bluuebunny/crossref_metadata_2025 huggingface dataset:
Writing the identity in radio frequency identity tags with focused ion-beam implantation of transistor gates
Authors: De Marco Anthony , Bandy William , Parsa Siavash , Kaufmann Henry , Melngailis John
Published: January 2006

The soon-to-be-ubiquitous radio frequency identity (RFID) tag consists of a Si chip (less than 1mm2) attached to an antenna on a plastic sheet. Each tag needs to have a unique, electronically readable identity number. Currently, the preferred direction of industry appears to be to fabricate all chips the same, and then program the unique identity into the chip electrically in a permanent or semi-permanent fashion. This may make the tags reusable and permit the identity number to be written by the customer. On the other hand, writing the identity into the chips permanently, during fabrication has advantages; mainly, low cost, less real estate, and less vulnerability to tampering or accidental loss of identity. Permanent programming of the chip is currently done using selective laser cutting of metal connections on the chip, but has not been widely adopted because of cost and reliability. We propose an alternate method whereby transistors are substituted for the metal links and selectively focused-ion-beam (FIB) implanted to permanently turn some of them off. Moreover, we have demonstrated that a low ion dose (∼1012∕cm2) is sufficient, so that the throughput is calculated to be practical. For post-fabrication implantation, the region above the transistor channel must be thinned to 100to200nm to use reasonable ion energies. (Of course, in-process implantation is also an option before the passivation layer is applied.) We have used n-type metal oxide semiconductor (NMOS) and p-type metal oxide semiconductor (PMOS) test transistors fabricated at Berkeley and etched away the oxide and part of the poly over the gate. This process did not alter the transistor characteristics. The transistors were implanted with a series of doses and energies using both FIB and broad-beam implantation (Ar, As, and B with broad-beam and Ga, As, and B with FIB). The required dose to turn transistors off is of order 1012∕cm2 as long as the ions have sufficient energy to alter the gate oxide and/or the channel. In PMOS transistors there is a strong shift in threshold voltage as well as a decrease in drain current, while in NMOS the main effect is the latter. Since Ga+ ions work, a robust FIB system can be used to implant the RFID tags. Moreover, neither high resolution nor high placement accuracy are needed. We only need to implant a given transistor without implanting its neighbors. Assuming a 200mm wafer with 30 000 chips, 120 transistors per chip, 2μm2 gate area, and a 100pA beam current results in an implant time of 6min∕wafer. Using a write-on-the-fly scheme the wafer would have to be scanned at 6cm∕s. Since 50μs are needed to implant each transistor, deflection and blanking times should not be limitations.
Effects of focused gallium ion-beam implantation on properties of nanochannels on silicon-on-insulator substrates
Authors: Pan A. , Wang Y. L. , Wu C. S. , Chen C. D. , Liu N. W.
Published: January 2006

Gallium dopants have been introduced into micrometer and nanometer sized silicon-on-insulator devices by means of focused ion beam maskless implantation. Structures of implanted devices before and after annealing have been characterized by cross-sectional transmission electron microscopy and Raman spectroscopy. The implanted/annealed micrometer devices exhibit uniformly lower electric resistance due to the presence of dopants; and the nanometer scale devices also show lower resistance but with a large device-to-device fluctuation. The fluctuation is likely to be the result of statistical nonuniformity in the spatial distribution of the end-of-range damage on the nanometer scale.
Selective growth of vertical ZnO nanowires on ZnO:Ga∕Si3N4∕SiO2∕Si templates
Authors: Hsu Cheng-Liang , Chang Shoou-Jinn , Hung Hui-Chuan , Lin Yan-Ru , Lu Tsung-Heng , Tseng Yung-Kuan , Chen I-Cherng
Published: January 2006

High density vertical single crystal ZnO nanowires were selectively grown on ZnO:Ga∕Si3N4∕SiO2∕Si templates at various temperatures by a two-step oxygen injection process of self-catalyzed vapor-liquid-solid (VLS) technology. It was found that tips of the ZnO nanowires are hexagonal. It was also found that average length of the ZnO nanowires increased while the average tip diameter of the ZnO nanowires decreased as the growth temperature increased. Furthermore, it was found that the ZnO nanowires grown at 500°C were “tube-shaped” while the ZnO nanowires grown at 700°C were “cone-shaped.” Photoluminescence (PL), x-ray diffraction (XRD), and energy depersive x-ray (EDX) results all indicate that the quality of our ZnO nanowires is good.
Ohmic contact formation mechanism of Ta∕Al∕Mo∕Au and Ti∕Al∕Mo∕Au metallizations on AlGaN∕GaN HEMTs
Authors: Mohammed Fitih M. , Wang Liang , Selvanathan Deepak , Hu Hubert , Adesida Ilesanmi
Published: January 2006

A comparative study of Ta∕Al∕Mo∕Au and Ti∕Al∕Mo∕Au metallizations for AlGaN∕GaN high electron mobility transistors is presented. By the optimization of surface treatment schemes and annealing temperature, contact resistances of 0.172 and 0.228Ωmm, and specific contact resistivities of 2.96×10−7 and 1.09×10−6Ωcm2 were obtained for Ti∕Al∕Mo∕Au and Ta∕Al∕Mo∕Au, respectively. Auger electron spectroscopy (AES), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were utilized to study microstructural changes occurring in the metallization layers as a result of heat treatment. Results indicate dynamic systems of severe intermixing between atoms from the metallization layers and epilayers resulting in changes in surface morphology, as determined by atomic force microscopy (AFM). The formation of intermetallics and interfacial compounds was observed. The combined effect of surface treatment and annealing-induced reaction is proposed as the mechanisms for low-resistance Ohmic contact formation.
Dynamic alignment control for fluid-immersion lithographies using interferometric-spatial-phase imaging
Authors: Moon Euclid E. , Mondol Mark K. , Everett Patrick N. , Smith Henry I.
Published: January 2006

We demonstrate the application of a high-sensitivity alignment method called interferometric-spatial-phase imaging (ISPI) to a nanometer-level overlay in fluid-immersion lithography, using step-and-flash imprint lithography as the test vehicle. As a stringent test we used alignment marks that consist of pure phase gratings in a fused silica template, immersed in a fluid of similar refractive index, resulting in a low-contrast alignment signal. Feedback control of alignment is demonstrated with mean=0.0nm and σ=0.1nm using an immersed template. Overlay results, with UV-exposed imprint fluid, were limited to ∼4nm, due to a mechanical disturbance. Because ISPI enables continuous monitoring of the alignment signal, we were able to identify the origin of the mechanical disturbance and can eliminate it in future experiments. In addition, we demonstrate the ability to actively reduce misalignment during the progression of crosslinking in the imprint fluid.
Resonant grating filters as refractive index sensors for chemical and biological detections
Authors: Wang Jian Jim , Chen Lei , Kwan Steven , Liu Feng , Deng Xuegong
Published: January 2006

A chemical and biological sensor based on a free-space waveguide resonant grating optical filter has been developed. Different from the conventional surface plasmon resonance sensors and the conventional waveguide mode sensors, which require either prism coupling or grating coupling, the proposed free-space optical sensor device does not require special separate coupling. The inherent 100% coupling efficiency at resonance can significantly boost probe efficiency. Both simulation and experimental results have demonstrated that the sensor could deliver a resolution of better than 0.001–0.0001 for refractive index sensing, which is enough for detecting various chemical and biological materials. More importantly, under an angular detection scheme, the proposed waveguide resonant grating sensor could be one order’s more sensitive than the conventional surface plasmon resonance sensor.
Effect of initial resist thickness on residual layer thickness of nanoimprinted structures
Authors: Lee Hae-Jeong , Ro Hyun Wook , Soles Christopher L. , Jones Ronald L. , Lin Eric K. , Wu Wen-li , Hines D. R.
Published: January 2006

Quantification and control of the residual layer thickness is a critical challenge facing nanoimprint lithography. This thickness must be known to within a few nanometers, yet there are very few nondestructive measurement techniques capable of extracting such information. Here we describe a specular x-ray reflectivity technique that can be used to not only quantify the thickness of the residual layer with sub-nm resolution, but also to extract the pattern height, the line-to-space ratio, and relative linewidth variations as a function of the pattern height. This is illustrated through a series of imprints where the initial film thickness is varied. For films with sufficient resist material to fill the mold, complete pattern filling is observed and the residual layer thickness is directly proportional to the initial film thickness. When there is insufficient resist material in the film to completely fill the patterns in the mold, a finite residual layer thickness of approximately 50–100Å is still observed.
Line edge roughness characterization with a three-dimensional atomic force microscope: Transfer during gate patterning processes
Authors: Thiault J. , Foucher J. , Tortai J. H. , Joubert O. , Landis S. , Pauliac S.
Published: January 2006

As critical dimensions (CD) for semiconductor devices shrink to a few tens of nanometers, the line edge roughness (LER) and linewidth roughness (LWR) becomes a critical issue. For this study, we used a new 3D CD-AFM which enables us to characterize LER and LWR along the features after each technological step of standard gate patterning processes. Isolated lines with CDs going from 20nm and 100nm were written with an e-beam lithography tool. First, we transfer the resist mask into silicon to determine the influence of different plasma chemistries on LER. Then, the resist mask is transferred into a standard CMOS gate stack: SiO2 hard mask, polysilicon, dielectric gate. The results after e-beam lithography show that the LWR measured at the bottom of the pattern is higher than the one measured at the middle. It can be attributed to the effect of backscattered electrons. Then, we show that for smaller dimensions, the trimming that occurs during the hard mask opening process weakens the resist and increases drastically the LWR in the polysilicon. This puts forward one limitation of standard processes for aggressive gate patterning. Finally, we do not observe any obvious trend on LER and LWR after the characterization of features coming from two different silicon etching chemistries. This conclusion is surprising. We attributed it to the tip size limitation in sidewall roughness detection on silicon.
Full field analysis of lithography performance for ArF immersion lithography
Authors: Li Yanqiu , Huang Guosheng
Published: January 2006

Full field analysis of pattern displacement caused by lens aberrations for ArF immersion lithography is presented for the critical dimension (CD) of the 65nm node. Pattern displacement (PD) is the most critical issue for lithography performance if the CD uniformity is constrained within ΔCD<±10%CD and the depth of focus is larger than 0.4μm. In-house MicroCruiser software was developed and generated mass groups of 36 Zernike coefficients with certain root mean square of wave-front error (rms WFE) and peak-to-valley value of WFE in order to study the cross talk between different Zernike coefficients. MicroCruiser communicated with PROLITH 8.0 commercial software and processed mass data automatically. The mass results of lithography performance were completed under different conditions of lens aberrations, mask types, and exposure-tool settings at each field point. The results show that with the same rms WFE, the PD will be larger if an alternate phase-shifting mask and conventional illumination are employed as compared the PD if a binary mask and annular illumination are used. For the impact of aberrations on imaging performance, the cross talk between different Zernike coefficients is more essential than a mere rms WFE.
Operation of nanocrystalline silicon ballistic emitter in low vacuum and atmospheric pressures
Authors: Ohta Toshiyuki , Kojima Akira , Hirakawa Hiroyuki , Iwamatsu Tadashi , Koshida Nobuyoshi
Published: January 2006

To make the specific features of nanocrystalline silicon (nc-Si) cold cathode clear, its emission characteristics are investigated in low vacuum and atmospheric pressure. The experimental nc-Si diode is composed of a thin Au film, a nanocrystallized polysilicon layer, an n-type silicon wafer, and a back contact. It is shown that the ballistic electron emission mode of the nc-Si device is kept alive until the vacuum pressure is increased to about 10Pa, and that a significant current signal is detected at the collector even in air. The current observed in air can be interpreted as a result of energetic electron attachment into oxygen molecules in proximity to the front surface. The effectiveness of this emitter for the use in air is applied to surface charging of an insulating polymer. The experimental results demonstrate that the surface of a polymer film located in air at a distance of 1mm from the device surface is quickly charged up to a certain negative potential determined from the collector voltage. The surface-emitting nc-Si ballistic emitter is useful not only in vacuum, but also in air and gas ambient for various applications.
Pattern-dependent microloading and step coverage of silicon nitride thin films deposited in a single-wafer thermal chemical vapor deposition chamber
Authors: Smith Jacob W. , Seutter Sean M. , Iyer R. Suryanaryanan
Published: January 2006

Less than 10% pattern-dependent microloading and greater than 95% step coverage are required for low temperature deposition of Si3N4 spacer and etch stop films in advanced logic and dynamic random access memory semiconductor applications. A single-wafer chemical vapor deposition chamber was utilized to analyze pattern loading effect on 130 nm and 90 nm patterned wafers. With silane-ammonia chemistry as the focus, a variety of processing methods were employed utilizing continuous and cyclical deposition modes. In addition, methods to modify diffusion and/or reaction rates were studied, such as remote plasma excitation and carrier gas modifications. Finally, chemistry-related variables were evaluated by changing the Si-source precursor. It was concluded that process chemistry and specifically precursor is the most dominant factor determining pattern loading effect.
Physical characterization of ZnO nanorods grown on Si from aqueous solution and annealed at various atmospheres
Authors: Yang Chih-Cheng , Chen San-Yuan , Lee Hsin-Yi
Published: January 2006

High-density ZnO nanorods were vertically grown on Si coated with ZnO film (ZnO∕Si substrate) from aqueous solution at low temperatures. The ZnO nanorods after annealed in various atmospheres still present good c-axis crystalline character but exhibit remarkable differences in photoluminescence (PL) properties. Enhancement of PL properties due to N2-atmosphere annealing for ultraviolet emission can be attributed to the reduction of defect density because the nonparamagnetic singly ionized state (N−) can easily occupy the oxygen vacancies as evidenced by Raman spectroscopy and electron paramagnetic resonance spectrometry. The extended x-ray absorption fine structure reveals that the annealing atmosphere shows no apparent influence on the deep-level defects of ZnO nanorods except that some ions are possibly trapped or adsorbed on the surface of the ZnO nanorods.
Observations of interfaces in direct wafer-bonded InP–GaAs structures
Authors: Lao Yan-feng , Wu Hui-zhen , Li Ming
Published: January 2006

Direct wafer-bonded InP–GaAs structures were studied by cross-sectional observations using a field-emission scanning-electron microscope (FESEM) and by infrared-absorbance spectra using a Fourier-transform infrared spectroscopy. FESEM observations demonstrate that the interfaces of 560 and 580 °C bonded InP–GaAs structures are smooth and uninterrupted, while interfacial gaps appear for the samples bonded at 620 and 680 °C. However, large dimensional areas of bonding interfaces cannot be observed by FESEM because its inspection size is limited to microregions. Experimental results show that infrared-absorbance measurements can be an effective method for quality examination of bonded InP–GaAs structures. By soaking wax into poorly bonded interfaces and using its absorption characteristics at 3.383, 3.426, and 3.509μm, interfacial gaps are indirectly measured by infrared spectra. Absorbance-intensity mappings at absorption peaks were used to image poorly bonded areas. Thus the interface quality of the whole wafer-bonded sample can be seen clearly. Nonuniform pressure applied over the sample during annealing step accounts for poorly bonded interfaces. Using the improved fixture, uniformly bonded InP–GaAs structures that do not have interfacial gaps were obtained.
Field emission of carbon nanotubes grown on carbon cloth
Authors: Jo S. H. , Huang J. Y. , Chen S. , Xiong G. Y. , Wang D. Z. , Ren Z. F.
Published: January 2006

Field emission of carbon nanotubes (CNTs) grown on carbon cloth under various growth conditions has been studied. Iron sulfate or stainless steel was used as the catalyst, acetylene (C2H2) or methane (CH4) was used as the carbon source, and argon (Ar), hydrogen (H2), or ammonia (NH3) was used as the carrier gas. It is found that the morphology of CNTs is strongly dependent on the growth conditions: temperature, gas combination, and growth time. In general, higher temperature produces better field emitters than lower temperature, C2H2∕Ar is better than C2H2∕NH3, but CH4∕H2 is the best, and longer growth time normally yields longer CNTs leading to better field emitters. The best sample was made from 0.18mol∕l iron sulfate catalyst with CH4∕H2 at 860 °C for 2 h: an emission current density of 1mA∕cm2 was obtained at 0.4V∕μm corresponding to a field enhancement factor of 3.5×104.
Effects of etch barrier densification on step and flash imprint lithography
Authors: Johnson S. , Burns R. , Kim E. K. , Dickey M. , Schmid G. , Meiring J. , Burns S. , Willson C. G. , Convey D. , Wei Y. , Fejes P. , Gehoski K. , Mancini D. , Nordquist K. , Dauksher W. J. , Resnick D. J.
Published: January 2006

Previous work with the mechanical properties of step and flash imprint lithography etch barrier materials has shown bulk volumetric shrinkage trends that could impact imprinted feature dimensions and profile. This article uses mesoscopic and finite element modeling techniques to model the behavior of the etch barrier during polymerization. Model results are then compared to cross section images of template and etch barrier. Volumetric shrinkage is seen to impact imprinted feature profiles largely as a change in feature height.
Light-emitting diodes with nickel substrates fabricated by electroplating
Authors: Chang P. H. , Chen N. C. , Wang Y. N. , Shih C. F. , Wu M. H. , Yang T. H. , Tzou Y. H. , Wang S. J.
Published: January 2006

AlGalnP light-emitting diodes (LEDs) with electroplated nickel substrate have been successfully fabricated. The AlGalnP LEDs were initially grown on a GaAs temporary substrate. After removing or thinning the GaAs substrate and coating a Au∕Ge layer, a 60μm thick nickel layer was electroplated on the Au∕Ge surface serving as the substrate. The results show that the electroplated nickel substrate is effective in the thermal dissipation capability and reflectivity. As compared to LEDs with a GaAs substrate, an increase in the light output by up to 88% has been obtained. Additionally, the proposed method is so reliable that light output degradation was less than 10% after 1500h operation at 60°C and 50mA.
Imaging characteristics and specification of mask mean-to-target and mask uniformity according to polarization status
Authors: Lee Sung-Woo , Finders Jo , Lee Suk-Joo , Woo Sang-Gyun , Cho Han-Ku
Published: January 2006

Maximum exposure latitude (EL), mask error enhancement factor (MEEF), and intrafield critical dimension (CD) uniformity are compared in TE and unpolarized (UNP) light. An ArF dry scanner with 0.85 numerical aperture and dipole illumination with inner and outer sigmas of 0.93 and 0.69 is used. 63 and 73nm nodes are chosen which have 126 and 146nm pitch sizes and Target CDs of 63 and 73nm. TE shows 56% and 10% larger maximum EL than UNP for 63 and 73nm nodes, respectively. TE shows 56% increased IFU compared with UNP at the 63nm node. MEEFs are 3.4 and 4.1 for TE and UNP light at the 63nm node, respectively. MEEFs of 1.4 and 1.5 are observed for TE and UNP light at the 73nm node. Mask mean-to-target (MTT) and uniformity specifications are compared according to polarization status. For the 63nm node, specifications of mask MTTs are ±1.28 and ±1.28nm and the mask uniformities are 1.43 and 1.18nm for TE and UNP light, respectively. For the 73nm node, ±2.62 and ±2.43nm of the mask MTT specifications are obtained with mask uniformities of 4.04 and 3.77nm at TE and UNP light. TE light shows 28% and 11% larger MTT and uniformity specification areas than UNP light for 63 and 73nm nodes.
Fabrication of high-secondary-electron-yield grids for spatial-phase-locked electron-beam lithography
Authors: Zhang Feng , Smith Henry I. , Dai Jianfeng
Published: January 2006

Poor placement accuracy is a major issue and inhibitor in all forms of electron-beam lithography (EBL), a direct result of the open-loop nature of EBL. In scanning-electron-beam lithography (SEBL), the beam position is not continuously monitored during exposure. Instead, one depends upon a laser-interferometer-controlled stage and secondary referencing. In SEBL, the beam can deviate from its intended position causing pattern-placement errors that are often worse than the resolution. Spatial-phase-locked electron-beam lithography (SPLEBL) is being developed at MIT to achieve nanometer-level absolute placement accuracy. In its global-fiducial-grid mode, SPLEBL directly references the beam location to an electron-transparent grid, placed on top of the e-beam resist, during exposure. Recently pattern-placement precision of ∼1nm was demonstrated with secondary electrons as the reference signal [J. T. Hastings, F. Zhang, and H. I. Smith, J. Vac. Sci. Technol. B 21, 2650 (2003)]. However, the fabrication process used for the reference grid was complex and would not be acceptable in manufacturing. In this article, we describe a process for putting down the grid that is user friendly and preserves its long-range spatial-phase coherence. We also investigated a variety of candidate grid materials (various low-Z metals and C60) for their secondary-electron yields and processibility.
Effects of nanoimprinted patterns in tissue-culture polystyrene on cell behavior
Authors: Hu W. , Yim E. K. F. , Reano R. M. , Leong K. W. , Pang S. W.
Published: January 2006

Tissue engineering seeks to develop functional tissues in a biomimetic environment in vitro. As the extracellular environment in vivo is composed of numerous nanostructures, fabrication of nanostructured substrates will be valuable for tissue engineering applications. In this article, we report a simple nanoimprint lithography (NIL) process to pattern nanostructures directly on tissue-culture polystyrene plates. By repeating this NIL process, three-dimensional scaffolds consisting of multiple-layer nanostructures were also fabricated. Bovine pulmonary artery smooth muscle cells were cultured on imprinted gratings ranging from 350nmto10μm. The smooth muscle cells attached and proliferated well on these imprinted substrates without additional surface treatment. Cell elongation and alignment were observed on the micro- and nanopatterns, with the effect significantly more pronounced on the nanostructures.
Arrays of high-Q high stability ultrahigh-frequency resonators for chemical/biological sensors
Authors: Kubena R. L. , Chang D. T. , Stratton F. P. , Joyce Richard J. , Hsu T. Y. , Lim M. K. , M’Closkey R. T.
Published: January 2006

The use of nanomechanical resonators for chemical and bioagent detection has attracted a large amount of interest in recent years, since the mass noise floor scales directly with the mass of the resonator for a given frequency stability. In order for this technology to be applied to hand-held units, the resonators should ideally be integrated with the oscillator and counter electronics, have high-Q and high frequency stability in air, and have low-temperature sensitivity. We present a quartz-based ultrahigh-frequency resonator/oscillator technology that addresses these important issues. Miniaturized shear-mode resonators with frequencies approaching 3GHz and f×Q products of >1.0×1013Hz have been fabricated on Si using low-temperature wafer bonding and deep reactive ion quartz etching. Allan deviation levels of 1.0×10−8 for 100s integration times have been measured for a 326MHz Pierce oscillator design. In addition, the temperature stability matches that expected for AT-cut crystal resonators. We present preliminary selective deposition results that indicate that arrays of these oscillators could be used for highly selective and high sensitivity low-cost sensors.
Understanding the impact of source displacement error on sub-90nm patterns using a fresnel zone plate
Authors: Shin Jangho , Hwang Chan , Lee SukJoo , Woo Sang-Gyun , Cho Han-Ku , Moon Joo-Tae
Published: January 2006

Illumination source radiance distribution has a significant impact on vertical-horizontal bias and critical dimension (CD) variation on production wafers. In this article, the impact of source displacement error (SDE) on sub-90nm patterning is studied. A Fresnel zone plate (FZP) is adopted as a metrology to quantify the amount of SDE. Experimental data show that some of pupil-fills may have more than 50mrad of SDE and it could cause a serious pattern shift and/or CD asymmetry. A detailed description of FZP design specifications and application results are presented. Finally, SDE tolerance limits to print sub-90nm features are discussed.
Three-dimensional digital scanner based on micromachined micromirror for the metrological measurement of the human ear canal
Authors: Prasciolu M. , Malureanu R. , Cabrini S. , Cojoc D. , Businaro L. , Carpentiero A. , Kumar R. , Di Fabrizio E.
Published: January 2006

Manufacturers of hearing aids have made initial testing of rapid prototyping of hearing aid shells using laser scans of ear impressions, but they have not performed any actual scans of the human ear canal. We report the direct scanning of the human external auditory canal by using an electromagnetically actuated torsion micromirror fabricated by using a micromachining technique as the scanner. This demonstrates the actual scanning of the human external auditory canal by a single integral microelectro-optical-mechanical system (MEOMS). A prototype three-dimensional (3D) scanning system was developed: It is based on the acquisition of optical range data by a conoscopic holographic laser interferometer using an electromagnetically actuated scanning MEOMS micromirror. A fabrication process, based on a poly(methylmethacrylate) sacrificial layer for the fabrication of a free-standing micromirror was used. Micromirror actuation was achieved by using a magnetic field generated with an electromagnetic coil stick. The micromirror and electromagnet coil assembly compose the opto-mechanical scanning probe used for entering the auditory canal. Based on an actual scan map, a 3D reconstructed digital model of the ear canal was built using a surface point distribution approach. The prototype system allows a no-invasive 3D imaging of the ear canal with spatial resolution in the 10μm range. Fabrication of two complete hearing aids from in vivo ear canal scanning is also accomplished.
Bubbles in immersion lithography
Authors: Switkes M. , Rothschild M. , Shedd T. A. , Burnett H. B. , Yeung M. S.
Published: January 2006

One of the major concerns in the emerging technology of liquid immersion lithography is the possibility of defects due to bubble formation in the immersion liquid. We have performed numerical simulations of the impact of bubbles on printing. The greatest impact is due to bubbles close to the resist surface; beyond several bubble diameters, the impact of a bubble is negligible. With this in mind, we have investigated one of the major candidates for producing near-surface bubbles, resist outgassing. We have imaged, with 0.25μm∕pixel resolution, the surface of an immersed resist immediately after exposure to 193nm radiation at a fluence of 2–20mJ∕cm2. Using a high outgassing 248nm resist, bubble formation is clear. However, in over 3000 frames of a model 193nm immersion resist, only one frame with bubble candidates was seen, and only at a fluence (20mJcm−2) far exceeding that of normal exposure conditions.
Wing-tilt-free gallium nitride laterally grown on maskless chemical-etched sapphire-patterned substrate
Authors: Wang Jing , Guo L. W. , Jia H. Q. , Xing Z. G. , Wang Y. , Chen H. , Zhou J. M.
Published: January 2006

A method is developed to overcome the problem of wing tilt that appears in lateral epitaxial overgrowth of GaN films. High-quality GaN films free of wing tilt were obtained reproducibly on wet chemical-etched maskless c-plane sapphire substrate using metalorganic chemical vapor deposition (hereafter called CantiBridge epitaxy). Symmetrical (0002) x-ray diffraction of a4.5-μm-thick GaN film is performed with the scattering plane parallel and perpendicular to the stripe direction. The corresponding full widths at half maxima of the (0002) peaks are about 147 and 144 arcsec, respectively, which is one of the best results reported to date. Scanning electron microscopy cross-section images show that GaN was selectively grown on the mesas and the lateral overgrowth GaN spanned the etched trenches. No GaN was found on the grooved sapphire trenches, which is very different from the usually observed phenomena in other lateral epitaxial overgrowth techniques. It is inferred that damage-free mesas and grooves benefit the elimination of wing tilt and they improve the quality of the lateral overgrown GaN. The results indicate that CantiBridge epitaxy is a promising technique for fabricating high-quality GaN-based materials and devices.
Photosensitive quantum dot composites and their applications in optical structures
Authors: Pang Lin , Tetz Kevin , Shen Yaoming , Chen Chyong-Hua , Fainman Yeshaiahu
Published: January 2006

Commercially available CdSe∕ZnS and PbSe colloidal semiconductor quantum dots were employed to produce both an electron beam sensitive poly(methyl methacrylate) (PMMA)-quantum-dot (QD) positive composite via a prepolymerization processing and an electron beam and ultraviolet (UV) light sensitive SU-8-QD negative composite via a direct dispersion procedure. Compared to the QDs in the original colloidal solutions, the photoluminescence of the composites shifts to shorter wavelength due to the oxidation of the surfaces of the QDs. Using the QD composites, optical integrated circuits such as grating and waveguide structures were fabricated by direct electron beam writing and UV optical lithography. The characterization results show promising applications in optoelectronics for the QD composites.
Diamond nanorods
Authors: Shenderova O. A. , Padgett C. W. , Hu Z. , Brenner D. W.
Published: January 2006

Diamond nanorods are one-dimensional carbon nanostructures consisting of all sp3 bonded carbon atoms. They represent an alternative class of carbon structure to fullerene nanotubes for potential applications in nanocomposites for mechanical reinforcement and thermal management, as well as in microelectronics. Synthetic routes for creating diamond nanorods (and related structures) and recent predictions of their stability, mechanical, and thermal properties are summarized in the article.
Numeric analysis of the role of liquid phase ultraviolet photochemistry in 193nm immersion lithography
Authors: Hinsberg William , Houle Frances
Published: January 2006

A quantitative evaluation of the photochemistry taking place in the water fluid layer during lithographic immersion exposure with 193nm radiation is described. This analysis uses a detailed kinetic model based on available literature mechanistic data and constructed with in-house simulation tools. Product yields from the intrinsic photochemistry of pure, degassed water, the effects of trace quantities of dissolved oxygen and organics on these photochemical reactions, and the potential impact of reactive photoproducts on a photoresist film in contact with the fluid are estimated.
Phase transformations in copper oxide nanowires
Authors: Han Sheng , Chen Hong-Ying , Chu Yuh-Bin , Shih Han C.
Published: January 2006

Cu nanowires were electrodeposited into the nanopores of self-ordered aluminum oxide films. CuO and Cu2O nanowires were fabricated by oxidizing Cu nanowires in air. Cu nanowires oxidized at 250°C transform only to Cu2O (grain size ∼21nm), they transform to a mixture of CuO and Cu2O above 350°C and finally to CuO with a preferred orientation of CuO (111) at 900°C.
Various driving modes of a field emission cathode
Authors: Choi Y. S.
Published: January 2006

Characteristics of various driving modes in a field emission display with carbon nanotube emitters are investigated through computer simulations. In triode structural field emission displays electron emission from the cathode electrode is induced by the extraction of external electric fields due to the gate electrode and anode electrode. By the relative value of gate and anode field strengths on emission material the driving mode may divide into four categories of gate extraction, gate-anode extraction, anode-gate extraction, and anode extraction modes. According to our simulation results, the best performance would be produced by the gate-anode and the anode-gate extraction modes, in which the gate and anode fields on emission material are compatible in strength.
Nanoscale fabrication in aqueous KOH solution using tribo-nanolithography
Authors: Kawasegi Noritaka , Park Jeong Woo , Morita Noboru , Yamada Shigeru , Takano Noboru , Oyama Tatsuo , Ashida Kiwamu
Published: January 2006

A simple process to fabricate a three-dimensional structure on silicon surface was developed by using tribo-nanolithography (TNL) in an aqueous KOH solution. An inclined rectangular structure can be fabricated by a process where a thin amorphous layer, having corrosion resistance against KOH, rapidly forms on the substrate at the diamond tip sample junction along the scanning pass of the tip, while simultaneously, the area not covered with the amorphous layer is being etched in KOH. An inclination of structure can be controlled by the scanning velocity. The scanning pitch is related to the corrosion resistance of the amorphous layer, rather than the change of inclination. We fabricated a structure having multiple inclinations based on these results, which indicates the possibility of using the TNL for three-dimensional nanofabrication.
Barrier height enhancement and stability of the Au∕n-InP Schottky barrier diodes oxidized by absorbed water vapor
Authors: Çetin H. , Ayyildiz E. , Türüt A.
Published: January 2006

We have fabricated the Au∕n-InP Schottky barrier diodes (SBDs) with and without an intentionally grown interfacial oxide layer. The oxide layer on chemically cleaned indium phosphide (InP) surface has been obtained by exposure to water vapor at 1ml∕min at 200°C before metal evaporation. The chemical composition of the surface oxides grown on the InP is investigated using x-ray photoelectron spectroscopy. Phosphorus is present as In(PO3)3, InPO4, P2O5 and elemental P. The influence of the oxide on the Schottky barrier formation and contact stability at the InP (100) surface upon subsequent metal deposition has been investigated. The transport properties of the metal-semiconductor contacts have been observed to be significantly affected by the presence of the interfacial oxide layer. Thus, the barrier height has been increased by ∼140meV for the Au∕n-InP SBD by means of the interfacial oxide grown by use of absorbed water vapor. Furthermore, in order to observe the effect of the aging in the Au∕n-InP SBD with and without the interfacial oxide layer, the current-voltage (I-V) measurements have also been repeated 7, 14, 28, 45, 56, and 70days after fabrication of these diodes. The obtained diode parameters were examined statistically and it was found that the reference and oxidized Au∕n-InP SBDs exhibited stable characteristics 14days after metal deposition.
Material and electrical analysis of hafnium titania bilayer dielectric metal-oxide-semiconductor field-effect transistors
Authors: Rhee Se Jong , Kang Chang Yong , Choi Chang Hwan , Zhang Manhong , Lee Jack C.
Published: January 2006

An approach of fabricating laminated titanium oxide on hafnium oxide bilayer dielectric has been developed for future high-performance device applications. The dielectric layers showed negligible intermixing and no silicide formation with silicon substrate. X-ray diffraction analysis demonstrated superior thermal stability (>950°C) of the hafnium titania bilayer dielectric. With the same total physical thickness of dielectric, a thicker titanium oxide layer resulted in improved electrical characteristics. It has been found that the hafnium titania bilayer dielectric metal-oxide-semiconductor field-effect transistor showed not only improved output current and transconductance, but also increased electron and hole mobility compared to hafnium binary oxide device.
Interfacial reactions in nickel/titanium ohmic contacts to n-type silicon carbide
Authors: Park Jae Hyun , Holloway Paul H.
Published: January 2006

The complex sequence of reactions and resulting material phases that occur during formation of ohmic contacts using a trilayer titanium/nickel/titanium structure on n-SiC have been studied. The Ti∕Ni∕Ti contacts on SiC were rectifying in the as-deposited state, but became ohmic upon annealing at 1000°C for 2min in a N2 ambient, resulting in a specific contact resistance (ρC) as low as 1×10−4Ωcm2. X-ray diffraction, Auger electron spectroscopy data and transmission electron microscopy analysis showed that Ni2Si, TiC and graphitic-bound C formed as a result of the annealing. The top Ti layer remained intact as predominantly titanium oxide with minor amounts of TiC. The Ni layer was converted to a double Ni2Si layer containing graphitic C nonuniformly distributed. The bottom Ti layer was converted to a TiC layer separating the two Ni2Si layers, and graphitic C was concentrated in a discontinuous layer near the Ni2Si∕SiC interface. The reasons for the formation of this complicated microstructure were discussed.
Advanced atomic force microscopy probes: Wear resistant designs
Authors: Liu H. , Klonowski M. , Kneeburg D. , Dahlen G. , Osborn M. , Bao T.
Published: January 2006

Tip [in this article, tip refers to the apex region of an atomic force microscopy (AFM) probe. A probe consists of substrate, cantilever, and tip.] wear is a phenomenon that can reduce the accuracy and reliability of AFM. As both tip size and specimen approach nanometer scale, tip shape change due to wear becomes critical to topographical measurements such as critical dimensions and deep trenches. This article presents probe designs with specific wear-resistant features. Three categories of probe modification were selected to lessen wear, thereby improving lifetime and performance. These are probe material, surface coatings, and selective shape.
Doppler writing and linewidth control for scanning beam interference lithography
Authors: Montoya Juan C. , Chang Chih-Hao , Heilmann Ralf K. , Schattenburg Mark L.
Published: January 2006

Scanning beam interference lithography (SBIL) is a technique which is used to create large-area periodic patterns with high phase accuracy. This is accomplished by combining interference lithography and an X-Y scanning stage. We previously reported parallel scan mode in which the stage scans in a direction parallel to the interference fringes. Here we present a method called Doppler scanning. In this mode, the stage is scanned perpendicular to the interference fringes. In order to obtain high-contrast latent gratings in the exposed photoresist, several parameters must be controlled. These parameters include vibration, fringe period error, time delay (for Doppler writing), dose, beam overlap, and polarization. In this article we present results of how the time delay, fringe period error, and exposure dose effect the contrast and linewidth of our latent grating images. Furthermore, SBIL has a unique ability to read gratings in a metrology mode configuration. This article also describes how Doppler metrology mode allows us to measure the time delay of our system.
Characterization of the synchrotron-based 0.3 numerical aperture extreme ultraviolet microexposure tool at the Advanced Light Source
Authors: Naulleau Patrick , Cain Jason P. , Anderson Erik , Dean Kim , Denham Paul , Goldberg Kenneth A. , Hoef Brian , Jackson Keith
Published: January 2006

Synchrotron-based extreme ultraviolet (EUV) exposure tools continue to play a crucial roll in the development of EUV lithography. Utilizing a programmable-pupil-fill illuminator, the 0.3 numerical aperture (NA) microexposure tool at Lawrence Berkeley National Laboratory’s Advanced Light Source synchrotron radiation facility provides the highest resolution EUV projection printing capabilities available today. This makes it ideal for the characterization of advanced resist and mask processes. The Berkeley tool also serves as a good benchmarking platform for commercial implementations of 0.3 NA EUV microsteppers because its illuminator can be programmed to emulate the coherence conditions of the commercial tools. Here we present the latest resist and tool characterization results from the Berkeley EUV exposure station.
Local critical dimension variation from shot-noise related line edge roughness
Authors: Kruit P. , Steenbrink S.
Published: January 2006

Shot noise effects are important to take into account both in the design of resists for lithography and in the design of lithography tools. The statistics of electron or photon arrival gives rise to dose variations, which translate to variations in the size of written features. It is possible to model the shot noise effects in an analytical equation, which shows the influence of all relevant parameters. The sequence of subsequent events in the resist: Secondary electron creation, acid generation, and acid diffusion are incorporated in the model. The model then allows the evaluation of the minimum resist sensitivity necessary for a certain required critical dimension control.
Lithographically fabricated optical cavities for refractive index sensing
Authors: Adams Mark , DeRose Guy A. , Loncar Marko , Scherer Axel
Published: January 2006

Since the development of distributed Bragg gratings, high resolution lithography and etching have been applied towards the concentration of light. The most important application of lithographically fabricated microcavities has been for the spectral control over laser emission. Here we describe the opportunities that arise from further miniaturization of laser cavities by using high index contrast photonic crystal mirrors and annular Bragg reflectors. We have used these optical cavities, with mode volumes as small as 10−17l, to perform spectroscopic analysis and compare the mode volumes and sensitivities of these geometries.
Analytical model of a gas phase field ionization source
Authors: Liu Xuefeng , Orloff Jon
Published: January 2006

High resolution focused ion beam technology is based on the use of field ionization sources. The most widely used source by far is the liquid metal ion source (LMIS) and most focused ion beam systems today employ it. The gas phase field ionization source (GFIS) is hardly employed today except in field ionization microscopy, but present day technology would allow its unique properties vis a vis the liquid metal ion source, including smaller virtual source size and energy spread, and the ability to produce ions from H, He, and heavier noble gases, to be exploited. If the GFIS is used as an ion source for a focusing column it would be useful to be able to calculate its emission properties (current versus voltage) as a function of emitter shape (a parameter not variable in a LMIS). Such a calculation had not been done precisely based on realistic emitter shapes. In this work, a theoretical description of the mechanism for ion production in a GFIS is presented. The comparison of the result with the experimental data for a H2–Ir GFIS is given, which shows reasonable agreement. With the present model, when used with the model for the optical properties of the GFIS (to be published), a focused ion beam (FIB) optical designer can make reasonable predictions about the properties of a GFIS-based FIB. Based on the modeling, we predict that a sub 1nm beam of He+ should be possible with ∼1pA current.
Investigation of overlay errors due to the interaction of optical and extreme ultraviolet mask fabrication processes
Authors: Zheng L. , Engelstad R. L. , Lovell E. G.
Published: January 2006

Overlay tolerances are becoming increasingly severe as lithography technology drives the minimum integrated-circuit feature size below 65nm. Manufacturable solutions at the lower nodes are essentially unknown. The goal of this article is to investigate overlay errors at the 45-nm node, for a mix-and-match of optical and extreme ultraviolet (EUV) lithographies. In particular, image placement errors induced during mask fabrication are predicted for a specified test pattern, which includes the possibility of having individual layers on the device wafer patterned by either optical or EUV lithographic processes. Finite element (FE) models have been developed to simulate the response of both optical and EUV masks during fabrication and chucking. In order to track image placement errors of the actual features within the pattern area, submodeling techniques were developed for the FE simulations. In addition, equivalent material properties were determined for the individual patterns used for the different optical and EUV masks. The FE simulations clearly indicate that the most significant source of overlay error is the fabrication of the optical reticle, primarily due to differences in chucking of the mask during e-beam patterning and exposure. Modeling results are being used by the industry to establish guidelines for reticle chucking and fabrication standards.
Polymer cell culture substrates with combined nanotopographical patterns and micropatterned chemical domains
Authors: Charest Joseph L. , Eliason Marcus T. , García Andrés J. , King William P. , Talin A. Alec , Simmons Blake A.
Published: January 2006

A combination of nanoimprint lithography and microcontact printing was used to create cell substrates with well-defined nanotopographic patterns of grooves overlaid with independently controlled micropatterned chemical domains. Qualitative analysis of osteoblast-like cells cultured on the substrates showed alignment of cells and cell features to the nanotopographic grooves when surface chemistry was either uniform or a pattern of dots. When surface chemistry on the substrate was a pattern of lanes, cells aligned to the lanes. On all substrates, small cellular extensions, or filopodia, displayed no particular alignment to either nanotopographic grooves or chemical patterns. Large cell extensions were observed only parallel to either nanotopographic grooves or chemical lanes. The techniques used provide an easily scaleable approach to creating cell substrates that will aid in studying the relative impact and interplay of chemical patterns and mechanical topography on cellular responses.