Passivation Step Research Articles

Self-Cleaning Poly(dimethylsiloxane) Film with Functional Micro/Nano Hierarchical Structures

This paper reports a novel single-step wafer-level fabrication of superhydrophobic micro/nano dual-scale (MNDS) poly(dimethylsiloxane) (PDMS) films. The MNDS PDMS films were replicated directly from an ultralow-surface-energy silicon substrate at high temperature without any surfactant coating, achieving high precision. An improved deep reactive ion etching (DRIE) process with enhanced passivation steps was proposed to easily realize the ultralow-surface-energy MNDS silicon substrate and also utilized as a post-treatment process to strengthen the hydrophobicity of the MNDS PDMS film. The chemical modification of this enhanced passivation step to the surface energy has been studied by density functional theory, which is also the first investigation of C4F8 plasma treatment at molecular level by using first-principle calculations. From the results of a systematic study on the effect of key process parameters (i.e., baking temperature and time) on PDMS replication, insight into the interaction of hierarchical multiscale structures of polymeric materials during the micro/nano integrated fabrication process is experimentally obtained for the first time. Finite element simulation has been employed to illustrate this new phenomenon. Additionally, hierarchical PDMS pyramid arrays and V-shaped grooves have been developed and are intended for applications as functional structures for a light-absorption coating layer and directional transport of liquid droplets, respectively. This stable, self-cleaning PDMS film with functional micro/nano hierarchical structures, which is fabricated through a wafer-level single-step fabrication process using a reusable silicon mold, shows attractive potential for future applications in micro/nanodevices, especially in micro/nanofluidics.

Effect of Urtica dioica on memory dysfunction and hypoalgesia in an experimental model of diabetic neuropathy

Diabetic neuropathy is considered as a disease of the peripheral nervous system, but recent evidences suggest the involvement of central nervous system as well. In this study we evaluated the effect of Urtica dioica (UD) extract against memory dysfunction and hypoalgesia on a mouse model of streptozotocin (STZ) induced diabetic neuropathy. STZ (50mg/kg, i.p. consecutively for 5 days) was used to induce diabetes, followed by treatment with the UD extract (50mg/kg, oral) and rosiglitazone (5mg/kg, oral) for 8 weeks. Cognitive functions were evaluated using Morris water maze and passive avoidance step through task. Pain thresholds were measured using thermal, mechanical and chemical induced hyperalgesia. We observed that chronic diabetes resulted in a decline in circulating insulin level, elevated blood glucose, reduced body weight, increased water intake, cognitive impairment and hypoalgesia. UD significantly reduced the blood glucose and polydypsia, as well as improved the body weight, insulin level, cognition and insensate neuropathy. In conclusion, UD showed results comparable to rosiglitazone in reversing the long standing diabetes induced complications such as central and peripheral neuronal dysfunction.

A study of the mechanisms causing surface defects on sidewalls during Si etching for TSV (through Si via)

In this paper we report three mechanisms causing surface defects on Si sidewalls during Si etching for TSV. The first mechanism causing surface defects was a downward surface-defect formation due to the participation of the residual polymerizing gas in the transition periods between passivation steps and etch steps. The second mechanism was an upward surface-defect formation due to etchant attacking the interface between the Si and the sidewall polymer. Although the sidewall polymer was thick enough to protect the Si surface, it was not possible to avoid surface defects if the etch step was not switched to the following passivation step in time. The third mechanism was a sponge-like surface-defect formation caused by either poor polymer depositions or voids inside the sidewall polymer. The sponge-like surface defects were formed by Si isotropic etching through the weak points of the sidewall polymer. All three surface defects were considered as the major factors on TSV integration and packaging reliability issues.

Systematic Approach to Time Division Multiplexed Si Etch Process Development

In silicon-substrate processing, it is frequently a requirement to create high-aspect-ratio anisotropic profiles. To do this Time Division Multiplexed processes are almost exclusively used. By alternating between a passivation step and an etching step, high-rate anisotropic profiles can be created. Each step is independent from one another, and to create the desired profiles, proper balancing of the individual steps is critical. Therefore characterization of each of these process steps is necessary. This study will characterize the steps used in a TDM process. Metrics for both deposition and etching are presented. Typical thin film measurement equipment is used; however in-situ optical emission interferometry (OEI) is also utilized to give real time measurements. We will show how process parameters can affect not only the rate, but also the uniformity of each step. By characterizing these steps individually we will show how it is possible to determine a balanced starting process for different applications.

A New Concept for Spatially-Divided Reactive Ion Etching with ALD-Based Passivation

Conventional Deep Reactive Ion Etching (DRIE) is a plasma etch process with alternating half-cycles of 1) Si-etching with SF6 to form gaseous SiFx etch products, and 2) passivation with C4F8 polymerizing as a protecting fluorocarbon deposit on the sidewalls and bottom of the etched features. We report on a novel alternative and disruptive technology concept of Spatially-divided Deep Reactive Ion Etching, where the process is converted from the time-divided into the spatially divided regime. The spatial division can be accomplished by ~20 to 100 μm high inert gas-bearing ‘curtains’ that confine the reactive gases to individual (often linear) injection slots constructed in a gas injector head. By horizontally moving the substrate back and forth under the head one can realize the alternate exposures to compose the overall cycle.Next improvement in the spatially-divided approach is the replacement of the CVD-based C4F8 passivation steps by ALD-based oxide (e.g. SiO2) deposition cycles. The method can have industrial potential in cost-effective creation of advanced 3D TSV interconnects and MEMS, but also in advanced patterning of, e.g., nanoscale FinFET devices with reduced line edge roughness, thus approaching Atomic Layer Etching accuracy.

Realization of complex three-dimensional free-standing structures on silicon substrates using controllable underetching in a deep reactive ion etching

We report the realization of three-dimensional free-standing structures with high complexity on silicon substrates without using surface micromachining. The etching is feasible using the reactive ion etching method in which three gases are used in a two-step etching process. The passivation step is carried out by means of hydrogen, oxygen and sulfur-hexafluoride (SF6) while the etching step uses SF6 in a low-density capacitive-coupled radio frequency reactor. The overall etching process can be adjusted to arrive at three-dimensional structures with desired underetchings. The formation of partially and fully suspended structures is reported. Multi-level floated structures have been realized using this method.

Mechanisms of rhythm generation of the human lumbar spinal cord in response to tonic stimulation without and with step-related sensory feedback

Independent studies have shown that the human lumbar spinal networks below a complete spinal cord injury can produce rhythmic motor outputs in response to step- related sensory feedback or sustained electrical spinal cord stimulation (SCS). Here we present our current studies ap- plying lumbar SCS in motor-complete spinal cord injured (SCI) individuals in the supine and supported standing posi- tion, and during assisted treadmill stepping, to explore the mechanisms of spinal rhythm generation. SCS could pro- duce rhythmic EMG activities without step-related sensory feedback; in each case, all muscles were active with a com- mon rhythm frequency. During SCS and passive treadmill stepping, muscle activities were normally synchronized to the imposed step frequency, but activities with an independ- ent rhythm frequency were generated as well. The results suggest rhythmic reflex actions and central spinal generation as two different causes of rhythm generation. Here, we present our current studies that explore the roles of sustained inputs and step-related sensory feedback to the human lumbosacral spinal cord in the generation of rhythmic motor patterns. We applied epidural or transcu- taneous lumbar SCS in motor-complete SCI individuals in the supine position (preventing hip extension and axial limb load that are otherwise critical for rhythm genera- tion), in a supported standing positions with the lower limbs being 'mechanically immobilized' (preventing movements at hip and knee), and during assisted and body-weight supported (BWS) treadmill stepping. Based on their characteristically different signal profiles, the hypothesis was that the non-patterned and patterned inputs to the spinal cord neural networks would reveal different mechanisms of rhythm generation. Methods

Perpendicular magnetic anisotropy in Ta/CoFeB/MgO systems synthesized on treated SiN/SiO2 substrates for magnetic memories

Ta(5nm)/CoFeB(1nm)/MgO(2nm) stacks have been deposited by magnetron sputtering on top of 8" Si/SiN/SiO2 substrates, where the effects of different passivation steps related to copper damascene processes have been simulated. It is shown that excellent thickness uniformity of the deposited stack is achieved on 8" areas, and strong uniaxial perpendicular magnetic anisotropy Ku up to 0.5–1×106J/m3 develops in the 1nm CoFeB following thermal annealing at 300°C for 2h, irrespective of the adopted passivation treatment. The CoFeB coercive field varies from 0.21 to 0.51kA/m for substrate surface roughness in the range of 0.45–0.55nm. These results are of relevance in the view of integrating into standard complementary metal-oxide semiconductor process, advanced magnetic memory concepts based on perpendicular magnetic anisotropy in ultrathin layers.

A new concept for spatially divided Deep Reactive Ion Etching with ALD-based passivation

Conventional Deep Reactive Ion Etching (DRIE) is a plasma etch process with alternating half-cycles of 1) Si-etching with SF6 to form gaseous SiFx etch products, and 2) passivation with C4F8 that polymerizes as a protecting fluorocarbon deposit on the sidewalls and bottom of the etched features. In this work we report on a novel alternative and disruptive technology concept of Spatially-divided Deep Reactive Ion Etching, S-DRIE, where the process is converted from the time-divided into the spatially divided regime. The spatial division can be accomplished by inert gas bearing 'curtains' of heights down to ∼20 μm. These curtains confine the reactive gases to individual (often linear) injection slots constructed in a gas injector head. By horizontally moving the substrate back and forth under the head one can realize the alternate exposures to the overall cycle.A second improvement in the spatially divided approach is the replacement of the CVD-based C4F8 passivation steps by ALD-based oxide (e.g. SiO2) deposition cycles. The method can have industrial potential in cost-effective creation of advanced 3D interconnects (TSVs), MEMS manufacturing and advanced patterning, e.g., in nanoscale transistor line edge roughness using Atomic Layer Etching.

A Novel Four-Mask Low-Temperature Polycrystalline Silicon PMOS Thin-Film Transistor With Advanced Terrace Structure for AMOLED Application

We propose a novel four-mask low-temperature polycrystalline-silicon PMOS structure. In this letter, we obtain the utmost simplified thin-film transistor (TFT) structure by eliminating the storage doping, passivation, and anode photomask steps. The proposed four-mask structure has a self-aligned terrace structure whose lightly doped drain (LDD) and gate-overlapped LDD are formed with only one photomask step. The on current of the four-mask PMOS TFT with an advanced terrace structure is similar to that of the conventional seven-mask TFT, while the off current of the new structure is lower than that of the conventional seven-mask TFT.

Gas chopping etching process for InP based nanostructures with high aspect ratios

The authors report a novel etching process for the fabrication of nanostructured III-V semiconductors with ultra-high aspect ratios. For the very first time, a time multiplexed etching process (gas chopping process) for an InP based material system has been successfully developed and demonstrated. The repetition of a Cl2/H2/Ar based etching step together with passivation and removal steps ensures very deep etching with straight walls without general restrictions by the etch depth. The newly developed process is very promising for the fabrication of deeply etched feedback gratings for lasers or nanophotonic devices requesting high aspect ratios, like lasers with surface defined distributed Bragg reflector/distributed feedback gratings or deeply etched photonic crystals. This new process allows the formation of vertical profiles with smooth surfaces and reduced footing effect. Using this gas chopping process for InP, a high mask selectivity of 15, good etching rate of 95 nm/min, and record values of the aspect ratio up to 41 could be demonstrated.

Cardiovascular Response of Individuals With Spinal Cord Injury to Dynamic Functional Electrical Stimulation Under Orthostatic Stress

In this pilot study, we examined how effectively functional electrical stimulation (FES) and passive stepping mitigated orthostatic hypotension in participants with chronic spinal cord injury (SCI). While being tilted head-up to 70 (°) from the supine position, the participants underwent four 10-min conditions in a random sequence: 1) no intervention, 2) passive stepping, 3) isometric FES of leg muscles, and 4) FES of leg muscles combined with passive stepping. We found that FES and passive stepping independently mitigated a decrease in stroke volume and helped to maintain the mean blood pressure. The effects of FES on stroke volume and mean blood pressure were greater than those of passive stepping. When combined, FES and passive stepping did not interfere with each other, but they also did not synergistically increase stroke volume or mean blood pressure. Thus, the present study suggests that FES delivered to lower limbs can be used in individuals with SCI to help them withstand orthostatic stress. Additional studies are needed to confirm whether this use of FES is applicable to a larger population of individuals with SCI.

One-shot genetic analysis in monolithic Silicon/Pyrex microdevices

Modern Lab-on-a-chip (LOC) platforms for genomic applications integrate several biological tasks in a single device. Combination of these processes into a single device minimizes sample loss and contamination problems as well as reducing analysis time and costs. Here we present a study of a microchip platform aimed at analyzing issues arising from the combination of different functions, such as DNA purification from blood, target amplification by PCR and DNA detection in a single silicon-based device. DNA purification is realized through two different strategies: 1) amine groups coating microchannel surfaces and 2) magnetic nanoparticles coated by chitosan. In the first strategy silicon/Pyrex microdevices coated with 3-aminopropyltriethoxysilane (APTES) or 3-2-(2-aminoethylamino)-ethylamino]-propyltrimethoxysilane (AEEA) were examined and their efficiency in human genomic DNA adsorption/desorption was evaluated. APTES treatment was the most suitable for the purification of a reasonable amount of DNA in a state suitable for the following PCR step. The second strategy has instead the main advantage of avoiding an elution step, since the DNA adsorbed on the magnetic nanoparticles can be used as PCR template. On-chip PCR was performed in a custom thermocycler, while the detection of PCR products was carried out by fluorescence reading. A complete genetic analysis was demonstrated on the monolithic silicon/Pyrex microchip, starting from less than 1 [Formula: see text]L of human whole blood and arriving at SNPs identification. The successful integration of DNA purification, amplification and detection on a single microdevice was proven without the need for biological passivation steps and possibly simplifying the realization of genomic detection devices.

Recent Progresses in GaN Power Rectifier

In this work, both “Schottky to Schottky” structure (STS) and pseudo-vertical Schottky barrier diode (pv-SBD) have been processed on GaN heteroepitaxially grown on sapphire or silicon by metal organic chemical vapor deposition (MOCVD) and characterized physically and electrically. Ni and Ti/Al were used to obtain respectively Schottky and Ohmic contacts using rapid thermal annealing (RTA). Adequate passivation steps and insertion of a resistive guard ring were also implemented in pv-SBD. The STS results, presented in this paper, evidence the impact of the substrate on the growth as well as all the progresses that have been done on GaN material quality. Furthermore, we demonstrate that high quality Schottky diodes can be obtained on GaN grown on sapphire by MOCVD. Indeed, ideality factors of 1.09 as well as a barrier height of 1.06 eV were obtained on pv-SBD devices that have a breakdown voltage over 600 V.

Impedance Identification Procedure of Three-Phase Balanced Voltage Source Inverters Based on Transient Response Measurements

Impedance-based models are commonly used to perform system-level stability analysis of distributed power systems. In this paper, a new impedance identification procedure for three-phase balanced voltage source inverters voltage source inverters (VSIs) is proposed. This procedure is based on the transient response of the inverter to simple passive load step tests. Transfer function models are obtained from the transient response by means of a well-established and easy to use identification algorithm. The performance of the proposal is validated through both simulation and experimental results obtained on VSIs for aircraft applications.

Robotic-assisted stepping modulates monosynaptic reflexes in forearm muscles in the human

Although the amplitude of the Hoffmann (H)-reflex in the forelimb muscles is known to be suppressed during rhythmic leg movement, it is unknown which factor plays a more important role in generating this suppression-movement-related afferent feedback or feedback related to body loading. To specifically explore the movement- and load-related afferent feedback, we investigated the modulation of the H-reflex in the flexor carpi radialis (FCR) muscle during robotic-assisted passive leg stepping. Passive stepping and standing were performed using a robotic gait-trainer system (Lokomat). The H-reflex in the FCR, elicited by electrical stimulation to the median nerve, was recorded at 10 different phases of the stepping cycle, as well as during quiet standing. We confirmed that the magnitude of the FCR H-reflex was suppressed significantly during passive stepping compared with during standing. The suppressive effect on the FCR H-reflex amplitude was seen at all phases of stepping, irrespective of whether the stepping was conducted with body weight loaded or unloaded. These results suggest that movement-related afferent feedback, rather than load-related afferent feedback, plays an important role in suppressing the FCR H-reflex amplitude.

Alternating SiCl4/O2 passivation steps with SF6 etch steps for silicon deep etching

Deep etching of silicon has been investigated in an inductively coupled plasma etch reactor using short SiCl4/O2 plasma steps to passivate the sidewalls of the etched structures. A study was first carried out to define the appropriate parameters to create, at a substrate temperature of −20 °C, a passivation layer by SiCl4/O2 plasma that resists lateral chemical etching in SF6 plasma. The most efficient passivation layer was obtained for a SiCl4/O2 gas flow ratio of 2:1, a pressure of 1 Pa and a source power of 1000 W. Ex situ analyses on a film deposited with these parameters show that it is very rich in oxygen. Silicon etching processes that alternate SF6 plasma etch steps with SiCl4/O2 plasma passivation steps were then developed. Preliminary tests in pulsed-mode conditions have enabled etch rates greater than 2 µm min−1 with selectivities higher than 220. These results show that it is possible to develop a silicon deep etching process at substrate temperatures around −20 °C that uses low SiCl4 and O2 gas flows instead of conventional fluorocarbon gases for sidewall protection.

Improvement of passivity of Fe–xCr Alloys (x < 10%) by cycling through the reactivation potential

Classically, 13% Cr is required for stable passivity of a Fe–Cr alloy in acidic and neutral solutions not containing inhibitors. Some authors (Mansfeld, Fujimoto) have published potential cycling procedures that generate thick Cr-rich films. In this work, a similar technique, but with a far smaller potential cycle, was used to enrich a surface layer in chromium, thereby increasing corrosion-resistance in otherwise non-passivating steels. This was achieved by potential stepping across the iron reactivation potential, firstly forming passive iron(III) oxide, then reducing it to soluble iron(II) ions, while ensuring the passivity of chromium. The use of potential stepping was found to result in a more robust film than that formed through a single continuous passivation step.

Realization of Three-Dimensional Si and $ \hbox{SiO}_{2}$ Nanowall Structures Using Reactive Ion Etching

We report the realization of highly sculptured 3-D silicon and SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanowall structures on silicon substrates with a single masking layer using a hydrogen-assisted deep reactive ion etching process. By precisely controlling the passivation and etching steps, it is possible to achieve the desired 3-D featured silicon structures, which are bases for SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 3-D nanowalls.

Thin film silicon solar cells by AIC on foreign substrates

This paper presents the fabrication of thin film crystalline silicon solar cells on foreign substrates like alumina, glass–ceramic (GC) and metallic foils (ferritic steel—FS) using seed layer approach, which employs aluminium induced crystallisation (AIC) of amorphous silicon. Effect of hydrogen content in a-Si:H precursor films on the AIC process has been studied and the results showed that defects in the AIC grown films increased with increase of hydrogen content. At the optimal thermal annealing conditions, the AIC grown poly-Si films showed an average grain size of 7.6, 26, and 8.1 μm for the films synthesised on alumina, GC, and FS, respectively. The grains were (1 0 0) oriented with a sharp Raman peak around 520 cm −1. Similarly, n-type seed layers were also fabricated by over-doping of as-grown AIC layers using a highly phosphorus doped glass solution. The resistivity of as-grown films reduced from 8.4×10 −2 Ω cm (p-type) to 4.1×10 −4 Ω cm (n-type) after phosphorus diffusion. These seed layers of n-type/p-type were thickened to form an absorber layer by vapour phase epitaxy or solid phase epitaxy. The passivation step was applied before the heterojunction formation, while it was after in the case of homojunction. Open circuit voltage of the junctions showed a strong dependence on the hydrogenation temperature and microwave (μW) power of electron cyclotron resonance (ECR) plasma of hydrogen. Effective passivation was achieved at a μW power of 650 W and hydrogenation temperature of 400 °C. Higher values of solar conversion efficiencies of 5% and 2.9% were achieved for the n-type and p-type heterojunction cells, respectively fabricated on alumina substrates. The analysis of the results and limiting factors are discussed in detail.