Plasma Etching Process Research Articles

Easy-to-use detection method for micro-arc discharge in plasma etching equipment by measuring current flowing to ground

A simple monitoring method for micro-arc discharge in plasma etching process has been developed. This method employs a current transformer, a Rogowski coil, which is externally attached to encircle a ground lead of a process chamber in plasma etching equipment without touching the lead. The results in this study demonstrate that this method can monitor the current flowing to ground, which reflects load current, and can detect micro-arc discharge occurring in plasma etching process. This easy-to-use, noncontact, and inexpensive method can contribute to improving the overall equipment effectiveness and the production yield in the wafer process in the mass production of LSI.

Effective patterning and cleaning of graphene by plasma etching and block copolymer lithography for nanoribbon fabrication

At a sub-20 nm resolution, patterning 2D materials is necessary in a large number of applications to enhance or control the overall material and device properties. In this work, the authors present their results on the fabrication of graphene nanoribbons using a block copolymer thin film as a lithography mask. A special emphasis is given to the development of new plasma etching processes to pattern graphene and to chemically clean the fabricated nanostructures. At the end, clean 10 nm wide graphene nanoribbons are obtained as confirmed by Raman spectroscopy, x-ray photoelectron spectroscopy, atomic force microscopy, and SEM characterizations. Block copolymer lithography and proper plasma etching conditions allow for easier graphene patterning on a large area and low-cost processing.

(Invited) The Mechanism of Surface Modifications of Photoresist Material in Plasma Etching Nano Processes

Etching plasmas employed for the fabrication of ultra large scale integrated circuits (ULSIs) have been causing serious damages to photoresist materials such as surface roughness formations and structural changes. So far, there have been many reports on suppressing these damages by some process techniques such as the UV, HBr plasma cure and so on. However, effects of individual species and photons in the plasma on the damages of photoresist materials have not been clarified enough. Especially, the effect of vacuum ultraviolet (VUV) photons on damages have never been quantitatively understood. Furthermore, beside the VUV photons, the synergetic effects of individual species of ion and radicals enhance the damages. As a result, the chemical structure alteration and the surface roughness formation of polymer materials are considered to be brought about. In the fabrication of the sub-45 nm devices and integrated circuits, it is extremely important to clarify the reaction mechanism of surface modification of photoresist materials induced by the plasma etching process. In this article, firstly, we have focused on the effects of VUV photons on damages on the 193 ArF photoresist materials by investigating the absolute density of VUV photon fluxes measured in the range of 115nm and 200nm in HBr plasma etching processes. The etching and measurement of VUV photons in the plasma were performed in the plasma beam system for understanding the fundamental reaction on the photoresists. This plasma beam system consists of an upper chamber (plasma chamber) and a lower chamber (process chamber). This equipment provided the beam source with the HBr plasma. The plasma beam system was pumped down to a base pressure of 10-5 Pa prior to the experiment. During the whole experiment, inductively coupled plasma (ICP) was generated by applying a radio-frequency (13.56 MHz) power of 400 W to the low-impedance antenna. Pure HBr, H2 or Ar gas was introduced into the plasma chamber at a flow rate of 1 sccm. The pressure of the plasma chamber was maintained at approximately 5 Pa. The chemical compositions of the surface of photoresists before and after the plasma beam irradiation were analyzed by in-situ XPS. On the basis of measured results, effects by VUV photons emitted from HBr on the surface modifications of photoresist materials were clarified. The VUV photons cleaved the MAA groups below the photon dosage of 16 × 1016 photons/cm2. The crosslinking of the photoresist and release of volatile products simultaneously generated the surface roughness. The reaction became saturated with high dosages [1]. Secondary, the sequential irradiation by VUV/radicals from HBr or H2 plasma and Ar ions on a photoresist have been performed. The irradiation by VUV and radicals before the ion irradiation (pre-treatment) suppressed the roughness increase by the ion bombardment but the VUV and radical irradiation after the ion irradiation (post-treatment) increased the roughness. The surface morphologies were also analyzed in detail after pre- or post-treatment on the photoresist by using the power spectral density. Such pre-treatment processes generated a dense and hard crosslinked layers which improved the etch resistance of the photoresist and improved the roughness [2]. The enhancement of roughness by post-treatment was correlated with the removal of the MAA groups and the nonuniformity of crosslinking reactions on the roughened photoresist by the ion irradiation. On the basis of these results, the mechanism of photoresist modifications by individual effects of VUV, ions and radicals and their synergetic effects by sequential irradiation experiments were systematically discussed and then perspectives for the damage less processes to be established in the etching nano processes are introduced. [1] Y. Zhang et al., Journal of Vacuum Science & Technology A, 35, 060606 (2017). [2] Y. Zhang et al., Japanese Journal of Applied Physics, 56, 126503 (2017).

(Invited) Fine Temperature Monitoring of Si Wafer for Plasma Processing

One of the critical parameters in many semiconductor-processing steps such as plasma etching, chemical vapor deposition, and so on, is the substrate temperature. For example, the etch rate and etch profile are sensitive to the substrate temperature in the plasma etching process. However, contact measurement such as thermo-couples and fluorescent temperature sensor cannot measure the accurate temperature, especially in low pressure due to poor thermal transfer between the wafer and the probe. We have developed the non-contact temperature measurement of substrates by using optical low-coherence interferometer. [1-6] The low-coherence interferometry is based on Michelson interferometry, and a white light such as a super-luminescent diode (SLD) was used as a low-coherence light source. SLD has the central wavelengths of 1325 nm and the full width at half maximum of 64.5 nm. The light which is reflected at the surface of Si substrate interfered with the light reflected at the scanning reference mirror. The interfered light was detected with a spectrometer and the signal which is a frequency domain spectrum was converted to a time domain signal by inverse Fourier transformation. The temperature of the Si substrate is derived from the change in the optical path length of Si substrate due to thermal expansion and changes in the refractive index. The temperatures of Si wafer and chamber parts made of Si were successfully monitored in the SiO2 plasma etching using capacitively coupled plasma. The performance was compared with that of fluorescent temperature sensor. From these results, we have demonstrated highly precise and rapid response measurement of the temperature of Si wafer at real time by using Fourier domain low coherence interferometer.

A Study on the Etching Residue of Nano-Scale Patterns in C4F8/CH2F2/O2/Ar Plasma

The demand for miniaturization and high integration of semiconductor devices has ever been increasing. In order to achieve the requirements of the semiconductor industry, plasma etching processes using fluorocarbon-based gases are being designed to have higher selectivity and ion energy. Generally, to have a higher selectivity to the mask material, a more polymerizing gas (i.e. low F/C ratio gas) is used [1, 2], and therefore the removal of etching residues formed inside the pattern after the etching process has a crucial effect on the performance of the semiconductor devices. As the pattern size becomes smaller, there is an area that cannot be cleaned by the conventional wet cleaning method. Recently, various dry-cleaning techniques using plasma radicals and ions have been proposed [3, 4]. However, for precise control and understanding of residue removal, a detailed compositional analysis of the etching residue must be performed. These studies are also very important in evaluating the effectiveness of dry-cleaning. However, little research has been done to investigate the characteristics of etching residues formed inside the nano-scale patterns (i.e. sidewall and bottom) in much detail. In this work, we conducted a study on the characteristics of the etching residues formed inside the nano-scale patterns. A C4F8/CH2F2/O2/Ar mixture gas plasma was used to form a high-aspect-ratio silicon dioxide contacts (HARCs) on a silicon wafer. The chemical compositions and binding states of etching residues inside the patterns were examined by an x-ray photoelectron spectroscopy (XPS) with angle changes in detail. To investigate the formation of etching residues, the plasma characteristics (i.e. radicals, ions and electrons) were examined in parallel using an optical emission spectroscopy (OES) and a Langmuir probe (LP) system. As a result of the analysis, it was observed that the etching residues formed on the sidewalls of the line and hole patterns changed to the same tendency. At the same time, it was confirmed that depending the etched depth, the composition of the residue on the sidewall of holes and lines changed. [1] Takahashi, Kunimasa, Masaru Hori, and Toshio Goto. "Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. I. O2 addition to electron cyclotron resonance plasma employing CHF3." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 14.4 (1996): 2004-2010. [2] Kwon, B. S., et al. "Ultrahigh selective etching of SiO2 using an amorphous carbon mask in dual-frequency capacitively coupled C4F8/CH2F2/O2/Ar plasmas." Journal of The Electrochemical Society 157.3 (2010): D135-D141. [3] Koh, Kyongbeom, et al. "Quasi atomic layer etching of SiO2 using plasma fluorination for surface cleaning." Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 36.1 (2018): 01B106. [4] Cagomoc, Charisse Marie D., et al. "RF plasma cleaning of silicon substrates with high-density polyethylene contamination." Japanese Journal of Applied Physics 57.1S (2017): 01AB04.

DREM2: a facile fabrication strategy for freestanding three dimensional silicon micro- and nanostructures by a modified Bosch etch process

Three dimensional (3D) silicon micro- and nanostructures enable novel functionalities and better device performances in various fields. Fabrication of real 3D structures in a larger scale and wider applications has been proven to be limited by the technical difficulties during the fabrication process, which normally requires multiple process steps and techniques. Direct top-down fabrication processes by modifying a plasma etch process have been proposed and studied in previous studies. However, the repeatability, size uniformity and the maximal number of stacked layers were limited. Here we report a facile single run fabrication strategy for three dimensional silicon micro- and nanostructures. A good uniformity of suspended layer thickness has to be achieved and up to 10 stacked layers have been fabricated in a single run without other additional steps or post-process procedures. This is enabled by a modified multiplexed Bosch etch process, so called DREM (deposit, remove, etch, multistep), while the DREM etch is used to transfer the patterns into silicon, an extra isotropic etch creates a complete undercut and thus freestanding structures come into form. This method is easy to program and provides well-controlled etch profiles.

Nitrogen reactive ion etch processes for the selective removal of poly-(4-vinylpyridine) in block copolymer films

Self-assembling block copolymer (BCP) patterns are one of the main contenders for the fabrication of nanopattern templates in next generation lithography technology. Transforming these templates to hard mark materials is key for pattern transfer and in some cases, involves selectively removing one block from the nanopattern. For poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP), a high χ BCP system which could be potentially incorporated into semiconductor nanofabrication, this selective removal is predominantly done by a wet etch/activation process. Conversely, this process has numerous disadvantages including lack of control and high generation of waste leading to high cost. For these reasons, our motivation was to move away from the wet etch process and optimise a dry etch which would overcome the limitations associated with the activation process. The work presented herein shows the development of a selective plasma etch process for the removal of P4VP cores from PS-b-P4VP nanopatterned film. Results have shown that a nitrogen reactive ion etch plasma has a selectivity for P4VP of 2.2:1 and suggest that the position of the nitrogen in the aromatic ring of P4VP plays a key role in this selectivity. In situ plasma etching and x-ray photoelectron spectrometry measurements were made without breaking vacuum, confirming that the nitrogen plasma has selectivity for removal of P4VP over PS.

Precision micro-mechanical components in single crystal diamond by deep reactive ion etching

The outstanding material properties of single crystal diamond have been at the origin of the long-standing interest in its exploitation for engineering of high-performance micro- and nanosystems. In particular, the extreme mechanical hardness, the highest elastic modulus of any bulk material, low density, and the promise for low friction have spurred interest most notably for micro-mechanical and MEMS applications. While reactive ion etching of diamond has been reported previously, precision structuring of freestanding micro-mechanical components in single crystal diamond by deep reactive ion etching has hitherto remained elusive, related to limitations in the etch processes, such as the need of thick hard masks, micromasking effects, and limited etch rates. In this work, we report on an optimized reactive ion etching process of single crystal diamond overcoming several of these shortcomings at the same time, and present a robust and reliable method to produce fully released micro-mechanical components in single crystal diamond. Using an optimized Al/SiO2 hard mask and a high-intensity oxygen plasma etch process, we obtain etch rates exceeding 30 µm/h and hard mask selectivity better than 1:50. We demonstrate fully freestanding micro-mechanical components for mechanical watches made of pure single crystal diamond. The components with a thickness of 150 µm are defined by lithography and deep reactive ion etching, and exhibit sidewall angles of 82°–93° with surface roughness better than 200 nm rms, demonstrating the potential of this powerful technique for precision microstructuring of single crystal diamond.

SF6 plasma treatment for leakage current reduction of AlGaN/GaN heterojunction field-effect transistors

Abstract In this study, we have investigated the effects of SF6 plasma treatment on the isolation leakage current characteristics of AlGaN/GaN heterojunction field-effect transistors (HFETs). The device isolation was performed by Cl2/BCl3-based plasma etching process followed by SF6 plasma treatment for 1 min. It was found that the SF6 plasma post-etching treatment was an effective method to improve the electrical isolation characteristics. X-ray photoelectron spectroscopy analysis was carried out to investigate the chemical bonding states of the etched GaN surfaces.

Polyimide-Based Capacitive Humidity Sensor.

The development of humidity sensors with simple transduction principles attracts considerable interest by both scientific researchers and industrial companies. Capacitive humidity sensors, based on polyimide sensing material with different thickness and surface morphologies, are prepared. The surface morphology of the sensing layer is varied from flat to rough and then to nanostructure called nanograss by using an oxygen plasma etch process. The relative humidity (RH) sensor selectively responds to the presence of water vapor by a capacitance change. The interaction between polyimide and water molecules is studied by FTIR spectroscopy. The complete characterization of the prepared capacitive humidity sensor performance is realized using a gas mixing setup and an evaluation kit. A linear correlation is found between the measured capacitance and the RH level in the range of 5 to 85%. The morphology of the humidity sensing layer is revealed as an important parameter influencing the sensor performance. It is proved that a nanograss-like structure is the most effective for detecting RH, due to its rapid response and recovery times, which are comparable to or even better than the ones of commercial polymer-based sensors. This work demonstrates the readiness of the developed RH sensor technology for industrialization.

Surface Modification of Electroosmotic Silicon Microchannel Using Thermal Dry Oxidation.

A simple fabrication method for the surface modification of an electroosmotic silicon microchannel using thermal dry oxidation is presented. The surface modification is done by coating the silicon surface with a silicon dioxide (SiO2) layer using a thermal oxidation process. The process aims not only to improve the surface quality of the channel to be suitable for electroosmotic fluid transport but also to reduce the channel width using a simple technique. Initially, the parallel microchannel array with dimensions of 0.5 mm length and a width ranging from 1.8 µm to 2 µm are created using plasma etching on the 2 cm × 2 cm silicon substrate <100>. The oxidation of the silicon channel in a thermal chamber is then conducted to create the SiO2 layer. The layer properties and the quality of the surface are analyzed using scanning electron microscopy (SEM) and a surface profiler, respectively. The results show that the maximum oxidation growth rate occurs in the first 4 h of oxidation time and the rate decreases over time as the oxide layer becomes thicker. It is also found that the surface roughness is reduced with the increase of the process temperature and the oxide thickness. The scallop effect on the vertical wall due to the plasma etching process also improved with the presence of the oxide layer. After oxidation, the channel width is reduced by ~40%. The demonstrated method is suggested for the fabrication of a uniform channel cross section with high aspect ratio in sub-micro and nanometer scale that will be useful for the electroosmotic (EO) ion manipulation of the biomedical fluid sample.

Double-sided masking and stress-release etching for the fabrication of high-aspect-ratio graphene micro-cantilever

Well-shaped micro/nano-structured suspended graphene is a versatile building block for micro/nano-electromechanical (MEMS/NEMS) devices. Directly ‘sculpting’ the suspended graphene membrane using an accelerated energetic electron/ion beam to form micro/nano-structured graphene possesses the merits of high resolution and well-processed flexibility. However, both the residual and process-induced stress in the membrane still challenge the obtaining of non-distorted freestanding graphene patterns. We report a featured double-sided masking and stress-release etching method to fabricate well-defined suspended graphene micro-ribbon. We demonstrated that the one-step low-energy (10 keV) electron beam induced the deposition of amorphous carbon (a-C) on both sides of the suspended graphene. The a-C layers were precisely self-aligned, not only allowing its use as reliable masks for the following plasma etch of suspended graphene, but showing potential for future applications of effectively ‘writing’ circuits/devices directly on both sides of a suspended 2D atomic-layered platform. A stress-release plasma etching process and its ‘self-crumpling’ mechanism were demonstrated. High-aspect-ratio micro-structured graphene (bridge and cantilever) with a good shape was obtained. This provides a promising and universal processing method for making suspended structures of 2D materials with in-plane flatness for potential MEMS/NEMS applications.

Fabrication of a Hydrophilic Line on a Hydrophobic Surface by Laser Ablation Processing.

A hydrophilic line on a hydrophobic surface was fabricated by using plasma etching and laser ablation processing in this paper. We fabricated the nanospikes on a polyimide surface by using the plasma etching processing. CHF3 plasma treatment for hydrophobic coating was conducted on these nanospikes. We fabricated the microgrooves on the hydrophobic nanospikes surface using laser ablation processing. The microgroove had hydrophilic characteristics. In order to measure the hydrophilic characteristics of the microgroove, a solution that was dispersed with silver nanoparticles was used. The hydrophilic line on the hydrophobic surface was dipped in the silver nanoparticle solution. The silver nanoparticles were attached on the hydrophilic microgroove and not on the hydrophobic surface. We concluded that the laser heat affected zone should be reduced for reducing the hydrophilic line width. This hydrophilic pattern on the hydrophobic surface can be used for cell growth, protein manipulation, the spotting of biomolecules, micro-fluidics and water collection. This functional surface can especially be used for an electric flexible circuit, which is newly proposed in this paper.

Nitride etching with hydrofluorocarbons III: Comparison of C4H9F and CH3F for low-k′ nitride spacer etch processes

The performance of low-k nitride spacer etch processes for fin-field effect transistor device fabrication was investigated using C4H9F based and CH3F based plasma gas chemistries. C4H9F showed a larger process window of O2 gas flow rate to obtain infinite etch selectivities of blanket SiN/SiO and SiN/poly-Si than CH3F. The etch selectivity increased in both gases with the reduction of duty cycle in synchronously pulsed plasmas. Low-k spacer formation using a 60-nm gate pitch testsite was demonstrated resulting in the minimized fin recess of 4.7 nm using C4H9F-O2-He plasma at a duty cycle of 30%. This was 2.2 times smaller than that by the CH3F-He plasma. Fifty percent extended etch time resulted in a fin recess of 5.1 nm, suggesting self-limiting behavior using C4H9F-O2-He plasma chemistry. Gap structure analysis on the blanket films suggested that the selective deposition of fluorocarbon, which enhances the selectivity, is driven by plasma assisted deposition in case of the C4H9F-O2-He plasma. These unique characteristics of C4H9F can facilitate innovative plasma etch processes for nitride-based materials patterning in a wide range of applications.

Novel Method for Metal-Insulator-Metal (MIM) Plasma Etching Residue Removal

After top plate etching process by metal-insulator-metal (MIM) manufacturing, a hard metallic polymer is formed and it is not easily to remove by ashing process or traditional polymer wet clean. The carbon fluoride gas with too much etching power such as CF4 is used as the etchant in current techniques, such that the second metal layer and the insulation layer may be damaged. In this paper, lower cost chemical was used for etch polymer removed. The chemical contain metal oxide etchant to oxidize the metal and metal oxidized polymer will be etched by fluorine function group which is mixed with this chemical. This method also can avoid metal or high K film damaged by CF4 gas in plasma etching process or O2 ashing process. The manufacturing method of the metal-insulator-metal device was shown in Figure1. However, this process has some issues. There have some useless polymer residue around the pattern sidewall when etching the top plate tantalum, tantalum nitride step. Figure 2 showed the polymer is hard to remove after subsequent wet cleaning process. In a subsequent process, these polymers make the film surface uneven and become the cause for short circuits during electrical connection, such that the performance of the metal-insulator-metal device is affected, and the yield and reliability are worsened as a result. Based on these issues, this paper provides a polymer cleaning method of a metal-insulator-metal device. Use carbon less etching gas for Ta/ TaN etching to avoid carbon rich polymer formation and post clean chemical composed by oxidant, such as H2O2, and metal oxide etchant, such as fluorine to remove excess polymer remaining on the metal-insulator-metal structure. The DSP is chemical used to remove the polymer. Two ratio of the DSP mixed solution with the hydrofluoric acidare 10000:1 and 1000:1.The baseline etching gases containing carbonand wet polymer remove is DSP mixed HF 10000:1. After etch, the CD-SEM result was showed in Figure 3(a). It showed the corner of MIM device top plate had heavy polymer residue. In order to remove the heavy polymer residue after etch, increasing the concentration of HF and the result was showed in Figure 3(b). Unfortunately, the polymer still remain and no any improvement. In order to reduce C source and TaClX can more efficient to oxidize, replace the etch gases from C-rich to C-less . Figure 4 showed the etch gases changed to C-less gas and the polymer seems become thinner than C-rich gas. And after DSP with HF 1000:1 the polymer seems almost removed but DSP with HF 10000:1 and ST-250 poly still have polymer remain. It seems the DSP with HF 10000:1 the HF concentration too low to corrosion the metal oxide. ST-250 of the fluorine function group is NR3HF and the solution pH=8, the fluorine function group didn’t react with metal oxide in the alkaline environment. Figure 4(b) shows higher concentration of HF is benefit for polymer remove because increase the metal oxide etchant and the TaClX almost oxidized to Ta2O5 then be react to H2[TaF7] which can be dissolved. The cross section SEM image shows the polymer around the pattern sidewall after the carbon rich etching gas, O2 asher and post-etched clean step, it seems hard and thicker which is shown as Figure 5(a). At the Figure 5(b), there seems no polymer remain by replacing C-less etch gases. In order to totally remove the polymer, prolong the process time of DSP with HF 10000:1 and 1000:1 and the CD-SEM data is shown in Figure 5. After wet process with the higher concentration of HF the polymer is totally remove but the lower HF concentration the polymer still remain. To verify the remove mechanism, double the wet process time with lower concentration of HF. And the result be shown in Figure 6(c), the polymer still remain. It proves that the concentration of HF is the key point to corrosion the metal oxide. The polymer types and polymer removed methods after etching process were studied. Carbon rich etch gases will restrain the metal polymer be oxidize at the O2 asher step. By change etch gas to lower carbon content and following post-etched clean step is easily to corrosion the metal oxide which be oxidized by O2 asher and wet oxidize chemical. The concentration of HF in DSP chemical is key point to remove the polymer. DSP to HF concentration between 1000:1 to 100:1 is suitable for post clean. The method is low cost and prevent use too much etching power etching gas to damage the device pattern. Figure 1

Superhydrophobic polymeric films with hierarchical structures produced by nanoimprint (NIL) and plasma roughening

The structuration of various polymeric films has been studied to create superhydrophobic surfaces. Nanoimprint lithography and/or plasma etching processes with CF4/Ar have been used on FEP, PMMA and PET polymer films. On the one hand, the effect of the CF4/Ar gases, the input power and the plasma treatment duration have been investigated in terms of etching and fluorination degree, and XPS analyses are precisely discussed. On the other hand, wettability performances were characterized. Relationships between the contact angle, the contact angle hysteresis and the surface structures have been investigated. The wetting behaviors and the transition between the Wenzel and the Cassie-Baxter states was discussed as a function of the roughness. We have prepared each studied polymer films in transparent and flexible superhydrophobic surfaces whose contact angle are ∼160° and hysteresis are ∼2°. A short plasma treatment time (10 s) is sufficient to obtain a superhydrophobic behavior on FEP and PMMA. Results indicate that hierarchical structures allow a more stable superhydrophobic state regarding inhomogeneities. Moreover, the use of plasma etching is suggested to overcome some limitations of the NIL in the case of structures with a high aspect ratio. Finally, a quick and large surface fabrication method for superhydrophobic films is detailed.

Fluorine-based plasmas: Main features and application in micro-and nanotechnology and in surface treatment

Abstract Fluorine cold plasmas produced by an electrical discharge in SF6, CF4, CHF3 or C4F8 gases, principally, have two main fields of application. The first and historical application is etching of materials for microelectronics and later for micro- and nanotechnology. The second concerns the modification of surface properties, mostly in terms of reflectance and wettability. After an introduction to cold plasmas and plasma–surface interaction principles, the article aims at presenting successively the evolution of fluorine plasma etching processes since the origin with respect to other halogen-based routes in microelectronics, the important and raising application in deep etching and microtechnology, and finally some examples in surface treatment.

Cost-Effective Fabrication of Inner-Porous Micro/Nano Carbon Structures.

This paper reports the fabrication of a new micro/nano carbon architecture array which owns the characteristics of inner-porous, desired conductivity and large effective surface area. The micro/nano inner-porous carbon structures were fabricated for the first time, with ordinary and cost-effective processes, including photolithography, oxygen plasma etching and pyrolysis. Firstly, micro/nano hierarchical photoresist structures array was generated through photolithography and oxygen plasma etching processes. By introducing a critical thin-film spin-coating step, and followed with carefully pyrolyzing process, the micro/nano photoresist structures were converted into innerporous carbon architectures with good electric connection which connected the carbon structures array together. Probably the inner-porous property can be attributed to the shrinkage difference between positive thin film and negative photoresist structures during pyrolyzing process. It is demonstrated that the simple method is effective to fabricate inner-porous carbon structures with good electric connection and the carbon structures can be used as electrochemical electrodes directly and without the addition of other pyrolysis or film coating processes. The electrochemical property of the carbon structures has been explored by cyclic voltammetric measurement. Compared with solid carbon microstructures array, the cyclic voltammetry curve of inner-porous carbon structures shows greatly enhanced current and improved charge-storage capability, indicating great potential in micro energy storage devices and bio-devices.

Biofunctional porous silicon micropatterns engineered through visible light activated epoxy capping and selective plasma etching

Porous silicon (PSi) is a versatile matrix with tailorable surface reactivity, which allows processing a diversity of biofunctional structures. An assembly process has been activated by catalyzing PSi oxidation with visible light, enabling subsequent binding with (3-glycidyloxypropyl)-trimethoxy-silane (GPTMS) in the submonolayer regime. A multispectroscopic approach has been followed to fully characterize the surface capped PSi. XPS has been used to trace the process of light induced oxidation and GPTMS assembly on supported PSi. Field emission SEM confirms that the surface topography is not modified by the activated assembly. To complement the chemical analysis of the bound GPTMS, FTIR and solid state NMR were used on functionalized PSi particles. Finally, the surfaces of GPTMS capped PSi have been successfully micropatterned by a masked Ar plasma etching process. The process gives rise to surface hydrophilic/hydrophobic contrasts, which are efficient in the selective binding of activated gold nanoparticles. The contrasts were applied to the local recognition of mouse serum proteins adsorbed on GPTMS functionalized PSi through an immunofluorescence assay. The results confirm the effectiveness of GPTMS capped PSi as adsorptive layer for immunosensing.

Across Substrate Lateral Dimensional Repeatability Using a Highly-Anisotropic Deep Etch Process on Fused Silica Material Layers

This letter reports the research performed on the measurement of the repeatability of the resultant lateral dimensions across fused silica substrates that were etched using an inductively-coupled plasma reactive-ion etch process. We have developed and previously reported a highly-anisotropic plasma etch process with the demonstrated etch depths of over 100 microns deep into fused silica substrates and aspect ratios greater than 10 to 1. The across substrate repeatability of the lateral dimensions of the etched features is an extremely important parameter for any plasma etch process. The measured etched feature lateral dimensional repeatability for an average etch depth of 100 microns was found to be approximately 2.41% across each wafer over a total of 120 measurements taken. The capability to etch highly-anisotropic deep features with repeatable dimensional control into fused silica has important implications for a number of important MEMS applications. [2017-0088]