bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-time diagnostics of II–VI molecular beam epitaxy by spectral ellipsometry
Authors: Duncan W. M. , Bevan M. J. , Shih H. D.
Published: July 2002

Spectral ellipsometry has been applied to in situ diagnostics of Hg1−xCdxTe molecular beam epitaxial growth. Spectral ellipsometry provides surface, composition, and film thickness properties of thin film electronic materials in real-time during growth and processing. This study is discussed in two parts. In the first part, the surface state properties of Hg1−xCdxTe and the substrate material Cd1−xZnxTe were studied under ultrahigh vacuum (UHV) conditions. By measuring the spectral ellipsometric quantities Ψ and Δ versus temperature under UHV conditions, the presence and desorption temperatures of surface species have been determined. Tellurium stabilized Cd1−xZnxTe surfaces were not observed to exhibit any apparent surface changes during heating under these conditions. Oxidized Cd1−xZnxTe surfaces, however, exhibit discontinuities in Ψ and Δ indica-tive of desorption of a surface species in the 300 °C range. Tellurium stabilized Hg1−xCdxTe surfaces also exhibit discontinuities in Ψ and Δ occurring at about 177 °C. In the second part of the study, dielectric functions at the growth temperature, 180 °C, were determined for Hg1−xCdxTe alloys and Cd0.96Zn0.04Te. Film compositions were monitored in situ and in real-time during Hg1−xCdxTe epitaxial growth based on this knowledge of growth temperature dielectric func-tions. An experimental analysis of measurement factors illustrates that compositional sensitivity for in situ Hg1−xCdxTe measurement is limited by uncertainties in the angle and plane of inci-dence. Simulations show an ultimate multiwavelength sensitivity of significantly better than ±0.0008 is possible for in situ composition measurements.
Preparation of GaSb(100) surfaces by ultraviolet irradiation
Authors: Bertru N. , Nouaoura M. , Bonnet J. , Lassabatere L. , Bedel E. , Mamy M.
Published: July 2002

The preparation of GaSb(100) surfaces by ultraviolet (UV) irradiation, prior to molecular beam epitaxy (MBE) growth, has been investigated. After optimization of the UV irradiation parameters (type of lamp, distance between the lamp and the sample, time exposure), GaSb surfaces present no detectable carbon contamination, a stoichiometry close to the MBE surface one, and a very good morphology. The oxide layers grown on the substrate surface have been analyzed by Auger electron spectroscopy and x-ray photoelectron spectroscopy. Large differences in the oxide composition, resulting from variations of the UV irradiation conditions, have been observed and analyzed. We discuss the experimental results and particularly the carbon desorption, in terms of oxide growth mechanisms and we propose a model of oxide growing in the optimal conditions.
Mapping of AlxGa1−xAs band edges by ballistic electron emission spectroscopy
Authors: Cheng X.-C. , Collins D. A. , McGill T. C.
Published: July 2002

We have employed ballistic electron emission microscopy (BEEM) to study the energy positions in the conduction band of AlxGa1−xAs. Epilayers of undoped AlxGa1−xAs were grown by molecular beam epitaxy on conductive GaAs substrates. The Al composition x took on values of 0, 0.11, 0.19, 0.25, 0.50, 0.80 and 1 so that the material was examined in both the direct and indirect band gap regime. The AlxGa1−xAs layer thickness was varied from 100 to 500 Å to ensure probing of bulk energy levels. Different capping layers and surface treatments were explored to prevent surface oxidation and examine Fermi level pinning at the cap layer/AlxGa1−xAs interface. All samples were metallized ex situ with a 100 Å Au layer so that the final BEEM structure is of the form Au/capping layer/AlxGa1−xAs/bulk GaAs. Notably we have measured the Schottky barrier height for Au on AlxGa1−xAs. We have also probed the higher lying band edges such as the X point at low Al concentrations and the L point at high Al concentrations. Variations of these critical energy positions with Al composition x were mapped out in detail and compared with findings from other studies. Local variations of these energy positions were also examined and found to be on the order of 30–50 meV. The results of this study suggest that BEEM can provide accurate positions for multiple energy levels in a single semiconductor structure.
Nonlinear modeling, identification, and feedback control design for the modern effusion cell
Authors: Tucker Matthew K. , Meyer David G.
Published: July 2002

In the molecular-beam epitaxy (MBE) process precise control over thickness, composition, and doping profiles are critical for end device performance. This article addresses the problem of accurately modeling and controlling the flux sources (effusion cells) used in MBE. A first-principles nonlinear dynamic model of an effusion cell is derived, investigated, tuned, and used for designing advanced closed-loop feedback schemes. The model is a coupled set of driven nonlinear ordinary differential equations. It provides the transient and steady-state time-dependent response of the cell to a given (heater power) input. Further, it provides output predictions of the produced molecular flux and the temperature read by a thermocouple built into all modern effusion cells. We show how to tune parameters in the model from actual experimental data using a nonlinear least squares identification algorithm. Simulations show excellent agreement with experimental data and empirical experience including reproduction of the well-known shutter transient event when the thermocouple temperature is regulated with a proportional-integral-derivative (PID) controller. The model further can be used to explore interesting effects. For example, the magnitude and duration of a shutter transient under PID regulation is different for gallium versus indium charged cells. This leads to a thin indium rich initial layer in the growth of InGaAs. The tuned model is used to investigate the efficacy of nested PID control designs and, finally, is used in an advanced feedback controller we design using differential geometric design methods of nonlinear control theory. Simulations show our advanced nonlinear controller eliminates flux transients over a wide range of operating conditions without the need for any recalibration or adjustment and provides superior tracking. The latter feature of superior tracking will become increasingly important as future devices call for new growth regimes and methods such as layers with continuously graded composition.
Limitations on threshold adjustment by backgating in fully depleted silicon-on-insulator metal-oxide-semiconductor field effect transistors
Authors: Tarr N. G. , Wang Y. , Soreefan R. , Snelgrove W. M. , Manning B. M. , Bazarjani S. , MacElwee T. W.
Published: July 2002

Fully depleted silicon-on-insulator metal-oxide-semiconductor field effect transistors with junction-isolated back gate electrodes formed by implanting boron through the silicon film and buried oxide into lightly doped n-type separation by implantation of oxygen substrates have been studied experimentally and through numerical device simulation. The useful range of threshold adjustment by back gate biasing is shown to be approximately ±300 mV for typical structures, irrespective of silicon film or buried oxide thickness, and is limited primarily by accumulation or inversion of the back surface of the silicon film for extreme values of back gate bias.
Electrical impedance analysis and etch rate maximization in NF3/Ar discharges
Authors: Langan J. G. , Rynders S. W. , Felker B. S. , Beck S. E.
Published: July 2002

We have investigated the etching of SiO2 and plasma chemically vapor deposited (CVD) SiNxHy (SiN) thin films in NF3/Ar plasmas as a function of pressure, NF3 concentration in Ar, and rf power. We have also independently measured the complex impedance and real power dissipation of the discharges. By simultaneously varying the pressure and NF3 concentration we have determined that the highest etch rates are obtained at low concentrations of NF3 in Ar (18%–25%) for both SiO2 and SiN at relatively high pressure (1550 mTorr). Etch rates of 14 800 Å/min for SiN and 1600 Å/min for SiO2 are achieved under these conditions. The SiN etch rate is found to be a strong function of the applied rf power, which also determines the pressure at which the highest etch rates are achieved. Both the SiN and SiO2 etch rates were found to be closely correlated to the argon and fluorine atom optical emission intensities. For NF3 partial pressures above 200 mTorr the NF3/Ar plasmas had very high impedance magnitudes (>5000 Ω) and low power coupling efficiencies (<25%). These results indicate that there is an optimal NF3 partial pressure for obtaining high etch rates which supplies sufficient reactant, but is low enough to maintain a low impedance and high power coupling efficiency. To explain these results we propose that the role of argon in NF3 based plasmas under these conditions is to lower the electronegativity of the discharge through dilution and/or reactions in the discharge. The results of this study provide insight into the optimization of processes which use fluorinated gases in plasmas at high pressures such as plasma enhanced CVD chamber cleaning where fast removal of silicon based materials is required.
Application of target factor analysis and linear least squares fitting to extracting chemical information from Auger depth profiles of a Mo/Si thin multilayer system
Authors: Morohashi T. , Hoshi T. , Nikaido H. , Kudo M.
Published: July 2002

Linear least square fitting (LLS) analysis was applied to Auger depth profile data to verify the chemical information which was extracted by target factor analysis (TFA) from a Si(2.5 nm)/Mo(5 nm) thin multilayer sample. The chemical state assignment was confirmed by measurement with external standard samples and each spectrum was used as the basis spectra for LLS. The profiles from the Si LMM and Mo MNN peaks constructed by LLS showed the clear existence of silicide layers with different thicknesses less than 1 nm at each interface, which was confirmed by TFA and transmission electron microscopy cross section. The usefulness and problems of combining LLS with TFA for characterization of this kind of complicated multilayer sample are discussed.
Boron incorporation with and without atomic hydrogen during the growth of doped layers on Si(100)
Authors: Silvestre Conrad , Thompson Phillip , Jernigan Glenn , Simons David
Published: July 2002

Solid source molecular beam epitaxy Si growths were done with and without atomic hydrogen (AH) to investigate the impact of AH on B segregation and activation. A series of 3 or 50 nm thick B-doped Si layers separated by 200 nm of undoped Si were grown at 0.1 nm/s on Si(100) substrates. In separate experiments, 10−4 Pa of AH was applied after (at 500, 600, and 710 °C) or during (at 710 °C) the 3 nm B-doped layer to determine if AH affected segregation. AH was applied before the 50 nm B-doped layer to observe if AH increased B activation between 600 and 800 °C. It was found that application of AH after the growth of the 3 nm B-doped layer had no effect on B segregation through 600 °C and increased B segregation at 710 °C, as measured by secondary ion mass spectrometry (SIMS). Application of AH during B-doped Si layer growth had no effect on B segregation. Application of 10−3 Pa of AH for 100 s prior to growth of the 50 nm B-doped layer improved surface order, as measured by low energy electron diffraction, and, at T⩾700 °C, increased B activation, as measured by spreading resistance profilometry (SRP). The differences between the SIMS and SRP data are postulated to be due to two forms of B: one electrically active and the other electrically inactive. The electrically inactive form is modeled by two paired B atoms on adjacent substitutional sites.
Low-cost modification for the high-frequency raster on the Cameca IMS-3F secondary ion mass spectrometer
Authors: Reedy R. C. , Young M. R. , Asher S. E.
Published: July 2002

The Cameca IMS-3F secondary ion mass spectrometry (SIMS) instrument, now three generations old, is still considered quality surface-analysis equipment. It was designed more than two decades ago, at a time when power transistors were the means of rastering high voltages at high frequencies. In our modification, we have replaced the high-frequency amplifiers with a simple operational amplifier (op amp) circuit that greatly enhances the capabilities of this instrument. In a Cameca dynamic SIMS instrument, the primary ion beam is focused into a small spot (∼5–100 μm) and then is rastered over an area generally between 25 μm×25 μm and 500 μm×500 μm. The raster signal is a sawtooth waveform with separate high and low-frequency components for X and Y, respectively. The transistor design of the raster amplifier does not produce a sharp waveform at high frequencies. Instead, the signal appears rounded at the top and bottom. This, in turn, allows the ion beam to spend more time at the edges of the rastered area, etching the sides at a greater rate, producing the so-called “dog ears” at the bottom of the SIMS crater. Under most analysis conditions, these dog ears are not a problem because the analysis area is much smaller than the rastered area (e.g., a 60-μm-diameter circular analysis area for a 250 μm×250 μm rastered area) and is taken from the center. However, when the sputter depth is great, or the analysis area approaches the size of the rastered area, there is a loss of depth resolution. Another problem occurs when sputtering through thin films deposited on glass or other insulating materials. During depth profiling, as the material is sputtered away, the edges reach the insulator before the analysis area, which causes a charge buildup. The operator must then stop the profile prematurely, resulting in a loss of information.
Growth characteristics and deposition mechanism of SrTiO3 thin films by plasma enhanced metalorganic chemical vapor deposition
Authors: Kim D. O. , Choi R. J. , Nahm K. S. , Hahn Y. B.
Published: July 2002

Dielectric SrTiO3 thin films were deposited on Pt/Si and Ir/Si substrates by plasma enhanced metalorganic chemical vapor deposition using high purity Ti(O-i-C3H7)4, Sr(tmhd)2, and oxygen. The deposition rates were quite dependent on bubbler temperature, substrate temperature, and rf source power. The dissociation of Ti(O-i-C3H7)4 was substantially enhanced by increasing the rf source power, while that of Sr(tmhd)2 increased with the substrate temperature. Surface morphology showed a smooth surface and good adhesion at the interface. Based on the growth characteristics of films, it was found that the deposition of SrTiO3 films was controlled by the decomposition rate of Sr(tmhd)2 on the substrate surface.
Double-gated microtip emitters for brighter field-emission displays
Authors: Py Christophe , Gao Mae , Das Suhit R. , Grant Peter , Marshall Paul , LeBrun Leslie
Published: July 2002

Reducing the aperture of the beams emitted by microtips is important to increase the luminance of field-emission displays. Double-gated microtip emitters have been fabricated where the second gate is used to focus the beam emitted by the tip under the action of the attracting field produced by the first gate. The first gate is designed in a volcano shape to shield the apex of the tip from the second gate that is recessed under the level of the first one. This is rendered possible by using a thin rf sputtered SiO2 layer with very good dielectric properties between the two gates. The beam aperture is reduced from 25° to 7° when the second gate is biased at a voltage 15 V lower than the tip. No reduction in emitted current is observed when the second gate is biased at that voltage, which results in an eightfold increase in current density.
The growth of thin, heavily doped layers for hot electron devices
Authors: Harris J. J. , Woodcock J. M.
Published: July 2002

Thin layers of GaAs, heavily doped with Sn, Si, or Be, have been incorporated into Schottky barrier diode and bulk unipolar (camel) diode structures. The effective barrier height of the Schottky diodes has been varied between 0.48 and 0.96 eV by changing the doping and thickness of the heavily doped layer adjacent to the metal contact, and camel diodes with barriers between 0.55 and 0.94 eV have also been fabricated. There is a quantitative discrepancy between the experimental and theoretical diode parameters, however, and possible explanations are discussed.
Channeling studies of III–V/III–V and IV/III–V semiconductor modulated structures
Authors: Chang Chin-An
Published: July 2002

He+-ion channeling spectrometry has been used to study the lattice crystallinity and interface structures of two different types of semiconductor superlattices: InAs–GaSb and Ge–GaAs, both (100)-oriented and grown by molecular beam epitaxy (MBE). The channeling measurements indicate good epitaxy, low density of defects, and very interesting interface structures for these superlattices. Contrary to the bulk zinc blende and diamond crystals where the dechanneling yield along the 〈110〉 axis is lower than the 〈100〉 one, the InAs–GaSb superlattices invariably show much higher 〈110〉 dechanneling yields than those along the [100] growth direction over a wide range of thickness for the individual layers. The Ge–GaAs superlattices, on the other hand, show very low dechanneling yields along both the [100] growth direction and 〈110〉 axis for the thicker layer structures; the dechanneling yields along the [100] axis, however, increase rapidly for the thinner-layer structures with little change of the 〈110〉 ones. These results are attributed to the different interface structures in these two superlattices. For the InAs–GaSb superlattices, an interface bond-relaxation model is suggested. For the Ge–GaAs superlattices, the channeling results are likely to be related to the difference in growth morphologies of the nonpolar Ge and polar GaAs lattices using MBE.
Electronic structure of metal–semiconductor interfaces
Authors: Batra Inder P.
Published: July 2002

In a recent paper, we investigated the electronic properties of a set of Ge–Al lattice-matched interfaces. These interfaces were constructed by placing an ideal (001)Ge substrate next to a 45° rotated (001)Al film. In all cases the Ge–Al interatomic distance was kept fixed at some ad hoc value. Using a self-consistent pseudopotential approach, we now extend these calculations to consider the case where the interlayer distance is fixed for the on top and interstitial model but the Ge–Al interatomic distance is allowed to vary. One striking result of our calculation is that the differences among diverse interface geometries lead only to small differences in electronic properties if the interlayer distance is kept fixed. Single atomic metal overlayer calculations by Chelikowsky, and Zhang and Schluter in different configurations show more pronounced differences. Our results indicate that inclusion of more than one metal layer tends to smear out these differences. We also calculate an optimal geometrical arrangement by minimizing the total energy of the system. We critically discuss the weakly interacting cluster model and the chemisorption model of metal–semiconductor interfaces and place our work in context. We also present a semiclassical calculation which relates the interface density of occupied states to surface quantized level spacing. It suggests a possible surface absorption experiment for determining this state density. Future ramifications of our idealized model and the role it can play in simulating interfacial chemical reactions are briefly stated.
Collective plasmon modes of a semiconductor superlattice
Authors: Bloss W. L.
Published: July 2002

The collective excitations of doped (or modulated doped) semiconductor superlattices are investigated. We focus primarily on the GaAs–Ga1−xAlxAs (type-1) superlattice in the limit that the quantum wells are far enough apart that wave function overlap between wells is negligible. The plasmon-type excitations under study here are driven entirely by long range Coulomb interaction between wells. In particular, we will discuss superlattice plasmons, LO-phonon superlattice plasmons, magnetosuperlattice plasmons, acoustic and optic plasmons for diawell superlattices, intersubband depolarization superlattice plasmons, and hybrid superlattice–intersubband depolarization plasmons. A novel realization of a structure which has tunable plasmons is suggested.
Lift-off process for achieving fine-line metallization
Authors: Milgram A. A.
Published: July 2002

A trilevel lift-off process using a soluble polyimide as the base layer is described. Al–Cu–Si metallizations are obtained with good pattern fidelity over 1 μm high structures with the use of substrate metallization temperatures of up to 325 °C. The process routinely produces metallizations 1 μm thick with linewidths less than 1.5 μm and pitch less than 2.5 μm.
Metal on polymer ion implantation mask
Authors: Tennant D. M.
Published: July 2002

A metal on polymer (MOP) mask technology is described which may be used for delineating ion implantation and proton bombardment regions. The MOP implant mask technique offers the high resolution patterning capabilities of metal liftoff yet may be removed in organic solvents. The high temperature polymer used showed no evidence of flow after an As implant dose of 1015 cm−2 at 150 kV. Several MOP lithographic schemes are suggested to meet a variety of implantation requirements. MOP implant masks may be of particular interest for compound semiconductors or electro-optic materials where native oxides are not generally used for implant masking.
High resolution mass spectrometry of liquid metal ion sources
Authors: Wilkens B. , Venkatesan T.
Published: July 2002

The mass spectra of In, Ga, and Au liquid metal ion sources (LMIS) exhibit large molecular ion clusters with the maximum observed number of atoms/cluster ranging from 6 for Ga to 12 for In. Au ion sources emit a large percentage of its ions in the form of clusters while the ratios of ion clusters to atomic ions for Ga and In sources are one part in 103 and 104, respectively. Emission characteristics (intensity, energy distributions, and deficits) of the emitted ions of different charge and mass states were measured as a function of ion source temperature, current and emission angle. The effects of these parameters on the emitted ion velocity distribution may yield information on the mechanism of ion formation and the observed energy spread. In all of the sources tested the (dI/dΩ) distribution of the molecular clusters was broad at low energy deficits and narrow at high deficits indicating different regions of formation. However, the atomic ion angular distributions for high and low ion energy deficits are nearly equal in width, but show distinct differences in shape. Models of ion formation are presented.
Local plasma oxidation and reactive ion etching of metal films for ultrafine line pattern inversion and transfer
Authors: Nulman J. , Krusius J. P.
Published: July 2002

A new ultrafine line pattern inversion and transfer technique based on local low temperature plasma oxidation and reactive ion etching of suitable metal films, such as aluminum, is presented. The patterned surface oxidized metal film may serve as a surface passivated interconnect or gate structure for integrated semiconductor devices, or be used as an etch mark for underlying layers. As an application a process for patterning self-aligned two layer gate lines composed of molybdenum silicide and polycrystalline silicon is given. Linewidths as small as 1500 Å have been achieved.
Enhanced oxygen adsorption on palladium silicide at room temperature
Authors: Butz R. , Wagner H.
Published: July 2002

Following Pd deposition on Si(111), Pd2Si formation was observed at room temperature up to a Pd coverage of about 10 Å. Exposure to oxygen revealed an estimated four times larger oxygen uptake on the thin Pd2Si layers with respect to pure Si. Thicker Pd2Si layers formed upon heating of unreacted Pd layers showed the same enhanced oxygen adsorption. The Si(LVV) Auger line shape does not indicate SiO2 formation but rather maintains the form characteristic for Pd2Si.
A dual grating alignment technique for x-ray lithography
Authors: Kinoshita Hiroo , Une Atsunobu , Iki Makoto
Published: July 2002

In order to realize a highly accurate alignment technique for submicron x-ray lithography, we have developed a new dual grating alignment technique capable of detecting both the lateral position and gap with resolutions of 0.01 and 0.1 μm, respectively. In a conventional dual grating alignment scheme, the alignment signal is the difference in intensities of +1st and −1st order diffracted light from a pair of grating marks on the mask and wafer. However, it is difficult to apply the above scheme to a practical alignment system in spite of its high detection sensitivity capability. The reason for this is that the alignment signal is very sensitive to variations in the gap between the mask and wafer. To overcome this disadvantage, we have analyzed the influence of the gap variations on position detection accuracy, and found that the sum of intensities between +1st and −1st order diffracted light reaches maximum when the gap is equal to a specific value. This characteristic applies to any lateral displacement value. Therefore, it is easy to control the gap by detecting the sum of diffracted light intensities. On the other hand, at the specific gap value mentioned above, the intensity sum reaches minimum or maximum, respectively, when the relative lateral displacement is equal to 0 or 1/2 grating pitch. In this case, the lateral displacement which indicates the maximum or minimum intensity is not affected by gap variations. Therefore, it is possible to align the lateral position by detecting the sum of intensities. By using this new dual grating alignment technique, very high accuracy alignment in a proximity mode can be realized.
Planarization phenomena in multilayer resist processing
Authors: White L. K.
Published: July 2002

The spun-on polymer sublayer in multilayer resist processing schemes change the underlaying topography in several ways. Step heights are reduced for small features and complex patterns, wall profiles are sloped, top corners of the step are more rounded, and effective feature sizes are changed. Although most spun-on polymer sublayers improve the topography, in many cases substantial thickness changes are still possible for the final resist coating. Small features (<5 μm) are usually planarized well with the sublayer and thicknesses variations for the top layer of resist are small. Somewhat larger features (5–30 μm) are not planarized as well and substantial final resist thickness variations become possible. Large features are not planarized well by either layer and tend to show only small thickness variations between the top and bottom of a step. Sloped-wall profiles reduce resist thickness changes at the edge of a step, but in terms of planarization they are only important to the degree they affect the feature size at the top of the step. For sublayer coated topography line features tend to be larger and space features tend to be smaller. These changes in feature size are important in determining thickness changes for subsequent spun-on polymer coatings. To obtain the greatest benefit from a multilayer resist processing scheme, the planarization properties of the sublayer play a crucial role.
Dependence of electrical characteristics of MBE Ga0.47In0.53As planar doped barriers on InP substrates
Authors: Brown A. S. , Palmateer S. C. , Wicks G. W. , Eastman L. F. , Calawa A. R.
Published: July 2002

The potential barrier height in planar-doped barrier structures is particularly sensitive to the concentration of background impurities present in the nominally undoped regions. MBE grown GaInAs lattice matched to InP typically has n-type background carrier concentrations in the 1016 cm−3 range. This high level can cause lowering of the barrier to near zero. By subjecting the InP substrates to a heat treatment process before growth in order to inhibit impurity outdiffusion higher purity GaInAs can be grown and planar-doped barrier devices with more reproducible characteristics are expected.
Growth of millimeter-wave distributed GaAs IMPATT structures by molecular beam epitaxy
Authors: Shih H. D. , Bayraktaroglu B.
Published: July 2002

Molecular beam epitaxy (MBE) grown wafers were used to fabricate GaAs distributed IMPATT (DIMPATT) diodes. All devices were of double-drift, flat-profile type and an additional AlxGa1−xAs layer was included in the structure to facilitate selective etching. The operation of DIMPATT diodes differ from the operation of conventional IMPATT’s since the electromagnetic waves are guided entirely within the device. Thus, the control of thickness and doping uniformity of the grown layers becomes extremely important. Additionally, the control of growth-related defects is critical since DIMPATT’s are inherently very large area devices. Details of MBE growth and device results are discussed.
Surface properties of semi-insulating indium phosphide
Authors: Roach James W. , Wieder H. H.
Published: July 2002

Electrical measurements on two-terminal structures and on A-MISFET’s, with 20 and 30 μm long channels, fabricated on SiO2 or Al2O3 coated semi-insulating InP, indicate that charge transport between their Au–Ge eutectic contacts takes place by a combination of electron transport in the accumulation layer and space charge limited current flow, both affected by deep level traps. Following application of a step voltage, the total time dependence current may be described qualitatively by I(t)=I0 exp (−t/τ2)+I1[1−exp (−t/τ1], where τ2≫τ1 and I0 is the accumulation current.
Dose control with high power ion beams on photoresist masked targets
Authors: Steeples K.
Published: July 2002

The effects associated with implanting high power ion beams into photoresist masked silicon wafers have been investigated. Outgassing from the photoresist mask can result in significant dose control errors when Faradays with conventional electrostatic suppression schemes are used. Sheet resistivity measurements show that these errors can be reduced by a factor of 3 when a magnetic suppression technique is employed. With magnetic suppression of secondary charged particles from target impact with an arsenic primary ion beam dose control accuracy is better than 2%, even under severe outgassing conditions. A semiempirical model confirms the sheet resistivity results.
High contrast x-ray mask preparation
Authors: Ono Toshiro , Ozawa Akira
Published: July 2002

Fabricating a high contrast and highly accurate gold absorber pattern has been considered for an x-ray mask. In this method, the polyimide patterns etched by O2-reactive ion etching are used for the plating mask. In electron beam pattern generation, few electrons are backscattered from the polyimide film. Those from the electroplating base are trapped in the polyimide film, which improves the electron beam resolution. In O2-reactive ion etching of the polyimide film, an accurate pattern without etch residue is obtained by using the carbon target. The titanium adhesion layer for the plating base is etched off by CBrF3-reactive ion etching without undercut. A gold pattern with 0.5 μm in width and 1.0 μm in thickness can be obtained within 0.1 μm accuracy by a combination of these technologies.
A high resolution EELS study of free-carrier variations in H+2/H+ bombarded (100)GaAs
Authors: Dubois L. H. , Schwartz G. P.
Published: July 2002

High resolution electron energy loss spectroscopy (EELS) has been used to examine whether thermal recovery of the near-surface free-carrier concentration in Te-doped (100) GaAs is accomplished following low energy (250–1500 eV) hydrogen ion bombardment. For hydrogen ion impact energies below 500 eV, the nominal bulk free-carrier density is recovered by annealing at 725 K for 2 h. For comparable ion doses, the net free-carrier concentration decreases monotonically at higher impact energies under similar annealing conditions. The threshold for damage retention occurs close to the value of transmitted energy which is necessary to create either a Ga or an As interstitial point defect.
Al/SiO2/WSi2/Si double-level metallization for charge-coupled-device imagers
Authors: Babbar H. L. , Anagnostopoulos C. N. , Fischer J. R.
Published: July 2002

Replacing aluminum with tungsten silicide in Al/SiO2/Al/Si double-metal systems reduced hillock formation and allowed the reflow of glass for better second-metal topography. The high contact resistance of tungsten silicide to n+-Si and poly-Si was reduced by implanting the tungsten silicide with phosphorus or arsenic. Charge-coupled-device (CCD) imagers were fabricated by this technique.
Molecular beam epitaxy growth of high performance GaAs power field effect transistors
Authors: Abrokwah J. K. , Geddes J. , Longerbone M.
Published: July 2002

GaAs power field effect transistors (FET’s) with the highest power output per unit gate width (0.46 W/mm) reported to data at Ka-band frequency were fabricated using molecular beam epitaxy material with active layer doping of 3.6×1017 cm3. Power output of 110 mW and conversion efficiency of 11% were achieved with half-micron gate GaAs FET’s in a 30 GHz amplifier with an associated gain of 3.4 dB. This report describes the molecular beam epitaxy (MBE) growth conditions and results of characterization of the power FET.
High-current and thermal-shock testing of TaSi2–polycide/Al-alloy composites
Authors: Faith T. J. , Irven R. S. , Bertin E. P.
Published: July 2002

High-current failure levels of TaSi2–polycide/Al-alloy bilevel-conductor composites were measured using 10 min increment step-stress tests. Al-alloy metallizations were Al and Al–1%Si; polycide and metal linewidths ranged from 2.5 to 3.0 μm; and interlevel-contact sizes ranged from 1.5 to 2.0 μm2. In all cases, the weak links in the bilevel composite were the interlevel contacts. In units with contact resistances less than 1 Ω, failures occurred at the positive contact at polycide-line current densities ≥1.4×107 A/cm2, which resulted in Joule heating of the polycide line to ≥400 °C. Polycide line damage and Al, which had migrated in the direction of the electric field, often extended to distances >100 μm from the failed contact. Early failures, highly localized at the negative contact, were consistently experienced by units with initial contact resistances above approximately 1 Ω. The failure levels decreased (to current densities as low as 5×106 A/cm2) with increasing initial contact resistance. Thirty cycles of thermal shock (−70 to +100 °C) resulted in no reduction in the current level at which high-current failure occurred in units with good contacts.
Excitonic recombination at the CdTe/(Cd,Mn)Te heterointerface
Authors: Zhang X.-C. , Chang S.-K. , Nurmikko A. V. , Kolodziejski L. A. , Gunshor R. L. , Datta S.
Published: July 2002

We discuss results of spectroscopic studies of the optical properties of Cd1−xMnxTe multiquantum wells. These structures are sources of intense luminescence at low temperatures. Dependence of luminescence spectra on temperature and external magnetic field show strong evidence for emission by localized excitons which are attracted to the heterointerfaces.
Production silicon molecular beam epitaxy apparatus for 4-in.-diam wafers
Authors: Tabe Michiharu
Published: July 2002

A high output production silicon molecular beam epitaxy apparatus for 4-in.-diam wafers is described. Throughput time in an ordinary operation is as short as 20 min/wafer with the help of cassette loading and high growth rates around 20 Å/s. Silicon is deposited from a sweep eb-gun with a hearth capacity of 50 cm3. Rotation of the wafer yields a thickness uniformity of <±5% across a 4-in. wafer. Antimony as a dopant is evaporated from a conventional Knudsen cell and doping uniformity of <±10% is obtained. The uniformity variation reflects temperature variations of ±5 °C across a typical wafer. Good heating uniformity is achieved with a graphite meander heater. Low temperature cleaning of the substrate surface is also described.
A new trench fabrication technique for silicon substrate utilizing undercutting and selective etching
Authors: Suyama Shiro , Yachi Toshiaki , Serikawa Tadashi
Published: July 2002

This paper presents the development of a new trench fabrication technique for silicon substrate utilizing undercutting and selective etching. The technique comprises (1) first aluminum film deposition and its etching with controlled undercut, (2) second aluminum film deposition, (3) second film liftoff, and (4) silicon substrate selective and anisotropic etching using the first and second films as etching masks. There are two predominant features of this technique. First, trench width is controlled by the first film undercutting. Second, highly selective and anisotropic etching of the silicon substrate is obtained employing the aluminum films as etching masks in configuration with planar plasma etching using CCl2F2 gas. Under optimum conditions, trenches of approximately 0.12 μm in width and 0.6 μm in depth are successfully fabricated.
Detection of pinholes in the insulator deposited on aluminum metallization
Authors: Karulkar Pramod C.
Published: July 2002

A method for detecting defects and pinholes in the insulator layer deposited on the aluminum metallization is described. This technique decorates the locations of potential shorts. The technique is useful in optimization of the dielectrics used in multilevel metallization systems for VLSI.
A deep level transient spectroscopy comparison of ion beam sputter deposition defects in high and low temperature annealed n-Si substrates
Authors: Auret F. D. , Bojarczuk N. A. , Schneider C. P.
Published: July 2002

Deep level transient spectroscopy was used to study the defects introduced during ion beam sputter deposition of Mo Schottky barrier devices on n-type Si. It was found that the sputter-induced defects in wafers annealed at 950 °C before sputter deposition were different from those in wafers that were annealed at 450 °C before sputter deposition. Hence, it was concluded that identical premetallization annealing should be done when comparing defects introduced by different processes.
Effect of growth conditions on stoichiometry in MBE-grown GaAs
Authors: Kobayashi K. , Kamata N. , Fujimoto I. , Okada M. , Suzuki T.
Published: July 2002

The effects of varying As4/Ga flux ratio r, substrate temperature and growth rate on the deviation from stoichiometry in GaAs grown by MBE have been investigated. The deviation from stoichiometry was directly measured by detecting intensity variation of a weak quasiforbidden (200) reflection of x rays. Using this new method, we obtained the following results: in the regions of r<1.0 and r>2.0, higher densities were detected in the As lattice plane. The behavior for r<1.0 is contrary to the expectation of decrease of As. A possible explanation for this higher reflection in r<1.0 is that some Ga atoms may exist at interstitial site in the As lattice plane. It is also seen that densities of atoms in the As lattice plane decrease with increasing substrate temperature. In correspondence with the results that the growth condition with flux ratio r=1.4 minimizes the deviation from stoichiometry, it is found that GaAs films grown under the condition r=1.4 show the highest quality of the electrical and optical properties.
Effect of electric field on the sharp photoluminescence spectra of undoped GaAs–Al0.25Ga0.75As multiple quantum well structures
Authors: Yu P. W. , Reynolds D. C. , Bajaj K. K. , Litton C. W. , Masselink W. T. , Fischer R. , Morkoç H.
Published: July 2002

Effects of an electric field on the low temperature (4.2 K) photoluminescence spectra from undoped GaAs–Al0.25Ga0.75As multiple quantum well samples grown by molecular beam epitaxy have been investigated. The photoluminescence in the semitransparent Schottky-barrier configuration is dominated by the transitions of the n=1 light-hole free exciton, the heavy-hole free exciton, the light and heavy hole excitons bound to a neutral donor, and the heavy hole-to-neutral donor. As the electric field is increased the photoluminescence intensity is shifted from the neutral donor bound heavy-hole exciton peak to the heavy hole-to-neutral donor peak and to the n=1 electron-to-neutral acceptor peak. More than two orders of magnitude change in intensity of the neutral donor bound heavy-hole exciton peak is observed in the electric field range studied. No discernible shift in the energy of any of the intrinsic and near-intrinsic emission is observed. However, some shift is observed for the n=1 electron-to-neutral acceptor transition. Relevant luminescence quenching mechanisms are discussed.
Raman scattering studies of donor transitions in semiconductor quantum-well structures
Authors: Perry T. A. , Merlin R. , Shanabrook B. V. , Comas J.
Published: July 2002

Raman scattering from bound electrons has been observed in Si-doped GaAs–A1xGa1−xAs multiple heterostructures. The donor-related features show broadening due to the dependence of the donor spectrum on the position of the impurity in the well. Transitions from 1s to 2s states and bound excitations associated with intersubband transitions were identified. The latter observation confirms the existence of resonant impurity states in quantum-well structures.
Ultrauniform InxGa1−xAs layers on InP grown by molecular beam epitaxy
Authors: Matsui Y. , Hayashi H. , Kikuchi K. , Iguchi S. , Yoshida K.
Published: July 2002

In the molecular beam epitaxial (MBE) growth of InxGa1−xAs, quite uniform and lattice-matched In0.53Ga0.47As epilayers have been obtained over large-size InP wafers. Composition variation of the epitaxial layer over an entire 2-in. φ wafer is less than ±0.7%; that is, the difference of lattice mismatch between the center and the edge of the wafer is less than 1×10−3. Around the center, composition variation is less than ±0.25% over lateral dimension of 2.5 cm. In this 2-in. φ epitaxial wafer, the relation between electron mobility and lattice mismatch is also studied.
Fabrication and resist exposure characteristics of 50 keV nanometer e-beam lithography system
Authors: Gamo Kenji , Yamashita Kazuhiro , Emoto Fumiaki , Namba Susumu , Samoto Norihiko , Shimizu Ryuichi
Published: July 2002

A 50 keV nanometer e-beam lithography system was fabricated using a Zr–W thermal field emitter. The system has a beam current ranging from 6×10−12 to 1×10−9 A, a minimum beam spot of 2.4 nm and a scanning field of 240×180 μm2. It was found that the total emission and the specimen current was stable with a fluctuation less than 0.5% for more than 3 h. To investigate nanometer pattern delineation characteristics, the effect of various exposure parameters on a delineated line width were measured and a line pattern with a width less than 20 nm was fabricated. A 40 nm wide one dimensional MOS structure was also fabricated using Ni liftoff and reactive sputter etching techniques.
Pattern profile control of polysilicon plasma etching
Authors: Kimizuka M. , Hirata K.
Published: July 2002

Profile control in plasma etching of polysilicon is described. Reactive gases are CCl2F2–H2 and CCl2F2–C2H6. Undercutting suppression and sloped wall pattern profile without undercutting are realized. Thin film formation on the etched pattern side wall is observed. These characteristics are explained by the plasma polymerization phenomena which occurs competitively with etching reaction.
Automatic column control for high speed electron beam delineator
Authors: Goto M. , Wada H. , Nakasuji M. , Yoshikawa Y. , Muraguchi Y. , Takigawa T. , Sasaki S. , Sano S.
Published: July 2002

An automatic column control system has been developed for practical usage in a high speed electron beam delineator. Direct digital control is used for processing complex VSB column adjustments, such as beam alignments, lens current adjustments, and astigmatism correction. This automation has improved column adjustment accuracy, adjustment time and column operation serviceability. The accuracy and adjustment times are at least four times better than those achieved by manual operation. For example, 4 h of lens adjustment time has been reduced to only 30 min. This automatic control has also improved the electron beam characteristics, such as beam current density distribution and beam edge resolution. Consequently, these characteristics have become sufficient for use in submicron lithography.
Optical properties of superlattice and MQW laser diode
Authors: Okamoto Hiroshi
Published: July 2002

MBE grown GaAs–AlxGa1−xAs superlattice structure was investigated in terms of crystallography (x-ray diffraction and direct lattice-image observation by TEM) and optical properties (controllability of Eg, oppoiste Burstein shift, structure dependent refractive index and room-temperature exciton). New device properties are described for an MQW laser diode/waveguide. These include anisotropic gain, low absorption loss, and stable longitudinal mode oscillation under high-speed modulation. An MQW laser diode in the long wavelength region is presented, which is made using the GaSb–AlxGa1−xSb material system. Future prospects are also described.
Josephson current deviation in small area junctions with double insulating layers
Authors: Nishino Toshikazu , Tarutani Yoshinobu , Kawabe Ushio
Published: July 2002

Fabrication of small-area Nb/Nb-oxide/Pb alloy Josephson junctions with areas defined by newly developed double insulating layers is described, and their measured current–voltage characteristics are presented in order to study the deviation in dc Josephson current in these junctions. The deviation in 1.69 μm2 junctions is found to be within ±9% of the current’s mean value. This deviation is mainly due to the deviation in junction size.
Variable-shaped EB sub-half-micron lithography applied to high-power GaAs FET’s
Authors: Suzuki K. , Itoh H. , Sugiura T.
Published: July 2002

This paper is the first on applying a variable-shaped electron-beam (EB) lithography process to microwave high-power GaAs FET’s with sub-half-micron (0.3–0.4 μm) gate length. By developing a new lift-off process using a trilevel resist structure, the gates with interdigital structure are offset toward source electrodes in deeply recessed channels (0.35 μm depth) in order to reduce source parasitic resistance and improve drain breakdown voltage. An 80% chip yield was obtained for the FET with 0.4 μm gate length (Lg) and 6 mm total gate width (ZT). For the FET with 0.6 μm offset gate and ZT=1.5 mm, 1.0 W output power with 5 dB associated gain (Ga), 8.5 dB linear gain (GL), and 27.4% power added efficiency were obtained at 10 GHz. The present device, which had the 1.6 dB back off at the −30 dB third-order intermodulation distortion (IM3) point, can also lead to significantly low distortion in linearity at microwave frequencies.
PGN as a good dry etching resistant negative electron beam resist
Authors: Lin Fei Y. , Gong B. M. , Ye Yong D. , Ku Chen C.
Published: July 2002

A novel negative-working electron beam resist with a good dry resistance and high resolution was obtained from the polyglycidyl ether of m-cresol-formaldehyde novolac (PGN). The dry etching resistance of the resist PGN is due to the excellent radiation and thermal stability of the novolac resin. It is found that the plasma etching resistance is slightly better than AZ-1350J. The epoxy groups enable the resist to have good adhesion to various susbtrates. Resolution of 0.7 μm lines and spaces is obtained easily from 0.5 μm resist film by direct electron beam writing. Depending on the molecular weight and epoxy content of PGN, sensitivity of at least 5.5×10−6C/cm2 is achieved at an accelerating voltage of 30 kV. The sensitivity increases with increasing molecular weight and epoxy content of PGN. Contrast is 1.0. In addition, PGN has excellent thermal stability. The resist profile does not degrade at 350 °C. We found that this resist is especially useful for dry etching processes.