bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of fluorine/carbon atomic ratio on superhydrophobic behavior of carbon nanofiber arrays
Authors: Hsieh Chien-Te , Chen Jin-Ming , Huang Yu-Hao , Kuo Rong-Rong , Li Chung-Tien , Shih Han-Chang , Lin Ta-Sen , Wu Chu-Fu
Published: February 2006

The present study has demonstrated the influence of the fluorine/carbon (F∕C) ratio on superhydrophobicity of carbon nanofibers (CNFs) prepared by a template-assisted synthesis. An approach to coat fluorocarbon on the surface of nanofibers is introduced via a thermal chemical vapor method, using perfluorohexane as the precursor. The resulting CNFs exhibit good water-repellent behavior owing to hydrophobic surface groups including −CF2 and −CF3 groups. Experiments indicate that the F∕C atomic ratio is the key factor for obtaining the hydrophobic properties. The surface contact angle increases with increasing F∕C ratio. Contact angles of the fluorinated CNFs as high as 161 ° can be achieved. The interfacial phenomenon between the water droplet and the solid surface is also analyzed by the Cassie-Baxter models.
Fabrication of single electron transistors with molecular tunnel barriers using ac dielectrophoresis technique
Authors: Hong S. H. , Kim H. K. , Cho K. H. , Hwang S. W. , Hwang J. S. , Ahn D.
Published: February 2006

We demonstrate the fabrication and characterization of single electron transistors composed of Au nanoparticles and insulating molecular tunnel barriers. We fabricated these devices by forming a 1,8-octanedithiol self-assembled monolayer on Au nanogap electrode pairs and by bridging them with colloidal Au nanoparticles using ac dielectrophoresis. We observed the typical characteristics of these single electron transistors at the temperature from 4.2 to 300 K. The measured data were consistent with the orthodox theory of Coulomb blockade.
Gate-controlled ZnO nanowires for field-emission device application
Authors: Li Seu Yi , Lee Chia Ying , Lin Pang , Tseng Tseung Yuen
Published: February 2006

Gate-controlled field-emission devices have great promise for a number of applications such as bright electron source or flat display array. The gate-controlled ZnO nanowire (NW) field-emission device was fabricated using lift-off fabrication process to synthesize side-gate control in the present investigation. This device effectively controls the turn-on electron beams and switches the drain current (Id) under a threshold gate voltage (VT) of ∼35V. In the meantime, the current density of the device is ∼1mA∕cm2 that is similar to carbon nanotube (CNT) field-emission level with a potential for the design of field-emission display (FED) devices. Furthermore, when the gate voltage (Vg) is equal to 0V, the turn-on electric field (Eto) for ZnO NWs is ∼0.8V∕μm and the effective-field-enhancement factor β is ∼7000. As Vg is increased to 10, 20, 30, and 40V, the Eto lowers to the range of∼0.8–0.6V∕μm and the β value increases to ∼7600–17800. The continuous increases in Vg lowers the turn-on electric field because the local electric field (Elocal) generated induces an extra force that enhances electron emission from the ZnO NWs. Besides, the transconductance (gm) value can approach 0.388mS while the Vg is increased to 44.5V. The devices have well-controlled behavior and exhibit better Fowler-Nordheim characteristic in comparison with classic CNT field-emission devices. The gated ZnO NW array has a good opportunity to be applied to FED devices and be integrated to the semiconductor industry in the future.
Structural and electrical characterizations of ultrathin HfO2 gate dielectrics treated by nitrogen-plasma atmosphere
Authors: Seong Nak-Jin , Lee Won-Jae , Yoon Soon-Gil
Published: February 2006

Ultrathin HfO2 gate dielectrics with 3.00 and 2.60nm thicknesses were prepared at 300°C by plasma-enhanced metal-organic chemical-vapor deposition. These HfO2 films were treated by N2 plasma at 300°C, and exhibit not only an excellent smooth surface morphology but also higher crystallization temperature and improved electrical properties. The N2-plasma treatment did not influence the interface charge density of the films. The 2.6nm HfO2 treated by N2 plasma showed a leakage current density of 3×10−3A∕cm2 at −1.5V, equivalent oxide thickness of 1.24nm, and flatband voltage of 2mV. We find that N2-plasma treatment in Hf-based ultrathin gate dielectrics can improve the electrical properties, as well as thermal stability.
Prediction of clamping pressure in a Johnsen-Rahbek-type electrostatic chuck based on circuit simulation
Authors: Kanno S. , Kato K. , Yoshioka K. , Nishio R. , Tsubone T.
Published: February 2006

We propose nonlinear resistance models for bulk resistance of a dielectric layer and contact resistance between a wafer and the dielectric layer used in an equivalent circuit model to predict the clamping or residual clamping pressure in Johnsen-Rahbek-type [A. Johnsen and K. Rahbek, J. Inst. Electr. Eng. 61, 713 (1923)] electrostatic chucks. It is found that the bulk resistance is presumed by a model on the basis of the space-charge-limited current model in insulator. It is also found that the contact resistance is expressed by a superposition of Ohmic resistance in the low-field strength region and a resistance on the basis of field emissions in the high-field strength region. In addition, the gap capacitance is determined based on the probability function of asperity height obtained from a surface roughness profile. The clamping pressure is simulated by calculating a charge stored in the gap, combined with the probability function with circuit simulation. Consequently, the calculation agrees with the measurement within 31% difference. It is also found that the calculation can reproduce the dependency of bulk resistance on the clamping pressure and the time response in residual clamping pressure.
Growth of GaAs on vicinal Ge surface using low-temperature migration-enhanced epitaxy
Authors: Tanoto H. , Yoon S. F. , Loke W. K. , Fitzgerald E. A. , Dohrman C. , Narayanan B. , Doan M. T. , Tung C. H.
Published: February 2006

In this article, we demonstrate the influence of substrate temperature during migration-enhanced epitaxy (MEE) process of GaAs epitaxy on a vicinal surface of Ge (100), 6° offcut towards the (111) plane. It was found that the offcut surface is not the sufficient condition for suppressing the formation of antiphase domains at the GaAs∕Ge interface. Rather, it has to be complemented by low substrate temperature during the MEE process. GaAs grown at 250°C, the lowest temperature among all the samples, exhibits the smoothest surface and best structural and optical qualities, as characterized by atomic force microscopy, cross-sectional transmission electron microscopy, and low-temperature photoluminescence, respectively. At this substrate temperature, As dimers are adsorbed onto the substrate surface more readily with negligible reevaporation, ensuring complete coverage on the Ge surface with double-atomic steps. Complete coverage by As proved to be crucial in preventing the occurrence of inversion boundaries, or at the very least ensure fewer As vacancies that may act as defect centers. Furthermore, low substrate temperature shortens the migration distance of Ga adatoms, minimizing their adsorption into the kinks and step edges, resulting in two-dimensional growth mode instead of step-flow growth mode.
Electrical transport properties of GaAs structures with a pair of Be and donor impurity delta-doped layers
Authors: Idutsu Y. , Shimogishi F. , Noh J. P. , Otsuka N.
Published: February 2006

Electrical transport properties of GaAs structures with a pair of acceptor and donor impurity delta-doped layers are studied. Beryllium is used as an acceptor impurity, while Se or Si is used as a donor impurity. The Be and donor impurity delta-doped layers are separated from each other with a 1-nm-thick spacer layer, and Be and donor impurity concentrations are varied among samples. In the samples with the p-type conduction where the Be doping concentration is higher than the donor impurity doping concentration, a transition from thermally activated conduction to metallic conduction occurs at room temperature with the resistivity at the transition being close to the quantum unit of resistance 12h∕e2. In the samples with the n-type conduction where the donor impurity concentration is higher than the Be doping concentration, no such transition is observed. The different transport properties between two groups of samples indicate that heavy holes in the Be delta-doped layer behave as a quasi-two-dimensional system at room temperature, while electrons in the donor impurity delta-doped layer can no longer be considered as a quasi-two-dimensional system at high temperatures due to significant spreading of their wave functions in the direction normal to the delta-doped layer. The temperature dependence of resistivity of p-type pair delta-doped samples with high Hall mobility exhibits a broad peak in the low-temperature range.
Evolution of sidewall roughness during reactive-ion etching of polymer waveguides
Authors: Pani S. K. , Wong C. C. , Sudharsanam K. , Premachandran C. S. , Iyer M. K.
Published: February 2006

Sidewall roughening of fluorinated polyether waveguides fabricated by reactive-ion etching in pure oxygen plasma was investigated. Variation of sidewall roughness (SWR) was observed by scanning electron microscopy, and was measured and confirmed by atomic force microscopy. Lower-pressure SWR variation along the vertical depth is due to the combination of both the shadowing and the first-order reemission effect, and higher-pressure SWR variation is postulated to be due to a continuous shadowing effect. It was discovered that the autocorrelation length (ACL) calculated from the experiment varies in a similar manner as the SWR does along the depth of the waveguides. This variation of ACL suggests that the surface-roughness evolution at the sidewalls during plasma etching possesses the same etch dynamics as that of planar thin-film etching. With the increase of pressure, the average value of roughness exponent increases.
Ion-implanted edge termination for GaN Schottky diode rectifiers
Authors: Mohammad S. Noor , Eddy Charles R. , Kub Francis
Published: February 2006

Two-dimensional theoretical simulations have been carried out to investigate the effect of an ion-implanted high-resistivity guard ring structure on the performance of n-GaN Schottky diode rectifiers for high-power applications. The guard ring, made of p-type implantation, exhibited a Gaussian profile. Calculated forward current-voltage characteristics, reverse breakdown voltage, and leakage current as functions of the peak implant doping and of the characteristic length of the implanted doping in the lateral x direction give a good estimate of the influence of guard ring on the device performance. A judiciously formed guard ring can yield a room-temperature reverse breakdown voltage as high as 3000V and a reverse leakage current as low as ∼10−8A. However, the reverse leakage current, for example, for an applied bias of −50V, increases to ∼10−5A at 400K. One crucial feature of the present study is the investigation of the optimal distance between the metal edge and the edge of the implanted region, which tends to significantly dictate the quality of the diode rectifiers.
Implementation of flash technology for ultra shallow junction formation: Challenges in process integration
Authors: Foggiato J. , Yoo W. S.
Published: February 2006

Several methods for annealing to form ultra shallow junctions are being developed encompassing short bursts of optical energy derived from the discharge of Xe-arc lamps. The flash technology heats the wafer surface to very high temperatures for dopant activation, yet minimizes dopant diffusion which is needed for sub 65nm technologies. A number of challenges remain in implementing the technology for volume fabrication, particularly the control of defect formation and the pattern sensitivity on the wafer surface. The plausible regions of flash energy combined with the assist temperature have been investigated to achieve good activation, yet maintain a low defect level. This has been verified through leakage characteristics of the source/drain extensions. Other aspects of implementation were investigated to formulate a processing sequence which achieves suitable device characteristics. A process integration methodology is described with corresponding device data, electrical and physical, to note improvements that have been made.
Modeling of B diffusion in the presence of Ge
Authors: Radic Ljubo , Saavedra Antonio F. , Jones Kevin S. , Law Mark E.
Published: February 2006

In order to investigate the B and Ge interaction in silicon, an implant/anneal experiment is performed. The initial Si pre-amorphization step defines the amorphous layer depth and the end-of-range point defect distributions for all samples. The following Ge implant provides a low Ge content, thus minimizing the strain and the band gap narrowing effects on the diffusion of the subsequent B implant. The control sample received Si and B implants. The annealed profiles of the control samples show B profile broadening consistent with the transient enhanced diffusion. The B tail diffusion in the Ge implanted samples is almost identical to that of the control samples, indicating that Ge does not act as a trap for the BI pair. The GeB complex, suggested in literature, was used to explain the higher profile peak magnitude in Ge implanted samples.
Co-implantation with conventional spike anneal solutions for 45nm n-type metal-oxide-semiconductor ultra-shallow junction formation
Authors: Collart E. J. H. , Felch S. B. , Pawlak B. J. , Absil P. P. , Severi S. , Janssens T. , Vandervorst W.
Published: February 2006

Co-implantation schemes for sub-65nm n-type extension formation have been explored. These included phosphorous (P) and arsenic (As) implants into crystalline Si as well as combinations using higher energy silicon pre-amorphization implant (PAI) steps together with low energy carbon (C) implantation. Dopant energies were varied between 500eV and 1keV, with C dose of1×1015cm−2 and P and As doses of 7×1014cm−2. The anneal step was a fast ramp-up and ramp-down spike at 1050°C. Comparisons with dopant-only implants or with PAI and dopant only showed these two schemes to give deeper, more gradual and less well activated junctions than when combined with C. The best result was obtained using a 25keV Si PAI, 6keV C and 1keV P, resulting in a junction depth of 20.5nm at 1×1019cm−3, and Rs=318Ω∕◻ and a 3nm∕dec trailing slope.
Nonlinear optical polymer patterned by nanoimprint lithography as a photonic crystal waveguide structure
Authors: Okinaka Motoki , Inoue Shin-ichiro , Tsukagoshi Kazuhito , Aoyagi Yoshinobu
Published: February 2006

A photonic crystal (PC) waveguide structure has been imprinted onto a nonlinear optical (NLO) polymer using thermal nanoimprint lithography (NIL). The imprint characteristics of Disperse Red 1 doped poly(methylmethacrylate) as the NLO polymer are evaluated by atomic force microscope. A waveguide structure with a uniform height of 650nm is obtained at an imprint temperature of 120°C. A peeling problem at the interfaces between constructing layers is solved by preparation of an appropriate substrate structure. Finally, polarized reflectivity measurement was performed for the imprinted PC waveguide structure. Several sharp dips corresponding to the formation of photonic band dispersion are observed. It was demonstrated that NIL is a direct path to the precise patterning of PC waveguide structures.
Resist effects at small pitches
Authors: Van Steenwinckel David , Lammers Jeroen H. , Koehler Thomas , Brainard Robert L. , Trefonas Peter
Published: February 2006

The ITRS roadmap and Moore’s law are driving us to print ever smaller features and ever tighter pitches. For these ultrasmall features and pitches, resist effects are expected to play a dominant role in limiting the overall lithographic process capability. To study the impact of resist parameters such as acid diffusion and quencher level on the lithographic performance, we have designed and formulated a matrix of 14 extreme ultraviolet (EUV) resists. In this article, we discuss results that we have obtained from EUV exposures of those resists on the 0.3 numerical aperture EUV Micro Exposure Tool at the Advanced Light Source at Lawrence Berkeley National Laboratories. In addition to exposure latitude and line edge roughness, acid diffusion lengths were characterized using a modification of the extended Nijboer–Zernike theory for each photoresist. A simple theory for the drop in resist contrast as function of the diffusion length is tested and leads to a verified correlation between exposure latitude and diffusion length. This theory gives guidelines to predict what acid diffusion lengths should be used for a certain lithography node. Line edge roughness analysis showed that shot noise statistics are present, and also points out that acid diffusion effects come into play. From the experimentally observed tendencies in this unique matrix of EUV photoresists, fundamental understanding was gained about prominent resist effects that will determine the lithographic performance of resist processes in future lithography nodes.
Room-temperature nanocontact printing using soft template
Authors: Nakamatsu Ken-ichiro , Tone Katsuhiko , Namatsu Hideo , Matsui Shinji
Published: February 2006

Direct pattern transfer technology by room-temperature nanocontact printing using hydrogen silsesquioxane (HSQ) and Ag paste, which takes advantage of adhesion properties of these transfer materials, has been developed. The use of poly(ethylene) laminated on poly(methylmethacrylate) sheet has been proposed as the soft template for the contact printing. The HSQ transferred pattern with 35nm linewidth was obtained onto Si surface. In addition, 1μm linewidth, and 2μm pitch Ag patterns were successfully transferred from the soft template to the SiO2∕Si substrate. The transferred Ag wiring with 1μm linewidth showed good conduction characteristic, resistivity to be 1.7×10−7Ωm.
Resist reflow process simulation study for contact hole pattern
Authors: Kim Sang-Kon
Published: February 2006

In the semiconductor lithography process, the thermal flow process after development resolves the patterning of sub-100-nm contact holes and the cost problem of resolution-enhancement technology. In this study, resist flowing behavior and contact hole shrinkage are described by using the thermal reflow length of the boundary-movement method and the analysis of image process. The viscosity variable affects the shrinkage of critical dimensions. This variable is extracted from the experimental data by using a proposed equation. These results agree well with the experimental results in both contact hole size and the vertical wall of profile according to the baking temperature and time. Although the most effective process of the 193-nm chemically amplified resist is the postexposure bake process for critical dimension, the parameter of the development process—the inhibition reaction order of the enhanced Mack model—is shown as the most controllable parameter for critical dimension in the thermal reflow process.
Scanning tunneling microscopy detection of individual dopant atoms on wet-prepared Si(111):H surfaces
Authors: Nishizawa M. , Bolotov L. , Tada T. , Kanayama T.
Published: February 2006

We have performed scanning tunneling microscopy (STM) observation of individual acceptor and donor atoms on hydrogen-terminated Si(111)-1×1 surfaces prepared by wet etching in a NH4F aqueous solution. Separate measurements of p- and n-type substrates showed that acceptors appear as protrusions in filled-state images and as depressions in empty-state images, while for donors the topography is reversed in both filled- and empty-state images. The same relation between the bias polarity and the dopant appearance is preserved for codoped substrates. These results demonstrate that the STM on the Si(111):H surface can detect acceptors and donors distinguishably, enabling us to measure dopant profiles across codoped areas such as p-n junctions.
P implantation doping of Ge: Diffusion, activation, and recrystallization
Authors: Satta A. , Janssens T. , Clarysse T. , Simoen E. , Meuris M. , Benedetti A. , Hoflijk I. , De Jaeger B. , Demeurisse C. , Vandervorst W.
Published: February 2006

We have studied doping profiles, activation levels, and defect annealing of P introduced in Ge by ion implantation at different doses and energy, and annealed under various conditions by rapid thermal annealing. Common to all implant energies, ion-implanted P in Ge exhibits a “box profile” at high implant doses, when a sufficiently high thermal budget is applied—similarly to the concentration-dependent diffusion of P introduced in Ge from a high-concentration solid source. Upon proper annealing conditions, the active P concentration is limited to (5–6)×1019at.∕cm3, implying a 50% activation level of the total retained atoms for high-dose implants and 100% for the low-dose implants. A low thermal budget is sufficient to fully regrow the amorphous layer formed by high-dose P implantations, without evidence of residual defects in the regrown germanium layer and at the end of range of the P implant.
Effect of stress on the evolution of mask-edge defects in ion-implanted silicon
Authors: Olson C. R. , Kuryliw E. , Jones B. E. , Jones K. S.
Published: February 2006

In an effort to extend the scaling of advanced complementary metal-oxide semiconductor devices, strain has been incorporated to enhance carrier mobility. In this study, the effect of strain on the solid-phase epitaxial regrowth process of patterned wafers was explored. Implants of 1×1015∕cm2 Si+ with an energy of 40keV were introduced into these patterned regions forming a continuous amorphous layer. After implantation, the oxide and nitride masks were removed and the wafers stressed uniaxially between 0 and 250MPa. The wafers were subsequently annealed under stress to crystallize the amorphous layer, which was monitored using transmission electron microscopy. It was found that without stress, defects formed at the mask edge where the vertical and lateral epitaxial regrowth fronts meet. These defects were threading dislocations which form at the amorphous-crystalline interface and propagate to the surface. Tensile stress levels of as little as 50MPa were found to begin to suppress the formation of mask-edge defects by altering the shape of the corner of the regrowing amorphous layer at the mask edge. Tensile stress appears to retard the lateral recrystallization velocity, creating the obtuse corner geometry necessary to prevent the occurrence of a pinch point at the corner and thereby suppressing defect formation. The evidence suggests that the half-loop threading dislocation nucleates at the corner. The role of varying the stress on the formation of mask-edge defects will be discussed.
Electron-beam focusing in 1:1 electron projection lithography system
Authors: Sidorkin Vadim , Moon Chang Wook , Mostafa Bourim El , Lee Seung Woon , Yoo In Keyong
Published: February 2006

Factors influencing the transferred image resolution in 1:1 electron projection lithography system are considered. The influence of Coulomb interaction between electrons, gradient of magnetic field, and angle between focusing electric and magnetic fields on the electron-beam focusing is estimated. In the presence of a magnetic-field gradient in the focusing system, the radius of an electron’s orbit is changed with a change of value of magnetic field B. As a result, after completing a whole turn, the center of electron’s orbit moves in the direction perpendicular to B and the magnetic-field gradient, which results in distortion of the transferred image. Coulomb interaction between electrons during their flight from the emitter toward the e-beam resist-coated wafer also results in diffusion of the transferred image and may be considered a crucial parameter that limits the high-resolution capability in the case of high emission currents. The presence of the angle between the direction perpendicular to the wafer and emitter planes and the magnet’s field direction results in an overall displacement of the transferred image and a variation of cyclotron orbit radius that depends on the distance between the emitter and wafer.
Doping integrity diagnostics of planar transistor channel structures by scanning nonlinear dielectric microscopy
Authors: Matsukawa Takashi , Masahara Meishoku , Tanoue Hisao , Kanemaru Seigo , Suzuki Eiichi
Published: February 2006

The integrity of doping in transistor structures was diagnosed using scanning nonlinear dielectric microscopy (SNDM). Nonlinear capacitance profiling and pinpoint capacitance-voltage analysis were done through SNDM, and the results clearly discriminated between a depletion layer and a tailing of carrier distribution due to outdiffusion of dopants in an n+∕p junction. This analysis was applied to n+∕p∕n+ and p+∕n∕p+ transistor channel structures formed with different process parameters. An increase in the n+ activation temperature from 800to950°C caused a narrowing of the p-type region in the n+∕p∕n+ structure. A decrease in the substrate doping concentration from 2×1018to2×1017cm−3 caused a depletion of the entire channel when the gate length was less than 200nm. The influence of channel depletion was proven to be more severe in p+∕n∕p+ transistor channel structures because boron had higher diffusivity than arsenic.
Dependence of local electronic structure in p-type GaN on crystal polarity and presence of inversion domain boundaries
Authors: Zhou X. , Yu E. T. , Green D. S. , Speck J. S.
Published: February 2006

Scanning probe techniques including scanning capacitance microscopy, scanning capacitance spectroscopy, scanning Kelvin probe force microscopy, and atomic force microscopy have been used to assess structure and local electronic properties of Ga-face and N-face p-type GaN and of inversion domain boundaries in p-type GaN. Epitaxial layers of p-type GaN were grown by molecular-beam epitaxy, and by adjustment of the Ga:N flux ratio samples containing both Ga-face and N-face material were obtained. Under identical growth conditions, net incorporation of electrically active Mg acceptors was found to be more efficient for material with Ga-face polarity. Only a very small dependence of surface potential on polarity was observed, in contrast to results reported for n-type GaN, in which a substantial dependence of Schottky barrier height on polarity has been found. In addition, elevated net concentrations of ionized Mg acceptors were observed in Ga-face regions in the immediate vicinity of some, but not all, inversion domain boundaries, consistent with theoretical suggestions that incorporation of high concentrations of Mg within an inversion domain boundary can lead to increased concentrations of Mg acceptors near the inversion domain boundary.
Resist-based measurement of the contrast transfer function in a 0.3 numerical aperture extreme ultraviolet microfield optic
Authors: Cain Jason P. , Naulleau Patrick , Spanos Costas J.
Published: February 2006

In order to meet the high-resolution printing potential of extreme ultraviolet (EUV) lithography, the projection optics must be of very high quality. The contrast transfer function (CTF), a measure of the aerial-image contrast as a function of pitch, describes one key aspect of projection optic quality. In order to support research into EUV lithography, a static microfield exposure tool (MET) based on a 0.3 numerical aperture optic and operating at a wavelength of 13.5nm has been developed at the Advanced Light Source, a synchrotron facility at the Lawrence Berkeley National Laboratory. This work presents the results of resist-based measurements of the CTF for the MET optic. Although the resist is not an ideal aerial-image detector due to its nonlinear response, it is still possible to study some key characteristics of the optics using such methods. These measurements are based on line/space patterns printed in several different EUV photoresists. The experimental CTF results are compared with the CTF from aerial-image simulations including the aberrations measured in the projection optic using interferometric and lithographic techniques. The measured CTF values are found to be significantly lower than predicted from the aerial-image simulations. CTF measurements are presented for both bright-field and dark-field mask patterns in order to investigate the effect of flare. Finally, the orientation dependence of the CTF is studied in order to evaluate the effect of nonrotationally symmetric lens aberrations. Neither flare nor nonrotationally symmetric aberrations were found to have a significant effect on the measured CTF. Photoresist resolution is believed to be the limiting factor in the observed contrast transfer function. These measurements, taken as a whole, provide valuable information about the imaging performance of the MET optic and aid in interpreting the results of other experiments performed using the MET and similar systems.
Change in electrical resistance caused by stress-induced migration
Authors: Aoyagi Minoru
Published: February 2006

Changes in the electrical resistance of aluminum and copper interconnections caused by stress-induced migration were studied using simple numerical simulations. When residual thermal stress in an interconnection is not sufficiently relaxed, the electrical resistance increases with storage time; subsequently, the interconnection disconnects suddenly after a set period. In this case, it is difficult to determine the lifetime of an interconnection by measuring the electrical resistance in advance because of this abrupt increase in resistance. The lifetime of copper interconnections is longer than that of aluminum interconnections. Simulation results for aluminum interconnections agree with high-temperature storage tests.
Photomask plasma etching: A review
Authors: Wu Banqiu
Published: February 2006

Photomask plasma etching was thoroughly reviewed over wide topics including history, equipment, etchant, absorbers, phase shifters, thermodynamics, and kinetics. Plasma etch obtained industrial applications for photomask fabrication in the 1990s and presently is a critical fabrication step for the “enabling” photomask industry. Among all types of photomasks (binary, embedded attenuated phase-shift mask, and alternating aperture phase-shift mask), chromium (Cr) containing material etching has been the basis and fundamental for all photomask etches. The main technological challenges for Cr etch occur on (isolated) dark features of a high load photomask due to the etch critical dimension (CD) bias dependence on the local loading. It determines the CD features on the Cr layer, phase shifter MoSi layer, and fused silica (quartz) layer. The CD deviation on pattern layers from the nominal value has been a challenge, especially for the Cr state-of-the-art 65nm node photomasks even though data sizing exists. Inductively coupled plasma plus bias power using radio frequency wavelength is the dominant configuration of the photomask plasma etcher, with improved loading and CD mean-to-target potential. Thermodynamic applications (Gibbs energy minimization method) on photomask plasma etch provide a quick, easy, and low cost method to estimate the plasma etch feasibility and defect reduction at different plasma gas input conditions. Empirical relationships between operational parameters and etch properties significantly improve the only design of experiment procedure for etch process optimization.
Near-surface secondary-ion-mass-spectrometry analyses of plasma-based B ion implants in Si
Authors: Buyuklimanli T. H. , Magee C. W. , Marino J. W. , Walther S. R.
Published: February 2006

Numerous experimental studies for near-surface analyses of B in Si have shown that the B distribution within the top few nanometers is inaccurately characterized by secondary-ion-mass-spectrometry (SIMS) depth profiling with O2 flooding or normal-incidence O2 bombardment. Furthermore, the presence of surface oxide adversely affects the Xj determination as well as the B profile shape when SIMS analyses are conducted while fully oxidizing the analytical area. Many comparisons of SIMS analyses with techniques such as elastic recoil detection, nuclear reaction analysis, and high-resolution Rutherford backscattering spectrometry, which are known to provide an accurate profile shape near the surface, have shown that SIMS analyses without fully oxidizing the analytical area agree well with these high-accuracy techniques at sufficiently high concentrations. The ability to measure both the B profile and an oxide marker with this SIMS technique also allows accurate positioning of the B profile with respect to the SiO2∕Si interface. This SIMS analysis protocol has been used to study the differences in near-surface dopant distribution for plasma-based implants (plasma doping). This study specifically focuses on the ion energy distribution behavior of BF3 and B2H6 implants, where the effects of the implant species chemistry were of interest, as well as studying the differences of the applied electric field.
Active dopant characterization methodology for germanium
Authors: Clarysse T. , Eyben P. , Janssens T. , Hoflijk I. , Vanhaeren D. , Satta A. , Meuris M. , Vandervorst W. , Bogdanowicz J. , Raskin G.
Published: February 2006

In order to reach the ITRS goals for future complementary metal-oxide semiconductor technologies there is a growing interest in using germanium as an alternative substrate material in view of its higher mobility. Different species and thermal budgets are presently being investigated in order to determine the most likely candidates for the required junction formation. A key issue is the accurate determination of the achievable electrical activation, i.e., the reliable measurement of the sheet resistance and electrical depth profile. In order to be applicable to Ge-based junctions, standard techniques such as the spreading resistance probe and scanning spreading resistance microscopy (SSRM) need to be reevaluated in terms of their performance and operational conditions. First, the significantly different behavior of germanium calibration curves (versus silicon) will be discussed. Next, the shape and characteristics of the probe imprints (Ge is softer than Si) and the differences in raw data behavior will be covered, such as the presence of a junction cusp for n+-p, but not for p+-n diodes. A preliminary germanium contact model will be presented, supporting all of the present experimental data (including SSRM current-voltage curves) based on the impact of surface states. Finally, the accuracy of the quantified resistivity and carrier depth profiles using Laplace-based modeling will be evaluated in comparison with alternative low penetration sheet resistance measurements, such as variable probe spacing, and secondary-ion-mass spectroscopy dopant profiles in the case of 100% activation.
Physical and electrical properties of Ta–N, Mo–N, and W–N electrodes on HfO2 high-k gate dielectric
Authors: Lu Jiang , Kuo Yue , Chatterjee Somenath , Tewg Jun-Yen
Published: February 2006

The influence of various types of metal nitride gate electrodes, i.e., tantalum nitride, molybdenum nitride, and tungsten nitride, on electrical characteristics of metal-oxide-semiconductor capacitors with hafnium oxide as the gate dielectric material has been studied. The result shows that both the physical and electrical properties of the high-k gate stack are influenced by the gate electrode materials and the post-metal-annealing temperature. Both the physical thickness and equivalent oxide thickness of the gate stack increased after the high-temperature N2 annealing step. The leakage current density decreased with the increase of the annealing temperature from 600to800°C. The work functions of these metal nitride electrodes decreased with the annealing temperature due to the variance of microstructure and chemical composition, as indicated by x-ray diffraction and second-ion-mass spectroscopy data. These metal nitride electrodes are suitable for n-channel metal-oxide-semiconductor device applications after 800°C N2 annealing because their work functions are between 4.05 and 4.25eV. The interface state density and oxide trap density of the high-k gate stack were also reduced by the high-temperature N2 annealing step.
Optical characterization of ZnMnO-based dilute magnetic semiconductor structures
Authors: Buyanova I. A. , Chen W. M. , Ivill M. P. , Pate R. , Norton D. P. , Pearton S. J. , Dong J. W. , Osinsky A. , Hertog B. , Dabiran A. M. , Chow P. P.
Published: February 2006

n -type ZnMnO spin injection layers were grown by pulsed laser deposition on top ofn-ZnMgO∕ZnO∕p-AlGaN∕p-GaN hybrid spin light-emitting diode (LED) structures synthesized by molecular-beam epitaxy. Both the ZnMnO∕ZnMgO∕ZnO∕AlGaN∕GaN structures and control ZnMnO samples show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5T, respectively. This indicates difficulties in generating spin polarization by optical spin orientation or possible efficient spin losses. The results are similar to those found earlier for GaMnN∕InGaN∕AlGaN spin-LED structures and indicate that these wide-band-gap dilute magnetic semiconductors with weak spin-orbit interaction and hexagonal symmetry are not attractive for spin-LED applications.
Effect of hydrogen plasma exposure on the amount of trans-polyacetylene in nanocrystalline diamond films
Authors: Teii Kungen , Ikeda Tomohiro , Fukutomi Atsushi , Uchino Kiichiro
Published: February 2006

The interactions between hydrogen-rich plasmas and nondiamond phases contained in nanocrystalline diamond films have been examined to explore a possibility of reducing the amount of nondiamond phases. Diamond films with average grain sizes of 15–25nm were deposited on silicon in microwave Ar-rich∕H2∕CH4 plasmas. The 1140cm−1 peak in the visible Raman spectra for the films was used as a signature of trans-polyacetylene (TPA) segments. The amount of TPA relative to amorphous carbon increased with increasing H2∕CH4 ratio in the Ar-rich∕H2∕CH4 plasmas or simply by exposing the as-grown film to hydrogen plasmas after deposition. However, the Raman peak of diamond, which was superimposed by the D peak of amorphous carbon, was little enhanced by exposure to these hydrogen-rich plasmas. It was also found that an increase in the relative amount of TPA was not always accompanied by an increase in hydrogen content in the films. The results were interpreted along the possible mechanisms of TPA formation, which are correlated to the content of hydrogen in the gas phase as well as in the solid phase.
Tunable growth of ZnO nanorods synthesized in aqueous solutions at low temperatures
Authors: Hsiao Chi-Sheng , Peng Cheng-Hsiung , Chen San-Yuan , Liou Sz-Chian
Published: February 2006

Highly arrayed ZnO nanorods were fabricated on the Si substrate buffered with patterned ZnO film (ZnOf∕Si) via wet-chemical process. The growth behavior and morphology of single-crystal ZnO nanorods (ZNs) were investigated in terms of the annealing temperatures of the sputtered ZnO film. We found that the growth morphology of ZnO nanorods is strongly dominated by the grain size of the ZnO film on the Si substrate. The ZnOf∕Si substrate was annealed at above a critical temperature to promote the crystallization of ZnO phase, and high-resolution transmission electron microscopy demonstrated that both ZNs and ZnOf on Si substrate are coherent. Furthermore, the ZNs seem to nucleate from the concave tip near the grain boundary between two ZnO grains in the ZnO film because of higher surface energy. However, a higher annealing temperature may lead to the formation of a larger ZnO crystal due to the coplanar coalescence behavior of several individual ZnO nanorods.
Interfacial energy and strength of multiwalled-carbon-nanotube-based dry adhesive
Authors: Zhao Yang , Tong Tao , Delzeit Lance , Kashani Ali , Meyyappan M. , Majumdar Arun
Published: February 2006

Vertically aligned multiwalled carbon nanotube (MWCNT) arrays can mimic the hairs on a gecko’s foot and act as a dry adhesive. We demonstrate the van der Waals interactions originated dry adhesion between MWCNT array surfaces and various target surfaces over millimeter-sized contact areas. The adhesive strengths were measured over 10N∕cm2 in the normal direction and about 8N∕cm2 in the shear direction with glass surface. The adhesion strength over repeated cycles is limited by the relatively poor adhesion of MWCNTs to their growth substrate, which was improved significantly by adding molybdenum to the catalyst underlayer. We also measured the interfacial work of adhesion as a fundamental adhesion property at the interface. Our measured values of a few tens of mJ∕m2, which falls in the range of typical van der Waals interactions energies, provide a direct proof of the van der Waals dry adhesion mechanism. Furthermore, in contrast to other dry adhesives, we show that MWCNT adhesives are electrically and thermally conducting, which makes them a unique interfacial material.
Dependence of SiO2 etch rate on sidewall angle as affected by bottom materials in a high-density CHF3 plasma
Authors: Lee Gyeo-Re , Min Jae-Ho , Lee Jin-Kwan , Moon Sang Heup
Published: February 2006

The dependence of SiO2 etch rate on sidewall angle, as affected by different bottom materials, in an inductively coupled CHF3 plasma was investigated. The bottom materials were SiO2, Si, and fluorocarbon polymer, and the bias voltage of the plasma was varied from −50to−400V. Differences in the angular dependency of the etch rate were observed for the different bottom materials at sidewall surface angles higher than 75°, in which case the amounts of bottom-emitted particles impinging on the sidewall surface were relatively large and the transfer of ion energy to the SiO2 substrate was relatively small due to the formation of a fluorocarbon passivation film. The extent that the bottom materials affected the dependence of etch rate on sidewall angle changed, depending on the bias voltage range. When the bias voltage was in the range between −50 and −200V, the effect of a SiO2 bottom was the smallest and those of Si and fluorocarbon polymer were essentially the same. However, at −400V, the effect was substantially larger for the fluorocarbon polymer bottom than for the other two materials, although it was slightly larger for Si than for SiO2. These differences, as a function of bias voltage range, can be attributed to two factors that determine the amounts of bottom-emitted particles: the thickness of the steady-state polymer film formed on the substrate surface during the etching process and the depth of ion-energy transfer to the polymer film. The thickness of the surface polymer film determines the amount of available source for particle sputtering and the depth of ion-energy transfer determines the extent to which incident ions contribute to the sputtering.
Morphology control of silicon nanotips fabricated by electron cyclotron resonance plasma etching
Authors: Hsu C. H. , Huang Y. F. , Chen L. C. , Chattopadhyay S. , Chen K. H. , Lo H. C. , Chen C. F.
Published: February 2006

Formation of well-aligned silicon nanotips etched monolithically from a silicon substrate has been demonstrated. The effect of the process temperature on the physicochemical etching of silicon and subsequent fabrication of these nanotips has been investigated. 2.2-μm-long nanotips were formed at the process temperature of 250°C and then decreased in length with increasing process temperature. Above 800°C, the formation of the silicon nanotips was inhibited. Spectroscopic evidence attributes this fact to the efficient formation of silicon carbide thin film at higher process temperatures, instead of discontinuous nanomasks at lower process temperatures that prevent etching of the substrate. Another reason for this inhibited formation of nanotips is the reduced etching rate of the silicon by agents such as atomic H at higher process temperatures.
Fabrication of photonic crystals using a spin-coated hydrogen silsesquioxane hard mask
Authors: O’Faolain L. , Kotlyar M. V. , Tripathi N. , Wilson R. , Krauss T. F.
Published: February 2006

We present a method for creating a hard mask for the dry etching of microphotonic structures and devices. We demonstrate that spin-on glass [hydrogen silsesquioxane (HSQ)] has sufficient dry etch resistance to allow the creation of high-quality, deeply etched photonic crystals. Furthermore, HSQ is a more favorable hard mask for the creation of active devices than plasma-enhanced chemical-vapor deposition (PECVD) silica, as less damage is incurred. It is also an economic and convenient replacement for PEVCD in photonic crystal fabrication. We examine this method and show that it can create photonic crystals of equivalent quality to those created using PEVCD masking.
Analysis and minimization of overtraining effect in rule‐based classifiers for computer‐aided diagnosis
Authors: Li Qiang , Doi Kunio
Published: February 2006

Computer‐aided diagnostic (CAD) schemes have been developed to assist radiologists detect various lesions in medical images. In CAD schemes, classifiers play a key role in achieving a high lesion detection rate and a low false‐positive rate. Although many popular classifiers such as linear discriminant analysis and artificial neural networks have been employed in CAD schemes for reduction of false positives, a rule‐based classifier has probably been the simplest and most frequently used one since the early days of development of various CAD schemes. However, with existing rule‐based classifiers, there are major disadvantages that significantly reduce their practicality and credibility. The disadvantages include manual design, poor reproducibility, poor evaluation methods such as resubstitution, and a large overtraining effect. An automated rule‐based classifier with a minimized overtraining effect can overcome or significantly reduce the extent of the above‐mentioned disadvantages. In this study, we developed an “optimal” method for the selection of cutoff thresholds and a fully automated rule‐based classifier. Experimental results performed with Monte Carlo simulation and a real lung nodule CT data set demonstrated that the automated threshold selection method can completely eliminate overtraining effect in the procedure of cutoff threshold selection, and thus can minimize overall overtraining effect in the constructed rule‐based classifier. We believe that this threshold selection method is very useful in the construction of automated rule‐based classifiers with minimized overtraining effect.