bluuebunny/crossref_metadata_2025 huggingface dataset:
Solders Fatigue Prediction Using Interfacial Boundary Volume Criterion
Authors: Zhao X. J. , Zhang G. Q. , Caers J. F. J. M. , Ernst L. J.
Published: December 2003

In this paper, an “interfacial boundary volume” based damage criterion was proposed in combination with the modified Coffin-Manson model to predict solder fatigue. This criterion assumes that mainly, the behavior of the thin solder layer at chip pad interface contributes to the solder fatigue, not the whole solder joint or the averaged strains from randomly selected elements. The damage parameter was thus calculated by averaging the visco-plastic strain range over the interfacial boundary layer volume in the solder and later related to the corresponding fatigue life of experimental test through least-squares curves fitting to determine the empirical coefficients in the Coffin-Manson equation. As a demonstrator, the solder joint fatigue in wafer level chip scale packaging under thermal shock loading was analyzed. An appropriate constitutive relation from Darveaux was used to model the inelastic deformation of the solder alloy, and the different stress-strain responses resulting from different designs were calculated. The analysis results were used to develop the empirical fatigue model based on the interfacial boundary volume damage criterion and then this fatigue model was used for prediction. The fatigue lives of chip scale packaging with variable solder land size and component size were analyzed using this model. The prediction results match well with those from experimental tests. For this demonstrator, it was also shown that the empirical model based on the interfacial boundary volume criterion was more accurate than the models obtained from other strain averaging methods.
Reliability Prediction of Area Array Solder Joints
Authors: Dudek Rainer , Do¨ring Ralf , Michel Bernd
Published: December 2003

Packages for high pin counts using the ball grid array technology or its miniaturized version, the chip scale package, inherently require reliability concepts as an integral part of their development. This is especially true for the latter packages, if they are combined with the flip chip technology. Accordingly, thermal fatigue of the solder balls is frequently investigated by means of the finite element method. Various modeling assumptions and simplifications are common to restrict the calculation effort. Some of them, like geometric modeling assumptions, assumptions concerning the homogeneity of the cyclic temperature fields, simplified creep characterization of solder, and the related application of Manson-Coffin failure criteria, are discussed in the paper. The packages chosen for detailed analyses are a PBGA 272 and a FC-CSP 230.
Numerical Simulation of Delamination in IC Packages Using a New Variable-Order Singular Boundary Element
Authors: Tay A. A. O. , Lee K. H. , Lim K. M.
Published: December 2003

Delamination of interfaces in integrated circuit (IC) packages gives rise to electrical and mechanical failures such as popcorn cracking. Hence it is important to be able to analyze the mechanics of delamination from small interfacial defects which may exist at interfaces due to contamination or random factors. This paper describes the mechanics of interfacial delamination and the application of the boundary element method to analyze delamination propagation at interfaces. Now, a crack tip at an interface between two materials has an order of singularity which is a function of the material properties. For an accurate analysis, a special variable-order singular boundary element has been developed and used. The effect of defect size and location along the pad-encapsulant interface on interfacial delamination has been studied. It was found that the energy release rate or stress intensity factor increases with defect size as well as proximity to the pad corner. This implies that when a small delamination near a pad corner delaminates the crack tip nearer the pad corner will propagate first. The analysis has also shown that this delamination, once started, will continue until the crack tip reaches the pad corner. If the variation of interface toughness as a function of mode mixity is known, the delamination propagation behavior can be determined. Depending on the shape of the curve describing the variation of interface toughness with mode mixity, the delamination growth can either be stable, catastrophic, or initially unstable followed by stable growth.
3D Nonlinear Stress Analysis of Tin Whisker Initiation on Lead-Free Components
Authors: Lau John H. , Pan Stephen H.
Published: December 2003

In this study, a three-dimensional (3D) nonlinear stress analysis of the tin whisker initiation on a pure matte Sn-plated copper substrate is investigated. The structure is subjected to a compressive stress acting at the Sn layer which is generated by the spontaneous chemical reaction of the Sn layer and the Sn5Cu6 layer. The Sn layer is assumed to be an elasto-plastic material. The results presented herein is useful in understanding why the compressive stress in the Sn layer can initiate a tin whisker near the weak spot of a SnOx layer.
Maskless Process for Fabrication of Ultra-Fine Pitch Solder Bumps for Flip Chip Interconnects
Authors: Lee R. T. P. , Zuruzi A. S. , Lahiri S. K.
Published: December 2003

The results of this study demonstrate the viability of a low cost maskless process for the fabrication of ultra-fine pitch solder bumps. The fabricated solder bump arrays have a pitch and diameter of 120 and 70 μm, respectively. Widely used eutectic 63Sn37Pb and lead-free 95.5Sn3.8Ag0.7Cu solders were used to form the bumps. No solder bridging was observed between adjacent bumps, and the solder bumps exhibited good dimensional uniformity. The solder bump to aluminum (Al) pad bond integrity was found to be excellent, as evidenced by the high stress to failure. The failure mode is predominately Al pad lift-off indicating a robust solder bump-pad joint.
Electrical Conductive Characteristics of Anisotropic Conductive Adhesive Particles
Authors: Dou G. B. , Chan Y. C. , Liu Johan
Published: December 2003

In anisotropic conductive adhesive (ACA) interconnections, the particles are electrical conductors providing current paths in the fine pitch electronic packaging as well as physical parts connecting with the chip bumps and the substrate pads through the mechanical deformation interfaces. The primary object of this fundamental research is to reveal the electrical conductive characteristics of Ni/Au coated resin particles. Such an ACA particle resistance is resulted from two metal coated layers, which are two parallel resistors in the circuit determined by the particle transformation degree. In order to investigate the effect of the particle transformation degree upon the particle resistance, the particle transformation factor is defined. The mathematical electrical resistance function of an ACA particle, an integral function of the transformation factor and the particle geometries, resin diameter, nickel layer thickness, and gold layer thickness, is worked out from the physical model of an ACA particle. To carry out the solutions of the function, MathCAD software is applied. According to the numerical solutions, the deeper the particle transformation, the thicker the metal coated layer thicknesses and the longer the resin diameter are, the lower the particle resistance is. In conclusion, it is stated that the ACA particle resistance is determined by the particle transformation and the particle geometries, however, the transformation and the nickel layer thickness are more sensitive than the resin diameter and the gold layer thickness. Finally, the resistance function will explain the conductive mechanism of the deformed ACA particle.
Mechanical and Electrical Properties of Au-Al and Cu-Al Intermetallics Layer at Wire Bonding Interface
Authors: Wei Tan Chee , Daud Abdul Razak
Published: December 2003

Mechanical and electrical properties of the Au-Al intermetallics layer were compared to the Cu-Al intermetallics layer. A thermal aging test was used to expedite the formation and growth of the intermetallics layer. Dynamic hardness, surface hardness, and intermetallic thickness of both bonding systems was compared. Unencapsulated samples were subjected to a ball shear test while encapsulated samples were electrically tested. Results showed that the Cu-Al intermetallics layer is relatively harder than Au-Al. Both intermetallic thicknesses grow linearly at about 18.0 and 0.07 nm/h, respectively, but the Au-Al intermetallic layer is 20 times thicker than Cu-Al before the aging test. The 1.5-μm growth of Au-Al intermetallic thickness acquired an additional shear force of 160 gf. The threshold value of the intermetallics layer thickness for the Au-Al and Cu-Al bonding system is 3.8 and 0.14 μm, respectively, before it shows degradation in shear force. Electrical resistance for the Au-Al system is higher than the Cu-Al system, especially at higher aging readout points.
Effect of Bonding Force on the Conducting Particle With Different Sizes
Authors: Yeung N. H. , Chan Y. C. , Tan C. W.
Published: December 2003

Finite element analysis was used to model the transient heat transfer problem and the mechanical influence of the conducting particle in the anisotropic conductive adhesive (ACF). Three-dimensional (3D) brick element was performed for the transient heat transfer analysis, and the result was found that heat was transferred and spread from the die to the ACF and its conducting particle very quickly; in around 0.5 sec the ACF can reach the bonding temperature of 220°C. For the mechanical stress analysis of the conducting particle, the degree of the deformation was increased as the bonding force increased. The conducting particle was subjected to the larger stress level as the smaller of the particle size. The stress concentration was located at the edge area and diminished at the center area. It was also found that the cracks were found at the four corners of the conducting particles which was due to the highest stress level subjected on that location. Moreover, if only considering the plastic particle, the stress level was concentrated at the center area and vanished at the edge area.
A Board Level Study of an Array of Ball Grid Components—Aerodynamic and Thermal Measurements
Authors: Cole Reena , Davies Mark , Punch Jeff
Published: December 2003

Electronic package manufacturers publish thermal characteristics of components, which are measured using standard tests, measuring a thermal resistance value for a single component on a standard test printed circuit board (PCB). This limits the applicability of the characterization, as it does not show what aerodynamic or thermal interaction each package will have in a real system. This paper presents a new board-level electronics system test vehicle consisting of an array of ball grid components on three different effective thermal conductivity multi-layer PCB’s. Aerodynamic and thermal measurements are presented. It appears that PCB’s populated with low profile electronic packages behave like flat plates, leading to the proposition that component temperatures can be calculated using flat plate predictions. It is shown how both the airflow and the board conductivity can have a critical effect on the junction temperature, and a simple design rule is suggested, in terms of influence factors, to take account of these effects. These will lead to better estimates of electronic system reliability in the early part of the design cycle.
Nanometer-level repeatable metrology using the Nanoruler
Authors: Konkola Paul T. , Chen Carl G. , Heilmann Ralf K. , Joo Chulmin , Montoya Juan C. , Chang Chih-Hao , Schattenburg Mark L.
Published: December 2003

We report on the measurement of the fringe-to-substrate phase error in our Nanoruler system. This system utilizes scanning beam interference lithography to pattern and measure large-area, nanometer-accuracy gratings that are appropriate for semiconductor and integrated opto-electronic metrology. We present the Nanonruler’s metrology system that is based on digital frequency synthesizers, acousto-optics, and heterodyne phase sensing. It is used to assess the fringe-to-substrate placement stability and the accuracy of the feedback signals. The metrology system can perform measurements in real time, on the fly, and at arbitrary locations on the substrate. Experimental measurements are presented that demonstrate the nanometer-level repeatability of the system. Dominant error sources are highlighted.
Damage-free extreme ultraviolet mask with TaBN absorber
Authors: Shoki Tsutomu , Kinoshita Takeru , Sakaya Noriyuki , Hosoya Morio , Ohkubo Ryo , Usui Yoh-ich , Kobayashi Hideo , Nagarekawa Osamu
Published: December 2003

This article presents the results of evaluation of process-induced damage and improved reflectivity of an extreme ultraviolet (EUV) mask fabricated using a blank consisting of a multilayer, a Si capping layer, a CrN buffer layer, and a TaBN absorber. Long-term storage causes a centroid wavelength shift and stress change in the multilayer. The multilayer blank annealed at 90 °C was quite stable in centroid wavelength and film stress against resist baking at 135 °C and air storage. After the CrN buffer layer was etched with a mixture of Cl2 and O2 gases, the mask featured reflectivity loss of 1.5% due to the additional oxide layer generated on the Si capping layer. The reflectivity loss was able to be completely restored to its original value by treatment with a diluted HF solution. An EUV mask with a high reflectivity of 65% and excellent reflectivity uniformity of 0.7% 3σ was demonstrated using a blank consisting of a 40-period multilayer and a Si capping layer through a newly developed damage-free process that includes HF treatment.
Micromachined atomic force microscopy sensor with integrated piezoresistive sensor and thermal bimorph actuator for high-speed tapping-mode atomic force microscopy phase-imaging in higher eigenmodes
Authors: Pedrak R. , Ivanov Tzv. , Ivanova K. , Gotszalk T. , Abedinov N. , Rangelow I. W. , Edinger K. , Tomerov E. , Schenkel T. , Hudek P.
Published: December 2003

This article describes microprobes for noncontact scanning force microscopy that make use of a direct-oscillating thermally driven bimorph actuator with integrated piezoresistive readout sensor. The sensitivity has been increased using direct current for biasing and alternating current for exciting the thermally driven cantilever in a higher flexural mode. The cantilever operates in the phase-shift atomic force microscopy (AFM) detection technique. The main advantage of phase imaging is the higher z resolution at high scan rates and much lower forces than in height imaging with contact AFM. Critical dimensions measurements illustrating the imaging capability and resolution of our new scanning proximal probe are demonstrated.
Pattern and probe-based aberration monitors for the human eye
Authors: Robins Garth , Neureuther Andrew
Published: December 2003

A pattern and interferometric probe method is described for measuring aberrations in the human eye. Both subjective (human reporting) and objective (external measurement) embodiments are suggested. Simulation studies of targets are given for defocus, astigmatism, coma and trifoil. The results for the simultaneous presence of these aberrations at a combined Strehl ratio of 0.67 indicate that the aberration levels could likely each be individually quantified to an accuracy of 0.02λ rms waves such that the vision could be improved to a Strehl ratio of 0.94.
Demonstrations of electronic pattern switching and 10× pattern demagnification in a maskless microion-beam reduction lithography system
Authors: Ngo V. V. , Akker B. , Leung K. N. , Noh Isaac , Scott K. L. , Wilde S.
Published: December 2003

A proof-of-principle ion projection lithography (IPL) system called maskless microion-beam reduction lithography (MMRL) has been developed and tested at the Lawrence Berkeley National Laboratory for future integrated circuits manufacturing and thin-film media patterning [V. V. Ngo et al., J. Vac. Sci. Technol. B 17, 6 (1999)]. This MMRL system is aimed at completely eliminating the first stage of the conventional IPL system [G. Stengl et al., J. Vac. Sci. Technol. B 10, 2824 (1992)] that contains the complicated beam optics design in front of the stencil mask and the mask itself. It consists of a multicusp rf plasma generator, a multibeamlet pattern generator, and an all-electrostatic ion optical column. Results from ion beam exposures on poly(methymethacrylate) and Shipley UVII-HS resists using 75 keV H+ are presented in this article. Proof-of-principle electronic pattern switching together with 10× reduction ion optics (using a pattern generator made of nine 50 μm switchable apertures) has been performed and is reported in this article. In addition, the fabrication of a microfabricated pattern generator [K. L. Scott et al., J. Vac. Sci. Technol. B 18, 6 (2000)] on a silicon on insulator membrane is also presented.
Comparative hydrogen sensing performances of Pd– and Pt–InGaP metal–oxide–semiconductor Schottky diodes
Authors: Tsai Yan-Ying , Lin Kun-Wei , Chen Huey-Ing , Lu Chun-Tsen , Chuang Hung-Ming , Chen Chun-Yuan , Liu Wen-Chau
Published: December 2003

The hydrogen sensing performances of Pd– and Pt–InGaP metal–oxide–semiconductor (MOS) Schottky diodes are systematically studied and compared under different operating temperature. It is known that, from experimental results, the Pd–InGaP MOS Schottky diode exhibits higher hydrogen detecting capability at lower hydrogen concentration regimes. On the contrary, the MOS Schottky diode with Pt catalytic material shows better hydrogen detecting capability and higher operating temperature. It is believed that the refractory Pt metal is responsible for detecting high hydrogen concentration in air, especially at high operating temperature. Furthermore, the temperature dependence of equilibrium constants is investigated and reported. In order to study the steady-state reaction kinetics, the van’t Hoff equation is used to estimate the values of initial heat of adsorption for both devices. Based on the Temkin isotherm model, the experimental results and theoretical simulation of hydrogen coverage are also studied and compared.
Mitigation of residual film stress deformation in multilayer microelectromechanical systems cantilever devices
Authors: Pulskamp Jeffrey S. , Wickenden Alma , Polcawich Ronald , Piekarski Brett , Dubey Madan , Smith Gabe
Published: December 2003

An approach to compensate for the residual thin film stress deformation of multilayer microelectromechanical systems (MEMS) devices is presented based upon analytical and numerical modeling and in-process thin film characterization. Thermal and intrinsic deposition stresses can lead to the warping of released MEMS structures. This detrimental phenomenon in many cases can prevent proper device operation. Ellispsometric and laser wafer bow measurements yield thickness and film stress values that are used to update the deflection model during device fabrication, allowing for the compensation of the fabrication process variability. The derivations of linear and nonlinear residual film stress induced deflection models are presented. These models are based upon Bernoulli–Euler beam theory and are thus restricted to the associated geometric constraints. The models are initially validated by comparison with surface micro-machined sol–gel lead–zirconate–titanate cantilever structures; with initial experimental results agreeing well with both.
Critical dimension control of a plasma etch process by integrating feedforward and feedback run-to-run control
Authors: El Chemali Chadi , Freudenberg Jim , Hankinson Matt , Collison Wenli , Ni Tom
Published: December 2003

In this article, we have derived a run-to-run (R2R) control design technique that integrates feedforward and feedback control on the etch process. The purpose is to minimize the effect of an oxygen flow disturbance during the resist trim on the polysilicon critical dimension (CD) after the main etch. The R2R controller manipulates the resist trim time based on feedforward measurements of the resist CD at the end of the lithography and feedback measurements from polysilicon CD at the end of the etch process. The purpose of the feedforward measurement is to adjust the resist trim time using a model of the relation between trim time, resist CD before the resist trim and polysilicon CD after the main etch. The purpose of the feedback measurement is to adjust this model to compensate for the oxygen flow disturbance during the resist trim. The resulting controller is called feedforward/feedback (FF/FB) controller. The FF/FB controller is tested using simulations and experiments conducted on an etch tool manufactured by Lam Research. The simulations and experimental results show that the FF/FB controller attenuates linear drift and shift in the polysilicon CD caused by the oxygen flow disturbance. Moreover, the results quantify the significant benefit of integrating feedforward and feedback control in addition to only using a feedforward control in minimizing the polysilicon CD deviations from the etch target.
Comparison of dry etching of AlGaAs and InGaP in a planar inductively coupled BCl3 plasma
Authors: Baek I. K. , Lim W. T. , Lee J. W. , Jeon M. H. , Cho G. S. , Pearton S. J.
Published: December 2003

We studied dry etching of AlGaAs and InGaP in a planar inductively coupled BCl3 plasma. The process parameters were planar ICP source power (0–500 W), reactive ion etching (RIE) chuck power (0–150 W), and chamber pressure (5–15 mTorr). The process results were characterized in terms of etch rate, surface morphology, and surface roughness. The planar inductively coupled BCl3 plasmas were also monitored with in situ optical emission spectroscopy (OES). BCl3 planar inductively coupled process (ICP) etching of AlGaAs showed very vertical sidewall, clean and smooth surface, while that of InGaP showed somewhat rough surface after etching. Etch rates of AlGaAs were generally higher than those of InGaP in the planar BCl3 ICP etching. It indicated that InClX byproducts had relatively low volatility during InGaP etching in the planar inductively BCl3 plasmas. Increase of ICP source power and RIE chuck power strongly raised etch rates of both AlGaAs and InGaP. That of pressure decreased etch rate of both materials. OES data showed that emission intensity of the planar BCl3 ICP was a strong function of ICP source power and chamber pressure, while it was almost independent of RIE chuck power.
SiC/Si-dots multilayer structures formed by supersonic free jets of CH3SiH3 and Si3H8
Authors: Ikoma Yoshifumi , Ohtani Ryota , Matsui Nobuaki , Motooka Teruaki
Published: December 2003

We have investigated the formation of multilayer structures of SiC/Si-dots on Si(100) by supersonic free jet chemical vapor deposition. CH3SiH3 and Si3H8 jets were used for SiC and Si-dots, respectively. The first epitaxial SiC layer with a thickness of ∼15 nm and polycrystalline Si-dots with a size of ∼100 nm were grown by the first CH3SiH3 and following Si3H8 jet exposures. When the CH3SiH3 and Si3H8 jets were directed onto the Si-dot surface, thin (∼5 nm) SiC layers and ∼50 nm Si-dots were grown and formed Si-dots/SiC/Si-dots/SiC/Si(100). By repeating these SiC and Si-dots growths, polycrystalline SiC/Si-dots multilayer was formed on Si(100).
Photoluminescence quenching mechanisms in GaInNAs/GaAs quantum well grown by solid source molecular beam epitaxy
Authors: Ng T. K. , Yoon S. F. , Fan W. J. , Loke W. K. , Wang S. Z. , Ng S. T.
Published: December 2003

The photoluminescence (PL) quenching characteristics of a thermal-annealed ∼7 nm GaInNAs/GaAs quantum well (QW) with In=30% and N=1.5% were studied from 4 to 150 K. It is found that the integrated PL intensity versus temperature characteristic can be well fitted by a double activation energy model. One of the centers with low activation energy EB=9 meV is thought to originate from a localized state that traps carriers at temperatures below ∼100 K. Therefore, EB is the thermal energy required to activate the localized state carriers to the e1 state of the GaInNAs QW. Another center with larger activation energy EA=38 meV has a more significant PL quenching effect at temperatures above ∼120 K. This center is possibly contributed by the EL6 defect level in the GaAs barrier layer, as a result of low V/III ratio of 15, and low growth temperature of 450 °C.
Fabrication of a continuous diamondlike carbon membrane mask for electron projection lithography
Authors: Amemiya Isao , Yamashita Hiroshi , Nakatsuka Sakae , Tsukahara Mitsuharu , Nagarekawa Osamu
Published: December 2003

Fabrication of 8 in. high-performance continuous diamondlike carbon (DLC) membrane masks for electron projection lithography is described. The mask substrate materials and structures were optimized by evaluating the lithographic performance of the mask. The optimum mask consists of a sandwich structure, consisting of a thicker DLC scatter/a CrNx etching stopper/and a thin DLC support membrane on a bulk silicon wafer. The internal stress of each film component can be controlled by adjusting the film deposition conditions. A DLC film can be easily etched by oxygen gas, and the CrNx etching stopper has a high etching durability. Highly accurate pattern properties can be obtained while also meeting performance requirements. The critical dimension accuracy of a DLC scatterer was less than ±5% with a 280-nm-feature size in a 135×43 mm field. The electron aperture transmittance of a 44-nm-thick DLC membrane, measured by energy and angular distribution analysis for membrane, was 13 times as high as the 150-nm-thick SiNx membrane.
Why optical lithography will live forever
Authors: Brunner Timothy A.
Published: December 2003

A lithographic process capable of manufacturing state of the art chips faces many difficult challenges. Not only must the process resolve the minimum feature size but overlay errors must be held to tight tolerances, exquisitely complex patterns must be printed with high yield, and the overall cost of the process must be acceptable. Achieving acceptable chip cost using an expensive exposure tool is strongly linked to high throughput, and this in turn is linked to resist processes with high sensitivity. In recent years, chemically amplified resist processes have dominated state-of-the-art production because of their high resolution and excellent sensitivity. This article will consider limitations of resolution for production lithography, both the resolution limits of the exposure tool itself and the resolution limits of the resist process. Among the most important considerations for production processes is the tradeoff between resist process sensitivity and resolution. Fundamental reasons underlying the success of optical lithography for manufacturing integrated circuits will be described. These considerations will illuminate the challenges and opportunities for future lithographic methods.
Demonstration of 20 nm half-pitch spatial resolution with soft x-ray microscopy
Authors: Chao W. , Anderson E. H. , Denbeaux G. , Harteneck B. , Pearson A. L. , Olynick D. , Salmassi F. , Song C. , Attwood D.
Published: December 2003

The full field, transmission soft x-ray microscope XM-1 is a valuable imaging instrument for many scientific and technological areas involving nanometer features. Operating from 300 to 1800 eV, it combines high spatial resolution, elemental discrimination, magnetic sensitivity, and a capability of imaging in various experimental conditions, such as with applied magnetic fields and electric currents. In this article, we report experiments that enable accurate spatial resolution measurement, using a new type of test pattern, made from thinned multilayer coatings. The resolution of the microscope was measured to be 20 nm, using this method.
Fabrication of large area subwavelength antireflection structures on Si using trilayer resist nanoimprint lithography and liftoff
Authors: Yu Zhaoning , Gao He , Wu Wei , Ge Haixiong , Chou Stephen Y.
Published: December 2003

In this article we report on the fabrication of subwavelength antireflection structures on silicon substrates using a trilayer resist nanoimprint lithography and liftoff process. We have fabricated cone-shaped nanoscale silicon pillars with a continuous effective index gradient, which greatly enhances its antireflective performances. Our measurements show that the two-dimensional subwavelength structure effectively suppresses surface reflection over a wide spectral bandwidth and a large field of view. A reflectivity of 0.3% was measured at 632.8 nm wavelength, which is less than 1% of the flat silicon surface reflectivity.
Interferometric-spatial-phase imaging for six-axis mask control
Authors: Moon Euclid E. , Chen Lynn , Everett Patrick N. , Mondol Mark K. , Smith Henry I.
Published: December 2003

We describe a unified approach to measuring alignment and gap with nanometer detectivity between two planar objects (e.g., a mask and a substrate) in close proximity. The method encodes lateral position in the phase of interference fringes, formed by diffraction from grating and checkerboard alignment marks, designed to enable a wide acquisition range. For gapping, the method incorporates, in the same mark, coarse-gap detection (30–300 μm) and absolute-gap detection at sub-30 μm using a chromatic Fabry–Pérot scheme. Fine detection of sub-30 μm gaps is inferred from the frequency and phase of fringes, calibrated using the chromatic Fabry–Pérot. Illumination with a variable-bandwidth source enables either “achromatic” aligning or “chromatic” gapping. Sub-nanometer detection and feedback control of mask position is demonstrated in X, Y, and θ. Overlay of exposed patterns is demonstrated to be <3 nm.
Electric field effects in single semiconductor quantum dots observed by scanning tunneling luminescence
Authors: Håkanson U. , Håkanson H. , Johansson M. K.-J. , Samuelson L. , Pistol M.-E.
Published: December 2003

Scanning tunneling microscopy (STM) and scanning tunneling luminescence were used to correlate the topography with the emission spectra from individual self-assembled InP quantum dots (QDs). We have investigated in detail how the electric field induced by the STM tip affects the emission from the QDs. This was done when exciting a QD, by altering the bias for constant current, by altering the current for constant bias, or by changing the tip position. An increased bias (increased electric field) leads to Stark shift of the QD emission, whereas a larger tunneling current results in state filling of the emission. Furthermore, when exciting the QD, the position of the STM tip is shown to have large effects on the QD luminescence.
High aspect ratio nano-oxidation of silicon with noncontact atomic force microscopy
Authors: Clement N. , Tonneau D. , Gely B. , Dallaporta H. , Safarov V. , Gautier J.
Published: December 2003

We report the formation of high aspect ratio ∼0.3 (height/width) oxide features with noncontact mode atomic force microscopy assisted lithography. The process requires high humidity levels, series of short pulses <100 ns, high voltage level >25 V, a tip oscillation amplitude ∼20 nm, and feedback “on.” We also show that the application of a voltage at magnitude higher than a certain limit damages the surface.
Switching characteristics of electrostatically actuated miniaturized micromechanical metallic cantilevers
Authors: Teh W. H. , Luo J. K. , Graham M. R. , Pavlov A. , Smith C. G.
Published: December 2003

We report the fabrication and characterization of the smallest near-curvature-free electrostatically actuated Ni micromechanical switches reported to date. Our smallest one, which measures 10.0 μm×4.0 μm×0.15 μm suspended over a 430 nm gap is realized by using electron beam cross-linked polymethylmethacrylate as the sacrificial layer and electroplated nickel as the main structural material. Tunnel barriers are defined via in situ formation of Al2O3 during the oxygen plasma dry release step with a metal–insulator–metal junction formed when the switch closes. The reliable curvature-free properties of these devices demonstrate low pull-in voltage drifts (<1.5 V), even after 1 billion switching cycles. Also, they did not reveal an appreciable physical change even after being subjected to sintering treatments of 450 °C for 30 min, making them promising candidates for encapsulations. These devices have low hysteretic switching behavior (∼0.5–4.5 V), as compared with similarly fabricated switches without the barrier, which remain stuck once turned on.
Generation mechanism of residual clamping force in a bipolar electrostatic chuck
Authors: Kanno S. , Usui T.
Published: December 2003

Clamping and residual clamping forces of a Johnsen–Rahbek-type (JR-type) bipolar electrostatic chuck (ESC), which has electrically independent dual electrodes, were measured. Area ratios of the ESC’s two electrodes ranged from 1 to 4.6. It was found that the clamping force per unit area decreases with increasing area ratio and that the residual clamping force per unit area increases with increasing area ratio. To reveal the mechanism of residual clamping force, an equivalent circuit model of a JR-type bipolar ESC was devised. The model showed that the residual clamping force is caused by the residual charge that results from the charge difference in two monopolar ESCs. The charge difference is due to the resistance dependency on voltage of the dielectric layer of the ESC. The wafer voltage calculated from the model agreed well with the voltage measured by an electrostatic voltmeter. It can be concluded that the model is suitable for simulating the performance of a bipolar ESC.
Annealing temperature dependence of contact resistance and stablity for Ti/Al/Pt/Au ohmic contacts to bulk n-ZnO
Authors: Ip K. , Baik K. H. , Heo Y. W. , Norton D. P. , Pearton S. J. , LaRoche J. R. , Luo B. , Ren F. , Zavada J. M.
Published: December 2003

E-beam deposited Ti/Al/Pt/Au contacts on undoped (n∼1017 cm−3) bulk ZnO showed minimum specific contact resistance, ρc, of ∼6×10−4 Ω cm2 after annealing at 250 °C. This value was essentially independent of the surface cleaning procedure employed, including sequential solvent cleaning or H2 plasma exposure. Higher annealing temperatures degraded the ρc, and Auger electron spectroscopy depth profiling revealed increasing intermixing of the metal layers. The Al outdiffuses to the surface at temperatures as low as 350 °C, and the contact metallization is almost completely intermixed by 600 °C.
n
-type doping characteristics of O-implanted GaN
Authors: Nakano Yoshitaka , Kachi Tetsu , Jimbo Takashi
Published: December 2003

Doping characteristics of O-implanted GaN have been investigated systematically from the viewpoint of annealing temperature. The implanted O atoms became electrically active as an n-type dopant after annealing above 1050 °C, but with a low activation efficiency of only 1.1%. From variable temperature Hall effect measurements, O-implanted GaN displayed a shallow ionization level of ∼18.3 meV after 1100 and 1200 °C anneals. In addition, secondary ion mass spectrometry measurements showed no measurable redistribution of the O atoms by the annealing. These results indicate poor probability of the O atoms occupying an N lattice site in GaN.
Electron field emission of radio frequency magnetron sputtered CNx films annealed at different temperatures
Authors: Li J. J. , Zheng W. T. , Jin Z. S. , Wang X. , Bian H. J. , Gu G. R. , Zhao Y. N. , Meng S. H. , He X. D. , Han J. C.
Published: December 2003

The carbon nitride films deposited by rf magnetron sputtering in a pure N2 discharge were annealed in vacuum up to 900 °C. The chemical composition and bonding structure of the films were studied using x-ray photoelectron spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. It was found that the nitrogen atoms were bound to sp, sp2, and sp3 hybridized carbon atoms in as-deposited films. The effects of the thermal annealing on bonding structure and the electron field emission characteristics of CNx films were investigated. The results showed that thermal annealing treatment caused a great loss of N content and favor formation of sp2 bonds in CNx films, which would significantly influence the field emission properties for the CNx films. The CNx films annealed at temperature of 750 °C showed the optimal electron emission properties. Besides, the correlation between the chemical bonding structures and electron emission properties for the CNx films was discussed.
Effects of substrate heating and biasing on nanostructural evolution of nonepitaxially grown TiN nanofilms
Authors: Li T. Q. , Noda S. , Okada F. , Komiyama H.
Published: December 2003

The effects of substrate heating and substrate biasing on the initial stage of nonepitaxial heterogeneous growth of TiN on Si(111) was studied by using high-resolution transmission electron microscopy. Although TiN films deposited at room temperature (RT) undergo a transition from continuous amorphous films to polycrystalline films with three-dimensional grains when the film thickness is increased from ∼1 to 2 nm, crystallization occurred at a substrate temperature, Ts=570 K, even for film thicknesses less than 1 nm. Compared with growth at Ts=RT, at Ts=570 K, the initial lateral grain size was only slightly larger, and the grains tended to be spherical and discontinuous at higher film thickness. At a substrate bias voltage, Vb=−70 V, the grains were laterally larger and planar. At a film thickness of 50 nm, the films deposited at Vb=−70 V showed the thermodynamically favored (200) preferred orientation, whereas the films deposited at Ts=570 K showed (111) preferred orientation with a weak (200) peak.
Si adatom diffusion on Si (100) surface in selective epitaxial growth of Si
Authors: Lim Seung-Hyun , Song Sukchan , Park Tai-su , Yoon Euijoon , Lee Jong-Ho
Published: December 2003

The growth temperature dependence of Si adatom diffusion on Si (100) surface was systematically investigated in a cold wall ultrahigh vacuum chemical vapor deposition system. Si epitaxial layers were selectively grown on local oxidation of silicon patterned Si substrates. By cross-sectional transmission electron microscopy analysis, the increase in Si growth rate on the Si (100) surface near the edge of (311) facet was observed at various growth temperatures. This can be understood as a consequence of the mass transport from the sidewall (311) facet to the top (100) surface. Based on a simple diffusion model, the surface diffusion lengths of Si adatoms along the [110] direction were estimated to be about 70, 140, and 200 nm at 550, 600, and 650 °C, respectively. The calculated activation energy of 1.4 eV for diffusion of Si adatoms from the temperature dependence of the diffusion length was relatively higher than those in previous reports obtained under ultrahigh vacuum environment. This difference was discussed in terms of the discrepancy in the surface states by hydrogen adsorption on the Si surface.
Molecular transfer lithography for pseudomaskless, high-throughput, aligned nanolithography
Authors: Schaper Charles D.
Published: December 2003

A class of high-resolution printing methods, collectively called molecular transfer lithography (MxL), involves the replication of surface patterns as water-soluble templates. The templates are manufactured by spin-casting a polyvinyl alcohol (PVA) film-forming solution on a master pattern. The resultant water-soluble templates are then bonded to the substrate using an intervening adhesive layer that solidifies through photocuring, thermal, or two-part reactive schemes. The templates are chemically removed by dissolution with water yielding a formed pattern in the adhesion layer. Other variations of MxL include the transfer of materials to the substrate such as metals deposited on the template surface. For higher quality prints and overlay, contact alignment tools for MxL are needed. This article describes the implementation of MxL transfer schemes by adaptation of standard contact aligners normally used for photolithography. The primary modification required for integration is the replacement of the quartz photomask with the conformable water-soluble template. Results are presented to demonstrate the replication capability of MxL to sub-100 nm and the use of contact aligners to achieve deep submicron feature sizes and to enable three-dimensional printing while providing an intermediate level of overlay accuracy.
Advances in nanolithography using molecular rulers
Authors: Anderson M. E. , Tan L. P. , Tanaka H. , Mihok M. , Lee H. , Horn M. W. , Weiss P. S.
Published: December 2003

The combination of conventional lithographic techniques with chemical self-assembly allows for the creation of nanostructures whose spacing and edge resolution reach nanometer-scale precision. The controlled placement and thickness of self-assembled multilayers composed of alternating layers of α,ω-mercaptoalkanoic acids and coordinated metal ions form precise “molecular ruler” resists that enable the production of tailored and lithographically defined metal patterns. Initial structures created by conventional techniques are referred to as parents and subsequent structures generated by the molecular ruler process are identified as daughters. We report the further creation of subsequent generation structures (granddaughters) that have sub-100 nm dimensions. The granddaughter structures are created by forming molecular rulers on parent and daughter structures, and can be isolated by removing sacrificial parent and/or daughter structures. This process has also been utilized in combination with parent structures created by the process of nanosphere lithography to produce arrays of metal features with 10 nm spacings. Since our original report, we have improved the throughput and reproducibility of the molecular ruler process by automating its iterative nature and by utilizing appropriate chemical lift-off solutions.
Development of void-free focused ion beam-assisted metal deposition process for subhalf-micrometer high aspect ratio vias
Authors: Ray Valery , Antoniou Nicholas , Bassom Neil , Krechmer Alex , Saxonis Andrew
Published: December 2003

Low resistance metal deposition in deep submicron vias is required for circuit rewiring in focused ion beam (FIB)-based integrated circuit modification. Voids in high aspect ratio deposition, associated with the application of traditional FIB process to tungsten deposition in vias with aspect ratios beyond 10:1 contribute substantially to the resistance of the via. Pinch off of the via aperture is frequently observed. The dynamics of tungsten deposition within vias was studied through a series of via cross sections with variable deposition dose, and revealed accelerated deposition growth on the walls at the top of the vias. Accelerated deposition on the sidewalls, where the primary beam interacts with the substrate at a glancing angle, suggested that the deposition growth is initiated by secondary charged particles generated at the point of primary beam impact rather than by the primary beam itself. The results are in agreement with mechanisms previously proposed and confirmed by experiments. In order to prevent the generation of secondary particles on the walls of the via, and the consequent pinch off closure of the via aperture, confining the primary beam to an area much smaller than the aperture of the via was attempted. With this process, secondary particles are generated at the bottom of the via and trapped within the via, which was expected to lead to bottom-up deposition growth. A dose series study of the deposition produced by the proposed process confirmed the uniform growth of the tungsten fill from the bottom of the via. Void-free depositions were made in 5 μm deep vias ranging in size from 0.5 μm by 0.5 μm to 0.2 μm by 0.2 μm, corresponding to aspect ratios from 10:1 to 25:1, respectively.
Nanoelectrode lithography and multiple patterning
Authors: Yokoo A.
Published: December 2003

Multiple patterning of a Si substrate is performed by nanoelectrode lithography, which transfers the nanoelectrode pattern by an electrochemical reaction. By repeating the process with a line-and-space-pattern nanoelectrode, a checked pattern is successfully fabricated. The fabricated pattern is used as an etching mask to wet etch a Si substrate. The etching process has two possible results. With one, the transferred pattern additionally acts as an etching mask. With the other, only the overlapping area of the transferred pattern can act as a mask. These results derive from the flexibility of nanoelectrode lithography.
Precision microcomb design and fabrication for x-ray optics assembly
Authors: Sun Yanxia , Heilmann Ralf K. , Chen Carl G. , Forest Craig R. , Schattenburg Mark L.
Published: December 2003

Silicon microcombs developed at our laboratory for the precision alignment and assembly of large-area foil optics have previously been demonstrated to achieve submicron-level assembly repeatability with submillimeter-thick flat substrates. In this article we report on a double-side deep reactive-ion etch fabrication process using silicon-on-insulator wafers which was developed to improve the microcombs’ manufacturing accuracy.
Development of improved photosensitive polycarbonate systems for the fabrication of microfluidic devices
Authors: White Celesta E. , Henderson Clifford L.
Published: December 2003

A technique was recently developed for the fabrication of microfluidic devices that involves using thermally sacrificial polymeric materials in conjunction with other conventional microelectronic processes. This method provides more versatility and choice for construction materials than other current techniques, and it enables the integration of higher levels of functionality into microfluidic systems (i.e., fully integrated multilevel fluidic systems with functional valves, pumping systems, other microelectromechanical system components, and microelectronic devices). This article describes recent results related to the development of photodefinable polycarbonates with improved properties for thermally sacrificial polymer applications. Results of the synthesis and characterization of a polycarbonate that can be directly patterned with the use of photoacid generators via acid-catalyzed thermolysis of polycarbonates are presented.
Complementary exposure of 70 nm SoC devices in electron projection lithography
Authors: Yamashita Hiroshi , Amemiya Isao , Takeuchi Kunio , Masaoka Hideki , Takahashi Kimitoshi , Ikeda Akihiro , Kuroki Yukinori , Yamabe Masaki
Published: December 2003

We demonstrate complementary exposure of 70 nm system-on-a-chip (SoC) devices in electron projection lithography using Nikon’s EB stepper, NSR-EB1A, and a high-performance Si stencil mask (4×) fabricated by HOYA. A gate level of the SoC device pattern data called Anaheim was processed for mask fabrication using a 10 PC-clustered hierarchical data processing system in which complementary splitting was executed by the M-Split developed by Selete and ISS. Data processing times and output data volumes of the complementary split and of proximity effect correction were all drastically reduced by using our hierarchical data processing method. We optimized stitching features to compensate for the critical dimension (CD) changes that can occur with stitching errors caused by complementary exposures. The complementary stitching accuracy obtained was better than 20 nm and the CD accuracy was better than 10 nm for 100 nm line and space patterns because of the use of stitching features.