Fabrication Of High Aspect Ratio Research Articles

Fabrication of high aspect ratio, non-line-of-sight vias in silicon carbide by a two-photon absorption method

The future of Moore’s Law for high-performance integrated circuits (ICs) is going to be driven more by advanced packaging and three-dimensional (3D) integration than by simply decreasing transistor size. 3D ICs offer low-power consumption, high-performance and a smaller footprint compared to conventional 2D ICs. The key enabling technology to 3D integration is the interposer that provides interconnects to route signals between the chiplets that comprise the IC. However, the fabrication of high-aspect ratio through wafer vias (TWVs), that provide electrical and mechanical connection between chiplets on the top and bottom of the interposer, is one of the important challenges that limit interposer performance. Current fabrication technologies are limited by tapering effects and the need for direct line of sight to the fabrication surface. These limit the possible aspect ratios of vias and require large, complicated surface traces to connect the vias to the chiplets. Here, we demonstrate the fabrication of high-aspect ratio, non-line-of-sight TWVs in silicon carbide (SiC). SiC provides better mechanical, chemical, and thermal performance than silicon (Si). The technique uses an electro-chemical etch process that utilizes two-photon absorption to create any arbitrary 3D structure in SiC allowing for direct, subsurface routing between chiplets.

Modeling the impact of incomplete conformality during atomic layer processing

Atomic layer processing (ALP) is a modern fabrication technique for the deposition or etching of materials, which provides precise control of film thickness, composition, and conformality on a nanometer scale. This makes it crucial for the fabrication of high aspect ratio (HAR) structures, such as 3D NAND memory stacks, as its self-limiting nature provides enhanced conformality compared to traditional processes. However, as the number of NAND stacks grows and the aspect ratio continues to increase, deviations from full conformality can often occur due to precursor desorption from the surface. In this regard, a model for surface coverage during ALD in the presence of desorption, leading to incomplete conformality, has been developed and implemented in process simulation frameworks. This work is an extension of our previous research which concentrated on developing an accurate modeling approach for ALD in HAR structures (L.Aguinsky et al., Solid State Electron. 201, 2023). The model combines existing Knudsen diffusion and Langmuir kinetics methods and includes the Bosanquet formula for gas-phase diffusivity and reaction reversibility. It has been incorporated into academic and commercial level-set-based topography simulators. The parameters for the model have been calibrated using published results for the ALD of Al2O3 from trimethylaluminum (TMA) and H2O in HAR geometries. The temperature dependence of the H2O step is likewise analyzed, revealing an activation energy of 0.178eV, which is consistent with recent experiments. In the TMA step, the Bosanquet formula leads to improved accuracy, and the same parameter set is able to reproduce multiple experiments, demonstrating that the model parameters accurately capture reactor conditions. Finally, the developed model is combined with atomic layer etching (ALE) to simulate the controlled, conformal deposition of HfO2 inside HAR 3D NAND structures.

The 3D Controllable Fabrication of Nanomaterials with FIB-SEM Synchronization Technology.

Nanomaterials with unique structures and functions have been widely used in the fields of microelectronics, biology, medicine, and aerospace, etc. With advantages of high resolution and multi functions (e.g., milling, deposition, and implantation), focused ion beam (FIB) technology has been widely developed due to urgent demands for the 3D fabrication of nanomaterials in recent years. In this paper, FIB technology is illustrated in detail, including ion optical systems, operating modes, and combining equipment with other systems. Together with the in situ and real-time monitoring of scanning electron microscopy (SEM) imaging, a FIB-SEM synchronization system achieved 3D controllable fabrication from conductive to semiconductive and insulative nanomaterials. The controllable FIB-SEM processing of conductive nanomaterials with a high precision is studied, especially for the FIB-induced deposition (FIBID) 3D nano-patterning and nano-origami. As for semiconductive nanomaterials, the realization of high resolution and controllability is focused on nano-origami and 3D milling with a high aspect ratio. The parameters of FIB-SEM and its working modes are analyzed and optimized to achieve the high aspect ratio fabrication and 3D reconstruction of insulative nanomaterials. Furthermore, the current challenges and future outlooks are prospected for the 3D controllable processing of flexible insulative materials with high resolution.

Formation of high aspect ratio through-glass vias by the combination of Ultrasonic micromachining and copper electroplating

Fabrication of high aspect ratio (>5) multiple copper-filled through-holes in non-conductive materials like glass and single-crystal‑silicon is reported by using a faster (>8 μm/s) ultrasonic micromachining (USM). A customized stainless tool having multiple tips arranged in a 6 × 6 area-array manner was used with ~1 μm-size Silicon carbide (SiC) abrasive particles. Numerical simulations were performed to find a suitable horn to reduce the losses during the transmission of ultrasonic wave propagation. A tapered horn profile was chosen to transmit the vibrations uniformly from the ultrasonic head to the multiple tips. A novel technique was proposed to measure the vibration amplitude at different ultrasonic power ratings. >250 experiments were carried out to investigate the effect of ultrasonic power ratings and tool feed rate on the geometric characteristic of microholes. Average etch rates as high as 8 μm/s and 6 μm/s were obtained for glass and silicon, respectively. These average etch rates are higher than those obtained with plasma etching and electrochemical discharge machining. Through-holes were created in a 1.1 mm thick glass substrate in <3 min. The importance of post-USM cleaning by ultrasonic agitation was highlighted, which helped in removing the abrasive particles stuck inside the through-holes. Copper was deposited inside these through-holes using a bottom-up electroplating approach. These copper-filled through-holes can be used as 3-dimensional (3D) interconnects required in various microsystems packaging-related applications.

Generation of high aspect ratio complex micro-features by micro-electrochemical milling employing novel flushing technique

Fabrication of high aspect ratio (HAR) complex micro features on high strength temperature resistant (HSTR) alloys is challenging by any conventional or non-conventional machining methods. In this study blind, HAR and complex micro features have been fabricated by micro electrochemical milling (MEM) on HSTR Cobalt alloy (Haynes-188) introducing a new strategic approach with novel flushing technique which could get rid of the need of pulsed DC power supply. Multiphysics simulation of the rotating micro-tool at different rpm and its impact on effective sludge removal has been analyzed and verified experimentally. In this study, most influencing parameters of MEM like voltage, feed rate, rpm of tool and milling layer depth have been selected to investigate their effects on the machining responses like width overcut, machined depth and surface roughness on Haynes-188 alloy. Comparison has also been made with constant and pulsed DC power source to know the influence of these process parameters on the MEM responses. Finally, several linear and non-linear blind, HAR (AR > 11) and intricate micro features have been fabricated successfully on cobalt alloy at the most suitable parametric combination, i.e., 7.5 V of machining voltage, feed rate of 0.3 mm/min, and tool rotation of 750RPM with 0.5 M of NaNO3 electrolyte.

Fabrication of high aspect ratio and tilted nanostructures using extreme ultraviolet and soft x-ray interference lithography

We demonstrate the fabrication of metal and dielectric nanostructures using interference lithography with extreme ultraviolet (EUV) and soft x-ray synchrotron radiation down to a 2.5 nm wavelength. These specific wavelengths are chosen because of the industrial relevance for EUV lithography and because they are in the vicinity of the oxygen absorption edge of the high-resolution hydrogen silsesquioxane photoresist, allowing for the exposure of thick layers. We investigate the requirements to fabricate such structures and demonstrate that tall metal nanostructures with aspect ratios up to 7 could be achieved by EUV interference lithography and subsequent electroplating. We use the unique depth-of-focus-free property of interference and achromatic Talbot lithography to fabricate uniformly tilted dielectric nanostructures.

High-throughput fabrication of high aspect ratio Ag/Al nanopillars for optical detection of biomarkers.

Nanomaterial-based optical techniques for biomarker detection have garnered tremendous attention from the nanofabrication community due to their high precision and enhanced limit of detection (LoD) features. These nanomaterials are highly responsive to local refractive index (RI) fluctuations, and their RI unit sensitivity can be tuned by varying the chemical composition, geometry, and dimensions of the utilized nanostructures. To improve the sensitivity and LoD values of these nanomaterials, it is common to increase both dimensions and aspect ratios of the fabricated nanostructures. However, limited by the complexity, prolonged duration, and elevated costs of the available nanofabrication techniques, mass production of these nanostructures remains challenging. To address not only high accuracy, but also speed and production effectiveness in these nanostructures' fabrication, our work reports, for the first time, a fast, high-throughput, and cost-effective nanofabrication protocol for routine manufacturing of polymer-based nanostructures with high sensitivity and calculated LoD in the pM range by utilizing anodized aluminum oxide (AAO) membranes as templates. Specifically, our developed platform consists of arrays of nearly uniform polystyrene nanopillars with an average diameter of ∼185 nm and aspect ratio of ∼11. We demonstrate that these nanostructures can be produced at a high speed and a notably low price, and that they can be efficiently applied for biosensing purposes after being coated with aluminum-doped silver (Ag/Al) thin films. Our platform successfully detected very low concentrations of human C-reactive protein (hCRP) and SARS-CoV-2 spike protein biomarkers in human plasma samples with LoDs of 11 and 5 pM, respectively. These results open new opportunities for day-to-day fabrication of high aspect ratio arrays of nanopillars that can be used as a base for nanoplasmonic sensors with competitive LoD values. This, in turn, contributes to the development of point-of-care devices and further improvement of the existing nanofabrication techniques, thereby enriching the fields of pharmacology, clinical analysis, and diagnostics.

Large area fabrication of high aspect ratio nano‐cylinders on micro‐pillars based on a colloidal crystal mask

The combination of microstructures and nanostructures has broad application prospects. However, most existing methods are oriented to fabricating microstructures and nanostructures separately, and the fabrication of nanostructures on a microstructured surface at the wafer level is rarely studied. In this work, a new method of fabricating large-area high aspect ratio nano-cylinders on micro-pillars based on a colloidal crystal mask is proposed. An experimental device for stripping and draining was designed to create a polystyrene colloidal crystal mask. Together with reactive-ion etching and metal-assisted chemical etching, high aspect ratio nano-cylinders on micro-pillars with controllable size were obtained on a 4-inch silicon wafer. Wetting tests were performed on four groups of fabricated structures of different sizes, and the results showed that all samples were superhydrophobic. Thus, a method for fabricating uniform, size-controllable, large-area high aspect ratio nano-cylinders on micro-pillars with great potential as a superhydrophobic engineering material is proposed.

Developing Cu pore-filling percentage in hard anodized anodic aluminum oxide templates with large diameters

This study aims to overcome a major challenge that is reaching high pore-filling percentage (FP) in the fabrication of high aspect ratio (HAR) nanowires (NWs) grown electrochemically in large diameter porous templates. By ultrathinning the barrier layer of hard anodized anodic aluminum oxide (AAO) templates with large pore diameters (Dp) of 110 and 180 nm, while also filling its branched sections with FeCoNi, the development of Cu FP was investigated for different Cu solution concentration (MCu = 0.05–0.3 M) in the fabrication of HAR Cu NW arrays using a pulsed electrochemical deposition technique under optimized parameters. At Dp = 180 nm, field-emission scanning electron microscopic investigations revealed that, increasing MCu increases the corresponding FP up to 62%, resulting in highly uniform NW arrays. Structural properties were investigated by X-ray diffraction analysis, indicating that different phase percentages of Cu and Cu2O are formed depending on Dp of AAO and MCu. The resulting HAR Cu NWs were also released from the hard templates to obtain free-standing NW arrays with a length of 70 μm, which may find potential use for large-scale nanodevice applications.

Conformal and Smooth TiN Film Growth By Using ALD Method

As the generation of memory devices evolve, the successful fabrication of high aspect ratio (HAR) features becomes more and more challenging. Apart from the traditional patterning, deposition and etch related issues, conformal film deposition onto these HAR structures becomes a critical parameter in determining the overall device yields. It is well established now that compared to conventional deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), atomic layer deposition (ALD) offers a pathway to highest conformality and step-coverage. On the other hand, film conformality, especially roughness property has trade-off relationship to step-coverage property. High-pressure process is appropriate to obtain high step-coverage performance in short ALD cycle time process, but roughness value becomes worse due to higher chance of crystalline film growth at high-pressure process condition. High roughness causes local variations in step-coverage and poses problems for deposition of subsequent layers and device performance.In the present study, we report that it is possible to obtain conformal and smooth TiN film by using low/high pressure two-step growth, initially low-pressure TiN growth, and secondly high-pressure TiN growth on the non-pattern and HAR pattern wafers. Eugenus’s versatile 300mm mini-batch system and HAR structures with approximately 120:1 (Dimension of bottom opening, and total height are approximately 17nm and 2μm, respectively) were used in this research, respectively. TiCl4 and NH3 were used as the precursors for TiN film deposition and grown TiN films were analyzed by using ellipsometry, atomic force microscopy (AFM) and transmission electron microscopy (TEM) to study the film properties and step-coverages. In addition, reactor-scale computational fluid dynamics (CFD) simulations were performed and correlated to on-wafer experimental results and utilized as a predictive tool.It was found that TiN film grown at low-pressure condition was more conformal and smoother than that grown at high-pressure condition, although step coverage value grown at low-pressure condition was worse than that grown at high-pressure condition. By optimizing low/high pressure two-step TiN growth condition, it was achieved that not only better roughness than that of pure high-pressure TiN, but also, better step coverage value than that of pure low-pressure TiN as well as than that of pure high-pressure TiN (Figure 1). Figure 1

Ion-Induced Nanopatterning of Bacterial Cellulose Hydrogels for Biosensing and Anti-Biofouling Interfaces

Hydrogels provide a solution-mimicking environment for the interaction with living systems that make them desirable for various biomedical and technological applications. Because relevant biological processes in living tissues occur at the biomolecular scale, hydrogel nanopatterning can be leveraged to attain novel material properties and functionalities. However, the fabrication of high aspect ratio (HAR) nanostructures in hydrogels capable of self-standing in aqueous environments, with fine control of the size and shape distribution, remains challenging. Here, we report the synthesis of nanostructures with a HAR in bacterial cellulose (BC) hydrogel via directed plasma nanosynthesis using argon ions. The nanostructures in BC are reproducible, stable to sterilization, and liquid immersion. Using in-situ surface characterization and semi-empirical modeling, we discovered that pattern formation was linked to the formation of graphite-like clusters composed of a mixture of C-C and C=C bonds. Moreover, our model predicts that reactive species at the onset of the argon irradiation accelerate the bond breaking of weak bonds, contributing to the formation of an amorphous carbon layer and nanopattern growth.

Fabrication of hollow coaxial Al2O3/ZnAl2O4 high aspect ratio freestanding nanotubes based on the Kirkendall effect

In this communication, fabrication of high aspect ratio Al2O3/ZnO/Al2O3 nanotubes is reported and morphological changes at elevated temperatures are investigated. The structures were made by implementing several fabrication methods, such as deep-UV lithography, atomic layer deposition (ALD), and plasma etch methods. During the fabrication, the ALD deposited Al2O3 and ZnO conformally passivated the prepared Si-holes template, resulting in the complex coaxial Al2O3/ZnO/Al2O3 pillars. By utilizing several scanning and transmission electron microscopy techniques, it is experimentally shown that at elevated temperatures, internal voids form in the nanotube due to diffusion of ZnO into surrounding Al2O3 and also ZnAl2O4 spinel structure forms. Finally, the porous tubes have been isolated from the surrounding silicon core using a conventional isotropic selective Si plasma etch process. The presented approach opens the opportunity to build complex optical metamaterial compositions, for example, for a new generation of sensors for gas and biomarker detection.

Optimization of photoresist development and DRIE processes to fabricate high aspect ratio Si structure in 5 nm scale

The fabrication of high aspect ratio (AR) Si structure with extremely small feature size is attracting more and more attention recently. In this work, a top-down scheme for fabricating nanostructures with 4.4 nm line width and 40:1 AR has been proposed and demonstrated. This technique utilizes electron beam lithography for nano-scale patterning and deep reactive ion etching (DRIE) for pattern transfer. In this method, a special development strategy is discussed to improve the perpendicularity of the photoresist mask, and a novel nano-scale barrel is utilized as the testing structure for the DRIE process optimization. To study the critical dimension (CD) variation in the DRIE process, the geometric morphology of the obtained vertical barrels is simulated by an ion transport model. It is found that the asymmetrical lateral etching encroachment decreased the CD loss by 50%. Without using a hard mask, this technique is fully compatible with Si-based microelectronic processes. Therefore, after further study of geometric properties of the obtained nano structure, this proposed microelectronic-compatible approach sheds light on manufacturing 3D nano devices towards 5 nm scale and beyond.

Fabrication and thermoresistive behavior characterization of three-dimensional silver-polydimethylsiloxane (Ag-PDMS) microbridges in a mini-channel

Polydimethylsiloxane (PDMS) microstructures, such as micro-pillars, have versatile applications as actuators in microfluidic devices. With the addition of functional materials, e.g., silver (Ag) particles, PDMS structures can also attain sensing properties such as electrical conductance. In this paper, we introduce a fabrication technique using sacrificial agar to develop novel double-side hinged PDMS and Ag-PDMS microstructures, called three-dimensional microbridges, suspended in the middle of a PDMS channel. The technique offers simple and consistent fabrication of high aspect ratio (∼44) microbridges with diameters of 90–200 μm. The design has advantages of yielding electrically-conductive Ag-PDMS microbridges in the bulk of the channel with accessible terminals at channel sidewalls for connection to external electrical instruments. This allowed us to investigate the electrical performance of Ag-PDMS microbridges and their thermoresistive behavior for future applications as temperature sensors. It was found that 70% Ag-PDMS microbridges with various diameters have electrical resistances in the range of 10–110 Ω, while demonstrating an exponential increase in resistance in response to the temperature of the fluid rising from 18 °C to 51 °C. These functionalized and three dimensional microbridges can be embedded in microfluidic devices and utilized as integrated sensors for measuring the bulk properties of fluids or the existence of target biological substances in the fluid.

Printing of metallic 3D micro-objects by laser induced forward transfer.

Digital printing of 3D metal micro-structures by laser induced forward transfer under ambient conditions is reviewed. Recent progress has allowed drop on demand transfer of molten, femto-liter, metal droplets with a high jetting directionality. Such small volume droplets solidify instantly, on a nanosecond time scale, as they touch the substrate. This fast solidification limits their lateral spreading and allows the fabrication of high aspect ratio and complex 3D metal structures. Several examples of micron-scale resolution metal objects printed using this method are presented and discussed.

Fabrication of high aspect ratio and open‐ended TiO2 nanotube photocatalytic arrays through electrochemical anodization

Well‐aligned, high aspect‐ratio and open‐ended TiO2 nanotube arrays secured within a Ti foil (TiO2 nanotubes cartridge) were successfully prepared through the double‐sided anodization method. With ∼210 µm of nanotube length, the anodic growth of TiO2 was accelerated and stabilized by the lactic acid‐containing ethylene glycol electrolyte. In the absence of lactic acid, the anodization led to detachment of nanotubes from the Ti foil after 5–6 h of high voltage (80 V) anodization. Transmission electron microscope image and Raman spectrum revealed that the as‐anodized TiO2 nanotube arrays without annealing treatment were partially crystalline anatase and demonstrated photocatalytic activity in the mineralization of formic acid. © 2015 American Institute of Chemical Engineers AIChE J, 62: 415–420, 2016

Self-ordered Porous Alumina Fabricated via Phosphonic Acid Anodizing

Self-ordered periodic porous alumina with an undiscovered cell diameter was fabricated via electrochemical anodizing in a new electrolyte, phosphonic acid (H3PO3). High-purity aluminum plates were anodized in phosphonic acid solution under various operating conditions of voltage, temperature, concentration, and anodizing time. Phosphonic acid anodizing at 150–180V caused the self-ordering behavior of porous alumina, and an ideal honeycomb nanostructure measuring 370–440nm in cell diameter was successfully fabricated on the aluminum substrate. Conversely, disordered porous alumina grew at below 140V, and anodizing at above 190V caused local thickening due to oxide burning. Two-step phosphonic acid anodizing allows the fabrication of high aspect ratio ordered porous alumina. HPO32− anions originated from the electrolyte were incorporated into the porous oxide during anodizing. Consequently, a double-layered porous alumina consisting of a thick outer layer containing incorporated HPO32− anions, and a thin inner layer without anions was constructed via phosphonic acid anodizing.

Process Development and Optimization for 3 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu \text{m}$ &lt;/tex-math&gt;&lt;/inline-formula&gt; High Aspect Ratio Via-Middle Through-Silicon Vias at Wafer Level

This paper presents challenges encountered in the fabrication of high aspect ratio (AR) via middle, through-silicon vias (TSVs), of 3 ${\mu }\text{m}$ top entrant critical dimension and 50 ${\mu }\text{m}$ depth. Higher AR TSV integration is explored due to the lower stress and copper pumping influence of TSVs observed in adjacent CMOS devices. The key process improvements demonstrated in this paper include 3 ${\mu }\text{m}$ TSV etch, dielectric liner coverage, metal barrier and seed layer coverage, and copper electroplating.

Fabrication of high aspect ratio (> 100:1) nanopillar array based on thiol-ene

Nanopillar arrays have attracted considerable attention lately based on confinement effects and large surface to volume ratios. In this study, we demonstrated an efficient low-cost method for fabrication of large-area high aspect ratio nanopillars based on thiol-ene. Anodic aluminum oxide (AAO) template with ordered deep hole array was employed as the master mold. The low-viscosity and highly rigid UV-curable thiol-ene polymer was used as the structure material. The deep holes were filled with the liquid thiol-ene by overcoming the surface tension. Upon curing under UV irradiation, the thiol-ene formed a rigid cross-linked polymer network. The thiol-ene nanopillars were achieved after releasing the AAO mold in the corrosive solution, due to the corrosive-resistance of the cross-linked polymer. Based on the novel method, we fabricated thiol-ene nanopillar array with the diameter of 296nm and aspect ratio of higher than 100:1. The experimental results demonstrated that the properties of thiol-ene polymer were excellent and the fabrication method was feasible.

Fabrication of Resorcinol-Formaldehyde Xerogel Based High Aspect Ratio 3-D Hierarchical C-MEMS Structures

INTRODUCTION In Lithium ion batteries, various type of carbon materials (activated carbon, carbon nanotubes, glassy carbon, organic aerogels etc.) have been investigated as potential electrode materials (1). Further to achieve enhanced power and energy density, 3-D electrode architecture is demonstrated more useful than the conventional thin film approach (2,3). The most promising way to fabricate 3-D electrode arrays was demonstrated using photo-patterning and pyrolysis of SU-8 photoresist (3). Further it was established mathematically that a fractal electrode design constitutes a more optimal design for energy conversion devices because of the maximization of electrochemically active surface area while minimizing the electrical work involved (4). However, the fabrication of a truly 3-D multiscale or fractal carbon electrodes remains a challenging task. In this study, we used resorcinol-formaldehyde xerogel (RFX) as an organic precursor to yield non-porous dense carbon (5). We first demonstrate the ease of fabrication of high aspect ratio (HAR) RFX 3-D structures by top-down (replica molding) followed by fabrication of arrays of carbon hierarchical microposts using bottom-up (electrospraying) approach. Finally, we show that RFX derived non-porous dense carbon films can be reversibly charged and discharged with Li ions and thus may be a potential contender as anode materials for 3-D microbattery architecture. EXPERIMENTAL We first fabricated 3-D HAR micro-arrays of SU-8 by photopatterning using photolithography which were then used as a master stamp to prepare negative mold in PDMS using replica molding. RF sol as synthesized by the polycondensation of resorcinol and formaldehyde in an organic solvent in the presence of an acidic catalyst was poured onto the PDMS template followed by controlled drying. Later the PDMS stamp was carefully peeled off to obtain patterned 3-D RFX HAR structures. Finally, SU-8 or RF sol based submicro- and nano- beads respectively were then conformally deposited on the 3-D RFX HAR structures by electrospraying followed by pyrolysis of the entire integrated constructs in an inert atmosphere to yield HAR 3-D hierarchical carbon structures. Electrochemical measurements RFX derived thin carbon films for electrochemical measurements were prepared by spin coating RF sol onto a Si wafer. Controlled drying and pyrolysis conditions were maintained to yield smooth uniform carbon films. The RFX derived carbon films so obtained were used as working electrodes while a Li foil was used as counter electrode in an electrochemical cell. The electrolyte used was 1M solution of lithium per chlorate in a 1:1 (v/v) mixture of EC:DMC. An electrochemical test cell made of Teflon was designed with an effective working electrode area of 0.654 cm2 to perform Galvanostatic (charge and discharge) experiments at two different current densities 76.4 and 152.7 µA cm-2between 0.05 and 3.0 V using a multichannel potentio/galvanostat (Gamry Instruments). RESULTS RFX derived HAR 3-D hierarchical structures Fig.1 (A) SEM images in first row shows array of cylindrical and cross geometry microposts made by replica molding in RFX while second row shows array of hierarchical carbon posts obtained after conformal deposition of SU-8 and RF sol derived electrospun submicron and nano sized beads; (B) Galvanostatic charge discharge cycle behavior for RFX derived carbon film; (C) comparison of specific capacity of RFX derived carbon with SU-8 derived carbon. Galvanostativc charge discharge cycling Galvanostatic discharge and charge cycles experiment was carried out at C/5 rate (Fig. 1B). Initial discharge capacity was very high compare to other cycles due to the formation of solid electrolyte interphase layer. The reversible capacity of the RFX derived carbon at a current density of 76.4 µA cm-2 was found to be 195.1 mAh/g which was similar to that of SU-8 derived carbon (~220 mAh/g) in similar conditions (3). After first discharge, reversible capacity was found to be nearly constant. However for RFX derived carbon, the irreversible specific capacity was found to be significantly less (0.0636 mAh/cm2) than what has been for SU-8 derived carbon (0.0788 mAh/cm2) (3) (Fig. 1C). SUMMARY RFX has been introduced as a polymer precursor to fabricate 3-D HAR structures that were used to yield hierarchical array of carbon posts by integrating electrospun nanostructures. Further we have shown that RFX derived carbon can be reversibly intercalated with Li ions. Interestingly, RFX derived carbon shows a significant reduction in irreversible capacity compared to photoresist derived carbon and thus could be an important contender as an anode material for Li ion batteries. REFERENCES 1. A.K.Shukla and T.P.Kumar, Curr. Sci. 94, 314 (2008).2. J.W.Long et al., Chem. Rev., 104 , 4463 (2004).3. G.T. Teixidor et al., J. Power Sources, 183, 730 (2008).4. B. Y. Park et al., J. Electrochem. Soc., 152, J136 (2005).5. C.S.Sharma et al., Bull. Mater. Sci, 32, 239 (2009).