bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical analysis of electron-beam exposure parameters and etching selectivity upon organosilicon bilayer resist images
Authors: Paraszczak J. , Rosenfield M. , Hatzakis M.
Published: July 2002

The imaging capabilities of bilayer resist structures, based upon poly (organosilicon) materials, have been investigated for use in one micron electron beam lithography. These systems work on the principle that the top film, the imaging layer, is thin compared to the image size and erodes slowly in an oxygen plasma. The bottom layer is insensitive to the incident radiation and erodes rapidly in the oxygen plasma. The etch rates and selectivities of the various components of the bilayer structure have been determined along with the response of the top layer to the imaging radiation. Using this information and absorbed electron energy profiles obtained from Monte Carlo simulations, a simple model of negative resist development and etching has been assembled. This model predicts the resist profiles obtained after development and etching and allows the effects of resist contrast, beam accelerating potential and etch selectivity to be independently determined. Using this model, the expected values of linewidth deviations due to proximity effect have been evaluated and compared with experimental values. It is shown that the parameters which describe the system, namely, the etch selectivity, the resist contrast curve, the exposing beam profile and accelerating potential affect the final resist profile in an interdependent manner. Furthermore, it is shown that the use of overetching in oxygen plasmas, which removes the bottom layer, can significantly affect the observed proximity effect, and hence, the observed resolution of these resist systems.
A minimum step fabrication process for the all-silicon channeling mask
Authors: Atkinson G. M. , Bartelt J. L. , Middleton P. L.
Published: July 2002

In this paper the all-silicon channeling mask is described and its advantages for masked ion beam lithography (MIBL) applications are discussed. A minimum step process for fabricating the all-silicon mask is presented in detail. The main process steps include epitaxial growth of silicon, membrane etching, and high resolution magnetron ion etching. Experimental parameters and fabrication results are presented.
Wafer flatness as a contributor to defocus and to submicron image tolerances in step-and-repeat photolithography
Authors: Underhill J. A. , Sundling D. L. , Kerbaugh M. L.
Published: July 2002

This paper presents the measured variation in submicrometer patterns (0.6 to 0.8 μm wide lines) as a function of defocus and exposure dose for an i-line lens with a 0.35 numerical aperture. The data were obtained by electrical measurement of reactively ion-etched, thin polysilicon patterns. It shows that a practical focal range for this lens is ≂2 μm total included range (TIR). This amount of defocus contributed less than 5% to the variations in the patterned linewidths. Contributions to the defocus tolerance are cited and wafer flatness requirements are postulated. The results of wafer flatness measurements before and after selected process steps and for regions equal to the size of step-and-repeat exposure fields are presented. Comparison between the results and the requirements shows that state-of-the-art wafers meet the need for submicron lithography.
Study of half-micron photolithography by means of contrast enhanced lithography process
Authors: Hirai Yoshihiko , Sasago Masaru , Endo Masayuki , Ogawa Kazufumi , Mano Yojiro , Ishihara Takeshi
Published: July 2002

A simple, but efficient, analysis method has been developed to evaluate material properties, process conditions, and effectiveness of contrast enhanced lithography (CEL). The method, realized as a result of the systematic calculation and concept, is based on the evaluation of the energy transmittance of the contrast enhancing material (CEM). In practical applications of the new method to the design and evaluation of both CEM characteristics and half-micron contrast enhanced photolithography, the method has been proved to be useful in the precise design as it shows good agreement with experimental results. The study has brought us pieces of important information on such design as the optimum exposure conditions, the ideal CEM characteristics, etc. Based on the information, we have developed a new CEM, water soluble photopolymer (WSP) for i and g lines. Through the simulation, it has been confirmed that the ultimate resolution can be improved by 20% to 30%.
A metal liftoff process facilitated by the use of contrast enhanced photolithography
Authors: West P. R. , Polasko K. J. , Fasoldt C. L.
Published: July 2002

A new single layer photolithographic liftoff process is described. Coating a thin layer of poly(vinylalcohol) on AZ 5200 series resists produces a surface inhibition effect which results in reentrant profiles. In combination with a contrast enhancing layer such a CEM-388, high resolution liftoff masks are obtained with excellent process latitude. The application of this new liftoff technique in 0.8-μm design rule processing is described.
A high-speed patterning controller for the EB60 electron beam lithography system
Authors: Morosawa Tetsuo , Shibayama Akinori , Murashita Toru , Fujinami Minpei
Published: July 2002

A high-speed patterning controller consisting of a pattern generator, beam deflection circuits, and a mark signal processor has been developed for the EB60 electron beam lithography system. To achieve a throughput of 16M shots per second and high accuracy for pattern writing during continuous movement of the stage, three key developments are incorporated into the pattern generator: (1) a buffer memory of 128M bytes for storing an entire VLSI chip pattern and eliminating the need for the repetitious storing of the same pattern data; (2) six-stage pipelining with a 400 MHz basic clock for performing dynamic corrections in under 60 ns (about five times faster than former systems); (3) feed-forward control architecture for eliminating the beam position error caused by the data transmission system delay time. The major and minor deflection systems are equipped with the beam deflection circuits consisting of high-accuracy digital to analogue converters (DACs) and high-speed amplifiers. For the minor field deflection system (12 bit accuracy with ±50V output), GaAs FET current switches are used in the DAC to achieve a typical settling time of less than 60 ns. For the major field deflection system (18 bit accuracy with ±500V output), static induction transistors (SITs) are used in the final stage of the amplifiers and high-stability feedback resistors with low temperature coefficients are also developed. As a result, a settling time of less than 4 μs is achieved for the minor field width step. To perform mark detection in under 50 ms per mark, a low noise electron detector and signal averaging hardware are developed for the mark signal processor. This patterning controller provides an electron beam lithography system with a high throughput and a high accuracy, which results in a shorter turn-around time for the fabrication of VLSIs with submicron critical dimensions.
An improved magnetic-collimating secondary electron energy filter for very large scale integrated diagnostics
Authors: Richardson Neil , Muray Andrew
Published: July 2002

Improvements in scanning electron microscope voltage contrast systems continue to be driven by the need to make accurate measurements of device performance and to identify failure mechanisms in very large scale integrated circuits. An optimized secondary electron energy filter, which forms an integral part of an electron-beam diagnostic system should have the following properties: efficient collection of secondary electrons emitted from the sample surface; accurate and reproducible device voltage measurement; no variation in the collection efficiency over the full field of view; and minimal transit time spread. This paper describes a combined variable-axis objective lens and magnetic-collimating energy analyzer which is well suited to this purpose. It collects secondaries emitted at arbitrary angles and parallelizes their velocities before filtering, resulting in a greatly reduced local field effect. Secondary electrons travel through the bore of the objective lens where they encounter the lens and additional magnetic fields, primary electron deflection fields, and electric fields. All these fields affect the performance of the collector/energy filter and a full characterization of the system is only possible through detailed calculation of the electron trajectories. In this paper, a realistic model of a magnetic-collimating energy filter is analyzed. Trade-offs in fine tuning such a system are empirically evaluated and the performance of a real system is presented.
PRISM: Process for resist profile improvement with surface modification
Authors: Yoshimura Toshiyuki , Murai Fumio , Shiraishi Hiroshi , Okazaki Shinji
Published: July 2002

The positive electron beam resist NPR is a composite of a novolac resin and a polymeric dissolution inhibitor. In this resist a surface modified layer is produced on the resist when development is interrupted. The dissolution rate of this layer at low dose is very low. A new process called prism (Process for Resist profile Improvement with Surface Modification) utilizing this layer is proposed. By repetitive development interruption, a steep and accurate resist profile is obtained with sidewall protection. This paper describes an investigation into the effects of development interruption on NPR. The surface modified layer produced by the interruption is investigated with gas analysis and x-ray photoelectron spectroscopy. It is found that the dissolution inhibitor poly(2-methylpentene-1-sulfone) accumulates at the resist surface. prism can be applied to other resists consisting of aqueous alkaline soluble base resins and polymeric dissolution inhibitors. Improvement of the resist pattern profile is observed in positive-type photoresists by prism.
A parallel processing approach to proximity correction
Authors: Otto O. W. , Griffith A. K.
Published: July 2002

We present an approach to proximity effect computation in which the program is hosted on a parallel processor to accelerate the computation. Our requirements are: (i) factor of 100 speed improvement over a VAX-11/780 (106 instructions/s), (ii) ability to handle dense patterns with 0.5-μm design rules, (iii) ability to handle arbitrarily sized chips, and (iv) affordable processing power. We have concluded that parallel processing is a viable approach to realizing these goals. A parallel processing implementation will permit proximity correction of complex very large scale integrated (VLSI) patterns in a few hours instead of hundreds of hours. The proximity correction program is the functional equivalent of the one we have described previously. The program maintains pattern hierarchy insofar as possible, partitions features to permit edge placement control to 0.025 μm, and performs dose computations based on a multiple Gaussian scattering model. We have estimated that the best aggregate computation time per original pattern feature (before partitioning) in a dense pattern environment is ∼100 ms on a VAX-11/780. We judge that reasonable throughput for real VLSI patterns will require a processing time below 1 ms per original pattern feature; hence, the factor of 100 speed improvement requirement. In this paper we describe our approach to structuring the programs so that a processor node deals with a small portion of the pattern at one time and to managing the computation so that most of the processor nodes are busy most of the time.
The effects of annealing encapsulant and ambient on the barrier height of WNx/GaAs contact and self-aligned gate field effect transistor fabrication
Authors: Cheung S. K. , Kwok S. P. , Kaleta A. , Yu K. M. , Jaklevic J. M. , Liang C. L. , Cheung N. W. , Haller E. E.
Published: July 2002

It was found that the barrier height of thermally stable WNx /GaAs Schottky contacts can be enhanced by a high-temperature annealing technique. In this study, the WNx /GaAs contact was annealed under different conditions including (i) furnace annealing under SiO2 encapsulant with N2 and arsine ambient, (ii) furnace annealing under arsine-overpressure capless annealing, and (iii) rapid thermal annealing (RTA) under SiO2 encapsulant and argon ambient. The temperature range for furnace annealing was 700–850 °C and for RTA, 700–950 °C. RBS analysis of all samples revealed no detectable interdiffusion at the WNx /GaAs interface up to an annealing temperature of 850 °C for furnace annealing and 950 °C for RTA. The Schottky barrier height increased from 0.59 eV, as deposited, to the commonly reported value of 0.72 to 0.74 eV, at the optimum temperatures for all the annealing conditions mentioned, with one exception. Barrier heights as high as 0.8 eV were obtained using furnace annealing under SiO2 encapsulant and arsine ambient. This corresponds to an enhancement up to 80 meV and is significant for improving the noise margin of GaAs integrated circuits, which is typically 200–300 mV. However, such annealing conditions also caused leakage current localized at the perimeter of the WNx /GaAs contact. Such a leakage current can be removed by slight mesa etching of the GaAs at the edges. WNx SAGFET structures were fabricated using both capless furnace annealing in an arsine ambient and RTA in an argon ambient. It was found that capless furnace annealing resulted in significantly better immunity to short-channel effects than that of RTA. Transconductance as high as 300 mS/mm was obtained with a gate length of 0.5 μm.
Band offset of the ZnSe–ZnTe superlattices: A fit to photoluminescence data by k⋅p theory
Authors: Rajakarunanayake Y. , Miles R. H. , Wu G. Y. , McGill T. C.
Published: July 2002

The ZnSe–ZnTe superlattices have attracted considerable attention as possible blue/green light emitters. Although these superlattices have been successfully fabricated and show intense photoluminescence, there are many basic issues about this system which still remain unresolved. The most important of them is the value of the valence band offset between ZnSe and ZnTe. We have studied the band structure of ZnSe–ZnTe superlattices. Our calculations are based on second order k⋅p theory and include the effects of strain and spin-orbit splitting on the superlattice band structure. We have investigated the dependence of the superlattice band gap on the valence band offset. Based on the assumption that the photoluminescence from the superlattice corresponds to a bound exciton at a Te1 isoelectronic center in ZnSe, we have fit the experimental photoluminescence data with k⋅p theory to obtain the best value of the valence band offset. The value we find is 0.97±0.10 eV. Alternatively, assuming that the photoluminescence was due to band-to-band transitions we obtain a valence band offset of 1.20±0.13 eV. We have also calculated the superlattice band gap as a function of the constituent material layer thicknesses for the first valence band offset quoted. We expect these results to be important in gaining an understanding of the value of the valence band offset, and the nature of the photoluminescence from this system.
Three-bond scission and the structure of the cleaved Si(111) surface
Authors: Haneman D. , Lagally M. G.
Published: July 2002

It is proposed that cleavage of Si to form Si(111) (2×1) occurs by the scission of three bonds between the closely spaced double layers, rather than by the severing of the single bond that connects the double layers. It is shown that three-bond scission occurs in the behavior of dislocations in Si. Models of the surface structure based on this cleavage process are presented and discussed in light of the current understanding of this surface.
The effect of strong localization on the mobility of electrons in modulation-doped inverted structures
Authors: Airaksinen V. M. , Harris J. J. , Lacklison D. E. , Beall R. B. , Hilton D. , Foxon C. T. , Battersby S. J.
Published: July 2002

Modulation-doped quantum well structures grown by molecular-beam epitaxy in which the two-dimensional electron gas samples both interfaces, have been characterized by Hall mobility and Shubnikov–de Haas measurements. In as-grown and annealed samples the low electron mobility associated with the inverted interface is attributed mainly to localization effects and is not influenced significantly by Si diffusion in these structures. The localization can be reduced by replacing the bulk (Al,Ga)As layers by a short period superlattice of equivalent band gap, resulting in improved mobilities.
Thermal modulation of photoluminescence in InP/Ga0.47In0.53As/InP quantum wells
Authors: Lin Z. H. , Wang T. Y. , Taylor P. C. , Stringfellow G. B.
Published: July 2002

InP/Ga0.47In0.53As/InP single quantum wells, which are grown by the organometallic vapor phase epitaxy technique, exhibit multiple peaks in thermally modulated photoluminescence (TMPL) spectra. In two samples with nominal well widths at 10 Å, at least four well-resolved negative and at least two positive TMPL peaks are observed. The number of peaks is related to the growth conditions, and the relative intensities of the peaks depend on the sample temperature and the PL excitation intensity. In the thinnest quantum wells at least some of these discrete peaks may be associated with regions where the well widths differ in thickness by single monolayer steps.
Two-dimensional distributions of secondary defects in focused ion beam implantation into Si
Authors: Tamura M. , Shukuri S. , Madokoro Y.
Published: July 2002

Annealing behavior of structure, nature, and two-dimensional depth distributions of secondary defects in one-line-scan, 70-keV focused ion beam B-implanted (100) Si have been investigated mainly using cross-sectional transmission electron microscopy observations. In as-implanted layers for doses above 3×1015/cm2, triangular amorphous regions are formed with a two-dimensional spread on the order of a 0.2 μm, which is approximately an ion beam diameter. Secondary defects generated by annealing above 800 °C are confined within these triangular regions. By contrast, when 8×1014/cm2 implanted layers are annealed at 1000 °C, two-dimensional spreads of the grown defects vary from 0.2 to 0.6 μm in each implanted layer. However, in annealing at 800 °C, these defects remain near the projected range of boron and their lateral spread is confined to a beam diameter. Some results are discussed in comparison with two-dimensional impurity distributions, 140-keV P++ implantation, and Monte Carlo simulations.
Oxidation effect on an x-ray induced reaction of a polyolefinsulfone-type resist
Authors: Mochiji Kozo , Soda Yasunari , Kimura Takeshi
Published: July 2002

The effect of ambient atmospheric conditions during x-ray exposure on the sensitivity of a new type positive resist, which contains poly(2-methylpentene-1-sulfone) as the radiation-sensitive compound, is studied. Resist sensitivity to x rays is seen to depend strongly on oxygen pressure during exposure. Sensitivity in air is only one-sixth of that in a vacuum. Using Fourier transform infrared spectral analysis of the resist film following x-ray irradiation, it is found that the alkyl radical of poly(2-methylpentene-1-sulfone) generated by x-ray irradiation is easily scavenged by the oxygen molecule in air, thus retarding its further unzipping decomposition.
Fabrication of one-dimensional GaAs wires by focused ion beam implantation
Authors: Hiramoto Toshiro , Hirakawa Kazuhiko , Ikoma Toshiaki
Published: July 2002

Novel, simple techniques were developed to fabricate very narrow GaAs conducting wires by utilizing direct focused ion beam (FIB) implantation. We employed two methods for fabrication of the wires. The first method makes use of high-resistivity (HR) regions formed by FIB implantation without successive annealing to define a very narrow conducting wire (HR method). In the second one, focused Si ions are line implanted into p-type GaAs, forming an n-type conducting wire in the p-type region. Then, reverse-bias is applied across the pn junction in order to make the wire narrower by expanding the depletion layer (PN method). This structure has an advantage that the thickness of the wire can be varied by bias voltage. Magnetoconductances measured in all the fabricated wires show evidences of weak electron localization and conductance fluctuations due to a quantum interference effect. The minimum widths of the wires are evaluated to be ∼20 nm (HR method) and ∼100 nm (PN method) by fitting the theory of one-dimensional weak localization to the experimental data. The phase coherent length of the electronic waves in the wires is also derived to be ∼120 nm at 1.3 K.
High-performance Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation-doped field-effect transistors prepared by molecular-beam epitaxy
Authors: Kuo J. M. , Feuer M. D. , Chang T. Y.
Published: July 2002

High-performance Ga0.4In0.6As/Al0.55In0.45As pseudomorphic modulation-doped field-effect transistors (MODFET’s) have been further improved by replacing the Al0.48In0.52As buffer layer with an Al0.55In0.45As/Al0.41In0.59As strained-layer superlattice (SLS) buffer layer, grown lattice matched to InP substrate by molecular-beam epitaxy (MBE). Extrinsic transconductance as high as 306 mS/mm at 300 K has been obtained along with complete pinch off behavior for 1.7 μm gate length devices. This is attributed to the dislocation filtering and impurity gettering effects of the Al0.55In0.45As/Al0.41In0.59As SLS. Structural characterization using double crystal x-ray diffraction also reveals the high quality of this SLS buffer layer.
A structure for measuring contact resistances immediately following metal deposition
Authors: Schlais John R. , Neudeck Gerold W. , Liu S. T.
Published: July 2002

A new method of preparing prepatterned contact resistance monitor wafers is presented that requires only two mask steps. After metalization, no masking, photolithography, or etching steps are needed to produce the three terminal structure. Because there is no photoresist bake, no Al–Si intermixing occurs and the wafer batch can be reclaimed prior to annealing if poor contacts were formed. The technique uses a standard low-pressure epitaxial reactor to perform the selective silicon etching, leaving a SiO2 overhang pattern to define the metal.
Reactive ion beam etching of polyimide thin films
Authors: Vanderlinde William E. , Ruoff Arthur L.
Published: July 2002

Reactive ion beam etching of polyimide thin films was investigated using x-ray photoelectron spectroscopy (XPS) and etch rate measurements. The etching mechanism and the near surface damage produced in polyimide by exposure to argon and oxygen ion beams were compared. The etch rate of polyimide by oxygen ions was studied as a function of ion current density and neutral oxygen molecular flux, and the results were found to match a model for the contribution of neutral fluxes to the etch process. Ion beam etching with inert argon ions was found to produce a graphitelike layer on polyimide. Reactive ion beam etching with oxygen ions resulted in much faster etching than for argon ions, and did not produce a graphitized layer.
A simplified silylation process
Authors: Shaw Jane M. , Hatzakis Michael , Babich Edward D. , Paraszczak Jurij R. , Witman David F. , Stewart Kevin J.
Published: July 2002

This paper discusses a simplified ‘‘silylation’’ process, which converts typical diazo-type photoresists into oxygen plasma etch barriers that are insoluble and thermally stable. Previous workers have reported on a silylation process that incorporates silicon in the resist in the gas phase. This paper reports on the use of a bifunctional silylation agent, which when diffused into the patterned resist using a solvent carrier, crosslinks the novolac resin, incorporating silicon in the matrix. The mechanism and the properties of the resist film after silylation such as thermal stability, reactive ion etch (RIE) resistance, silicon content, and solubility will be discussed.
The passivating effect of Si(100)–As surface and the adsorption of oxygen
Authors: Zhong Z. T. , Wang D. W. , Fan Y. , Li C. F.
Published: July 2002

The interaction of oxygen with a Si(100)–As surface has been studied by a homemade combined surface analysis spectrometry with a molecular beam epitaxy system. This paper confirms that an As layer is a good passivation film for the Si surface and describes a study concerning all processes of oxygen adsorption on a Si(100)–As surface for the first time. It is shown that the oxygen coverage at saturation is 0.5 monolayer, i.e., adsorption sites are reduced by one-half with the existence of an As layer and the initial sticking coefficient SSi–Aso on the Si(100)–As surface was found to be 5.6×10−3, which is ten times less than that for a clean Si(100) surface. The passivating effect of the As on the Si surface is interpreted with the existence of lone-pair states instead of dangling-bond states.
Activation analysis of rapid thermally annealed Si and Mg implanted semi-insulating GaAs
Authors: Tandon J. L. , Leybovich I. S. , Bai G.
Published: July 2002

Electronic properties of Si and Mg implants in undoped semi-insulating GaAs are studied. The activation of the implants is achieved by rapid thermal annealing. The effects of implantation dose and anneal temperature on the measured electrical activity are investigated. In spite of similar depth distributions and implantation damage characteristics, a marked difference between the activations of the Si and the Mg ions is observed for the dose range considered (3×1012 –1×1014 cm−2). Lattice strain measurements performed by x-ray rocking curves indicate that the residual implantation damage after annealing is not largely responsible for this difference. The difference is mostly electronic in character, as also suggested by photoluminescence measurements. At high annealing temperatures, changes in the compensating properties of undoped semi-insulating GaAs are suspected, and are found to play an important role in the activation of implanted ions, affecting the n- and p-type dopants conversely.
Effect of nitridation on the density of interface states in W–Ti/n-GaAs Schottky diodes
Authors: Chen H. , Sadwick L. P. , Sokolich M. , Wang K. L. , Larson R. D. , Chi T. Y.
Published: July 2002

The effective density of interface states that exist at the metal–semiconductor Schottky barrier formed between W–Ti and silicon implanted (n-type) GaAs has been characterized using forward-biased capacitance–voltage (C–V) measurements. The Schottky diodes were fabricated by sputtering from a tungsten titanium target under different nitrogen gas ambients of 0%, 6%, and 12%. The nitrogen incorporation and interface stability were verified by secondary ion mass spectroscopy (SIMS) and Rutherford backscattering (RBS). The results of this study clearly show that the lowest effective density of interface states was obtained for the highest nitrogen ambient of 12% at a deposition rate of 10 nm/min.
Reactive ion etching of InP using CH4/H2 mixtures: Mechanisms of etching and anisotropy
Authors: Hayes T. R. , Dreisbach M. A. , Thomas P. M. , Dautremont-Smith W. C. , Heimbrook L. A.
Published: July 2002

Reactive ion etching of InP with CH4/H2 mixtures, a promising process for optoelectronic device fabrication, has been studied to understand the mechanisms of etching and anisotropy. Special attention has been paid to the polymer film that deposits on inert surfaces in the discharge; deposition rates have been used as a monitor of the discharge chemistry as well as for process optimization. Surface analysis shows that under etching conditions that maximize the InP etch rate while minimizing polymer deposition, the hydrocarbon coverage on the InP surface equals typical ‘‘adventitious’’ carbon levels, and the surface is significantly depleted of P. The etch rate here is limited by the flux to the surface of hydrocarbon reactants responsible for In desorption. The absence of a significant hydrocarbon film on the vertical-etched surfaces under conditions of 8:1 anisotropy precludes a surface inhibitor mechanism of anisotropy, implicating instead energy deposition via ion bombardment as the major contributor to the enhanced vertical etch rate. As the feedstock methane fraction is increased, more stoichiometric surfaces are obtained, the polymer deposition rate and the abundance of gas phase hydrocarbon oligomers increases, and ultimately, polymer forms on the InP. Here the InP etch rate is limited by transport through the permeable polymer overlayer. Reactions with polymer-coated chamber walls are important in determining InP etch and polymer deposition rates, illustrating the need for chamber seasoning to obtain reproducible results. PH3 is identified by mass spectrometry as the primary P-containing volatile product, while the primary In-containing volatile product remains unidentified.
Applications of contrast enhancement material to photobleachable deep ultraviolet resist
Authors: Endo Masayuki , Tani Yoshiyuki , Sasago Masaru , Nomura Noboru , Das Siddhartha
Published: July 2002

The applications of a contrast enhancement material, which is composed of 5-diazo-meldrum’s acid as a photobleachable reagent, poly(styrene-co-maleic acid half-isopropylate) as a matrix resin, and diethylene glycol dimethyl ether as a solvent, to a photobleachable deep UV resist are presented. The contrast enhancement material with high-contrast capability was very effective on such a resist, and high-aspect-ratio patterns of the resist were successfully obtained. The material characterizations of the contrast enhancement material have been also demonstrated using positive resist optical lithography model (PROLITH).
A novel optical lithographic process for fabrication of sub-half-micron Schottky barrier gate structures
Authors: Pedrotti K. D. , Robinson G. D. , Vachss F.
Published: July 2002

The ever increasing demand for sub-half-micron lithography for the production of gate structures for high electron mobility transistor (HEMT) and metal–semiconductor field effect transistor (MESFET) devices is greatly stimulating development of production-worthy technologies to realize this goal. When the sub-half-micron lithography regime is approached the tendency is to assume that optical lithography is no longer a viable procedure and that electron beam lithography (EBL) or x-ray lithography are the only alternatives. We have demonstrated a portable conformable mask process using poly(dimethylgutarimide) (PMGI) and Shipley 1400-27 resist to define 0.25 μm wide lines, using optical contact lithography for the definition of 1 μm lines, followed by deep UV flood exposure. This process is then used to define and lift narrow gates defined with metal layers up to 1 μm thick. Model diffraction calculations are compared to the resultant structures.
Lateral resolution of Si induced disordering of superlattices
Authors: Dobisz E. A. , Marrian C. R. K. , Craighead H. G. , Schwarz S. A. , Harbison J. P.
Published: July 2002

The lateral resolution that can be obtained by Si induced compositional mixing of an AlAs–GaAs superlattice is addressed. We examine two cases: one in which the Si is introduced into the crystal by ion implantation using a mask with a sharp edge and second in which the Si is diffused into the heterostructure from a stripe at the surface. The Si diffusion was simulated using a Si pair diffusion model with an explicit finite difference method. The Si concentration contours are fit in one dimension to SIMS data of the Si concentration. A pair equilibrium constant, K=1×1019 cm−3, and a pair diffusion constant, Dp=6×10−14 cm2 s−1, gave a reasonable fit to the data. Comparison of the SIMS data to TEM micrographs showed that compositional mixing occurred in the regions of high Si concentration (>2×1018 cm−3). The two-dimensional Si concentration contour plots for isotropic diffusion were compared with TEM micrographs of superlattices patterned by compositional mixing. Clearly the mixing is anisotropic, with the disordering extending further in the growth direction than in the lateral direction by factors of 4 and greater. Resolution of 60 nm was obtained.
Two-layer resist fabrication by new portable conformable masking i-line lithography
Authors: Endo M. , Sasago M. , Hirai Y. , Ueno A. , Nomura N.
Published: July 2002

A new technique for submicron optical lithography is reported. Water-soluble contrast enhancing material for i-line exposure prevented the undercut profile of negative photoresist and attained high-aspect-ratio rectangular patterns. New portable conformable masking i-line lithography using the water-soluble contrast enhancing material could successfully fabricate a two-layer resist composed of negative photoresist RU-1100N as a top layer and positive deep ultraviolet resist poly(dimethylglutarimide) as a bottom layer.
A figure of merit for contrast study in two-dimensional structures
Authors: Mathur B. P. , Kundu N. N. , Gupta S. N.
Published: July 2002

Image contrast and edge slope are frequently used to assess image quality. But in the case of two-dimensional geometries, the definition of contrast is not appropriate, as the maximum and minimum values of intensities may be different at the center, corners, etc. Similarly, edge slope may be different in different planes. Recently, a figure of merit (FOM) has been proposed to evaluate the image quality of two-dimensional structures by a single parameter. In this paper, both contrast and FOM have been calculated as a function of the parameters of the optical system. It has been shown that in the case of near micron geometries, the variation in the contrast and edge slopes is sometimes misleading, whereas the FOM gives more accurate information of the image fidelity.
Current induced heating of the codeposited metal–silicon runners to form low-resistivity crystallized disilicides
Authors: Murarka S. P. , Sun S. P.
Published: July 2002

Thin-film silicide runners were found to be annealed by an electric current through such runners. Results obtained using a 2660-Å-thick codeposited Ta–Si film and a current density of 3×105 A/cm2, clearly show that such localized annealings can be achieved by use of this method. The possibility of using such technique to selectively anneal upper-level patterned conductors in the integrated circuits has been suggested.
Study of strain in pseudomorphic InGaAs heterostructures related to the enhanced performance of p-channel heterostructure field effect transistor devices
Authors: Grider D. E. , Horning R. D. , Arch D. K. , Ruden P. P. , Nohava T. E. , Narum D. N. , Daniels R. R.
Published: July 2002

Results of a study of strain and its relation to InGaAs channel p-heterostructure insulated gate field effect transistors (HIGFET) device performance are presented. Measurements of the strain in a pseudomorphic InGaAs channel p-HIGFET device heterostructure using x-ray rocking curves in conjunction with a dynamical x-ray diffraction calculation are discussed. The strain in the InGaAs layer was found to increase by over 45% from the center to a position 2.5 cm from the center of a 3-in wafer. This variation is discussed in terms of across-wafer nonuniformity in the composition and thickness of the InGaAs. InGaAs channel p-HIGFET devices fabricated on a number of positions across the same 3-in. wafer yielded 1.0 μ gate length devices with room temperature transconductance (gm) values of up to 67 mS/mm. The relationship between the measured strain and p-HIGFET device characteristics are also discussed.
ArF excimer laser processing of plasma enhanced chemical vapor deposition silicon oxynitride thin films: Changes in deep ultraviolet transparency and composition
Authors: Cox J. N. , Friedrich L. B. , Heath L. L. , Sun B. L.
Published: July 2002

A series of silicon oxynitride thin films prepared by plasma enhanced chemical vapor deposition was characterized by Fourier transform infrared (FTIR), wavelength dispersive x ray, and ultraviolet/visible spectroscopies. Changes in deep-UV transparency and in composition of these and similar films on silicon, sapphire, and quartz wafers were then studied as a function of exposure to the output at 193 nm of an ArF excimer laser. Single-pulse and high-repetition-rate exposures at different average pulse energies were performed. No changes were observed in the single-pulse experiments, while the films increased in UV transparency and decreased in hydrogen content in the high-repetition-rate experiments. The effects observed were greater for films on quartz and sapphire, than for films on silicon. While not precluding a UV photon assisted mechanism, these results suggest that the changes in transparency and composition occur via local heating of the film. On the basis of a 10-μm film, the laser exposure of the film on quartz increased its transparency at 200 nm from 1% T before irradiation to 10% T, a contrast of 10, while the film on sapphire increased from 10% T before irradiation to 25% T, a contrast of 2.5. The primary effect of the irradiation upon composition was to reduce both the NH and SiH contents; however, these results, when compared with data on unirradiated samples with a variety of compositions, indicate that it was the change in SiH content that most directly affected the UV transparency. Thus the photomodifiable, UV absorbing defect is associated with SiH bonds in the glass. Changes in other features of the FTIR spectra were also observed. Overall, the local modification of the UV transparency of silicon oxynitride thin films was readily achieved by current excimer laser technology. While the effect occurred for films on silicon, the results show that the greatest contrast at the lowest laser fiuence would be achieved in heavily hydrogenated films on quartz.
Electrical characterization of i
n s
i
t
u fabricated n+-Si/GaAs interfaces
Authors: Arai Kunihiro , Mizutani Takashi
Published: July 2002

A very low Schottky barrier height of 0.1 eV for an in situ fabricated n+-Si/GaAs interface is verified by C–V measurement. The height is approximately equal to the conduction-band discontinuity of the interface, in spite of a high density of misfit dislocations (lattice mismatch: 4%). Thermal stability of the interface is assured for annealing temperatures up to 850 °C. As an example application, an AlGaAs/GaAs metal–insulator semiconductor-like heterostructure field effect transistor using n+-Si for gate material is successfully fabricated.
Pulsed electron beam lithography in soft vacuum
Authors: Krishnaswamy J. , Li L. , Collins G. J. , Hiraoka H. , Caolo Mary Ann
Published: July 2002

Large-area (cm2 ) proximity patterning of selected microelectronic polymers using soft vacuum (0.05 Torr) pulsed electron beams is described using polymers with widely differing electron sensitivities (2–80 μC/cm2 at 20 keV). The short duration (∼100 ns) electron beams are produced in the pulsed mode (25–28 keV electrons, 2–3 J/pulse). These electrons impinge upon thin polymer films in the presence of an ambient gas to produce electron initiated bulk polymer chemical reactions including partial self-development. In soft vacuum, pulsed electron beams are shown to be capable of transferring submicron (∼0.5 μm) features from an electron transmitting stencil mask onto poly(methylmethacrylate) (∼3 μm thick) films. Wide-area exposure (field size ∼20 mm) is also demonstrated for micron feature sizes. Soft vacuum lithography appears well suited to microelectronics packaging lithography where resist thickness is substantial, linewidths are 1–10 microns, areas to be processed are large (100 cm2 ), and where registration requirements are not so critical.
Improved pattern fabrication of naphthoquinonediazide-based deep ultraviolet resist by alkaline surface treatment
Authors: Endo Masayuki , Sasago Masaru , Nomura Noboru , Das Siddhartha
Published: July 2002

This paper presents the high-aspect-ratio pattern fabrication method for KrF excimer laser lithography. The alkaline surface treatment of a resist before exposure can enhance the contrast of a conventional naphthoquinone-diazide-based deep UV positive resist. It has been found that the improvement depends upon the structure of the resist. High-aspect-ratio sub-half-micron patterns of the deep UV resist with an easy azo-coupling reaction were successfully attained using this simple method without compromising sensitivity.
Design and application of an e-beam test system for micropackaging boards
Authors: Schmid R. , Brunner M. , Schmitt R. , Lischke B. , Bergh N. Then , Wörner M.
Published: July 2002

Mechanically probing test systems for the electrical testing of microwiring substrates are reaching their technological and economic limits. An electron beam test system for testing microwiring substrates is presented as an alternative. In contrast to other methods it uses only one primary energy for charging networks and reading their voltage, which results in a simpler instrumentation. The primary energy of 10 keV allows reliable charging of all relevant materials. The pad voltage is read by analyzing the energy of the generated electrons to indicate shorts and opens in the networks. An electron probe of 40 μm diameter can be positioned with a fast electrostatic deflection system to an accuracy of 10 μm on an area of 10×10 cm2 in a current laboratory system. Microwiring substrates with pads down to 100 μm in size can be tested. The test is based on CAD data without restrictions on the layout. Experimental results show reliable fault capture.
A new precise optical autofocus system
Authors: Fein Michael E. , Kelderman Herman F. , Neukermans Armand P. , Loh Alan E. , Wolze David
Published: July 2002

A new optical configuration, called the inverse confocal microscope, is used in the automatic focusing system of a microspectroreflectometer that is used for film thickness measurement. At best focus, a conventional confocal microscope maximizes the transmission of light through an aperture. In contrast, the inverse confocal arrangement minimizes transmission. The focussing precision so far demonstrated is comparable to the 0.08 micron quantization error of the control system used.
A thermochemical model for the plasma etching of aluminum in BCl3/Cl2 and BBr3/Br2
Authors: McNevin S. C.
Published: July 2002

This article describes a quantitative Recipe Map which has been constructed to target the controllable gas flows, wafer loading, and temperature settings predicted to result in the optimum BCl3/Cl2 and BBr3/Br2 plasma etching of aluminum for a given reactor and background oxygen pressure. The numerical predictions of this Recipe Map are based on modeling the plasma as a steady state flow system in which all thermodynamically predicted chemical reactions occur with collision limited kinetics, and where, in addition, physical sputtering removes material from the ion-bombarded surfaces. Anisotropic etching is caused by the sputtering of deposited oxide which allows the chemical etching of the underlying Aluminum. Although this model is very simple, its numerical predictions are in good qualitative agreement with the observed Al etching dependence on the processing parameters in both single wafer and hex etchers. In particular, the effect of wafer loading can be quantitatively evaluated using simple formulas.
Susceptor and proximity rapid thermal annealing of carbon-implanted InP
Authors: Katz A. , Pearton S. J.
Published: July 2002

AuGe contacts to n-type layers formed by carbon implantation into semi-insulating InP substrates demonstrate superior performance on material activated by annealing within an enclosed SiC-coated graphite susceptor (700 °C, 10 s), compared to the more conventional proximity approach. This superiority is due to the better substrate surface morphology achieved. Activating the implants within the graphite susceptor eliminates P outdiffusion and formation of pits. In addition, annealing within the susceptor provides much better protection against edge degradation and slip formation.
Analysis for effects of mask defects to resist pattern using a three-dimensional photolithography simulator
Authors: Ito Tetsuo , Kadota Kazuya , Nagao Masaki , Sugimoto Aritoshi , Nozaki Masahiro , Kato Takeshi
Published: July 2002

A three-dimensional (3D) photolithography simulator was developed which is composed of the two-dimensional (2D) mask aerial image simulator, simulator for 2D intensity pattern in aligner (STIPAL), and the 3D resist image simulator, resist process 3D simulator (RESPROT). STIPAL can calculate the mask aerial image in projection printing considering lens aberrations and reticle defects which are very important factors influencing submicron pattern transfer, in addition to the parameters of lens NA (numerical aperture), source wavelength λ, partial coherency σ and defocusing. RESPROT can simulate the 3D resist image in a conventional resist process and contrast enhancement lithography (CEL) using the mask aerial image data calculated by STIPAL. Resist pattern printability or fidelity in the submicron process can be analyzed by these simulators. Resist linewidth shifts caused by reticle defects and lens aberrations were analyzed. Effects of a dark defect (a surplus pattern) or a clear defect (a lack of pattern) on the resist linewidth shifts are almost the same when defocusing and/or lens aberration do not occur. When defocusing and/or lens aberration occur, however the resist linewidth shift caused by a dark defect is larger than that caused by a clear defect. A high resolution photoresist and CEL can decrease the resist linewidth shift caused by mask defects. Further, CEL can decrease oval distortion of the submicron contact hole pattern caused by lens aberration.
A study of the GaAs–Si(100) interface using laser probing of thermal desorption kinetics
Authors: Smilgys Russell V. , Oostra Doeke J. , Leone Stephen R.
Published: July 2002

The thermal desorption kinetics of Ga from initially As-terminated Si(100) is investigated using laser-induced fluorescence spectroscopy. During the Ga desorption process the surface does not remain fully As terminated because a significant fraction of the initial As coverage simultaneously desorbs with the Ga. For Ga coverages ≥ 0.55±0.1 ML (1 ML=6.8×1014 atoms cm−2), Ga desorbs from As-terminated Si initially by a fractional order kinetic mechanism. Lower Ga coverages desorb more slowly and by a first order mechanism. The results suggest that at high coverages Ga desorbs initially from islands, and then at lower coverages from a two-dimensional (2D) layer. Based on the distinct differences between Ga desorption from bare Si(100) and the desorption of Ga from the 2D Ga/As interfacial layer, this layer is probably GaAs-terminated Si(100). These results on the GaAs system are compared with those previously reported on the InAs system, which show that In interacts with As on Si(100) less strongly than does Ga.
Electronic states of Sb, Bi, Au, and Sn clusters on GaAs(110)
Authors: Menon Madhu , Allen Roland E.
Published: July 2002

Using Hellmann–Feynman molecular dynamics, one can calculate the atomic motion, equilibrium geometries, and electronic states for clusters of atoms on semiconductor surfaces. Here we report studies that were motivated by the scanning tunneling microscopy and spectroscopy observations of Feenstra and co-workers. Although the geometries and electronic structures vary from one simulation to another, we typically find states in or near the upper part of the band gap for Sb, Bi, Au, and Sn on GaAs(110). The character of these states is rather complicated and geometry dependent, but they tend to be largely associated with the cluster and the surface Ga atoms. That is, they can be roughly viewed as split off from the Ga-derived conduction bands by the perturbation resulting from the semiconductor–cluster bonding.