bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermally Induced Delamination Buckling of a Thin Metal Layer on a Ceramic Substrate
Authors: Liu C. J. , Ernst L. J. , Wisse G. , Zhang G. Q. , Vervoort M.
Published: December 2003

Interface delamination failure caused by thermomechanical loading and mismatch of thermal expansion coefficients and other material properties is one of the important failure modes occurring in electronic packages, thus a threat for package reliability. To solve this problem, both academic institutions and industry have been spending tremendous research effort in order to understand the inherent failure mechanisms and to develop advanced and reliable experimental and simulation methodologies, thus to be able to predict and to avoid interface delamination before physical prototyping. Various damage mechanisms can be involved and can result in interface delamination phenomena. These are not all sufficiently addressed and/or reported so far, probably because of the complexities caused by the occurrence of strong geometric and materials nonlinearities. One of the phenomena being insufficiently understood so far is the so-called buckling-driven delamination of thin metalic layers on ceramic substrates. This phenomenon will be discussed in the present paper.
Three- and Four-Point Bend Testing for Electronic Packages
Authors: Shetty Santosh , Reinikainen Tommi
Published: December 2003

This study demonstrates the application of three-point and four-point bending tests for evaluating the reliability of chip scale packages under curvature loads. A three-point bend test is conducted on 0.5-mm-pitch chip-scale packages (CSPs) mounted on FR4 (Flame Retardant) substrates. This test is simulated by using the finite element method and the results are calibrated experimentally to formulate a reliability model. A three-point bend scheme is an ideal choice for generating reliability models because multiple packages can be tested under multiple loads in a single test. This reliability model can be used to predict the durability of the packages in the real product under any printed wiring board (PWB) curvature loading conditions. A four-point bending simulation is also demonstrated on the test substrate. Four-point bending test is an ideal method for testing a larger sample size of packages under a particular predefined stress level. This paper describes the bending simulation and testing on packages in a generic sense. Due to the confidentiality of the test results, the package constructional details, material properties, and the actual test data have not been presented here.
Impact of Die Attach Material and Substrate Design on RF GaAs Power Amplifier Devices Thermal Performance
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom
Published: December 2003

The latest commercial applications for microelectronics use GaAs material for RF power amplifier (PA) devices. This leads to the necessity of identifying low cost packaging solutions with high standards for reliability, electrical, and thermal performance. A detailed thermal analysis for the wirebonded GaAs devices is performed using numerical simulations. The main interest of the study focuses on the impact of die attach thermal conductivity (1.0–50.0 W/mK), substrate’s top metal layer thickness (25–50 μm), and via wall thickness (25–50 μm) on GaAs IC device overall thermal performance. The study uses a two-layer organic substrate. The peak temperatures reached by the PA stages range from 99.6°C to 120.3°C, below the prohibitive/critical value of 150°C (based on 85°C ambient temperature). The increase of die attach thermal conductivity from 1.0 to 7.0 W/mK led to a decrease in peak temperatures of up to 18°C, with larger decay between 1 and 2.4 W/mK. The largest temperature differences were obtained by varying the thermal via thickness, as opposed to only increasing the top metal layer thickness. The peak temperatures and corresponding junction-to-ambient thermal resistances are thoroughly documented. With the same die attach thickness, for a thermal conductivity much larger than 7 W/mK, the impact on the PA’s peak temperature is insignificant. The die attach solder material (with a large thermal conductivity) leads to only a small (2.5°C) decrease in the PA junction temperature.
Humidity-Induced Voltage Shift on MEMS Pressure Sensors
Authors: Chiou J. Albert , Chen Steven , Jiao Jinbao
Published: December 2003

The pressure sensor is one of the major applications of microelectromechanical systems (MEMS). An absolute pressure sensor utilizes anodic bonding to create a vacuum cavity between the silicon diaphragm and glass substrate. The manifold absolute pressure (MAP) sensing elements from a new supplier have exhibited negative voltage shifts after exposure to humidity. A hypothesis has been established that poor anodic bonding causes an angstrom-level gap between the silicon substrate and glass. Once moisture enters the gap in a vapor form and condenses as water droplets, surface tension can induce a piezoresistive stress effect that causes an unacceptable voltage shift. Finite element analyses were performed to simulate the phenomenon and the results correlated well with experimental observations.
Four-Terminal Measurement and Simulations for Sheet Resistance in Piezoresistive Sensing Elements
Authors: Chen Steven , Chiou J. Albert
Published: December 2003

We have seen some wafers rejected with abnormally large within-wafer variation for the input resistance (Rin) of the X-ducer in the pressure sensing element. Input resistance consists of p+,p−, the resistance of aluminum lines, and its contact resistance to p+ and p−. A four-terminal measurement (FTM) is used to characterize piezoresistors for our pressure sensing elements. The purpose in using a FTM is to find which process causes this abnormally large input resistance. Good agreement has been obtained between the finite element analysis (FEA) and experimental measurement results for this FTM technique. The difference between the conventional van der Pauw method and FEA approach is also compared and presented. It is concluded that p+ variation is the major process to cause this abnormally large input resistance. This methodology was used to diagnose the process-related problem without using special test patterns. Therefore, the development cost and cycle time was significantly reduced.
A Vapotron Effect Application for Electronic Equipment Cooling
Authors: Lorenzini Giulio , Biserni Cesare
Published: December 2003

This research is aimed at investigating by experimental means a possible use of the Vapotron Effect for the cooling of electronic devices. The problem deals with a particular kind of subcooled boiling which is able to enhance heat exchange between a non-isothermal finned surface, simulating the packaging of an electronic component, and a refrigerant fluid (water in the case here presented) flowing on it. The experimental set up is first described in detail then employed to perform a number of tests aiming at a full characterization of the pulsatile nature of the phenomenon; the average heat transfer coefficient for the Vapotron Effect in a state of forced convection has been experimentally determined. The experimental tests have shown the existence of a relation that couples temperature trend of water in the cavities between the fins and cycle of events characterising the phenomenon. These results will be applied in the future to the study of more dynamic phenomena. A comparative analysis concerning the thermal performances of the Vapotron Effect concludes the paper.
Room-temperature single-electron charging effects in an ambipolar single-walled carbon nanotube grown by chemical vapor deposition
Authors: Amlani Islamshah , Zhang Ruth , Tresek John , Tsui Raymond K.
Published: December 2003

We present single-electron charging effects in a 150 nm long ambipolar semiconducting single-walled carbon nanotube grown by chemical vapor deposition. The Coulomb blockade model explains all essential features of the data. Due to the ambipolar characteristic, the device can be tuned to be either p or n type by applying a gate voltage. In the p-type region, a single quantum dot is formed and charging behavior is observable up to 150 K. In the n-type region, transport takes place through a coupled dot system and the charging effects can be clearly seen up to room temperature. We also qualitatively discuss the model that explains the formation of two electrostatically coupled dots in the n-type region.
Evaluation of the cleanliness of the ion-assisted Mo–Si deposition process for extreme ultraviolet lithography
Authors: Hau-Riege Stefan P. , Mirkarimi Paul B. , Walton Christopher C. , Sperry Victor , Larson Cindy
Published: December 2003

Particles are a serious concern in the fabrication of reticles for extreme ultraviolet lithography because they nucleate perturbations in the reflective multilayer film that can print in the lithographic image. We call these perturbations defects. It has been suggested that reticle substrates can be planarized and the high-spatial-frequency roughness of the multilayer film can be reduced by using an ion-assisted Mo–Si deposition process. In this article we discuss the cleanliness of this ion-assisted deposition process. Within one cleaning cycle, we improved the cleanliness of the deposition process without ion assist from 3–4 to 0.26 particles/cm2. Of these, 0.09 particles/cm2 are due to manual handling of the wafers. We found that in our experimental setup, the added particle density using a process with ion assist is more then six times larger than the added density without ion-assist, suggesting that further work is necessary to develop a clean ion-assisted deposition process. We characterized the chemical composition of some of the added particles and found that they contain Al, C, Fe, Mo, and Si.
Nanoparticle beam formation and investigation of gold nanostructured films
Authors: Khabari A. , Urban F. K. , Griffiths P. , Petrov I. , Kim Y.-W. , Bungay C.
Published: December 2003

The object of the present work is the formation of a nearly collimated beam of gold nanoparticles with a high deposition rate and investigation of the resulting nanostructured gold film deposited onto (111) silicon substrates. The shape, size, and orientation of nanostructured gold crystals were analyzed by transmission electron microscopy and x-ray diffraction, and optical properties were investigated by ellipsometry. It was found that the optical properties of gold nanostructured films are completely different from the optical properties of conventionally deposited films reported in the literature. It was also found most crystals were grown on (111) plane with an indication of an expitaxial contact between the film and the substrate. The crystallite size was approximately 8 nm in diameter. High-resolution transmission electron microscopy also revealed that the gold nanophase crystals are cubo-octahedral with larger surface areas (octahedral part) at (111) orientation.
Thermal stability of Pd supported on single crystalline SiO2 thin films
Authors: Min B. K. , Santra A. K. , Goodman D. W.
Published: December 2003

The effect of annealing temperature on a model Pd/SiO2 catalyst has been investigated using Auger electron spectroscopy (AES) and scanning tunneling microscopy. Pd clusters on a single crystalline SiO2 thin film are not altered with respect to size or shape upon heating to 700 K; however, interdiffusion and sintering of the Pd clusters take place between 750 and 1050 K. At 1000 K, AES data imply the formation of Pd–silicide. Above 1050 K, desorption of Pd occurs concomitant with the decomposition of SiO2.
Proton implantation effects on electrical and optical properties of undoped AlGaN with high Al mole fraction
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Pashkova N. V. , Pearton S. J. , Zavada J. M. , Wilson R. G.
Published: December 2003

Electrical and optical properties of undoped n-AlGaN films with Al composition close to 40% were studied before and after implantation of various doses of 100 keV protons. In the virgin samples, the electrical properties were determined by deep donor defects with an energy level near 0.25 eV from the conduction band edge and a concentration of ∼1018 cm−3. Other deep centers present had energy levels of 0.12, 0.3, and 0.45 eV. The luminescence spectra were dominated by two defect bands near 2.3 and 3.6 eV. Proton implantation significantly decreased the concentration of major donors even at the lowest doses of 1012 cm−2. For higher doses the Fermi level became progressively deeper and the data indicated complexing of defects present in the sample with either primary radiation defects or/and hydrogen introduced by implantation. The effect of the proton implantation on the intensity of luminescence bands was complicated but overall the intensity of defect bands was increased with implantation.
Wavelet monitoring of plasma etching
Authors: Kim Byungwhan , Choi Won Sun , Lim Myo Teak
Published: December 2003

In device manufacturing sites, plasma states are conventionally monitored by measuring the etch rate. A means for plasma monitoring is presented. This was accomplished by characterizing profile variations by means of a discrete wavelet transformation (DWT). The sensitivity of wavelet coefficients was evaluated as a function of plasma faults, which were simulated with the variations in the process parameters, including radio frequency source power, bias power, and SF6 flow rate. For each plasma fault, wavelet sensitivity was conducted separately for vertical, lateral, and overall profiles. Wavelet coefficients demonstrated high sensitivity to detecting plasma faults. Improved sensitivity was obtained as they were monitored individually. Compared to conventional etch rate- or profile anisotropy-based sensitivity, the wavelet-based one was considerably enhanced. By the demonstrated high sensitivity, the proposed DWT-based profile monitoring can be effectively used to monitor and diagnose plasma processes.
Electron beam induced conductivity in poly(methylmethacrylate) and SiO2 thin films
Authors: Bai Min , Pease R. Fabian W. , Meisburger Dan
Published: December 2003

Electron beam charging and discharging of insulating samples is greatly influenced by electron beam induced conductivity (EBIC). Most prior studies on EBIC focused on inorganic materials; measuring EBIC in organic resist was hampered by high extrinsic leakage and low induced conductivity. We describe here EBIC in thin (1 μm) films of poly(methylmethacrylate) (PMMA) and thermal SiO2. The measurements were made using the external bias method, with the insulating thin film sandwiched between a metal electrode and a highly doped silicon substrate. Under the same exposure conditions, we found the induced conductivity in PMMA to be almost two orders of magnitude less than that in SiO2. The induced current in PMMA responds linearly to the bias, regardless of the polarity, but the induced current in SiO2 is surprisingly dependent on not only electron beam energy, but also on bias polarity. When the top metal electrode is biased positively and the electron beam has high enough energy to penetrate the electrode and the oxide, the results indicate that an internal emission of electrons from the silicon substrate into the oxide contributes substantially to the total measured current.
Imprint lithography for integrated circuit fabrication
Authors: Resnick D. J. , Dauksher W. J. , Mancini D. , Nordquist K. J. , Bailey T. C. , Johnson S. , Stacey N. , Ekerdt J. G. , Willson C. G. , Sreenivasan S. V. , Schumaker N.
Published: December 2003

The escalating cost for next generation lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990’s, several research groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1999, Colburn et al. [Proc. SPIE 379 (1999)] discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as step and flash imprint lithography. The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of the wafer and template. This article traces the development of nanoimprint lithography and addresses the issues that must be solved if this type of technology is to be applied to high-density silicon integrated circuitry.
Predicting the thermomechanical distortion of extreme ultraviolet lithography reticles for preproduction and production exposure tools
Authors: Abdo A. , La Fontaine B. , Engelstad R.
Published: December 2003

The thermomechanical distortion of extreme ultraviolet lithography (EUVL) reticles during exposure may lead to significant image placement (IP) errors. As throughput requirements for high-volume manufacturing (HVM) increase, the necessary illumination power levels rise, resulting in further distortion of the reticle. The thermal response of the EUVL reticle is predicted using finite element models for a typical HVM exposure tool. The effect of increasing the EUV source power on reticle heating is investigated by comparing the thermal distortion expected in exposure tools using different throughput values corresponding to the α tool, β tool, and the HVM exposure tool (γ tool). The effect of imperfect contact between the EUVL reticle and the chuck surface on the IP errors due to thermal distortion is studied for different effective contact area ratios. Also, an alternative design concept is proposed, aimed at providing a solution to the microparticle trapping problem (between the reticle and the chuck).
Fabrication of high-numerical-aperture phase zone plates with a single lithography exposure and no etching
Authors: Gil Dario , Menon Rajesh , Smith Henry I.
Published: December 2003

We present a process for fabricating phase zone plates and other diffractive-optical elements that is capable of achieving high resolution, requires only a single lithography step, and no etching. For this process we use the negative resist hydrogen silsesquioxane (HSQ) (Dow Corning), which is sensitive to both electrons and x rays. HSQ’s extraordinarily high resolution (∼10 nm) and its SiO2-like properties make it an optimal choice for fabricating diffractive-optical elements that operate in the ultraviolet and deep ultraviolet. HSQ has an index of refraction very close to that of fused silica, and a negligible absorption down to 157 nm. As a result, if it is spun to the thickness corresponding to the desired phase step for the optic, patterning and development are the only required process steps. It is often desirable to place an absorbing layer on the areas surrounding the diffractive elements to prevent unwanted radiation from reaching the substrate when the optics are used for lithography and microscopy applications. We have developed a method that achieves this by means of a metal evaporation followed by a selectively controlled chemical etching (Fulton/Dolan process). We present e-beam and x-ray lithographic exposures in HSQ of phase zone plate arrays, and provide a full description of the selectively controlled chemical etching process as applied to the fabrication of diffractive optics. The focusing properties of the fabricated arrays are also presented.
Relation between spatial resolution and reaction mechanism of chemically amplified resists for electron beam lithography
Authors: Kozawa Takahiro , Saeki Akinori , Nakano Atsuro , Yoshida Yoichi , Tagawa Seiichi
Published: December 2003

The generation of acids in chemically amplified electron beam resists needs the cation radicals of base polymer and electrons, both of which are generated via the ionization of base polymer on the exposure. This leads to the separation of several nanometers between protons and counter anions. The separation deserves special attention from the viewpoint of resolution blur. The distribution of counter anions was examined with a simulation based on the Smoluchowski equation.
Effect of bismuth oxide as a buffer layer on metal–lanthanum-substituted bismuth titanate–insulator–semiconductor structures
Authors: Kang Sang-Woo , Rhee Shi-Woo
Published: December 2003

We have investigated metal/ferroelectric/insulator/semiconductor (MFIS) structures with lanthanum-substituted bismuth titanate (BLT) as a ferroelectric layer and bismuth oxide as an insulating buffer layer between BLT and Si substrate. BLT films and Bi oxide films were prepared by the direct liquid injection metal organic chemical vapor deposition process. The morphology of the Bi oxide film was changed with the increase of its thickness and the annealing temperature. Bi oxide on silicon was converted into Bi silicate during annealing at 750 °C. The morphology of the BLT films deposited on Bi oxide depended on the morphology of the Bi oxide film and on the reaction with Bi oxide during the annealing process, which was confirmed by transmission electron microscopy and energy dispersive x-ray spectroscopy. The maximum memory window was 0.83 V at the sweep voltage of 5 V with the Bi oxide film annealed at 650 °C and with a thickness of 5 nm. With BLT/Bi oxide annealed at 750 °C, the window was decreased due to the reaction between the BLT film, Bi oxide film, and Si substrate, and the leakage current density was increased. By inserting the buffer layer, the MFIS structure had a lower leakage current density than metal/ferroelectric/semiconductor structure.
20 nm polysilicon gate patterning and application in 36 nm complementary metal–oxide–semiconductor devices
Authors: Xu Qiuxia , He Qian , Liu Ming , Zhao Yuying , Chen Baoqing , Han Zhengsheng , Ye Tianchun , Wu Dexin
Published: December 2003

Plasma etching with high selectivity and anisotropy for 20 nm poly-Si gate patterning on EOT of 1.4 nm gate oxynitride is developed in a Cl2/HBr/O2 gas mixture successfully. Direct write e-beam lithography is used for an SAL601 chemically amplified negative resist pattern. Using a combination of resist ashing and TEOS hard mask trimming process, sub-25 nm TEOS SiO2 mask patterns are obtained in the control. Various gas mixtures based on Cl2, HBr, and O2 have been used to study the etching characteristics of poly-Si on EOT of 1.4 nm gate oxynitride. The O2 content as well as HBr are very sensitive to etch rate, selectivity, and the protection of the sidewalls of polysilicon, owing to SiO2-like film, SiOxBry, formed on the etched surface confirmed by x-ray photoelectron spectroscopy. And the ratio of Cl2/HBr/O2 in gas mixture is also tightly related to the etching profile. Using a four-step etching process under optimum conditions the selectivity of poly-Si to oxide is much higher than 500:1, in fact, after polysilicon etching the net deposition of oxide is observed, and no damage on the active area beside the gates for EOT of 1.4 nm gate oxide is observed, too. The etching profile of the 20 nm poly-Si gate pattern is perfectly vertical and an overall narrowing by an estimated 5 nm is observed for oxide masked poly-Si gate etching. The possible mechanism is discussed. This etching process combined with resist ashing and the TEOS hard mask trimming process are implemented successfully to the fabrication of high performance 36 nm gate length complementary metal–oxide–semiconductor (CMOS) devices and 42 nm gate length 32 frequency dividers with 57 stage/201 stage CMOS ring oscillators embedded, the EOT of gate oxynitrid is 1.4 nm, and very good results are obtained.
Magnesium oxide gate dielectrics grown on GaN using an electron cyclotron resonance plasma
Authors: Gila B. P. , Onstine A. H. , Kim J. , Allums K. K. , Ren F. , Abernathy C. R. , Pearton S. J.
Published: December 2003

Magnesium oxide was grown by gas source molecular beam epitaxy on (0001) oriented metalorganic chemical vapor deposition n-GaN using elemental Mg and atomic oxygen supplied from an electron cyclotron resonance plasma source. X-ray diffraction (XRD) indicated that the oxide was single crystal for TSUB=350 °C and mostly polycrystalline for TSUB=100 °C. Reflection high energy electron diffraction suggests that the films deposited at the lower temperature begin with a single crystal nucleation layer then quickly become polycrystalline. For both growth temperatures, the magnesium oxide was highly textured toward the (111) direction, with the polycrystalline samples showing a broader XRD peak but smoother surfaces. Single crystal MgO grown at 350 °C had high current leakage, prohibiting electrical measurements. A breakdown field of 2.3 MV/cm and an interface state density of 4×1011 cm−2 eV−1 were measured for the polycrystalline (TSUB=100 °C) magnesium oxide/GaN heterostructure.
Near edge x-ray absorption fine structure measurements of the interface between bottom antireflective coatings and a model deprotected photoresist
Authors: Jablonski Erin L. , Sambasivan Sharadha , Lin Eric K. , Fischer Daniel A. , Devadoss Chelladurai , Puligadda Rama
Published: December 2003

The interface between bottom anti-reflective coatings (BARCs) and a model deprotected photoresist, poly(4-hydroxystyrene) (PHS), was investigated using near edge x-ray absorption fine structure spectroscopy to identify mechanisms responsible for pattern degradation at the BARC/photoresist interface. Interactions at this interface can lead to pattern deviations such as footing, undercut, and pattern collapse. It was found that a residual layer is only formed when the bilayer is subject to ultraviolet exposure. The spectra of the BARC surfaces after photoresist processing and development show a combination of spectral features from both PHS and the BARC formulations. The data suggest that the residual layer results from interactions between crosslinker and photoresist that occur during normal photoresist processing.
Printing-based performance analysis of the engineering test stand set-2 optic using a synchrotron exposure station with variable sigma
Authors: Naulleau Patrick , Goldberg Kenneth A. , Anderson Erik H. , Bokor Jeffrey , Harteneck Bruce , Jackson Keith , Olynick Deirdre , Salmassi Farhad , Baker Sherry , Mirkarimi Paul , Spiller Eberhard , Walton Chris , O’Connell Donna , Yan Pei-Yang , Zhang Guojing
Published: December 2003

While interferometry is routinely used for the characterization and alignment of lithographic optics, the ultimate measure of performance for these optical systems is the transfer of an image or pattern into photoresist. Simple yet flexible exposure systems play an important role in this task because they allow complex system-dependent effects to be isolated from the printing results. One such tool has been implemented for alpha-class extreme ultraviolet (EUV) optics at Lawrence Berkeley National Laboratory using a synchrotron-based illumination source with programmable coherence. This static microfield exposure system has been used to characterize a four-mirror optical system designed for the EUV engineering test stand prototype stepper. Here we present a detailed performance analysis based on the large volume of lithographic data collected from this 0.1 NA system. Process window results are presented for dark field and bright field nested features down to a half pitch of 70 nm (k1 factor of 0.52) where a depth of focus of approximately 1 μm with 10% exposure latitude is demonstrated.
Atomic layer deposition of metal and nitride thin films: Current research efforts and applications for semiconductor device processing
Authors: Kim H.
Published: December 2003

Atomic layer deposition (ALD) has been studied for several decades now, but the interest in ALD of metal and nitride thin films has increased only recently, driven by the need for highly conformal nanoscale thin films in modern semiconductor device manufacturing technology. ALD is a very promising deposition technique with the ability to produce thin films with excellent conformality and compositional control with atomic scale dimensions. However, the applications of metals and nitrides ALD in semiconductor device processes require a deeper understanding about the underlying deposition process as well as the physical and electrical properties of the deposited films. This article reviews the current research efforts in ALD for metal and nitride films as well as their applications in modern semiconductor device fabrication.
Resolution improvement for a maskless microion beam reduction lithography system
Authors: Jiang Ximan , Ji Qing , Ji Lili , Chang Audrey , Leung Ka-Ngo
Published: December 2003

A maskless ion projection lithography technique called maskless microion beam reduction lithography (MMRL) has been developed at Lawrence Berkeley National Laboratory. As a candidate for a next generation lithography system, MMRL is designed to achieve sub-70 nm resolution. By adding a 100 μm diam limiting aperture at the focal plane of the ion beam, an aperture angle of 0.56 mrad [corresponding to numerical aperture (NA)=5.6×10−4] at the image plane has been obtained. Small NA can decrease the geometrical and axial chromatic aberrations of the MMRL system. Thus resolution better than 150 nm has been obtained. Simulation results indicate that the resolution can be further improved by decreasing the aperture diameter and minimizing the limiting aperture induced aberrations. Meanwhile, the single-shot exposure time can still be as low as 193 ms at NA≈10−5 if the high brightness ion source design is employed in the MMRL system.
Simulating fluid flow characteristics during the scanning process for immersion lithography
Authors: Wei A. , Abdo A. , Nellis G. , Engelstad R. , Chang J. , Lovell E. , Beckman W.
Published: December 2003

Immersion lithography has been proposed as a method for improving optical lithography resolution to 50 nm. The premise behind the concept is to increase the index of refraction in the space between the lens and wafer by insertion of a high refractive index liquid in place of the low refractive index air that currently fills the gap. Because the liquid will act as a lens component during the lithographic process, it must maintain high uniform optical quality. One source of optical degradation may be due to changes in the liquid’s index of refraction caused by a change in temperature. During the exposure process, energy is deposited onto the wafer, causing a rise in temperature. Consequently, any liquid in direct contact with elevated temperature portions of the wafer will also experience an increase in temperature. Two-dimensional computational fluid dynamics models were created to assess the thermal and fluid effects of the exposure process on the liquid temperature. This article presents the results of the numerical thermal and flow simulations. Both aligned and opposing flow directions were investigated for a range of inlet pressures that is consistent with what can be expected with active filling jets.
Approach to critical dimension error budget analysis and specification estimation by the Monte Carlo method
Authors: Lee Sung-Woo , Yeo Gi-Sung , Lee Jung-Hyeon , Cho Han-Ku , Han Woo-Sung
Published: December 2003

A systematic approach to determine the specifications for process latitude in a 80 nm node device is suggested based on critical dimension (CD) error budget analysis using the Monte Carlo method. Using an aerial image simulation with the Gaussian convolution model, CD error budget analysis is performed on line/space (L/S), island, and contact patterns in a 90 nm node device. The portions contributed by mask uniformity are 60%, 66%, and 50% for the L/S, island, and contact patterns, respectively, and they occupy a dominant part in comparison with ones from other factors. The contact pattern occupies 12% for focus variation, which shows the larger portion than the analysis result for L/S and island patterns. The contribution of the 1 nm grid size in the mask layout is approximately 10% of the in-field uniformity. The residual terms which include variations from aberration, inaccurate measurement, postexposure baking, development, line-edge roughness, etc. occupy 21% for L/S and contact patterns, and 16% for island patterns. Based on CD error budget analysis, specifications in a 80 nm node device are calculated. The portion contributed by each process variation in the 80 nm node device is assumed to be approximately equal to those in the 90 nm node device. The specifications for mask uniformity are 6.8 and 5.8 nm for L/S and island patterns, respectively, while they are 2.9 nm for the contact pattern. The small margin for the contact pattern is due to a large mask error enhancement factor. The contact pattern shows a drastic decrease in flare, focus margin, illumination uniformity, and mask transmittance. In the 80 nm node device, the grid size of the mask layout to generate the patterns should be reduced to less than 0.3 nm.
Deep dry etching of GaAs and GaSb using Cl2/Ar plasma discharges
Authors: Giehl Alexander R. , Gumbel Michael , Kessler Matthias , Herhammer Norbert , Hoffmann Goetz , Fouckhardt Henning
Published: December 2003

Deep dry etch processes for GaAs and GaSb are investigated. Reactive ion etching in Cl2/Ar plasma discharges is used to pattern GaAs and GaSb with a single-layer soft mask resist. Soft masks have many advantages over (metal) hard masks such as easy and inexpensive processing, low pinhole density, and high etching reproducibility. Using TI35ES, an image reversal resist developed by MicroChemicals, GaAs etch profiles of up to 25 μm depth and GaSb structures of more that 50 μm depth are obtained revealing considerable dimensional stability. Even for etch durations of more than 50 min the resist can be easily removed from the sample surface after the etch process. Roughnesses of etched surfaces of less than 1 nm (rms, measured by atomic force microscopy) are obtained after reactive ion etching for both materials. Photoluminescence measurements reveal that the surface stoichiometry is conserved during the etching step. Deep dry etching of GaAs and GaSb can be exploited for example to fabricate fiber or capillary connections to and between optoelectronic devices or to create substrate windows for backside-illuminated photodetectors in the infrared wavelength range.
Fabry–Pérot structures for attenuated phase-shifting mask application in ArF and F2 lithography
Authors: Chen H. L. , Wu H. S. , Lee C. C. , Ko F. H. , Fan Wonder , Hsieh C. I.
Published: December 2003

We demonstrate a structure for an attenuated phase-shifting mask (APSM) which is based on a three-layer Fabry–Pérot structure for ArF (193 nm) and F2 (157 nm) excimer laser based lithographies. The APSM structure is composed of a metal/dielectric/metal stack. The optical characteristics of the Fabry–Pérot structure meet the following requirements: 180° phase shift, transmittance in the range of 4%–15%, reflectance of less than 10% at the exposure wavelength, and high inspection contrast at the inspection wavelength. Common dielectric and metal materials, such as chromium, tungsten, amorphous silicon, silicon dioxide, aluminum oxide, and aluminum nitride films, can be used to construct the Fabry–Pérot structure. The top metal layer can also prevent charge accumulation during electron-beam writing.
Testing new chemistries for mask repair with focused ion beam gas assisted etching
Authors: Stanishevsky Andrei , Edinger Klaus , Orloff Jon , Melngailis John , Stewart Diane , Williams Alvina , Clark Richard
Published: December 2003

In modern photolithography mask repair, shorter exposure wavelengths, smaller dimensions, and tighter process latitudes pose new challenges. We have systematically investigated focused ion beam (FIB) gas assisted etching (GAE) of chrome and mask transmission at 193 nm ultraviolet (UV) irradiation for various FIB parameters. The gases, used either alone or in binary combinations, include XeF2, Cl2, NH3, CO, CO2, Br2, H2O, and O2. While the bromine GAE appears to be the most effective among single gases in etching chrome, the quartz transmission after chrome removal remains ∼50% compared with unexposed material, and residue is present. The gas mixtures NH3/Br2 and CO2/Br2 were found to reduce the amount of residue and to enhance the chromium mask etching rate compared to Br2-only etching. This enhancement occurs in a narrow range of gas partial pressures, and the FIB process may need to be optimized further. The best transmission at 193 nm UV irradiation of the FIB GAE repaired regions achieved to date with no postprocessing is ∼95% of the transmission of a blank mask. We also applied laser power to heat the area where the ion beam is incident. No increase in Cr removal rate was seen for the Br based chemistries. Some increase in removal rate was seen for Cl2+O2 and XeF2 but the overall rate with both gas and laser power was barely higher than sputtering alone.
Transient temperature measurements of resist heating using nanothermocouples
Authors: Chu Dachen , Wong Wai-Kin , Goodson Kenneth E. , Pease R. Fabian W.
Published: December 2003

Resist heating is one of the major factors that causes feature size variation and pattern displacement in photomask fabrication. A number of models have been published to predict the rise in temperature during resist heating, but no transient temperature experimental results are available to verify those models. We have fabricated thin film gold/nickel thermocouples with junction areas as small as 100 nm2 on silicon and 500 nm2 on quartz. Microsecond scale transient resist heating measurements were obtained using these thermocouples. Irradiation by a 15 keV, 150 nA electron beam of 1.7 μm radius for 100 μs yielded temperature rises at the resist bottom surface of approximately 62 K on quartz substrates and of 18 K on silicon substrates. Simulation results using a multilayer Green’s function model are in reasonable agreement with these experimental data for smaller temperature rises but tend to overestimate by about 10% for larger rises in temperature. In our experiments, a 100 ms exposure is equivalent to a dose of 150 μC/cm2. Under the same electron beam conditions electron dosages of 5 and 15 μC/cm2 result in temperature rises of 25 and 40 K, respectively, on quartz substrates.
Chemical recognition based on micromachined silicon cantilever array
Authors: Abedinov N. , Popov C. , Yordanov Zh. , Ivanov Tzv. , Gotszalk T. , Grabiec P. , Kulisch W. , Rangelow I. W. , Filenko D. , Shirshov Yu.
Published: December 2003

We report on the performance of a measurement system for the recognition of individual analytes and their binary mixtures which is based on a multiarray of four micromachined silicon cantivelers actuated at their resonance frequency. The cantilevers have been functionalized by organic polymers [polydimethylsiloxane (PDMS) and polyvinylpyridine (PVP)] and amorphous nitrogen-rich carbon nitride films. We found that the sensitivity and selectivity of the cantilevers coated with CNx films change according to the layer thickness. Our results show that the selected combination of sensitive layers ensures a wide range of specific, reversible and reproducible sensor responses upon exposure to methanol, 2-propanol, water and their binary mixtures. Further, it was found that the differences in recovery times of PDMS and CNx films after exposure to the two alcohols and their mixtures could be used especially for low analyte concentrations as a second characteristic in addition to the resonance frequency shift for the identification of individual components in the mixtures.
Polymer inking as a micro- and nanopatterning technique
Authors: Bao L.-R. , Tan L. , Huang X. D. , Kong Y. P. , Guo L. J. , Pang S. W. , Yee A. F.
Published: December 2003

A polymer inking technique was developed to form micro- and nanopatterns on a substrate. In this process, a polymer thin film is spin coated on a patterned mold. After contacting the substrate at a suitable temperature and pressure, the polymer on the protruded surfaces of the mold is transferred to the substrate and a positive image of the mold is obtained. A selective surface treatment method has been developed to improve the edge smoothness of the inked pattern. During selective surface treatment, the protruded surfaces of the mold are first treated with a flat poly(dimethylsiloxane) stamp impregnated with a silane that has medium surface energy. The mold is then immersed into the solution of another silane with very low surface energy to treat the trenches of the mold. Because the surface energy of the sidewalls is lower than that on the protrusions, polymer dewetting from the sidewalls is promoted, which makes the polymer film discontinuous along the edges of patterns. Therefore, inked polymer patterns from the protrusions of the mold show very smooth edges and smaller dimensions compared to that of the mold. The dimension change of the inked pattern is dependent on the selection of polymer materials. It was found that patterns inked from poly(carbonate) showed larger dimension shrinkage (∼75%) compared to that from poly(methyl methacrylate) (∼30%). This offers a viable approach to obtain predictable submicrometer features using a mold with much larger feature sizes.
Evolution of line-edge roughness during fabrication of high-index-contrast microphotonic devices
Authors: Barwicz Tymon , Smith Henry I.
Published: December 2003

We have investigated the evolution of line-edge roughness during fabrication of high-refractive-index-contrast microphotonic devices. First, we present a method for estimating the spectral density of line-edge roughness. Then, the effect of common fabrication steps on line-edge roughness is reported. Spectral-density estimates are obtained from high-resolution micrographs acquired with a scanning electron microscope. Line edges are detected in the micrographs and then analyzed using various statistical methods. The impacts on roughness of liftoff, reactive-ion etching, and two non chemically-amplified electron-beam resists are quantitatively evaluated. We found that smooth sidewalls require adequate coverage of sidewalls via polymerization during reactive-ion etching, and a sharp resist profile when liftoff is used. In general, roughness can be greatly reduced by adjusting fabrication parameters. The method described in this article can be used as an efficient process optimization tool for fabrication of high-refractive-index-contrast microphotonic devices.
Linear phase ring illumination monitor
Authors: McIntyre Greg , Neureuther Andrew R.
Published: December 2003

A phase shifting mask pattern consisting of an Airy pattern multiplied by a linear phase progression is introduced as a quantitative monitor for the angular distribution of illumination in optical projection printing. The proximity effect spillover from the pattern rings is in phase at the center position only for illumination from the designed off-axis illumination direction. Thus, a quantitative analysis of the intensity in a particular pupil location is available simply by measuring intensity at the center of the pattern. A theoretical analysis is presented and image simulation studies are made of an implementation based on four-phase mask making. The results show that the signal strength is high (about 1/3–1/5 of the clear field intensity per ring), the angular discrimination is good (about 0.5/ring number), and that linear phase rings are reasonably unaffected by aberrations. Mask requirements suggest this technique is most advantageous for monitoring dipoles or quadrupoles. Since the patterns print at normal exposure levels, they may also be included on product wafers to fingerprint the illumination during production.
Growth of semiconductor gallium nitride nanowires with different catalysts
Authors: Zhang Jun , Zhang Lide
Published: December 2003

Semiconductor gallium nitride nanowires had been prepared by different catalysts using chemical vapor deposition. In, Fe, Ni, and Au nanoparticles were used in the growth of semiconductor GaN nanowires. Preliminary results indicate that the In, Fe, and Ni are efficient catalysts in the large-scale synthesis of GaN nanowires and the size of the nanowires depends on the size of catalyst particle. The nanowires have a diameter of 20–100 nm and a length of up to several hundreds of micrometers. The growth of GaN nanowires obeys the vapor–liquid–solid mechanism. However, no GaN nanowires were observed on the substrate when Au was used. It may be because of the poor solubility between Au and nitrogen. Au does not have any catalytic activity in this system.
Deep level defects and doping in high Al mole fraction AlGaN
Authors: Bradley S. T. , Goss S. H. , Brillson L. J. , Hwang J. , Schaff W. J.
Published: December 2003

We have used depth-dependent cathodoluminescence spectroscopy (CLS) and secondary ion mass spectrometry (SIMS) to investigate the nature of deep level defects and their effect on Si doping of high Al mole fraction (25%–100%) AlGaN. SIMS results provide correlations between AlGaN deep level emissions from CLS and elemental impurities distributed through the epitaxial bulk films. The highest Al mole fraction (xAl) samples exhibit deep level optical emissions that correlate with O and C impurities measured by SIMS. These O impurities appear to introduce donors at low and intermediate Al compositions versus deep levels in Al-rich alloys. The CLS energy onset of near band edge peak emissions track the b=1 theoretical band gap for 0⩽xAl⩽0.98 while their peak emissions deviate monotonically. Temperature-dependent CLS reveal an activation energy decrease of the near band edge emission intensity from 54 to 36 meV for xAl>∼0.80. The absence of free carriers for xAl>0.80 is consistent with Si donor compensation due to deep levels associated with oxygen.
Vertically aligned carbon nanotubes grown by plasma enhanced chemical vapor deposition
Authors: Sato Hideki , Takegawa Hitoshi , Saito Yahachi
Published: December 2003

Plasma enhanced chemical vapor deposition, which enables growth of carbon nanotubes directly onto substrates, is potentially suitable for preparing carbon nanotubes as electron sources in field emission displays. In this article, we report the growth of aligned carbon nanotubes by microwave plasma enhanced chemical vapor deposition and investigate the effect of various parameters on the growth. Comparison among three catalysts (Fe, Co, and Ni) revealed that Fe gives the longest carbon nanotubes, while Co gives the carbon nanotubes with the smallest diameter. The growth of the carbon nanotubes strongly depends on the treatment time in the plasma. Field emission characteristics from the carbon nanotubes grown by the microwave plasma enhanced chemical vapor deposition are also shown.
Dose control for fabrication of grayscale structures using a single step electron-beam lithographic process
Authors: Hu Fei , Lee Soo-Young
Published: December 2003

Many optoelectronic devices include multidimensional (grayscale) semiconductor structures such as diffractive optical elements (DOE’s), blazed gratings, and photonic band gap (PBG) crystals. Their performance is known to be highly sensitive to dimensional accuracy of features in the multidimensional structure. Therefore, it is essential to have a tight control of the feature size in the fabrication process. Grayscale electron(e)-beam lithography enables a single step lithographic process for fabrication of such multidimensional structures and therefore has several advantages over using a binary lithographic process multiple times. As the feature size decreases, proximity effect in the e-beam lithographic process can make dimensions of the written features in a device substantially different from the ideal ones so that performance of the device is significantly degraded. In this paper, an efficient dose control scheme for grayscale e-beam lithography, which attempts to minimize the difference between the spatial exposure distribution and the “shape” of a multidimensional structure, is described along with results from an extensive computer simulation.