Nanoscale Topography Characterization for Direct Bond Interconnect

Nuclear pore complexes (NPCs) are supramolecular nanomachines that mediate the exchange of macromolecules and inorganic ions between the nucleus and the cytosol. Although there is no doubt that large cargo is transported through the centrally located channel, the route of ions and small molecules remains debatable. We thus tested the hypothesis that there are two separate pathways by imaging NPCs using atomic force microscopy, NPC electrical conductivity measurements, and macromolecule permeability assays. Our data indicate a spatial separation between the active transport of macromolecules through the central channel and the passive transport of ions and small macromolecules through the pore periphery.

This article discusses advanced developments and applications of chemical mechanical polishing (CMP) published recently in the selected papers indexed by Web of Science. The topics covered are advances in slurry and abrasives, pads and conditioning, CMP for semiconductor device manufacturing, CMP for other applications, modeling and simulations, and CMP with ultrasonic vibrations, lasers, photocatalysts, or UV lamps. Nonspherical abrasive particles have been developed for CMP, resulting in increased material removal rates (MRRs). Advanced conditioning methods have been proposed to uniformly generate pad surface shapes. Fixed abrasive CMP has advantages with higher MRRs. New models for designing the pad and conditioner have been proposed, and more uniform pad shapes can be obtained. Integrated advanced process control improves the wafer-to-wafer variation. Dental implants treated by CMP perform equally or better than the baseline-machined implants and the biphasic calcium phosphate-treated implants. The slurry distribution and the abrasive behavior can be simulated by means of multiphase modeling. Molecular dynamics simulations can explore the mechanism of CMP. CMP of wafers can be simulated using an atomic force microscope with its tapping mode. Theoretical models have been developed to calculate removal depths, study the chemical action in CMP, and explore the crystal orientation effects. CMP assisted by ultrasonic vibrations increases CMP MRRs and lowers the roughness of polished surfaces. CMP assisted by using UV lamp power, femtosecond lasers, or photocatalysts enhances CMP MRRs.

In atomic force microscopy (AFM), sharp and wear-resistant tips are a critical issue. Regarding scanning electrochemical microscopy (SECM), electrodes are required to be mechanically and chemically stable. Diamond is the perfect candidate for both AFM probes as well as for electrode materials if doped, due to diamond's unrivaled mechanical, chemical, and electrochemical properties. In this study, standard AFM tips were overgrown with typically 300 nm thick nanocrystalline diamond (NCD) layers and modified to obtain ultra sharp diamond nanowire-based AFM probes and probes that were used for combined AFM-SECM measurements based on integrated boron-doped conductive diamond electrodes. Analysis of the resonance properties of the diamond overgrown AFM cantilevers showed increasing resonance frequencies with increasing diamond coating thicknesses (i.e., from 160 to 260 kHz). The measured data were compared to performed simulations and show excellent correlation. A strong enhancement of the quality factor upon overgrowth was also observed (120 to 710). AFM tips with integrated diamond nanowires are shown to have apex radii as small as 5 nm and where fabricated by selectively etching diamond in a plasma etching process using self-organized metal nanomasks. These scanning tips showed superior imaging performance as compared to standard Si-tips or commercially available diamond-coated tips. The high imaging resolution and low tip wear are demonstrated using tapping and contact mode AFM measurements by imaging ultra hard substrates and DNA. Furthermore, AFM probes were coated with conductive boron-doped and insulating diamond layers to achieve bifunctional AFM-SECM probes. For this, focused ion beam (FIB) technology was used to expose the boron-doped diamond as a recessed electrode near the apex of the scanning tip. Such a modified probe was used to perform proof-of-concept AFM-SECM measurements. The results show that high-quality diamond probes can be fabricated, which are suitable for probing, manipulating, sculpting, and sensing at single digit nanoscale.

This paper explores strategies for fabricating and maintaining a sharp atomic force microscope (AFM) tip suitable for AFM data storage applications. To this end, AFM cantilevers have been incorporated into micromachined sled carriers and air-bearing sliders. These supports act to limit the maximum loading force on the AFM tip and allow for improved vibration immunity for the AFM cantilever in comparison to macroscopic loading schemes. Readback from a patterned rotating disk has been demonstrated using these devices. Silicon-carbide AFM cantilevers with diamond tips have been fabricated in a process compatible with that of the sleds and sliders. Molded silicon-nitride tips defined by the intersection of three surfaces have also been fabricated for AFM cantilevers. The molds for plane-plane-concave tips are defined by two silicon {111} planes and a silicon-dioxide curved surface. By geometry, the three surfaces necessarily have a unique intersection point, which may improve the consistency in sharpness of these tips relative to conventional pyramidal tips.

InGaN/GaN light emitting diode (LED) structures with different GaN barrier growth temperatures have been grown by metalorganic chemical vapor deposition (MOCVD). Atomic Force Microscopy (AFM)-Conductive AFM (CAFM) analysis has been performed to study the submicron scale electrical properties of the LED structures. The effect of high O impurity concentration, introduced during the low temperature barrier layer growth, on the MQW LED structure has been explored. It is observed that (VGa-ON)2- point defects formed in the MQW layer serve as deep-level traps and lead to defect-assisted tunneling. Increasing barrier growth temperature decreases O impurity incorporation and thus improves the device performance. INTRODUCTION InGaN/GaN MQW structures grown by MOCVD have been widely studied in the solid state lighting field for the past few decades. The role of introduced impurities and point defects formed during the epitaxial growth process and their effects on the optical properties of MQW structures have drawn a great deal of attention. Several previous investigations have been done on the effects of GaN barrier growth temperature on the characteristics of InGaN/GaN MQWs [1-3], in which the InGaN quantum wells were grown at low temperature from 700-760oC, while the growth temperature of the GaN barriers was varied over the range of 700-950oC. It was suggested that GaN barriers grown at temperatures below 800oC leads to the generation defects and In inclusions and higher barrier growth temperature up to 910oC improves the crystal quality of GaN barrier by suppressing the formation of deep level related defects. In the present work, the electrical properties of InGaN/GaN LED structure with same barrier growth temperature as the well temperature is studied. The effects of induced O impurity are discussed.EXPERIMENT The InGaN/GaN MQW and LED samples were grown on (0001) sapphire substrates with low temperature GaN buffer layers using Veeco K465i MOCVD reactor. 2.2µm undoped GaN layer and 2.7µm n-GaN layer were grown at 1085oC. 4 pairs of In0.14Ga0.86N/GaN (2.6 nm/10 nm) quantum wells were grown at 760oC for LED structure Al. 6 pairs of such quantum wells were grown at 760oC and 860oC for the InGaN wells and GaN barriers, respectively, for LED structure B1. 20nm p-AlGaN layer and 95nm p-GaN layer were grown at 980oC on top of the MQW structures to form the LED structures. AFM analysis was done on a Bruker Icon system and by using TESPA probe. CAFM module is mounted to the AFM system for conductivity studies of the sample. Extended-tunneling AFM tip holder and PFTUNA probes are used for AFM-CAFM analysis.EXPERIMENT RESULTS An AFM-CAFM study on LED structure with various reverse biases has been done on A1 and shown in Figure 2. Notice that in Figure (b) and (c), the color bar is from 450nA to 300nA, while 450nA to -400nA in Figure (d). High density of spots of early breakdown has been observed when the reverse bias increases. The high reverse current at those spots may owe to the defect-assisted tunneling by deep-level traps located in the MQW active layer [4]. This is consistent with the high O concentration and high point defects density in the MQW layer reported in Ref. [3]. These point defects cause leakage and deteriorate the device performance [5].CONCLUSION In summary, the InGaN/GaN MQW LED structure with 760oC quantum barrier growths has been investigated by AFM-CAFM system to study the submicron electrical properties of the sample. High density of spots of early breakdown caused by defect-assisted tunneling by (VGa-ON)2- complex point defects located in the MQW layer. These point defects cause leakage and deteriorate the device performance.

This research regards to a two-dimensional lateral pushing nanomanipulation using Atomic Force Microscope (AFM). Yet a reliable control of the AFM tip position during the AFM-based manipulation process is a chief issue since the tip can jump over the target nanoparticle and then the process can fail. However, a detailed Modeling and understanding of the interaction forces on the AFM tip is important for prosperous manipulation control and a nanometer resolution tip positioning. In the proposed model, Lund-Grenoble (LuGre) dynamic friction model is used as friction force on the contact surface between the nanoparticle and the substrate. This model leads to a stick-slip behavior of the nanoparticle that is so similar to the experimental behavior in nanoscale. Derjaguin interaction force is applied between the AFM tip and the nanoparticle which considers both attractive and repulsive interactions. The AFM is modeled by lumped-parameters model. A controller is designed based on the proposed dynamic model in order for positioning the AFM tip during a desired nanomanipulation task. Optimal sliding mode approach is used to design the controller. In this approach sliding surface which is used in the sliding mode approach is selected optimally based on the linear quadratic (LQ) method.

A facile approach for functionalizing atomic force microscopy (AFM) tips with nanoparticles (NPs) will provide exciting opportunities in the field of tip-enhanced vibrational spectroscopy and in probing the interactions between NPs and biological systems. In this study, through successive exposure to polydopamine and AgNO3 solutions, the apex of AFM tips was functionalized with silver nanoparticles (AgNPs). The AgNP-modified AFM tips were used to measure the interaction forces between AgNPs and supported lipid bilayers (SLBs) formed on mica, as well as to probe the penetration of SLBs by AgNPs, with an emphasis on the effect of human serum albumin (HSA) proteins. AgNPs experienced predominantly repulsive forces when approaching SLBs. The presence of HSA resulted in an enhancement in the repulsive interactions between AgNPs and SLBs, likely through steric repulsion. Finally, the forces required for AgNPs to penetrate SLBs were higher in the presence of HSA probably due to the increase in the effective size of the nanoscale protuberances on the AFM tip stemming from the formation of protein coronas around the AgNPs.

Nanoabrasive wear induced by an AFM diamond tip on stainless steel

With the advent of scanning probe microscopes, probe-based datarecording technologies are being developed for ultrahigh areal densityrecording, where the probe tip is expected to be scanned at velocities up to100 mm s−1. In one technique, a conductive atomic force microscope (AFM) tip is scanned over a phasechange chalcogenide medium and phase change is accomplished by applying either ahigh or low magnitude of current which heats the interface. Another technique isferroelectric data storage, where a conducting AFM tip is scanned over a leadzirconate titanate (PZT) film, a ferroelectric material. Ferroelectric domains can bepolarized by applying short voltage pulses between the AFM tip and the bottomelectrode layer that exceed the coercive field of the PZT film, resulting in nonvolatilechanges in the electronic properties. Tip wear is a serious concern in both datastorage methods. The understanding and improvement of tip wear, particularly atthe high velocities needed and at high interface temperatures for high data raterecording, is critical to the commercialization of these data storage technologies.This paper presents a review of nanotribological and nanomechanical studieson the materials used in phase change and ferroelectric probe-based recording.Although this work is aimed at probe-based data recording, it is also relevantto the development of robust AFM probes and to the study of nanocontacts ingeneral.

<p>An unconventional fabrication technique of nanoelectrode was developed using atomic force microscopy (AFM) and hydrogel. Until now, the precise control of electroactive area down to a few nm<sup>2</sup> has always been an obstacle, which limits the wide application of nanoelectrodes. Here, the nanometer-sized contact between the boron-doped diamond (BDD) as conductive AFM tip and the agarose hydrogel as solid electrolyte was well governed by the feedback amplitude of oscillation in the non-contact mode of AFM. Consequently, this low-cost and feasible approach gives rise to new possibilities for the fabrication of nanoelectrodes. The electroactive area controlled by the set point of AFM was investigated by cyclic voltammetry (CV) of the ferrocenmethanol (FcMeOH) combined with quasi-solid agarose hydrogel as an electrolyte. Single copper (Cu) nanoparticle was deposited at the apex of the AFM tip using this platform whose electrocatalytic activity for nitrate reduction was then investigated by CV and Field Emission-Scanning Electron Microscopy (FE-SEM), respectively.</p>

The dislocation density in freestanding gallium nitride wafers was measured using atomic force microscope (AFM) imaging of chemical mechanically polished (CMP) samples and with transmission electron microscopy (TEM). Etch pits were introduced after chemical mechanical polishing of the gallium side of the GaN wafer and the pits easily imaged with the AFM. TEM was also utilized to measure the dislocation density. Good agreement was found between the dislocation density measured by TEM and the etch pit density measured by AFM, demonstrating that chemical mechanical polish of the GaN(0001) surface decorates threading dislocations and that the AFM technique provides a reasonably accurate and convenient measure of the dislocation density. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Direct surface probing of cell wall-defective mutants of Saccharomyces cerevisiae by atomic force microscopy

The aggregation of proteins into fibrillar structures called amyloid is a characteristic of many diseases, including several neurodegenerative disorders. Although amyloid formation is inherent to several serious diseases, the mechanism of fibril formation and the modes of toxicity are not yet known. High concentrations of fibrillar aggregates of ¿-synuclein protein are found in the brains of patients suffering from Parkinson's disease. We exploit different contrast modes of high resolution atomic force microscopy (AFM) on fibrils formed by the wild-type alpha-synuclein protein, and by the familial disease-related A30P, E46K and A53T variants, to get more insight into the in vitro process of fibril assembly. From quantitative analysis of height images measured in tapping mode AFM, we obtained data that are compatible with a twisted hierarchical assembly model [1] for all protein variants. The E46K mutant displays the most distinct and smallest periodicity. The modulation depth for all mutants is very similar, and is smaller for wild-type protein commensurate with the lower fibril height. The detailed morphology observed in phase images indicates however that fibrils may also be formed through the association of fibril segments. To study the mechanical properties of fibrils we applied force while scanning in contact mode, resulting in characteristic deformation of protein fibrils with a periodicity corresponding to the modulation observed in tapping mode. Our observations suggest that the hierarchical assembly model may not be the exclusive mechanism of alpha-synuclein fibril assembly, but that multiple modes of fibril assembly play a role in alpha-synuclein fibril formation.

ABSTRACTEpitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400 °C under metaland oxygen-rich conditions in terms of metal-to-reactive oxygen ratio by plasma-assisted molecular beam epitaxy (MBE). Several atomic force microscopy (AFM) techniques were used to characterize the surface morphology and electrical properties of these GZO films in ambient conditions. Local I-V spectra indicate that layers grown under both O-rich and metal-rich conditions are highly resistive until a relatively high voltage sweep (±12 V) is used. After removal of an insulating surface layer, conduction is possible at lower voltages, but eventually the film resistivity increases and it again becomes insulating. In addition to local I-V spectra, local charge injection and subsequent surface potential measurements were used to probe surface charging characteristics. For charge injection experiments, a reverse-bias voltage is applied to the sample while scanning in contact mode with a metallized tip. The resultant change in surface potential due to trapped charge is subsequently observed using scanning Kelvin probe microscopy (SKPM). The layers deposited in a metal-rich environment demonstrate the expected behavior, but the O-rich layers show anomalous negative and positive charging. Finally, surface photovoltage (SPV) measurements using above-bandgap UV illumination were performed. The GZO layers produce SPV values of 0.4 to 0.5 eV, where the films deposited in an O-rich environment have slightly higher SPV values and faster restoration.

This paper describes a process to perform nanoscale welding of multi-walled carbon nanotubes (MWCNTs) using a conductive atomic force microscopy (AFM) tip. An AFM tip can be used not only to apply a mechanical force to push, drag or scratch a sample, but also to exert an electrostatic force between the conductive tip and a sample substrate by applying a bias voltage. This electrostatic field will be extremely high, due to the phenomenon of local field enhancement. Such a high electric field will provide enough energy for the metal atoms to evaporate from the conductive tip. In this paper, a model is developed to simulate the electrostatic field by adjusting the distance and the bias voltage between the conductive tip and substrate. The simulation results show that the radius of the conductive tip, the bias voltage and the gap distance will all affect the electric field intensity. In our experiments, MWCNTs are first assembled between a pair of electrodes using a dielectrophoresis (DEP) technique. Then, an electrostatic field is applied to weld MWCNTs onto the surface of microelectrodes. The experimental results show that MWCNTs can effectively be welded and the electronics performance can also be greatly improved.