bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of S and Se on the Schottky-barrier height and interface chemistry of Au contacts to GaAs
Authors: Waldrop J. R.
Published: July 2002

The electrical properties and interface chemistry of Au Schottky-barrier contacts formed on n-type GaAs (100) surfaces that had prior exposure (at room temperature) to elemental S or Se are compared to those of Au contacts to clean surfaces (ideal contacts). The interface Fermi-level energy EiF and chemistry during contact formation were investigated by x-ray photoemission spectroscopy (XPS). The Schottky-barrier height φB was measured by current-voltage and capacitance-voltage methods on the same interfaces characterized by XPS. The exposure of clean GaAs to elemental S or Se results in formation of a ∼5 Å surface layer of Ga and As chalcogenides via a limited chemical reaction. The Schottky-barrier height for Au contacts to the S or Se exposed surfaces had a 0.2 eV variation (0.8–1.0 eV) centered about the φB=0.89 eV value for the ideal Au contact. Changes in EiF over a ∼0.4 eV range occur in response to changes in interface chemistry during surface treatment sequences that include S and Se exposure and Au deposition.
A critical review of heterojunction band offsets
Authors: Duggan Geoffrey
Published: July 2002

Early work by Dingle and co-workers on the GaAs-(AlGa)As heterojunction established the fraction of the energy gap difference appearing in the conduction band to be 0.85. The experimental evidence and techniques which established this fraction and the subsequent evidence that has led to the questioning of its previous, almost universal, acceptance will be critically reviewed. Experimental evidence for the offset ratio in this system being dependent upon growth sequence will be discussed. Existing theoretical models will be discussed in the context of the above experimental work.
Adsorption of germanium and of oxygen on cleaved InP(110) surfaces: Auger electron spectroscopy and measurements of work function and of surface photovoltage
Authors: Koenders L. , Bartels F. , Ullrich H. , Mönch W.
Published: July 2002

The deposition of germanium as well as the chemisorption of molecular oxygen cause the formation of depletion layers on cleave InP(110) surfaces initially exhibiting flat bands, and on p- as well as on n-type doped samples the Fermi level is finally pinned (1.11±0.02) eV above the valence-band top Evs. From the surface band bending vs Ge coverage curves the energies of the chemisorption-induced surface states, i.e., their effective occupation levels, were evaluated as Evs +1.08 eV for the surface donors and Evs +1.15 eV for the surface acceptors. Chemisorbed oxygen, in contrast to germanium, introduces no surface dipoles on InP(110) and is thus incorporated rather than adsorbed. Both the unstimulated and the photon-stimulated interactions of unexcited molecular oxygen with InP(110) surfaces result in a phosphorous loss. After exposures of 1013 L of oxygen in the dark and when simultaneously illuminated by the light of a xenon-arc lamp the phosphorous loss is equivalent to a depletion of one and 1.65 InP layers, respectively, while the oxygen uptake amounts to 0.6 and 1.35 monolayers, respectively. Thus, an indium-oxide layer forms on InP(110) which finding is in agreement with the nonexistent chemisorption dipoles.
A new cross sectional thinning technique for transmission electron microscopy
Authors: Sweeney J.
Published: July 2002

A new method for obtaining transmission electron microscope (TEM) cross sections is presented which combines electron beam lithography, optical lithography, and reactive ion etching. The technique uses an electron beam to position and define a line pattern in a desired area. With the aid of a highly selective mask the pattern is transferred into the substrate with reactive ion etching. Uniform features 0.1 μm thick, 0.4 μm high, and 10 μm long have been fabricated for cross sectional viewing in TEM.
Al–Ga–GaAs multimetal Schottky diodes prepared by MBE
Authors: Svensson Stefan P. , Andersson Thorwald G.
Published: July 2002

Ga adsorption on a GaAs(001) c(2×8) surface prepared by MBE leads to cluster growth at room temperature. This has been observed directly from scanning electron microscopy (SEM) as well as in UV photoelectron spectra (UPS). Schottky diodes prepared from pure Ga metal show a large barrier height (φb≊1 eV). By depositing a thick Al layer on top of such a discontinous Ga film the properties of the bare areas will be characteristic for the Al–GaAs junction (φb=0.75 eV). The resulting metal semiconductor structure can be described with two parallel, ‘‘intermixed’’ diodes (Ga–GaAs and Al–GaAs) with varying relative areas depending on the amount of deposited Ga. The effective barrier height of this structure may consequently be tuned between 0.75 and 1 eV by controlling the Ga coverage on the GaAs, still retaining Al as the top metal for bonding of the device. Results are shown where the barrier has been increased from 0.75 up to 0.87 eV by a Ga surface coverage ranging from 0% to 50%.
Uniformity and crystalline quality of CoSi2/Si heterostructures grown by molecular beam epitaxy and reactive deposition epitaxy
Authors: Kao Y. C. , Tejwani M. , Xie Y. H. , Lin T. L. , Wang K. L.
Published: July 2002

The crystal quality and the lateral uniformity of CoSi2/Si epitaxial heterostructures grown by three different techniques have been investigated. The growth techniques used were molecular beam epitaxy (MBE), reactive deposition epitaxy, and solid phase epitaxy (SPE). The growth of the silicide and of silicon epilayers was carried out under ultra high vacuum conditions. Crystal quality was determined by Rutherford backscattering spectroscopy (RBS), and the surface morphology was studied using scanning electron micrographs. The crystal quality and lateral uniformity of silicide films grown by MBE in a proper condition were better than those grown by the other two techniques. Silicide films with minimum RBS channeling yields of 3% were successfully obtained using MBE. Further effort is needed to improve the lateral uniformity of the silicide films for fabrication of Si/CoSi2/Si epitaxial heterostructures.
Application of the GHOST proximity effect correction scheme to round beam and shaped beam electron lithography systems
Authors: Owen Geraint , Rissman Paul , Long Marsha F.
Published: July 2002

The GHOST proximity effect correction scheme has been applied to a round beam lithography system and also to a shaped beam system. It is shown that the image contrast of the GHOST scheme is constant at all spatial frequencies at which forward scattering is insignificant: the flatness of the modulation transfer function corresponds to the removal of the proximity effect. The effects of errors in the correction dose, the correction beam diameter, and the registration between the pattern and correction exposures have been calculated analytically, and it is shown that the allowable tolerances for these parameters are wide.
Determination of microscopic structural quality of molecular beam epitaxial grown GaAs/AlGaAs interface by high-resolution photoluminescence spectroscopy
Authors: Singh Jasprit , Bajaj K. K. , Reynolds D. C. , Litton C. W. , Yu P. W. , Masselink W. T. , Fischer R. , Morkoç H.
Published: July 2002

High-resolution photoluminescence measurements performed on several GaAs/Al0.25Ga0.75As multiquantum well structures revealed extremely sharp excitonic transitions separated in energies corresponding to roughly half-monolayer fluctuations in the well sizes. To understand these observations, a model for the interface in molecular beam epitaxy (MBE) is developed using studies of crystal growth. Results of this structural model are coupled with the theory of the effects of interface roughness on photoluminescence linewidth. A comparison of the experimental and theoretical studies shows that an interface formed under optimized growth conditions can be described by an interfacial layer made up of GaAs and AlGaAs islands. The sizes and the relative concentrations of these islands depend upon the precise instant at which the interface is formed. Consequences of this model for photoluminescence spectroscopy are discussed.
Nitrocellulose as a positive or negative self-developing resist
Authors: Geis M. W. , Randall J. N. , Mountain R. W. , Woodhouse J. D. , Bromley E. I. , Astolfi D. K. , Economou N. P.
Published: July 2002

Nitrocellulose functions as a self-developing resist when exposed to heavy ions (Ar+). However, when the resist is exposed to light ions (H+) the resist decomposes losing its nitrates and forming a nonvolatile residue. This residue consists primarily of carbon as determined by x-ray photoelectron spectroscopy (XPS). Nitrocellulose exposed to light ions, therefore, does not self-develop but forms a carbon-rich skin on the resist surface. These areas are protected by this skin during subsequent flood exposure with heavy ions, resulting in a negative resist image of the light ion exposure. The self-developing properties of nitrocellulose also make possible unique processing steps. One example is a dry lift-off. This has been accomplished by patterning the resist and evaporating metal onto the substrate and resist surfaces. The metal on the resist is lifted off with a jet of hot, dry nitrogen which volatilizes the resist and blows away the metal leaving only the metal previously deposited on the substrate.
Photodefinable carbon films: Control of image quality
Authors: Lyons A. M. , Hale L. P. , Wilkins C. W.
Published: July 2002

The direct photolithographic definition of insulating, semiconductive, and conductive films was achieved by pyrolyzing positive photoresist (HPR-206). Control of the feature dimensions was realized by two setps, UV irradiation followed by slowly increasing the pyrolysis temperature. A cross-linked polymeric shell is produced which is resistant to pattern flow. Parameters investigated for their effect on final feature size include UV dose, pyrolysis atmosphere, rate of temperature increase, pyrolysis temperature, and original feature size. The preparation of patterned films from pyrolyzed photoresist eliminates several processing steps and demonstrates the potential of direct lithography of carbon for integrated circuit manufacture.
Kinetics of the formation of normal and inverted molecular beam epitaxial interfaces: A reflection high-energy electron diffraction dynamics study of GaAs/AlxGa1−xAs(100) multiple quantum wells
Authors: Yen M. Y. , Lee T. C. , Chen P. , Madhukar A.
Published: July 2002

The static and dynamic behavior of reflection high-energy electron diffraction intensity is employed to demonstrate the existence of surface kinetics controlled optimum conditions for the customary molecular beam epitaxial growth of GaAs/AlAs superlattices. The quality of the interfaces formed even under such optimum conditions is shown to be critically dependent upon the individual layer thicknesses, even for ultrathin layers, and to deteriorate with the total superlattice thickness. Growth interruption after individual layer growth is shown to be only of partial, but significant, value in minimizing the adverse effect of the layer thickness.
Titanium silicide formation by ion beam mixing and rapid thermal annealing
Authors: Mattiussi G. A.
Published: July 2002

The need for and use of ion beam mixing of metal silicides for very large scale integrated (VLSI) circuit technology is discussed in the form of a literature review and tutorial paper. Where possible, the formation of titanium disilicide (TiSi2) is discussed, although other metal silicides are considered. Throughout the paper, the relevance of ion beam mixing to the formation of devices is emphasized. In addition, the integration of this technique into a VLSI process flow is presented. It is concluded that for the technique of ion beam mixing to be considered for VLSI processing, research should be concentrated on micrometer-sized features. In addition, ion beam mixing of Ti and SiO2 requires further investigation since the self-aligned complementary metal-oxide-semiconductor (CMOS) process demands negligible interaction between these two materials. With this in mind, it is suggested that ion beam mixing of W and Mo silicides presents an easier target.
Residue formation on Si surfaces in a CHF3 discharge environment
Authors: Vitkavage D. J. , Mayer T. M.
Published: July 2002

Ion beam simulation techniques are used to study fluorocarbon residue formation and substrate composition and structure modifications of silicon by CHF3 plasma environment. Fluorocarbon residues are shown to grow by direct ion incorporation or ion activated growth processes in ion beams over the energy range 50–1000 eV. At ion energy >150 eV concurrent sputtering of the overlayer film results in a steady state film thickness of ∼30 Å, relatively independent of ion energy. Films are fluorine deficient, with C/F ratio of 1–3 depending on ion energy, dose, and film thickness. Energetic ion (300 eV) penetration of the film results in continuous Si etching and substantial substrate modification. For 560 eV ion energy an ion-mixed interfacial layer of approximately 25 Å thickness is produced which contains substantial O, C, and F. A deeper (>150 Å) damaged layer is observed due to H+ implantation. Removal of overlayer films and interfacial layers by standard cleaning procedures is addressed.
Optimal surface and growth front of III–V semiconductors in molecular beam epitaxy: A study of kinetic processes via reflection high energy electron diffraction specular beam intensity measurements on GaAs(100)
Authors: Chen P. , Kim J. Y. , Madhukar A. , Cho N. M.
Published: July 2002

A systematic examination of the influence of each growth parameter on the surface kinetic processes in GaAs molecular beam epitaxy growth has been undertaken employing reflection-high-energy-electron-diffraction intensity dynamics measurement on GaAs(100) As-(2×4) surfaces. It is found that for growth temperature near congruent temperature the recovered growth front of grown GaAs is characterized by the lowest, though metastable, surface step distribution and thus appears optimal for formation of interfaces. The competition between the various growth condition dependent surface kinetic processes and their consequences for the surface and interface morphology are revealed by this systematic study.
Barrier height reduction in Au–Ge Schottky contacts to n-type GaAs
Authors: Iliadis A.
Published: July 2002

Current–voltage (I–V) and capacitance–voltage (C–V), measurements were combined with Auger electron spectroscopy (AES) to study the effects of heat treatment on Au–Ge Schottky contacts to n-type GaAs in the temperature range below the Au–Ge eutectic point (∼360 °C). Upon deposition and heat treatment of the contacts, the data showed two distinct stages of transformation at the metal–semiconductor interface. In the first stage a small fraction of Ge atoms, formed an interface layer with an effective n-type doping of one order of magnitude higher than the initial doping of the epitaxial layer and resulted in a current transport mechanism consistent with thermionic-field emission (TFE). In the second stage, while the effective interface doping remained the same, a substantial reduction of the barrier height from φb  (TFE)=0.75 eV at 250 °C heat treatment to φb  (TFE)=0.34 eV at 300 °C heat treatment was evident and was attributed to the increased disorder at the interface resulting from the indiffusion of the remainder large fraction of Ge (and Au) atoms. The effects of heat treatment appeared to predominantly increase the disorder rather than the doping at the emerging ‘‘heterointerface.’’
Dopant redistribution in silicide–silicon and silicide–polycrystalline silicon bilayered structures
Authors: Murarka S. P. , Williams D. S.
Published: July 2002

Dopants in any layer of the silicide–silicon or silicide–polycrystalline silicon bilayer structures are found to distribute readily throughout the bilayer affecting the electrical and the mechanical properties of the composite. In this paper the phenomenon of dopant redistribution in such structures is reviewed. The factors that influence the redistribution processes are (a) the diffusivity of dopants in the structure; (b) the solid solubility of dopants in the silicide and in the silicon; (c) the segregation coefficient of dopant at the surface and at the interfaces, and (d) the evaporative or the reactive losses of dopant to the heat-treating environment. Each of these factors is discussed. The available experimental results are reviewed in view of these considerations. It is shown that there are a large number of variables and that the available experimental results only provide a technological base for the use of dopants in the structures studied. To obtain a fundamental understanding of the process that determines the dopant redistribution, more carefully planned experiments will be necessary.
Unique very low temperature plasma-enhanced chemical-vapor deposition glass process for hot and cold wall commercial reactors
Authors: Dorrance R. H. , Schoenberg K. E. , Streif T. A.
Published: July 2002

High-quality glass and phosphosilicate glass films have been deposited as low as 165 °C in hot and cold wall plasma-enhanced chemical-vapor deposition (PECVD) commercial reactors. The dependence of hydrogen incorporation, chemical stability in buffered oxide etch, and the inducement of hillock growth in underlying Al films upon the deposition conditions have been investigated. In both hot and cold wall commercial reactors a unique process has been developed at 165 °C to deposit glass films which exhibit properties not unlike PECVD glass deposited at 380 °C. Hillock growth induced in Al films during glass deposition is eliminated at 165 °C. Deposition rate, uniformity, etch rate, refractive index, particle and pinhole density, and film stress are reported.
Control of dislocations in GaAs grown on Si(211) by molecular beam epitaxy
Authors: Ahearn J. S. , Uppal P. , Liu T. K. , Kroemer H.
Published: July 2002

The dislocation arrangements in GaAs films grown on Si substrates with (211) surface orientations were directly determined using transmission-electron microscopy in planar and cross-sectional views. The dislocations consisted of high density networks at the GaAs–Si interface and arrays of linear dislocations that propagated from the interface to the surface of the film on the (11̄1̄) planes. Burger’s vector determination of the arrays indicated that dislocations are introduced into the film primarily by a glide process and that the linear arrays are a remnant of the interface network. When strained layer InxGa1−xAs/GaAs superlattices were used, the linear arrays were observed to form a closed dislocation network, with the top of the loop structure coincident with the top of the superlattice. The dislocation density was markedly reduced above the superlattice. Our results indicate that careful control of the strain can be an effective means of altering dislocation distributions in the films.
Calculation of the valence band offsets of common-anion semiconductor heterojunctions from core levels: The role of cation d orbitals
Authors: Wei Su-Huai , Zunger Alex
Published: July 2002

The valence band offsets of the common-anion CdTe–HgTe, CdTe–ZnTe, ZnTe–HgTe, and GaAs–AlAs semiconductor pairs are calculated from the core level energies. The good agreement obtained with experiment for lattice-matched systems and a simple electrostatic model analysis suggest interface dipoles to have only a small effect. Furthermore, the microscopic origin of the failure of the common-anion rule in lattice-matched systems is identified: it is found that participation of cation d orbitals (neglected by tight-binding and pseudopotential approaches alike) in the valence band maxima is responsible for much of the band offset in these systems.
Studies of energy dissipation in resist films by a Monte Carlo simulation based on the Mott cross section
Authors: Murata K. , Kawata H. , Nagami K. , Hirai Y. , Mano Y.
Published: July 2002

The present paper applies a more accurate Mott cross section, which is calculated by the partial wave expansion to a Monte Carlo simulation of the electron energy dissipation process in resist films on substrates. Calculated spatial distributions of absorbed energy in a PMMA film on an Au substrate at 10 and 20 keV have shown an appreciable difference between the old and new models. A comparison between the two models will be made for developed resist profiles. Discussions also extend to a correction of the scattering probability near the resist–substrate boundary. This correction is significant when there is a large difference in atomic number between a film and a substrate.
Fabrication of large scale optical components in silicon by reactive ion etching
Authors: Darbyshire D. A. , Pitt C. W. , Stride A. A.
Published: July 2002

An improved procedure for etching silicon utilizes reactive ion etching in an SF6 plasma. The etch rate of single-crystal 〈111〉 silicon was measured as a function of power density and gas pressure. Etch rates of 3.5 μm/min were obtained at a pressure of ∼25 Pa and a power density of 0.25 W/cm2. Silicon-to-aluminum and silicon-to-photoresist etch rate ratios of better than 300:1 and 30:1, respectively, were achieved. The operation at high gas pressure resulted in improved etching uniformity and reduced surface pitting. A similar result was observed when a low concentration (5%) of oxygen was introduced into the SF6 plasma.
Electron scattering distribution in InP at 50 kV
Authors: Tennant D. M. , Doran G. E. , Howard R. E. , Denker J. S.
Published: July 2002

High-resolution patterning of InP is gaining importance for electronic and photonic applications such as distributed feedback lasers and high-speed transistors. Electron-beam lithography is the highest resolution and most flexible technology for these applications. Unfortunately, backscattered electron effects become an imposing limitation when both coarse and fine pattern features are combined or fill factor variations are encountered in a single writing level. These effects are substantially larger in InP than in Si, and it is necessary to better understand the electron scattering consequences to properly correct for proximity exposure. We have used point exposures in polymethylmethacrylate resist to make the first determination of the electron energy distributions on InP at 50 keV. These results are more directly useful for proximity corrections than the earlier data from line exposures on InP. We also report the first experimental estimates of the backscatter exposure coefficient ηe which is about twice that observed on Si. Optimum exposure conditions for various pattern requirements are also discussed.
Focused-ion-beam milling, scanning-electron microscopy, and focused-droplet deposition in a single microcircuit surgery tool
Authors: Sudraud P. , Ben Assayag G. , Bon M.
Published: July 2002

Inspection by microtomography of active devices, tuning, and repair of III–V microstructures and microcircuits have been performed using the capabilities of combined scanning-electron microscope (SEM) and low-voltage (0.5–20 kV) focused-ion-beam (FIB), or focused-droplet beam (FDB) system. In this instrument, the ion or droplet beams are focused simultaneously on the same point of the sample as the electron beam. In situ (SEM) images of the region to be machined or coated are displayed before, during, and after erosion or metal deposition. Gallium and indium FIB probes of 10 to 20 kV were used to cut functional parts of devices such as heterojunction bipolar transistors or field-effect transistors. Strong chemical contrast in the SEM mode displays very distinctly the different levels of the structure. This constitutes a promising method for fast nondestructive on-line control testing of a given device. Cuts of electrical connections have been realized. Surface resistance effects induced by the ion impact have been observed. Accurate resistor adjustment has been realized by FIB milling and controlled by in situ monitoring of the resistance. Indium and gold droplet beams have been focused on GaAs substrates. Best emission and focusing conditions have been determined giving deposited domains smaller than the structures previously obtained. Conducting connections have been fabricated by scanning the FDB and monitored by in situ recording the resistance during the establishment of the conducting bridges.
Dry etching induced damage on vertical sidewalls of GaAs channels
Authors: Pang S. W. , Goodhue W. D. , Lyszczarz T. M. , Ehrlich D. J. , Goodman R. B. , Johnson G. D.
Published: July 2002

Damage on the vertical sidewalls of narrow GaAs structures has been investigated. The structures consisted of narrow conducting channels between Ohmic pads. The channels were defined by either masked ion beam lithography or electron beam lithography with channel widths varying from 0.08 to 1.5 μm. Reactive ion etching and ion beam assisted etching were used to remove the epitaxial material outside the channels down to the semi-insulating substrates. Conduction in the channels was monitored by measuring current–voltage characteristics between the Ohmic pads. It is found that saturation current depends on the dry etching conditions such as ion energy, etching species, and impurity redeposition. Ion beam etching of GaAs substrates at different angles was used to separate out the effects of the inert ion species of reactive ion etching and ion beam assisted etching. Large increases in leakage current and impurity concentrations were obtained when the sample was mounted in the plane parallel to the direction of the ion beam, indicating that redeposition from fixtures and chamber walls can be significant. Controllable etching with minimal damage in GaAs is obtained by using low ion energy, reactive gases, and a contamination-free environment in the chamber. By optimizing the etching conditions, conduction was observed for channels with mirror-smooth sidewalls and widths as small as 0.08 μm.
A substrate doping variation study of the pinning states at metal/GaAs(110) interfaces
Authors: Miyano K. E. , Cao R. , Kendelewicz T. , Spindt C. J. , Mahowald P. H. , Lindau I. , Spicer W. E.
Published: July 2002

Schottky barrier formation at metal/n-GaAs(110) interfaces has been studied with photoemission spectroscopy by varying the substrate doping from 4×1016 to 5×1018 cm−3. The results challenge certain assumptions that have been made in past barrier formation models. For the clustered systems investigated—In, Ga, and Ag on n-GaAs— the issue of lateral inhomogeneity of the interface state density is considered. Assuming that the interface states exist only beneath the clusters, lateral variation of the surface potential is expected. An increase of the substrate doping reduces the lateral depletion and should thereby affect this variation. However the core level line shapes exhibit no evidence of an inhomogeneous surface potential for any doping or coverage, even when the depletion length is in the neighborhood of the average cluster spacing. Consequently scenarios are considered in which pinning states are more uniformly distributed than the overlayer material itself. In modeling low-coverage potential barrier formation, one might suppose that the net interface charge for a given low coverage is independent of the substrate doping. Under this assumption the total band bending for a given coverage is expected to be inversely proportional to the dopant concentration. For the systems examined in this study—In, Ga, Ag, Sn, and Sb on n-GaAs—an inverse relationship between band bending and doping is observed, but the dependence is much weaker than a proportionality. In the context of a defect model of the interface charge states, this weakened dependence may be explained in terms of a defect state whose nature depends on the local Fermi level position, as has been suggested by Walukiewicz [J. Vac. Sci. Technol. B 5, 1062 (1986)]. The effect of metallic screening from the overlayer on the doping dependence of band bending is also considered.
Prediction of equilibrium concentrations of defects and factors that influence them
Authors: Sankey Otto F. , Jansen Robert W.
Published: July 2002

An extensive theoretical study has been made on the factors that influence the formation of native defects and extrinsic impurity incorporation in semiconductors. A complete set of reaction equations within equilibrium statistical mechanics is used to predict defect concentrations of intrinsic and extrinsic defects. The competing reactions involving host atoms include vacancies, antisites, and interstitial defects and the extrinsic impurity reactions include anion and cation site substitutional and interstitial site impurities. The extrinsic and intrinsic reactions form a coupled system. Examples are given to illustrate how various factors influence defect abundances, and such factors include temperature, stoichiometry, the host material, and the chemical potential of the electron/hole system. It is found that extrinsic impurities have a profound effect on native defect abundances. The defect formation energies used in the theory are obtained from a recently developed pseudoatomic-orbital scheme using the local density approximation and pseudopotentials.
Submicron patterned doping of GaAs using a thin solid Si dopant source by transient excimer laser melting
Authors: Sugioka Koji , Toyoda Koichi
Published: July 2002

Patterned doping of GaAs using a thin solid Si dopant source by pulsed excimer laser melting is described. Linewidths as narrow as 0.3 μm are demonstrated. The power-dependent linewidth of the doped region agrees well with calculations of transient heat conduction in the substrate.
Errors in registration mark detection for electron lithography
Authors: Erasmus S. J. , Holley G.
Published: July 2002

Registration marks for electron lithography are usually detected by scanning with an electron beam and measuring the backscattered electron (BE) signal. If the registration mark is on the axis of the lithography tool, the BE signal is symmetric and the mark position may be found accurately. Practical electron lithography often requires that registration marks be found off axis, for example, near the edges of an exposure field. In this case, it is shown by both experiment and Monte Carlo calculation that the registration signals become asymmetric which causes registration errors. It is also shown that these errors can be reduced by a suitable choice of BE detector shape and position.
Characterization of damage on GaAs in a reactive ion beam etching system using Schottky diodes
Authors: Sugata S. , Asakawa K.
Published: July 2002

Chlorine (Cl2) reactive ion beam etching (RIBE)-induced damage on the GaAs wafer has been characterized by studing the characteristics of Schottky diodes fabricated on the etched surfaces. The ideality factors and the Schottky barrier heights measured by the current–voltage characteristics for ion extraction voltage range from 30 to 200 V at Cl2 gas pressure of 2×10−3 Torr and are comparable to those of the reference sample cleaned by HCl. Both the n value and the barrier height degrade for ion extraction voltage of more than 300 V. For higher Cl2 gas pressure, the damage on the etched surface is less. These results suggest that with the low-energy ions and high-Cl2 gas pressure, the damage of the GaAs surface is reduced significantly. The electron deep levels induced by RIBE disappear after annealing at 400 °C for 10 min.
Focused ion beam processes for high-T
c superconductors
Authors: Matsui S. , Ochiai Y. , Kojima Y. , Tsuge H. , Takado N. , Asakawa K. , Matsutera H. , Fujita J. , Yoshitake T. , Kubo Y.
Published: July 2002

Focused ion beam (FIB) processes have been developed for Y–Ba–Cu–O superconductor films. A Y–Cu liquid metal ion source has been fabricated, using a Y67 –Cu33 eutectic alloy as the ion source. As-sputtered Y–Ba–Cu–O film etch rate ratios to GaAs(100) and Si(100) substrates are 0.28 and 1.4 for 130-keV Au+ FIB ion etching, respectively. Y–Ba–Cu–O submicron patterns have been demonstrated by using FIB lithography and Cl2 reactive ion beam etching. Moreover, a Y–Ba–Cu–O superconducting line with 4-μm linewidth has been fabricated by annealing an as-sputtered Y–Ba–Cu–O line pattern. Tc control of Y–Ba–Cu–O film has been achieved by 200-keV Ne+, using conventional ion implantation and 300 keV Si++ FIB ion implantation.
Practical results of photomask repair using focused ion beam technology
Authors: Saitoh K. , Onoda H. , Morimoto H. , Katayama T. , Watakabe Y. , Kato T.
Published: July 2002

Practical results of photomask defect repair using focused ion beam (FIB) technology are presented. From Auger electron analysis, the deposited carbon film for clear defect repair contains 22% gallium, which is an element of the ion beam. Substrate damage produced by ion beam irradiation can be removed incorporating CHF3+O2 reactive ion etching. Printing results using a 5:1 stepper show that the FIB technology can be applied to photomask production.
Focused ion beam induced deposition of opaque carbon films
Authors: Harriott L. R. , Vasile M. J.
Published: July 2002

A one-step process for the repair of micron and submicron sized clear defects in photomasks is described. Opaque films are deposited at the intersection of the flux of organic monomers from a gas jet and a focused Ga ion beam. Focused ion beam induced deposition differs from other ion-induced, electron beam, and laser processes due to the very high ion current density, and the sputtering of the material as it is being deposited. We have explored the deposition–sputtering rate competition for several precursor materials as a function of gas jet pressure (molecular flux) and ion beam dose rate (scanning conditions). The deposition rate for our process is linear with ion dose at 330 Å per 1017 ions/cm2 and independent of dose rate over a wide range of conditions. The deposited films are cross-linked polymers containing as much as 25 at. % Ga, adhere to either Cr or glass, and are chemically inert. Scanning slit microdensitometry measurements show a white-light extinction coefficient of 2.2×10−3 Å−1. As a result, opaque deposits can be made at the same ion dose and beam scanning conditions used for Cr removal in mask repair.
Processing and characterization of GaAs grown into recessed silicon
Authors: Adkisson J. W. , Kamins T. I. , Koch S. M. , Harris J. S. , Rosner S. J. , Reid G. A. , Nauka K.
Published: July 2002

GaAs has been grown by molecular-beam epitaxy in silicon recesses to form a planar structure suitable for integration of GaAs and silicon devices. The layers were examined using scanning electron microscopy, transmission electron microscopy, and cathodoluminescence. Epitaxial regions inside the well appeared comparable to GaAs grown on unpatterned silicon wafers. Crystal quality of the epitaxial GaAs, determined by cathodoluminescence, appeared to be independent of the distance from the edge of the well; however, (111) stacking faults were present in the GaAs along the sidewalls of the well.
Growth and properties of doped CdTe films grown by photoassisted molecular-beam epitaxy
Authors: Hwang S. , Harper R. L. , Harris K. A. , Giles N. C. , Bicknell R. N. , Schetzina J. F. , Dreifus D. L. , Kolbas R. M. , Chu M.
Published: July 2002

Photoassisted molecular-beam epitaxy (PAMBE), in which the substrate is illuminated during film growth has been successfully employed to prepare n-type CdTe:In and p-type CdTe:Sb films. The n-type layers exhibit large electron mobilities at low temperatures. Field effect transistors have been fabricated from selected CdTe:In layers grown by PAMBE which show good device characteristics. The p-type CdTe:Sb films exhibit bright photoluminescence of excitonic origin at low temperatures. At 300 K, hole mobilities of 81 cm2/V s and carrier concentrations in excess of 1018 cm−3 have been achieved by the PAMBE technique.
The impact of epitaxial layer design and quality on GaInAs/AlInAs high-electron-mobility transistor performance
Authors: Brown A. S. , Mishra U. K. , Henige J. A. , Delaney M. J.
Published: July 2002

Ga0.47In0.53As–Al0.48In0.52As high-electron mobility transistors (HEMT’s) exhibit high transconductance and gain because of the high conductivities achievable in the structures. The effect of epitaxial layer design (spacer thickness and active channel thickness) on conductivity is examined. Device characteristics are examined as a function of active channel thickness. Reduced output conductance is observed for a 200 Å channel, but with a reduced transconductance.
Molecular-beam epitaxy growth of GaAs/InAs structures on (001)InP by alternating III/V fluxes
Authors: Katsumi R. , Ohno H. , Ishii H. , Matsuzaki K. , Akatsu Y. , Hasegawa H.
Published: July 2002

Modified molecular-beam epitaxy in which group V flux is suspended during 1 monolayer (ML) deposition of group III elements, is employed for growth of strained GaAs/InAs superlattices on InP substrates with a GaInAs buffer layer. By the reflection electron diffraction intensity study and by x-ray photoelectron spectroscopy, the modification of growth procedure is shown to result in fast formation of a flat growth front without intermixing, which is necessary for superlattice growth. GaAs/InAs superlattice structures grown by the present method are characterized by x-ray diffraction and transmission electron microscopy.
Ultrathin poly(methylmethacrylate) resist films for microlithography
Authors: Kuan S. W. J. , Frank C. W. , Yen Lee Y. H. , Eimori T. , Allee D. R. , Pease R. F. W. , Browning R.
Published: July 2002

To improve pattern fidelity of electron beam lithography in the nanometer regime a new class of ultrathin resist (less than 20 nm) has been investigated. Such films can be exposed with very low energy (<1 keV) electrons to virtually eliminate proximity effects or, at conventional electron energies, to allow easier proximity effect correction. In a previous study we investigated ultrathin (14 nm) poly(methylmethacrylate) (PMMA) films, prepared both by spin casting and Langmuir–Blodgett (LB) techniques, as high resolution electron beam resists. We reported that the pinhole density in 14-nm LB PMMA films was considerably lower than the density in spin-cast PMMA films of comparable thickness. 45-nm-wide lines were fabricated in 50-nm thick chromium films using LB PMMA films as resists. In this paper, we have investigated the lithographic performance of LB PMMA films with thicknesses ranging from 0.85 (one monolayer) to 7.7 nm (nine monolayer) exposed with different electron beam energies. Two distributions of pore-line defects, with diameter less than 20 nm, have been observed in the films after exposure and pattern transfer into chromium. The first distribution, observed only with PMMA resist films thinner than seven layers, was uniform over the sample, and the number of the defects increased dramatically as the film thickness decreased. The second type was only observed around the exposed regions in the films thinner than nine layers. For the second type, the number of defects was found to depend on the beam energy and substrate type. Sources of the two types of defects will be discussed, and the experimental results will be compared with a Monte Carlo simulation.
Conducting polyanilines: Discharge layers for electron-beam lithography
Authors: Angelopoulos Marie , Shaw Jane M. , Kaplan Richard D. , Perreault Stanley
Published: July 2002

This paper describes the use of electrically conducting polyanilines as discharge layers for electron-beam (e-beam) lithography. The emeraldine oxidation state polyaniline is a soluble material which can be doped by various cationic reagents, most commonly protonic acids, to afford conductivity on the order of 10° Ω−1 cm−1. The conducting polyanilines are incorporated as thin interlayers (2000 Å) in a multilayer resist system consisting of a planarizing underlayer (2.8 μm) and the imaging resist (1.2 μm) on top. We find that various acid-treated polyanilines eliminate charging during e-beam patterning of the resist, i.e., zero pattern displacements are observed as compared to the case where a conducting interlayer is not incorporated into the resist system. In the latter case placement errors greater than 5 μm are observed as a result of charging. A minimum conductivity of 10−4 Ω−1 cm−1 is required for the polyaniline interlayers in order to observe zero pattern displacement. In addition, we have simplified the doping reaction for polyaniline by inducing the conductivity photochemically or by e-beam exposure with the use of onium salts. This process resulted in the development of a new photo and e-beam conducting resist material.
A 1:1 electron stepper
Authors: Delong A. , Kolar̆ík V.
Published: July 2002

A new approach to the design of a 1:1 electron stepper has been suggested. A metal-insulator–metal (MIM) cathode is used in place of the photoemission one. The mechanism of the electron emission from the MIM cathode is markedly different from that of photoemission. In the MIM cathode the electrons from the base metal layer move through the thin dielectric layer, in which a strong electric field is generated (about 7×108 V m−1), into the outer thin metal layer. Those electrons that have enough energy remaining after scattering in the dielectric and outer thin metal layer (to overcome the work function barrier of the outer metal layer) will escape into the vacuum. Compared to photoemission, the described mechanism has some advantages if considered for use in electron projection lithography. For example, an emission current density of the order of 10−4 A cm−2; the cathode can be easily and quickly switched on and off with the image of the mask and independently of the orientation marks; and finally, the possibility of preparing cathodes outside the vacuum chamber of the stepper and their storing. To verify the advantages of the MIM cathode and experimental 1:1 electron stepper has been constructed and orientation experiments have been evaluated.
Effect of hydrogen implantation on shallow and deep levels in GaAs growth by molecular-beam epitaxy
Authors: Bosacchi A. , Franchi S. , Gombia E. , Mosca R. , Vanzetti L. , Allegri P. , Avanzini V. , Capizzi M. , Coluzza C.
Published: July 2002

GaAs layers grown by molecular-beam epitaxy (MBE) have been postgrowth hydrogenated by implanting low-energy hydrogen ions with a Kaufman source. Changes in the concentration of deep and shallow levels have been studied by DLTS and C–V measurements, respectively, for different hydrogen doses. A close match is obtained between the present results and those obtained for GaAs grown by the same MBE machine in hydrogen backpressure. Therefore, it is concluded that MBE growth with hydrogen results in hydrogen incorporation in the layers, and hence, in the passivation of shallow and deep levels.
Arsenic and gallium atom location on silicon (111)
Authors: Patel J. R. , Zegenhagen J. , Freeland P. E. , Hybertsen M. S. , Golovchenko J. A. , Chen D. M.
Published: July 2002

The x-ray standing-wave method is a powerful technique for accurately locating the position of impurity atoms at surfaces, interfaces, and in bulk crystals. Using UHV to prepare crystal surfaces and in situ x-ray experiments, we have addressed a number of problems in surface physics. Specifically the location of As atoms on Si(111) has been accurately established and has allowed for the first time a direct test of theoretical, density functional, total energy minimization, calculation of atom positions. For As, with only nearest neighbor relaxations, there is excellent agreement between theory and experiment. For Ga on silicon (111) the situation is much more complex. At low coverages (∼1/3 monolayer) the adatom T4 site for Ga has been accurately measured. X-ray standing waves were used to establish the vertical position and the in-plane registration site of Ga to the substrate silicon atoms was established both by standing waves and tunneling microscopy. At higher coverages, Ga occupies substitutional sites in the top half of the Si(111) double plane, but contracted inwards by about one-half of the distance between the Si(111) double planes. The consequences of the large surface strain generated by this contraction is discussed in the context of the standing wave and tunneling microscopy results. In addition, the atom positions that prevail when both Ga and As atoms are deposited on Si(111) are described.
Observation of polarization dependence of absorption in a quantum well wire array grown directly by molecular-beam epitaxy
Authors: Tsuchiya M. , Gaines J. M. , Yan R. H. , Simes R. J. , Holtz P. O. , Coldren L. A. , Petroff P. M.
Published: July 2002

The polarization dependence of absorption in an (Al,Ga)As–GaAs quantum well wire array was investigated. A theory incorporating the optical selection rule for a one-dimensional quantum system was developed. The optical anisotropy thus predicted was observed in photoluminescence excitation spectra of a quantum well wire array prepared directly by molecular-beam epitaxy on a tilted substrate. The ratio of the electron light-hole exciton peak intensity to the electron heavy-hole exciton peak intensity depends strongly on the incident light polarization. The observed anisotropy is shown to agree very well with the theory, which is the first evidence of two-dimensional quantum confinement in quantum well wires with widths of a few nanometers.
Resolution characteristics of a novel silicone-based positive photoresist
Authors: Tanaka Akinobu , Ban Hiroshi , Imamura Saburo , Onose Katsuhide
Published: July 2002

A novel silicone-based positive photoresist (SPP) is developed for a two-layer resist system. SPP is composed of an alkali-soluble silicone polymer (APSQ) and a diazonaphthoquinone compound as a sensitizer. APSQ is newly synthesized by means of acetylation of polyphenylsilsesquioxane (PSQ). A fine SPP pattern below 0.5 μm can be fabricated with a g-line stepper (NA=0.6) using a two-layer resist system. Moreover, a 0.4 μm line/space pattern is successfully fabricated at a defocus of ±0.4 μm. The high oxygen reactive ion etching (O2RIE) resistance of SPP makes possible the fabrication of a submicron pattern with a high aspect ratio in a two-layer system. Pattern width loss can be negligible during O2RIE of a 2 μm thick bottom resist when a 0.6 μm thick SPP is used as the top imaging layer.
Atomic arrangement at Cr/GaAs(110) interfaces
Authors: Liliental-Weber Zuzanna , O’Keefe Michael A.
Published: July 2002

To further explore the mechanism of Schottky barrier formation at a metal–semiconductor interface, high-resolution electron micrographs were simulated in order to interpret the contrast observed experimentally at Cr/GaAs(110) interfaces. Calculations for a wide range of defocus and sample thickness values, based on an assumed ideal arrangement of atoms at the interface, do not explain the observed contrast. Analytical data suggest that the interface is As rich. In this paper, therefore, only those point defects that lead to As-rich interfaces were considered. Among such point defects, Ga vacancies seem likely to contribute to such experimentally observed contrast.
Arsenic doped ZnSe grown by molecular-beam epitaxy
Authors: Shibli S. M. , Tamargo M. C. , Skromme B. J. , Schwarz S. A. , Schwartz C. L. , Nahory R. E. , Martin R. J.
Published: July 2002

We have been able to incorporate As into molecular-beam epitaxy (MBE) grown ZnSe in the range of 1017–1021 atoms/cm3 using Zn3As2 as the As source. This contrasts with very low As levels we obtained using an As cracker cell. The As incorporation is highly nonlinear with Zn3As2 flux and depends on the excess Se used. Several samples doped with Zn3As2 show low temperature photoluminescence with near band edge emission dominated by shallow acceptor levels. We will describe the details of several growth variations studied and their influence on As incorporation.
Boron evaporator for doping silicon thin films
Authors: Denhoff M. W.
Published: July 2002

A clean, stable boron evaporator has been designed and constructed. The design involves heating one end of a boron rod by a combination of radiation and electron beam heating. The evaporator was tested by doping polycrystalline silicon thin films by coevaporation. Doping levels up to 2×1020 cm−3 were obtained with 100% electrical activation. No metallic contamination was found in the thin films using secondary ion mass spectroscopy.