bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphous silicon solar cells
Authors: Ovshinsky S. R.
Published: July 2002

The direct conversion of sunlight into electricity has been a utopian dream. The ability to generate electricity in this manner is, of course, exciting since it utilizes nondepletable fuel and is nonpolluting. However, since the 1950’s, the approach to accomplish this aim has been primarily through the utilization of expensive crystalline silicon solar cells. We describe here how noncrystalline materials, that is, amorphous materials, can be produced as continuous, large-area, thin-film devices with efficiencies, stabilities, and costs which will permit them, for the first time, to compete realistically with conventional fuels such as oil, gas, uranium, and coal.
High-voltage shaped e-beam lithography
Authors: Jones G. A. C. , Sargent P. M. , Norris T. S. , Ahmed H.
Published: July 2002

A high-voltage (100 kV) variable-shaped electron beam lithography system has been developed. With this system it is possible to improve the edge resolution in variable-shape lithography to better than 0.1 μm even at high beam currents. In addition the other advantages of high-voltage lithography such as reduced proximity effect, improved line width control in lithography over steps in the substrate, and better profiles on thick resist overlayers are also obtained. Experimental results are compared with simulation from a Monte Carlo based model of the electron column which predicts the benefits of working at higher beam voltage than the conventional 20 kV. Results are presented which show current profiles and exposures in resist of patterns with sizes from 5 μm×5 μm to ∼1 μm×1 μm with sub 0.1 μm resolution at beam voltages of 70 kV and greater while maintaining a beam current of >3 μA.
Surface morphologies of GaAs layers grown by arsenic-pressure-controlled molecular beam epitaxy
Authors: Wang Y. H. , Liu W. C. , Chang C. Y. , Liao S. A.
Published: July 2002

Surface morphologies of the molecular beam epitaxy (MBE)-grown GaAs layers using background arsenic-pressure-control method were investigated. The growth parameters, such as substrate temperatures, growth rates, epilayer thicknesses, As/Ga ratios, doping concentrations, substrate types, etc., are related to the observed oval defect density. Protrusions and Ga-droplet induced oval defects were formed during growth. The origin of the oval defects in our system is found to be the gallium oxide, not Ga ‘‘splitting’’ from the effusion cell. Surface preparations are also another important factor in reducing the oval defect density. Special triangular pyramidal defects with concave or acute top surfaces were found. They have the same major axis as oval defects. Also found were defects with perpendicular orientation to the oval defects. Such defects are attributed to contaminations on the surface and can be eliminated.
Observation of h/e Aharonov–Bohm interference effects in submicron diameter, normal metal rings
Authors: Umbach C. P. , Washburn S. , Webb R. A. , Koch R. , Bucci M. , Broers A. N. , Laibowitz R. B.
Published: July 2002

Clear evidence of Aharonov–Bohm oscillations with respect to the flux quantum Φ0=h/e has been observed in the magnetoresistance of single, submicron diameter, normal metal rings. The rings were fabricated using contamination nanolithography in a personal computer controlled, high resolution, scanning transmission electron microscope. The magnetoresistance oscillations developed below T≂1 K, and, surprisingly, persisted without attenuation for more than 1000 periods.
Development of nanometric electron-beam lithography system (JBX-5D II)
Authors: Shearer M. Hassel , Takemura H. , Isobe M. , Goto N. , Tanaka K. , Miyauchi S.
Published: July 2002

The production of VHSIC and microwave devices has shown that submicron lithography by e-beam, optical, or x-ray systems is rapidly becoming feasible. There is, however, a demand developing for a nanolithography tool for producing GaAs devices and for investigating the physics of scaling of silicon semiconductor devices. We have developed an electron beam lithography system, the JBX-5D II, which is effective in fabricating both submicron and nanometric devices. The system employs a high brightness single crystal (100) LaB6 cathode and an in-lens octupole deflector. The JBX-5D II is fully computer controlled which permits automatic switching of the accelerating voltage between 50 and 25 kV, of writing modes between large and small currents, and of different scanning fields. The ability to switch writing modes permits rapid writing of devices with geometries as small as 10 nm with a fine beam and a coarser beam to be used on larger geometries. The present paper deals with some of the characteristics occurring after switching between writing modes. Experimental results will also be reported on voltage stability and probe currents. The mark detection technology for nanometer writing will be presented along with experimental results for an 80 Å probe size.
Repair techniques for silicon transmission masks used for submicron lithography
Authors: Behringer U. F. W. , Vettiger P.
Published: July 2002

This paper describes several methods for the repair of stencil masks as used for electron- or ion-beam shadow projection systems. Such a mask consists of a thin membrane about 3 μm thick with pattern as physical holes. The fabrication process is described elsewhere [H. Bohlen et al., in Proceedings of the Electron and Ion Beam Science and Technology Conference 1978; U. Behringer et al. (unpublished)]. This mask may contain pinholes besides the desired pattern holes; also pattern holes may deviate from their designed size. The first step in the repair process is for a resist layer to be spun onto the whole mask area. Even larger holes with dimensions up to 1 mm are closed in such a way. In a second step, the resist layer is again opened at the pattern positions. We have investigated different methods to reopen the design pattern. The ‘‘block-out’’ method uses a second transmission mask with an identical pattern. Owing to the statistical distribution of the defect holes, only the designed pattern holes will be reopened. The so-called ‘‘writing methods’’ use a scanning e-beam system to reopen the circuit pattern. The structural resist works as a substrate for a gold deposition from the reverse side of the transmission mask. After the gold deposition, this resist layer is removed by an O2 plasma leaving behind a self-supporting Au layer closing the undesired openings. Another repair method, the so-called ‘‘darning method,’’ closes defect holes in the mask by contamination writing.
Hysteresis predicted in I–V curve of heterojunction resonant tunneling diodes simulated by a self-consistent quantum method
Authors: Berkowitz H. L. , Lux R. A.
Published: July 2002

Simulation of a heterojunction tunneling diode using a self-consistent quantum model predicts hysteresis in the I–V characteristics. The transport of electrons through the diode is modeled by simultaneous solution of Poisson’s equation with a charge density derived from ensemble-averaged solutions to a one-dimensional Schrödinger equation. The resulting potentials and charge distributions are dominated by space charge effects. We find for a considerable range of bias voltage, the current is a double valued function of bias. The high and low current states are distinguished by the amount of charge stored in the barrier region of the diode.
The Si/GaAs (110) heterojunction: Strain, disorder, and valence-band discontinuity
Authors: List R. S. , Woicik J. C. , Lindau I. , Spicer W. E.
Published: July 2002

We have studied the effects of strain on band offsets through a combined photoemission and polarization dependent surface extended x-ray absorption fine structure (SEXAFS) study of thin Si overlayers on the 4% lattice-mismatched GaAs (110) substrate. By selectively orienting the heterojunction interface either parallel to or perpendicular to the x-ray polarization vector, we have independently measured from SEXAFS the Si–Si nearest-neighbor bond lengths of bonds lying either in the plane or out of the plane of the interface, respectively. The in-plane bond lengths were larger by a maximum of 2% for our thinnest coverage of 4 monolayers. An ideal pseudomorphic overlayer would have a 4% difference between these bond lengths. We therefore infer a large density of dislocations even in such thin overlayers. From our photoemission measurements we found no resolvable (>0.05 eV) differences in the valence-band discontinuity between Si overlayers which were either crystalline and 2% anisotropically strained, crystalline and unstrained, or amorphous and unstrained.
Initial stages of Schottky barrier formation: Temperature effects
Authors: Stiles K. , Kahn A. , Kilday D. G. , Margaritondo G.
Published: July 2002

Recent experiments on the formation of Schottky barriers reveal a temperature-dependent pinning of the Fermi level (EF) which cannot be explained in terms of the current published models. Al, Au, Ag, In, and Sn are evaporated on room temperature (RT) and low temperature (LT=80 K) cleaved n- and p-GaAs(110). We find a substantial decrease in surface metal clustering at LT, leading to more homogeneous films, especially with Al, In, and Sn. Interface mixing and chemical reaction are also partly inhibited. Cancellation of the semiconductor surface relaxation is observed for Al and Sn. From the electronic point of view, low temperature has opposite effects on the pinning rate of EF on n- and p-GaAs. Pinning on n-GaAs as a function of coverage is dramatically retarded. Pinning on p-GaAs remains faster than on n-GaAs, as fast as at RT, faster for Al and In. These asymmetric rates make it impossible to explain the initial stages of Schottky barrier formation for all substrates with a single mechanism. They suggest that several independent but concomitant mechanisms might be at work in the pinning process.
Three-dimensional photolithography with conformal GeSe resist
Authors: Vadimsky Richard G.
Published: July 2002

Arrays of 80-μm-high mesas and 250-μm-deep wells were formed in silicon using conventional etching techniques. Oxide and metal patterns were photodefined over the sloping walls of these structures using the inorganic resist Ag2Se/Ge0.15Se0.85. A 2000-Å-thick conformal coating of the chalcogenide Ge0.15Se0.85 was sputter deposited onto the etched silicon wafers. Sensitized in a Ag(CN)−2 containing aqueous bath, the resist was exposed through a mask on a contact printer. Patterns were delineated using established wet chemical developing procedures and then transferred to underlying oxide or metal to form implant windows or metal conductors, respectively. Image defocusing over the depth of the etched silicon features produced some linewidth changes down the sloping walls, but useful conductors were fabricated.
Quantitative analysis of resolution and stability in nanometer electron beam lithography
Authors: Kratschmer E. , Rishton S. A. , Kern D. P. , Chang T. H. P.
Published: July 2002

A technique for the measurement of the beam diameter and the positional stability of an electron beam with respect to the substrate using an anisotropically etched silicon edge is described. Measurements are done either in a scanning beam mode to measure the beam diameter or in a stationary beam mode to measure beam positional noise. This technique has been used for a quantitative analysis of the resolution and stability in a 8-nm spot size electron beam lithography system. The detection limit of the beam position stability measurements is <0.1 nm. Applications for the measurement of mechanical vibrations and acoustical noise, deflection amplifier noise, magnetic interference, and eddy currents in magnetic deflection systems are discussed.
Sub-0.5-μm lithography with a new ion projection lithography machine using silicon open stencil masks
Authors: Buchmann L.-M. , Csepregi L. , Heuberger A. , Müller K. P. , Chalupka A. , Hammel E. , Löschner H. , Stengl G.
Published: July 2002

An ion projection lithography system was equipped with an open stencil mask manufactured by applying silicon technology. By exposing poly(methylmethacrylate) and SiO2 to He+ ions, the pattern, transferred with a 9.5:1 reduction, showed structures with a minimum linewidth of 0.25 μm. The emphasis of this work concentrated on the various effects which produce distortion of the mask. Whereas linear dilation of the foil caused by compressive stress and enhanced by the network structure could be offset by means of the ion optical system, anisotropic distortion which resulted from the unequally distributed openings in the pattern had to be minimized by applying a suitable design. With a field effect transistor test pattern, an average distortion of 0.15 μm has been obtained in a 20×21 mm2 area of the mask. Only minor contributions to pattern deviations were expected from the temperature increase and sputter erosion.
A comparison of different deposition techniques for fabricating polysilicon contacted emitter bipolar transistors
Authors: Bagri Ravi , Neudeck Gerold , Klaasen William , Pak James , Logsdon James
Published: July 2002

Four methods for fabricating polysilicon contacted bipolar junction transistors (BJT’s) have been investigated. In the first method polysilicon was deposited using low-pressure chemical vapor deposition (LPCVD) at 620 °C. In the remaining three methods a-Si was first deposited and then recrystallized to form polysilicon. In the second method a-Si was deposited using LPCVD at 580 °C. The third method used plasma-enhanced chemical vapor deposition (PECVD) to deposit a-Si:H. The fourth method involved a plasma etch with argon or hydrogen prior to deposition of a-Si:H using PECVD. The results indicated that using the PECVD method for depositing a-Si:H without any prior plasma-etch step and recrystallizing it to form polysilicon resulted in the highest current gain (β) enhancement of 3.5 and also allowed the reduction of the polysilicon anneal temperature down to 800 or 900 °C from 1000 °C. The compactness in the spread of the peak β values for the devices fabricated using this technique also reflects its ability for reproducible fabrication of polysilicon contacted shallow emitter BJT’s.
Quantitative analysis by submicron secondary ion mass spectrometry
Authors: Satoh H. , Owari M. , Nihei Y.
Published: July 2002

In order to apply secondary ion mass spectrometry (SIMS) to quantitative analysis of submicron areas, we made a high-spatial resolution SIMS (submicron SIMS) by combining a focused metal ion beam, a plane-focusing mass spectrometer, and a multichannel parallel detection system. A 35 kV, 100 pA beam with diameter on the sample of <0.1 μm was used. During measurements, this high-current density ion beam can destroy the sample with a large sputtering rate when slowly rastered. This causes rapid changes in both absolute and relative intensities of secondary ions. In our system, a 120-channel parallel detector covers the 1:2 mass range of m/e dispersion. By using this submicron SIMS, quantitative factors in the analysis of microstructures on the surface were investigated. Sputtering yield and, consequently, secondary ion intensity depend largely upon the angle between the primary beam and the sample surface just under the beam irradiation; such topographic effects distort the quantitative results. In order to avoid such distortions, it was found to be advantageous to shave off the analyzed feature from one edge to the other. By using such a sputtering method, the incident angle of the primary beam to the surface being sputtered is held constant. Accordingly, the quantitative power of submicron SIMS was greatly improved.
Monte Carlo calculations of the beam flux distribution from molecular-beam epitaxy sources
Authors: Adamson S. , O’Carroll C. , McGilp J. F.
Published: July 2002

Flux distributions from Knudsen cell sources used in molecular-beam epitaxy have been determined using Monte Carlo techniques. The increased beaming effect as the cell empties, which produces an increase in film thickness variation across the substrate, is found to be less pronounced than the widely used analytic theory of Clausing predicts. Tilting a full cell is shown to produce flux distributions which are asymmetric about the cell axis, but the effect decreases as the tilted cell empties.
Quantitative lithographic performance of proximity correction for electron beam lithography
Authors: Bojko R. J. , Hughes B. J.
Published: July 2002

We have developed a method for measuring the improvement in lithography produced using proximity correction. We have used this method to characterize the performance of the Cambridge Instruments proximity correction software. The goal of this work is to explore the parameter space of the correction. We have used our measurement technique to show quantitatively the effect on lithographic performance of: scattering fit model (double Gaussian, triple Gaussian, and double Gaussian plus exponential), variation in scattering coefficients, and variation of computation parameters (integration grid size). For our study, we have used a common e-beam process: 0.5 μm thick PMMA resist on silicon, with a 20 KeV, 75 nm Gaussian beam. We have studied several geometries with dimensions as small as 0.2 μm. We have found that feature sizes of the proximity corrected exposures are quite insensitive to large variations in input parameters. Variation of the double gaussian parameters alpha and eta of ±30% from their best-fit value produced <1% change in feature size, while feature size changed by ≊2% for each 10% change in the beta parameter. Over the range of feature sizes measured (0.2–3.0 μm) there was less than 10 nm difference between patterns corrected using the double Gaussian, triple Gaussian, and the double Gaussian plus exponential models.
Novel method for measuring and analyzing surface roughness on semiconductor laser etched facets
Authors: Herrick Robert W. , Sabo Lori G. , Levy Joseph L.
Published: July 2002

We introduce a method of measuring the surface profile of etched facets on semiconductor lasers, giving direct, quantitative results. Unlike previous techniques which attempt to infer facet quality from electro-optic performance or subjective analysis of micrographs, this technique provides the actual facet profile. We show how this information can be used for process improvement, and accurate numerical simulation of facet reflectivity.
Off-angle emission characteristics of liquid Au–Si–Be ion sources
Authors: Arimoto H. , Fujii T. , Komuro M.
Published: July 2002

Energy distributions (ED) of singly and doubly charged monatomic ion species (M+ and M++) emitted from a Au–Si–Be liquid metal (LM) ion source were measured by using a sector magnet. The energy spreads of Si+ and Si++ decrease with an increase in the inclined emitter tip angle of 0°–20°. The drastic decrease in the Si+ energy spread results from a disappearance of a shoulder on the low energy side accompanying the main peak in the profile. The reason for the disappearance of the shoulder may be that the energy deficit of field ionized ions decreases and merges in the main peak because of a weaker electric field strength on the off-angle position. At the same time, a tail in the low energy region which is produced by charge transfer (CT) collision with doubly charged ions and neutral atoms also disappears with increasing the inclined angle, although the intensity of M++ does not decrease seriously. This may be due to the difference in ion trajectories for both species caused by the difference in an initial velocity at the location where the CT collision takes place. Based on the drastic decrease in the energy spread, the figure of merit in the focused beam is also discussed.
Measurement of the CdSe/ZnTe valence band offset by x-ray photoelectron spectroscopy
Authors: Yu E. T. , Phillips M. C. , McCaldin J. O. , McGill T. C.
Published: July 2002

We have used x-ray photoelectron spectroscopy (XPS) to measure the valence band offset in situ for CdSe/ZnTe (100) heterojunctions grown by molecular-beam epitaxy. XPS measurements were performed for films of CdSe (100) and ZnTe (100), and for heterojunctions consisting of either ∼25 Å of CdSe grown on ZnTe or ∼25 Å of ZnTe grown on CdSe. Observations of reflection high energy electron diffraction patterns indicated that CdSe films deposited on ZnTe were grown in cubic zinc blende form, rather than the natural wurtzite structure of CdSe. Our measurements yielded a CdSe/ZnTe valence band offset ΔEv=0.64±0.07 eV. The corresponding conduction band offset for CdSe/ZnTe is ΔEc=1.22±0.07 eV for room temperature band gaps for ZnTe and for cubic CdSe of 2.25 and 1.67 eV, respectively.
Criterion to judge whether the resist heating effect will occur
Authors: Saito Kenich , Sakai Tomoaki
Published: July 2002

A specific criterion for judging whether the resist heating effect will occur under given beam and resist conditions is proposed. The criterion is directly applicable to direct-writing variably shaped electron-beam systems and chain-scission type resists. After studying the relationship between resist temperature and pattern deformation, it is hypothesized then verified experimentally that pattern deformation occurs when temperature at the shot edge point is higher than the glass transition temperature of the resist. Experiments revealed that chemically amplified resists are more resistant to the resist heating effect than chain-scission type resists. Applying the hypothesis to resist temperature calculations, a constant figure was derived that represents the criterion for high-throughput writing systems. The figure suggests the beam and resist conditions that are required for high-throughput pattern writing without the resist heating effect.
Selected-area epitaxy of CdTe
Authors: Benson J. David , Dhar N. K. , Martinka M. , Boyd P. R. , Dinan J. H. , Benz R. B. , Wagner B. K. , Summers C. J.
Published: July 2002

Selected-area epitaxy of CdTe grown by chemical-beam epitaxy and migration-enhanced epitaxy was achieved at reduced temperatures (above 225 °C) on (001) GaAs substrates patterned with SiO2. CdTe single-crystal growth was observed on the GaAs surface while no deposition was detected on the SiO2. Selected epitaxy was further demonstrated in reduced-area patterns with dimensions suitable for the monolithic integration of infrared focal plane and processor arrays. Growth selectivity was confirmed by scanning Auger microscopy, scanning electron microscopy, reflection high-energy electron diffraction, and x-ray double-crystal rocking curve analysis. A method is proposed to reduce the growth temperature to below 200 °C; a temperature appropriate for epitaxy of device-quality HgCdTe.
Nanoscale metal–semiconductor–metal photodetectors with subpicosecond response time fabricated using electron beam lithography
Authors: Liu M. Y. , Chou S. Y. , Hsiang T. Y. , Alexandrou S. , Sobolewski R.
Published: July 2002

Metal–semiconductor–metal photodetectors (MSM PDs) with finger spacing and width as small as 25 nm have been fabricated using high-resolution electron beam lithography. Measurements using an electro-optic sampling system show that the fastest detector has a full width at half-maximum response time of 0.87 ps and a 3 dB bandwidth of 510 GHz. Monte Carlo simulation of detector response time is studied and compared with experimental data. Finally, scaling rules for high-speed MSM PDs are proposed.
Fabrication of parallel quantum wires in GaAs/AlGaAs heterostructures using AlAs etch stop layers
Authors: Grundbacher R. , Chang H. , Hannan M. , Adesida I.
Published: July 2002

A procedure utilizing AlAs etch stop layers coupled with wet etch processes has been developed to accurately control etch depth in the fabrication of uniform parallel quantum wires (QWs) in GaAs/AlGaAs heterostructures. Wires are defined in poly(methylmethacrylate) by electron beam lithography and then transferred into the heterostructure using citric acid/hydrogen peroxide solutions. The use of the etch stop layers permits wires to be accurately patterned by shallow or deep etching and allows for a comparative study of the effect of etch depth on the active dimensions of the wires. It is shown that shallow-etched QWs have active electron channels wider than deep-etched ones due to minimization of sidewall depletion. Also, it is demonstrated that sidewall passivation is achieved with silicon nitride and this aids in making the active electron channel width closer to the physical width of the QWs. Gated QW devices with wires as long as 10 μm have exhibited quantum conductance at 4.2 K which shows that the fabricated wires are damage-free.
Electron cyclotron resonance sputter removal of SiO2 on silicon wafers
Authors: Gopinath V. , Salbert G. T. , Grotjohn T. A. , Reinhard D. K.
Published: July 2002

The in situ sputter removal of oxide layers prior to subsequent depositions or growth is increasingly important as device sizes and hence interlayer contact sizes shrink. Electron cyclotron resonance (ECR) plasma sputter removal of oxides has been investigated since it offers the combination of high plasma densities and low ion energy induced substrate damage. In this study, ECR argon discharge sputter removal of SiO2 was investigated using a 9 and 25 cm diam discharge. The uniformity and rate of oxide removal on 3 and 6 in. silicon wafers were investigated with respect to pressure (0.6–2 mTorr), microwave power (200–800 W), radio-frequency induced bias (−30 to −80 V) and downstream position (6.3–11.8 cm) of the wafer. Uniformity and rate results show good correlation to ion density measurements and to an ambipolar plasma diffusion model.
Development of an electron-beam process for the fabrication of x-ray nanomasks
Authors: Gentili M. , Grella L. , Di Fabrizio E. , Luciani L. , Baciocchi M. , Figliomeni M. , Maggiora R. , Mastrogiacomo L. , Cerrina F.
Published: July 2002

We report on the development of an e-beam lithography process for the fabrication of x-ray masks for nanolithography with minimum feature size down to 65 nm. The process is based on accelerating voltages below 50 kV, with a single layer of 0.55 μm thick PMMA. Particular emphasis is addressed to the study and the control of the various variables affecting the ultimate practical resolution, i.e., the developer concentration, the accelerating voltage, the exposure latitude, the reproducibility of the results and the effect of the beam diameter. Monte Carlo simulation was used to separate the effect of forward- and backscattering. Dense and reproducible 65 nm-resolution arrays of gold electroplated lines have been achieved at 50 kV on silicon nitride membranes. Some of the fabricated nanomasks have been successfully replicated by synchrotron radiation lithography.
Pattern formation in amorphous WNx by low temperature electron cyclotron resonance etching for fabrication of x-ray mask
Authors: Inoue Takayoshi , Kanayama Toshihiko , Komuro Masanori
Published: July 2002

In order to obtain finer feature sizes on x-ray masks, it is required to select the x-ray absorber material, while refining the pattern definition technique. WNx deposited under suitable conditions is completely structureless. Its density is close to that of W. Therefore, it is promising as an x-ray absorbing material. Patterning was tried in 500 nm thick WNx using focused ion beam and low temperature electron cyclotron resonance plasma etching, which resulted in a 60 nm pattern with a smooth side wall.
Printing of phase-shifting mask defects
Authors: Kostelak R. L. , Pierrat C. , Garofalo J. G. , Vaidya S.
Published: July 2002

Using both simulations and experimental data, the impact of defect type, size, and location for the three leading phase-shifting techniques, alternate aperture, sized rim shifter, and attenuated, was investigated. Location of the defect was determined to play a major role in the printability of a given defect. Specifically, corner defects located on the inner edge of a rim-shifted pattern posed significant detectability and printability problems. As expected for the vast majority of defects, phase-shifting approaches enhanced the printability of the defect. However, the attenuated approach revealed a unique class of defects that caused much less linewidth deviation than their counterparts on conventional masks. These were the missing chromium/unetched quartz defects. A systematic study of the impact of phase, size, and position for both classes of defects: extra shifter and missing chromium, on an attenuated phase-shifting masks revealed that the design of the attenuated blank was critical in minimizing the impact of defects. Two possible blank configurations were proposed: a partially embedded shifter and a fully embedded configuration. By intelligently selecting the design of the attenuated blank, the impact of defect printability could be reduced.
Process issue improvement of surface image transfer technique: Depth-of-focus characteristics and their comparison with simulation results
Authors: Tomo Y. , Ogawa T. , Nagayama T. , Kimura M.
Published: July 2002

There are several disadvantages concerning surface image transfer technique for contact hole fabrication in KrF excimer laser lithography utilizing absorbing photoresist SAL601 (Shipley, chemically amplified negative type). A long development time (MF622, Shipley, 10 min) is the first disadvantage, but this can be improved by using concentrated developer (MF312-CD38, Shipley) without loss of focus margin. Pattern transfer thicknesses limited to an oxide layer of less than 0.2 μm is the second disadvantage, but this can be improved to a thickness of 0.8 μm by using more anisotropic etching conditions. Small depth of focus (DOF) is the third and the most critical disadvantage, and this can be improved by employing low numerical aperture (NA) and high σ (coherency factor) exposure conditions (NA=0.35, σ=0.9). Comparison between the DOF characteristics for a 0.4 μm contact hole using SAL601 and a two-dimensional photointensity simulation has resulted in a simple metric to predict the DOF by mask edge intensity loss from perfect focus to defocus. Although the correlation between the loss and the DOF is weak, the loss is ∼0.025–0.045. The observed DOF results for 0.35 and 0.32 μm contact holes were in the range of the prediction obtained by the metric except NA=0.45 and σ=0.3 with 0.35 μm contact hole case.
Imaging dissolution rate monitor: Mapping the photoresist response
Authors: Sullivan Monroe , Taylor James W.
Published: July 2002

A 2048 channel linear charge coupled device array dissolution rate monitor (DRM) has been constructed and tested for the characterization of x-ray photoresists during development to measure and quantify: exposure uniformity, onset and magnitude of surface roughening, and resist contrast and sensitivity for various processing conditions. DRM measurements were made on Shipley XP-90104C photoresist, and a simple empirical model of surface roughening was proposed based on scanning electron and atomic force microscope images of the resist surface. In addition, resist contrast, sensitivity, time to clear, and normalized remaining thickness curves were all calculated from a single wafer and used to characterize the photoresist. The DRM has been used to measure the inhomogeneity of various x-ray exposure window materials used to isolate the ultrahigh vacuum environment. These can cause variations in the intensity of the beam and consequently yield exposure inhomogeneity. The Be window had significantly more exposure field variation (±5%) than the poly-Si window (±1%). Vibrating the Be window during exposure reduces the exposure variation to ±1%.
Optimization design program for chemically amplified resist process
Authors: Pan S.-W. , Reilly M. T. , Taylor J. W. , Cerrina F.
Published: July 2002

In this article, a novel optimization program applicable to chemically amplified resist (CAR) process development, which is based on the method named as chemically amplified resist process optimization design developed in CXrL, is described. This program is separated as three subprograms. The first program called vertices is used to find most efficient sampling space. The second program called OPTIM1 is used to find the optimal process conditions. The third program called OPTIM2 is used to find the design center (maximum process tolerance space) of a CAR process with minimum experimental runs. In this article, the process optimization of AZ PF-514 has been used as an example to show that the program can identify the optimal process condition as well as the maximum tolerable parameter space with minimum experimental runs.
Insolubilization mechanism of chemically amplified negative photoresists
Authors: Yamaguchi Atsumi , Kishimura Shinji , Tsujita Kouichiro , Morimoto Hiroaki , Tsukamoto Katsuhiro , Nagata Hitoshi
Published: July 2002

This article reports on the difference of chemical reactions of polyvinylphenol (PVP) and novolak resin as a base polymer with a melamine cross-linker. Measurements by gel permeation chromatography (GPC) and solubility testing using alkaline developer and acetone indicate that a cross-linking reaction is predominant for dissolution inhibition in the case of the resists comprising PVP (PVP-type resists), while protection of hydroxyl groups for the developer is predominant in the case of the resists comprising novolak resin (novolak-type resists). The dissolution characteristics show that the novolak-type resists have higher contrast than the PVP-type resists. As the concentration of the melamine cross-linker increases, the resolution of the PVP-type resist becomes higher, while that of the novolak-type resist becomes lower. Significant differences in chemical reactions and lithographic performances were found between PVP and novolak resin for chemically amplified negative photoresists.
Study of electron beam patterning of resist on tungsten x-ray masks
Authors: Cummings K. D. , Resnick D. J. , Frackoviak J. , Kola R. R. , Trimble L. E. , Grant B. , Silverman S. , Haas L. , Jennings B.
Published: July 2002

In this article, the effects of tungsten and resist thicknesses and exposure energy on tungsten x-ray masks have been investigated making use of both experimental and theoretical data. It was found that proximity effects in the patterned resist can be reduced by an appropriate choice of resist and absorber thickness as well as increased electron energy. The control of linewidths for isolated lines, clustered lines, and isolated spaces is sufficient for 0.25 μm design rules without proximity correction and with good process latitude. In addition, it was found that this process has resolution down to 0.1 μm.
Effect of mask absorber thickness on x-ray exposure latitude and resolution
Authors: McCord M. A. , Wagner A. , Seeger D.
Published: July 2002

Reducing the absorber thickness on an x-ray mask has significant advantages in mask fabrication. Masks become easier to pattern and repair, and pattern placement errors caused by absorber stress are reduced. However, thinner absorbers can also affect the x-ray wafer printing process. As the absorber thickness is reduced, more radiation leaks through nominally opaque areas on the mask. This radiation undergoes a phase shift as it passes through the absorber which can result in improved resolution due to partial cancellation of diffraction effects on the wafer. The principle is similar to the attenuated phase-shift masks being studied for optical lithography. A mask was fabricated with a range of absorber thickness from 0.34 to 0.59 μm. The varying thicknesses were placed in close proximity on the mask to minimize any exposure or process variations that might occur across the mask and wafer. Prints were made on silicon wafers using a synchrotron radiation source at the IBM advanced lithography facility with a Suss stepper and a commercially available chemically amplified positive resist. Preliminary results were also obtained with a negative resist. The patterns were inspected for resolution, exposure latitude, and pattern fidelity. Results show a small improvement in printing performance as the absorber becomes thinner.
Constructive three-dimensional lithography with electron-beam induced deposition for quantum effect devices
Authors: Koops Hans W. P. , Kretz Johannes , Rudolph Michael , Weber Markus
Published: July 2002

Two- and three-dimensional patterns and structures can be grown by electron-beam induced deposition from organic and metalorganic precursors. Using a very fine electron beam in a dedicated field emission scanning electron microscope produces nanometer size deposits which extend from surfaces to heights in the micrometer range. The material is fed to the sample through a nozzle which presents a small leakage flux to the specimen chamber. Having an image processor attached to the microscope allows two- and three-dimensional deposition of material to be controlled. Selecting special speed rates for the motion of the beam generates inclined deposits even at a 90° beam landing angle. Combining a tilted sample and the two-dimensional way of structuring yield three-dimensional structures. These nanostructures have very special characteristics with respect to resistivity and shape. Selecting dimethyl- gold-trifluoro-acetylacetonate as precursor, a current of 1 nA, and a low electron energy of 10 keV for the deposition process, resistors of 700 Ω are obtained with a specific resistivity of 10−2 Ω cm.
Growth of GaAs light modulators on Si by gas source molecular-beam epitaxy for 850 nm optical interconnects
Authors: Cunningham J. E. , Goossen K. W. , Walker J. A. , Jan W. , Santos M. , Miller D. A. B.
Published: July 2002

The growth of GaAs quantum well modulators on Si for photonic switching applications is reported. Comparison of modulator’s quantum confined Stark effect atop different miscut Si surfaces demonstrate the need for a highly ordered array of bilayer steps as an initial Si surface condition for heteroepitaxy. Proton implantation into the SiO2/Si system via an electron cyclotron resonance plasma to lower the Si oxide desorption temperature, while perserving step ordering of the surface, is explored.
Atomic layer-by-layer epitaxy of cuprate superconductors
Authors: Bozovic I. , Eckstein J. N. , Virshup G. F.
Published: July 2002

A technique for atomic layer-by-layer epitaxy of cuprate superconductors and other complex oxides has been developed at Varian. The samples are engineered by stacking molecular layers of different compounds to assemble multilayers and superlattices, by adding or omitting atomic monolayers to create novel compounds, and by doping within specified atomic monolayers. Apart from manufacturing trilayer Josephson junctions with IcRn≳5 mV, this technique enables one to address fundamental issues such as the dimensionality of HTSC state, existence of long-range proximity effects, occurrence of resonant tunneling etc., as well as to synthesize novel metastable HTSC compounds.
Growth morphologies of (001), (100), and (010) oriented Er5Ba7Cu12Oy high-temperature superconductor thin films on various substrates
Authors: Choudhary K. M. , Seshadri P. , Black M.
Published: July 2002

Er5Ba7Cu12Oy thin film is a high-temperature superconductor material (Tc=93 K). The growth morphologies of Er5Ba7Cu12Oy thin films on various substrates were studied by scanning electron microscopy. The films were prepared by molecular beam deposition and postgrowth annealing. The Er5Ba7Cu12Oy thin films on LaAlO3 (100) [and SrTiO3 (100)] substrates showed small amount of (100) oriented grains on top of a (001) epilayer if the films were annealed in the 850–865 °C range (film thickness=0.4 μm). The (001) oriented Er5Ba7Cu12Oy/cubic-ZrO2(100) thin films showed a ‘‘spherullite’’-type growth morphology. On MgO (100) [and cubic-ZrO2(100)] substrates, Er5Ba7Cu12Oy thin films with mixed (010) and (001) growth orientations were obtained.
Structural properties of highly mismatched InGaAs-based devices grown by molecular beam epitaxy on GaAs substrates
Authors: Goorsky M. S. , Eldredge J. W. , Lord S. M. , Harris J. S.
Published: July 2002

We examined the structural properties of optical modulators consisting of multi-quantum wells and InGaAs relaxed buffer layers grown on (001) GaAs substrates by MBE. The effects of different linearly graded buffer layers was a key component of this study. For all samples, high resolution x-ray techniques determined that the buffer layers were completely relaxed in both 〈110〉 directions. The epitaxial layers did not possess any overall crystallographic tilt with respect to the substrate. The strained layer superlattices were pseudomorphic as well. We determined that the crystal quality of multiquantum wells grown on the InGaAs buffers decreases with increasing composition gradient in the underlying buffer layer. The improved material quality correlates with sharper exciton resonance from the more slowly graded samples and suggests that the proximity of the buffer layer strain fields to the active multi-quantum wells plays a significant role in optical and structural properties.
Raman scattering study of the intermixing of AlAs monolayers in GaAs grown by molecular-beam epitaxy
Authors: Katzer D. S. , Shanabrook B. V. , Gammon D.
Published: July 2002

In this article we present results from a Raman scattering study of AlAs monolayers in GaAs grown by molecular beam epitaxy. A recent model for the LO phonons in AlxGa1−xAs developed by Molinari et al. [Appl. Surf. Sci. 56–58, 617 (1992); Phys. Rev. B 45, 4280 (1992)] gives excellent qualitative agreement with our measurements. We show that intermixing between AlAs and GaAs is reduced through the use of low substrate temperatures and migration-enhanced epitaxy. We show the utility of the LO phonon model for obtaining quantitative information about the Al concentration in a monolayer. We also discuss the utility of using Raman scattering to help determine the optimum growth conditions to minimize intermixing of GaAs/AlAs interfaces and for mapping Al flux variations across a sample.
Low-temperature growth and characterization of GaAs epitaxial layer on (111)B GaAs substrates
Authors: Kim G. H. , Gray J. L. , Yoo H. M. , Ohuchi F. S.
Published: July 2002

Unique properties of homoepitaxial (111) GaAs layers grown at low temperatures have not been realized mainly due to very narrow temperature range for the layer-by-layer growth. In this study, molecular-beam epitaxy growth of GaAs (111) layers on a tilted (111)B substrate at 350 °C is reported. Reflective high-energy electron diffraction observation during the low-temperature growth shows an initial surface structure of (2 × 2) which changes to (1 × 1) at the beginning of the growth. Diffraction spots appear at the growth layer thickness of 75 nm. These extra spots are attributed to twins and stacking faults confirmed by transmission electron microscopy. GaAs (111) layers grown at 350 °C have a high density of twins and a specular surface. High-temperature growth of (111) GaAs on a low-temperature buffer layer leads to a tenfold increase in the surface roughness.
Random-period superlattice quantum wells
Authors: Shih Y. C. Albert , Sadra K. , Streetman B. G.
Published: July 2002

We report a study of a novel quantum well structure, the random-period superlattice quantum well (RSLQW), consisting of an AlAs/GaAs superlattice (SL) sandwiched between two AlGaAs layers, where the periods in the SL are intentionally randomized. Photoluminescence (PL) measurements are performed to probe the optical properties of the RSLQW structures. Theoretical calculations are employed to correlate the type of transition and transition energy with the experimental observations. Phonon sidebands are identified in the PL spectra of RSLQWs, in which type II transitions are predicted by calculation results. Compared to the findings in periodic superlattice quantum wells, some RSLQWs show significantly stronger PL signals. However, all the RSLQW samples exhibit larger degradation of radiative recombination efficiency with increasing temperature.
Accurate measurements of transients and intentional rates of change in molecular beam epitaxy growth rate calibrations
Authors: Fernandez Rouel , Harwit Alex , Kinell Don
Published: July 2002

Shuttering the arsenic flux off and on is known to induce reflection high-energy electron diffraction (RHEED) intensity oscillations during continuous molecular beam epitaxy growth long after the regular oscillations have damped out. These RHEED intensity oscillations are shown to be useful for quantifying the flux variations from group III cells. Flux transients from opening the gallium and aluminum shutters, and intentional flux changes produced by changing cell temperatures have been accurately measured using this technique. After opening a group III shutter, two transients have been observed in this system. In the case of gallium, a relatively short-time transient less than 300 s long is typically observed. This short time transient is characterized by a 3% drop in the flux. Sometimes, however, a longer transient with a time constant of about 20 min occurs. The longer transient usually gives a 3% to 4% rise in the growth rate. The aluminum cell consistently displays only a long-time constant transient. Intentional rates of change in growth rates are also easily measured with the induced RHEED intensity oscillations. For example, near a 1 μm/h growth rate, linearly increasing the gallium cell temperature by 15 °C over 5 min results in a linear rate of change in the growth rate of 11.0±0.5 (Å/h)/s. Linearly ramping down the gallium cell temperature by 15 °C in 5 min results in a rate of change of −12.4±0.7 (Å/h)/s.
Near-field optics: Light for the world of NANO
Authors: Pohl D. W. , Novotny L.
Published: July 2002

The wealth of optical phenomena offers interesting opportunities in the world of nanometer dimensions. The field of radiation has to be confined and controlled for this purpose by material structures such as small apertures or slits. Many optical effects manifest themselves in a novel way if the relevant dimensions are small compared to the wavelength. Our theoretical understanding therefore lags somewhat behind the experimental results which have made rapid progress in the past two to three years. This paper concentrates for this reason on the description of a model scanning near-field optical microscope which allows us to gain some insight into the complex problems of coupling light into a nanometer-sized structure, the distribution and possible field enhancement inside such structures, and the radiation from the nanoscale structure into the macroscopic world, where it can be detected by conventional means.
Development of plasma source ion implantation in China
Authors: Tang Bao Yin
Published: July 2002

In recent years, the plasma source ion implantation (PSII) technique has been developed in China. It is called all orientation ion implantation. Experimental devices have been built in Harbin Institute of Technology, Southwestern Institute of Physics, Dalian University of Technology, Sichuan University, and China Textile University, respectively. In this article, two typical devices are described, preliminary results of the PSII-ion beam enhanced deposition and production of diamondlike carbon films, and some computer simulation programs are reported briefly. Some experiments show that addition of rare-earth metal ions, or heavy metal ions, or Xe+, Kr+ in the nitrogen plasma may make the effectiveness of the surface modification better. Future considerations are also described in the article.