bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray photoelectron spectroscopy damage characterization of reactively ion etched InP in CH4–H2 plasmas
Authors: Feurprier Y. , Cardinaud Ch. , Turban G.
Published: July 2002

The plasma–surface interaction during CH4–H2 reactive ion etching processing of InP is described in detail by means of plasma diagnostics (optical emission spectroscopy and mass spectrometry) and x-ray photoelectron spectroscopy (XPS) surface analysis. The influence of the input power is carried out for different CH4–H2 mixtures in terms of InP etch rate, etch product and CH3 radical detection and surface damage characterization. In particular detailed XPS results allow the study of the changes in the stoichiometry and amorphization of the surface with the input power. In addition, for a given power, the quality of the etched surface improves by increasing the fraction of methane in the gas mixture. As an example, the best surface stoichiometry (InP0.86) is obtained for a pure methane plasma running at a high power (300 W). In general, it is shown that the lower the P depletion, the lower the amorphization, which is indicative of a general improvement of the etched surface quality. Based on the XPS results, a three-layer model is proposed for the representation of the surface in the course of etching. The damaged layer situated over the bulk InP is composed of a superficial P-depleted layer and of a stoichiometric amorphized InP layer. Using the curve-fitting of the P 2p spectra, the thickness of the different layers is estimated. As an example, a damaged layer as low as 37 Å thick is obtained for pure methane plasma at 15 mTorr and a power of 300 W, whereas our standard conditions (10% CH4–H2, 50 mTorr, and 80 W) give a damaged layer of 90 Å. The experimental observations give evidence of the need for both ion bombardment and active neutral species to obtain etching. The improvement of the etch process is then explained by an improved In removal rate which is actually the limiting step in the etching mechanism of InP.
Poisoning of Spindt-type molybdenum field emitter arrays by CO2
Authors: Chalamala Babu R. , Wallace Robert M. , Gnade Bruce E.
Published: July 2002

The effect of CO2 on the emission characteristics of Spindt-type molybdenum field emission cathode arrays is investigated. Exposure of active field emitters to CO2 results in emission degradation. The degradation ranges from (11.8 ± 3.8)% for 10 L to (77.2 ± 12.6)% for 5000 L CO2 exposures. The emission loss results from the formation of molybdenum oxide on tip surfaces, resulting in an increased work function. Work function changes of 0%–7.5% have been measured. The emission changes resulting from CO2 exposures are similar to the effects observed with O2 exposures. The emission degradation mechanism is the interaction of oxygen with molybdenum forming surface molybdenum oxides, thus resulting in a higher surface work function and lower emission current. The emission degradation resulting from CO2 exposure is compared to the emission enhancement produced by exposure to CH4.
High-density, inductively coupled plasma etch of sub half-micron critical layers: Transistor polysilicon gate definition and contact formation
Authors: Westerheim A. C. , Jones R. D. , Mager P. J. , Dubash J. H. , Dalton T. J. , Goss M. W. , Baum S. K. , Dass S. K.
Published: July 2002

Sub-half-micron device design rules require precise control over two critical etch layers: transistor polysilicon gate definition and contact formation. The definition of the transistor polysilicon gate electrode is essential to the performance of the device. In addition, the small geometries and thin underlying gate oxide demand a high level of control over the gate dimensions. The design rules also require the formation of high-aspect-ratio contacts and vias with nearly vertical sidewalls and minimal critical dimension variation. To define these features, a deep-ultraviolet photolithography process was developed, incorporating a bottom antireflective coating (ARC). The etch processes used to translate these features into polysilicon (gates) and oxide (contacts) required an in situ ARC dry–develop step and a fast etch rate for high throughput with good uniformity while maintaining a high selectivity to any underlying layers. To achieve these stringent requirements, low-pressure, high-density-plasma reactors with independent substrate bias power control were needed.
Neural optimal etch time controller for reactive ion etching
Authors: Limanond Suttipan , Si Jennie , Tseng Yuan-Ling
Published: July 2002

In this article we address a neural network-based end point detection scheme for reactive ion etching process. We use the etch time as the critical parameter to indicate process end point. Further, our approach involves the use of a neural network-based predictive model relating various in situ measurements and end point detection signal to the resulting film thickness remaining in combination with an optimization algorithm. This circumvents the need for monitoring and operating on noisy end point detection signal typically associated with conventional detection schemes. Finally, we present simulation studies based on production data to further demonstrate the associated design procedures and the feasibility of the algorithm.
Optimum annealing conditions for boron implanted SiGe epilayers
Authors: Jiang R. L. , Liu W. P. , Jiang N. , Zhu S. M. , Shen B. , Chen Z. Z. , Zheng Y. D.
Published: July 2002

Si 0.8 Ge 0.2 strained epilayers were grown on Si substrates by rapid thermal process/very low pressure-chemical vapor deposition and implanted with boron at 40 keV for a dose of 2.5×1014 cm2. Rapid thermal annealing (RTA) and steady-state furnace annealing with different temperatures and time periods were performed for comparison. Results indicate that RTA is better than furnace annealing. The optimum annealing conditions are RTA at 750–850 °C for 10 s or at 700 °C for 40–50 s. At these conditions the implantation induced damage can be removed; the carrier mobility was about 300 cm2/V s and the activity was nearly 100%. The experiments also indicate that a Si cap layer can protect the crystals.
Photolithographic patterning of phosphor screens by electrophoretic deposition for field emission display application
Authors: Kang Sang Won , Yoo Jae Soo , Lee Jong Duk
Published: July 2002

The patterning of phosphor screens was carried out using a lithographic technique and electrophoretic deposition of phosphor particles for high-resolution field emission display applications. The electrophoretic deposition and photolithography steps were established. Patterned phosphor screens were fabricated by controlling process parameters such as electrophoretic deposition rate in combination with a well-controlled photoresist process in order to achieve proper pixel size with clear boundaries.
Role of V-shaped stacking faults in Au/n-type ZnMgSSe:Cl Schottky diodes
Authors: Wang Ching-Wu
Published: July 2002

The microstructural, optical, and electronic characteristics of both Cl-doped ZnMgSSe epilayers and Schottky diodes grown by the molecular beam epitaxy method on n+-type GaAs (100) substrates with different thicknesses of Cl-doped ZnSe buffer layers were investigated via three measurements: transmission electron microscopy, photoluminescence, and deep level transient spectroscopy. The V-shaped stacking faults, originating at or near the ZnSe:Cl (buffer layer)/GaAs interface and extending into the ZnMgSSe:Cl epilayer, were discovered to have the evident inclination to exist in samples with thicker ZnSe:Cl buffer layers and higher growth temperatures. Evidence also revealed that the stacking faults not only produced poor optical quality of ZnMgSSe:Cl thin film, but also created more interface state densities at the Au/n-type ZnMgSSe:Cl Schottky junction. Such results are the main factors to damage the I–V characteristics of Au/n-type ZnMgSSe:Cl Schottky diode, including the less forward conduction current density, the bigger turn-on voltage, and the larger reverse leakage current followed by the smaller reverse breakdown voltage.
Evaluation of development speed of a photoresist by means of electrical conductivity measurement
Authors: Takeda T. , Saka M.
Published: July 2002

A method was examined for evaluating the electrical conductivity of a photoresist to predict its development speed. The conductivity of organic solutions of the photoresist base polymer at various frequencies was found to have a positive correlation with the dissolution speed of the photoresist base polymer into an alkaline developer. In addition, the influence of the measurement temperature and of the concentration of the polymer solution on the conductivity was investigated. It is shown that a prediction of development speed of a photoresist by measuring its conductivity is possible.
Deep levels in low temperature GaAs probed by field effect deep level transient spectroscopy
Authors: Halder N. C. , Goodman T.
Published: July 2002

Low temperature (LT) GaAs grown on semi-insulating GaAs by molecular beam epitaxy has been investigated by field effect deep level transient spectroscopy at several reverse bias fields ranging from −1×105 to −4×105 V/cm. The activation energy, capture cross section, and electron–phonon coupling parameter all have been found to be modulated by the applied field. The theories of the Schottky effect and the electron–phonon coupling effect have been considered to interpret the electron conduction mechanisms in LT GaAs.
Tandem accel lens advantageous in producing a small spot focused ion beam
Authors: Nomura Setsuo
Published: July 2002

This article presents a novel electrostatic lens which is particularly advantageous in producing a smaller spot focused ion beam (FIB). The lens has a tandem structure made up of conventional einzel lenses operated in the acceleration (accel) mode. The structure allows the lens to work under significantly lower excitation voltages compared with conventional accel lenses, making it possible to converge high energy FIB at short focal lengths to minimize aberrations. The minimum spot size obtainable for a 30 keV FIB with 1 pA current has been calculated for various objective lens applications under a restriction where the excitation voltage should be below the beam voltage (30 kV). Spot sizes are 7.3, 6.6, and 4.8 nm for the conventional accel, decel, and tandem accel lenses discussed in this article, respectively.
Electron field emission from a silicon subsurface based on a generalized Airy function approach
Authors: Khairurrijal  , Miyazaki Seiichi , Hirose Masataka
Published: July 2002

An analytical approach in calculating electron field emission current from a silicon subsurface layer is presented. By employing a nontriangular quantum well model for the silicon subsurface layer, wave functions of electrons in the silicon subsurface layer are given on the basis of generalized Airy functions. After tunneling through a vacuum barrier, the electrons from the silicon subsurface layer are represented by outgoing waves at infinity. Such a boundary condition results in a complex subband-state energy, which simultaneously provides a subband energy level and a tunneling probability per unit time. A negative differential resistance characteristic is shown, being consistent with the experimental result.
Designing test interconnect structures for micro-scale stress measurement: An analytical guidance
Authors: Shen Y.-L. , Guo Y. L.
Published: July 2002

A method to examine the design of test interconnect structures used in micro-scale stress measurements was sought in this study. Three-dimensional finite element analyses of thermal stresses in metal interconnects with various geometrical features were carried out. Aluminum lines with different aspect ratios, passivated and unpassivated, bearing the L- and T-shaped angles that result in local variations in tensile stress, were characterized. The evolution of stresses and stress gradient along the line was quantified. Implications to the design of test metallization structures for spatially resolved stress measurements were discussed. The effects of corner curvature were shown to be confined only to a small area so the stress pattern is dominated by the global line geometry. Examples of the stress profile in a voided metal line were also given, which illustrate the extent of stress gradient expected to be encountered in measurements if the line contains voids.
Novel field emitter array technology for subhalf-micron diameter gates
Authors: Yoshiki M. , Furutake N. , Takemura H. , Okamoto A. , Miyano S.
Published: July 2002

We have successfully developed a novel field emitter array (FEA) technology with low leakage current between each emitter and its subhalf-micron diameter gate. The device has two features: (1) a locally oxidized layer and (2) an additional Si3N4 layer as a second insulator layer. In a fabricated FEA with a 0.38-μm-diam gate, the insulator thickness was 0.26 μm, two times thicker than that of the conventional structure, and the creeping distance was ten times longer. Its emission threshold voltage is 32 V, and its leakage current has been reduced to less than a tenth of previous levels.
Electron field emission from amorphous silicon
Authors: Silva S. R. P. , Forrest R. D. , Shannon J. M. , Sealy B. J.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) is used commercially for large area device fabrication in active matrix flat panel displays as the switching element in thin film transistors. We have found that a-Si:H thin films can be conditioned to field emit electrons at relatively low electric fields. Once conditioned, emission from nonoptimized films at macroscopic vacuum fields below 20 V/μm is routinely obtained. The threshold fields for electron emission appears to be dependent on the film thickness and fields below 10 V/μm have also been recorded. The Schottky junction between the a-Si:H and Cr is important to the electron emission process at low fields and plays a major role in helping to fully deplete the a-Si:H film such that electrons that enter the conduction band of the film by thermionic emission over the barrier (or tunneling through the barrier) can become “hot.” If the emission is localized, it still appears to be controlled by space charge and the back contact barrier. We have examined the electron emission from multilayer structures that contain Schottky and ohmic back contacts as well as thin n+surface layers. Although the electron emission can be fitted to a Fowler–Nordheim type curve, the values obtained for the barrier and emission area for the nominally flat thin films are unrealistic. We explain the observed emission using a space charge induced hot electron model, where the a-Si:H acts as an interlayer in which the electrons are heated.
Influence of the composition of a NbNx thin-film field emitter array on emission characteristics
Authors: Nagao M. , Gotoh Y. , Ura T. , Tsuji H. , Ishikawa J.
Published: July 2002

We fabricated NbNx thin-film field emitter arrays by the ion beam assisted deposition technique which can prepare transition-metal nitride thin films at a relatively low temperature of about 500 °C. The emitter arrays were fabricated by depositing NbNx thin films on Si cones. The nitrogen composition of the film is controlled by selecting the deposition condition, such as the arrival rate ratio of N to Nb flux. We investigated the influence of the nitrogen composition of the NbNx thin-film field emitter arrays on electron emission characteristics. The emitter arrays with a higher nitrogen composition emitted electrons at a lower voltage and showed more stable emission than those with a lower composition. We compared the emission stability of the NbNx emitters with that of the Si emitters. The emission from the NbN emitter (composition ∼1.0) was more stable than that from the Si emitter by a factor of 10 in terms of the noise power.
Model for etch depth dependence on GaAs via hole diameter
Authors: Abraham-Shrauner Barbara , Nordheden Karen J. , Lee Yao-Sheng
Published: July 2002

Reactive ion etching of via holes for grounding of monolithic microwave integrated circuits has become the industry standard. It is well known that the via etch rate decreases as a function of decreasing via mask diameter as well as increasing etch depth. A model has been developed which relates the experimental etch rates in Cl2/BCl3/Ar plasmas to the ion and neutral fluxes incident on the wafer. This model provides a useful tool for designers and process engineers to predict etch depths and average etch rates as functions of via diameter and total etch time.
Fabrication and characterization of a two-dimensional electron gas in modulation doped ZnTe/Cd1−xMnxSe quantum wells
Authors: Knobel R. , Smorchkova I. P. , Samarth N.
Published: July 2002

The II–VI semiconductors ZnTe and CdSe are nearly lattice-matched materials which have a type-II band alignment with a large offset (∼1.35 eV) of conduction band edges. Even though donors in ZnTe create deep levels, we have successfully made two-dimensional electron gases in this system through modulation doping of a CdSe layer sandwiched between n-doped (chlorine) ZnTe layers. In addition, we have fabricated “magnetic” two-dimensional electron gases, where a small amount of Mn is included in the CdSe quantum well, with the aim of studying spin-dependent phenomena in reduced dimensions. We find efficient transfer of electrons into the (Cd, Mn)Se quantum well, even when the doping layer is separated from the well by up to 150 nm of intrinsic ZnTe. By utilizing narrow spacer layers, carrier concentrations of up to 2×1013 cm−2 are demonstrated. Low temperature magnetotransport measurements of nonmagnetic samples indicate a Hall mobility typically in the range 5000–10 000 cm2/V s, but somewhat lower quantum mobilities (∼3000 cm2/V s). In the magnetic samples, while both the carrier concentrations and the Hall mobility are relatively unaffected by the presence of the Mn ions, a dramatic decrease in the quantum mobility is observed.
Growth and morphology of Er-doped GaN on sapphire and hydride vapor phase epitaxy substrates
Authors: Birkhahn R. , Hudgins R. , Lee D. , Steckl A. J. , Molnar R. J. , Saleh A. , Zavada J. M.
Published: July 2002

We report the morphological and compositional characteristics and their effect on optical properties of Er-doped GaN grown by solid source molecular beam epitaxy on sapphire and hydride vapor phase epitaxy GaN substrates. The GaN was grown by molecular beam epitaxy on sapphire substrates using solid sources (for Ga, Al, and Er) and a plasma gas source for N2. The emission spectrum of the GaN:Er films consists of two unique narrow green lines at 537 and 558 nm along with typical Er3+ emission in the infrared at 1.5 μm. The narrow lines have been identified as Er3+ transitions from the H11/22 and S3/24 levels to the I15/24 ground state. The morphology of the GaN:Er films showed that the growth resulted in either a columnar or more compact structure with no effect on green light emission intensity.
Double exchange-related interfacial tunneling and the corresponding giant magnetoresistance in granular La1−xSrxMnO3 perovskites
Authors: Zhang Ning , Zhong Wei , Ding Weiping
Published: July 2002

Fine grain manganese perovskites La1−xSrxMnO3 have been synthesized by using the inorganic sol-gel method. The grain size-dependent and the doping level-dependent magnetic transport properties in the fine grain system have been studied. The interfacial tunneling associated with the double exchange interaction and the corresponding tunnel-type magnetoresistance have been observed in the samples with an average grain size no greater than 0.12 μm in the doping range 0.05⩽x⩽0.45 for temperatures below the Curie point. The magnetization, the heat capacity, and the oxygen stoichiometry for the sample system have been measured to demonstrate that the interfacial tunneling originates from the difference in magnetic configuration between the surfaces and the cores of the grains, and the corresponding giant magnetoresistance results from the field-induced change of the surface magnetic ordering.
Relaxation of strained Si layers grown on SiGe buffers
Authors: Samavedam S. B. , Taylor W. J. , Grant J. M. , Smith J. A. , Tobin P. J. , Dip A. , Phillips A. M. , Liu R.
Published: July 2002

Thin strained Si layers grown on SiGe layers graded to 20% Ge were studied for resistance to relaxation. It was observed that in the presence of ∼105/cm2 threading dislocations from the underlying graded layers, the barrier to misfit dislocation formation is sufficiently reduced to induce relaxation in Si layers even when the layer thickness is less than the predicted critical thickness. Raman spectroscopy revealed that elastic strain accumulation in the uniform SiGe layers is a significant contributor to strain relaxation in the Si cap layers. Upon annealing, thermal mismatch causes the Si layers to relax further, but most of the strain relaxation is accommodated by elastic strain increase in the SiGe layers. This prevents the rampant increase in defect density that would otherwise accompany the strain relaxation. Annealing in an oxidizing ambient appears to pin pre-existing threading dislocations causing nucleation of new threading dislocations and short misfit segments to relieve the thermal mismatch stresses.
Minigaps in strained silicon quantum wells on tilted substrates
Authors: Thornton T. J. , Ge F. , Andresen A. , Pivin D. , Bird J. , Ferry D. K.
Published: July 2002

The two-dimensional electron gas formed at the inverted surface of a tilted silicon substrate shows unusual magnetotransport properties due to the presence of a minigap in the density of states. For metal–oxide–semiconductor inversion layers the strong scattering at the interface limits the mobility to values μ<10–20 000 cm2/V s. To achieve mobilities approaching 105 cm2/V s we have used strained Si:SiGe quantum wells grown on substrates tilted away from the (001) normal by 0°, 2°, 4°, 6°, and 10°. Their transport properties have been measured in the temperature range of 20–500 mK. All the samples show strong Shubnikov–de Haas oscillations. For the 2° and 4° samples the envelope of the fast oscillations is modulated by a longer period oscillation at low magnetic fields. We attribute the slow oscillation in the 2° and 4° samples to the presence of a minigap. For the 6° and 10° samples the minigap is higher than the Fermi energy and is not expected to influence the transport properties.
Remote plasma enhanced chemical vapor deposition SiO2 in silicon based nanostructures
Authors: Rack M. J. , Hilt L. L. , Vasileska D. , Ferry D. K.
Published: July 2002

In the depletion gate approach to silicon-based nanostructures, a deposited oxide covering tiny metallic or silicide gate structures must function as a metal-oxide-semiconductor field effect transistor gate oxide. Depending upon the implementation, it may form the Si/SiO2 interface or be placed upon a very thin thermal oxide. In the former case, bonding between the silicon and SiO2 must be nearly perfect in order to achieve the high mobility required for observing quantum effects. In the latter case, the deposited oxide must not allow leakage current to obscure effects being observed, nor degrade the previously established thermal interface during deposition. Remote plasma enhanced chemical vapor deposited (RPECVD) silicon dioxide has been studied for use in silicon-based nanostructures. For thin oxides deposited at low temperature, oxide surface roughness has been shown to perturb the potential landscape seen by an electron traveling in a silicon inversion layer. [M. J. Rack, D. Vasileska, D. K. Ferry, and M. Siderov, J. Vac. Sci. Technol. B 16, 2165 (1998).] We have further explored processing parameters that influence the deposited oxide surface roughness, presumably roughened primarily by gas phase nucleation, and examined the correlation between roughness and oxide reliability. We found that processing conditions that reduce the oxide roughness and unwanted oxidation of the depletion gate structures are not necessarily those that produce the best silicon/oxide interfaces, nor the most defect-free bulk oxides in our RPECVD system. Specific processes tailored for particular device strategies are presented. The low temperature process at 175 °C is extensively explored.
Infrared study of Si surfaces and buried interfaces
Authors: Milekhin A. , Friedrich M. , Hiller K. , Wiemer M. , Gessner T. , Zahn D. R. T.
Published: July 2002

Multiple internal reflection and transmission IR spectra of hydrophobic and hydrophilic Si wafers, Si wafers with thermally grown SiO2 layers, and Si wafers bonded at high and room temperature were investigated. It was found that the surface of the as-prepared hydrophobic wafer is terminated by hydrogen and water molecules, while the IR spectra of hydrophilic wafer demonstrate only the presence of water molecules at the surface. IR spectra of Si wafers covered by a thermally grown SiO2 layer exhibit a number of the strong absorption bands assigned to combinational phonon bands in SiO2. The wafer bonding leads to the appearance of siloxane and hydroxyl groups at the buried interface whose absorption bands were observed in IR spectra. A rearrangement of atoms at the buried interface takes place after annealing of Si bonded wafers. IR spectra of room temperature bonds show a large number of water molecules and presence of the hydrogen in the oxide layer at the interface.
Atomic force microscopy of oxidative coupling reactions of phenols with FeCl3 in the solid state
Authors: Zeng Qingdao , Wang Chen , Bai Chunli , Zeng Pengju , Li Yan , Yan Xinjian
Published: July 2002

The solid-solid chemical reactions of phenols or ketones, such as β-naphthol (1) or anthron (2), with FeCl3⋅6H2O by ultraviolet irradiation give coupling dimeric products. The mechanisms are studied using atomic force microscopy (AFM) and known crystal packing data. AFM reveals that the crystal face (100) of 2 or (001) of 1 exhibits stumpy protrusions all over the surface from the contact edge of the crystals, respectively, whereas the long side face (010) of 2 gives volcanoes. All of those are guided by the crystal structure. Molecular interpretations of the AFM features are given.
Simulation of thermionic emission from aluminum gallium nitride cathodes at elevated temperatures
Authors: Hatfield C. W. , Bilbro G. L.
Published: July 2002

Al x Ga 1−x N semiconductor data were used to design a cathode with its layer thicknesses, doping level, and compositional grading specified. Semiconductor device theory was used to determine the thermal equilibrium condition in the cathode at various temperatures in order to compute the energy barrier for emitted electrons. The resulting current density was estimated from thermionic emission theory, and the results suggest that these cathodes could provide a current density of 100 A/cm2 or more at temperatures below 600 K. Such cathodes should prove quite useful for many types of vacuum devices, particularly microwave tubes.
Rapid annealing study of neutron-irradiated GaAs by Rutherford backscattering spectrometry/channeling
Authors: Liu Jian , Wang Pei-xuan
Published: July 2002

The behavior of GaAs crystals irradiated with neutrons of various fluence has been investigated using Rutherford backscattering spectrometry/channeling. The results show that the neutron irradiation (from 1014 to 1017 n/cm2) has little effect on the critical angle (Ψ1/2). During annealing, the rate of lattice reordering increases with the temperature rising. For the fluence of 1015 n/cm2, the activation energy of defect annihilation E1=0.35 eV, which may be attributed to the recombination of vacancies with migrating interstitials. The activation energy E2=0.13 eV for the neutron fluence of 1017 n/cm2 may, probably, correspond to the recombination of vacancies with interstitials in the most neighborhoods.
Finite linewidth observed in photoluminescence spectra of individual In0.4Ga0.6As quantum dots
Authors: Spithoven J. L. , Lorbacher J. , Manke I. , Heinrichsdorff F. , Krost A. , Bimberg D. , Dähne-Prietsch M.
Published: July 2002

The photoluminescence of In0.4Ga0.6As quantum dots was investigated by scanning-near-field optical microscopy at temperatures between 300 and 4 K. Using etched, metal-coated fiber tips, the pure signal of individual quantum dots could be detected. The spectra are found to consist of Lorentzian-shaped emission lines with linewidths ranging from 10 to 20 meV at room temperature, reducing to less than the spectrometer resolution of 1 meV at 4 K. This behavior is in contrast to the expectation of extremely small linewidths amounting to a few μeV, and can be related to lifetime effects mediated by thermal excitation of the carriers in the dots. Furthermore, the spectra show a redshift by about 8 meV upon increasing the excitation intensity, indicating biexcitonic effects.
Nanolithography using extreme ultraviolet lithography interferometry: 19 nm lines and spaces
Authors: Solak H. H. , He D. , Li W. , Cerrina F.
Published: July 2002

Development of photoresist materials for the extreme ultraviolet lithography (EUVL) technology is one of the major challenges facing the researchers in this area. In addition to answering the well known challenges presented by the EUV radiation like the high absorption coefficients, the candidate materials should have the necessary resolution well below 100 nm feature size. We have developed an EUV interferometric lithography system for testing resists using high resolution patterns. The system is based on undulator radiation from an electron storage ring and a Lloyd mirror interferometer. We have achieved 19 nm line and space patterns (37 nm pitch) using this system. To our knowledge this is the highest resolution grating period achieved so far in any photon based lithography technique. Results showing printed grating patterns on various commercial resists are presented and practical and theoretical issues limiting the pattern quality are discussed.
Technique for optical characterization of exposure tool imaging performance down to 100 nm
Authors: Grodnensky I. , Suwa K. , Farrar N. , Johnson E. , Pan J.
Published: July 2002

A new technique for accurate and fast characterization of exposure tool imaging performance is presented. It is based on optical measurements of a macroscopically large length of test marks printed in a photoresist in a two-step process. In the first step, the line of the specific critical dimension (CD) is exposed with energy of one-half the nominal energy for a fully formed image. In the second step, the line of the same CD but with a slightly different orientation is exposed with the same energy as in the first step in such a way that its image superimposes the image exposed in the first step. The length of the resulting test mark is linearly proportional to the width of a line printed in a regular exposure process and is inversely proportional to sin(α), where 2α is an angle between two orientations. The coefficient of proportionality is found to be constant for a given resist process over broad ranges of CD variations caused by defocusing, aberrations, exposure dose change, etc. The mark length is measured rapidly with high accuracy by an optical scanning system and the result is then converted into the CD value. A measurement precision (3σ) of 0.5 nm is achieved for sub-150 nm CDs. Results of deep ultraviolet exposure tool characterization at CDs down to 100 nm are presented.
More exact method of determination of the trap concentration of deep levels: Application to molecular beam epitaxy-grown, low temperature GaAs
Authors: Halder N. C. , Zhao X.
Published: July 2002

To determine the trap concentration of the deep levels in semiconductors, more exact formulation than used previously has been developed. As an example, we have selected molecular beam epitaxy-grown, Si-doped, low temperature (LT) GaAs and considered the λ effect. The effect of reverse bias field and forward pulse on the deep level trap concentrations has been investigated. Experimental data were obtained from the field effect deep level transient spectroscopy measurement and capacitance voltage characteristics at appropriate temperatures. The LT-GaAs was found to possess rather high trap concentrations in all the deep levels included in the present investigation.
Low resistance small metal contact for high temperature application
Authors: Kim J. S. , Kang W. T. , Lee W. S. , Yoo B. Y. , Shin Y. C. , Kim T. H. , Lee K. Y. , Park Y. J. , Park J. W.
Published: July 2002

A reliable small metal contact (∼0.18 μm) withstanding high temperature post-thermal budget (∼800 °C for 30 min) is developed for a bit-line (BL) contact of gigabit scaled dynamic random access memories with capacitor-over BL structure. Cobalt (Co) salicidation on the source/drain regions is indispensable to have low BL contact resistance (Rc). The CoSix layer under the contact hole prevents the contact liner (Ti) from reacting with the sub-silicon. Thus, TiSix agglomeration as well as dopant-TiSix interaction is suppressed even with relatively high postannealing temperature. Thin SiN layer on the CoSix is an effective etch stopper during contact etch and protects the thin CoSix layer from the etch damage. Use of an Ar+ soft inductively coupled plasma cleaning instead of the wet chemical cleaning after contact etch is another key factor to attain a reliable BL contact process. The low Rc and contact leakage are ensured when ion–metal–plasma Ti/TiN liner is utilized.
Photoluminescence study of InAlAs quantum dots grown on differently oriented surfaces
Authors: Zhou Wei , Xu Bo , Xu Huai-zhe , Jiang Wei-hong , Liu Feng-qi , Gong Qian , Ding Ding , Liang Ji-ben , Wang Zhan-guo , Zhu Zuo-ming , Li Guo-hua
Published: July 2002

We reported the optical properties of self-assembled In0.55Al0.45As quantum dots grown by molecular beam epitaxy on (001) and (n11)A/B(n=3,5)GaAs substrates. Two peaks were observed in the photoluminescence (PL) spectra from quantum dots in the (001) substrate and this suggested two sets of quantum dots different in size. For quantum dots in the high-index substrates, the PL spectra were related to the atomic-terminated surface (A or B substrate). The peaks for the B substrate surfaces were in the lower energy position than that for the (001) and A type. In addition, quantum dots in the B substrate have comparatively high quantum efficiency. These results suggested that high-index B-type substrate is more suitable for the fabrication of quantum dots than (001) and A-type substrates at the same growth condition.
Atomic force microscope tip-induced anodization of titanium film for nanofabrication of oxide patterns
Authors: Huh Chul , Park Seong-Ju
Published: July 2002

Nanometer-scale oxide patterns were fabricated on Ti films deposited on Si(100) surface by means of atomic force microscope tip-induced anodization. The application of a negative bias voltage to a heavily doped silicon tip relative to the sample substrate permitted nanoscale lines and dots of titanium oxide to be formed directly on the titanium surfaces. Their sizes were dependent on the relative humidity, the scanning rate of the tip, and the pulse duration time. The spatial resolution of titanium oxide patterns was improved by increasing the tip scan rate and also by lowering the relative humidity. The smallest linewidth obtained in this experiment was about 18 nm. With increasing pulse duration time, the growth rate of oxide rapidly decreased. This result can be attributed to the decrease of the transport rate of ionic species through the existing oxide layer due to a reduction of electric field strength with increasing the oxide thickness.
Integration of Pt/Ru electrode structures by metalorganic chemical-vapor deposition on poly-Si/SiO2/Si
Authors: Choi Eun-Suck , Yang Jung-Hwan , Park Jong-Bong , Yoon Soon-Gil
Published: July 2002

The electrode structures of Pt(130 nm)/Ru(80 nm) were integrated on polysilicon by metalorganic chemical-vapor deposition. It was found that the ruthenium buffer layer plays an important role in preventing the oxidation of polysilicon during annealing at 700 °C in oxygen (760 Torr). The microstructure and conductivity of the platinum bottom electrodes depended greatly on the annealing conditions of the ruthenium buffer layer. The surface morphology and the conductivity of Pt/Ru (annealed at 700 °C in a vacuum) films annealed at 700 °C in oxygen were superior to those of Pt/Ru (annealed at 500 °C in a vacuum) films annealed under the same conditions. The electrode structures suggested here may be applied to the integration of ferroelectric thin films.
Status and review of two-dimensional carrier and dopant profiling using scanning probe microscopy
Authors: De Wolf P. , Stephenson R. , Trenkler T. , Clarysse T. , Hantschel T. , Vandervorst W.
Published: July 2002

An overview of the existing two-dimensional carrier profiling tools using scanning probe microscopy includes several scanning tunneling microscopy modes, scanning capacitance microscopy, Kelvin probe microscopy, scanning spreading resistance microscopy, and dopant selective etching. The techniques are discussed and compared in terms of the sensitivity or concentration range which can be covered, the quantification possibility, and the final resolution, which is influenced by the intrinsic imaging resolution as well as by the response of the investigated property to concentration gradients and the sampling volume. From this comparison it is clear that, at present, none of the techniques fulfills all the requirements formulated by the 1997 Semiconductor Industry Association roadmap for semiconductors [National Technology Roadmap for Semiconductors (Semiconductor Industry Association, San Jose, CA, 1997)]. Most methods are limited to pn-junction delineation or provide a semiquantitative image of the differently doped regions. However, recent comparisons have shown that the techniques can provide useful information, which is not accessible with any other method.
Dopant dose loss at the Si–SiO2 interface
Authors: Vuong H.-H. , Rafferty C. S. , Eshraghi S. A. , Ning J. , McMacken J. R. , Chaudhry S. , McKinley J. , Stevie F. A.
Published: July 2002

The phenomenon of dopant dose loss through trapping at the Si–SiO2 interface has important consequences for metal–oxide–semiconductor device fabrication. It represents also a challenge to analytical techniques, since the trapped dopants appear to exist in one or a few monolayers thickness at the interface. In this work, we report on a complementary approach, using both electrical device data and accurate process modeling, as well as analytical dopant profiling with secondary ion mass spectroscopy, to investigate important features of the phenomenon, such as dose dependence, detrapping, and transient enhanced diffusion effects. This approach enabled the development of dose loss models suitable for design of current and future complementary metal–oxide–semiconductor technologies.
Apparent depths of B and Ge deltas in Si as measured by secondary ion mass spectrometry
Authors: Jiang Z. X. , Alkemade P. F. A. , Tung C.-H. , Wang J. L. F.
Published: July 2002

The apparent depths of B and Ge deltas in Si were measured with secondary ion mass spectrometry using 1–4 keV O2+ beams at oblique incidence (40°–80° with respect to the surface normal). The real depths of the Ge deltas were obtained via calibration against transmission electron microscopy (TEM). The measured centroids of the Ge delta peaks were 0.5±0.4 nm shallower than the real (TEM) depths, independent of angle and energy. For B there was a clear angular dependency of the centroid position, but the energy dependency was virtually absent (viz., differential shift <0.2 nm/keV/ion). Repeated analyses during a 2.5 year period showed a reproducibility in Ge delta peak position of 0.04 nm. Surprisingly, the slow but continuous growth of the native surface oxide had no effect on the apparent Ge delta depths. The profile shift of B towards the surface was attributed to the high sputter rate during the surface transient and to B outdiffusion under oxygen bombardment. It was concluded that decreasing the beam energy did not reduce the B shift; the positive effect of a thinner surface transient layer was nullified by a larger (equilibrium) oxygen concentration. In contrast, indiffusion of Ge compensated at all energies and angles the (apparent) Ge shift due to the transient high sputter rate.
Increased electron mobility of InAsSb channel heterostructures grown on GaAs substrates by molecular beam epitaxy
Authors: Kudo Makoto , Mishima Tomoyoshi , Tanaka Takeshi
Published: July 2002

We have designed and grown high-electron-mobility heterostructures that use InAsySb1−y group V alloys as a channel material and that can be used in high-speed transistors and magnetic field sensors. The group V alloys were formed by modulating As2 and Sb2 beams during growth. The composition was controlled by changing the group V shutter cycle. The electron mobility in the InAsySb1−y channel, which is only 20–30 nm thick and is sandwiched between Al0.15In0.85Sb high-resistivity barrier layers, was increased to 28 000 cm2 V−1 s−1 at room temperature by reducing the lattice mismatch between the channel layer and the barrier layer. This mobility is an order of magnitude greater than that of the strained Al0.15In0.85Sb/InSb/Al0.15In0.85Sb heterostructure grown as a reference. The electron mobility in the InAsySb1−y channel sandwiched between Al0.5Ga0.5Sb barrier layers was also increased from 19 500 cm2 V−1 s−1 (y=1.0) to 24 500 cm2 V−1 s−1 (y=0.86) at room temperature by reducing the lattice mismatch between the channel layer and the barrier layer. These increases in mobility indicate that the lattice mismatch must be reduced in order to achieve a high electron mobility of such heterostructures grown mismatched on GaAs substrates.
Selectivity enhancement of GaAs/AlGaAs dry etching by a pulse-excited inductively coupled plasma source
Authors: Matsukura Y. , Tanaka H. , Wada J.
Published: July 2002

SiCl 4 / SF 6 GaAs/AlGaAs selective dry etching by a pulse-excited inductively coupled plasma source with operating pressure lower than 1.0 Pa was investigated. With 10 kHz and 50% duty ratio pulsed excitation, GaAs/AlGaAs etching selectivity was doubled (>200) compared to continuous wave (cw) operation, in which the selectivity was not adequate enough (∼100) to use for device fabrication. With pulsed excitation, we speculate that the electron temperature and [Cl]/[F] radical density ratio decrease. Pulse parameters such as the duration of the “on” and “off” periods and the duty ratio dependence are also investigated, showing that the selectivity was determined by the duty ratio of the pulse. The advantage of pulse excitation over conventional cw excitation is clearly shown.
Electron emission process of phosphorus-doped homoepitaxial diamond films
Authors: Kimura Chiharu , Koizumi Satoshi , Kamo Mutsukazu , Sugino Takashi
Published: July 2002

Electron emission is investigated for phosphorous (P)-doped homoepitaxial diamond films grown by microwave plasma chemical vapor deposition. A comparative study of field emission characteristics is performed for P-doped homoepitaxial diamond films with different electrical resistivities and with different cathode metals. A reduction in the turn-on voltage occurs with decreasing electrical resistivity. A variation in the turn-on voltage occurs with cathode metals. It is revealed that the internal electron emission at the diamond/metal contact has an influence on the field emission characteristics. Moreover, field emission characteristics are measured at various spacings between the anode electrode and diamond surface and at various distances from the cathode metal to the diamond surface just below the anode electrode. No significant change of the average electric field strength between the anode electrode and diamond surface is found between P-doped homoepitaxial diamond films with low and high electrical resistivities. It is suggested that space charge limited current is flowing in the diamond film with high resistivity.
Elevated source drain devices using silicon selective epitaxial growth
Authors: Samavedam S. B. , Dip A. , Phillips A. M. , Tobin P. J. , Mihopolous T. , Taylor W. J. , Adetutu O.
Published: July 2002

Elevated source drain (ESD) structure in deep submicron metal oxide semiconductor field effect transistors (MOSFETs) can help reduce parasitic series resistance and simultaneously achieve shallow contacting junctions to minimize short channel effects. A self-aligned ESD structure in conventional complimentary metal–oxide–semiconductor processing can be achieved using silicon selective epitaxial growth (SEG). A robust low thermal budget high quality SEG process using a commercial rapid thermal chemical vapor deposition reactor for ESD formation has been demonstrated. The preclean sequence prior to SEG is the key to achieve facet-free epitaxy. Low line-to-line leakage confirms the high selectivity to nitride and oxide. The growth on exposed polysilicon (poly) gates leads to gate linewidth widening and lower gate sheet resistance. ESD parametric data suggest that the well doping needs to be optimized to counter the slight increase in n+-p diode leakage. Capacitance–voltage simulations indicate that the gate to drain capacitance initially decreases and then increases with SEG thickness.
Modeling anomalous depth dependent dissolution effects in chemically amplified resists
Authors: Cheng Mosong , Tyminski Jacek , Croffie Ebo , Neureuther Andrew
Published: July 2002

A postexposure bake (PEB) model for JSR KRF-K2G resist has been established for bake temperature and time effects based on using large area exposures on production equipment. Data from top antireflective coated (TARC) K2G resist were well behaved and provided key understanding of the PEB processes. Data from K2G without TARC showed inhibition of surface dissolution that is possibly due to photoacid evaporation. Both processes showed an intrinsic thickness reduction of 50 nm in the first 30 s of PEB and then a continued decrease of 4 nm/min of bake time. This model was fit with the dissolution rates deduced from the coated K2G as a function of activated site concentration. The rates from large area data agree well with dissolution rate monitor (DRM) data and the DRM simulation allowed characterization of the depth dependent effects due to evaporation when TARC was not applied. The methodology of large area exposure allowed the simulation parameters to be quantitatively determined effectively.
Channeling-induced asymmetric distortion of depth profiles from polycrystalline-TiN/Ti/TiN(001) trilayers during secondary ion mass spectrometry
Authors: Ramanath G. , Greene J. E. , Petrov I. , Baker J. E. , Allen L. H. , Gillen G.
Published: July 2002

Asymmetric depth profiles of elemental and molecular secondary ions are obtained during secondary ion mass spectrometry analyses of polycrystalline-TiN/Ti/TiN(001) trilayers using a Cs+ ion beam. The sputter-etching rate R and the secondary ion yield Y from TiN(001) layers are strongly dependent on the incidence angle of the primary ion beam. When the azimuthal angle between the incident beam and one of the in-plane 〈100〉 directions in TiN(001) is varied from 0° to 40°, RTiN(001) varies by more than 40% and YTiN(001) by nearly a factor of 3. In contrast, for polycrystalline TiN layers, RpolyTiN and YpolyTiN are invariant with incident beam angle. Channeling of primary ions and secondary recoils through 0.106-nm-wide channels between highly aligned (100) or (010) planes in TiN(001), and the lack of such correlated long-range alignment in polycrystalline TiN, are the major reasons for the observed differences. Channeling in the TiN(001) layer results in a sharp decrease of YTi in the Ti layer immediately prior to the Ti/TiN(001) interface and increases the interface width, thus degrading depth resolution. These profile distortion effects can be eliminated either by sample rotation during profiling or by using an O2+ primary beam.