bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of in situ and ex situ plasma-treated metalorganic chemical vapor deposition titanium nitride thin films
Authors: Lim Boon Kiat , Park Hun Sub , See Alex K. H. , Liu Er Zhuang , Wu Shao Hui
Published: December 2002

Titanium nitride (TiN) thin films deposited by metalorganic chemical vapor deposition, using tetrakis-dimethyl-amino-titanium as a precursor, are known to have high sheet resistivity. A plasma treatment in forming gas ambient is one way of reducing the high sheet resistivity down to that of the films deposited by physical vapor deposition. This plasma treatment is normally done in situ (without breaking the vacuum) immediately after deposition. However, an ex situ (breaking vacuum after deposition) plasma treatment will provide a more economical way of manufacturing in which less time is required in the chemical vapor deposition chamber, hence allowing high deposition throughput. Furthermore, the plasma treatment can be done in a high-pressure chamber, which translates into low cost. In this study, we compared film properties of TiN with in situ and ex situ plasma treatments. Analyses were performed on chemical composition, sheet resistance, amount of Ti atoms, via resistance and reliability using x-ray photoelectron spectroscopy, four-point probe, x-ray fluorescence, and a current–voltage multiprobe. The ex situ plasma treatment was capable of removing carbon from the TiN film, but not without a sacrifice of the reliability and electrical performance of the TiN film. Further development on the ex situ plasma treatment must be made to improve the reliability and electrical performance of the TiN film.
Dry etching of GaP with emphasis on selective etching over AlGaP
Authors: Epple J. H. , Sanchez C. , Chung T. , Cheng K. Y. , Hsieh K. C.
Published: December 2002

A technique to etch GaP by reactive ion etching was developed and the effects of different etching parameters were studied. Also, selective etching of GaP over AlGaP was examined and demonstrated. Etching is achieved by using SiCl4, which will react with GaP to form volatile compounds. Selective etching is accomplished when SiF4 is used in addition to SiCl4. The addition of the fluorine-based gas will result in a nonvolatile etch-inhibiting layer, AlF3, when aluminum is present on the sample surface. By adjusting etching parameters, a selectivity as high as 126 is demonstrated. The presence of the AlF3 etch-inhibiting layer is verified by Auger electron spectroscopy, and the removal of this layer by buffered oxide etch is demonstrated. In addition, a direct comparison of etch rates for GaP and GaAs was made, and etch rates were found to be similar.
Submicron pattern transfer to binary semiconductors via micromolding in capillaries
Authors: Pisignano Dario , Gigli Giuseppe , Visconti Paolo , Zocco Anna , Perrone Alessio , Cingolani Roberto
Published: December 2002

We report on the high-resolution patterning of III–V semiconductors through polymeric masks by a soft lithographic technique based on micromolding in capillaries. The basic study of the capillarity process and the optimization of the technological steps allowed us to transfer patterns on both GaAs and InP with resolution of 800 nm over areas up to 1 cm2 and of a few microns over areas up to 4 cm2.
Fabrication of spin-current-induced domain-wall-nucleation device in planar configuration
Authors: Kimura Takashi , Wakaya Fujio , Gamo Kenji
Published: December 2002

We proposed the control of the domain-wall-nucleation process by injection of the spin-polarized current into the wire end of the ferromagnetic wire via the nonmagnetic material, and attempted to observe the change of the switching field due to the spin injection in two-type planar-configuration devices. In one device using focused ion beam (FIB) in situ etching, the changes of the switching field, which were consistent with the spin-injection model, were very small. This may be because the irradiation effects induced by the FIB etching modify the properties of the ferromagnetic wire near the etched region. In the other device using multi-angle deposition, the clear changes of the switching field were observed and were quantitatively consistent with the model based on the spin-transfer effect. The interface fabricated by the multi-angle deposition may be useful for forming the ideal ferromagnet/nonmagnet interface.
Multilevel silicon diffractive optics for terahertz waves
Authors: Walsby E. D. , Wang S. , Xu J. , Yuan T. , Blaikie R. , Durbin S. M. , Zhang X.-C. , Cumming D. R. S.
Published: December 2002

A multilevel microfabrication process has been developed to produce silicon Fresnel lenses for terahertz waves. A repeated binary fabrication process was used to create lenses with up to eight levels in complexity and these lenses have been compared to both less complex structures and refractive optic lenses. The microfabrication required deep reactive ion etching and multilevel resist processing using SU8 photoresist. At the design frequency of 1 THz an eight-level lens showed significant improvement in intensity at the focus and had much reduced energy lost into sidelobes compared with refractive lenses.
Comparative study of Ga- and N-polar GaN films grown on sapphire substrates by molecular beam epitaxy
Authors: Huang D. , Reshchikov M. A. , Visconti P. , Yun F. , Baski A. A. , King T. , Morkoç H. , Jasinski J. , Liliental-Weber Z. , Litton C. W.
Published: December 2002

We report the surface, structural, and optical properties of typical Ga- and N-polar GaN films grown on sapphire substrates by molecular beam epitaxy. The Ga-polar films were grown on AlN buffer while the N-polar films were grown on GaN buffer layers. Atomic force microscopy imaging shows that the as-grown and chemically etched Ga-polar films have a flat and pitted surface while the N-polar surface is rougher with isolated columns or islands. Transmission electron microscopy demonstrates a low density of inversion domains in the Ga-polar films, while a much higher density of inversion domains was observed in the N-polar films. X-ray diffraction curves show a narrower (002) peak for Ga-polar films than that for N-polar films. On the other hand, both Ga- and N-polar films show a similar width of (104) peak. Despite their rough surfaces, high density of inversion domains, and broader (002) x-ray diffraction peaks, N-polar films with low dislocation density were demonstrated. In addition, higher PL efficiency for the N-polar films than that for the Ga-polar films was observed.
Investigation of active Si pitting and its impact on 0.15 and 0.30 μm n-type metal–oxide–semiconductor and p-type metal–oxide–semiconductor transistors
Authors: Chua C. S. , Chor E. F. , Goh F. , See A. , Chan L.
Published: December 2002

The causes of pitting on an active silicon surface and its impact on 0.15 and 0.30 μm n-type metal–oxide semiconductor (NMOS) and p-type metal–oxide–semiconductor (PMOS) transistors have been assessed. During polysilicon gate patterning, the gate oxide at the source/drain regions of the NMOS transistors may be etched away due to insufficient selectivity of the etch chemistry, improper etch chamber configuration, pattern density, and the adoption of dual-doped gate technology. The exposed silicon substrate has poor selectivity against the polysilicon gate, this causes Si pitting to occur on the source/drain active regions of the NMOS transistors. However, there is no significant pitting observed for the PMOS transistors due to the slower etch rate of the undoped polysilicon of the PMOS transistors. Pitting on the active areas severely degrades the device parameters, such as drive current, series resistance, and transconductance. This is worse for the 0.15 μm NMOS transistors compared to the 0.30 μm NMOS transistors. The channel resistance of the 0.30 μm transistors is much larger than any increase in the external resistance caused by the pitting. As a result, Si pitting has negligible effects on the device performance of long channel devices.
Scanning electron microscope with polarization analysis: Micromagnetic structures in ultrathin films
Authors: Oepen Hans Peter , Steierl Gerold , Kirschner Jürgen
Published: December 2002

The basics of the scanning electron microscope with polarization analysis are presented and special features of the microscope are discussed. The spin polarization of the secondary electrons allows for a high contrast as the topography of the sample is strongly suppressed. The feature of the method is that the orientation of the magnetization is measured and used for domain imaging. For complex domain patterns that makes the interpretation easy and direct. Examples are shown how the high surface sensitivity is used for the investigation of all kind of samples. The decoration by a thin ferromagnetic film makes even contaminated and samples with strongly spoiled surfaces accessible for scanning electron microscope with polarization analysis (SEMPA) investigation. Recently, the magnetic resolution of SEMPA has been pushed into the range of a few nm.
Fabrication of Si field emitter arrays integrated with metal–oxide–semiconductor field-effect transistor driving circuits
Authors: Nagao M. , Tamura Y. , Matsukawa T. , Kanemaru S. , Itoh J. , Tokunaga K.
Published: December 2002

Si field emitter arrays (FEAs) were monolithically integrated with metal–oxide–semiconductor field-effect-transistor (MOSFET) based driving circuits on a Si chip for the first step toward developing the field-emission-display-on-a-chip (FED-on-a-chip), which is a candidate for the next-generation FED. We developed a fabrication process of Si FEAs integrated with MOSFET driving circuits. A 4×4 matrix Si FEA, emission-control MOSFET, and simple driving circuits consisting of a shift register were integrated on the same chip. The operation of each element, such as MOSFET-controlled Si FEAs and logic circuits for the driver, was confirmed. The emission current from the Si FEA can be controlled by the built-in MOSFET at a voltage of less than 5 V, which can be driven by the built-in driving circuits. The operation of the 4×4 matrix FEA with driving circuits was demonstrated. This is the first operation of the FEA integrated with MOSFET logic circuits. The detailed design and fabrication processes are described.
Photospeed considerations for extreme ultraviolet lithography resists
Authors: Dentinger Paul M. , Hunter Luke L. , O’Connell Donna J. , Gunn Scott , Goods Daniel , Fedynyshyn Theodore H. , Goodman Russell B. , Astolfi David K.
Published: December 2002

Photospeed is a prime consideration for wafer throughput of extreme ultraviolet (EUV) lithography. Faster photoresists additionally provide system advantages such as less thermal management of the mirrors and mask, and potentially increased component lifetimes. However, there are some predicted detrimental considerations when using fast photoresists such as shot noise. In this article, we report details of the formulation of photoresists exposed at 248 nm and identical formulations exposed at 13.4 nm. Compositions typically contained co- or terpolymers of poly-4-hydroxystyrene, t-butyl acrylate and as an option, styrene, a photoacid generator of bis-t-butylphenyl iodonium camphorsulfonate or perfluoroxbenzensulfonate and tetrabutyalummonium or triphenylsulphonium hydroxide base. With these formulations, the EUV photospeed was varied from 34 to 2.7 mJ/cm2. Scanning electron microscope analysis was done for all wafers at Sandia using GORA software to determine the line-edge roughness (LER). Identical formulations were exposed at photon dense deep UV (DUV) wavelengths and comparatively photon-sparse EUV wavelengths. Therefore, ratioing the LER of identical formulations exposed at DUV minimizes the confounding effects of formulation changes that affect dissolution, resolution, etc. A plot of the line-edge roughness ratio of LEREUV/LERDUV as a function of the photospeed was used to gain insight into the effect of shot noise on the LER of dense lines. If shot noise effects were dominating the LER for EUV, then the ratio would increase above the nominal value as the dose to size was decreased. It is clear that the current generation of DUV resists, with the invention of no new material required, can be reformulated to satisfy the photospeed specification of 5 mJ/cm2 for EUV lithography and no shot noise effects have been observed.
Fabrication of high electron mobility transistors with T-gates by nanoimprint lithography
Authors: Chen Y. , Macintyre D. , Boyd E. , Moran D. , Thayne I. , Thoms S.
Published: December 2002

T-gates are commonly used in high frequency low noise transistors on III–V materials since they provide a combination of short gate length and low gate resistance. Nanoimprint lithography can produce minimum pattern feature sizes equivalent to those attainable by high resolution electron beam lithography and it has potential advantages in terms of speed and cost. The imprint lithography step must be reliable and compatible with existing device process flows. In this article we describe a bilayer resist imprinting procedure for the fabrication of 120 nm T-gates for high electron mobility transistors. The results of transistor dc characterization are also presented and are similar to those obtained for transistors fabricated on the same material with gates realized by electron beam lithography.
Distributed axis electron-beam system for lithography and inspection—preliminary experimental results
Authors: Pickard D. S. , Campbell C. , Crane T. , Cruz-Rivera L. J. , Davenport A. , Meisburger W. D. , Pease R. F. W. , Groves T. R.
Published: December 2002

A distributed-axis system can be used to avoid the space-charge limits of conventional electron-beam lithography systems. Our approach is to use a uniform magnetic field to simultaneously focus an array of beams. We have built a test bed and report the first experimental results. Sub-100 nm resolution has been obtained and is presently limited by aperture size and interference. Sub-10 nm resolution should be possible given a suitably small source.
Scattering mask concept for ion-beam nanolithography
Authors: Ruchhoeft P. , Wolfe J. C. , Torres J. L. , Bass R.
Published: December 2002

In this article, we demonstrate the concept of scattering masks for ion-beam proximity lithography. In this process, stencil mask openings are fabricated with larger-than-nominal sizes and are coated with a conformal scatter layer that reduces the size of the features at the mask surface. The process reduces the complexity of etching high aspect-ratio mask openings. Printed images of masks with 100 and 40 nm circular openings, fabricated from masks with 225 nm openings, are shown. The printing process has excellent exposure latitude: less than a 20% change in critical dimension is observed for a 33% change in dose for 40 nm structures. We show that the diffuse background exposure that results from ions traversing through the scatter layer is around 0.1% of the primary exposure for a 2 μm pitch pattern.
Advanced die-to-database inspection technique for embedded attenuated phase shift mask
Authors: Yamashita Kyoji , Isomura Ikunao , Tsuchiya Hideo , Watanabe Toshiyuki , Inoue Hiromu , Endo Satoshi , Tokita Masakazu
Published: December 2002

We have developed a deep ultraviolet die-to-database inspection system MC-3500 for the 130 nm node and beyond. The system involves comparison of a mask image scanned at a wavelength of 257 nm and a reference data calculated from complex amplitude of objects with 200 Mpixel/s throughput. An approximation of Hopkins formulation in the region of a large partial coherence factor gives a nonlinear filtering scheme for embedded attenuated phase shift mask (EPSM). The nonlinear filtering was evaluated for intensity fidelity of the reference image using comparison with Hopkins formulation. Evaluation results show that phase optimization is effective in eliminating excessive image ringing and the minimum feature size to maintain fidelity is found to be over 3 pixels. The technique is promising in applications to high-transmission EPSM.
Development of data conversion system for electron beam projection lithography
Authors: Kato Kokoro , Nishizawa Kuninori , Haruki Tamae , Inoue Tadao , Kamijo Koichi , Kojima Shinichi , Minami Hideyuki , Okamoto Kazuya
Published: December 2002

Electron beam projection lithography (EPL) has been developed as one of the most promising candidates for the next generation lithography below 70 nm node devices. Stencil masks, which are used in the EPL technology as masks, have brought new necessities of data conversion such as dividing the data into two complementary masks. The patterns have to be divided and dispatched optimally onto each of the complementary masks in order to make the stencil masks manufacturable. We have developed a data conversion system for EPL, called “EPLON.” EPLON provides a solution to the problems mentioned and converts the data available on EPL. In this article, our method of converting the complementary mask data is presented.
Profile simulation of gas chopping based etching processes
Authors: Volland B. E. , Ivanov Tzv. , Rangelow I. W.
Published: December 2002

A simulation program based on a phenomenological surface etching reaction model and on a reactant transport model including shadowing and diffuse particle reflection at the sidewalls was developed to investigate the dependence of the etching rate and profile quality of gas chopping deep reactive ion etching processes on process parameters and sample temperature. The simulations are in good agreement with the experimental results. The dependence of the heating characteristics on the geometry (area, thickness) of teeny microelectromechanical systems devices or membrane-like silicon samples during microstructuring by means of plasma etching was investigated using finite element simulations. It was found that membrane-like samples are considerably heated unless the membrane area is sufficiently small (<≈5 mm φ) and/or is sufficiently thick (≈500 μm).
Effect of high numerical aperture lens on lithographic performance in 157 nm lithography
Authors: Itani Toshiro , Suganaga Toshifumi , Kanda Noriyoshi , Kim Jae-Hwan , Watanabe Kunio , Cashmore Julian , Gower Malcolm
Published: December 2002

157 nm lithography is the most promising candidate for the post-193 nm lithography at the sub-70 nm technology node of semiconductor devices. In order to realize sub-70 nm resolution using 157 nm lithography, the critical components such as F2 laser, optics, photomasks, and resists have been studied extensively [Bloomstein et al., J. Vac. Sci. Techol. B 15, 2112 (1997); Rothschild et al., J. Photopolymer Sci. Technol. 13, 369 (2000); Rothschild et al. (unpublished); Itani and Wakamiya, Microelectron. Eng. 61–62, 49 (2002)]. Moreover, for improving the numerical aperture (NA) of the projection lens and thus the resolution capability at 157 nm, liquid immersion interference lithography at 157 nm has been studied and has obtained a minimum resolution of less than 70 nm lines and spaces [Switkes, Bloomstein, and Rothschild, Appl. Phys. Lett. 77, 3149 (2000); Switkes and Rothschild, J. Vac. Sci. Technol. B 19, 2353 (2001)]. In this article we will report on the feasibility study of a high NA (0.85 NA) projection lens on a 157 nm microstepper, focusing on the resolution capability, the residual aberrations of the lens, and the effect of intrinsic birefringence of CaF2 upon imaging performance. These issues have been evaluated experimentally and combined with simulation analysis of the lithographic performance. Simulation results of focus margin versus exposure latitude have demonstrated suitable values for mass production of actual semiconductor devices. We estimate that such high NA optics are effective for improving the resolution and process margin, particularly when combined with resolution enhancement techniques. We confirmed that 157 nm lithography with high NA optics could realize sub-70 nm patterns, and it has sufficient potential for mass production of the sub-70 nm technology node for semiconductor devices.
Electrostatic effects during dissolution of positive tone photoresists
Authors: Schmid Gerard M. , Burns Sean D. , Tsiartas Pavlos C. , Willson C. Grant
Published: December 2002

Positive tone photoresist function is based upon modulation of the dissolution rate of an acidic polymer in aqueous base developer. During dissolution, a negative surface charge accumulates at the surface of the photoresist film as acidic sites on the polymer are ionized by the basic developer. This negative surface charge causes a depletion of hydroxide ions in the developer solution immediately adjacent to the film. One effect of this phenomenon is to reduce the dissolution rate relative to rates predicted from the bulk base concentration. The depletion of base at the resist/developer interface has been studied through the application of the Poisson–Boltzmann equation and through Monte Carlo simulations. It is shown that the extent of depletion of hydroxide at the surface of the film is related to the bulk developer concentration and the local geometry of the interface. Interfacial geometry is found to be most influential on the length scale of 1–10 nm. When electrostatic effects are considered in conjunction with the equilibrium of the acid–base reaction, the fractional ionization of the surface of the film is significantly lower than previously calculated. Understanding the relationship between the acid–base equilibrium and electrostatic equilibrium represents an important step in our efforts to understand the fundamental dissolution mechanism of positive tone photoresists.
Evaluation of calixarene—derivatives as high-resolution negative tone electron-beam resists
Authors: Sailer H. , Ruderisch A. , Kern D. P. , Schurig V.
Published: December 2002

We present a systematic evaluation of calixarene derivatives as high-resolution negative tone resists for electron-beam lithography with a focus on their sensitivities. We studied the effect of a modification of the calixarene molecules to trimethysilyl ethers as well as the effect of an introduction of an allyl group and showed that the introduction of double bonds into the molecules can improve the sensitivity of the resists while their position does not seem to be important. The high-resolution capability of tetraallylcalix[4]arene was confirmed by fabricating an 18 nm dot array.
Sub-50 nm stencil mask for low-energy electron-beam projection lithography
Authors: Yoshizawa Masaki
Published: December 2002

Low-energy electron-beam-proximity projection lithography using a stencil mask is proposed for sub-70 nm node lithography. In this study, the anisotropic nature of Si wet etching is utilized for the fabrication of sub-50 nm stencil masks. A 20-nm-width aperture with a right angle and a 90-nm-width crossbeam with a smooth edge are obtained using silicon-on-insulator (SOI) wafers. 20-nm-thick Pt is calculated to be thick enough to block 2 keV electrons and it is shown that the evaporation of 10-nm-thick Pt from both sides of a membrane causes no significant degradation of sub-50 nm holes. It is estimated that a 25-nm-width aperture with a 100 nm pitch is feasible using an SOI wafer with an 18-nm-thick surface Si layer and a mask writer with a 50 nm resolution.
Partially hydrogenated poly(vinyl phenol) based photoresist for near UV, high aspect ratio micromachining
Authors: Chatzichristidi M. , Raptis I. , Argitis P. , Everett J.
Published: December 2002

A negative resist platform based on a low Mw epoxy novolac polymer, partially hydrogenated poly(vinyl phenol)s and suitable onium salt photoacid generators is presented and evaluated for high aspect ratio micromachining. The high content of hydroxyl groups in this resist system allows development in standard aqueous base solutions (TMAH 0.26 N). The effects of material parameters such as the degree of poly(vinyl phenol) hydrogenation and the onium salt hydrophobicity on the development process are examined. The cross-linked areas of this resist can be easily removed by commercial wet photoresist strippers after processing. Experimental data demonstrate a promising lithographic performance with an aspect ratio of 7:1 for 5 μm closely spaced lines under exposure at 365 nm.
Optical waveguides with apodized sidewall gratings via spatial-phase-locked electron-beam lithography
Authors: Hastings J. T. , Lim Michael H. , Goodberlet J. G. , Smith Henry I.
Published: December 2002

We describe a technique to fabricate Bragg gratings in the sides of optical waveguides using a single lithographic step. This technique is particularly suited to the apodized gratings required for add/drop filters in dense-wavelength-division multiplexing. Apodization minimizes cross talk between channels and improves the filter response. Silicon-on-insulator rib waveguides with both uniform and apodized gratings were fabricated using direct-write spatial-phase-locked electron-beam lithography (SPLEBL). This approach combines SPLEBL’s pattern-placement accuracy with the flexibility of direct-write device prototyping. The resulting grating-based devices exhibited substantially reduced side-lobe levels.
Testing an electrostatic deflection innovation: Initial experimental results
Authors: Retsky Michael , Stein Richard
Published: December 2002

When deflecting a charged particle beam into small angles, electrostatic deflection is commonly used. For larger angles, magnetic is the usual choice mainly because the deflection aberrations are two- or threefold less. Methods to reduce electrostatic deflection aberrations have been proposed over the years but a major solution has not been identified. This subject has recently been revisited and, based on computations, it has been proposed that electrostatic deflection aberrations can be reduced 10-fold if the beam is injected asymmetrically into the gap between two conventional shaped oppositely charged conducting plates. According to this theory, with the proper injection offset, the only surviving aberration is astigmatism that is totally correctable with a quadrupole prior to deflection. The predicted optimal offset was either 33% or 42% (depending on the method of calculation) from the center toward the attracting plate. We have built a demountable test bed to experimentally determine if the innovation is correct. The beam is deflected by shaped plates according to a previously reported design. This plate design was predicted to provide ±38.1° of deflection for a beam 0.050 in. in diameter with undetectable deflection aberrations at optimal offsets. Compared to the calculated design, the voltages used in the demountable test bed are smaller (6 compared to 20 kV), the throw distance from the plate entrance to the screen is smaller (4.5 compared to 12 in.), and the deflection angle is ±28.2° but otherwise the setups are very similar. Initial data from the test bed are deflection of a 0.010 in. diam probe after injection into the deflection plate gap at various offset positions. It is found that 1/3 of the way from center toward the attracting plate, there is a 0.2 in. wide section of the deflection versus offset curve that is flat indicating a segment in which the aberrations are not detectable. Based on these initial results, the concept is valid and the injection offset was where it was predicted to be.
Submicron thermocouple measurements of electron-beam resist heating
Authors: Chu Dachen , Bilir D. Taner , Pease R. Fabian W. , Goodson Kenneth E.
Published: December 2002

Pattern distortion caused by resist heating is believed to contribute significantly to errors in feature size and pattern placement. A number of models have been proposed to predict the temperature rise of resist heating but experimental results are scarce. We fabricated and calibrated thin film gold/nickel thermocouples with (400 nm)2 junction size and used these to measure work-piece heating during electron-beam exposure. Irradiation by a 15 kV electron beam of 600 nA and 2 μm radius caused a temperature rise of 70 K, about 15% lower than the calculated result. The discrepancy may be due to the differences between the energy deposition profiles used in modeling and those prevailing in the experiments.
Fabrication of complete 8 in. stencil mask for electron projection lithography
Authors: Amemiya Isao , Yamashita Hiroshi , Nakatsuka Sakae , Kimura Ikuru , Tsukahara Mitsuharu , Yasumatsu Satoshi , Nagarekawa Osamu
Published: December 2002

We fabricated an 8 in. stencil mask having the complementary pattern of the 70 nm rule system-on-chip device. The 8 in. stencil mask was realized from the development of a mask substrate fabricated by using the sputtering method to form a scattering silicon membrane and an intermediate stopper layer. The intermediate layer material, which functions as an etching stopper, was CrNx. This material has demonstrated high performance in stencil mask fabrication, which is described in detail. The stress in the CrNx could be controlled within ±20 MPa by adjusting the deposition condition. The deposited silicon membrane stress could be easily adjusted in the range of 0–10 MPa. The etching selectivity, when the substrate backside etching was performed, was over 1000 under the low bias power. When the deep etching process was performed using SF6 and CHF3 etching gases for the mask pattern formation, the Si/CrNx etching selectivity was over 100 under the low bias power condition. The mask substrate, which is made up of a 2-μm-thick deposited silicon membrane and 0.35-μm-thick CrNx stopper layer, enabled an 8 in. stencil mask to be fabricated for use with electron projection lithography. In complementary mask split, we used “M-Split” which was developed by Selete and ISS as a pattern split software.
Hybrid assembly technique using alternating current field for molecular electronic measurements
Authors: Amlani Islamshah , Rawlett Adam M. , Nagahara Larry A. , Tsui Raymond K.
Published: December 2002

We present an approach to facilitate transport measurements of electronic molecules. The technique consists of forming a self-assembled monolayer of the investigated molecule on prepatterned electrodes and then bridging the electrodes with nanoparticles using an alternating electric field. This technique can potentially allow screening of a large number of electronic molecules in a facile manner. Application of an alternating current field is equally useful for trapping other nanometer-scale structures such as carbon nanotubes. As an example of our hybrid technique, we report preliminary transport measurements of a test molecule that has been reported using a different test bed. Our results show qualitative agreement with previously published data.
Magnetic dichroisms in absorption and photoemission for magnetic characterization in x-ray photoelectron emission microscopy
Authors: Kuch W. , Chelaru L. I. , Offi F. , Kotsugi M. , Kirschner J.
Published: December 2002

Magnetic contrast for the operation of a photoelectron emission microscope (PEEM) with synchrotron radiation is provided by magnetic dichroisms. Besides the most frequently employed magnetic dichroism, magnetic circular dichroism in x-ray absorption spectroscopy, energy filtering of photoemitted electrons allows one to also use magnetic dichroisms in photoelectron emission as complementary contrast mechanisms. We demonstrate that it is possible to obtain magnetic contrast in photoemission using PEEM equipped with a simple retarding field electron energy analyzer. Magnetic domain images of an ultrathin film of 10 atomic monolayers of Fe on W(001), obtained by three different contrast mechanisms (circular magnetic dichroism in x-ray absorption, circular magnetic dichroism in Fe valence band photoemission, and linear magnetic dichroism in Fe 3p photoemission) are presented and compared.
Correction of chromatic and spherical aberration in electron microscopy utilizing the time structure of pulsed excitation sources
Authors: Schönhense G. , Spiecker H.
Published: December 2002

A theoretical ansatz for correction of the chromatic and spherical aberration of round-lens systems in photoemission and low-energy electron microscopy (PEEM/LEEM) is presented. The method is based on fast switching of electrical acceleration or lens fields. It exploits the highly precise time structure of pulsed photon sources like electron storage rings for synchrotron radiation or pulsed lasers as well as pulsed photocathodes of a LEEM. The initial results indicate that the approach is a promising alternative to the implementation of multipole or mirror correctors in the electron optical column of a microscope.
Two-dimensional transverse cross-section nanopotentiometry of actively driven buried-heterostructure multiple-quantum-well lasers
Authors: Ban D. , Sargent E. H. , Dixon-Warren St. J. , Calder I. , Grevatt T. , Knight G. , White J. K.
Published: December 2002

We report results of two-dimensional local potential measurement of the transverse cross-section of operating buried-heterostructure (BH) multiple-quantum-well lasers. The measured two-dimensional image of potential distribution resolved clearly the multiquantum-well active region and the p-n-p-n current-blocking structure of the BH laser, showing close correlation to the scanning spreading resistance microscopy image. Nanopotentiometry measurements were also performed on the p-n-p-n current-blocking structure of a BH laser under different forward bias voltages. The nanopotentiometry results provide direct insight into the behavior of p-n-p-n current-blocking layers intended to minimize current leakage. Our results demonstrate the application of nanopotentiometry to the delineation of complex buried structures in quantum optoelectronic devices.
Low stress development of poly(methylmethacrylate) for high aspect ratio structures
Authors: Rooks M. J. , Kratschmer E. , Viswanathan R. , Katine J. , Fontana R. E. , MacDonald S. A.
Published: December 2002

Magnetic head fabrication for >100 Gbit/in.2 areal density requires minimum lithographic feature size <0.15 μm, with aspect ratios of 8:1–10:1. Electron-beam lithography can provide adequate resolution for research and development of magnetic heads, and at 100 kV can provide greater than 10:1 aspect ratios in 1–3 μm thick single-layer resist poly(methylmethacrylate). Poly (methylmethacrylate) (PMMA) is well known for withstanding the rigors of plating baths, but at these thicknesses requires a nonswelling, low-stress developer such as the LIGA mixture (also known as “GG Developer (U.S. Patent No. 4,393,129)”). In this work we present the results of isopropyl alcohol:water development for thick PMMA, and describe the dependence of resist contrast on the temperature of the developer. We also demonstrate the advantage of ultrasonic agitation during development. These development techniques have brought resist profiles in PMMA to the theoretical limit predicted by Monte Carlo simulations.
Sub-70 nm extreme ultraviolet lithography at the Advanced Light Source static microfield exposure station using the engineering test stand set-2 optic
Authors: Naulleau Patrick , Goldberg Kenneth A. , Anderson Erik H. , Attwood David , Batson Phillip , Bokor Jeffrey , Denham Paul , Gullikson Eric , Harteneck Bruce , Hoef Brian , Jackson Keith , Olynick Deirdre , Rekawa Seno , Salmassi Farhad , Blaedel Ken , Chapman Henry , Hale Layton , Mirkarimi Paul , Soufli Regina , Spiller Eberhard , Sweeney Don , Taylor John , Walton Chris , O’Connell Donna , Tichenor Daniel , Gwyn Charles W. , Yan Pei-Yang , Zhang Guojing
Published: December 2002

Static microfield printing capabilities have recently been integrated into the extreme ultraviolet interferometer operating at the Advanced Light Source synchrotron radiation facility at Lawrence Berkeley National Laboratory. The static printing capabilities include a fully programmable scanning illumination system enabling the synthesis of arbitrary illumination coherence (pupil fill). This new exposure station has been used to lithographically characterize the static imaging performance of the Engineering Test Stand Set-2 optic. Excellent performance has been demonstrated down to the 70 nm equal line/space level with focus latitude exceeding 1 μm and dose latitude of approximately 10%. Moreover, equal line/space printing down to a resolution of 50 nm has been demonstrated using resolution-enhancing pupil fills.
Ion projection sensitized selective Cu electroplating on uncoated p-Si
Authors: Spiegel A. , Bruenger W. H. , Dzionk C. , Schmuki P.
Published: December 2002

We present a resistless technique with the potential to produce metallic nanostructures. By combining ion projection direct structuring (IPDS) and selective electroplating, structures as small as 200 nm have been obtained on p-Si (100). IPDS is based on ion projection lithography (IPL) which uses an open stencil mask and 4–10 times ion optical demagnification of the mask structures onto the wafer; IPL can expose resist at doses of some 1012 ions/cm2 with smallest feature sizes of 50 nm. IPDS does not need any resist; rather it uses the fact that impinging ions create defects at the wafer surface, which can be used to selectively trigger electrochemical reactions. So far Cu, Au, and Ni nanostructures have been produced by this process. Ion doses of 1012–3×1013 ions/cm2 (Xe+, Ar+) have been processed. Applications lie in the field of microelectrochemical systems and biosensor technology.
Simulation of critical dimension error using Monte Carlo method and its experimental verification
Authors: Zinn Sonny Y. , Lee Sung-Woo , Choi Sung-Woon , Sohn Jung-Min
Published: December 2002

In order to assess the effects of process parameter variations, we developed an optical lithography simulation program that handles the parameter variations statistically by the Monte Carlo (MC) method and predicts the mean and standard deviation of critical dimensions (CDs). As an application of the simulation program, we analyzed the error sources that contribute to the in-shot wafer CD uniformity. For experiments, we employed an attenuated phase-shift mask that is actually used for manufacturing a memory device. The CD uniformity of the mask was 4 nm on wafer scale. We performed a MC simulation using mask uniformity of 4 nm, illumination uniformity of 3%±1% (where the error stands for three times the standard deviation), defocus of 0.0±0.2 μm, mask transmittance error of ±0.3%, and mask phase error of ±5°. Simulation gave wafer CD uniformities of 19.2 and 13.3 nm for 0.7 and 0.8 NA, respectively. These predictions agree reasonably well with experimental values 21.7 and 11.4 nm. The error sources were analyzed for both values of NA. In either case, the contribution of mask uniformity is very significant, being about 85%.
Delay-time and aging effects on contrast and sensitivity of hydrogen silsesquioxane
Authors: van Delft Falco C. M. J. M.
Published: December 2002

Hydrogen silsesquioxane (HSQ) has been shown to behave as a negative tone inorganic e-beam resist with a resolution better than 20 nm established. In this article, delay-time and aging effects on contrast and sensitivity have been investigated. The effect of a 1 week delay in air between softbake and exposure is much larger than either the aging effect or the effect of the softbake temperature. A pre-exposure delay in air seems to decrease the sensitivity and to enhance the contrast of HSQ. A general correlation between sensitivity and contrast has been established for various pre-exposure and postexposure treatments for 20, 50, and 100 kV exposures. The possible causes for the various delay-time effects are discussed.
Development of electromagnetic lenses for multielectron beam lithography system
Authors: Haraguchi T. , Sakazaki T. , Hamaguchi S. , Yasuda H.
Published: December 2002

High-throughput electron-beam (EB) lithography systems require high current. However, beam blur increases because of the individual Coulomb interaction among the electron beams. Isolating the electron beam into 4–16 perfectly independent beamlets is effective. As for the electromagnetic lens, many openings in the parallel flat plates can form the compound eye lens. This lens is called the lotus root lens (LRL). Simulations and experiments with the LRL were carried out. In the case of LRL of 4×4 openings with a 22 mm pitch, the uniformity of magnetic field along the axis was within 0.2%. The basic lens function between two openings separated by 44 mm in the LRL with 21 openings in the conventional column qualitatively evaluated. The LRL should be a potential platform for a multicolumn cell system that provides a multibeam direct-writing system that utilizes variable-shaped beam or character projection as unit-column optics.
Conductance-atomic force microscope characterization of focused ion beam chip repair processes
Authors: Marchman H. , McMurray J. , Wildman H.
Published: December 2002

Measurements of electrical test structure resistances have traditionally served as the primary metrics for judging the merit of new and existing focused ion beam (FIB) chip repair processes. However, more understanding of physical changes occurring on the sample surface after various FIB processes can be gained through the use of a relatively new version of atomic force microscopy (AFM) that employs electrically conductive tips. This technique is referred to as “conducting-AFM,” or C-AFM, and provides spatial mapping of both surface height and electronic conduction simultaneously at each image pixel. A key advantage is that electrical leads and large probing pads are not necessary for determining the electrical behavior of a desired region. Results from C-AFM have also been compared with spectroscopic analysis in order to spatially correlate the elemental composition and electrical conductivity of FIB-induced reaction products.
Low-energy electron microscopy/x-ray magnetic circular dichroism photoemission electron microscopy study of epitaxial MnAs on GaAs
Authors: Bauer E. , Cherifi S. , Daeweritz L. , Kaestner M. , Heun S. , Locatelli A.
Published: December 2002

Epitaxial MnAs films on GaAs(001) substrates are studied at room temperature and in the completely ferromagnetic state below room temperature with low-energy electron microscopy, x-ray magnetic circular dichroism photoemission electron microscopy, and low-energy electron diffraction. The combination of these techniques shows a clear relation between the two-phase structure of the layers and their magnetic domain structure.
Scanning photoelectron microscopy study of as-grown and heat-treated chemical vapor deposition boron-doped diamond films
Authors: Zakharov A. A. , Ralchenko V. , Khmelnitskii R. , Lindau I.
Published: December 2002

The electronic structure of as-grown and high temperature (1625 °C) annealed chemical vapour deposition boron-doped (1–4 ppm) diamond films has been studied using a scanning photoelectron microscope with lateral resolution in the 1 μm range. The fresh surfaces have been obtained by cleaving free-standing films in situ at a pressure of 7×10−11 Torr. The major part of the contrast in photoelectron images is due to topography effect but grain structure (grain size 10–50 μm) can be also detected. The detailed study of separate grains shows that as-grown films demonstrate significant intensity in the vicinity of the Fermi level with a characteristic band tail which is believed to result from static and dynamic site disorder. In annealed films a sharp drop in Fermi level intensity is observed and samples show charging effects in scanning electron microscope measurements. As-grown films contain different types of defects which appear as electrically active trapping centers and give rise to the increased density of states at the Fermi level. The evolution of the defect structure and possible boron redistribution upon annealing explains the much lower photoemission signal around the Fermi level in heat-treated films.
Effect of photoacid generator concentration on sensitivity, photoacid generation, and deprotection of chemically amplified resists
Authors: Pawloski Adam R. , Nealey Paul F.
Published: December 2002

The dependence of resist processes (sensitivity, efficiency of photoacid generation, polymer deprotection) on the concentration of the photoacid generator (PAG) in formulations of chemically amplified photoresist was investigated as a function of the concentration of photoacid that was generated upon exposure. Although the sensitivity of a photoresist formulation improved by increasing the concentration of PAG in the resist formulation, the concentration of photoacid required to achieve an appropriate extent of deprotection to render development also increased. Using a standard addition technique, the efficiency of photoacid generation was quantified for resist systems consisting of triphenylsulfonium triflate as the PAG in an environmentally stable chemically amplified photoresist-type polymer primarily composed of 4-hydroxystyrene and tert-butyl acrylate monomers. Determination of the apparent efficiency of photoacid generation (the resist C parameter) allowed the concentration of photoacid within the resist film to be calculated for any exposure dose. Deprotection of the polymer was measured using infrared spectroscopy and analyzed as a function of the photoacid concentration within the resist. We determined from these results that the increase in the concentration of photoacid required for development of the resist was caused by a change in the deprotection process during the postexposure bake and was not due to dissolution inhibition by the unexposed PAG.
Polarization contact: Concept and initial assessment
Authors: Lam Michael , Neureuther Andy
Published: December 2002

Simulations using the aerial image simulator SPLAT are performed to analyze various structures for printing contacts, motivated by trying to condense the double exposure of two lines into a single exposure. The polarization contact uses polarization bars in the arms of two crossed orthogonal lines as a means to generate a contact in a single exposure. Characterizations of the contact structures are possible by investigating their normalized unit contours. From cut lines of these contours, each structure can be understood based solely on its geometries. The scaling property of optical systems allows these unit spread functions to ultimately characterize its behavior. The structures are similar in their response to 1 Rayleigh unit of defocus, with each structure having an intensity ratio of peak defocus to perfect focus of about 0.79. Dense contacts are generated using a polarization-phase carpet that condenses a double exposure with phase shifting into a single exposure, at a cost of 75% less throughput.
Optimizing vacuum ultraviolet attenuated phase shift masking materials
Authors: Smith B. W. , Bourov A. Y. , Liu Y.
Published: December 2002

Extensive vacuum ultraviolet (VUV) optical data have been collected for sputter-deposited thin films of masking material compounds for use at 157 nm. The use of VUV optical data and effective media modeling has lead to 27 possible material candidates for further study. These composite material films consist of a silicon dioxide host combined with various oxides and nitrides, generally of refractory metals. By adjusting material stoichiometry through control of deposition parameters (target composition ratios, pressure, power, flow rates, etc.), films have been tailored for specific optical properties. By using extinction coefficient/refractive index relationships for 180° phase shift, 4%–25% transmission, and <15% reflectivity, evaluation of the materials is possible. Additional detailed analysis of three specific composite materials is shown for use as attenuated phase shift masking at 157 nm. In each case, silicon dioxide is the host material within the film and the various metal oxides provide the appropriate absorption. The use of fluoride film etch stop materials is also described as a method to improve etch selectivity.