ion beam is extracted by a multiaperture three-grid optics to obtain higher ion currents at low-ion energies. At a rf-power of 500 W for oxygen the 2-in. beam diameter leads to an ion current of 40 mA which is equivalent to 2 mA/cm2. Data on the beam divergence and the ion energy of the beam have been taken. A divergence of 2.3° could be measured. Different reactive and nonreactive gases were tested and the source operates without lifetime problems.
A comparison of boron emission characteristics for liquid metal ion sources of PtB, PdB, and NiB
Authors: Swanson L. W. , Bell A. E. , Schwind G. A.
Published: July 2002

The relative abundance, angular intensities, and energy distribution of B+ emitted from liquid metal ion sources of Ni4B6, Pd4B6, and Pt4B6 alloys on carbon are measured as functions of total emission current. Evidence is presented that shows the NiB system to possess the highest concentration of B in the liquid phase which, in turn, leads to the highest electric field at the emitting site for this system. While the NiB system exhibits the highest angular intensity for the B+ species, it also displays the highest value of the energy spread of B+.
A new method for improving gallium liquid metal ion source stability
Authors: Galovich C. S. , Wagner A.
Published: July 2002

The influence of backsputtered molybdenum and tin on gallium liquid metal ion source emission and focused currents is examined. In a typical ion gun arrangement, extractor and aperture surfaces act as sources of contaminant material. By selecting appropriate materials for the construction of these components, the stability of focused gallium ion currents is substantially improved. Materials which form a lower melting point solution when mixed with gallium, i.e., indium and tin, yield stable source operation and longer lifetimes. The implications of the long-term use of these materials in an ion gun are discussed, as well as the increased ability to analyze the effects of residual gases and secondary electrons on source operation.
Design of a low-aberration lens for focused ion beams
Authors: Tsumagari Takashi , Ohiwa Hajime , Noda Tamotsu
Published: July 2002

An electrostatic optical system with an intermediate beam crossover has been designed to produce a focused ion beam. In order to obtain the finely focused beam at the target, low magnification and low aberration are required for the illumination system because of the large size of the beam crossover. Chromatic aberration, which is dominant in focused ion beam systems with liquid metal ion sources, has been reduced by shortening the focal length of the objective lens in the illumination system. Using an objective lens with cone-shaped electrodes (focal length of ∼20 mm), calculation gave the maximum current densities of 0.93 and 100 A/cm2 for 5- and 150-kV beams, respectively, at the target under the following conditions: a virtual source size of 30 nm, angular current density of 20 μA/sr, and energy spread of 10 eV.
Energy distributions of liquid metal alloy ion sources
Authors: Arimoto H. , Miyauchi E. , Hashimoto H. , Komuro M.
Published: July 2002

The energy distributions of liquid metal ion sources using Au–Si–Be, Pd–Ni–Si–Be–B, Al–Si, and Pt–Si alloys have been measured. Profiles of singly charged ion species which are strongly dependent on alloy systems typically exhibit an abrupt rise at the high-energy position and gradual decay at the low-energy position in the profiles. This gradual decay, which appears rather like a subsidiary shoulder, may be caused by free space field ionization in addition to field evaporation. Profiles also have long tails at both the high- and low-energy positions. These tails can be explained by charge transfer collision between ions and neutral atoms coming from the outer space. The intensity of the tails is discussed on the basis of the charge transfer collision process.
Study of aging effects in a chemical amplification resist: SAL601-ER7
Authors: Liu Hua-yu , Seeger Judith , Poon Elaine , Olsen Robert J. , Graziano Karen A. , Anderson Susan E.
Published: July 2002

The shelf life and film life of the electron beam resist, Microposit SAL601-ER7 from Shipley, were studied. Solutions and films of this resist were found to exhibit a performance degradation which is a function of the storage time and temperature. Refrigeration significantly improves the stability of the resist. Component studies were used to determine that the shelf life problem is due to an interaction between the novolak resin and melamine crosslinker. Results indicate that considerable stability can be realized by using less reactive crosslinkers in the resist formulation.
Vapor phase silylation of resist images
Authors: Hiraoka H. , Patlach A. , Wade C.
Published: July 2002

The silylation of novolak resin-based resist images has been reported, in which a volume expansion of the photoresist image upon silylation with hexamethyldisilazane (HMDS) has been noted. The volume expansion becomes noticeable only when silylation occurs through the whole resist thickness and is particularly noticeable in geometries <1 μm. The volume expansion becomes insignificant with an estimated volume expansion of about 3% when silylation is restricted to only a superficial layer of about 100 nm thickness of the resist images >0.35 μm width. For vapor phase silylation at 95 °C, 1,1,3,3-tetramethyldisilazane and tetramethyl-2,5-disila-1-azacyclopentane were used along with HMDS, bis(dimethylamino)methylsilane and others. We studied the oxygen RIE resistance and bilayer resist image transfer of the silylated images, and carried out depth analysis of silicon incorporation by Rutherford backscattering spectroscopy (RBS). Without UV exposure the HMDS-silylated layer is very shallow, and considerable image flow occurs during the silylation reaction. Silylation with tetramethyldisilazane penetrates deeper and occurs at a faster rate, as shown by RBS data, but no swelling and no thermal flow of resist images were observed. Although a definite correlation was noted between the silicon distribution and oxygen RIE resistance, this resistance can differ considerably depending on the silylation agent, even when a similar silicon distribution is obtained. This is due to differing degrees of crosslinking.
Short-wavelength annular-field optical system for imaging tenth-micron features
Authors: Wood O. R. , Silfvast W. T. , Jewell T. E.
Published: July 2002

We have found that the 1:1 Offner annular-field system can provide high-resolution imaging in the extreme ultraviolet (XUV) when used at numerical apertures (NA’s) around 0.1. For example, when illuminated with radiation at wavelengths shorter than 15 nm, a 0.0835-NA system with a 233.6-mm-diam primary mirror should be able to image 0.1-μm lines and spaces in a 100-micron-wide, 50-mm-radius ring-shaped field at high contrast.
High-performance electron beam lithography for 0.5 μm semiconductor device fabrication
Authors: Sakashita T. , Nomura N. , Hashimoto K. , Koizumi T. , Harafuji K. , Misaka A. , Sawada N. , Kawakita K.
Published: July 2002

High-performance electron beam (e-beam) lithography is applied for fabricating contact holes with submicron size, using a new trilayer resist process. This technology consists of proximity effect correction software and the H+ ion shower irradiation technique onto a trilayer resist. The proximity effect correction software based on a dose modulation method was developed to control the dimensional accuracy of submicron patterns, by using the calculation of the double Gaussian exposure intensity distribution (EID) function. The dimensional accuracy of 0.5 μm contact hole and line and space patterns were kept within 0.05 μm. The H+ ion shower irradiation technique was adopted to decrease the charging problem. Ion shower was irradiated onto the bottom layer of the trilayer resist at 40 keV, 1×1016 ions/cm2. The sheet resistance of the bottom layer resist was decreased from 1013 Ω/⧠ to 107 Ω/⧠ by the H+ ion shower irradiation. The field butting error due to the charging problem was improved to 0.1 μm/3σ, and also the overlay accuracy was improved to 0.12 μm/3σ. When this high performance e-beam lithography was applied to fabricate 0.5 μm size contact holes, the yield of the 106 contact hole chains was improved to 90% by using selectively deposited W film on the bottom of the contact holes.
Advanced direct write electron beam lithography for GaAs monolithic microwave integrated circuit production
Authors: Hanes L. K. , Morris A.
Published: July 2002

Direct write electron beam lithography has been used for several years to pattern submicrometer and sub-half-micrometer gates for GaAs monolithic microwave integrated circuit (MMIC) devices. The e-beam systems used at this process step have generally been vector scan Gaussian beam machines operated in a step and write exposure mode. These systems have very low throughput and are better suited to research and development environments than large volume production. In order to meet the production requirements at the new Raytheon Monolithic Microwave Center, we have sought to adapt the Perkin–Elmer advanced electron beam lithography equipment (AEBLE)-150 system for use on GaAs. Results of early usage of the AEBLE system for direct write GaAs will be presented. Eightfold improvement in throughput for typical MMIC devices compared to results obtained on an earlier model e-beam machine will be shown. Both metalized (by liftoff) and etched alignment markers have been used; alignment strategy and a comparison of these alignment marks will be discussed. Results from the AEBLE demonstrating sub-half-micrometer lighography on GaAs will be presented. System issues related to handling GaAs wafers and areas in need of improvement will be briefly discussed.
One-dimensional ballistic transport in AlGaAs/GaAs electron waveguides
Authors: Behringer R. E. , Mankiewich P. M. , Timp G. , Howard R. E. , Baranger H. U. , Cunningham J. , Sampere S.
Published: July 2002

Recently, there has been growing interest in exploring the limits to scaling of semiconductor devices, and in understanding their characteristics in the regime where quantum effects and ballistic transport dominate. Using high-resolution fabrication techniques on high-mobility, modulation-doped AlGaAs/GaAs, it is possible to confine the two-dimensional electron gas (2DEG) to structures that are smaller than both the inelastic and elastic scattering lengths, and are comparable in size to the electron wavelength. The conduction of such a device should be one dimensional and ballistic. Unlike large samples, the resistance of these ballistic devices does not follow classical equations; it is primarily caused by electron interference and scattering from the geometry of the sample, not by impurities. On this scale, these structures behave as electron waveguides not as diffusive conductors. We have used electron-beam lithography and high-resolution reaction ion etching to produce samples with well controlled, complicated geometries. These devices use either depletion from an etched surface, or the application of a gate voltage to electrostatically confine the 2DEG to a narrow conducting channel. Transport measurements exhibit electron interference effects, nonlocal resistance fluctuations, resistance that does not scale with length, and quantization-of-resistance as a function of width and carrier density. The experiments correspond well to theoretical calculations of simple electron waveguides, and show that in these one-dimensional ballistic devices, the measured resistance is primarily caused by scattering from the structure of the sample itself.
Focused ion-beam crater arrays for induced nucleation of diamond film
Authors: Kirkpatrick A. R. , Ward B. W. , Economou N. P.
Published: July 2002

Diamond thin-films on nondiamond substrates characteristically exhibit a highly disordered polycrystalline microstructure and poor surface morphology. A major factor involved in this unsatisfactory growth behavior is a very-low density-of-nucleation on most surfaces. It is feasible that ion milling by a focused ion-beam can be utilized to introduce precise arrays of effective nucleation sites for diamond-film deposition. Possibilities for improved diamond-film microstructure and morphology are expected to result.
Exploration of scattering from topography with massively parallel computers
Authors: Gamelin J. , Guerrieri R. , Neureuther A. R.
Published: July 2002

Rigorous simulation of electromagnetic scattering from wafer topography has been achieved using the massively parallel Connection Machine CM-2. The program, based on a finite-difference time domain algorithm, can be applied to key structures in lithography and alignment with interpenetrating, isolated, or nonperiodic layers while incorporating dynamic effects such as bleaching of photoresist. The accuracy of the program is demonstrated by comparison with results from diffraction gratings analyzed by integral equation methods and by sample simulations of exposure and reflection from dielectric films. Several prototypical two-dimensional problems are explored to demonstrate the capabilities of the method including asymmetry effects in alignment, dynamic exposure near reflective steps, and diffraction in contrast enhancement materials. Steady-state calculations for a 20 λ by 10 λ structure are shown to require approximately 75 s on a prototype 1K processor system with projected performance of <5 s on a fully configured 32K (or larger) machine.
Resonant tunneling across and mobility modulation along surface-structured quantum wells
Authors: Ismail K. , Chu W. , Tiberio R. T. , Yen A. , Lezec H. J. , Shepard M. I. , Musil C. R. , Melngailis J. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We present results of fabrication and transport measurements on surface-structured quantum wells. The structures are fabricated on GaAs/AlGaAs modulation-doped layers. Three different devices are examined: the grid-gate lateral-surface-superlattice, the planar-resonant-tunneling field-effect transistor, and the multiple parallel quantum wires. In the first two structures, transport is perpendicular to the field-induced potential barriers. At 4.2 K, we observed evidence for resonant tunneling in both types of devices. In the third type of structure, transport is through isolated quantum wires parallel to the barriers. The presence of one-dimensional energy subbands, and mobility modulation, above and below the two-dimensional value, were observed.
Metrology package for electron beam exposure tool evaluation: Application to EBES4
Authors: Kung E.H. , Kostelak R. L. , Biddick C. J. , Vaidya S.
Published: July 2002

Throughout the stages of electron beam (e-beam) exposure tool development and application, the machine performance needs to be accurately characterized. A series of tests have been developed and implemented to diagnose and optimize the AT&T in-house EBES4 system for both mask making and direct wafer writing. The techniques employed for these tests will be described, and the evaluation results and how they lend themselves to machine diagnostics will be illustrated for EBES4.

The tests consist of a complement of optical inspection, scanning electron microscopy (SEM) imaging, MARKET analysis, and electrical probe metrology. Optical and SEM techniques served to examine the machine writing characteristics and exposure pattern quality. Partially developed images in positive resists accentuated errors due to improper exposure. Electrical probe metrology was used to quantify and optimize machine accuracy. Compared to conventional optical and SEM measurement techniques, electrical metrology offers the advantages of higher throughput, superior resolution and sensitivity, much better accuracy and precision, and abundant statistics. The standard manufacturing electron beam exposure system (MEBES) MARKET program was utilized to measure pattern misplacement due to intrafield and interfield distortions. The magnitude of stripe shear and butting errors was quantified by electrical linewidth measurement. The 256 μm stripe butting error on EBES4 has a mean value of 0.011 μm and 3 σ of 0.066 μm. Employing simple electrical testers such as box-in-box and bridge resistors, EBES4 demonstrated pattern placement precision of 0.069 and 0.066 μm, ‘‘‖mean‖+3σ,’’ in the x and y directions, respectively. Aligning globally to zero-level fiducial marks, machine level to level registration capability for direct writing was determined to be 0.093 and 0.110 μm, ‖mean‖+3σ, in the x and y directions, respectively. Again, with the aid of electrical testers, linewidth control across a 90 mm square writing area at 20 kV on EBES4 was measured to be 0.027 μm (3σ) for 0.375 μm isolated features. Such machine evaluation data can be used to prove-in system specifications, and can be fed back to both the machine designers and the users for system optimization and integrated circuits design rule development, respectively.
Silicon chemisorption on silver(111) and (100)
Authors: Chang Y. , Hwu Y. , Margaritondo G.
Published: July 2002

Photoemission spectra of silicon overlayers on Ag(111) and Ag(100) substrates reveal a significant difference in the interface width with respect to Ag deposited on silicon. The Schottky barrier height derived from our data, although affected by some residual uncertainty on possible band-bending effects, suggest instead independence of the deposition sequence.
Fluoride etch masks for high-resolution pattern transfer
Authors: Scherer A. , Van der Gaag B. P. , Beebe E. D. , Lin P. S. D.
Published: July 2002

We use thermally evaporated fluoride films as dry etch masks to fabricate sub-100 nm wide features into III–V heterostructures. Fluorides are compatible with lift-off processing and display excellent resistance to halide etch gas mixtures. Among the advantages which these materials offer over conventional metal masks are their thermal stability, good adhesion, high resistivity, the avoidance of ‘‘flags’’ arising from angle evaporation, and the ease with which they can be removed from the surface. By adjusting the composition of these fluorides and thereby controlling their grain size, we can optimize the resolution and erosion rates of our masks and fabricate structures with lateral sizes below 20 nm.
Electron beam testing of integrated circuits with multilevel metal
Authors: Radzimski Z. J. , Ricks D. A. , Wolcott J. S. , Russell P. E.
Published: July 2002

The use of voltage contrast techniques on passivated devices with multilevel metallization is discussed. The electric field distribution within a multilevel metal device is calculated using finite difference methods. This is used to determine the voltage coupled to the surface of a passivated device at points accessible to an electron beam probe. Additionally, a planar electrostatic grid is used to create an extraction field above the surface of the device. This extraction field is shown to dominate the surface charge buildup due to alterations in the secondary electron trajectories; thus allowing low energy electrons to be redirected to the device surface. This effect is compared with the effects of the field strength on the equipotential distribution; especially at the device surface.