bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of integrated-circuit vacuum processes: 1959–1975
Authors: Waits Robert K.
Published: July 2002

The quarter of the century from 1950 to 1975 witnessed the introduction of an extraordinary sequence of revolutionary silicon semiconductor products: the transistor, the monolithic integrated circuit (IC), the semiconductor memory, and the microprocessor. This ever-increasing complexity was made possible by a series of breakthroughs in manufacturing technology, fabrication processes, and measurement methods. Often an innovation involving vacuum technology appeared at just the right time to make possible the next technological leap. The metallization process is a good example. The components in the first practical IC were connected with a patterned layer of vacuum-evaporated aluminum. For the metal–oxide–silicon field-effect transistor to be reliable, a sodium-free evaporation process was required. The magnetically focused electron-beam evaporation source propitiously arrived to save the day. As metal connections became narrower, strange failures began to occur. The scanning electron microscope (operating under vacuum) was a new tool that let us examine the surface of an IC as if we were standing on its surface and gazing around. The metal failures were seen to be microcracks in the metal lines as they crossed over steps in the circuit topography. Geometrical analysis showed that shadowing during vacuum deposition caused the discontinuities. Heating the wafers to ∼350 °C increased the mobility of the depositing aluminum atoms so that they would fill in the gaps during film growth. Metallization failures due to electromigration, and the shorting of shallow junctions by silicon diffusion into the aluminum, had to be cured by adding small amounts of copper and silicon to the aluminum. Magnetron sputter sources came to the rescue. During these years, ion implantation, plasma etching, and low-pressure and plasma-enhanced chemical vapor deposition, all became mainstream manufacturing processes, without which today’s (and tomorrow’s) ICs would not be possible.
Molecular beam epitaxial growth of InGaAsP
Authors: Holah G. D. , Meeks E. L. , Eisele F. L.
Published: July 2002

The growth of high mobility In1−xGaxAsyP1−y on Fe-doped semi-insulating InP substrates using molecular beam epitaxy is reported. Room temperature mobilities up to 4600 cm2V−1s−1 have been obtained which are the highest yet reported. Photoluminescence data has been obtained for the first time for material grown by molecular beam epitaxy and show that lasing quality material has been grown. Material has been grown with band gaps near 1.55 μm which is the optimal wavelength for long distance data transmission in optical fibers.
AlAs–GaAs superlattices for optimum photoluminescence intensity
Authors: Laidig W. D. , Lee J. W. , Wortman J. J. , Littlejohn M. A.
Published: July 2002

Data are presented on a series of consecutively grown superlattices with different layer thicknesses. For each sample, the ratio of the GaAs layer thickness to the AlAs layer thickness was kept constant. In addition, the total thickness of the superlattice was the same for each sample, resulting in a set of samples differing only in the number and separation of AlAs–GaAs interfaces. Photoluminescence from these structures shows an initial intensity drop followed by a substantial intensity increase as the layer thicknesses are decreased. Data are also presented on a series of samples grown consecutively under identical growth conditions, with the exception that the substrate temperature was varied between 580 and 725 °C. Photoluminescence from these superlattices indicates the optimum growth temperature is in the region of 640–670 °C, where the photoluminescence intensity is a factor of 50 greater than for samples grown at lower temperatures. A calibration method, relating indicated growth temperature to actual growth temperature is described.
MBE growth and characterization of single crystal silicon oxides on (111) and (100)silicon
Authors: Maloney Timothy J.
Published: July 2002

Silicon molecular beam epitaxy has been used to prepare thin (500 Å) films of single crystal silicon oxide material, having from 25%–30% oxygen content, on (111) and (100)Si wafers. The films, called SiOz herein, were grown by evaporating silicon in the presence of oxygen at a wafer temperature around 675 °C. Single crystal films of pure silicon on top of (111)SiOz films have also been grown. The oxide material may be single crystal Si2O on (111)Si, but the ease of growing SiOz films on (100)Si indicates that perhaps oxygen incorporates in some other way. Auger data resembled AES data for amorphous SIPOS, while capacitance–voltage measurements possibly indicated a band gap step. This form of SiOz could be very significant if it can be used as a wide band gap semiconductor, compatible with silicon, and suitable as a wide band gap emitter for heterojunction bipolar transistors and ICs.
Surface and interfacial properties of Ga0.47In0.53As–Al2O3 MIS structures
Authors: Mullin Donald P. , Wieder H. H.
Published: July 2002

Field-effect-controlled electrical and galvanomagnetic measurements have been made on transistorlike five-terminal metal insulator semiconductor (MIS) structures using n-type 0.25 μm thick Ga0.47In0.53As epitaxial layers grown on semi-insulating InP substrates. These layers have an electron density n=3.5×1016 cm−3 and a mobility μn=7.5×103 cm2/V-s; 0.13 μm thick Al2O3 dielectric layers, grown by a rf plasma-assisted low temperature chemical-vapor deposition (CVD) process were employed as gate insulators under 0.01 cm2 vacuum-deposited aluminum gates. Hall effect and resistivity measurements were made on such structures and the experimentally observed gate voltage dependent change in resistivity and Hall coefficient of the conducting channel under the gate have been related to the corresponding change in the depletion depth of the surface space charge region. The data were used to derive the density of the surface states and their position within the fundamental band gap of Ga0.47In0.53As. We find that the surface Fermi level E*F of virgin MIS structures is pinned ∼0.2 eV below the conduction band minimum (0.55 eV above the valence band maximum) of Ga0.47In0.53As, in agreement with the experimentally measured and theoretically calculated barrier height of metal Ga0.47In0.53As diodes. Annealing at 120 °C for 16 h reduces the density of interface states by more than a factor of 2 and eliminates Fermi level pinning allowing the surface potential to be displaced over a substantial fraction of the fundamental band gap, in agreement with data derived from C–V measurements made on MIS structures with different types of dielectric layers using different annealing procedures.
An optical characterization of defect levels induced by MBE growth of GaAs
Authors: Contour J. P. , Neu G. , Leroux M. , Chaix C. , Levesque B. , Etienne P.
Published: July 2002

GaAs layers grown under As4 flux at 585 °C by MBE (p-type NID layers and n-type doped layers) have been studied by photoluminescence at 1.9 K (UV excitation, selectively excited photoluminescence, and excitation spectroscopy). The photoluminescence lines betwen 1.5110 and 1.5040 eV ascribed to excitons bound to point defects associated with the use of an As4 source have been more carefully studied in order to specify the nature of the transitions involved. Two hole spectra, and donor acceptor pair bands analysis allow to identify the excited states of two acceptor levels. The first one is attributed to the carbon contamination, the second one to which the 1.5109 eV exciton is bound is also a shallow acceptor level showing a negative chemical shift and a binding energy of 22.9 meV.
On the dependence of Schottky barrier height and interface states upon initial semiconductor surface parameters in GaAs {001}/Al junctions
Authors: Barret C. , Massies J.
Published: July 2002

Single crystal Al growth was achieved in situ by molecular beam epitaxy (MBE) onto n-type GaAs {001} epitaxial layers with surfaces ranging from the C(8×2) Ga rich to the 1×1 As rich compositions. Two kinds of characterization have been undertaken on Schottky diodes defined by photolithography: classical barrier height measurements by the current–voltage method and interface states spectrum determination by Schottky capacitance spectroscopy. From these experiments two types of results have been obtained: (i) there is no significant influence of the initial semiconductor surface stoichiometry nor of the metal work function on the Schottky barrier height; (ii) three kinds of interface states appear in the upper half of the band gap. The dependence of these states to the initial semiconductor surface stoichiometry is only weak. These results are discussed in light of the existing models of metal semiconductor interfaces.
Nitrocellulose as a self-developing resist with submicrometer resolution and processing stability
Authors: Geis M. W. , Randall J. N. , Deutsch T. F. , Efremow N. N. , Donnelly J. P. , Woodhouse J. D.
Published: July 2002

Nitrocellulose films have been shown to function as self-developing resist layers that are sensitive to both low energy ion bombardment by heavy ions such as Ar+ or Xe+ and to 193 nm UV radiation from a pulsed excimer laser. The resist develops at 0.6 μm s−1 for a beam of 2 keV Ar+ ions (1 mA cm−2), and has a sensitivity of ∼2 μm cm2 J−1 for ArF laser radiation, together with a demonstrated optical resolution of 300 nm. The decomposition products of the self-developing resist consist primarily of water, nitrogen, carbon monoxide, nitric oxide, and carbon dioxide. When exposed to light ions, electrons, ArF laser radiation at energy densities less than 20 mJ cm−2, or heat, the resist decomposes leaving a nonvolatile residue. The formation of this residue is believed to be responsible for the comparative stability of nitrocellulose under reactive ion etching. The reactive ion etching rate in CHF3 is about twice as fast for nitrocellulose as for SiO2. The etching rate can be reduced by the addition of volatile metal salts to the nitrocellulose, but this also reduces the rate of self-development produced by heavy ion bombardment.
A critical examination of submicron optical lithography using simulated projection images
Authors: Rosenbluth Alan E. , Goodman Douglas , Lin B. J.
Published: July 2002

It may be possible to extend optical lithography well into the submicron regime, given a multilayer resist system that confines imaging to a thin layer, and that eliminates reflection from the substrate. The necessary exposure and focus tolerances are determined by simulating the projection of partially coherent, diffraction-limited images onto an ideal multilayer resist system. Exposure–defocus diagrams are then generated by requiring that critical dimensions satisfy a ±10% tolerance. We investigate the prospects for submicron lithography with 0.75 and 0.5 μm minimum features. Two lens systems are analyzed; a commercially available 0.28 NA lens operating at 436 nm, and an advanced 0.35 NA lens operating at 365 nm. The features studied include contact holes, rectangular lines and spaces, and equal line space gratings, and are representative of many typical IC mask patterns. Linewidth tailoring or biasing allows these features to be printed within tolerance simultaneously if the exposure can be controlled within ±6%. The corresponding depth of focus is about 3 μm for the 0.75 μm features, and 1.5 μm for the 0.5 μm features. More general shape correction may be needed to print objects of arbitrary complexity.
Superlattice buffers for GaAs power MESFET’s grown by MBE
Authors: Schaff W. J. , Eastman L. F. , Van Rees B. , Liles B.
Published: July 2002

A study of three different types of buffers for GaAs power MESFET’s has been performed. Materials characterization was carried out by photoluminescence, DLTS and Hall measurements, and, as a final test, microwave performance of FET devices made from these materials was determined. It has been found that superlattice buffered structures consisting of 100 periods of 270 Å Al0.45Ga0.55As/30 Å GaAs show improvement in material quality and microwave performance over those of GaAs buffered devices.
Molecular beam epitaxial growth of GaAs millimeter-wave IMPATT diode material
Authors: Hoke W. E. , Labossier W. L.
Published: July 2002

GaAs millimeter-wave IMPATT diode material has been grown by molecular beam epitaxy. The epitaxial structure contained the double-drift Read doping profile. Silicon and beryllium were used as the N- and P-type dopants, respectively. The N and P spikes were 300 Å wide and separated by 800 Å of doped material. The substrate temperature was 590 °C and the growth rate was 1 μm/h. Although some Debye spreading is present in this thin-layered structure, useful doping versus depth information was obtained by capacitance–voltage (C–V) profiling. From the C–V measurements and secondary ion mass spectrometry measurements we did not observe any significant diffusion of the silicon and beryllium dopants with the above growth conditions. The maximum doping level of the spikes was 1×1018 cm−3. The epitaxial material was fabricated into single-mesa IMPATT diodes. Sharp reverse breakdown characteristics were obtained. The uniformity of the breakdown voltages over a 1 in. radius of the wafer was excellent. Initial rf measurements have been performed at 60 GHz. A cw power of 1.24 W with 11.4% efficiency was measured at 60.5 GHz. The diodes exhibit good ruggedness. Junction temperatures in excess of 250 °C have been obtained without burnout.
Morphological and chemical considerations for the epitaxy of metals on semiconductors
Authors: Ludeke R.
Published: July 2002

The generally strong chemical interactions between semiconductors and metals introduce additional complexities in the experimental characterization and modelling of epitaxial growth. This article reviews the relevant epitaxial parameters and growth modes in relation to what is known to occur on semiconductors. A salient property of some metals and semimetals is their tendency to form covalent bonds, whose directionality strongly influences the epitaxial relationship between substrate and overgrowth. Both the substrate orientation and, for the binary semiconductors, the stoichiometry of the substrate, strongly influence the epitaxial relationships. Representative examples of the different growth modes are discussed in relation to interfacial bonding, with emphasis on the growth differences between Al, a reactive metal, and Ag, a nonreactive metal on GaAs. The latter part of the article discusses some of the outstanding issues of the epitaxy of metals on semiconductors and possible approaches to their solution.
Heats of solution and substitution in semiconductors
Authors: Kraut Edgar A. , Harrison Walter A.
Published: July 2002

The heats of solution and substitution for one semiconductor in another are important quantities for an understanding of heterojunction formation. Harrison’s universal-parameter tight-binding method (1983) is used to obtain predictions for these quantities and for cohesive energies, defect formation energies, and solid-state core shifts as well. The cohesive energies and solid-state core-shifts are compared with experiment and antistructure defect energies are compared with earlier calculations by Van Vechten. Cohesive energies are accurate to about one-half an electron volt per bond. Agreement between experimental and theoretical cohesive energy differences is better. Predicted heats of solution and substitution depend on cohesive energy differences and therefore are likely to be realiable and are in accord with experiment in the few cases where experimental values are available. Antistructure defect formation energies agree well with Van Vechten’s earlier work. Predicted solid-state core shifts are only accurate to a few electron volts.
Control and characterization of metal–InP and GaAs interface structures formed by laser-enhanced reactions
Authors: Richter H. W. , Brillson L. J. , Kelley M. K. , Daniels R. R. , Margaritondo G.
Published: July 2002

We have used pulsed laser annealing to produce highly localized chemical reactions at the Al–InP and Al–GaAs interfaces. At successive stages of these laser induced reactions, we have monitored atomic movement and chemical structure on a microscopic scale using soft x-ray photoemission spectroscopy (SXPS) and Auger electron spectroscopy (AES). We have found a finite range of energy density such that a chemical reaction is promoted without disrupting the surface morphology. The reactions and atomic movements are explained by simultaneous melting of the Al overlayer and a thin layer of the semiconductor substrate.
Thermal-wave measurements and monitoring of TaSix silicide film properties
Authors: Smith W. Lee , Opsal Jon , Rosencwaig Allan , Stimmell James B. , Allison Jane C. , Bhandia Aloke S.
Published: July 2002

There presently exists the need to measure the postanneal thickness of silicide films deposited on Si. In addition, there exists the need to monitor the deposition parameters of silicide films, since variations in the deposition process may alter the film stoichiometry, density, and preanneal electrical resistivity. In this paper we describe results of efforts to satisfy these needs using a thermal-wave Therma-Probe 100.
Xerographic photoreceptors
Authors: Mort J.
Published: July 2002

A brief survey is given of the use of amorphous materials as xerographic photoreceptors. Included are a discussion of the basic physics and materials parameters required for operational devices and the methods of fabrication. The review includes current material classes such as chalcogenides and organic solids and new potential photoreceptors based on hydrogenated amorphous silicon.
Screening energy variations in silicon, silicon dioxide, and silicides
Authors: Wagner C. D. , Joshi A. , Gulbrandsen L. , Deal B. E.
Published: July 2002

Precise determinations by x-ray photoelectron spectroscopy of the Auger parameter for silicon, using a combination magnesium–gold x-ray source, disclose significant differences among values for crystalline, amorphous, and sputtered silicon. Detectable differences were found for silicon as an oxide for oxide films of different thickness. These differences appear to be due to the effect of disorder upon the polarizability of the atomic environment. The sharp change in polarizability across the silicon–silicon oxide interface would tend to broaden greatly the spectral lines from interface species; any observation of distinct lines from the interface requires three-dimensional aggregates in multiatom dimension, or an extremely ordered layered structure in the transition region. Silicon as a silicide has a parameter value more than 1 eV larger than that of crystalline silicon. Shifts in the values for the associated metal atoms are also indicated. The technique thus offers another way to examine physical and chemical states in surface layers.
Tensile stress in sputtered molybdenum silicide films
Authors: Ohfuji Shin-ichi , Nagano Jin
Published: July 2002

Isothermal changes in tensile stresses depending on the amount of MoSi2 formed in sputter deposited films which have multilayered structures of molybdenum and silicon (atomic ratio, Si/Mo=2) have been investigated. The amount of MoSi2 formed in the films was controlled isothermally by changing a layer thickness parameter t* from 0 to 220 Å which was the sum of both the molybdenum layer and silicon layer thicknesses. The films were deposited on oxidized silicon wafers and sintered in the temperature range 440–1000 °C. The tensile stress increases to 1.5×10 10 dyn cm−2 linearly with increasing 1/t* and saturates with further increase in 1/t*. Since 1/t* is proportional to the amount of MoSi2 formed in the films, the stress is found to increase with an increasing amount of crystallized MoSi2 in the films and to saturate when the whole multilayered films are completely converted into MoSi2 films. Furthermore, it is suggested that relaxation of the tensile stress occurs in proportion to the amount of crystallized MoSi2.
Ion implantation of arsenic in chemical vapor deposition tungsten silicide
Authors: Hara Tohru , Takahashi Hiroyuki , Chen Shih-Chang
Published: July 2002

Impurity profiles in arsenic implanted chemical vapor deposition (CVD) tungsten silicide (WSix) have been studied. Arsenic was implanted in WSi2.6 layer deposited on silicon substrates, and impurity profile measurements were performed by Rutherford backscattering spectrometry (RBS) techniques. Observed profiles in the as-deposited silicide can be fitted well with calculated Gaussian distribution. Carrier concentration profile measurements of silicon substrates indicate that tailing of the profile due to a channeling did not occur. Therefore, a sufficient masking effect has been achieved by this layer for use in a self-aligned gate implantation process. When annealing was done, the dissolution of excess silicon occurred from the nonstoichiometry silicide. Arsenic ion implanted into the silicide diffused into the silicon substrate. As a result, deeper junctions with a lower surface concentration is formed by furnace annealing. However, shallow junctions were formed by rapid thermal annealing (RTA).
Laser-driven metal cluster segregation in oxide matrices
Authors: Marinero E. E. , Pamler W. , Chen M. , Jipson V. , Lee W. Y.
Published: July 2002

We report on metal atom segregation within an oxide matrix as a consequence of absorption of short (≂12 ns) excimer laser pulses at 249 nm. The segregation phenomenon is investigated by the example of Au-TeO2 thin films on glass substrates using transient reflectivity and transmissivity techniques as well as ESCA analysis. ESCA depth profiles show drastic modification of the film composition upon laser exposure. Whereas the distribution of Au and TeO2 is homogeneous for the as-deposited films, the laser-irradiated areas show a total depletion of Au in the surface region exposed to the laser. We interpret this as a laser-driven segregation of TeO2 to the surface and correspondingly of Au towards the substrate. The time-resolved optical experiments show that the segregation takes place within 30 ns following the laser pulse. The reflectivity and transmissivity changes are characterized by a sharp fluence threshold corresponding to the melting of the film surface.
Reflection high energy electron diffraction intensity behavior during homoepitaxial molecular beam epitaxy growth of GaAs and implications for growth kinetics and mechanisms
Authors: Lewis B. F. , Grunthaner F. J. , Madhukar A. , Lee T. C. , Fernandez R.
Published: July 2002

The dynamic behavior of GaAs surfaces during and after growth by MBE has been probed by detailed measurements of the specular beam intensity in RHEED patterns from the surfaces. The damping of the intensity oscillations observed after growth has commenced is shown to be a strong function of arsenic pressure with high pressure causing strong damping and rough growth fronts. The specular beam intensity after steady-state growth has been interrupted shows first an initial fast increase with the largest increase occurring at low arsenic pressure, and then a slow recovery to its equilibrium no-growth intensity at a rate that increases with arsenic pressure. Measurements of the intensity recovery after short growths on an equilibrated no-growth surface provide new information about the growth front behavior during the first few monolayers of growth. The surface recovers in the shortest time after deposition of either a small fraction of a monolayer or slightly more than an integer number of monolayers. Recovery is slow after deposition of half a monolayer due to the resulting high step density. Surprisingly, recovery is slowest after deposition of 1.0 monolayer, indicating that such surfaces are very different from the equilibrium no-growth surface.
Quantitative Auger analysis by depth profiling of line shapes: Application to native oxide-InSb interfaces
Authors: Bregman J. , Shapira Yoram
Published: July 2002

We report on a technique developed for improving quantitative analysis of Auger electron spectroscopy data by monitoring line shapes, peak energies, and ratios, in addition to peak heights, as a function of sputtering time. The technique proves to be useful for analysis of InSb-native oxide interfaces due to the sensitivity of the AES lines of the different constituents to their chemical state. Thus important information can be obtained on the detailed structure and composition of these oxides and their interfaces, specifically, concerning quantitative determination of interface boundaries. The technique is discussed with typical results and possible extension to other interfaces.
Automated growth of AlxGa1−xAs and InxGa1−xAs by molecular beam epitaxy using an ion gauge flux monitor
Authors: Wunder R. , Stall R. , Malik R. , Woelfer S.
Published: July 2002

We demonstrate the use of a nude ion gauge flux monitor coupled to a high resolution digital voltmeter in setting the beam fluxes for the growth of In0.53Ga0.47As on InP by molecular beam epitaxy (MBE). Computer control has been implemented for both the flux setting and growth operations. Typical lattice mismatches were less than 1.5×10−3. We have also demonstrated, to the best of our knowledge, the first totally automated growth of In0.53Ga0.47As on InP by MBE. This growth incorporated computerized flux settings, oxide removal, and growth and gave a lattice mismatch of 1.0×10−3.
Tunable barrier heights and band discontinuities via doping interface dipoles: An interface engineering technique and its device applications
Authors: Capasso F. , Mohammed K. , Cho A. Y.
Published: July 2002

We present, for the first time, a technique to effectively tune barrier heights and band discontinuities at semiconductor heterojunctions using doping interface dipoles (DID). The DID consists of two ultrathin ionized donors and acceptor sheets in situ grown within 100 Å of the heterointerface by MBE. Using a DID the photocollection efficiency of an AlGaAs/GaAs abrupt heterojunction has been increased by one order of magnitude. Detailed investigations show the importance of nonequilibrium and hot electron transport effects and tunneling in heterostructures with DIDs. Several new applications of this concept are discussed. A DID can be used to convert a type I heterojunction in a type II or staggered heterojunction. A DID at the heterointerfaces of superlattice and staircase avalanche photodiodes can further enhance the ionization of electrons at the conduction band steps. The speed of heterojunction photodetectors such as the ones employing InP/Ga0.47In0.33As can be enhanced by a DID without requiring grading of the interface. The effects of doping fluctuations in the charge sheets of the DIDs on transport properties across the heterointerface are also briefly discussed. The DID represents a new interface engineering technique in the sense that it allows one to selectively engineer the energy band diagram of a heterostructure within less than 100 Å from the heterointerface and as such has important implications for the physics of interfaces and the design of novel devices.
SiO2 planarization by two-step rf bias-sputtering
Authors: Mogami T. , Morimoto M. , Okabayashi H. , Nagasawa E.
Published: July 2002

A new angled-surface-moving model for surface planarization by rf bias sputtering is proposed. This planarization is achieved by angular selective etching of SiO2 films on top of metal stripes. A two-step rf bias-sputtering technique was developed, based on the new model. In this technique, the substrate bias voltage was changed in two steps during bias sputtering. The first step was to fill gaps without microcracks. The second step was to planarize at higher substrate bias. The planarized SiO2 layer surface, deposited on thermally oxidized Si wafers with Mo stripe patterns, had good flatness. A planarized 4-level metallization test structure was fabricated by the two-step rf bias-sputtering.
Germanium incorporation in heavily doped molecular beam epitaxy grown GaAs:Ge
Authors: Li Ai-zhen , Milnes A. G. , Chen Z. Y. , Shao Y. F. , Wang S. B.
Published: July 2002

Germanium is normally an n-type dopant in MBE GaAs but compensation and p-type action has been observed under certain conditions. Studies have been made of the growth conditions under which  p+ and  n+ layers are obtained with heavy Ge fluxes during MBE GaAs growth on GaAs substrates at 570 °C. Both  p+ and n+ dopings in excess of 1020 cm−3 have been observed. The production of  p-type layers is favored by As4/Ga ratios of 2–3:1 and high Ge fluxes. For As4/Ga ratios of 4–5:1 and Ge fluxes corresponding to dopings of the order of mid-1018 cm−3 or less, the layers grown are n-type. For As4/Ga ratios greater than 6:1, the layers may be n+ type with concentrations that are 1020 cm−3 or higher as given by capacitance measurements or van der Pauw measurements. Photoluminescence studies at 4 K for 1020 cm−3 doped layers show a broadband with a maximum at 1.27–1.33 eV for n+ layers, and for  p+ layers a broadband luminescence with evidence of peaking at about 1.38 and 1.35 eV. Transmission electron microscope studies show almost no tendency for the formation of a second phase or microprecipitation in the most heavily doped (2×1020 cm−3  p and n) specimens. Finally, the paper considers the possible role of the species GeGa, GeAs, (GeGaVGa), and (GeAsVGa) and other complexes in the doping effects observed.
GaAs/AlGaAs multiquantum wells grown on nonpolar semiconductor substrates
Authors: Masselink W. T. , Fischer R. , Klem J. , Henderson T. , Morkoç H.
Published: July 2002

We report the first study of single-crystalline GaAs grown by molecular beam epitaxy (MBE) on a nonpolar substrate. In this study, GaAs was grown under various conditions on Ge(100). Surface morphologies were specular and quite strongly dependent on surface preparation. Photoluminescence spectra from such GaAs is quite intense and is dominated by donor–acceptor recombination at 1.479 eV which appears to be Ge0Ga−Ge0As. We also observe its phonon replica at 1.442 eV and the recombination of bound excitons at 1.514 eV. This and capacitance–voltage measurements indicate incorporation of Ge from the substrate into the GaAs. Photoluminescence from GaAs/AlGaAs multiple quantum well structures originates from the same processes as in bulk GaAs; in quantum wells, however, the transitions occur at higher energies due to the enhancement of the GaAs band gap. The observed energies are in good agreement with theoretical predictions. We have also studied the growth of GaAs on Si(100) and on Ge films on Si(100).
High speed precision X-Y stage
Authors: Reeds John , Hansen S. , Otto O. , Carroll Allen M. , McCarthy Donald J. , Radley Jack
Published: July 2002

A unique X-Y stage has been developed for use in an electron-beam lithography system. It is designed to accommodate wafer sizes up to 6 in. The stage uses conventional linear ways and ball bearings, but incorporates a unique capstan/swinging drive bar design to couple the servomotors to the X and Y stage elements. Major components of the stage are made from titanium to achieve maximum stiffness to weight ratio. The capstan drive gives very rigid coupling between the servomotor and the stage. This drive stiffness permits rapid and precise positioning of the stage by the servosystem. The rotary capstan uses a ferrofluidic seal, permitting the servomotors to be outside the vacuum chamber without requiring bellows seals. A prototype of the stage has extremely low vibration levels, and can slew at velocities up to 10 cm per s. It can step 2 mm and settle to 10 μm in 52 ms, and achieve submicron position accuracy in 70 ms. Maximum acceleration capability is 0.8 g. Stage position is sensed by a laser interferometer and associated pulse-counting circuitry. A microprocessor reads the position counters every 0.5 ms. The motor drive currents are computed from feedbacks proportional to position error and observed velocity, and from feedforwards proportional to desired velocity and acceleration. Stiffness at low frequency is enhanced by feedback derived from the integral of position error. Low harmonic excitation of the system in which the stage resides is guaranteed by smoothly varying preprogrammed trajectories derived by triple integration of jerk (acceleration rate) commands. A powerful high-level control strategy has been developed in which sequences of traversal time and traversal distance of contiguous segments are converted to appropriate jerk commands for smooth continuous motion. The strategy includes, as an integral part, constraints for maximum velocity and acceleration. Trajectory commands are interpreted by the same microprocessor which computes the servomotor currents. Desired position, velocity, and acceleration are updated by the microprocessor every 0.5 ms in accord with the sequence of jerk commands provided by the control computer, in synchronization with pattern generator operation.
A study of the growth conditions necessary for reproducible preparation of high perfection CdTe films on InSb by MBE
Authors: Farrow R. F. C. , Wood S. , Greggi J. C. , Takei W. J. , Shirland F.A. , Furneaux J.
Published: July 2002

The critical role of growth-related parameters including substrate preparation conditions, source conditioning, growth rate, and growth temperature has been identified in MBE growth of high-perfection CdTe films on InSb from a single CdTe effusion source.
Ion beam lithography: An investigation of resolution limits and sensitivities of ion-beam exposed PMMA
Authors: Karapiperis L. , Dubreuil D. , David Ph. , Dieumegard D.
Published: July 2002

High resolution thin-membrane masks are duplicated in PMMA by contact printing with 250 keV Ga+ ions. Upon development, minimum feature widths on the order of 70 nm are obtained. Broadening of ion-exposed lines in PMMA as a function of development time is studied. A microscopic investigation of PMMA irradiated with 50 keV H+ ions and 250 keV Ga+ ions at doses near the development threshold reveals peculiar morphological modifications prior to, and following development. The modification of theoretical energy dissipation distributions with the inclusion of recoil atoms in heavy-ion irradiation of resists is investigated with the aid of a Monte Carlo simulation program (RECUL). Using the three-dimensional energy distributions thus obtained, developed-line profiles are simulated.
GaAs and AlGaAs anisotropic fine pattern etching using a new reactive ion beam etching system
Authors: Asakawa K. , Sugata S.
Published: July 2002

High aspect-ratio anisotropic etching for GaAs has been obtained with Cl2 plasma in a new reactive ion beam etching (RIBE) system equipped with an ultrahigh vacuum chamber. A vertical wall with 0.5 μm thickness and 7 μm height was obtained at a 500 V ion extraction voltage and etching gas pressure of 8×10−4 Torr. A normalized etching rate was 2 ( μm/min)/(mA/cm2) which corresponds to a sputtering yield of 23 atoms/ion. Such a high aspect-ratio etching was mainly owing to use of a high-temperature (250 °C) baked photoresist mask with a sharp cut profile. GaAs and AlGaAs equirate etching, which is often difficult in the conventional reactive ion etching (RIE), has also been obtained using this system. It was found that decrease of the AlGaAs etching rate in the RIE is attributed to Al2O3 formation due to residual H2O during etching.
Excimer laser replication of ion-implanted photomasks
Authors: Stangl B. , Mitterauer J. , Ruedenauer F. G. , Marowsky G.
Published: July 2002

It is demonstrated that medium energy (10 keV) writing implantation of heavy ions into thin PMMA films produces photomasks which are locally opaque to UV and deep UV light. An excimer laser is an excellent illumination source for lithographic replication of these patterns because of its high UV light output and low spatial coherence. The writing beam implantation is performed on an electrostatic ion gun incorporating a liquid metal ion source (LMIS) of high brightness. Due to their similar spatial resolution limits, LMIS writing ion beam implantation and excimer laser illumination is an inherently compatible combination of mask production and mask replication techniques.
Electron-beam investigation and use of Ge–Se inorganic resist
Authors: Chen A. S. , Addiego G. , Leung W. , Neureuther A. R.
Published: July 2002

Electron-beam exposure and computer simulation are used to characterize the performance of Ge0.1Se0.9 inorganic resist and examine the fundamental mechanisms of resist action. A first-order model based on the energy density of electrons deposited in the active region along the interface of the sensitized layer and the resist is developed. Resist sensitivity as a function of sensitized-layer thickness and accelerating voltage are calculated with the Monte Carlo method and compared with experimental results. Special test patterns including multiscanning are designed to explore lateral diffusion of silver in the sensitized layer and proximity effect due to backscattering. With Ge0.1Se0.9 resist and e-beam direct writing sub-half-micrometer working lithography can be achieved on silicon substrate at incident doses comparable with that needed for polymethylmethacrylate (PMMA) polymer resists.
Aberrations of electrostatic systems with machining error
Authors: Tsumagari T. , Murakami J. , Ohiwa H. , Noda T.
Published: July 2002

An aberration theory has been developed for analyzing the effects of machining errors of electrostatic ion-optical systems comprising round lenses and octupole deflectors. The relationship has been investigated between the machining error and the induced perturbation, or the difference between the perturbed potential and the ideal one. The aberration formulas based on Sturrock’s perturbation characteristic function are shown. A computer program has been developed for analyzing electrostatic beam-scanning systems and a submicron ion-probe system is analyzed. The results show that lens errors may be corrected by a stigmator and that beam blurring by deflector error is negligible.
Novel self-aligned gate AlxGa1−xAs/n-GaAs superlattice modulation-doped field-effect transistors
Authors: Abrokwah J. K. , Cirillo N. C. , Arch D. , Daniels R. R. , Hibbs-Brenner M. , Fraasch A. , Vold P. , Joslyn P.
Published: July 2002

We report the first results on superlattice modulation-doped field-effect-transistors (FET’s) fabricated using self-aligned gate by the ion-implantation process. The charge control superlattice layers consisted of Si-doped GaAs (N=4×1018/cm3) and undoped Al0.36Ga0.64As of period 50 Å. 1 μ gate enhancement-mode MODFET’s exhibited an extrinsic transconductance as high as 335 mS/mm and a source resistance of 0.7 Ω mm at 300 K. From x-ray diffraction analysis, conventional furnace anneal was found to intermix the superlattice layers. However, sharp 〈200〉x-ray diffraction satellite peaks were preserved after rapid anneal, which indicate that rapid thermal annealing does not degrade the structures significantly. Photoluminescence analysis indicated a shift in the emission peak of only 15 meV at 300 K, indicating interfacial broadening of less than one monolayer. Shifts in the threshold voltage Vt in these superlattice MODFET’s in the temperature range of 300–77 K were reduced to a range of 100–140 mV, as compared to standard n-(Al, Ga)As/GaAs MODFET’s with 140–300 mV shifts. The Vt shift in the superlattice MODFET’s suggests the possibility of effects of residual ‘‘DX’’ traps.
HgTe–CdTe superlattices grown on lattice-mismatched GaAs substrates
Authors: Wroge M. L. , Leopold D. J. , Ballingall J. M. , Peterman D. J. , Morris B. J. , Broerman J. G. , Ponce F. A. , Anderson G. B.
Published: July 2002

HgTe–CdTe superlattices were grown by molecular beam epitaxy on GaAs(100) substrates with CdTe buffer layers. The large (14.6%) lattice mismatch between CdTe and GaAs is relieved by a two-dimensional array of misfit dislocations with a period of 3.1 nm. X-ray diffraction, infrared transmittance, and Hall effect measurements are reported for thick (>5 μm) single crystalline superlattices.
Structural changes of the interface, enhanced interface incorporation of acceptors, and luminescence efficiency degradation in GaAs quantum wells grown by molecular beam epitaxy upon growth interruption
Authors: Bimberg D. , Mars D. , Miller J. N. , Bauer R. , Oertel D.
Published: July 2002

A comparison of the luminescence of GaAlAs/GaAs/GaAlAs quantum wells (QW) grown by molecular beam epitaxy with and without a 1–100 s interruption of the growth at the interfaces is presented. Well widths of 2 and 5 nm are studied as model systems. The luminescence from the noninterrupted samples consists of Gaussian shaped doublets. A line shape theory is outlined, allowing for the first time a determination of the distribution of the microscopic chemical and crystallographic disorder of the interfaces from the spectra. All samples were grown under nominally identical conditions and all show the same Gaussian distribution of the interface position. The full width at half maximum of the distribution function is 1.25 Å. The interfaces in these samples are believed to have an island-like character with a typical island size of much less than 17 nm. Interruption of the growth by a few seconds changes the luminescence line shape function qualitatively. The spectrum splits into doublets, with doublet fine structure. The energies of the two main components agrees with that expected from excitonic recombination in wells with widths Lz equal to m, and (m+1) times the thickness of a GaAs layer, where m is an integer. The interfaces are therefore believed to smooth with increasing growth interruption time and islands much larger than 17 nm form rapidly at the free GaAs surface. The luminescence associated with carbon acceptors on interface sites increases linearly up to a factor of 10 with increasing growth interruption time up to 100 s and the total luminescence efficiency deteriorates rapidly for times larger than 30 s. It is argued that the efficiency decrease does not result from incorporation of carbon, which we clearly observe, but from the incorporation of other nonradiative centers. Growth interruption was never observed to cause an increase of the quantum efficiency by more than 20%. Quantum wells with interface disorder but perfect bonds seem to have a quantum efficiency which is close to the maximum possible.
Optical evidence of staggered band alignments in (Al,Ga)As/AlAs multi-quantum-well structures
Authors: Wilson B. A. , Dawson P. , Tu C. W. , Miller R. C.
Published: July 2002

Photoluminescence spectra from AlxGa1−xAs/AlAs multi-quantum-well structures are presented which provide the first direct optical confirmation of staggered band alignments in this technologically important material system. Above a critical Al concentration, the X minima are expected to become the lowest-energy conduction-band states in the heterostructure, so that photoexcited electrons and holes are separated and are trapped in alternate layers. In this regime we observe photoluminescence spectra which occur below the band gap of either of the individual materials in the samples and exhibit properties characteristic of band-to-band recombination. We attribute this emission to the spatially-indirect recombination of electrons confined to the AlAs X minima and holes in the AlxGa1−xAs heavy-hole valence band. This transition also provides a direct and highly accurate measure of the valence-band offset without requiring precise knowledge of other system parameters such as the Fermi energy, effective masses, and exciton or dopant binding energies. The confirmation of a staggered band alignment has important implications for future device applications.
A low-energy metal-ion source for primary ion deposition and accelerated ion doping during molecular-beam epitaxy
Authors: Hasan M.-A. , Knall J. , Barnett S. A. , Rockett A. , Sundgren J.-E. , Greene J. E.
Published: July 2002

The design, operation, and use of a single-grid, electron impact, ultrahigh vacuum (UHV) compatible, low-energy ion gun capable of operating with a low vapor pressure solid source material such as In are described. The gun consists of a single chamber which combines the functions of an effusion cell, a vapor transport tube, and a glow discharge ionizer. It has been operated over a wide range of In pressures from 10−5 to 10−3 Torr (10−3 to 10−1 Pa) and provides total current densities of up to 300 μA cm−2, without magnetic discharge confinement, at ion energies Ei from 50 to 400 V. Accelerated In+ (Ei=100 eV) doping during Si(100) crystal growth by molecular-beam epitaxy (MBE) resulted in increases in the In incorporation probability ranging from approximately one to four orders of magnitude above values obtained for thermal In doping at film growth temperatures between 570 and 800 °C. Accelerated beam doping profiles were also much more abrupt than thermal beam profiles. Initial results of experiments designed to investigate the role of ion/surface interactions during nucleation and the early stages of crystal growth in UHV showed that for deposition on amorphous substrates, the use of a partially ionized In+ beam (Ei=150–300 eV) resulted in a progressive shift towards larger average island sizes, a decreased rate of secondary nucleation, and a more uniform island size distribution.
Silicon epitaxy on germanium using a SiH4 low-pressure chemical-vapor deposition process
Authors: Fujinaga Kiyohisa , Takahashi Yasuo , Ishii Hiromu , Kawashima Izumi , Hirota Shoh-ichi
Published: July 2002

This work describes a process of Si epitaxy on a (100)Ge surface using a SiH4–H2 gas low-pressure chemical-vapor deposition (LPCVD) system. Germanium epitaxial film formed on (100)Si wafers using GeH4–H2 gas in a LPCVD reactor was used as the experimental substrates. It was found that Si grew epitaxially through a SiH4 thermal decomposition reaction on the clean Ge surface within a growth temperature range of 650 to 730 °C. By contrast, (110)-oriented polycrystalline Si grew at a higher temperature of 790 °C. It was clarified that the reason for this polycrystalline Si growth at 790 °C was that the Si epitaxy was disturbed by the Si oxide layer which forms immediately on the Ge surface through susceptor-induced SiO in the LPCVD reactor.
Molecular-beam epitaxial growth and characterization of pseudomorphic GaInAs/AlInAs modulation-doped heterostructures
Authors: Kuo J. M. , Lalevic B. , Chang T. Y.
Published: July 2002

New Ga0.47−u In0.53+uAs/Al0.48+uIn0.52−uAs pseudomorphic modulation-doped field-effect transistor (MODFET) heterostructures are proposed and grown by molecular-beam epitaxy on InP:Fe substrates. For heterostructures with u=0.07, Hall mobilities as high as 12 050, 59 970, and 87 300 cm2/V s at 300, 77, and 4.2 K, respectively, were measured. The corresponding sheet carrier densities in the dark were in excess of 1012 cm−2. No significant light sensitivity or persistent photoconductivity effects were observed. Shubnikov–de Haas oscillations confirmed the two dimensionality of the electron gas and indicated population of two electron subbands. Pseudomorphic MODFETs fabricated on such a heterostructure exhibit dc transconductances as high as 271 and 227 mS/mm at room temperature for 1.6 and 2.9 μm gate lengths, respectively. These results show that this material system is a strong candidate for the development of next generation high speed MODFETs that can be integrated with photonic devices.