Deep Etching Research Articles

High Aspect Ratio Machining of Nanocarbon Materials by Reactive Ion Etching

AbstractWe demonstrate anisotropic, vertical deep etching of graphite and densely packed carbon nanotube (CNT) thick layer beyond the micrometer scale, which representing the first step toward nanocarbon bulk micromachining. This micromachining process is compatible with standard lithography and therefore allows the fabrication of graphite and CNT architectures with 1 μm lateral resolution and up to 10 μm scale depth.

Possibilities of usage a scanning electron microscopic study by microstructure control of aluminium cast alloys

The contribution describes the real morphology of all structural parameters (Si particles and different intermetallic phases) in recycled (secondary) aluminium cast alloy. The morphology, distribution and volume of Si particles and intermetallic phases in α-matrix influence mechanical and fatigue properties of casts and therefore it is important to study the real morphology of these structural parameters. The morphology were studied by using scanning electron microscopy by using different possibilities of preparing samples. The first group of samples were prepared by standard methods – metallography samples and the second group of samples were prepared by using deep etching for highlighting the 3D morphology of structural parameters. This study confirmed the differences in morphology observation by using these two method.

Nearly perfect GaN crystal via pit-assisted growth by HVPE

We demonstrated 5 mm-thick bulk gallium nitride (GaN) with nearly perfect crystal quality. To achieve this, intentional etch pit formation by in situ dry HCl etching and ex situ wet etching in H3PO4 solution was employed on freestanding GaN templates followed by regrowth by hydride vapor phase epitaxy (HVPE). This consecutive etching gave rise to a number of large and deep etch pits on the whole surface of the freestanding GaN. We believe that these can reveal the etch pits originating from the dislocations with the edge, and mixed components. Intentionally formed etch pits were partially covered with the fresh regrown bulk GaN layer, being transformed into voids. Dislocations cannot propagate into new GaN layers through the voids, thus resulting in the reduction of dislocation density. 5 mm-thick bulk GaN exhibits a smooth, transparent surface and extremely high crystal quality with full width at half maximum (FWHM) of 21 arcsec in (0002) X-ray rocking curve and etch pit density (EPD) of 3 × 102 per cm2. This method can provide a promising way to fabricate bulk GaN with extremely low dislocation density, suitable for the fabrication of high-performance devices.

Studies of the laser etching on painted plastic parts to prevent the risks of engraving failures at mechatronic devices

Nowadays, the automotive mechatronic devices are developed with many symbols engraved over the painted plastic parts. Many risks are coming due to painting layer, which could be dry or not, the paint thickness variability it is also one important aspect. The paper’s aim is to present the studies of the laser etching process and the risk reduction of the possible failure by using the 2D optical measurement of different parameters for the laser beam, also using the 3D scanning in order to see the deep etching of the paint. The experiments will let the team know what should be the parameter setting for the painted plastic materials delivered in production in different time after the painting, therefore to reduce the over-adjusting and first part approval process duration.

Proposal for small heat-affected zone, high aspect ratio processing for metal

One of the difficulties in laser processing is removal of the heat-affected zone (HAZ), such as resolidified material on the surface of the work material. If a processing technology can be developed to minimize the generation of HAZ, the function loss caused by HAZ can be reduced.In this paper, Deep Electrochemical Etching with Laser assistance (DEEL) is proposed as a new and precise machining technology for metal. DEEL has the potential to make small and precise parts, such as stents, without HAZ. To investigate DEEL, laser processing and electrochemical machining (ECM) were first carried out to find a suitable machining condition. Second, DEEL processing was carried out with the obtained machining conditions. The machining characteristics of DEEL were considered by measuring the machining depth and observing the machined surface. Finally, low HAZ and high aspect ratio complex machining with DEEL were experimentally demonstrated on a microscopic tube.

Fabrication process for 200 nm-pitch polished freestanding ultrahigh aspect ratio gratings

A fully integrated fabrication process has been developed to fabricate freestanding, ultrahigh aspect ratio silicon gratings with potassium hydroxide (KOH)-polished sidewalls. The gratings are being developed for wavelength-dispersive, soft x-ray spectroscopy on future space telescopes. For this application, the grating needs to have a large open-area fraction and smooth sidewalls (roughness < 1 nm) to maximize efficiency. The prototype gratings fabricated with the process presented here have been tested on a synchrotron beamline and have demonstrated an absolute diffraction efficiency greater than 30% for 2 nm-wavelength x-rays in blazed orders. This efficiency is greater than twice the efficiency of previously fabricated gratings. The fabrication process utilizes silicon-on-insulator wafers where the grating and a cross support are etched in the device layer, and an additional structural support is etched in the handle layer. The device layer and handle layer are both etched via deep reactive-ion etching using a Bosch process. The buried SiO2 layer stops both etches and is removed at the end of the process to create a freestanding structure. The gratings have a pitch of 200 nm, a depth of 4 μm, and the bars are polished via KOH. The polishing process reduces both the roughness and the grating-bar thickness. The finished gratings span an area of approximately 10 by 30 mm, supported by 1 mm-wide hexagons in the handle layer.

Dispersion characteristics of nanometer-scaled silicon nitride suspended membrane waveguides**Project supported by the National Natural Science Foundation of China (Nos. 61435002, 61527823 61321063).

We investigate the dispersion properties of nanometer-scaled silicon nitride suspended membrane waveguides around the communication wavelength and systematically study their relationship with the key structural parameters of the waveguide. The simulation results show that a suspended membrane waveguide can realize anomalous dispersion with a relatively thinner silicon nitride thickness in the range of 400 to 600 nm, whereas, for the same membrane thickness, a conventional rib or strip silicon nitride waveguide cannot support anomalous dispersion. In particular, a waveguide with 400 nm silicon nitride thickness and deep etch depth (r = 0.05) exhibits anomalous dispersion around the communication wavelength when the waveguide width ranges from 990 to 1255 nm, and the maximum dispersion is 22.56 ps/(nm·km). This specially designed anomalous dispersion silicon nitride waveguide is highly desirable for micro-resonator based optical frequency combs due to its potential to meet the phase-matching condition required for cascaded four-wave-mixing.

Tip-Based Nanomanufacturing of Nanofluidics Using Atomic Force Microscopy

Presently, nanomanufacturing capabilities limit the commercialization of a broader range of nanoscale structures with higher complexity, greater precision and accuracy, and a substantially improved performance. Atomic force microscopy (AFM)-based nanomachining is a promising technique to address current limitations and is considered a potential manufacturing (MFG) tool for operations such as machining, patterning, and assembling with in situ metrology and visualization. Most existing techniques for fabrication of nanofluidic channels involve the use of electron-beam lithography, which is a very expensive process that requires a lengthy calibration procedure. In this work, atomic force microscopy (AFM) is employed in the fabrication of nanofluidic channels for medical applications. Channels with various depths and widths are fabricated using AFM indentation and scratching. A nanoscale channel is mainly used in the study of the molecular behavior at single molecule level. The resulting device can be used for detecting, analyzing and separating biomolecules, DNA stretching, and separation of elite group of lysosome and other viruses. The nanochannels are integrated between microchannels and act as filters to separate biomolecules. Sharply developed vertical microchannels are produced from deep reaction ion etching. Poly-dimethylsiloxane (PDMS) bonding is performed to close the top surface of the silicon device. An experimental setup is used for testing by flowing fluid through the channels. A cost evaluation shows 47.7% manufacturing-time and 60.6% manufacturing-cost savings, compared to more traditional processes.

Rapid Solidification of Sn-Cu-Al Alloys for High-Reliability, Lead-Free Solder: Part I. Microstructural Characterization of Rapidly Solidified Solders

Particles of Cu x Al y in Sn-Cu-Al solders have previously been shown to nucleate the Cu6Sn5 phase during solidification. In this study, the number and size of Cu6Sn5 nucleation sites were controlled through the particle size refinement of Cu x Al y via rapid solidification processing and controlled cooling in a differential scanning calorimeter. Cooling rates spanning eight orders of magnitude were used to refine the average Cu x Al y and Cu6Sn5 particle sizes down to submicron ranges. The average particle sizes, particle size distributions, and morphologies in the microstructures were analyzed as a function of alloy composition and cooling rate. Deep etching of the samples revealed the three-dimensional microstructures and illuminated the epitaxial and morphological relationships between the Cu x Al y and Cu6Sn5 phases. Transitions in the Cu6Sn5 particle morphologies from faceted rods to nonfaceted, equiaxed particles were observed as a function of both cooling rate and composition. Initial solidification cooling rates within the range of 103 to 104 °C/s were found to be optimal for realizing particle size refinement and maintaining the Cu x Al y /Cu6Sn5 nucleant relationship. In addition, little evidence of the formation or decomposition of the ternary-β phase in the solidified alloys was noted. Solidification pathways omitting the formation of the ternary-β phase agreed well with observed room temperature microstructures.

Use of Microscopy in the Study of Self-Hardening Al-Alloy for Automotive Application

Self-hardening secondary Al-Zn-Si-Mg alloys represent an innovative class of light Al-Si alloys. The most important and relevant feature of the self-hardening alloys is related to their good performance, without the need of any heat treatment. Mechanical properties depend upon the morphologies, type and distribution of the phases. It is therefore important to study the intermetallic phases occurring in the secondary Al-alloys, where they found more than in the primary-Al alloys. Study of intermetallic phases in the alloy was performed on an optical microscope using classical etching technique (by 0.5 % HF) to invocation black-white contrast as well as unconventional methods for invocation colour contrast (etching by Weck-Al) to the observed surface of the sample. The colour metallography results were correlated with the information obtained by standard etching. The microstructures of the samples were analysed by scanning electron microscopy after standard etching and deep etching (with HCl) too. After deep etching we are able to see the 3D morphology of eutectic Si particles and intermetallic phases.

Three-Electrode on-Chip Sensors for Voltammetric Detection of Trace Metals in Natural Waters

This paper reports on the fabrication and electrochemical characterization of newly designed three-electrode on-chip devices for in situ voltammetric detection of trace metals in marine environment. Sensitivity values higher than those previously reported in literature were obtained for cadmium (Cd(II)), lead (Pb(II)), copper (Cu(II)), zinc (Zn(II)) [1] and arsenite (As(III)) [2]. The key novelty of these devices is the on-chip integration of a reference electrode (RE) towards the miniaturization of the voltammetric in situ profiling system [3].Compared to the microdisc arrays reported by Belmont et al. [1], [4], our sensors also differ in number of iridium (Ir) microdiscs (190 vs. 100), center to center distance of the microdiscs, as well as deposition/patterning techniques used during the fabrication. The sensors were fabricated on silicon wafers passivated with silicon nitride (Si3N4). Ir deposited by sputtering was patterned by Ion Beam Etching, followed by a Si3N4layer deposited by Plasma-Enhanced Chemical Vapor Deposition and subsequently patterned by Deep Reactive-Ion Etching to define the microelectrodes and bonding pads. Ir electrodes were used as either counter electrode (CE) without further modification or as a seed layer for the fabrication of the working and reference electrode (WE, RE). The WE was obtained by plating Ir microdisc array with mercury or gold nanoparticles for direct quantification of respectively cadmium, lead, copper , zinc [5] and arsenite [2], the RE was realized by plating the Ir with silver (Ag) by galvanostatic electrodeposition and chloridizing Ag to silver chloride (AgCl). A schematic view of the sensor is shown in Figure 1 as well as a picture of the microfabricated device. The electrode surface topography and cleanness were analyzed by Scanning Electron Microscopy (SEM) showing an excellent quality of the Si3N4 layer patterning in terms of geometry definition and absence of fabrication residue (as seen in Figure 2). The material properties and the electrochemical behavior of the Ir-based electrodes were characterized by cyclic voltammetry: the integrity of the thin-film Ir layer was assessed in degassed 1 M H2SO4(Figure 3a) and the absence of shielding effect was demonstrated in 1 mM potassium ferricyanide at different scan rates from 1 mV/s to 50 mV/s, as shown by the S-shaped current response in Figure 3b. The measured diffusion controlled steady-state current (118.9±2.24 nA) was found to be in good agreement with the theoretical value calculated for a recessed geometry (119.5 nA). Afterwards SU-8 was patterned by photolithography around the WE and RE to serve as containment ring for an antifouling agarose gel membrane. The pseudo-reference Ag/AgCl RE was tested in seawater showing a potential of about 37 mV against an Ag/AgCl/3 M KCl RE stable over more than 2 months as shown in Figure 4, and in synthetic solutions with different chloride concentrations giving a potential slope of 50.1 mV/decade at 25 °C. The use of an Ionic Liquid (IL) poly(vinyl chloride) (PVC) membrane [6] is currently under investigation in order to develop an all-solid-state RE towards a versatile use in brackish water as well. The first Square Wave Anodic Stripping Voltammetry (SWASV) measurements were carried out in synthetic solutions of Pb(II), Cu(II) and Cd(II) or As(III) against an external RE. Figure 5 shows the SWASV measurements obtained for different concentrations of Pb(II), Cd(II) and Cu(II) in 0.1 M NaNO3 background electrolyte for 600 s deposition time. Registered sensitivity values were 2.73 nAnM-1 min-1, 1.23 nAnM-1 min-1, 1.29 nAnM-1 min-1 and 0.6 nAnM-1 min-1for Pb(II), Cu(II), Cd(II) and As(III), respectively. SWASV measurements against on-chip RE are currently under investigation.

Scanning SQUID susceptometers with sub-micron spatial resolution.

Superconducting QUantum Interference Device (SQUID) microscopy has excellent magnetic field sensitivity, but suffers from modest spatial resolution when compared with other scanning probes. This spatial resolution is determined by both the size of the field sensitive area and the spacing between this area and the sample surface. In this paper we describe scanning SQUID susceptometers that achieve sub-micron spatial resolution while retaining a white noise floor flux sensitivity of ≈2μΦ0/Hz1/2. This high spatial resolution is accomplished by deep sub-micron feature sizes, well shielded pickup loops fabricated using a planarized process, and a deep etch step that minimizes the spacing between the sample surface and the SQUID pickup loop. We describe the design, modeling, fabrication, and testing of these sensors. Although sub-micron spatial resolution has been achieved previously in scanning SQUID sensors, our sensors not only achieve high spatial resolution but also have integrated modulation coils for flux feedback, integrated field coils for susceptibility measurements, and batch processing. They are therefore a generally applicable tool for imaging sample magnetization, currents, and susceptibilities with higher spatial resolution than previous susceptometers.

Deep dry etching of fused silica using C4F8/Ar inductively coupled plasmas

This paper reports the etching process of fused silica by inductively coupled plasmas (ICP) for through glass via (TGV) applications. Mixed C4F8 and Ar were used as etching gases in present experiments. The effects of key factors, including etching gases, chamber pressure and substrate temperatures, on etch rate and via profile were studied. Results showed that a high etch rate of about 0.75 μm/min with smooth and vertical sidewall of TGVs can be obtained. Compared to Ar flux and chamber pressure, the effect of C4F8 flux on etch rate is more remarkable. Vertical vias (>89°) can be achieved by increasing the substrate temperature and decreasing the mixing ratio of C4F8 and Ar. Besides, micro-pillars at the bottom of via were observed when the substrate temperature was set at 0 °C. As the substrate temperature reached to 80 °C, micro-pillars were removed clearly. Optimized results indicate that the ICP etching is an effective method for fabricating TGV.

Cryogenic Etching of High Aspect Ratio 400 nm Pitch Silicon Gratings.

The cryogenic process and Bosch process are two widely used processes for reactive ion etching of high aspect ratio silicon structures. This paper focuses on the cryogenic deep etching of 400 nm pitch silicon gratings with various etching mask materials including polymer, Cr, SiO2 and Cr-on-polymer. The undercut is found to be the key factor limiting the achievable aspect ratio for the direct hard masks of Cr and SiO2, while the etch selectivity responds to the limitation of the polymer mask. The Cr-on-polymer mask provides the same high selectivity as Cr and reduces the excessive undercut introduced by direct hard masks. By optimizing the etching parameters, we etched a 400 nm pitch grating to ≈ 10.6 μm depth, corresponding to an aspect ratio of ≈ 53.

A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited.

Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30-70% in visible and near-infrared light.

High-precision motion of magnetic microrobot with ultrasonic levitation for 3-D rotation of single oocyte

In this study, we propose an innovative driving method for a microrobot. By using acoustic levitation, the microrobot can be levitated from the glass substrate. We are able to achieve positioning accuracy of less than 1 μm, and the response speed and output force are also significantly improved. Silicon-based microrobots can be made into diverse shapes using deep reactive-ion etching (DRIE). Using custom-designed microrobots allows for the 3-D rotational control of a single bovine oocyte. Orientation with an accuracy of 1° and an average rotation velocity of 3 rad/s are achieved. This study contributes to the biotechnology. In the study of oocytes/embryos, manipulation is used for the enucleation, microinjection, and investigation of the characteristics of oocytes, such as the meiotic spindle and zona pellucida using PolScope. These studies and their clinical applications involve the three-dimensional (3-D) rotation of mammalian oocytes. The overall out-of-plane and in-plane rotations of the oocyte are demonstrated by using an acoustically levitated microrobot. In addition, by using this approach, it becomes much easier to manipulate the cell to investigate the characteristics of the single cell and analyze its mechanical properties.

Planar microlens with front-face angle: design, fabrication, and characterization

This paper studies the effect of microlens front-face angle on the performance of an optical system consisting of a planar-graded refractive index (GRIN) lens pair facing each other separated by a free-space region. The planar silica microlens pairs are designed to facilitate low-loss optical signal propagation in the free-space region between the opposing optical waveguides. The planar lens is fabricated from a 38-μm-thick fluorine-doped silica layer on a silicon substrate. It has a parabolic refractive index profile in the vertical direction, which is achieved by controlled fluorine incorporation in the silica film to collimate the optical beam in the vertical direction. Horizontal beam collimation is achieved by incorporating a horizontal curvature at the front face of the lens defined by deep oxide etch. A generalized 3×3ABCDGH transformation matrix method has been derived to compute the coupling efficiency of such microlens pairs to take front-face angles that may be present due to fabrication variations or limitations and possible input/output optical fiber offset/tilt into considerations. Pairs of such planar GRIN lens with various free-space propagation distances between them ranging from 75 to 2500 μm and with front-face angles of 1.5 deg, 2 deg, and 4 deg have been fabricated and characterized. Beam propagation method simulations have been carried out to substantiate the theoretical and experimental results. The results indicate that the optical loss is reasonably low up to 1.5 deg of front-face angles and increases significantly with further increase in the front-face angle. Analysis shows that for a given system with specific microlens front-face angle, the optical loss can be significantly reduced by properly compensating the vertical position of the input and output fibers.

Out-of-Plane Strain Effects on Physically Flexible FinFET CMOS

We present a comprehensive electrical performance assessment of hafnium silicate (HfSiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) high-κ dielectric and titanium-nitride (TiN) metal-gate-integrated FinFET-based complementary-metal-oxide-semiconductor (CMOS) on flexible silicon on insulator. The devices were fabricated using the stateof-the-art CMOS technology and then transformed into flexible form by using a CMOS-compatible maskless deep reactive-ion etching technique. Mechanical out-of-plane stresses (compressive and tensile) were applied along and across the transistor channel lengths through a bending range of 0.5-5 cm radii for n-type and p-type FinFETs. Electrical measurements were carried out before and after bending, and all the bending measurements were taken in the actual flexed (bent) state to avoid relaxation and stress recovery. Global stress from substrate bending affects the devices in different ways compared with the well-studied uniaxial/biaxial localized strain. The global stress is dependent on the type of channel charge carriers, the orientation of the bending axis, and the physical gate length of the device. We, therefore, outline useful insights on the design strategies of flexible FinFETs in future free-form electronic applications.

Design and fabrication of a large area freestanding compressive stress SiO2 optical window

This paper reports the design and fabrication of a 7.2 mm × 9.6 mm freestanding compressive stress SiO2 optical window without buckling. An application of the SiO2 optical window with and without liquid penetration has been demonstrated for an optical modulator and its optical characteristic is evaluated by using an image sensor. Two methods for SiO2 optical window fabrication have been presented. The first method is a combination of silicon etching and a thermal oxidation process. Silicon capillaries fabricated by deep reactive ion etching (deep RIE) are completely oxidized to form the SiO2 capillaries. The large compressive stress of the oxide causes buckling of the optical window, which is reduced by optimizing the design of the device structure. A magnetron-type RIE, which is investigated for deep SiO2 etching, is the second method. This method achieves deep SiO2 etching together with smooth surfaces, vertical shapes and a high aspect ratio. Additionally, in order to avoid a wrinkling optical window, the idea of a Peano curve structure has been proposed to achieve a freestanding compressive stress SiO2 optical window. A 7.2 mm × 9.6 mm optical window area without buckling integrated with an image sensor for an optical modulator has been successfully fabricated. The qualitative and quantitative evaluations have been performed in cases with and without liquid penetration.

Photoswitched Cell Adhesion on Azobenzene-Containing Self-Assembled Films.

Stimuli-responsive surfaces that can regulate and control cell adhesion have attracted much attention for their great potential in diverse biomedical applications. Unlike for pH- and temperature-responsive surfaces, the process of photoswitching requires no additional input of chemicals or thermal energy. In this work, two different photoresponsive azobenzene films are synthesized by chemisorption and electrostatic layer-by-layer (LbL) assembly techniques. The LbL film exhibits a relatively loose packing of azobenzene chromophores compared with the chemisorbed film. The changes in trans/cis isomer ratio of the azobenzene moiety and the corresponding wettability of the LbL films are larger than those of the chemisorbed films under UV light irradiation. The tendency for cell adhesion on the LbL films decreases markedly after UV light irradiation, whereas adhesion on the chemisorbed films decreases only slightly, because the azobenzene chromophores stay densely packed. Interestingly, the tendency for cell adhesion can be considerably increased on rough substrates, the roughness being introduced by use of photolithography and inductively coupled plasma deep etching techniques. For the chemisorbed films on rough substrates, the amount of cells that adhere also changes slightly after UV light irradiation, whereas, the amount of cells that adhere to LbL films on rough substrates decreases significantly.