bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of wafer temperature variations using photoresist reticulation thresholds
Authors: Luckman Gregory
Published: July 2002

This article presents a technique for using the onset of reticulation, or hazing, of a novolac-diazonaphthoquinone (DNQ) photoresist to monitor differences in peak temperatures between silicon wafers subjected to plasma processing. The technique exploits the lowering of the reticulation threshold temperature with progressive light exposure and consequent photolysis of the resist’s DNQ photoactive compound. Either near ultraviolet or white fluorescent room lights can serve as the light exposure source and are used to establish areas on a wafer with varying concentrations of DNQ. With a range of reticulation threshold temperatures present on a single wafer, wider plasma process latitude is achieved. This makes it more likely that reticulation occurs at least somewhere on a wafer. It also makes it easy to compare results on different wafers by comparing the areas that reticulate. The method resembles the use of thermal dots, but employs only the resist materials commonly present in plasma etching processes. The technique is simple, cheap, and requires no viewports or feedthroughs. Using the technique, it is shown that wafers become hotter on a bare aluminum electrode than on an anodized aluminum electrode and that silicon wafers partially transparent in the infrared become hotter than those opaque in the infrared. The results also demonstrate the degree of temperature uniformity between wafers in a batch tool. Further applications of the technique are suggested. Literature on resist degradation in plasma is reviewed and a new microscopic mechanism is proposed for the reticulation that causes the hazy resist film appearance.

The mechanism is a phase separation of unmodified resist polymer chain molecules from polymer chain molecules modified by exposure to the plasma. The proposed mechanism is used as an heuristic model for assessing the accuracy of a calibration procedure for the hazing onset temperature, which is also presented. The calibration exploits the fact that hazing of a resist film on a wafer occurs if the wafer is subjected to a plasma process and then ramped up in temperature on a hot plate. The calibration procedure exploits the variation of reticulation temperature with DNQ conversion. Under one set of run conditions the calibration indicated a peak wafer temperature between 406 and 412 K. This was compared to a calibration using thermal dots, which indicated a peak temperature between 400 and 405 K, and with the stated thermal flow temperature of the resist, 398 K. The calibration results indicate the limitations of relying on resist thermal flow data to estimate peak wafer temperatures in plasma processes.
Microstructural modification by fast atom beam milling of nanotextured ultrathin metal films
Authors: Devaud Genevieve , Douglas Kenneth
Published: July 2002

We have formed ultrathin metal films with nanometer-scale features by metal shadowing of two-dimensional protein crystals followed by fast atom beam milling. In this process, the metal overlayer is formed into a screen consisting of hexagonal arrays of 10 nm size holes with a 22 nm periodicity. Thin films of Ti, Ta, Pt, Pt/C, Pt/Ir, Pt/Ir/C, Va, Cr, Ni, Ag, Zr, and Nb show dramatic differences in their response to this method of nanotexturing. Evaluation of film morphology by transmission electron microscopy before and after milling reveals a correlation between microstructural characteristics and the features of the nanostructures formed by different metals. The dominant factor for determining the uniformity and quality of the formed nanostructure is a thin film which is amorphous or very fine grained after milling. Overall pattern uniformity and individual hole boundaries which are smooth and round are necessary for optimal patterning. Crystallization and grain growth seem to negatively affect patterning quality, resulting specifically in extensive bridging between holes which generally have irregular boundaries.
Laser induced deposition of tungsten on GaAs from WF6
Authors: Lecours A. , Izquierdo R. , Tabbal M. , Meunier M. , Yelon A.
Published: July 2002

Laser induced deposition of tungsten from WF6 on GaAs using a focused continuous wave scanning argon-ion laser was investigated. Deposits were prepared with H2 as a reducing agent, as well as without it. Deposition of tungsten is found to occur in a narrow process window, suggesting the existence of a competing etching reaction. Film composition and structure were analyzed by scanning electron microscopy and Auger electron microscopy. Surface reactions were studied by x-ray photoelectron spectroscopy. The data suggest that the GaAs surface participates in the reaction with WF6, leading to the formation of GaF3 which may poison the initiation of the deposition process.
Growth and characterization of novel multilayer heterostructures for the monolithic integration of resonant-cavity photodiodes and heterojunction bipolar transistors
Authors: Dodabalapur A. , Chang T. Y. , Chandrasekhar S.
Published: July 2002

We describe the layer structures, crystal-growth conditions, and characteristics of novel multilayers in the InGaAlAs/InGaAs/InAlAs materials system for the monolithic integration of heterojunction bipolar transistors (HBTs) and resonant-cavity photodiodes. The photodiodes are formed of the base and collector regions of the HBT layer. The use of a resonant cavity improves the quantum efficiency for an absorbing layer of given thickness. The HBTs had high current gains and well-behaved Gummel plots. The absorption and photocurrent characteristics of the resonant photodiodes show a ∼100% enhancement at resonance.
Optimization of interfaces in arsenide–phosphide compounds grown by gas source molecular-beam epitaxy
Authors: Moy A. M. , Chen A. C. , Jackson S. L. , Liu X. , Cheng K. Y. , Stillman G. E. , Bishop S. G.
Published: July 2002

A novel source switching procedure in gas source molecular-beam epitaxy to achieve abrupt interfaces in lattice-matched InP/GaInAs has been demonstrated. In this process, a two-step gas source switching procedure was used at the InP-to-GaInAs interface and a single growth pause was employed at the GaInAs-to-InP interface. Gas source switching procedures were optimized through characterizing multiple quantum well samples using photoluminescence and double crystal x-ray diffraction measurements. Single quantum wells grown using the optimized switching procedure displayed the narrowest luminescence linewidth values compared to other documented samples grown by gas source molecular-beam epitaxy.
Thermal stability of Mo–Al Schottky metallizations on n-GaAs
Authors: Huang T. S. , Peng J. G. , Lin C. C.
Published: July 2002

The contact stability and electrical characteristics of sputtered Mo–Al alloy metallizations (Mo74Al26, Mo27Al73, Mo12Al88) on n-GaAs have been investigated. The contacts were annealed by rapid thermal processing in the temperature range of 500–1000 °C for 20 s. X-ray diffraction, Auger depth profiling, scanning electron microscopy, and transmission electron microscopy (TEM) were used to study the structural characteristics. The Schottky diodes were assessed using the current–voltage measurements. The Mo74Al26/GaAs and Mo27Al73/GaAs contacts were stable up to 900 °C anneal, while interfacial reactions in 800 °C annealed Mo12Al88/GaAs contact were observed. Variations of the film surface morphologies and the degradation of the diodes after annealing can be well correlated to the interfacial stabilities. For all thermally stable Mo–Al/GaAs diodes, the Schottky barrier heights increased with annealing temperature. The AlxGa1−xAs at the interface, which contributes to the enhancement of the barrier height, has been clearly verified by the dark field cross-sectional TEM viewed along the 〈100〉 of GaAs.
Effect of substrate temperature on ultrahigh vacuum interfaces of indium oxide/GaAs(110)
Authors: Golan A. , Shapira Yoram , Eizenberg M.
Published: July 2002

The effect of substrate temperature during deposition on indium oxide/n-GaAs(110) interfaces, fabricated by means of reactive evaporation of indium in the presence of ∼1×10−4 Torr oxygen onto ultrahigh vacuum cleaved GaAs(110) surfaces, has been studied using Auger electron spectroscopy and electron energy loss spectroscopy. The results show that the indium oxide layer growth at room temperature and at 200 °C follows the Stransky–Krastanov model. However, the low temperature growth is characterized by the presence of In clusters at the interface and only minor surface oxidation of the GaAs substrate takes place. At high substrate temperatures, the interface is fully oxidized and includes both indium and arsenic oxide. The results are discussed in view of our earlier reported measurements of indium oxide/GaAs diodes produced under high and ultrahigh vacuum conditions.
Electro- and photoluminescence studies from ultrathin SimGen superlattices
Authors: Presting H. , Menczigar U. , Kibbel H.
Published: July 2002

We have observed strong photoluminescence signals in the near infrared (hν∼0.8 eV) from short-period SimGen strained layer superlattices (SLS) by growing the SLS on a step graded buffer by molecular beam epitaxy [H. Presting and H. Kibbel, Thin Solid Films 222, 215 (1992)]. These luminescence signals are about one order of magnitude stronger than the signals observed so far which can be attributed to the excellent material quality of the SLS which has been achieved by growing at higher temperatures (Tg=500 °C) and using the technique of Sb surfactant. In addition the SLSs were grown on the step graded buffer which results in a two to three orders of magnitude lower threading dislocation density at the interface compared to the ‘‘simple’’ buffers [H. Presting and H. Kibbel, Thin Solid Films 222, 215 (1992); F. K. Le Goues, B. S. Meyerson, and J. F. Morar, Phys. Rev. Lett. 22, 2903 (1991); E. A. Fitzgerald, J.-H. Xie, M. L. Green, D. Brasen, D. R. Kortan, J. Michel, Y.-J. Mii, and B. Weir, Appl. Phys. Lett. 59, 811 (1991)]. Electroluminescence signals observed from p-i-n-doped diodes with an ‘‘SF’’-type buffer show broad signals at a different wavelength the origin of which is still unclear.
Effect of lanthanum doping on the electrical properties of sol-gel derived ferroelectric lead–zirconate–titanate for ultra-large-scale integration dynamic random access memory applications
Authors: Sudhama C. , Kim J. , Lee J. , Chikarmane V. , Shepherd W. , Myers E. R.
Published: July 2002

Thin films of lead–zirconate–titanate [(PZT) Pb(Zr0.5Ti0.5)O3] possess demonstrably adequate charge storage densities and endurance to read/write cycling for ultra-large-scale integration dynamic random access memory (DRAM) applications. Lanthanum (donor) doping is expected to reduce the (p-type) conductivity to acceptable levels (<10−6 A/cm2). In this study, six thin films of 200 nm sol-gel derived lanthanum-doped PZT, with the [La]/([La]+[Pb]) concentration ratio varying from 0 to 0.23, have been examined for electrical and reliability properties. The difference between the maximum polarization attained (Pmax, bit ‘‘1’’) and remanent polarization (Pr, bit ‘‘0’’) is denoted as Qc′, and is the relevant charge storage density in the DRAM cell. Qc′ is seen to decrease with an increase in La concentration, contrary to predictions based on an assumption of stoichiometric compositions. A 5% La content results in more than a decade drop in leakage current density (JL) in comparison with undoped PZT, and after refresh annealing (at 450 °C for 1/2 h in O2), the film exhibits a Qc′ value of 7.2 μC/cm2 at 3 V, which is believed to satisfy the 64 Mb DRAM requirements. JL increases almost exponentially with the La concentration beyond 5%, indicating that the increasing volatility of Pb in the oxygen-rich ambient overwhelms the effect of the enhanced La doping concentration, probably due to a departure from the equilibrium composition Pb(1−1.5x)LaxVx/2(Zr0.5Ti0.5)O3, (where V represents a Pb vacancy). Constant voltage stressing indicates an operating lifetime (at room temperature) of about ten years (at 3 V) for the 5/50/50 film. Good fatigue properties are also observed.
Concentration dependence of Ge segregation during the growth of a SiGe buried layer
Authors: Godbey D. J. , Ancona M. G.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) measurements of a series of films with varying x and cap thicknesses were made to determine the Ge profile in both thin Si cap layers and the Si1−xGex buried layers grown at 500 °C. The inelastic mean free path of 267 eV electrons through a silicon overlayer was measured to be 1.2 nm. The Ge profile was inferred by simulating the surface segregation process using a two-state exchange mechanism, and comparing the expected XPS spectra to the obtained data. The resulting model predicts a floating surface layer rich in Ge during the growth of the Si1−xGex layer and the Si cap that results in distortion of both interfaces of the buried layer. The interface formed upon beginning the growth of the buried Si1−xGex layer can be wide, and estimates of the width of the ‘‘leading’’ interface range from ∼20 monolayers (MLs) for an x=0.05 layer, and ∼10 MLs for an x=0.1 layer grown at 500 °C.
High resolution x-ray photoemission spectroscopy studies of thin SiO2 and Si/SiO2 interfaces
Authors: Hattori Takeo
Published: July 2002

The important results for the control of the SiO2/Si interface structure in atomic scale have been obtained recently. In the present article the structural imperfections in the ultrathin oxide, which cannot be determined uniquely by x-ray photoemission spectroscopy, in addition to the early stage of interface formation are discussed. The Si 2p photoelectron spectra arising from Si–Si bonds in the oxide near the interface were confirmed from the measurement of reflectance in vacuum ultraviolet. The Si 2p photoelectron spectra arising from Si–H bonds in the oxide were confirmed by multiple internal reflection infrared absorption spectroscopy.
Electron-beam block exposure system for a 256 M dynamic random access memory
Authors: Sakamoto K. , Fueki S. , Yamazaki S. , Abe T. , Kobayashi K. , Nishino H. , Satoh T. , Takemoto A. , Ookura A. , Oono M. , Sago S. , Oae Y. , Yamada A. , Yasuda H.
Published: July 2002

A block exposure system is developed to expose a 256 M DRAM pattern. Four mask deflectors deflect beams to select one of 48 blocks of stencil patterns in a 5 mm region in diameter on a mask. Each mask pattern is extracted as a unit of repetitions from the dynamic random access memory (DRAM) pattern, which is demagnified to 1/100 on a wafer. In a 256 M DRAM contact hole layer, only two blocks are used to expose memory cell regions. Forty-six blocks are for sense amplifier and decoder regions. The total shot number of the layer is decreased to 21.5×106 with the block exposure system, which is about 1/8 of that with a conventional shaped beam system. One chip is exposed in 11.5 s. Throughput is 10 wafers (6 in.)/h for the contact hole layer.
Molecular beam epitaxy growth of pseudomorphic II–VI multilayered structures for blue/green laser diodes and light-emitting diodes
Authors: Han J. , He L. , Grillo D. C. , Clark S. M. , Gunshor R. L. , Jeon H. , Salokatve A. , Nurmikko A. V. , Hua G. C. , Otsuka N.
Published: July 2002

This article reports results involving the molecular beam epitaxial growth of the quaternary (Zn,Mg)(S,Se) compound as well as the incorporation of this quaternary into a pseudomorphic separate confinement heterostructure laser diode configuration. It was found that the quaternary (Zn,Mg)(S,Se) can accommodate much more strain as compared to binary ZnSe; the films remained essentially pseudomorphic, with low defect densities, for strains in the studied range from −0.225% (tension) to 0.137% (compression) at room temperature. The relationship between the surface morphology and the strain is also described in this paper. Lasing was routinely obtained at room temperature under pulsed injection. A threshold lasing voltage of as low as 7 V was observed in index-guided diode lasers.
Electrical and optical properties of heavily n-doped GaSb–AlSb multiquantum well structures for infrared photodetector applications
Authors: Brar Berinder , Samoska Lorene , Kroemer Herbert , English John H.
Published: July 2002

A detailed analysis of the electrical and optical properties of GaSb–AlSb quantum well infrared photodetector structures is presented. Hall effect measurements were performed, and a two-band conduction model was employed to extract the electron concentration in the L subband, indicating that at typical detector operating temperatures T=80 K there are at least 1012 cm−2 carriers in the L subband. Temperature-dependent dark current measurements indicate that the dark current mechanism in detector structures consists of a tunneling regime for T<100 K, and a thermionic regime for T≳100 K. An activation energy of 170 meV is extracted from the temperature dependence of the thermionic dark current. Photoluminescence and absorption measurements were also used to obtain information on the subband levels relative to the bottom of the well, and to investigate the effect of doping on the quality of the GaSb quantum wells. We also report on a method to push the intersubband transition to longer wavelengths by growing center-loaded structures in which a thin layer of AlSb is deposited in the center of the well in order to raise the energy of only the ground state in the well.
Two-dimensional spreading resistance profiling: Recent understandings and applications
Authors: Vandervorst W. , Privitera V. , Raineri V. , Clarysse T. , Pawlik M.
Published: July 2002

Conceptually the use of spreading resistance measurements for two-dimensional profiling has been introduced two years ago. In the mean time our understanding has improved towards a better interpretation of the experimental results. A simulation program has been realized which allows to simulate the spreading resistance scans along the specially beveled surface. An ‘‘in situ’’ calibration procedure for measuring with high accuracy, the probe size and separation has been developed and a new formula, with less experimental involved parameters, for calculating the lateral spread has been derived. The technique has been applied to a study of the lateral diffusion of B as a function of annealing time. The effect of different masking material (polycrystalline silicon, thick oxide) has been studied. Other recent applications of this technique include the determination of the lateral straggling of channeling implants and the lateral diffusion of transition metals.
Scanning tunneling microscopy morphological study of the first stages of growth of microwave chemical vapor deposited thin diamond films
Authors: Vázquez L. , Sánchez O. , Albella J . M.
Published: July 2002

Thin diamond films have been grown by the microwave chemical vapor deposition method on polished silicon substrates using a methane concentration of 1.5% in hydrogen and deposition times between 7 and 60 min. The films were studied in air by scanning tunneling microscopy (STM). For short deposition times we have found small isolated diamond crystals (100 nm wide and 20 nm high), growing on the scratches produced by the initial polishing of the silicon surface, along with a smooth granular structure. As the deposition time increases to 15 min, the granular structure shows a slight faceting whereas the crystal size increases appreciably. This deposition period is characterized by a lower growth rate than that observed for longer times, which is explained as due to the presumably high nondiamond component of the granular structure. At 30 min a continuous film is formed with predominant {111} faces. The same trend is found for samples grown after 60 min. STM images show that {111} surfaces are rougher than {100} ones supporting the 2×1 reconstruction of the {100} surface during diamond growth.
Mechanism of particle formation in the sputtering and reactive ion etching of Si and SiO2
Authors: Yoo Won Jong , Steinbrüchel Christoph
Published: July 2002

Particle formation from Si and SiO2 substrates in Ar sputtering plasmas and CCl2F2/Ar reactive ion etching (RIE) plasmas has been investigated using laser light scattering, electron microscopy, and optical emission spectroscopy. Nearly spherical particles with sizes down to 50 nm are collected downstream from the substrate even before the onset of light scattering or at pressures below the threshold for cloud formation. Si atoms are seen readily by optical emission during sputtering, but not during RIE, of both Si and SiO2. The rate of particle formation correlates with the density of Si atoms in the plasma. Hence, it is suggested that Si atoms are probably the species responsible for particle nucleation in sputtering and RIE, and formation of a particle cloud occurs only when the transport of Si atoms out of the sheath edge region becomes inefficient, as evidenced by redeposition in sputtering and by polymerization in RIE.
Measurement of heterojunction band offsets using ballistic electron emission microscopy
Authors: O’Shea J. J. , Sajoto T. , Bhargava S. , Leonard D. , Chin M. A. , Narayanamurti V.
Published: July 2002

Ballistic electron emission microscopy (BEEM) has been used to study electron transport across single barrier AlxGa1−xAs/GaAs heterostructures. The structures, grown by molecular beam epitaxy, utilized a p-type δ-doped sheet to cancel the band bending near the Schottky interface, enabling a direct measurement of the conduction band offset at room temperature. The band offset at room temperature for x=0.21 is 0.19 eV and for x=0.42 is 0.33 eV. Measurements at 77 K gave values of 0.20 eV for x=0.21 and 0.35 eV for x=0.42. These results demonstrate that BEEM can be used to probe the transport properties of semiconductor heterostructures which are spatially beneath the Schottky barrier.
First-principles study of Zn- and Se-stabilized ZnSe(100) surface reconstructions
Authors: García Alberto , Northrup John E.
Published: July 2002

We have carried out first-principles pseudopotential calculations to study the formation energies of various ZnSe(100) surface reconstructions. Both Zn- and Se-terminated models are treated, using as a guide the satisfaction of the electron counting rule (i.e., charge compensation at the surface by the filling of all the Se dangling bonds and the emptying of the Zn dangling bonds). In order to treat structures with different stoichiometries, we determine the surface energy as a function of the Zn chemical potential, which is allowed to vary in a range determined by the energies of bulk Zn, Se, and ZnSe. A c(2×2) reconstruction with half-monolayer coverage of twofold coordinated Zn atoms is stable in the Zn-rich limit. Under moderately Se-rich conditions, the surface adopts a (2×1) Se-dimer phase. In the extreme Se-rich limit we predict the stability of a reconstruction with one and a half monolayer coverage of Se. The new structure can account for the high growth rates observed in atomic layer epitaxy and migration enhanced epitaxy experiments at relatively low temperatures.
Step bunching and step equalization on vicinal GaAs(001) surfaces
Authors: Pond K. , Lorke A. , Ibbetson J. , Bressler-Hill V. , Maboudian R. , Weinberg W. H. , Gossard A. C. , Petroff P. M.
Published: July 2002

Terrace width distributions have been calculated from scanning tunneling microscopy (STM) images of molecular-beam epitaxy (MBE)-grown GaAs(001) surfaces misoriented by both 1° and 2° towards the (111)A direction. This analysis reveals a peak in the terrace width distribution at approximately 40–50 Å, regardless of the original miscut, with larger terraces forming in order to preserve the angle of vicinality. Growth of a tilted superlattice (TSL) improves the periodicity of the surface. A statistical analysis of the STM image of a 1° TSL capped with three monolayers of GaAs reveals a bell-shaped distribution of terrace widths with a peak at the average terrace width. These results suggest that MBE growth of vicinal GaAs(001) does not result in equalized steps but that the growth of a TSL does tend towards step equalization. The differences between these two growth regimes are discussed.
Field emission from an elliptical boss: Exact and approximate forms for area factors and currents
Authors: Jensen K. L. , Zaidman E. G.
Published: July 2002

Field emission from metallic or semiconductor tips, in comparison to planar surfaces, is complicated by current enhancement effects and changes in the image charge. It is shown that the approximations typically used for the calculation of the transmission coefficient, namely, a ‘‘linearized’’ Wentzel–Kramers–Brillouin approach and methods based upon the Fowler–Nordheim approach, are inappropriate for small spherical surfaces but adequate for elliptical surfaces. The derivation of the approximate approaches is given, as well as a simple analytical formula for the average emitting area, which may be derived based on the Fowler–Nordheim equation. By use of the elliptical approximation for the tip geometry, a simple scale factor is sufficient to deal with spherical and pointed tips.
Silicon vacuum microdiode with on-chip anode
Authors: Yoon Yeong J. , Lu Yicheng , Lalevic B. , Zeto Robert J.
Published: July 2002

A vacuum microdiode was fabricated with a silicon avalanche cathode and an on-chip microanode. The image reverse process followed by proper heat treatment was employed to form a photoresist sacrificial layer in shaping a microanode. The distance of ∼3 μm between cathode and anode was achieved by adjusting the number of depositions of photoresist. On the top of the sacrificial layer, a multilayer (Al/TiW/Al) structure was deposited, which provided the microanode with good conductivity and mechanical strength. The dimension of the microanode was 8 (or 18) μm in width and more than 30 μm in length. The I–V characteristics of this vertical-type microdiode demonstrated the enhancement of current emission due to a strong electric field at relatively low anode voltages.
Electron–electron scattering in microcolumns
Authors: Thomson M. G. R.
Published: July 2002

Field-emission electron-beam columns a few millimeters in length have been proposed as a route to gaining improved probe currents and probe sizes because of their reduced lens aberrations. The probe current and probe size in such columns will be strongly influenced by electron–electron interactions. These effects have been studied theoretically as functions of electron energy and column length to allow comparisons with instruments of conventional size. The scattering within the column has been analyzed using analytic approximations. The results show important differences in the lateral scattering effect which leads directly to broadening of the focused probe. The region close to the cathode has been treated using both Monte Carlo and analytic methods. The energy broadening from a field-emission electron gun will be similar in all cases for equal emission angular current density, and the contribution to the final probe will depend on the chromatic aberration coefficient of the focusing lens. We conclude that small, low energy columns will have improved properties as long as the physical size and lens aberration coefficients are reduced in proportion to the beam energy, and that for low energy scanning electron microscopes, reducing the overall size is very advantageous. The scattering effects are not uniformly distributed throughout the length of the column, and design changes to reduce the lateral scattering effect for given current are discussed.
Diffractive techniques for lithographic process monitoring and control
Authors: Sohail S. , Naqvi H. , Zaidi Saleem H. , Brueck Steven R. J. , McNeil John R.
Published: July 2002

Diffraction-based techniques have been shown to provide convenient, nondestructive, rapid metrology for lithography steps during semiconductor fabrication. Monitoring diffraction from latent images provides the capability to determine exposure tool focus to an absolute accuracy of 0.1 μm. Exposure dose and subsequently post-exposure bake have also been monitored using diffraction from latent images. Moiré alignment and overlay measurement techniques with nm-scale precision are demonstrated. Using 0.47-μm pitch gratings, a 1-nm translational sensitivity is demonstrated. A novel double-period moiré grating is used to provide both coarse (∼10 μm) and fine (∼1 μm) capture ranges for integration with existing stage positioning systems. A new diffraction-order interferometry technique for nm-precision remote overlay readout is demonstrated, with potential application to latent image structures immediately after exposure. We also present diffraction-based techniques to measure (critical dimensions) of ≥0.4-μm linewidth photoresist gratings. The results obtained are in excellent agreement with scanning electron microscope measurements.
Self-aligned dry-etching process for waveguide diode ring lasers
Authors: Liang James J. , Ballantyne Joseph M.
Published: July 2002

A dry-etching process that produces very smooth facets in the AlGaAs/GaAs material system is described. Chemically assisted ion beam etching (CAIBE) is used to fabricate the facets, with SiO2 as the etch-mask. Reactive ion etching (RIE) is used to transfer the resist pattern to the underlying SiO2 layer. RIE operating conditions, including gas type, power density, and etching pressure were characterized to achieve smooth SiO2 sidewalls. It is found that CF4 etching at low power density of 0.10 W/cm2 and low pressure of 1 mTorr produces very smooth SiO2 sidewalls. As a result, excellent etched facets are obtained by CAIBE, using SiO2 as the etch-mask. This dry-etching process is being used to fabricate waveguide diode ring lasers. A self-aligned etching process, which defines both the ridge and the facets for the ring lasers in the same lithography step, is also discussed.
Surface characterization of sputtered niobium films by scanning tunneling microscopy
Authors: Lacquaniti V. , Maggi S. , Monticone E. , Picotto G. B.
Published: July 2002

Scanning tunneling microscopy (STM) was used to analyze the surface topography of rf sputtered Nb films, 10–1000 nm thick. Surface crystalline sizes within 100 nm have been observed. Grain sizes deduced from STM have been compared to those evaluated from x-ray diffractometry. The effect of both deposition rate and substrate temperature on surface roughness has also been studied on 100 nm thick Nb samples. All the results show a behavior typical of thin films grown under low mobility conditions, where a columnar structure prevails.
Theory of scanning tunneling microscopy and spectroscopy on hydrogen-adsorbed Si(100) surface
Authors: Uchiyama Toshihiro , Tsukada Masaru
Published: July 2002

The hydrogen (H) termination of the 2×1 and 3×1 structure and the initial stage of H adsorption on the Si(100) surface are theoretically investigated. For this study, the electronic states induced by the H atoms are calculated in the first-principles local density functional method. The scanning tunneling microscopy (STM) images and the scanning tunneling spectroscopy (STS) spectra are also simulated. The results clarify what the STM depicts on the H-adsorbed Si(100) surfaces. On the termination, two ball-like spots each corresponding to the H atom form a beam shape. At the initial adsorption, the bright spot observed in the images is assigned to the remaining Si atom of the reacted dimers. However, the observed STS spectra of both the surfaces cannot be reproduced. The physical reasoning to amend this discrepancy in the spectra is discussed.
Measurement of the piezoelectricity of films with scanning tunneling microscopy
Authors: Winters R. , Reinermann M. , Enss C. , Weiss G. , Hunklinger S.
Published: July 2002

A scanning tunneling microscope (STM) is used to measure the piezoelectric constant of thin films including its sign with high lateral spatial resolution. Since a STM offers an extraordinarily high vertical resolution, even weak piezoeffects can be studied. Test measurements with an X-cut quartz in air at room temperature showed qualitatively correct behavior, but the measured value of the piezoelectric constant varied both temporally and spatially due to the nonideal characteristics of the tunneling contact. In order to circumvent this difficulty we used a novel compensation technique, in which the piezoelectric sample is mounted on an X-cut quartz. We present measurements of the piezoelectric constant of sputtered ZnO films which yielded two different values, one of them being considerably higher than the piezoelectric constant of bulk ZnO.
Ballistic electron emission microscopy of strained and relaxed In0.35Ga0.65As/AlAs interfaces
Authors: Ke Mao-long , Westwood D. I. , Wilks S. , Heghoyan S. , Kestle A. , Matthai C. C. , Richardson B. E. , Williams R. H.
Published: July 2002

We report here our investigations upon both strained and relaxed In0.35Ga0.65As/AlAs interfaces using the ballistic electron emission microscopy (BEEM) and current–voltage (I–V) techniques. Six samples, of different InGaAs thickness and doping density, were grown by molecular beam epitaxy and were designed to assess the importance of strain relaxation/dislocations in barrier formation. In the heavily dislocated situation (thicker InGaAs film) the obtained barrier most likely resulted from Fermi level pinning. However, this was obviously not the case for both the pseudomorphic and lightly dislocated situations (thinner InGaAs films). It was also noted that the measured barriers varied more widely over space in the lightly dislocated layer than that in the pseudomorphic case and that the simultaneously obtained topographic and BEEM images points to a better interface in the pseudomorphic layer than that in the partially relaxed situation.
Thermal stability of AlGaAs/GaAs single quantum well structures using photoreflectance
Authors: Hughes P. J. , Li E. H. , Weiss B. L.
Published: July 2002

The thermal stability of two AlGaAs/GaAs single quantum well structures was investigated using room-temperature photoreflectance. Rapid thermal annealing between 800 and 1000 °C for times up to 180 s showed spectral ‘‘blue’’ shifts for both the ground state and higher order interband transitions of the quantum well due to Al and Ga interdiffusion across the well/barrier interface resulting in a modification of the quantum well confinement profile. The sensitivity of these transition energies to Al–Ga interdiffusion depended on both the quantum well structure and annealing conditions. The results were correlated with a theoretical model, which was developed previously to determine the effects of interdiffusion on the subband structure of quantum well samples, to give characteristics interdiffusion lengths of less than 20 Å for these annealing conditions. These interdiffusion lengths corresponded to limited interdiffusion and was confirmed from polarization sensitivity measurements where the anisotropic polarization behavior of the quantum well was maintained for these annealing conditions. The analysis of these results agrees well with the model and gives Al/Ga interdiffusion coefficients of ∼2.9×10−17 and ∼9.2×10−17 cm2/s at 900 and 1000 °C, respectively.
Scanning probe anodization: Patterning of hydrogen-terminated silicon surfaces for the nanofabrication of gold structures by electroless plating
Authors: Sugimura Hiroyuki , Nakagiri Nobuyuki
Published: July 2002

We have developed a nanofabrication method that uses patterned anodic silicon oxide as a template for pattern transfer to a gold (Au) nanostructure. The oxide patterns were prepared on a hydrogen-terminated silicon (Si–H) surface by scanning probe anodization, that is, electrochemical nanolithography based on scanning probe microscopy. These anodic oxide patterns were transferred to Au patterns through area-selective electroless plating, in which Au deposition proceeds selectively on the unanodized Si–H area while the anodic oxide surface remains free of deposits. Due to low Au nucleation density on the Si–H surfaces, Au lines formed by the electroless plating were discontinuous when their linewidth narrowed to less than 50 nm. The nucleation density was increased by a chemical etching of the Si–H surface prior to plating. We have successfully fabricated a continuous Au line as narrow as ∼30 nm.
An electron-beam microcolumn with improved resolution, beam current, and stability
Authors: Kratschmer E. , Kim H. S. , Thomson M. G. R. , Lee K. Y. , Rishton S. A. , Yu M. L. , Chang T. H. P.
Published: July 2002

We have built and tested a 1 keV electron-beam microcolumn that focuses 1 nA of beam current into a 10 nm full width half-maximum beam diameter at a working distance of 1 mm. The electron source is a miniaturized Zr/O/W Schottky field emitter with 150 μA/sr angular emission current density operating at about 1800 K at a distance of only 100 μm from a silicon membrane extractor electrode. The actual microcolumn is 3.5 mm long assembled mainly from silicon membrane electrodes. Improved einzel lens design and fabrication allowed the operation of this beam focusing element in the accelerating mode. Spherical and chromatic aberrations were reduced by factors of about 2–3, respectively, as compared to the retarding lens mode. Excellent beam current stability with less than 1% variation over several hours has been observed.
Charge injection and extraction on organic dot structures by atomic force microscopy
Authors: Hieda Hiroyuki , Tanaka Kuniyoshi , Gemma Nobuhiro
Published: July 2002

We describe the manipulation of the charged state of nanoscale organic ‘‘dot’’ structures using the atomic force microscope. Electric charges were injected into single dots by contact electrification from an atomic force microscope tip to which voltage was applied. On measuring the charge distribution two-dimensionally, it was found that the injected charges were stably confined in the dot structures for an extended period. The number of injected charges could be controlled down to single elementary charge. Further, injected charges could be reextracted from the dots by using a tip with reduced applied voltage. However, complete extraction from highly charged dots was difficult, which suggests that some transfer of charge from dots to adjacent regions may occur.
Nanometer-scale modification of tribomechanical properties of Si(111):H surfaces performed and investigated by a conducting-probe scanning force microscope
Authors: Teuschler T. , Mahr K. , Miyazaki S. , Hundhausen M. , Ley L.
Published: July 2002

Hydrogen-terminated Si(111) surfaces were patterned on the nanometer scale by field-induced oxidation with a conducting-probe scanning force microscope. The same scanning force microscope tip was then used to measure the resulting sample topography and its local tribomechanical properties. The formation of oxide patterns with homogeneous height up to several nanometers is accompanied by a relative increase of the friction force of up to ∼30% over the oxide layers which scales linearly with oxide height. Force modulation microscopy in the resonance mode provides a material contrast between the oxide layer and the surrounding substrate.
Electron-beam induced etching of resist with water vapor as the etching medium
Authors: Kohlmann-von Platen K. T. , Bruenger W. H.
Published: July 2002

H2O vapor as the etching medium has been investigated for electron beam induced etching of an organic resist. The aim was the determination of the dependencies on the process parameters. The etch rate increases with decreasing beam energy and increasing H2O vapor flux (i.e., molecules per time and area). At 5 keV beam energy, the achieved etch rate is 55 nm/min. By lowering the beam energy to 1 keV (maximum of the secondary electron yield) and increasing the scan speed (approximately 1–5 MHz), a pronounced rise to the etch rate is expected.
High-resolution silicon patterning with self-assembled monolayer resists
Authors: Lercel M. J. , Whelan C. S. , Craighead H. G. , Seshadri K. , Allara D. L.
Published: July 2002

Single crystal and polycrystalline silicon films have been patterned and etched with a novel high-selectivity process using self-assembled monolayer resists of octadecylsiloxanes (ODS). The highest resolution patterning of sub-10 nm features has been demonstrated by scanning force microscopy imaging of ODS layers patterned with a focused electron beam. An all-dry UV/ozone developer has been used to remove residual carbon from the electron beam exposed regions to improve etch selectivity. The positive tone pattern transfer process consisted of a short buffered hydrofluoric acid wet etch to remove the silicon native oxide followed by a high-selectivity, low ion energy etch using Cl2 and BCl3 in an electron cyclotron resonance reactive ion etch. Features have been etched up to 90 nm deep into Si(100) wafers and minimum feature sizes obtained are ∼25 nm. Poly-Si films on SiO2 insulator layers have been similarly patterned and have been used in a combined process with photolithographic definition of microbridges to form narrow conducting channels in the poly-Si.
Attenuated phase shift mask materials for 248 and 193 nm lithography
Authors: Smith B. W. , Butt S. , Alam Z. , Kurinec S. , Lane R. L.
Published: July 2002

In order to push resolution toward diffraction limits for 248 and 193 nm lithography, it is likely that some combination of optical enhancement may be needed. The attenuated phase shift mask approach may prove to be one of the less complex techniques available. Four materials are presented which may meet optical and process requirements for use as attenuated phase shift mask films: a molybdenum silicon oxide composite, an aluminum/aluminum nitride cermet, an understoichiometric silicon nitride, and a tantalum silicon oxide composite. All of these materials are shown to be capable of 4%–15% transmission at 193 nm with thicknesses that produce a π phase shift. Evaluation of addition film properties including plasma reactive ion etch and long wavelength transmission helps in establishing materials which may be most production worthy.
Energy distributions of field emitted electrons from carbide tips and tungsten tips with diamondlike carbon coatings
Authors: Yu Ming L. , Kim Ho-Seob , Hussey Brian W. , Chang T. H. Philip , Mackie William A.
Published: July 2002

We have measured the energy distributions of electrons field emitted from tungsten carbide, HfC〈100〉, and ZrC〈100〉 tips, and tungsten field emitters with diamondlike carbon coatings. Multiple-peaked energy distributions were observed from instability induced emission sites on the carbide tips. Energy distributions of electrons field emitted from the diamondlike carbon coated tungsten tips were broader than those from metal tips. They also showed a shift towards lower energies with increases in the emission current.
Voltage contrast in submicron integrated circuits by scanning force microscopy
Authors: Böhm Christoph , Sprengepiel Jörg , Otterbeck Markus , Kubalek Erich
Published: July 2002

A scanning force microscope can be used to measure a device’s internal electrical potential with high spatial and temporal resolution. We present experimental results taken with a scanning force tester constructed in our lab that offers nanometer spatial resolution and gigahertz measurement bandwidth. The results are comparable to network analyzer results.
Reactive ion etching of GaSb and GaAlSb using SiCl4
Authors: Ou S. S.
Published: July 2002

Reactive ion etching of GaSb and GaAlSb using pure SiCl4 was investigated. Etching rate and etching profiles were characterized as functions of working pressure, chamber background pressure, flow rate, and power density. The etching rate and profile of metal organic chemical vapor deposited-grown GaSb and GaAlSb thin films are strongly dependent on background pressure and applied power. These interesting characteristics can be applied to control selective or nonselective etchings for device fabrication. Etching profiles exhibited a high degree of anisotropy and smooth surface morphologies.
Optical characterization of low temperature grown GaAs by transmission measurements above the band gap
Authors: Streb D. , Ruff M. , Dankowski S. U. , Kiesel P. , Kneissl M. , Malzer S. , Keil U. D. , Döhler G. H.
Published: July 2002

We report on transmission measurements on low temperature grown GaAs and standard GaAs for a spectral range 0.8–2.8 eV. We measured a drastic reduction of absorption due to annealing over the whole spectral range. The absorption changes depend on the annealing temperature and occur in two individual phases. Additional transmission measurements on samples without antireflection coating confirm our earlier results of an annealing induced refractive index change of Δn≊0.2.
Structure of the SiNx/GaAs (110) interface modified with ultrathin Si and sulfur passivation
Authors: Huang L. J. , Lau W. M. , Tang H. T. , Lennard W. N. , Mitchell I. V. , Landheer D. , Baribeau J.-M. , Ingrey S.
Published: July 2002

The SiNx/GaAs (110) interface structure of the metal-insulator-semiconductor (MIS) capacitors modified with ultrathin Si or Si/Ge (5 to 15 Å) heterolayers and sulfur passivation were studied by capacitance-voltage (CV) measurements, high resolution medium energy ion scattering and extended x-ray absorption fine structure with synchrotron radiation. The results showed that Si/S multilayer passivation can improve the interface properties of the MIS capacitors made on n-type GaAs (110). The element depth profiling in a subnanometer scale and the atomic structure measurements showed that a Si or Si/Ge heterolayer on sulfur passivated GaAs (110) can substantially limit Ga(As) precipitation at the interface but cannot completely suppress the incorporation of Ga(As) into the Si heterolayer. These results can be used to interpret the observed CV characteristics of the capacitors and to understand the limitation of the passivation approach.
Evidence for the occupation of DX centers in In0.29Al0.71As
Authors: Young A. P. , Wieder H. H.
Published: July 2002

We present the first results on In0.29Al0.71As which conclusively show a large number of traps that are not in equilibrium with the conduction band at low temperatures, the signature of a DX centerlike defect. From low-temperature gated resistivity, Hall and Shubnikov–de Haas measurements of relaxed, In0.29Al0.71As/In0.3Ga0.7As modulation doped heterostructures, we find a significant negative shift in the threshold voltage, Vg(ns→0), as the cooling bias is shifted to more negative values. Simultaneously, we observe a decrease in the mobility measured at the two-dimensional electron gas as the cooling bias is decreased, an indication of the ‘‘negative U’’ behavior of DX centers. Finally, we observe Fermi level pinning which we attribute to the occupation of a DX center level. From simulation of the heterostructure at large positive gate biases, and the change in the threshold voltage, we are able calculate the donor ionization energy of this trap to be 320 meV below the InxAl1−xAs conduction-band edge, over twice the depth of the DX center in AlxGa1−xAs.