bluuebunny/crossref_metadata_2025 huggingface dataset:
Integration of vertical-cavity surface-emitting devices by molecular beam epitaxy regrowth
Authors: Saito Hideaki , Kosaka Hideo , Sugimoto Mitsunori , Ogura Ichiro , Kasahara Kenichi , Sugimoto Yoshimasa
Published: July 2002

We used two-step molecular beam epitaxial (MBE) growth to integrate monolithically single and double vertical-cavity structures on a wafer. This technique is useful for making a single vertical-cavity surface-emitting laser–thyristor with a low threshold and a double vertical-cavity heterojunction phototransistor with both a high responsivity and a large spectral bandwidth. Regrowth on a patterned distributed Bragg reflector after thermal desorption of a passivating GaAs layer resulted in the laser in the single-cavity section having a threshold current density of 1.0 kA/cm2, which is comparable to that of one grown by conventional one-step MBE. Controlling thickness to within ±0.3% resulted in the regrown double-cavity section having a bandwidth of 5 nm.
Potential applications of fusion neutral beam facilities for advanced material processing
Authors: Williams J. M. , Tsai C. C. , Stirling W. L. , Whealton J. H.
Published: July 2002

Surface processing techniques involving high energy ion implantation have achieved commercial success for semiconductors and biomaterials. However, wider use has been limited in good part by economic factors, some of which are related to the line-of-sight nature of the beam implantation process. Plasma source implantation (or plasma immersion ion implantation) is intended to remove some of the limitations imposed by directionality of beam systems and also to help provide economies of scale. The present paper will outline relevant technologies and areas of expertise that exist at Oak Ridge National Laboratory in relation to possible future needs in materials processing. Experience in generation of plasmas, control of ionization states, pulsed extraction, and sheath physics exist. Contributions to future technology can be made either for the immersion mode or for the extracted beam mode. Existing facilities include the High Power Test Facility, which could conservatively operate at 1 A of continuous current at 100 kV delivered to areas of about 1 m2. Higher instantaneous voltages and currents are available with a reduced duty cycle. Another facility, the High Heat Flux Facility can supply a maximum at 60 kV and currents of up to 60 A for 2 s on a 10% duty cycle. Plasmas may be generated by use of microwaves, radio-frequency induction, or other methods and plasma properties may be tailored to suit specific needs. In addition to ion implantation of large steel components, foreseeable applications include ion implantation of polymers, ion implantation of Ti alloys, Al alloys, or other reactive surfaces.
Calculated I–V characteristics of a gold liquid metal ion source for a prototype emitter modeled as a cone–sphere
Authors: Miskovsky Shana Nicole , Miskovsky N. M. , Cutler P. H.
Published: July 2002

The operational properties of liquid metal ion sources (LMIS) have been studied extensively the last three decades. Nevertheless, debate still exists on the emitter shape and the mechanism(s) responsible for ion emission. It is generally believed that prior to onset, the applied electric field causes a (cuspidal) deformation of the liquid emitter surface. This study will use the cone–sphere as a prototype for the emitter surface. The advantage of the cone–sphere model is its ability to replicate analytically the emitter shapes seen experimentally, since one can independently choose the radius of curvature, R, the ‘‘form factor’’ k (which determines the amount of ‘‘necking’’) and the asymptotic cone angle. The I–V characteristics of a cone–sphere model of a Au LMIS were calculated using the image hump (IH) and charge exchange (CE) models for the field evaporation process. Field evaporation is assumed to be thermally activated and follow an Arrenhius expression of the form exp(−Qn/kT), where Qn is the activation energy. The multidimensionality of the source is accounted for in the calculation of the exact field variation on the three-dimensional surface of the liquid emitter. The calculation of Qn in the image hump model follows a standard procedure. However, the evaluation of Qn for the charge exchange model differs from that done by others. First, the atomic energy curve for Au is calculated using the universal binding energy curve of Smith et al. [J. R. Smith, J. Ferrante, and J. H. Rose, Phys. Rev. B 25, 1149 (1982)]. The intersection of the atomic and ionic potential energy curves is determined as a function of field. The quantity Qn is then the energy difference between the minimum of the atomic energy curve and its value at the intersection. The I–V characteristics for Au obtained using the CE model are in better qualitative agreement with experimental results for Au and Cs than the IH model in the voltage range from 1 to 10 kV. In paricular, the calculated curves exhibit a definitive onset voltage, a sharp rapid rise, and saturation behavior.
Single-crystal epitaxial Ge-based ohmic contact structure for III–V nanoelectronic and mesoscopic devices
Authors: Dubey M. , Jones K. A. , Casas L. M. , Eckart D. , Pfeffer R. L.
Published: July 2002

Single-crystal epitaxial layer ohmic contacts are very promising in the fabrication of shallow junction nanoelectronic and mesoscopic devices based on III–V compounds. A single-crystal Ge film is grown epitaxially on GaAs or InGaP lattice matched to GaAs and a Au or Pd layer is deposited on top of it using an ultrahigh vacuum (10−9–10−10 Torr) electron beam (UHV e-beam) deposition system. The interface between the Ge and thermally cleaned GaAs or InGaP is almost atomically abrupt, smooth, and oxide free, and there is a minimum of disruption of the underlying layers. When deposited at an appropriate temperature, the metals are highly oriented and have large grains. They can be diffused through the Ge film to initiate the formation on an ohmic contact in a controlled manner. A detailed analysis of interface quality, crystal structure and defect propagation in GaAs/Ge/Au, GaAs/Ge/Pd, InGaP/Ge structures is presented. High-resolution transmission electron microscopy, double-crystal x-ray diffraction, Rutherford backscattering spectroscopy, and Auger electron spectroscopy were used to characterize the materials.
Effects of heavy atoms added into a resist on energy absorption in x-ray lithography
Authors: Murata Kenji , Yasuda Masaaki , Kawata Hiroaki , Matsuda Tadahito
Published: July 2002

A Monte Carlo simulation has been performed for photoelectrons and Auger electrons generated in Si or Ge doped polymethyl methacrylate (PMMA) resist (Si5xC5(1−x)H8O2 or Ge5xC5(1−x)H8O2) films for the enhancement of dry etching resistance under Mo Lα x-ray exposure. It is found that the addition of such heavy elements, especially Ge, into the resist is very effective for reducing the spatial spreading of energy absorption. Calculations for line and space patterns with an equal 100 nm width show that the interproximity effect between the patterns decreases significantly with an increasing content of heavy atoms doped. It is also shown that about the same resolution as obtained for a pure PMMA resist with an Al Kα x ray (1.5 keV) can be achieved with a Mo Lα x ray (2.3 keV) by adding Ge atoms with a content of x=0.1–0.2 into the resist.
GaAs heteroepitaxial growth on Si substrates with thin Si interlayers in situ annealed at high temperatures
Authors: Yodo T. , Tamura M.
Published: July 2002

The structural quality of GaAs/Si films can be improved by incorporating a Si interlayer. In this paper, we discuss the effect on the GaAs structural quality of a high-temperature anneal, either in situ between the deposition of the Si layer and subsequent GaAs, or ex situ after the film has been fully grown. The Si interlayer has been found to act as both a cap layer for an in situ high-temperature anneal and a blocking layer of dislocations. The full width at half maximum (FWHM) of the x-ray rocking curve of (400)GaAs diffraction in 1-μm-thick GaAs/Si films decreased from 625 to 388 s upon the incorporation of a Si interlayer. Furthermore, the FWHM was decreased to 200 s by adding an ex situ anneal at 900 °C for 1 min after growth. However, it was found in GaAs/Si films with Si interlayers that a 78 meV acceptor level due to a Ga antisite defect was observed from photoluminescence (PL) at 77 K, and that oval defects were generated from secondary electron-microscope observations. These phenomena suggested in addition to the improved quality that the Si leads to a surface segregation of As, and that Ga droplets are left behind. It was also shown from both the PL peak-energy shift and the broadening of the PL linewidth that the layer structure of the Si interlayer would be destroyed through out-diffusion from Si during an ex situ anneal at temperatures greater than 950 °C in GaAs/Si films.
Effect of an Al2O3 interlayer on linewidth control in electron beam writing on tungsten substrates
Authors: Moel A. , Gomei Y. , Sugihara S. , Takigami Y.
Published: July 2002

We studied the effect of a 100-nm-thick Al2O3 interlayer between resist and tungsten on the feature size and edge roughness of e-beam written features from 0.06 to 0.15 μm. We found that this interlayer leads to an essentially constant improvement (independent of feature size) of about 0.0025 μm in the edge roughness at the bottom of the resist patterns compared to features written on resist directly on top of tungsten. This improved edge roughness may be attributed to an increase in the contrast of the deposited energy profile at the resist/Al2O3 interface. The effect of the Al2O3 layer is most pronounced around the Al2O3/resist interface.
Synthesis of focusing-and-deflection columns
Authors: Szilagyi M. , Mui P. H.
Published: July 2002

Szilagyi and Szép have demonstrated that focusing lenses of high performances can be constructed from a column of circular plate electrodes. Later, Szilagyi modified that system to include dipole, quadrupole, and octupole components by partitioning each plate into eight equal sectors. It has already been shown that the additional quadrupole components can indeed bring about substantial improvements in the focusing of charged particle beams. In this article, that design procedure is expanded to construct columns capable of both focusing and deflecting particle beams by just introducing additional dipole components. In this new design, the geometry of the system remains unchanged. The only extra complication is the demand for more individual controls of the sector voltages. Two sample designs, one for negative ions and one for electrons, are presented showing that in both cases a ±2.3 mrad diverging beam can be focused down to a spot of less than 50 nm in radius over a scanning circular area of radius 0.25 mm. The details of the two systems are given in Sec. IV along with the source conditions. The performance of the negative ion system is found to be comparable to the published data. For the relativistic electron system, the interaction of individual components to reduce various aberrations is investigated.
Series resistance of in-plane-gated transistors and quantum point contacts
Authors: de Vries D. K. , Wieck A. D.
Published: July 2002

By using large-scale models made of conductive polyethylene, the series resistance of constrictions in a two-dimensional electron gas can be estimated without any computational effort.
Thermally stable AuGe–Au ohmic contacts for single doped InP high electron mobility transistor structures
Authors: McTaggart R. A. , Hur K. Y. , Lemonias P. J. , Hoke W. E. , Aucoin L. M.
Published: July 2002

Optimization of thermally stable ohmic contacts to single doped, InP high electron mobility transistor (HEMT) structures was performed using AuGe–Au. Pulse doped and uniformly doped lattice matched HEMT structures were utilized to investigate the effects of doping profiles on contact resistance, Rc. The lowest contact resistance was obtained on pulse doped structures (Rc<0.1 Ω mm). Uniformly doped structures yielded Rc<0.2 Ω mm. AuGe–Au contacts were similarly fabricated on pseudomorphic HEMT structures incorporating an Al0.65In0.35As Schottky layer to monitor the change in Rc resulting from the increase in band gap discontinuity. The use of a pseudomorphic Schottky layer resulted in Rc of ≳0.3 Ω mm.
High growth rate of III–V compounds by free carrier gas chemical beam epitaxy
Authors: Benchimol J. L. , Juhel M. , Petitjean M. , Ancilotti A.
Published: July 2002

We present in this article a simple and economic gas line designed for low vapor pressure metalorganic sources introduced into a chemical beam epitaxy chamber without carrier gas. This gas line was tested with triethylgallium and trimethylindium for the growth of GaAs and InP layers. The high conductance of the line allowed minimizing the heating of the source and reaching growth rate as high as 12 μm/h for GaAs. The lower InP growth rate was attributed to the higher viscosity of trimethylindium compared to triethylgallium.
Novel phosphorus and antimony sources for use in metalorganic molecular beam epitaxy
Authors: Abernathy C. R. , Bohling D. A. , Muhr G. T. , Wisk P. W.
Published: July 2002

Trisdimethylaminoarsenic and phenylarsine have proven to be useful replacements for AsH3 for growth of GaAs and AlGaAs by metalorganic molecular beam epitaxy. This paper will discuss the P analogs, namely, trisdimethylaminophosphorus (DMAP) and phenylphosphine (PhPH2), as well as trisdimethylaminoantimony (DMASb). All of these sources decomposed readily at the growth surface without precracking. InP surfaces were maintained with each source over a wide range, 375–525 °C, as were GaAs substrates over the range of 375–600 °C. Using DMAP, GaP was grown at rates up to 200 Å/min with slightly less carbon contamination than obtained with similar flows of PH3. When trimethylindium (TMI) or elemental In was introduced, however, neither the DMAP nor the PhPH2 readily decomposed, thus leaving In droplets on the surface. InP was successfully grown by thermally cracking these compounds prior to injection to the chamber. The dependence of cracking efficiency and impurity uptake on cracker temperature will also be presented. DMASb was found to produce just the opposite effect of DMAP, apparently preventing the adsorption of triethylgallium, tri-isobutylgallium, or trimethylaminealane on the surface for sufficient time to allow decomposition and hence growth to occur.
Submicron Al filled via formation by high-temperature sputter deposition and via electrical properties
Authors: Nishimura H. , Ogawa S. , Yamada T.
Published: July 2002

Submicron Al–Si–Cu filled via formation by a high-temperature sputter deposition method employing Ti underlayers and via electrical properties were studied. It was found that degree of filling, via chain resistance, and variation of the via chain resistance depend on the Ti underlayer thickness. The via chain resistance and its variation with thick Ti underlayer (50–100 nm) are smaller than those with thin Ti underlayer (20 nm). This might be because of improvement in wettability of Al–Si–Cu films at via sidewall, which is caused by uniform interfacial reaction between the Ti underlayer and the Al–Si–Cu film. It was shown that Al films at the via holes consist of one or two single crystalline. With Ti underlayer thickness of 20 nm, electromigration resistance for Al–Si–Cu filled via chains with low resistance was a factor of about 20 times greater than that of Al unfilled vias by a conventional sputter deposition method. On the contrary, the filled via chains with high resistance failed at an initial stage during electromigration testing. Also, it was found that via resistance increase during electromigration is caused by the depletion of Al–Ti–Si compounds in the vicinity of the Al plug via interface.
Beam position stabilization by suppression of electrons reentering the electron-beam column
Authors: Kato Junichi , Morita Hirofumi , Saito Kenichi , Shimazu Nobuo
Published: July 2002

The electron trap proposed in this paper provides high beam positioning stability. It keeps reflected electrons and secondary electrons from reentering the column from the specimen. The effect of the trap is evaluated numerically and experimentally, and the results show that it can reduce beam positioning drift by a factor of 6.
Effect of multiple reflection of laser beam and pattern displacement on overlay accuracy in synchrotron radiation stepper
Authors: Araki K. , Itoh T. , Koga K. , Kusumoto S. , Yasui J. , Sangawa U. , Aoki S.
Published: July 2002

This article describes the alignment accuracy of an x-ray stepper that was developed by SORTEC Co. and Matsushita Electric Industrial Co. The quantitative relationship between the phase modulation of an alignment signal and the overlay accuracy is discussed. Phase modulation is caused by multiple reflection of an alignment laser beam between a mask and wafers. The alignment capability of an alignment system can be evaluated from the overlay accuracy near the alignment marks, and is about 20 nm (3σ) for alignment on a resist-patterned wafer. The overlay accuracy in an exposure field worsens with increasing distance from alignment marks. The reason behind this is wafer deformation which causes pattern placement offsets characterized by the position on the wafer. By subtracting the offsets, the overlay accuracy of less than 22 nm (3σ) is obtained. Following the same procedure, the overlay accuracies for a metalized wafer were 65.2 nm for the x axis and 35.3 nm for the y axis (3σ).
Study of the electrical active defects induced by reactive ion etching in n-type silicon
Authors: Biavati M. , Perez-Quintana I. , Poggi A. , Susi E.
Published: July 2002

The defects induced in the Si substrate by a CHF3/Ar plasma dry etch of SiO2 on Si were studied by correlating the reactive ion etching (RIE) induced changes in the minority-carrier bulk lifetime and surface recombination velocity with the data on damage obtained by the capacitance–voltage (C–V) and current–voltage (I–V) characteristics. Wet etched control samples were used to distinguish the defects induced by the processing in itself from the RIE-induced defects. The influence of rf power was studied. No damage or contamination of the Si substrate was detected; a modification of the surface electric properties was observed in the samples etched at low rf power, and attributed to the presence of a residue layer.
Higher mobility of charge carriers in InAs/GaAs superlattices through the elimination of InGaAs alloy disorders on GaAs
Authors: Baeta Moreira M. V. , de Oliveira A. G. , Py M. A.
Published: July 2002

In this work, we present the Hall electrical properties for molecular beam epitaxy grown modulation-doped field-effect transistors structures using a short-period superlattices channel of (InAs)1.1±0.1 (GaAs)n where the indexes 1.1 and n represent the number of InAs and GaAs monolayers, respectively. These properties are compared with those of structures using the alloy in the channel and the variables were the indium content (y=0.08±0.01–0.25±0.01) and the channel thickness (80–150 Å). The mobility and the free carrier concentration were obtained as a function of the illumination intensity of a light-emitting diode at 77 K. Our results indicate that for indium content around y=0.08±0.01, the electrical properties are independent of using short-period superlattices or alloy channels. For an indium content around y=0.25±0.01 the electrical properties change significantly for the two structures. For the same carrier concentration (n=2.8×1012 cm−2), we observed for the sample having the short-period superlattices structure mobilities 33% higher than those for the alloy structure. Our conclusion is that the scattering associated with the alloy disorder increases with the indium content and that this deleterious effect can be reduced, replacing the alloy layer with short-period superlattices.
Exposure strategies for polymethyl methacrylate from in situ x-ray absorption near edge structure spectroscopy
Authors: Zhang X. , Jacobsen C. , Lindaas S. , Williams S.
Published: July 2002

We have observed the chemical changes in PMMA irradiated by x rays in situ. The chemical changes are monitored by micro-x-ray absorption near edge structure spectra at the carbon absorption edge. The loss of the ester group (C=O) and formation of C=C bonds have been determined quantitatively from changes in the intensities of the respective π* resonant peaks as a function of dose. Samples prepared under different conditions were examined. From the dose dependence of bond formation, scission and linking, the performance of the resist can be predicted, so that the preparation strategy, dose, and development can be optimized.
Low-pressure plasma deposition of photosensitive organosilicon polymers
Authors: Hagedorn M. S. , Higman T. K. , Fayfield R. T. , Chen J.
Published: July 2002

Plasma deposition of monosubstituted organosilicon precursors can result in layers containing extensive Si–Si bonded backbones. When these films are simultaneously exposed to ultraviolet light and oxygen, the Si–Si bonds are scissioned and oxygen inserted to form Si–O–Si polymer chains. It is shown that these films can be deposited by a low-pressure dc plasma source. The plasma is created by electronic excitation of Xe and methylsilane with an axial magnetic field to confine the plasma near the substrate surface. The plasma has a narrow spread of relatively low (10–20 eV) particle energies. In this way the production of undesirable gas phase reactions is limited. The ability to work at low pressure, with correspondingly low deposition rates, makes it possible to deposit thin resist layers which are suitable for nanolithographic applications.
Estimation of charge buildup during plasma processing by measuring metal–oxide thickness
Authors: Machida K. , Itsumi M. , Minegishi K. , Arai E.
Published: July 2002

A simple method for estimating charge buildup on gate oxide during plasma processing is proposed. This method is based on the observation that metal oxidation rate at the SiO2–metal interface is accelerated by the electric field formed by electrons diffused from the SiO2 surface to the metal surface during plasma processing. The thickness of the metal oxide caused by electron-induced charge buildup can be estimated by ellipsometry analysis. We applied the method to biased electron cyclotron resonance (ECR) plasma deposition of SiO2, compared the metal oxidation enhancement for biased ECR plasma deposition with that for exposing electron beams directly and also compared with the injected charge density Qinj for gate–oxide breakdown during biased ECR plasma deposition evaluated by time-dependent dielectrics breakdown measurements. In this way, we clarify that (i) the oxidation enhancement takes place at an electron-beam exposure of over 10 C/cm2, and (ii) the Qinj of over 10 C/cm2 is closely related to gate–oxide breakdown. These results confirm that the metal–oxide thickness is strongly associated with the degradation in gate–oxide yield related to the injected electrons and that the charge buildup damage is caused by electrons diffused during biased ECR plasma deposition.
Size-dependent photoluminescence energy and intensity of selective electron cyclotron resonance-etched strained InGaAs/GaAs quantum boxes
Authors: Reed J. D. , Chen Y.-P. , Tentarelli E. S. , Schaff W. J. , Eastman L. F.
Published: July 2002

A selective electron cyclotron resonance etch process was developed that etched GaAs over a 100 Å In0.20Ga0.80As quantum well. The etch produced sharp anisotropic profiles with zero detectable resist erosion and a smooth etched surface. The etch was specifically tailored for transferring quantum box patterns with lateral dimensions ranging from 700 to 120 nm into the quantum well structure. Migration enhanced molecular beam epitaxy was used to regrow a GaAs cladding on the box sidewalls. Room temperature photoluminescence measurements of the quantum boxes showed a relative shift of 15.5 meV to higher emission energy and a reduction in intensity by a factor of 100 as the box lateral dimension was decreased. The roles of strain and misfit dislocations in these structures are discussed.
Fabrication of high aspect ratio structures for microchannel plates
Authors: Shank S. M. , Soave R. J. , Then A. M. , Tasker G. W.
Published: July 2002

Substrates for microchannel plates have been fabricated using Si micromachining techniques. High aspect ratio pores are constructed using reactive ion etching and streaming electron cyclotron resonance etching, and low-pressure chemical vapor deposition (LPCVD). In one process, 40 μm deep pores with 2 μm openings on 4 μm centers are directly etched in Si. Alternatively, pores with aspect ratios of 30:1 are constructed in a low-stress SiNx membrane using a sacrificial template process whereby pillars of Si are etched and then subsequently backfilled with a dielectric using LPCVD.
Combining and matching optical, electron-beam, and x-ray lithographies in the fabrication of Si complementary metal–oxide–semiconductor circuits with 0.1 and sub-0.1 μm features
Authors: Yang Isabel Y. , Silverman Scott , Ferrera Juan , Jackson Keith , Carter James M. , Antoniadis Dimitri A. , Smith Henry I.
Published: July 2002

In the fabrication of large-area Si complementary metal–oxide–semiconductor circuits with 100 and sub-100 nm features, it is inefficient to use direct-write electron-beam (e-beam) lithography for all of the layers, in part because of the exceedingly long writing times. Instead, a strategy of ‘‘mix and match’’ is preferred, in which coarse features on all layers are defined by optical projection and only the fine features are written by e-beam lithography. We describe a strategy that combines optical, e-beam, and x-ray lithographies, and solves the problem of scale matching and distortion in such a mix-and-match scheme. Layers that include only coarse features are exposed directly on Si wafers using a G-line stepper. This same stepper is also used to expose, on a chrome-coated quartz wafer, arrays of e-beam field alignment marks along with any coarse features required in this ‘‘critical layer.’’ This pattern is then transferred by deep ultraviolet proximity printing onto an x-ray mask and plated up in gold. The e-beam writes the fine features using the e-beam field-alignment marks as reference. Because the arrangement of the e-beam field-alignment marks reflects the distortion and scale of the optical stepper, overlay in the final circuit on the wafer is ensured. Furthermore, considerable e-beam writing time is saved. The final pattern is transferred onto the device wafers using x-ray lithography.
In situ processing of high-T
c YBaCuO superconducting devices by focused ion beam micromachining at low temperature
Authors: Ben Assayag G. , Gierak J. , Hamet J. F. , Prouteau C. , Flament S. , Dolabdjian C. , Gire F. , Lesquey E. , Günther G. , Dubuc C. , Bloyet D. , Robbes D.
Published: July 2002

A focused ion beam (FIB) system coupled to a scanning electron microscope, including a new helium-cooled stage and electrical feedthroughs, has been put into operation. It allows real-time electron imaging during FIB machining while the sample is maintained at a minimum temperature of 25 K by continuous-flow helium cooling. Simultaneously, electrical characteristics can be monitored, recorded, and stored. Experimental results on high-critical-temperature superconducting thin films are given, exhibiting the evolution of the device’s response during the FIB-induced modifications. Two structures were realized at liquid-nitrogen temperature: a low-noise microbolometric sensor and a short-channel superconducting quantum interference device-like structure in YBaCuO material exhibiting a behavior of coherent vortex flow, micromachined by FIB. These experiments demonstrate the possibility of a precise in situ control of the critical current of micro- and nanobridges.
The effect of aperturing on radiation damage-induced pattern distortion of x-ray masks
Authors: Resnick D. J. , Cummings K. D. , Dauksher W. J. , Johnson W. A. , Seese P. A. , Chen H. T. H. , Wells G. M. , Engelstad R. , Cerrina F.
Published: July 2002

A finite element model has been used to study the distortion issues associated with nonuniform irradiation of an x-ray mask membrane. Results clearly demonstrate that small changes in stress can lead to large in-plane distortions unless the membrane field is uniformly exposed. If the mask membrane is uniformly exposed, the distortion can be minimized, allowing the mask to stay within its pattern placement error budget. The model has also been experimentally confirmed. While uniform exposure will be critical for controlling in-plane distortions, new issues such as resist processing and pattern registration within the membrane field must now be addressed.
Evaluation of a diamond-based x-ray mask for high resolution x-ray proximity lithography
Authors: Ravet M. F. , Rousseaux F. , Chen Y. , Haghiri-Gosnet A. M. , Carcenac F. , Decanini D. , Bourneix J. , Launois H. , Bachmann P. K. , Lade H. , Wiechert D. U. , Wilson H.
Published: July 2002

A high resolution x-ray mask compatible with a commercial stepper has been realized with a diamond membrane and electroplated gold structures. The membrane was optimized to satisfy all the requirements needed for x-ray proximity lithography using soft x rays at the super-ACO synchrotron facility. Patterning was optimized using a conventional 50 keV vector scan generator. High density high resolution gold gratings were obtained with linewidth down to 60 nm with periods as small as 120 nm. It was found that the resolution for our current studies was mainly limited by the resist thickness and not by the diamond surface morphology or the electrodeposition process. Alignment performance has been evaluated. Preliminary results show that diamond material with a 20 nm root-mean-square surface roughness is acceptable for good alignment performance.
Domain formation and annealing in an adsorbed liquid crystal monolayer observed by scanning tunneling microscopy
Authors: Stevens F. , Dyer D. J. , Walba D. M.
Published: July 2002

A monodomain monolayer of adsorbed liquid crystal molecules was observed by scanning tunneling microscopy (STM). Voltage pulses applied to the STM tip while scanning caused formation of rotated domains in the two-dimensional crystalline monolayer. The new domains annealed out over several minutes, reforming the initial monodomain. This shows that the STM tip can influence the structure of adsorbed monolayers and suggests that the voltage pulses often used to achieve images of organic adsorbates may influence monolayer formation and not simply reshape the STM tip.
Photo-Hall studies of modulation-doped field-effect transistors with short-period superlattice channels rather than alloy channels
Authors: Moreira M. V. B. , de Oliveira A. G. , Py M. A.
Published: July 2002

We studied the photo-Hall mobility and the photo-Hall density of modulation-doped field-effect transistor structures using either an InGaAs alloy channel or a short-period superlattice channel. In defining the short-period superlattice channel we changed the thicknesses of the InAs and GaAs layers and the number of InAs/GaAs interfaces. The thicknesses of the InAs layers varied from 0.5 to 1.6 monolayers, those of GaAs layers from 4 to 20 monolayers, and the number of InAs/GaAs interfaces varied from 3 to 7. As a consequence the total short-period superlattice channel thicknesses varied too, but they were kept below the critical layer thickness to relax the pseudomorphic structure. The persistent photoconductivity effect at 77 K and the use of a red light emitting diode as the illumination source were employed to induce variation of the Hall mobility and the Hall density in the conduction channel. For the short-period superlattice samples our results indicate that the Hall mobility increases (a) with a reduction in the number of InAs/GaAs interfaces; (b) by employing an integral number of InAs monolayers; and (c) by increasing the thickness of the GaAs layers. These results suggest that the three effects are effective in producing surface smoothing. When the short-period superlattice samples are compared with samples having an InGaAs channel, we have shown that for an indium content around 8% the electrical properties are basically the same. On the other hand, for an indium content around 25% the mobility increases up to 35% proving that use of the short-period superlattice channel is useful in reducing the atomic disorder. The scattering associated with the alloy disorder increases with the indium content, and the deleterious effect of disorder can be reduced by replacing the alloy channel by a short-period superlattice channel.
Ultrafine pattern x-ray mask fabricated using the sidewall method
Authors: Xia A. D. , Fu S. J. , Hong Y. L. , Tian Y. C. , Hu Y. G. , Zhang X. Y. , Lu J. , Li F. Q.
Published: July 2002

A 50 nm line x-ray mask was fabricated by using a sidewall process. The gold film which was taken as an absorber was deposited by ion-beam sputtering onto the very vertical sidewall surfaces of a polyimide grating. It was demonstrated that the smoothness and the small sidewall angle play an important role in the fabrication of the higher resolution x-ray mask using sidewall methods.
Influence of CH4/H2 reactive ion etching on the deep levels of Si-doped AlxGa1−xAs (x=0.25)
Authors: Pereira R. G. , Van Hove M. , de Potter M. , Van Rossum M.
Published: July 2002

We study the passivation and recovery of shallow and deep levels in Si-doped AlGaAs exposed to CH4/H2 and H2 reactive ion etching (RIE). The carrier concentration depth profile is determined by capacitance–voltage measurements. The activation energy to recover the silicon donors is found to be 1.1 eV for samples exposed to CH4/H2 RIE and 1.3 eV for samples exposed to H2 RIE. We study the behavior of DX centers in Si-doped AlGaAs layers after RIE exposure and subsequent thermal annealing by using deep level transient spectroscopy. For CH4/H2 RIE a new emission is detected at the high temperature side. We identify this emission as the DX3 center, which is assigned to a DX center with three aluminum atoms surrounding the Si donor. This DX center is only detected on the samples exposed to CH4/H2 RIE. We explain the formation of this deep level to the highly selective removal of Ga atoms in favor of Al atoms. Consequently Al-rich regions are created near the surface.
In situ fiber optic thermometry of wafer surface etched with an electron cyclotron resonance source
Authors: Thomas S. , Berg E. W. , Pang S. W.
Published: July 2002

The effect of plasma heating on wafer temperature during etching has been studied. Si and InP were etched using a high ion density discharge generated by an electron cyclotron resonance source. The wafer temperature was measured using fiber optic thermometry as microwave power, rf power, chamber pressure, and gas flow were varied. Wafer temperatures increased with both rf and microwave power, and decreased with chamber pressure. For a rf power of 50 W, chamber pressure of 1 mTorr, a source distance of 13 cm, and a 10 sccm Ar flow, an increase in microwave power from 50 to 500 W caused the temperature to increase from 62 to 186 °C. An increase in the rf power from 50 to 300 W increased the wafer temperature to 145 °C. Additionally, the effectiveness of using He flowing at the backside of the wafer for temperature control was analyzed. By setting the backside He pressure at 3 Torr, the temperature increased to only 29 °C. Time dependent etch characteristics of InP were studied and related to the in situ temperature measurements. At 100 W of microwave power, the InP etch rate increased from 100 to 400 nm/min as the wafer temperature rose from 20 to 150 °C. As the temperature increased above 150 °C, the profile became more undercut and the surface morphology improved. By setting the stage temperature to −100 °C and using 3 Torr of He pressure at the backside of the wafer, the InP etch rate remained constant during etching and undercutting was suppressed. For 500 W of microwave power, a fast InP etch rate of 2 μm/min was obtained when the wafer temperature was <110 °C, and it increased to over 4 μm/min when the temperature was ≳150 °C.
ArF surface modification resist process with enhanced water sorption ability
Authors: Matsuo Takahiro , Endo Masayuki , Shirai Masamitsu , Tsunooka Masahiro
Published: July 2002

Surface modification resist (SMR) process, which gives negative-tone image owing to the polysiloxane formation in the exposed resist surface using chemical vapor deposition, was studied for subquarter micron pattern fabrication. SMR was based on the hydrolysis of alkoxysilane and the subsequent condensation reaction in the presence of an acid catalyst and water. This article describes the application of SMR to ArF excimer laser lithography with enhanced water sorption ability. We propose the copolymer of propylideneimino p-styrenesulfonate (PPISS) and methyl methacrylate with enhanced water sorption ability in order to improve the selectivity of the polysiloxane formation. PPISS generates sulfonic acid and acetone which acts as the diffusion promoter of water molecules. It was demonstrated that the hydrolysis reaction was promoted and the polysiloxane was more selectively formed with high sensitivity by using the proposed polymer. The influence of PPISS units ratio for the selectivity of polysiloxane formation and dry etch durability was investigated. Below 0.2 μm patterns fabrication was demonstrated by optimizing the ratio of the PPISS unit which functioned as the selective generation of acid and acetone.
Absolute distance measurement interferometry for alignment systems for advanced lithography tools
Authors: Dunn Thomas J. , Lee Teik-Meng , Jain Kanti
Published: July 2002

We describe a novel interferometer which enables the absolute measurement of distances between two objects. This system was developed for integration into an alignment system for an x-ray lithography tool but also has many other potential applications. The absolute distance measuring interferometer system consists of two frequency-stabilized lasers which probe the resonances of a high-finesse, Fabry–Pérot (FP) interferometer. The two lasers are independently locked to adjacent resonant peaks of the FP cavity transmission spectrum. The frequency difference between two adjacent longitudinal modes of the cavity is known as the free spectral range (FSR) and is inversely related to the optical path length of the cavity. The FSR of the cavity is measured by analyzing the frequency content of the mixed optical signal from both lasers with a spectrum analyzer. This approach provides a real-time measurement of the FSR and directly measures the absolute optical path between the two cavity mirrors. We have successfully constructed a working prototype system and measured the FSR of an 8.3-cm-long, high-finesse, optical cavity to within 5 Hz, which translates to a resolution of 2.3 Å. We present an overview of the program, the latest experimental results, and the status of its application to an x-ray stepper.
Patterning accuracy estimation during stage acceleration in the electron beam direct writing system EX-8D
Authors: Hattori K. , Magoshi S. , Ando A. , Satoh S. , Sunaoshi H. , Suenaga M. , Housai H. , Hashimoto S. , Wada H. , Sugihara K.
Published: July 2002

We have evaluated patterning accuracy during stage acceleration of EX-8D in which a beam deflection control system has been installed to compensate a beam positional shift depending on both the stage velocity and position. From the fact that there is no difference in patterning accuracy between stage acceleration phase and constant velocity phase, it was found that the control system functions accurately. We have also analyzed beam position deviation. The analysis results showed that improvement of the laser interferometer resolution, stabilization of the objection lens, and elimination of the ambient magnetic field change are necessary to achieve 1 Gbit class ultra-large- scale integrated patterning of 0.15 μm within 10% beam position fluctuation. By adopting continuous writing during stage acceleration and deceleration while turning, the improvement of the throughput was also confirmed without reducing the patterning accuracy.
Application of scanning probe methods for electronic and magnetic device fabrication, characterization, and testing
Authors: Born A. , Hahn C. , Löhndorf M. , Wadas A. , Witt Ch. , Wiesendanger R.
Published: July 2002

Selected examples of the application of scanning probe methods for the fabrication, characterization, and testing of electronic and magnetic devices are presented. In particular, promising combinations of conventional photolithography or e-beam lithography with scanning probe methods are described. The combination of atomic-scale self-organization processes with scanning probe microscopy and manipulation experiments possibly can lead to a novel class of atomic-scale devices which could be fabricated on a reasonable time scale.
Selective dry etching of oxide films for spacer applications in a high density plasma
Authors: Allen Lynn R. , Yu-Wang Victoria , Sato Masyuki
Published: July 2002

The use of a high density plasma to etch oxide side wall spacers was investigated. Process trends and the optimum process conditions required were determined. Oxide and polysilicon etch rates, uniformities, and the selectivity of oxide to polysilicon were all measured. The resulting etch chemistry had an oxide etch rate of 350 nm/min with a selectivity of oxide to polysilicon of 30:1.
Process technology for monolithic high-speed Schottky/resonant tunneling diode logic integrated circuits
Authors: Lei P.-M. , Subramaniam S. , Bernstein G. H. , Williamson W. , Gilbert B. K. , Chow D. H.
Published: July 2002

A seven-layer process was developed to fabricate monolithic high-speed logic circuits, requiring integration of Schottky diodes and resistors with interband resonant tunneling diodes (RTDs). With this process technology, we have demonstrated a functionally complete logic family based on RTDs with a maximum operating frequency in excess of 12 GHz and a minimum power dissipation on the order of 0.5 mW per gate.
Optimizing the reactive ion etching of p-InGaP with CH4/H2 by a two-level fractional factorial design process
Authors: Chan R. H. , Cheng K. Y.
Published: July 2002

The reactive ion etching of p-InGaP and p-GaAs using CH4/H2 was examined through design of experiment techniques. The etch rate of InGaP and GaAs, the etch rate ratio of InGaP over GaAs, and the dc bias were optimized by fractional factorial design as a function of total gas flow rate, methane composition, total pressure, and rf power. It was found that the rf power and the total chamber pressure were the most significant parameters in the reactive ion etching process. Models were created to describe the change of each response over a range of etching parameters.
Characterization of silicon nitride films formed by synchrotron radiation-excited chemical vapor deposition
Authors: Kyuragi Hakaru
Published: July 2002

From a standpoint of physical, chemical, and electrical properties, silicon nitride films formed by synchrotron radiation-excited chemical vapor deposition with SiH4+N2 gas mixture are characterized. These properties are compared with the properties of films deposited by other low-temperature processes. It is found that the present film has such features as lower hydrogen content (<4×1021 cm−3), higher film density (2.9–3.05 g/cm3), lower etching rate against BHF (<10 nm/min), and potentially improved electrical properties considering that deposition was performed at substrate temperatures as low as 200 °C. Deposition kinetics, the effect of bias on film properties, and ways to improve the electrical properties are also discussed.
Scanning scattering microscope for surface microtopography and defect imaging
Authors: Lorincik J. , Marton D. , King R. L. , Fine J.
Published: July 2002

A recently developed optical-scatter instrument, the scanning scattering microscope (SSM) produces two-dimensional images of very small surface features and of variations in surface topography. In its present configuration, the lateral resolution is better than 10 μm and its sensitivity to surface roughness is in the angstrom (rms) range. The performance of the SSM has been demonstrated using calibration gratings, Si(100) surfaces, and Ge thin films grown on silicon; intercomparison also was made with atomic force microscope measurements. These results indicate that this scanned optical technique is a very useful noncontact method for evaluating surface microtopography.
Three dimensional axisymmetric space charge simulation via boundary elements and emitted particles
Authors: Hartman Robert L. , Mackie William A. , Davis Paul R.
Published: July 2002

The boundary element (i.e., charge density) method can often be used to reliably and efficiently compute field strengths and field emission currents where space charge is not a factor. In order to approximate space charge effects, launching and tracking of simulated particles are added to a basic boundary element scheme. Quantities of most interest include the emitted current and gate current once the startup transients die out. Simplistic initial attempts at such a simulation reveal difficulties in the following areas: (1) choosing a single time step suitable for all emitted particles; (2) computing the effect of newly emitted particles on the tip field controlling the next emission step; and (3) stabilizing the computed result. Methods for combating these problems are implemented and tested in the case of concentric spheres where one dimensional potentials can be reliably numerically approximated by use of an ordinary differential equation solver. Finally, the resulting code is applied to laboratory geometries.
Phonon scattering in novel superlattice-asymmetric double barrier resonant tunneling structure
Authors: Banoo K. , Daniels-Race T. , Wallis C. R. , Teitsworth S. W.
Published: July 2002

The scattering effects (specifically LO-phonon scattering) in a 45 Å AlAs/80 Å GaAs/33 Å AlAs asymmetric double barrier resonant tunneling (ADBRT) structure with a short period GaAS/Al0.3Ga0.7As superlattice incorporated on one side of the double barrier have been studied and characterized. Enhanced levels of current conduction were produced in the ADBRT due to the superlattice miniband electron transport under forward bias. And the effect of the said superlattice on the phonon scattering phenomena exhibited by the entire device was subsequently examined. Magnetic field fan diagrams at 4.2 K under reverse bias showed a new feature at an energy of 22 meV that could be explained on the basis of previously unreported GaAs LO-phonon scattering processes from the first excited emitter level. Finally, quenching of phonon-assisted tunneling in reverse bias on decreasing the period of the superlattice was also observed.
Sulfur contamination of (100) GaAs resulting from sample preparation procedures and atmospheric exposure
Authors: Butcher K. S. A. , Egan R. J. , Tansley T. L. , Alexiev D.
Published: July 2002

X-ray photoelectron spectroscopy with argon ion depth profiling was employed to investigate sulfur deposition from a standard 3H2SO4:H2O2:H2O etchant onto (100) GaAs. From these experiments it appears that etching with 3H2SO4:H2O2:H2O leaves a mixed sulfide/oxide layer, with free sulfur at the top surface of this layer. The sulfide within the layer was found to be bound to gallium, and recognition of the presence of sulfur allowed the clarification of the Ga(3d) photoelectron peak position for Ga2O3. No evidence of sulfate formation was found. Removal of the sulfur contamination using a solution of HCl:H2O was investigated. Also, atmospheric contamination of samples exposed to room conditions for six months was observed.