bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of three-dimensional mode converters for silicon-based integrated optics
Authors: Fritze M. , Knecht J. , Bozler C. , Keast C. , Fijol J. , Jacobson S. , Keating P. , LeBlanc J. , Fike E. , Kessler B. , Frish M. , Manolatou C.
Published: December 2003

One of the key challenges facing silicon-based integrated optics is the coupling of light from standard optical fibers to submicron silicon waveguides. As a solution to this problem, we present an adiabatically tapered three-dimensional mode converter based on graytone optical lithography and silicon-on-insulator substrates. Our goal has been to preserve complementary metal–oxide–semiconductor process compatibility to the greatest extent possible. Adiabatic tapers are robust with respect to fabrication imperfections. The graytone lithography fabrication process is discussed, and results are presented from optical coupling experiments. Minimizing silicon surface roughness is critical, and methods are presented for achieving rms roughness values on the subnanometer scale.
Ion-enhanced chemical etching of HfO2 for integration in metal–oxide–semiconductor field effect transistors
Authors: Sha Lin , Puthenkovilakam Ragesh , Lin You-Sheng , Chang Jane P.
Published: December 2003

High-density chlorine plasmas were used to chemically etch HfO2, a promising high dielectric constant material, where the etch rate scaled up linearly with the square root of ion energy at energies above 50 eV. Higher etch rates were obtained at lower pressures and high microwave powers, where the electron temperature and ion densities were high. Optical emission spectroscopy and quadrupole mass spectrometry were used to identify the etching products, which are mainly highly chlorinated hafnium (HfCl3 and HfCl4) and ClO. Surface chlorination was confirmed after etching was confirmed by x-ray photoelectron spectroscopy. The addition of BCl3 in the Cl2 plasmas was found to significantly enhance the HfO2 etch rate and improve the etching selectivity to Si from ∼0.01 in a pure Cl2 plasma to ∼0.9 in a pure BCl3 plasma at an ion energy of 75 eV. The etching selectivity was improved to 4 as the ion energies reduced towards the etching threshold energy in a pure BCl3 plasma. BCl3 plasmas were found effective in patterning HfO2 for fabricating the metal–oxide–semiconductor field effect transistors, enabling a complete removal of HfO2 from the source and drain regions yielding high electron mobility.
Investigation of substrate rotation at glancing incidence on thin-film morphology
Authors: Dick B. , Brett M. J. , Smy T.
Published: December 2003

Films deposited by evaporation at glancing angles form structures dependent on the speed of substrate rotation. If the substrate is held stationary, oblique columns are grown. For slow substrate rotation, helices are formed while faster rotation yields pillars. Silicon and silicon dioxide films grown under similar conditions were found to follow the typical morphological trend. In contrast, aluminum films formed by glancing angle deposition (GLAD) were found to be facetted structures which were peaked and isolated at high rotation speeds (dφ/dt>42 rpm), and flat for dφ/dt∼1.5 rpm. The results suggest that the primary limiting factor controlling GLAD microstructure growth may be a combination of both material temperature and crystal structure of the resulting film.
Thickness effects on properties of GaInNAs quantum dots grown by molecular-beam epitaxy with nitrogen plasma source
Authors: Yew K. C. , Yoon S. F. , Sun Z. Z.
Published: December 2003

Self-assembled GaInNAs quantum dots (QDs) were grown on a GaAs (001) substrate by solid-source molecular-beam epitaxy equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were investigated using atomic-force microscopy (AFM) and photoluminescence (PL) measurements. The growth experiment was conducted using indium and nitrogen compositions of 50% and ∼1%, respectively, at different nominal thicknesses of 3 monolayers (MLs) to 6 MLs. AFM images suggest the onset of QD formation at ∼3 MLs and QD coalescence at ∼6 MLs. The highest PL intensity at low temperature (5 K) was obtained from the sample with nominal thickness of 5 ML, consistent with the highest QD density observed from AFM measurement. Under the present experimental conditions, GaIn0.5N0.01As QDs of 5–6 MLs gave the best optical property in terms of the lowest full width at half maximum and highest PL intensity. The reduced barrier potential of a strain-compensated layer (SCL) of GaNAs inserted between the substrate and GaInNAs QD layer was able to extend the PL emission wavelength by more than 140 nm compared to the sample without the GaNAs SCL.
Adhesion and stiction: Mechanisms, measurement techniques, and methods for reduction
Authors: Bhushan Bharat
Published: December 2003

Solid–solid adhesion occurs at contacting asperities in two contacting solids. A thin liquid film with a small contact angle, present at the interface, can result in the so-called liquid-mediated adhesion. This may result in high adhesion during normal pull and high static friction during sliding, both commonly referred to as “stiction.” The problem of high stiction is especially important in an interface involving two very smooth surfaces under lightly loaded conditions. This article provides a critical and comprehensive review of mechanisms of adhesion and stiction, various measurement techniques, and methods used to reduce stiction in magnetic storage devices and micro/nanoelectromechanical systems.
Etching mechanisms of low-k SiOCH and selectivity to SiCH and SiO2 in fluorocarbon based plasmas
Authors: Posseme N. , Chevolleau T. , Joubert O. , Vallier L. , Mangiagalli P.
Published: December 2003

This study is dedicated to an analysis of the etch mechanisms of SiOCH, SiO2 and SiCH in fluorocarbon plasmas. The etching of these materials is performed on blanket wafers in a magnetically enhanced reactive ion etcher reactor using fluorocarbon based chemistry (CF4/N2/Ar). After partial etching, the Fourier transform infrared spectroscopy and mercury probe measurement indicate that the remaining substrate of SiOCH is not altered by the reactive plasma. A decrease in the etch rate of SiOCH, SiO2 and SiCH is observed either with increasing Ar dilution or polymerizing gas addition as CH2F2 and C4F6. X-ray photoelectron spectroscopy analysis of the surface after partial etching shows that the thickness of the fluorocarbon layer formed at the film surface and its composition play a key role in controlling etch rate and selectivity of SiOCH, SiO2 and SiCH. The etch rate of these materials is getting lower when the fluorocarbon layer thickness increases and also when its fluorine concentration decreases. The fluorocarbon layer thickness and composition depend on the plasma chemistry but also on the concentration and nature of impurities (C and H) in the etched materials. Etch rates are presented and discussed with respect to plasma parameters and material composition in terms of etching mechanisms.
Electrical properties of SiO2 films with embedded nanoparticles formed by SiH4/O2 chemical vapor deposition
Authors: Rassel R. M. , Kim T. , Shen Z. , Campbell S. A. , McMurry P. H.
Published: December 2003

This article uses real-time particle measurements as well as physical, chemical, and electrical film measurements to report on the properties of films with embedded particles formed during low-pressure chemical vapor deposition of SiO2 from silane and oxygen. The depositions were carried out at pressures and temperatures ranging from 0.3 to 2.0 Torr and 200–800 °C, using an O2/SiH4 ratio of 20. Aerosol size distributions were measured using a particle beam mass spectrometer. The effects of these particles on film properties, such as stoichiometry, particle concentration, dielectric constant, and current–voltage characteristics are presented along with transmission electron microscopy images to support findings. In addition the charge retention properties of these particle-incorporated films are discussed.
3D structuring of multilayer suspended membranes including 2D photonic crystal structures
Authors: Leclercq J. L. , Rojo-Romeo P. , Seassal C. , Mouette J. , Letartre X. , Viktorovitch P.
Published: December 2003

New types of switching devices with spatial and spectral resolution combining photonic crystal (PC) and micro-opto-electro-mechanical structures (MOEMS) are proposed. They are based on multilayer suspended high refractive index III–V-based semiconductor membranes, some of these membranes being laterally structured to form a bidimensional PC. We present a method for fabricating these devices implying an original approach that combines micro- and nanotechnologies. The PC is patterned by using electron beam lithography and reactive ion etching. The MOEMS structure is an InP-air gaps multilayer realized by a combination of classical processing of epitaxially grown layers with a selective postprocess micromachining of sacrificial epilayers. Primary demonstrator acting as a wavelength selective and “switchable” coupler including a triangular lattice of PC holes on top of a InP–air gap pair-based Bragg reflector has been realized. We present the preliminary results on the technological fabrication and optical characterizations.
Picometer resolution measurement of the frequency spectrum of a periodic structure written by a MEBES electron beam pattern generator
Authors: Jourlin Y. , Tishchenko A. V. , Pedri C. , Parriaux O. , Zanzal A. , Unruh J.
Published: December 2003

A differential diffractive interferometric technique allows the high resolution retrieval of the spatial frequency profile along a long grating of supposedly constant period from the measurement of the phase of the two interference products detected by a double read head sensor upon its fly over the grating under test. The application of the technique to a 100 mm long grating written by a fifth generation MEBES e-beam writer reveals a maximum deviation of 2 pm from a nominal period of 1.070442 μm.
Influence of gate patterning on line edge roughness
Authors: Leunissen Leonardus H. A. , Jonckheere Rik , Ronse Kurt , Derksen Giljam B.
Published: December 2003

It is shown by simulation that the line edge roughness (LER) on the gates causes fluctuations on transistor performance [J. A. Croon et al., “Line edge roughness: Characterization, modeling, and impact on device behavior,” Proceedings of the IEDM, 2002; “Experimental investigation of the impact of line-edge roughness on MOSFET performance and yield” (to be published)]. Efforts are underway to investigate the influence on device performance experimentally. In this article, the transfer of the LER of the resist pattern into the poly silicon layer is investigated. For the experimental setup isolated gate lines ranging between 50–180 nm were patterned with an e-beam lithography. The resist line patterns are generated with some additional programmed LER. After the e-beam lithography step the processing was continued with etching the poly-Si, resist strip, and SiON removal. Using an offline software analysis tool for the edge detection based on SEM pictures, it was possible to determine the influence of processing on both types of roughness. The analysis shows that the LER pattern is transferred to a large extent into the poly-Si. The 3σ-value roughness is influenced only slightly. The linewidth decreases approximately 10 nm between the two measurements (after litho and etch). This result is confirmed by linewidth measurements on a CD-SEM. An additional numerical study shows that the high frequency LER (period of a few nm) is smoothed out as the etching decreases the linewidth and thus erases small bumps.
Nonlithographic approach to nanostructure fabrication using a scanned electrospinning source
Authors: Czaplewski David , Kameoka Jun , Craighead H. G.
Published: December 2003

We have used deposited polymeric nanofibers as nonlithographic templates for the fabrication of semiconductor nanostructures. We deposited oriented poly(methyl methacrylate) (PMMA) fibers, with diameters ranging from 85 to 350 nm, on the surface of various substrates using a microfabricated electrospinning source. By utilizing the small apex of a microfabricated source, a stable Taylor cone was formed as an electrostatically driven source of polymer solution directed toward the substrate. By attaching the target substrate to a rotating counter electrode, isolated and oriented PMMA fibers were deposited. We used these fibers as etch masks to pattern nanostructures in the surface of a silicon wafer. This method provides a simple, nonlithographic approach to forming nanostructures on a wide variety of substrates, such as silicon, aluminum, silicon dioxide, silicon nitride, and glass. The fiber deposition can be oriented with respect to surface features, allowing for realization of nanodevice architectures.
High power 121.6 nm radiation source
Authors: Yan Jianxun , Gupta Mool C.
Published: December 2003

A high power 121.6 nm radiation source based on dielectric barrier discharge (DBD) has been developed. Lamp parameters such as gas pressure, discharge tube diameter, electrode area and gap were optimized to maximize the 121.6 nm radiation power. Higher rf power was coupled to discharge by applying a flexible rf network, which matched the impedance between the source and discharge. The discharge was optimized by simulation using XOOPIC software to model the lamp. The simulation results were in agreement with our experimental measurements. The stable, high power (8 W) radiation source was achieved and it could be used as a reliable source for lithography and other applications.
Fabrication of SiC microelectromechanical systems using one-step dry etching
Authors: Jiang Liudi , Cheung R. , Hassan M. , Harris A. J. , Burdess J. S. , Zorman C. A. , Mehregany M.
Published: December 2003

A simple one-step inductively coupled plasma etching technique has been developed for the fabrication of SiC resonant beam structures. Straight cantilever and bridge devices have been made successfully. The structures have been actuated and resonant frequencies ranging from ∼120 kHz to ∼5 MHz have been measured. Comparison of the theoretically simulated and experimentally measured resonant frequencies shows the presence of significant tensile stress in bridge structures while the cantilever beams are free of stress. The degree of the tension in the bridge structures has been found to be independent of the bridge length.
Method for testing electronic self-assembled monolayers using a flip-chip arrangement
Authors: Spector S. J. , Wynn C. M. , Switkes M. , Kunz R. R. , Deneault S. J. , Rothschild M.
Published: December 2003

We present an approach to testing large numbers of molecular-scale devices using flip-chip structures fabricated with standard micromachining techniques. The key fabrication step is the anisotropic etching of silicon to form a knife-edge structure which is 25 nm wide at its tip. To perform the testing, two chips are placed knife edge to knife edge with one chip rotated 90°. The intersecting edges from nanometer-scale probe surfaces. The test chips include micromachined stand-offs that precisely set the gap between the knife edges and enable the use of simple test apparatus to control the positioning of the probes. Preliminary test results are presented.
Fabrication of sawtooth diffraction gratings using nanoimprint lithography
Authors: Chang Chih-Hao , Heilmann R. K. , Fleming R. C. , Carter J. , Murphy E. , Schattenburg M. L. , Bailey T. C. , Ekerdt J. G. , Frankel R. D. , Voisin R.
Published: December 2003

We report a process which integrates interference lithography, nanoimprint lithography, and anisotropic etching to fabricate replicated diffraction gratings with sawtooth profiles. This new process greatly reduces grating fabrication time and cost, while preserving the groove shape and smoothness. Relief gratings with 400 nm period inverted triangular profiles and 200 nm period gratings with 7° blaze angle were replicated from silicon masters with surface roughness of less than 1 nm. This process was developed for fabricating the off-plane blazed diffraction gratings for the NASA Constellation-X x-ray telescope.
Fabrication methods for a quantum cascade photonic crystal surface emitting laser
Authors: Tennant D. M. , Colombelli R. , Srinivasan K. , Troccoli M. , Painter O. , Gmachl C. , Capasso F. , Sergent A. M. , Sivco D. L. , Cho A. Y.
Published: December 2003

Conventional quantum cascade (QC) lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration. Surface emission in edge emitting QC lasers has therefore necessitated redirecting the waveguided laser emission using a second order grating. This paper describes the methods used to fabricate a 2D photonic crystal (PC) structure with or without a central defect superimposed on an electrically pumped QC laser structure with the goal of achieving direct surface emission. A successful systematic study of PC hole radius and spacing was performed using e-beam lithography. This PC method offers the promise of a number of interesting applications, including miniaturization and integration of QC lasers.
Large scale ultraviolet-based nanoimprint lithography
Authors: Vratzov B. , Fuchs A. , Lemme M. , Henschel W. , Kurz H.
Published: December 2003

Limits in resolution and accuracy of large scale ultraviolet (UV)-based nanoimprint lithography using rigid quartz molds and spin coated UV curable resists are presented. The resolution and precision parameters are closely followed from pattern in the mold through imprints in the resist and finally compared with structures transferred into silicon by special etching processes. Specific attention is paid to the simultaneous patterning of nano and microscale structures. The applicability for functional nanoelectronic components is demonstrated by the fabrication of an NMOS transistor based on SOI, whose channel width is reduced to 50 nm.
Correcting deviations in the shape of projected images in the electron beam block exposure column
Authors: Yamada Akio , Yabe Takayuki
Published: December 2003

The block exposure column has a mask with one hundred stencils in a deflection area. Each mask pattern projected by electron beams is reduced in size to 1/60th and imaged onto a wafer. Deviations in image shapes are dependent on deflected beam trajectories and imaging beam currents. We show techniques to measure the image shapes using reflected electron signals. Correction methods are proposed to reduce the deviations. After the corrections, the block exposure can expose images of every mask pattern of the size 5×5 μm with the image size deviation less than 11 nm, which includes 5.8 nm of an isotropic expansion and 9.6 nm of distortions.
Correction for local flare effects approximated with double Gaussian profile in ArF lithography
Authors: Osawa Morimi , Yao Teruyoshi , Aoyama Hajime , Ogino Kozo , Hoshino Hiromi , Machida Yasuhide , Asai Satoru , Arimoto Hiroshi
Published: December 2003

A method has been developed for correcting line width variations due to midrange flare with a scattering range of over a few tens of micrometers (which we call local flare). It is shown that the conventional single Gaussian point spread function (PSF) is not sufficient and that a double Gaussian point spread function is needed to explain the line width variation caused by local flare. The remaining errors after correction are discussed under the assumptions that the mask correction is linear with respect to local flare intensity and is independent of pattern layout considering the order of the local flare correction (LFC) and optical proximity correction (OPC). This simple sizing method can reduce the critical dimension (CD) variation regardless of whether LFC is done before or after OPC. The LFC performance was evaluated using actual 90-nm-node LSI data. A much faster correction time than that of OPC was achieved by introducing the area density map method. The CD variation due to local flare was reduced from 22 to 5 nm.
First dynamic exposure results from an electron projection lithography tool
Authors: Suzuki Kazuaki , Fujiwara Tomoharu , Kojima Shinichi , Hirayanagi Noriyuki , Yahiro Takehisa , Udagawa Jin , Shimizu Sumito , Yamamoto Hajime , Suzuki Motoko , Takekoshi Hidekazu , Fukui Saori , Hamashima Muneki , Ikeda Junji , Okino Teruaki , Shimizu Hiroyasu , Takahashi Shinichi , Yamada Atsushi , Umemoto Takaaki , Katagiri Satoshi , Ohkubo Yukiharu , Shimoda Toshimasa , Hirose Keiichi , Tanida Toru , Watanabe Yoichi , Kaminaga Takeshi , Kohama Yoshiaki , Mori Futoshi , Takemoto Shigeru , Yoshioka Takeshi , Hirose Hiroshi , Morita Kenji , Hada Kazunari , Kawata Shintaro , Sato Tatsuo , Sato Yu , Tokunaga Masateru , Okamoto Kazuya , Kakizaki Yukio , Miura Takaharu
Published: December 2003

Electron projection lithography (EPL) is one of the promising technologies below the 65 nm node, especially for contact hole and gate layers. Nikon is developing an EPL exposure tool as an electron beam (EB) stepper and the first generation EB stepper is now being manufactured. The voltage of 100 kV is adopted for electron beam acceleration. The subfield size is 0.25 mm×0.25 mm on the wafer and the deflection width of the electron beam is 5 mm on the wafer. The magnification of the projection optics is 1/4. A 5 mm×25 mm area from the φ200 mm reticle can be exposed by the combination of beam deflection and stage scanning motion (dynamic exposure). This area is called “a mechanical stripe.” After one mechanical stripe exposure, the reticle and wafer stages turn around and the next exposure of the adjacent mechanical stripe starts as a scan and stitch stage motion. Finally, a 20 mm×25 mm exposure field from the φ200 mm reticle is exposed. We report the first dynamic exposure in the history of EPL although only a φ100 mm reticle was used. A 5 mm×10 mm area was used as the mechanical stripe and 10 mm×10 mm exposure fields were exposed. 100 nm nested lines were resolved in the entire exposure field and stitching accuracies of 17–18 nm (3σ) are obtained. There remain systematic errors, and stitching accuracy less than 15 nm will be achieved after fine adjustment of the subfield positions. We feel the reality of EPL is now sufficiently proven.
Defect analysis in thermal nanoimprint lithography
Authors: Hirai Yoshihiko , Yoshida Satoshi , Takagi Nobuyuki
Published: December 2003

The fracture defect of the polymer in thermal nanoimprint lithography is studied based on numerical simulation and experiments. Hot pressing, cooling, and releasing steps in nanoimprint lithography are investigated in detail by a numerical simulation study. The applied pressure after the polymer deformation below the glass transition temperature will induce a stress concentration at the corner of the polymer pattern. On the other hand, the difference of the thermal expansion coefficients between the mold and the substrate causes lateral strain, and the strain is concentrated at the corner of the pattern. These strains induce defects and cause fracture defects at the base part of the pattern during the mold releasing step. To eliminate the defects, the applied pressure is released below the glass transition temperature, and slow cooling is introduced to relax the stress concentration. The result shows successful fabrication of fine patterns with a high aspect ratio.
Distributed axis electron beam technology for maskless lithography and defect inspection
Authors: Pickard D. S. , Groves T. R. , Meisburger W. D. , Crane T. , Fabian Pease R.
Published: December 2003

The limitations to the throughput of electron beam systems employing a single axis are now well known. Accordingly there is increased activity in the exploration of multiaxis systems. The approach described here features both common focusing and common deflection, thus simplifying the problem of pattern stitching. Another feature, thought by some to be a disadvantage, is that the imaging is at unity magnification. We have designed and built a test stand that presently features one axis (or beamlet) in a large homogeneous magnetic field so that the extension to multiple axes can be seen to be straightforward. With this arrangement we have demonstrated that the resolution can be at least in the 30–50 nm range, that operation at low voltage (down to 260 V) is possible, that we can operate using multiple axes, and that secondary electrons generated by one beamlet can be confined so that it is possible to use this arrangement for high-speed inspection.
Fabrication of ultrashort T gates using a PMMA/LOR/UVIII resist stack
Authors: Chen Y. , Macintyre D. S. , Cao X. , Boyd E. , Moran D. , McLelland H. , Holland M. , Stanley C. R. , Thayne I. , Thoms S.
Published: December 2003

In this article, we report a procedure for the fabrication of ultrashort T gates using high resolution electron beam lithography and a PMMA/LOR/UVIII resist stack. The intermediate lift-off resist (LOR) layer improves the quality of gate lithography, and consequently, device yields. It is unaffected by wet chemical gate recessing procedures and we report the application of the procedure to the fabrication of pseudomorphic and metamorphic high electron mobility transistors (pHEMTs) with 50 nm T gates. Fabricated pHEMTs had a gm of 600 mS/mm and ft of 200 GHz. Metamorphic HEMTs had a gm of 1500 mS/mm and ft of 350 GHz. We believe these are the fastest transistors of their kind in the world.
Thermal analysis of projection electron beam lithography using complementary mask exposures
Authors: Babin S. , Kuzmin I. , Yamashita H. , Yamabe M.
Published: December 2003

In projection electron beam lithography (EBL), most of the e-beam energy is deposited in the resist and substrate as heat. The temperature rise and its effect on critical dimension (CD) variation and placement error were studied at 100 kV projection EBL for exposure conditions used on a full scale production tool. A few writing strategies were considered. Analytic estimation of temperature rise was followed by numerical simulations using the temperature simulation software tool. Local temperature increases by a maximum of 10.7 °C was found at 5 μC/cm2 exposure dose, which corresponds to a few nanometers CD variation and can be over 10 nm depending on the resist and beam blur. Global substrate heating leads to a few tens of nanometers placement error that may suggest a need for better wafer cooling or active placement correction.
Statistical limitations of printing 50 and 80 nm contact holes by EUV lithography
Authors: Gallatin G. M. , Houle F. A. , Cobb J. L.
Published: December 2003

Nanoscale photolithography requires accurate formation of very small resist images using high energy photons and a high sensitivity resist. Historically it has been presumed that the primary technical challenges for design of a photoresist that will image with high accuracy under these conditions are shot noise effects, i.e., statistical variation of overall photon intensity from place to place on the wafer, and line-edge roughness. While these issues have been examined to various degrees, other aspects of the resist response have not received comparable attention. These include the effect of the statistics of the chemical reactions during post-expose bake and dissolution on resist images, and the effect of the fluctuations of the spatial distribution of photons within a printed feature. In order to examine the impact of all of these we have carried out a series of simulations of resist image formation as a function of dose for arrays of 50 and 80 nm contact holes printed with EUV (13.4 nm) radiation using an experimentally validated reaction-diffusion model that mimics ESCAP-class photoresists. The results show that intensity and spatial fluctuations of the light as well as simple variations in the local chemistry all affect contact size. The simulations indicate that the degree of precision contemplated for printed nanoscale features will require an extraordinary level of control over the resist chemistry and processing.
X-ray and electron-beam lithography of three-dimensional array structures for photonics
Authors: Romanato F. , Cojoc D. , Di Fabrizio E. , Galli M. , Bajoni D.
Published: December 2003

The possibility to realize three-dimensional (3D) photonic crystals and the capability to internally insert a waveguide path poses a big challenge from the fabrication point of view. We present a fabrication method for a 3D lattice with designed linear defects by multitilt x-ray exposures and electron-beam lithography. This combination of different lithographies has been developed to control the design and the realization of the linear defects inside the three-dimensional structure. This method has been applied for the fabrication of Nickel Yablonovite lattices with a lattice parameter of 1.8 μm and a total thickness of 15 μm, a value that allows us to achieve a full three-dimensional optical behavior as confirmed by variable angle reflectance measurements.
Algebraic model for the printability of nonplanar phase defects
Authors: Lam Michael , Neureuther Andy
Published: December 2003

Algebraic thin-mask models for the printability of phase defects have been extended to the case of post and void phase defects that electromagnetically behave differently than their physical height. Any two of the three model parameters [average magnitude (M), phase (φdefect), and defect area (A)] are shown to be adequate for predicting the intensity dip for isolated defects and by implication all that is likely necessary for modeling linewidth change when defects are adjacent to features. Simple models for estimating the near-field effective brightness and near-field effective phase from defect geometries are given. The image behavior through focus of isolated defects allows the extraction of all necessary parameters and allows differentiation of phase posts and voids. SPLAT generated images using the extracted parameters show excellent agreement with the images from rigorous simulations with TEMPEST. The algebraic model can thus serve as a multidirectional link between geometries, electromagnetic scattering analyses, lithographic performance, and (by extension) inspection.
Fabrication of high Q square-lattice photonic crystal microcavities
Authors: Hennessy K. , Reese C. , Badolato A. , Wang C. F. , Imamoǧlu A. , Petroff P. M. , Hu E.
Published: December 2003

This work discusses the fabrication of two-dimensional photonic crystal microcavities (PCMs) in a thin GaAs membrane. We have developed a fabrication process for square-lattice, single-hole-defect devices, a class of PCMs that is critically sensitive to fabrication accuracy, demonstrated coupling of InAs quantum dots to the cavity modes, and shown the sensitivity of the emission to the quality of the fabrication process. Reactive ion etching conditions were optimized to produce photonic crystal holes with smooth, straight sidewalls. To achieve uniform hole sizes throughout the device, we developed a method to correct the proximity effect introduced while defining the photonic crystal holes using electron-beam lithography. Resulting cavities have resonances with quality factors as high as 4000, which proves the quality of our fabrication.
Reduction of ultraviolet-radiation damage in SiO2 using pulse-time-modulated plasma and its application to charge coupled 44 device image sensor processes
Authors: Okigawa Mitsuru , Ishikawa Yasushi , Samukawa Seiji
Published: December 2003

We found that vacuum-ultra/violet (VUV) light emitted by plasmas causes dark current in charge coupled device (CCD) image sensors. When a CCD was irradiated with inductively coupled plasmas using helium (He), argon (Ar) or oxygen (O2) gas, the He plasma caused higher plasma-induced dark current in the CCD than the Ar or O2 plasmas. To investigate the influence of VUV radiation in He plasma, the plasma-induced electric current in SiO2 was measured using two types of on-wafer monitoring devices to separate the effects of He ions and He VUV radiation. One monitoring device has an aluminum filter that only allows He VUV 58.4 nm to pass through, and the other has no filter. We performed time-resolved-measurement experiments using the two types of devices in pulse-time-modulated He plasma (He-TM plasma). With the filter device, the decay of the VUV intensity after plasma off corresponded completely to the decay of the plasma-induced current curve. On the other hand, in the no-filter device, decay curve of the plasma-induced current coincided with that of the electron density in the plasma. In other words, the TM plasma does not reduce the ion-induced current, but can completely reduce the photoinduced current in SiO2. In the CCD image sensor we found that the TM plasma dramatically suppresses plasma-induced dark current. Consequently, the effect of TM plasma on the CCD dark current is due to the influence of reducing the photons in the plasma.
Etching of 4H–SiC in a NF3/CH4 inductively coupled plasma
Authors: Kim Byungwhan , Lee Suk Yong , Lee Byung Teak
Published: December 2003

In this study, SiC was etched in a NF3/CH4 inductively coupled plasma. Process parameters and experimental ranges are radio frequency (rf) source power 700–900 W, bias power 50–150 W, pressure 6–12 mTorr, and NF3 percentage 20%–100%. The etch rate and profile angle were examined as a function of process parameters. For optimization, effects of various parameter combinations were investigated by means of a 24 full factorial experiment. Main effect analysis revealed that the etch rate is the most significantly affected by NF3 percentage. In contrast, the source power effect was the most insignificant for both etch rate and profile. For the dc bias less than about 385 V, the etch rate was strongly correlated to the dc bias induced by the source power. This correlation was observed for variations in other parameters. This reveals that the dc bias played an important role in determining the etch rate. For variations in NF3 percentage, both etch rate and profile angle behaved in a conflicting way. The highest etch rate optimized by the experimental design is 450 nm/min, obtained at 700 W source power, 150 W bias power, 12 mTorr, and 100% NF3 percentage.
Monitor and control for development technology
Authors: Ito S. , Hayasaki K.
Published: December 2003

One consequence of the expected shift to low-k1 lithography is the existence of many process fluctuations that make the control of the development processes increasingly important. To control the critical dimension uniformity in the wafer, a low-impact dispensing method for developer was investigated. During the development, the dissolution status is measured as the change of the zeroth order diffracted lights at monitor pattern. This article discusses the best dispense-nozzle-scan condition of a low-impact dispense nozzle and accuracy of the monitor-control-development process that controls according to the change of the zeroth order diffracted lights.
Nanoimprint lithography process optimization for the fabrication of high electron mobility transistors
Authors: Macintyre D. S. , Chen Y. , Gourlay D. , Boyd E. , Moran D. , Cao X. , Elgaid K. , Stanley C. R. , Thayne I. , Thoms S.
Published: December 2003

We previously reported a procedure for the fabrication of high electron mobility transistors (HEMTs) using nanoimprint lithography [Y. Chen et al., Microelectron. Eng. 67,68, 189 (2003)] to produce T-shaped gates with 120 nm foot widths. The most recent batch of transistors fabricated by this original procedure had a peak transconductance of 450 mS/mm and fT of 40 GHz. In this article we describe a number of refinements to the original process with the main aims to improve performance and yield of devices. The work had two parallel strands. The first involved the development of improved silicon stamping tools to limit resist trenching effects and to produce stamping tools with smaller foot widths. T-shaped tools with 50 nm foot widths were produced from this work. The second strand of work was to optimize various aspects of transistor design and the imprint conditions used to fabricate gates which resulted in pHEMTs with a peak transconductance of 480 mS/mm and an fT of 75 Ghz.
High transparency resists for 157 nm lithography
Authors: Itani Toshiro , Ishikawa Seiichi , Irie Shigeo , Hagiwara Takuya
Published: December 2003

157 nm lithography resist based on monocyclic fluorinated polymer with a blocking group of cyclohexylcyclohexanoxymethyl (CCOM) was developed. The transmittance was more than 70% at the resist thickness of 200 nm that corresponds to the absorption coefficient of 0.80 μm−1 at a 157 nm exposure wavelength. The dry-etching rate was improved 1.75 times that of the KrF resist based on polyhydroxystyrene under the conditions of fluorocarbon-based plasma oxide etching. Furthermore, this resist has higher dissolution rate contrast compared with the polymers with the other blocking groups that we evaluated. The resolution limit of 55 nm lines and spaces pattern was obtained using a 150 nm resist thickness. We found that this monocyclic fluorinated polymer with a blocking group of CCOM simultaneously enabled higher transparency, higher dry-etching resistance, and superior imaging performance.
Effects of quantum noise and binocular summation on dose requirements in stereoradiography
Authors: Maidment Andrew D. A. , Bakic Predrag R. , Albert Michael
Published: December 2003

In the case of a quantum‐noise limited detector, signal detection theory suggests that stereoradiographic images can be acquired with one half of the per‐image dose needed for a standard radiographic projection, as information from the two stereo images can be combined. Previously, film–screen stereoradiography has been performed using the same per‐image dose as in projection radiography, i.e., doubling the total dose. In this paper, the assumption of a possible decrease in dose for stereoradiography was tested by a series of contrast‐detail experiments, using phantom images acquired over a range of exposures. The number of visible details, the effective reduction of the dose, and the effective decrease in the threshold signal‐to‐noise ratio were determined using human observers under several display and viewing conditions. These results were averaged over five observers and compared with multiple readings by a single observer and with the results of an additional observer with limited stereoscopic acuity. Experimental results show that the total dose needed to produce a stereoradiographic image pair is approximately 1.1 times the dose needed for a single projection in standard radiography, indicating that under these conditions the human visual system demonstrates almost ideal binocular summation.
Commissioning 6 MV photon beams of a stereotactic radiosurgery system for Monte Carlo treatment planning
Authors: Deng Jun , Ma C.‐M. , Hai Jenny , Nath Ravinder
Published: December 2003

The goal of this work is to implement a beam commissioning procedure to generate a multiple source model using a set of standard measurement data for possible Monte Carlo treatment planning in the clinic for a Cyberknife stereotactic radiosurgery system. The required measurement data include the central axis depth dose curve (PDD), the dose profile atof 60 mm cone at 80 cm source‐to‐surface distance (SSD), and the cone output factors for cones of 5 mm to 60 mm at 80 cm source‐to‐axis distance (SAD). The employed dual source model has the same structure as the one that has been studied in our previous work while most of the parameters of each source are extracted from the measurement data rather than the beam phase space. The energy spectra will be extracted from the central axis PDD, the fluence distributions will be deconvoluted from the dose profile atand the source distributions will be determined from the measured cone output factors. Monte Carlo dose calculations in various water phantoms have been performed to verify the beam commissioning procedure. The agreement between the measurements and the commissioning results was within 2%/1 mm for the central axis PDDs and the dose profiles at various depths when an IC‐3 chamber was used and within 2% for the cone output factors for various collimator sizes of 5 to 60 mm. Largest difference (9.5%) was observed for the 7.5 mm cone when an IC‐10 chamber was used. The large differences can be attributed to the volumetric averaging effect of the IC‐10 chamber, whose dimension is comparable to the field of the small cones. The overall agreement between the measurements and the commissioning results is clinically acceptable, which implies that our commissioning tool is adequate for clinical applications of Monte Carlo dose calculations for the Cyberknife stereotactic radiosurgery system.
Tomosynthesis‐based localization of radioactive seeds in prostate brachytherapy
Authors: Tutar Ismail B. , Managuli Ravi , Shamdasani Vijay , Cho Paul S. , Pathak Sayan D. , Kim Yongmin
Published: December 2003

Accurately assessing the quality of prostate brachytherapy intraoperatively would be valuable for improved clinical outcome by ensuring the delivery of a prescribed tumoricidal radiation dose to the entire prostate gland. One necessary step towards this goal is the robust and rapid localization of implanted seeds. Several methods have been developed to locate seeds from x‐ray projection images, but they fail to detect completely‐overlapping seeds, thus necessitating manual intervention. To overcome this limitation, we have developed a new method where (1) a three‐dimensional volume is reconstructed from x‐ray projection images using a brachytherapy‐specific tomosynthesis reconstruction algorithm with built‐in blur compensation and (2) the seeds are located in this reconstructed volume. In contrast to other projection‐based methods, our method can detect completely overlapping seeds. Our simulation results indicate that we can locate all implanted seeds in the prostate using a tomosynthesis angle of 30° and seven projection images. The mean localization error is 1.27 mm for a case with 100 seeds. We have also tested our method using a prostate phantom with 61 implanted seeds and succeeded in locating all seeds automatically. We believe this new method can be useful for the intraoperative quality assessment of prostate brachytherapy in the future.
Adaptive temporal resolution optimization in helical cardiac cone beam CT reconstruction
Authors: Manzke R. , Grass M. , Nielsen T. , Shechter G. , Hawkes D.
Published: December 2003

Cone beam computed tomography scanners in combination with heart rate adaptive reconstruction schemes have the potential to enable cardiac volumetric computed tomography (CT) imaging for a larger number of patients and applications. In this publication, an adaptive scheme for the automatic and patient‐specific reconstruction optimization is introduced to improve the temporal resolution and image quality. The optimization method permits the automatic determination of the required amount of gated helical cone beam projection data for the reconstruction volume. It furthermore allows one to optimize subvolume reconstruction yielding an increased temporal resolution. In addition, methods for the assessment of the temporal resolution are given which enable a quantitative documentation of the reconstruction improvements. Results are presented for patient data sets acquired in low pitch helical mode using a 16‐slice cone beam CT system with parallel ECG recording.
Computer‐aided diagnosis in high resolution CT of the lungs
Authors: Sluimer Ingrid C. , van Waes Paul F. , Viergever Max A. , van Ginneken Bram
Published: December 2003

A computer‐aided diagnosis (CAD) system is presented to automatically distinguish normal from abnormal tissue in high‐resolution CT chest scans acquired during daily clinical practice. From high‐resolution computed tomography scans of 116 patients, 657 regions of interest are extracted that are to be classified as displaying either normal or abnormal lung tissue. A principled texture analysis approach is used, extracting features to describe local image structure by means of a multi‐scale filter bank. The use of various classifiers and feature subsets is compared and results are evaluated with ROC analysis. Performance of the system is shown to approach that of two expert radiologists in diagnosing the local regions of interest, with an area under the ROC curve of 0.862 for the CAD scheme versus 0.877 and 0.893 for the radiologists.
Surface and build‐up region dosimetry for obliquely incident intensity modulated radiotherapy 6 MV x rays
Authors: Dogan Nesrin , Glasgow Glenn P.
Published: December 2003

This study investigates the surface dose and build‐up region dosimetry for oblique IMRT beams. The dependence of surface and build‐up region doses of (perpendicular incidence) and (oblique incidence) IMRT fields on field size was measured and compared with open field dosimetry. Measurements were performed using a parallel‐plate chamber and KODAK EDR2 films in a polystyrene phantom for a and a 6 MV photon beam at depths of 0 mm (surface) through Data were normalized to the value of each field. Four intensity modulated delivery patterns were created and delivered using step‐and‐shoot IMRT: (1) six static strips (2) 12 static strips (3) intensity modulated beam patterns created by using the inverse planning optimization software for and (4) for field sizes. The percent depth doses (PDDs) of beam at the surface and 5 mm were lower by 8.8% and 1.6%, respectively, compared to the open field. The PDDs of beam at the surface and 5 mm were lower by 6.7% and 2.4%, respectively, compared to the open field. This study showed that IMRT itself is not contributing to greater skin doses.
Application of the spirometer in respiratory gated radiotherapy
Authors: Zhang Tiezhi , Keller Harry , O'Brien Matthew J. , Mackie Thomas R. , Paliwal Bhudatt
Published: December 2003

The signal from a spirometer is directly correlated with respiratory motion and is ideal for target respiratory motion tracking. However, its susceptibility to signal drift deters its application in radiotherapy. In this work, a few approaches are investigated to control spirometer signal drift for a Bernoulli‐type spirometer. A method is presented for rapid daily calibration of the spirometer to obtain a flow sensitivity function. Daily calibration assures accurate airflow measurement and also reduces signal drift. Dynamic baseline adjustment further controls the signal drift. The accuracy of these techniques was studied and it was found that the spirometer is able to provide a long‐term drift‐free breathing signal. The tracking error is comprised of two components: calibration error and stochastic signal baseline variation error. The calibration error is very small (1% of 3 l) and therefore negligible. The stochastic baseline variation error can be as large as 20% of the normal breathing amplitude. In view of these uncertainties, the applications of spirometers in treatment techniques that rely on breathing monitoring are discussed. Spirometer‐based monitoring is noted most suitable for deep inspiration breath‐hold but less important for free breathing gating techniques.