bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning thermal lithography: Maskless, submicron thermochemical patterning of photoresist by ultracompliant probes
Authors: Basu Amar S. , McNamara Shamus , Gianchandani Yogesh B.
Published: December 2004

This article introduces a scanning probe lithography technique in which ultracompliant thermal probes are used in the selective thermochemical patterning of commercially available photoresist. The micromachined single-probe and multiprobe arrays include a thin-film metal resistive heater and sensor sandwiched between two layers of polyimide. The low spring constant (<0.1N∕m) and high thermal isolation provided by the polyimide shank is suitable for contact mode scanning across soft resists without force feedback control. The probes provide what is effectively a spatially localized postexposure bake that crosslinks the photoresist in the desired pattern, rendering it insoluble in developer. For 450-nm–1400-nm-thick AZ5214E (Clariant Corp.), line and dot features with sizes of 450–1800nm can be printed using probe powers of 13.5–18mW, and durations of 1–60s per pixel. Variation of feature sizes with process parameters is described.
Assessment of image placement errors induced in electron projection lithography masks by chucking
Authors: Chang J. , Engelstad R. L. , Lovell E. G. , Trybula W. J. , Wood O. R.
Published: December 2004

Electron projection lithography (EPL) is under active development, with potential applications at the sub 65nm nodes. In order to meet the stringent error budgets in this regime, image placement (IP) errors induced by chucking the mask during e-beam patterning, metrology, and exposure must be characterized and minimized. The focus of this study is to assess the distortions induced in200-mm-diam EPL stencil masks by chucking during e-beam patterning and EPL exposure. High-throughput test masks (with 3.39mm square membrane windows) were evaluated, to assess IP errors throughout a typical mask process flow. Finite element structural models were developed to simulate the response of the test mask during each processing step. Finally, the results of the analysis were used to identify and characterize the sources of IP errors.
Nanometer gap measurement and verification via the chirped-Talbot effect
Authors: Moon Euclid E. , Chen Lynn , Everett Patrick N. , Mondol Mark K. , Smith Henry I.
Published: December 2004

We describe a noncontact, optical method of measuring, with nanometer-level sensitivity, the gap between two planar objects in close proximity, such as a substrate and either a proximity-lithography mask or an imprint template. Interference fringes from a chirped-checkerboard mark on one object are observed using a nonexposing wavelength with long-working-distance, oblique-incidence microscopes. The gap is determined from the spatial frequency and phase of the fringes. We verify the gap measurement using a variation of the Talbot effect with the chirped-checkerboard mark. The two forms of gap measurement are complementary since one is suited to measuring and setting gap prior to exposure, and the other is ideal for confirmation of the gap that existed during exposure.
Assessment of lithographic process variation effects in InGaAsP annular Bragg resonator lasers
Authors: Green William M. J. , Scheuer Jacob , DeRose Guy A. , Yariv Amnon , Scherer Axel
Published: December 2004

Optical microresonators based on an annular geometry of radial Bragg reflectors have been designed and fabricated by electron-beam lithography, reactive ion etching, and an epitaxial transfer process. Unlike conventional ring resonators that are based on total internal reflection of light, the annular structure described here is designed to support optical modes with very small azimuthal propagation coefficient and correspondingly large free spectral range. The effect of lithographic process variation upon device performance is studied. Laser emission wavelength and threshold optical pump power are found to vary between similar devices given different electron doses during electron-beam lithography. As the resonance wavelength and quality factor of these resonators are very sensitive to environmental changes, these resonators make ideal active light sources that can be integrated into large arrays for gas and liquid sensing applications and are easily interrogated.
Variable cell projection as an advance in electron-beam cell projection system
Authors: Yamada Akio , Yabe Takayuki
Published: December 2004

As an advance in the electron-beam cell projection system, we have developed a deflection control and correction unit of the variable cell projection (VCP) system, which can increase the variety of projected images through a block of patterns on a CP mask. We estimate the extent of the minimum spacing between two patterns distinguished by partial illumination to be 58 nm on a wafer, which is due to the beam blur of 28 nm and the illuminating beam edge rotation of 6 mrad relative to the CP mask patterns. Exposure results show that the VCP can actually distinguish the patterns separated by 80 nm on a wafer. We also show that the VCP can improve the uniformity of linewidths of exposed patterns by about 5 nm compared with the simple VSB method.
Experimental and simulation comparison of electron-beam proximity correction
Authors: Leunissen L. H. A. , Jonckheere R. , Hofmann U. , Ünal N. , Kalus C.
Published: December 2004

In electron-beam lithography, electron scattering in the resist, and underlying substrate limits the control over feature sizes [M. Parikh, J. Vac. Sci. Technol. 19, 1275 (1981)]. To correct for this effect, one applies the so-called “proximity correction” that adjusts the beam dose of each individual feature. The algorithms that are commonly used to calculate this correction model the electron scattering as a double-Gaussian function. However, a point-spread function (PSF) describes the scattering process more accurately. Therefore, we have investigated whether the use of the PSF in the proximity correction algorithm leads to an increase in feature size control; as compared to the double-Gaussian PSF. In order to compare the two PSFs directly, we have performed a proximity correction on a pattern of contact holes, using each of the approximations. Our measurements show that the algorithm using the PSF performs a substantially better proximity correction, leading to a more accurate control over the contact hole sizes. Moreover, we have developed a method to assess the proximity correction’s success using the SELID [M. Bohn et al., Proc. SPIE 5256, 695 (2003)] simulation program. This strongly reduces the need for costly and time-consuming experiments.
Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. V. Effects of C∕F ratio in plasma gases
Authors: Min Jae-Ho , Lee Gyeo-Re , Lee Jin-Kwan , Heup Moon Sang
Published: December 2004

The effects of C∕F ratio in fluorocarbon gases, used in the plasma etching of SiO2, on the properties of sidewalls of etched trenches, as affected particularly by the redeposition of particles emitted from the bottom, were investigated using three different plasma gases, CF4, CHF3, and C4F8. The use of a Faraday cage and step-shaped substrates permitted an effective analysis of the chemical and physical properties of the sidewall surface in a scale larger than that for micro-patterns. The step-shaped substrates consisted of one bottom and two sidewalls: One of the sidewalls was affected by bottom-emitted particles, designated as sidewall (A), and the other was unaffected by the particles, designated as sidewall (B). Comparison of the surface properties of the two sidewalls allowed us to observe the redeposition effect, independently from other complicated phenomena involved in the plasma etching. For all cases of CF4, CHF3, and C4F8, the rate of film deposition on sidewall (A) was larger than that on sidewall (B), which indicated that the formation of a passivation layer on the sidewall was accelerated by the redeposition of bottom-emitted particles. The contribution of redeposition to the formation of a sidewall passivation layer rapidly decreased with an increase in C∕F ratio, in the order CF4>CHF3>C4F8 approaching zero for C4F8. The change in the surface roughness of sidewall (A) with C∕F ratio was correlated with the contribution of redeposition particles, instead of the thickness and carbon content of the polymer film formed on the sidewall. The chemical composition of carbon-containing polymer layer of sidewall (A) and the extent of chemical etching of the SiO2 layer beneath the polymer layer were distinctly different for the three plasma gases.
Fabrication and evaluation of highly manufacturable nanoscale flow-through parallel electrode structures
Authors: Nam Wook Jun , Fonash Stephen J. , Cuiffi Joseph D.
Published: December 2004

A unique nanoscale gap configuration having parallel-plate electrodes and an integrated flow structure was designed, developed, and fabricated using micro- and nanomachining techniques. This structure is highly manufacturable and shows an excellent fabrication yield (more than 90%). Applications data are presented for 30 and 50nm gap spacing structures used to monitor the formation of a 6-mercapto-1-hexanol self-assembled monolayer on the device electrode surfaces. The structure was found to be very robust in a high, inter-electrode electric-field environment (∼6×106V∕cm in air).
High fidelity blazed grating replication using nanoimprint lithography
Authors: Chang Chih-Hao , Montoya J. C. , Akilian M. , Lapsa A. , Heilmann R. K. , Schattenburg M. L. , Li M. , Flanagan K. A. , Rasmussen A. P. , Seely J. F. , Laming J. M. , Kjornrattanawanich B. , Goray L. I.
Published: December 2004

We report progress in using nanoimprint lithography to fabricate high fidelity blazed diffraction gratings. Anisotropically etched silicon gratings with 200nm period and 7.5° blaze angle were successfully replicated onto 100mm diameter wafers with subnanometer roughness and excellent profile conformity. Out-of-plane distortion induced by residual stress from polymer films was also analyzed and found to be extremely low. The replicated blazed gratings were tested and demonstrated high x-ray diffraction efficiencies. This process was developed for fabricating blazed diffraction gratings for the NASA Constellation-X x-ray telescope.
Optical inspection of next generation lithography masks
Authors: Pettibone Don , Stokowski Stan
Published: December 2004

For the last 5years a joint venture has pursued a research program studying and enhancing the ability of optical inspection tools to meet the inspection needs of extreme ultraviolet (EUV) and other next generation lithographies (NGLs). In this article we present a survey of results we have obtained for patterned inspection of NGL masks. The NGL technologies that we have studied include two electron projection lithographies, EUV, and step and flash imprint lithography (SFIL). We discuss the sensitivity of the inspection tools and mask design factors that affect tool sensitivity. In contrast to conventional photomask inspection, which primarily utilizes transmitted light for inspection, almost all NGL mask inspections are performed in reflected light. Much of the work has been directed towards EUV mask inspection and how to optimize the mask to facilitate inspection. Early EUV masks had an optical contrast of 40% or lower. Our partners have succeeded in making high contrast EUV masks ranging in contrast from 70% to 98%. Die to die and die to database inspections, at a wavelength of 257nm, of EUV masks have been achieved with a sensitivity that is comparable to what can be achieved with conventional photomasks, with a minimum detected defect size of 80nm square defects. We have inspected scattering with angular limitation projection electron-beam masks successfully. Electron-beam stencil masks, such as that used in projection reduction exposure with variable axis immersion lenses, pose a problem in that their high aspect ratio of mask thickness to minimum feature width results in low resolution transmission images. Reflected light images provide high-resolution images suitable for inspection, but will not be sensitive to defects below the inspection surface. We have run inspections on SFIL masks in die to die, reflected light in an effort to provide information concerning possible cumulative damage due to imprinting and to provide feedback on defect densities, types and sizes to improve the masks. Our defect sensitivity on SFIL masks is approximately 100nm, though we cannot run at the highest sensitivity due to large numbers of nonprogrammed defects. We have also used an inspection system, at a wavelength of 364nm, to inspect both unpatterned EUV substrates (no coatings) and blanks (with EUV multilayer coatings), and demonstrated a sensitivity of approximately 100nm to polystyrene latex spheres. This information has helped drive down the defect densities on EUV blanks and substrates by some three orders of magnitude. Extensions of conventional optical lithography have pushed out the introduction of NGL technology to the 33nm or possibly the 22nm node. Mask inspection technology will need substantial improvements in resolution to meet the NGL inspection requirements below the 45nm node.
Piezoelectric projective displays
Authors: Park Bong Mo , Ha Sang Woon , Lee Gil Sik , Wong Hoi-Yee , Feldman Martin , Yun Sang Kyeong
Published: December 2004

We report the fabrication of monolithic phase grating modulators in single crystal 0.67PMN-0.33PT. Diffraction was observed for a period (b) to thickness (T) ratio >2.5. Very strong diffraction was obtained at a period of 250μm, electrode width of 100μm, and a substrate thickness of 50μm. Under these conditions, the overall diffraction efficiency into the first orders at optimal voltage applied to the modulator was about 57%. Modulators containing linear arrays of elements are attractive alternatives to acousto-optic modulators, and rectangular arrays may be used for image projection.
Scanning-spatial-phase alignment for zone-plate-array lithography
Authors: Menon Rajesh , Moon Euclid E. , Mondol Mark K. , Castaño Fernando J. , Smith Henry I.
Published: December 2004

In this article, we describe a technique for level-to-level alignment in zone-plate-array lithography that does not require an external microscope, yet provides overlay superior to conventional microscopes.
High reflectance of reflective-type attenuated-phase-shifting masks for extreme ultraviolet lithography with high inspection contrast in deep ultraviolet regimes
Authors: Chen H. L. , Cheng H. C. , Ko T. S. , Ko F. H. , Chu T. C.
Published: December 2004

Phase-shifting masks are a vital resolution enhance technique that will be used in extreme ultraviolet (EUV) lithography beyond the 20nm node. In this article, we demonstrate a structure for a reflective-type attenuated phase-shifting mask, which is based on a Fabry–Perot structure with common materials in EUV masks. The mask structure not only performs 180° phase shift with high reflectance at EUV wavelength, but also has high inspection contrast at deep ultraviolet (DUV) wavelength. The top layer of mask structures exhibits good conductivity, which can alleviate the charging effect during electron-beam patterning. The reflectance ratio of the absorber stack could be tuned from 32.6% (TaN∕SiO2∕Mo) to 4.4% (TaN∕SiO2∕TaN) by choosing different bottom layers and thickness. The inspection contrast could be raised to 99% with large thickness-control tolerance.
Dependence of acid generation efficiency on the protection ratio of hydroxyl groups in chemically amplified electron beam, x-ray and EUV resists
Authors: Yamamoto Hiroki , Kozawa Takahiro , Nakano Atsuro , Okamoto Kazumasa , Tagawa Seiichi , Ando Tomoyuki , Sato Mitsuru , Komano Hiroji
Published: December 2004

In chemically amplified resists for ionizing radiation such as an electron beam, protons of acids come from not acid generators but base polymers. This means that the modification of base polymers has a great effect on the acid generation efficiency. The relation between relative acid yield and protecting groups of poly(4-hydroxystyrene) was examined. The selection of protecting groups is important for the acid generation efficiency and the acid distribution uniformity.
Fluid refractive index measurements using rough surface and prism minimum deviation techniques
Authors: Synowicki R. A. , Pribil Greg K. , Cooney Gerry , Herzinger Craig M. , Green Steven E. , French Roger H. , Yang Min K. , Burnett John H. , Kaplan Simon
Published: December 2004

Two techniques are presented for measuring the refractive index of fluids. The first is a reflective technique where liquid is applied to a rough surface to hold the liquid during measurement. Ellipsometric psi and delta data are acquired and analyzed to determine the fluid refractive index. The second technique is refractive and uses a hollow prism cell to contain the liquid. The fluid index is then determined using the prism minimum deviation technique. Both techniques have been applied over a very wide spectral range from the vacuum ultraviolet to the infrared and have been implemented on a research spectroscopic ellipsometer system (VUV-VASE®) with continuously variable angle of incidence. The refractive index of several candidate immersion fluids for 157 and 193nm immersion lithography are reported over the spectral range from 156to1700nm in a nitrogen-purged environment. The advantages and disadvantages of both techniques are discussed. Results were checked against values measured on very accurate prism minimum deviation equipment at NIST, and agreement with NIST has been found to be good on all fluids measured.
Near-field optical lithography using a planar silver lens
Authors: Melville David O. S. , Blaikie Richard J.
Published: December 2004

A variation of proximity lithography has been proposed using a planar metallic film in a near-field configuration, where metal acts as a near-field “superlens.” We report here on experimental evidence of such optical lithography with a planar silver lens. Silver layers of varying thickness (85–120nm) placed at specific distances (40–60nm) below a patterned mask were able to image the mask’s features onto a photoresist located after a gap (26–60nm) below the silver. The entire structure was exposed from above with a mercury lamp. Feature sizes as small as 250nm (at a 500nm period) were imaged, demonstrating the lensing ability of the planar silver slab.
Wavelength tuning of an antenna-coupled infrared microbolometer
Authors: Gritz Michael A. , Metzler Meredith , Malocha Donald , Abdel-Rahman Mohamed , Monacelli Brian , Zummo Guy , Boreman Glenn D.
Published: December 2004

Wavelength tuning is demonstrated in an antenna-coupled infrared microbolometer. With a 300-mV control voltage, we observed a tuning range of 0.15 μm near 10 μm. A metal-oxide-semiconductor capacitor underneath the antenna arms causes the shift of resonance wavelength with applied voltage. We develop a device model that agrees with measured results.
Advanced nanoscale material processing with focused ion beams
Authors: Lugstein A. , Basnar B. , Smoliner J. , Bertagnolli E. , Weil M.
Published: December 2004

We present an approach for the generation of metallic Ga dots and In nano-crystallites which, in contrast to conventional bottom-up or top-down processes, is based on a subtractive self-organization process relying on material decomposition induced by focused ion beam exposure. The diameters of the Ga dots range from 120to850nm with an aspect ratio of about 0.4 at a dot density of up to 7×107∕cm2. Two-dimensional ordered arrays of freestanding dots were fabricated by a site control technique relying on prepatterned holes and an irradiation mediated migration and agglomeration. By the analogous technique we generated indium nanocrystallites on the (100) InAs surface with sizes ranging from about 50nm to a few microns obviously due to a preferential loss of arsenic atoms during Ga+ focused ion beam irradiation. The influence of the ion dose, the beam energy, and the dose rate on the surface evolution was investigated by atomic force microscopy, scanning electron microscopy, Auger electron spectroscopy, and x-ray diffraction measurements.
Fabrication of ordered array of tungsten nanoparticles on anodic porous alumina by electron-beam-induced selective deposition
Authors: Xie Guoqiang , Song Minghui , Mitsuishi Kazutaka , Furuya Kazuo
Published: December 2004

Using an ordered nanopore array of anodic porous alumina membrane obtained by a two-step anodization process, ordered array of tungsten nanoparticles was fabricated using an electron-beam-induced selective deposition process. The nanoparticles were preferentially formed in the pores in the electron-beam irradiated area. The microstructure and composition of as-deposited nanoparticles were characterized. The as-deposited nanoparticles contain many nanocrystallites. The nanocrystallites were identified to be the equilibrium phase of bcc structure metal W at room temperature.
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mechanically buttressed high aspect ratio zone plates: Fabrication and performance
Authors: Olynick Deirdre L. , Harteneck Bruce D. , Veklerov Eugene , Tendulkar Mihir , Liddle J. Alexander , David Kilcoyne A. L. , Tyliszczak Tolek
Published: December 2004

High performance zone plates are critical for advancing the state-of-the-art in x-ray microscopy, both in terms of spatial and energy resolution. Improved resolution, increased energy bandwidth, and enhanced efficiency can be achieved through the fabrication of smaller, higher aspect ratio outer zones. Using electron beam lithography, we have fabricated and obtained initial performance data from a 25nm outer zone width zone plate, with a 7:1 aspect ratio, using a hydrogen silsesquioxane (HSQ)/cross-linked polymer bilayer process. We investigated the effectiveness of buttresses, i.e., mechanical supports perpendicular to the zones, on our ability to achieve higher aspect ratios which conventionally would be unreachable due to resist collapse. Optimum buttress spacing is affected by film thickness, linewidth, collapse mechanisms, and resist modulus. For 25nm zones, etched into 150nm cross-linked polymer (AZPN114), buttress spacings of approximately two times the resist thickness or ten times the zone width are sufficient to prevent collapse during plating. We find that high aspect ratio features not only have to be able to withstand collapse during liquid immersion, but also during dry etching processes. In addition, we show that a 50% feature bias and longer development times (8min in 1% TMAH based solutions) allow smaller dense feature sizes by eliminating resist webbing frequently observed in electron-beam imaging of HSQ.
Repair of step and flash imprint lithography templates
Authors: Dauksher W. J. , Nordquist K. J. , Le N. V. , Gehoski K. A. , Mancini D. P. , Resnick D. J. , Casoose L. , Bozak R. , White R. , Csuy J. , Lee D.
Published: December 2004

In order for step and flash imprint lithography (S-FIL) to become a truly viable manufacturing technology, infrastructure including template repair must be commercially available. Extensive template repair studies were undertaken using RAVE’s nm 650 tool which is predicated on an AFM platform and relies upon a nanomachining technique for opaque defect removal. On S-FIL templates, the standard deviation for depth repairs in quartz from the target depth was found to be 3.1nm (1σ). At 21.5nm (1σ), the analogous spread in edge placement data for opaque line protrusions was somewhat higher. Trench cuts through lines were successfully created with a minimum size of about 55nm. The effectiveness of the repairs on the template was verified by imprinting experiments. The range of depth offsets studied (−15to+15nm) had no bearing on the imprinting process. The edge placement on wafers virtually mirrored the edge placement of the repaired templates. Connections between features which were created by trench cuts on the template were filled with the imprint monomer and measured slightly larger than the minimum gap size. Finally, imprinted wafers were used to pattern transfer features into 100nm of oxide.
Phase measurement of reflection of EUV multilayer mirror using EUV standing waves
Authors: Miyake Akira , Amemiya Mitsuaki , Masaki Fumitaro , Watanabe Yutaka
Published: December 2004

Projection optics of an EUV lithography system consists of multilayer mirrors. Phase of the incident beam is shifted on reflection at the multilayer mirror [Y. Watanabe et al., Jpn. J. Appl. Phys. 30, 3053 (1991)]. If the phase shift at reflection of a multilayer is not well controlled, it becomes the cause of wavefront aberration. The phase shift depends on the incident angle and the wavelength of the beam. The phase shift is also dependent on the structure of the multilayer. Certain kinds of structural change cause non-negligible variation of the phase shift with very little change of wavelength dependency of reflectivity. Therefore, not only reflectivity measurement but also measurement of phase shift is essential to manufacture multilayer mirrors for projection optics. X-ray standing wave technique has been used to characterize multilayer structure [B. Lai et al., Nucl. Instrum. Methods Phys. Res. A 266, 684 (1988); T. Kawamura and H. Takenaka, J. Appl. Phys. 75, 3806 (1996)]. Intensity of electric field, which generates photoelectrons, near a multilayer surface depends not only on the intensity of incident beam but also on the phase shift and the reflectivity. EUV reflectivity and photo-yield of Mo∕Si multilayer samples were measured using a laser produced plasma source (LPP) based EUV reflectometer [A. Miyake, Proc. SPIE 5037, 647 (2003)]. Thickness ratio Γ is the ratio of the thickness of molybdenum layer to the multilayer period. Γ of each sample is changed by 2% step. According to a simulation, it corresponds to variation of phase shift by 0.02πstep, in other words, variation of wavefront by 10mλstep. Measured wavelength dependencies of photo-yield for each sample are clearly separated. From the results of this experiment, it is shown that phase shift on multilayer reflection can be detected at a resolution of 0.02πrad.
Gas delivery and virtual process chamber concept for gas-assisted material processing in a focused ion beam system
Authors: Ray Valery
Published: December 2004

Gas-assisted etching and material deposition using gaseous precursors have become a critical part of integrated circuit modification and other applications of focused ion beam (FIB) systems. Widely used methods of gas injection in FIB systems are either needle-type or shroud-type gas delivery nozzles. Each of these methods of gas delivery has significant drawbacks. Release of the gas from the needle-type nozzles is detrimental for the vacuum level in the main chamber of the system, as the gas quickly dissipates from the process area. Insertion of shroud concentrators into the primary ion beam path and the path of secondary electrons leads to a significant decline in the signal-to-noise ratio of the FIB image. Proposed “CUPOLA” geometry of the gas delivery nozzle could allow one to effectively concentrate process gas in the area of interest, as is currently done by shroud concentrators, and, according to secondary-electron trajectory simulations, would significantly improve the signal level of the secondary-electron image, as compared to the shroud concentrators.
Astigmatism measurement by lateral shearing interferometer
Authors: Liu Zhiqiang , Sugisaki Kasumi , Ishii Mikihiko , Zhu Yucong , Saito Jun , Suzuki Akiyosi , Hasegawa Masanobu , Murakami Katsuhiko
Published: December 2004

In the lateral shearing interferometer for EUVL PO at-wavelength measurement, a grating is used to separate and shear the test wavefront. Normally, the astigmatism component of the test wavefront is difficult to be measured from the phase distribution tilt because the grating position influences it also. We found the grating position influences the tilt component of the interferogram phase distribution along the shear direction only. A part of the astigmatism can be measured from the tilt component perpendicular to the shear direction. To measure the other part of astigmatism, we perform a measurement with the shear direction in 45°. From the tilt component of the phase distribution in 135°, the other part of the astigmatism can be measured. By these two measurements, the whole astigmatism can be measured. We analyzed the measurement errors and showed the conditions for high accuracy astigmatism measurement.
Impacts of 30-nm-thick resist on improving resolution performance of low-energy electron beam lithography
Authors: Yoshizawa Masaki , Moriya Shigeru , Oguni Kumiko , Nakano Hiroyuki , Omori Shinji , Kitagawa Tetsuya , Kotera Masatoshi , Niu Hirohisa
Published: December 2004

Exploring the resolution performance of various electron beam lithography with the acceleration voltage of 2–100kV showed that line edge roughness (LER) and resolution limit of resist patterns was in linear relation with blur of latent image profile. Reducing resist thickness is effective in decreasing the blur of low-energy electron-beam proximity projection lithography (LEEPL) because 47% of the blur is due to scattering of 2keV electrons in 70-nm-thick resist film. The impact of thinning the resist thickness on the LER and the exposure latitude in LEEPL was investigated by simulation and experiment. A Monte Carlo simulation shows that the LER of a 100-nm-width space pattern decreases to 5.5 from 10.4nm with reducing the resist thickness to 20 from 70nm. Exposing the photosensitive polyorganosilazane resists (Clariant (Japan) K.K.) by LEEPL-3000 underpinned that latent image quality was improved by thinning the resist. The exposure latitude of 80-nm-diameter dense contact holes increased to 25 from 16% with reducing the resist thickness to 30 from 50nm. It is necessary for taking an advantage of the improved latent image of the 30-nm-thick resist in resolving the 90-nm-pitch patterns to mitigate the edge roughness probably caused by the properties of a highly interfacial resist.
Optical study of spin injection dynamics in InGaN∕GaN quantum wells with GaMnN injection layers
Authors: Buyanova I. A. , Bergman J. P. , Chen W. M. , Thaler G. , Frazier R. , Abernathy C. R. , Pearton S. J. , Kim Jihyun , Ren F. , Kyrychenko F. V. , Stanton C. J. , Pan C.-C. , Chen G.-T. , Chyi J.-I. , Zavada J. M.
Published: December 2004

The spin injection dynamics of GaMnN∕InGaN multiquantum well (MQW) light emitting diodes (LEDs) grown by molecular beam epitaxy were examined using picosecond-transient and circularly polarized photoluminescence (PL) measurements. Even with the presence of a room temperature ferromagnetic GaMnN spin injector, the LEDs are shown to exhibit very low efficiency of spin injection. Based on resonant optical orientation spectroscopy, the spin loss in the structures is shown to be largely due to fast spin relaxation within the InGaN MQW, which itself destroys any spin polarization generated by optical spin orientation or electrical spin injection. Typical photoluminescence decay times were 20–40ns in both commercial GaN MQW LEDs with emission wavelengths between 420–470nm and in the GaMnN∕InGaN multi-quantum well MQW LEDs. In the wurtzite InGaN∕GaN system, biaxial strain at the interfaces give rise to large piezoelectric fields directed along the growth axis. This built-in piezofield breaks the reflection symmetry of confining potential leading to the presence of a large Rashba term in the conduction band Hamiltonian which is responsible for the short spin relaxation times.
Microstructure and resistivity characterization of CuAu I superlattice formed in Cu∕Au thin films
Authors: Zhang W. , Brongersma S. H. , Richard O. , Brijs B. , Palmans R. , Froyen L. , Maex K.
Published: December 2004

Stoichiometric AuCu alloy has been well studied in bulk form, but the resistivity of very thin films has rarely been reported. In fact, thin copper and gold films show a strong deviation from bulk resistivity due to the size effect, which motivates us to study CuAu I thin films and understand the properties of nanoscale metallization in more details. Very thin films of ordered CuAu I phase were formed by interdiffusion of Cu∕Au bilayers, in which the intermetallic phase formation was characterized by glancing angle x-ray diffraction and transmission electron microscopy. It was found that Kirkendall voids were created during the interdiffusion. Also, as it turned out, the resistivity of such thin CuAu I films changed only slightly with decreasing film thickness, which was different from pure copper and gold thin films.
Damascene Cu electrodeposition on metal organic chemical vapor deposition-grown Ru thin film barrier
Authors: Cho Sung Ki , Kim Soo-Kil , Han Hee , Kim Jae Jeong , Oh Seung Mo
Published: December 2004

Ru thin film grown by metal organic chemical vapor deposition (MOCVD) was applied in this study as a substrate for superconformal Cu electrodeposition as well as a Cu diffusion barrier at a Cu∕Ru∕SiO2∕Si multilayer system for microelectronics. Bis (ethyl-π-cyclopentadienyl) Ru-based MOCVD Ru thin film had a roughness of about 12% of its thickness and well-developed textures with high purity. It also showed good step coverage in damascene trench structure. Pd catalyst-mediated Cu electrodeposition on Ru surface accomplished formation of continuous Cu film. For gap filling in single damascene structure, bumps indicative of bottom-up acceleration and superfilling were observed during two-step Cu electrodeposition on Ru substrate which involved seeding and filling with conventional three additives system. 30nm-thick Ru film effectively worked as a barrier for interdiffusion and∕or reaction between layers even after annealing at 800°C for 30min. With the exception of slight agglomeration of Cu at elevated temperature, no silicidation or AES-profile broadening was observed in a Cu∕Ru∕SiO2∕Si system.
Evaluation of atomic exchange in GaAs∕GaP interfaces by tetragonal distortion measurements
Authors: Ferrer J. C. , Peiró F. , Cornet A. , Armelles G.
Published: December 2004

The quantification of interdiffusion processes in the interfaces of GaAs quantum wells, with thickness ranging from one to six atomic layers, grown by atomic layer molecular beam epitaxy in a GaP matrix is addressed. The atomic row positions have been determined from high resolution transmission electron microscopy images. The distortion of distances and angles between neighboring rows with respect to those expected in the strained structure has been related to changes in chemical composition. This method appears more efficient for this system than other methods based on the analysis of the atomic row contrast. Results show that interdiffusion occurred at the GaAs∕GaP interfaces. The arsenic profiles in the quantum well suggest that the main contribution of interdiffusion comes from atomic exchange. The experimental profiles have been fitted to a simple model of segregation giving segregation coefficients around 0.45. The results are compared to simulations based on Raman measurements performed on the same samples.
Strain and electrical characterization of metal-oxide-semiconductor field-effect transistor fabricated on mechanically and thermally transferred silicon on insulator films
Authors: Lu F. , Bickford J. , Novotny C. , Yu P. K. L. , Lau S. S. , Henttinen K. , Suni T. , Suni I.
Published: December 2004

Silicon-on-insulator (SOI) substrates were created from two methods of ion cutting: thermal exfoliation (TE) and mechanical exfoliation (ME). These SOI films are characterized to discern the differences in electrical and other properties induced by the ME and TE processes. p-metal-oxide-semiconductor field-effect transistor were fabricated on these SOI substrates as well as on bulk silicon and their I-V characteristics measured and compared to point out materials differences created by the two methods. X-ray diffraction measurements were also performed to supplement the exploration of the TE and ME material properties. Overall the FETs fabricated from the ME SOI outperformed those made from the TE SOI and had similar Ion∕Ioff ratios and off-state drain-source leakage currents to the FETs fabricated from bulk Si.
Optical and electrical properties of AlCrN films grown by molecular beam epitaxy
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Frazier R. M. , Liefer J. Y. , Thaler G. T. , Abernathy C. R. , Pearton S. J , Zavada J. M.
Published: December 2004

Doping of AlN with Cr at percent level concentrations produces ferromagnetism persisting to above 300K. We have examined the electrical and optical properties of Cr-doped AlN grown by molecular beam epitaxy under conditions that produce single-phase or multiple phase material, as measured by x-ray diffraction. The band gap of single-phase AlN decreases from 6.2 to 6.1eV for a Cr concentration of 2at.%. This change originates from the Franz-Keldysh broadening of the band edge due to potential fluctuations caused by heavy Cr doping. The effect was more pronounced in multiple-phase samples (the secondary phases are Cr2N and AlxCry), producing an apparent band gap of 5.8eV. Two strong defect absorption bands with thresholds of 3 and 5eV are introduced by the Cr doping. The resistivity of single-phase AlCrN samples is higher than the resistivity of similarly grown undoped AlN films. Multiple-phase AlCrN samples show a high conductivity of the hopping type. The optical transmission spectra of multiphase AlCrN indicates appreciable absorption by free carriers and strong scattering, both most likely due to the presence of conducting inclusions.
Imprint lithography issues in the fabrication of high electron mobility transistors
Authors: Thoms S. , Macintyre D. S. , Moran D. , Thayne I.
Published: December 2004

In earlier work we described procedures for the fabrication of High Electron Mobility Transistors (HEMTs) using nanoimprint lithography to produce T-shaped resist profiles for gate metallization. For reliable liftoff the T-gate process requires a clear undercut in resist, and this is intrinsically impossible with imprint lithography. In addition, the imprinting process resulted in fracture defects in the resist unless release was carried out at elevated temperatures. Both these problems required improvement. In this article we describe an improved method for obtaining metallized imprinted T-gates by creating resist undercut using a double angled evaporation. HEMTs with self-aligned gate structures were fabricated using this procedure. Multilayer resist stacks were used to investigate resist flow during imprinting and we show that such stacks are not suitable for liftoff enhancement of T-gates. We further show how resist fracture defects can be minimized by increasing the pattern density on the die.
Single electron memory devices utilizing Al2O3 tunnel oxide barriers
Authors: Yadavalli Kameshwar K. , Anderson Nicolas R. , Orlova Tatiana A. , Orlov Alexei O. , Snider Gregory L. , Elam Jeffrey
Published: December 2004

We report experiments on single electron memory devices where the charging of a floating gate, which serves as a memory node, is done through aluminum oxide tunnel barriers and detected by a single electron transistor (SET) electrometer. The aluminum oxide tunnel barriers are fabricated through two different approaches. In one, the oxygen plasma oxidation of an as-deposited aluminum floating gate is used to grow aluminum oxide. In the other method, aluminum oxide is deposited on a titanium/gold floating gate by means of atomic layer deposition (ALD). Measurements performed on these devices at a temperature of 300mK indicate the presence of a definite threshold for charging through the tunnel oxide barriers. A nonvolatile memory behavior is observed with each bit represented by about 15 electrons.
Influence of Coulomb effects on electron projection lithography process
Authors: Yamamoto Jiro , Yamashita Hiroshi , Yamabe Masaki , Arimoto Hiroshi
Published: December 2004

Electron projection lithography (EPL) is an attractive candidate for next-generation lithography. In EPL, Coulomb effects consisting of a global space charge and stochastic Coulomb effect are a concern because of the huge beam current exposure required. We discuss the influence of the Coulomb effects in EPL. Proximity and Coulomb effects are known to degrade resolution and dose margin. To discriminate between the influence of Coulomb effects on exposure results from those of the proximity effect, we used complementary exposures. We found that a resolution of 1:1 L&S at a 6.9μA beam current on a wafer was 100nm and at a 1.3μA beam current was 65–70nm. These results roughly met specifications of the EPL system, NSR-EB1A. We found, however, that the beam blur varied within a subfield, and the difference between CD at 0.5 and 6.4μA at 100nm was 12nm due to the different beam blur, even if the space-charge effect was corrected by refocusing. To achieve accurate CD control, the proximity effect must thus be corrected considering beam blur distribution in the subfield.
Pattern transferring technique using reversal mask process
Authors: Kato Hirokazu , Abe Junko , Onishi Yasunobu
Published: December 2004

In the reversal mask process, the mask material film is deposited over the resist patterns. There is a problem in that the film step height at the surface of the mask material reduces the etch-back margin of the mask material. This is inevitable as long as the mask material film is deposited by spin-coating and no planarization process is used. In this article, the dependence of film step height on the half-pitches (periodic feature) or the widths (isolated feature) of the resist patterns is measured by means of both experiment and calculation. As a solution to avoid the effect of the film step height, a pattern transferring technique which makes use of a multiple exposure process and the reversal mask process is proposed and the fabrication of dense contact hole patterns was demonstrated. This technique is proven to be one of the practical applications of the reversal mask process and at the same time to be an effective method of fabricating the kind of patterns which a conventional single-exposure process is not able to fabricate due to insufficient lithography margin.
Nanostructures produced by ultraviolet laser irradiation of silicon. I. Rippled structures
Authors: Pedraza A. J. , Guan Y. F. , Fowlkes J. D. , Smith D. A.
Published: December 2004

One- and two-dimensional (1D and 2D) nanorippled structures produced in silicon by ultraviolet laser irradiation were investigated using atomic force and scanning electron microscopy. One- and two-beam illumination of the substrate was used to generate the nanostructures. Single-beam irradiation was done using p-polarized laser light, while the two-beam incidence was achieved employing a Lloyd’s mirror arrangement to reflect part of the beam onto the substrate. The structures were characterized by direct measurement of the ripple spacing or by measurements done on the fast Fourier transform of their atomic force microscopy (AFM) images. Under single-beam illumination, only 1D gratings were generated on the substrate surface. The grating lines were perpendicular to the projection of the electric field of the incident light on the substrate surface. For the two-beam illumination, it was very difficult to obtain the Lloyd’s mirror characteristic interference pattern due to the poor coherency of the laser employed. Nonetheless, the use of a Lloyd’s mirror not only enhanced the production of rippled structures strongly but also produced 2D gratings. The gratings generated with this arrangement are many millimeters long and cover the entire laser illuminated area. In contrast with one-beam illumination, linearly polarized light was not required to promote the rippled structures. Experimental evidence strongly suggests the following: (1) the p component of the laser light is responsible for ripple formation; (2) ripples can propagate with increasing number of pulses; and (3) the ripple structure is produced while the silicon is melted. The occurrence of melting is further supported by a computer simulation of the thermal field during the laser pulse. An estimate done using the lubrication approximation indicates that liquid is displaced from the hotter into the cooler regions by the gradient of surface tension. At angles of incidence equal or larger that 50°, the ripple spacing data indicate that incident laser light promotes the generation of plasma oscillation in the liquid silicon. These surface electromagnetic waves are responsible for the formation of ripples with lines that run parallel to the projection of the wave vector of the incident wave on the substrate surface. The simple irradiation procedure used to produce these nanostructures opens the possibility of using them as a template for ordering other nanostructures on a vast scale.
DNA nanopatterning with self-organization by using nanoimprint
Authors: Ohtake Toshihito , Nakamatsu Ken-ichiro , Matsui Shinji , Tabata Hitoshi , Kawai Tomoji
Published: December 2004

Recently, DNA properties have been investigated to realize new functional biodevices. However, there are few reports on DNA nanopatterning to make bionanodevices. Therefore, we have attempted DNA nanopatterning by using a nanoimprint method. On a glass substrate coated with poly-L-lysine, which is known as a material for DNA immobilization by UV radiation, about 100 μl of a 1μg∕μl DNA solution was applied and was dried at 60 °C for an hour, and was irradiated by UV for 2 min. Further 4% polyvinyl alcohol (PVA) solution was coated on the substrate. The substrate was imprinted at 100 °C and 6 MPa for 5 min, and a mold was applied with a SiO2 on Si substrate fabricated by electron-beam lithography and dry etching. Etching of the DNA substrate was done by reactive ion etching in O2 atmosphere. Finally, the PVA layer washed down by water, and the DNA nanopatterning was obtained.
Addressable field emitter array: A tool for designing field emitters and a multibeam electron source
Authors: Bauerdick S. , Burkhardt C. , Kern D. P. , Nisch W.
Published: December 2004

We have developed an array of 25 electrically addressable field emitters. This device is a very suitable tool for experimentally designing miniaturized electron sources with improved emission characteristics. The field emission tip itself is fabricated by a combination of electron beam induced deposition and physical vapor deposition. Thus it is possible to vary the geometrical setup of tip and extraction electrode easily and also to define the emitter material exactly. The influence of most important parameters on the tip shape has been examined and deposition of three-dimensional structures is shown. Analysis of Fowler–Nordheim-plots indicates that during first operation and increased exposure to argon, nitrogen, and oxygen a change in tip radius is the predominant effect. Two arrays of field emitters with different tip heights have been examined to show the variation in emission pattern and current distribution.
Selective growth of sculptured nanowires on microlithographic lattices
Authors: Horn Mark W. , Pickett Matthew D. , Messier Russell , Lakhtakia Akhlesh
Published: December 2004

We have grown helicoidal nanowire assemblies on a variety of topographic substrates with regular microlithographic patterns, thereby demonstrating that sculptured thin films with transversely latticed architecture can be grown by physical vapor deposition. The transverse feature-separations are as low as 100–300 nm, and mesa regions are circular posts as small as 60 nm in diameter. The initial as well as the subsequent stages of growth on topographic substrates can be understood using simple geometric shadowing arguments.