Ion Etching Technique Research Articles

A Silicon-Based Porous Thin Membrane as a Cancer Cell Transmigration Assay

This paper presents a novel microfabricated Boyden chamber in silicon with well-defined pore sizes and controlled membrane thickness for cell migration analysis. The chip-based chamber is fabricated employing lithography and deep reactive ion etching techniques on a double-sided polished silicon wafer. The device contains micro-pores with a silicon oxide layer at the top and a deep microfluidic channel at the bottom, which is anodically-bonded to a glass wafer for sealing and facilitating the imaging and chemoattractant feeding. The applicability of the chip has been demonstrated through the distinct migratory behaviors of highly metastatic breast cancer cells, MDA-MB-231, through pores with 8 $\mu \text{m}$ in diameter, 50 $\mu \text{m}$ in spacing, and 30 $\mu \text{m}$ in thickness. Employing the above technique, the membrane thickness variation among different chips was below 10%. Utilizing this micro-Boyden chamber device, we have shown that MDA-MB-231 cells migrated distinctively in higher rate than the cells which had gone through sphingosine kinase inhibitor drug treatment or no chemoattractant feeding over a course of 12 hours. Furthermore, we validated the performance of the micro-Boyden chamber by quantifying the migration rate of the cancer cells under different chemoattractant gradient profiles. [2016-0103]

Tuning the thickness of exfoliated quasi-two-dimensional β-Ga2O3 flakes by plasma etching

We demonstrated the thinning of exfoliated quasi-two-dimensional β-Ga2O3 flakes by using a reactive ion etching technique. Mechanical exfoliation of the bulk β-Ga2O3 by using an adhesive tape was followed by plasma etching to tune its thickness. Since β-Ga2O3 is not a van der Waals material, it is challenging to obtain ultra-thin flakes below a thickness of 100 nm. In this study, an etch rate of approximately 16 nm/min was achieved at a power of 200 W with a flow of 50 sccm of SF6, and under these conditions, thinning of β-Ga2O3 flakes from 300 nm down to ∼60 nm was achieved with smooth morphology. We believe that the reaction between SF6 and Ga2O3 results in oxygen and volatile oxygen fluoride compounds, and non-volatile compounds such as GaFX that can be removed by ion bombardment. The opto-electrical properties were also characterized by fabricating solar-blind photodetectors using the plasma-thinned β-Ga2O3 flakes; these detectors showed fast response and decay with excellent responsivity and selectivity. Our results pave the way for tuning the thickness of two-dimensional materials by using this scalable, industry-compatible dry etching technique.

Reactive Ion Etching Process of Micro Mechanical Pendulum

This paper describes the reactive ion etching (RIE) technique of micro mechanical pendulum chip. Micro mechanical pendulum chip processed by the RIE has excellent performances and surface of the chip is smoother than the chip by wet etching. Properties of chip are closely associated with the process parameters. Reactive ion etching technique improves the problems such as intricate lateral etching and surface deficiency of the wet etching. On the basis of method and many experiments of the ion etching, relation between etching rate, etching uniformity, sidewall profiles and process parameters was analyzed and a set process parameters with greater etching effect was obtained. The set process parameters includes etching depth 55μm, etching uniformity (U) 0.63% and selectivity (P) 90:1, etching rate (V) 5.75μm/min, verticality of sidewall 90°±1°.

High-conductivity silicon based spectrally selective plasmonic surfaces for sensing in the infrared region

Plasmonic perfect absorbers have found a wide range of applications in imaging, sensing, and light harvesting and emitting devices. Traditionally, metals are used to implement plasmonic structures. For sensing applications, it is desirable to integrate nanophotonic active surfaces with biasing and amplification circuitry to achieve monolithic low cost solutions. Commonly used plasmonic metals such as Au and Ag are not compatible with standard silicon complementary metal–oxide–semiconductor (CMOS) technology. Here we demonstrate plasmonic perfect absorbers based on high conductivity silicon. Standard optical lithography and reactive ion etching techniques were used for the patterning of the samples. We present computational and experimental results of surface plasmon resonances excited on a silicon surface at normal and oblique incidences. We experimentally demonstrate our absorbers as ultra-low cost, CMOS-compatible and efficient refractive index sensing surfaces. The experimental results reveal that the structure exhibits a sensitivity of around 11 000 nm/RIU and a figure of merit of up to 2.5. We also show that the sensing performance of the structure can be improved by increasing doping density.

Metal enhanced fluorescence on super-hydrophobic clusters of gold nanoparticles

We used optical lithography, electroless deposition and deep reactive ion etching techniques to realize arrays of super-hydrophobic gold nanoparticles arranged in a hierarchical structure. At the micro-scale, silicon-micro pillars in the chip permit to manipulate and concentrate biological solutions, at the nano-scale, gold nanoparticles enable metal enhanced fluorescence (MEF) effects, whereby fluorescence signal of fluorophores in close proximity to a rough metal surface is amplified by orders of magnitude. Here, we demonstrated the device in the analysis of fluorescein derived gold-binding peptides (GBP-FITC). While super-hydrophobic schemes and MEF effects have been heretofore used in isolation, their integration in a platform may advance the current state of fluorescence-based sensing technology in medical diagnostics and biotechnology. This scheme may be employed in protein microarrays where the increased sensitivity of the device may enable the early detection of cancer biomarkers or other proteins of biomedical interest.

All-Silicon Ultra-Broadband Infrared Light Absorbers.

Absorbing infrared radiation efficiently is important for critical applications such as thermal imaging and infrared spectroscopy. Common infrared absorbing materials are not standard in Si VLSI technology. We demonstrate ultra-broadband mid-infrared absorbers based purely on silicon. Broadband absorption is achieved by the combined effects of free carrier absorption, and vibrational and plasmonic absorption resonances. The absorbers, consisting of periodically arranged silicon gratings, can be fabricated using standard optical lithography and deep reactive ion etching techniques, allowing for cost-effective and wafer-scale fabrication of micro-structures. Absorption wavebands in excess of 15 micrometers (5–20 μm) are demonstrated with more than 90% average absorptivity. The structures also exhibit broadband absorption performance even at large angles of incidence (θ = 50°), and independent of polarization.

Development of thin quartz glass utilising through‐glass‐via (TGV) formation by dry etching technology

The manufacturing process of through-glass-via (TGV) structure and direct implications on the design of quartz-based interposer applications for three-dimensional integrated circuit packaging technology is presented. First detailed substrate thickness formed by dry etching with various associated structures based on the use of thin quartz as a substrate material was analysed. Then, the holes etched in glass wafers by photolithography and inductively coupled plasma-reactive ion etching techniques was evaluated. The fabricated TGV morphology showed an excellent characterisation between substrate thickness, via diameter, and via shape for a vertical interposer. Finally, TGV structure with a diameter of 50 µm × 150 µm thin quartz wafer exhibit high usability for thin wafer processing with the optimised fabrication parameters was obtained.

A unique patterned diamond stamp for a periodically hierarchical nanoarray structure

A diamond stamp with a hierarchical pattern was designed for the direct preparation of a periodic nanoarray structure, which was prepared by the reactive ion etching technique with a hierarchical ultrathin alumina membrane (HUTAM) as a mask. The optimal etching conditions for fabricating the diamond stamp were discussed in order to realize a vertical nanopore structure, avoiding structural damage from lateral etching. By using this diamond stamp, a polymer film with the desired hierarchical nanorod array structure can be obtained easily via the simple stamping process, which greatly simplifies the processing procedure. More importantly, the stamp is reusable because of its super-hardness, which ensures the reproducibility of the nanorod array pattern. Another merit is that the smooth surface of the etched diamond can avoid the use of a release agent. Our results prove that this hard stamp can be used for quick preparation of an elaborate periodic nanoarray structure. This study is significant in that it solves the problems of high cost and easy damage of stamps in nanoimprint lithography, and it might inspire more sophisticated applications of such an ordered structure in nanoplasmonics, biochemical sensing and nanophotonic devices.

Fabrication, Simulation, and Experimental Characterization of EWT Solar Cells With Deep Grooved Base Contact

In this paper, we present a new solar cell design conceived for low–medium concentrator photovoltaic applications. The proposed cell is based on the emitter-wrap-through concept featuring grooved p-doped hole base contacts. The cell is fabricated by realizing an array composed of holes of two alternating doping types obtained by means of a deep reactive ion etching technique. Measurements under 1-sun illumination confirm the advantages of the considered architectures in terms of short-circuit current density and photon collection properties with respect to conventional front- and back-contact solar cells. Three-dimensional numerical simulations, calibrated starting from the measured dark J–V characteristics, are exploited to investigate the performance under concentrated light (maximum efficiency 21.4% at 44 suns) and to understand, especially in the case of highly resistive substrates, the impact of the p-doped holes depth in terms of resistive losses.

Mid-Infrared Sensing Using Heavily Doped Germanium Plasmonics on Silicon Substrates

The quest for novel plasmonic materials has been a lively area of research over the last few years. In the mid-infrared (mid-IR) spectral region, in particular, localized plasmon resonances in nanoparticles and nano-antennas hold promise for enhanced IR spectroscopies, with key applications in biology, medicine, and security. In this frame, the development of a CMOS-compatible plasmonic platform in the mid-IR could have disruptive effects for future technologies, allowing for cost-effective sensing devices integrated with electronics [1-2]. We report on the growth, fabrication and optical characterization of heavily-doped Ge antennas integrated on a Si substrate and we exploit them for the sensing of solid-phase and liquid-phase analytes [3-5]. Epitaxial Ge is grown on Si by plasma-enhanced chemical vapor deposition, exploiting phosphorous as the dopant and achieving plasma frequencies up to 1950 cm-1 (5.1 µm wavelength) corresponding to activated doping of 8.1 x 1019 cm–3. Through modelling and simulation of a series of key figures of merit we demonstrate that n-Ge has performance as a mid-infrared plasmonic material that is within an order of magnitude of noble metals such as gold and with properly designed antennas has the potential to provide enhancements of up to 3 orders of magnitude. We demonstrate two-wire gap antennas fabricated by electron-beam lithography and reactive ion etching techniques, displaying localized plasmon resonances in the important 8 to 13 µm molecular fingerprint region. We target the sensing of a thin polydimethylsiloxane (PDMS) layer (thickness of about 40 nm) and demonstrate experimentally an enhancement of two orders of magnitude in the collected signal for resonances around 800 cm–1 (12.5 µm wavelength), as derived from a comparison with the results of detailed numerical simulations. Further measurements of the ~700 cm–1 (14.3 µm wavelength) C–Cl bond duplet of 2-chloroethyl methyl sulfide, a mustard chemical warfare (CW) agent simulant, demonstrates potential security applications. This part of the mid-infrared spectrum has a host of molecular absorption lines important for the sensing of both CW agents and explosives, both of which are of interest for airport and counter terrorism security screening. Our results represent a first experimental benchmark for group-IV mid-IR plasmonics and confirm that future CMOS sensing platforms could benefit significantly from plasmonic enhancements provided by integrated heavily-doped Ge-based devices. The research leading to these results has received funding from the European Union’s Seventh Framework Programme under grant agreement n°613055. [1] R. Soref, Nature Phot. 4, 495-497 (2010). [2] R. Soref, J. Hendrickson, and J.W. Cleary, Opt. Exp. 20, 3814-3824 (2012). [3] L. Baldassarre, E. Sakat, J. Frigerio, A. Samarelli, K. Gallacher, E. Calandrini, G. Isella, D.J. Paul, M. Ortolani, and P. Biagioni, Nano Lett. 15, 7225-7231 (2015). [4] P. Biagioni, J. Frigerio, A. Samarelli, K. Gallacher, L. Baldassarre, E. Sakat, E. Calandrini, R.W. Millar, V. Giliberti, G. Isella, D.J. Paul, and M. Ortolani, J. Nanophot. 9, 093789 (2015). [5] A. Samarelli, J. Frigerio, E. Sakat, L. Baldassarre, K. Gallacher, M. Finazzi, G. Isella, M. Ortolani, P. Biagioni, and D.J. Paul, Thin Solid Films 602, 52 – 55 (2016). Figure 1

Black Germanium fabricated by reactive ion etching

A reactive ion etching technique for the preparation of statistical “Black Germanium” antireflection surfaces, relying on self-organization in a Cl2 etch chemistry, is presented. The morphology of the fabricated Black Germanium surfaces is the result of a random lateral distribution of pyramidal etch pits with heights around (1450 ± 150) nm and sidewall angles between 80° and 85°. The pyramids’ base edges are oriented along the crystal directions of Germanium, indicating a crystal anisotropy of the etching process. In the Vis–NIR, the tapered Black Germanium surface structure suppresses interface reflection to <2.5 % for normal incidence and still to <6 % at an angle of incidence of 70°. The presented Black Germanium might find applications as low-cost AR structure in optoelectronics and IR optics.

Dry etched SiO2 Mask for HgCdTe Etching Process

A highly anisotropic etching process with low etch-induced damage is indispensable for advanced HgCdTe (MCT) infrared focal plane array (IRFPA) detectors. The inductively coupled plasma (ICP) enhanced reactive ion etching technique has been widely adopted in manufacturing HgCdTe IRFPA devices. An accurately patterned mask with sharp edges is decisive to accomplish pattern duplication. It has been reported by our group that the SiO2 mask functions well in etching HgCdTe with high selectivity. However, the wet process in defining the SiO2 mask is limited by ambiguous edges and nonuniform patterns. In this report, we patterned SiO2 with a mature ICP etching technique, prior to which a thin ZnS film was deposited by thermal evaporation. The SiO2 film etching can be terminated at the auto-stopping point of the ZnS layer thanks to the high selectivity of SiO2/ZnS in SF6 based etchant. Consequently, MCT etching was directly performed without any other treatment. This mask showed acceptable profile due to the maturity of the SiO2 etching process. The well-defined SiO2 pattern and the etched smooth surfaces were investigated with scanning electron microscopy and atomic force microscope. This new mask process could transfer the patterns exactly with very small etch-bias. A cavity with aspect-ratio (AR) of 1.2 and root mean square roughness of 1.77 nm was achieved first, slightly higher AR of 1.67 was also get with better mask profile. This masking process ensures good uniformity and surely benefits the delineation of shrinking pixels with its high resolution.

Investigations on etching resistance of undoped and boron doped polycrystalline diamond films by oxygen plasma etching

The reactive ion etching (RIE) technique was used to etch the undoped and boron-doped diamond (BDD) polycrystalline films using oxygen plasma. The effect of boron within the BDD coatings on the morphology was investigated. BDD films exhibited much superior etching resistance than the undoped diamond films, wherein the (111) planes of BDD films were more etching resistant than (100) planes due to much higher boron concentration. However, this is in contradiction to undoped diamond films whose (111) planes were etched more quickly. The results would help to better design a particular and efficient etching method for undoped and BDD films to get a well-patterned microstructures.

Direct Determination of 3D Distribution of Elemental Composition in Single Semiconductor Nanoislands by Scanning Auger Microscopy.

An application of scanning Auger microscopy with ion etching technique and effective compensation of thermal drift of the surface analyzed area is proposed for direct local study of composition distribution in the bulk of single nanoislands. For GexSi1 − x-nanoislands obtained by MBE of Ge on Si-substrate gigantic interdiffusion mixing takes place both in the open and capped nanostructures. Lateral distributions of the elemental composition as well as concentration-depth profiles were recorded. 3D distribution of the elemental composition in the d-cluster bulk was obtained using the interpolation approach by lateral composition distributions in its several cross sections and concentration-depth profile. It was shown that there is a germanium core in the nanoislands of both nanostructure types, which even penetrates the substrate. In studied nanostructures maximal Ge content in the nanoislands may reach about 40 at.%.

Mask-less deposition of Au–SnO2 nanocomposites on CMOS MEMS platform for ethanol detection

Here we report on the mask-less deposition of Au–SnO2 nanocomposites with a silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) micro electro mechanical system (MEMS) platform through the use of dip pen nanolithography (DPN) to create a low-cost ethanol sensor. MEMS technology is used in order to achieve low power consumption, by the employment of a membrane structure formed using deep reactive ion etching technique. The device consists of an embedded tungsten micro-heater with gold interdigitated electrodes on top of the SOI membrane. The tungsten micro-heater is used to raise the membrane temperature up to its operating temperature and the electrodes are used to measure the resistance of the nanocomposite sensing layer. The CMOS MEMS devices have high electro-thermal efficiency, with 8.2 °C temperature increase per mW power of consumption. The sensing material (Au–SnO2 nanocomposite) was synthesised starting from SnO nanoplates, then Au nanoparticles were attached chemically to the surface of SnO nanoplates, finally the mixture was heated at 700 °C in an oven in air for 4 h. This composite material was sonicated for 2 h in terpineol to make a viscous homogeneous slurry and then ‘written’ directly across the electrode area using the DPN technique without any mask. The devices were characterised by exposure to ethanol vapour in humid air in the concentration range of 100–1000 ppm. The sensitivity varied from 1.2 to 0.27 ppm−1 for 100–1000 ppm of ethanol at 10% relative humid air. Selectivity measurements showed that the sensors were selective towards ethanol when they were exposed to acetone and toluene.

Effect of plasma ion etching on Si nano wires towards superhydrophobicity

Superhydrophobic surfaces have attracted due to their potential applications such as self-cleaning surfaces etc. Many techniques have demonstrated in fabricating the artificial superhydrophobic surfaces such as CVD, Organic coatings etc. In this paper we present simple approach to fabricate non wettable superhydrobic surface on silicon Nanowires (Si NW) surface by H2 ion etching technique through ECR device which is very efficient in producing the high ion density plasma at low pressure and at moderate energy. Large area high density (Si NW) were fabricated by two step Metal assisted chemical etching (MACE)of silicon using silver(Ag) as the catalyst along with pre immersion method.H2 Plasma ion etching treatment was applied on the surface of the SiNW at the constant microwave power. The morphology of Si NWs is changed with the application of plasma which was revealed by Scanning electron microscopy. Water contact angles have been systematically measured for SiNWs&H2 plasma treated SiNWs by increasing the etching time. It was observed that in H2 ion plasma treated SiNWs, the water contact angle changed dramatically from 22.6 0to 1460 almost near to super hydrophobic nature. And these result suggest that the hydrogen plasma condition must be carefully regulated to achieve the superhydrophobic surface on silicon which is essential for many applications like Biosensors and Microfluidic surfaces.

Effect of Plasma, RF, and RIE Treatments on Properties of Double-Sided High Voltage Solar Cells with Vertically Aligned p-n Junctions

Si-based solar cells with vertically aligned p-n junctions operating at high voltage were designed and fabricated. The plasma treatments and antireflection coating deposition on the working surfaces of both single- and multijunction cells were made using the special holders. It was shown that additional treatment of solar cells in argon plasma prior to hydrogen plasma treatment and deposition of diamond-like carbon antireflection films led to the improvement of the cell efficiency by up to 60%. Radio frequency waves support plasma generation and improve photoelectric conversion mainly due to reduction of internal stresses at the interfaces. Application of reactive ion etching technique removes the broken layer, reduces elastic strain in the wafer, decreases recombination of charge carriers in the bulk, and provides cell efficiency increase by up to ten times.

Size Effect on Interlayer Coupling and Magnetoresistance Oscillation of Magnetic Tunnel Junction Embedded With Iron Nanoparticles

Here, we investigate the size effect of perpendicular-anisotropic double-barrier magnetic tunnel junction (MTJ) devices embedded with iron nanoparticles. A sputtering system in conjunction with the postannealing process is employed to prepare the sheet film and standard lithography techniques followed by the ion etching technique are used to fabricate the micrometer to submicrometer MTJ devices. A strong ferromagnetic coupling is observed as we reduce the size of the device to submicrometer scale, which is due to the reduction of magnetostatic energy of the device. Furthermore, a magnetoresistance (MR) oscillation is observed at room temperature while reducing the size of the device. MR peaks at low bias fields are believed to have magnon contributions, whereas the peaks observed at higher bias fields are responsible for phonon-assisted tunneling. Zero-bias anomalies are also observed and are more prominent in antiparallel states of the devices.

Interface interaction of Co atop Bepp2 with different substrate temperatures

The interaction at organic–ferromagnetic interfaces in organic spin-valves has a considerable effect on efficient spin injection or detection. In this work, Al/Co films were deposited on the organic Bepp2 layers at two different substrate temperatures to investigate the interface interaction. The interaction including penetration, interdiffusion and chemical reaction has been studied by the surface morphology measurement, X-ray photoelectron spectroscopy combined with Argon ion etching technique and magnetic properties measurement. It was found that the interfacial penetration and chemical reaction were serious, forming plenty of holes and non-ferromagnetic metallic carbide and oxides owing to the high energy of sputtered Co atoms into the organic Bepp2 layer when depositing Co on Bepp2 layer at the substrate temperature of 24°C. However, this phenomenon weakened when lowering the temperature to −13°C. Our results show that the low substrate temperature can reduce the penetration of the top metal electrode into the organic layer and weaken the chemical reaction between the top electrode and organic layer, which could pave a way for obtaining high-spin injection and extraction efficiency in organic spin-valve devices.

Vascular stents with submicrometer-scale surface patterning realized via titanium deep reactive ion etching

Herein, we report progress towards realization of vascular stents that will eventually provide opportunity for evaluating cellular response to rationally-designed, submicrometer-scale surface patterning in physiologically-relevant contexts, i.e. those that provide exposure to the complex multicellular milieu, flow-induced shear, and tissue-device interactions present in vivo. Specifically, using our novel titanium deep reactive ion etching technique (Ti DRIE), we discuss recent advances that have enabled: (a) fabrication of precisely-defined, grating-based surface patterns on planar Ti foils with minimum feature sizes as small as 0.15 μm; (b) creation of cylindrical stents from micromachined planar Ti foils; and (c) integration of these processes to produce the first submicrometer-scale surface-patterned Ti stents that are compatible with conventional balloon catheter deployment techniques. We also discuss results from elastoplastic finite element simulations and preliminary mechanical testing of these devices to assess their mechanical performance. These efforts represent key steps towards our long-term goal of developing a new paradigm in stenting, where rationally-designed surface patterning provides a physical means for facilitating healing, and thus, improving outcomes in vascular intervention applications.