含氟表面活性剂对多晶硅绒面微结构的影响

在酸制绒液中加入含氟表面活性剂,对多晶硅片制绒。然后通过扫描电子显微镜观察多晶硅表面织构,并在此基础上分析含氟表面活性剂对腐蚀效果的影响。实验结果表明:虽然传统酸液对多晶硅制绒是各向同性的,但加入含氟表面活性剂后,酸腐蚀出现各向异性腐蚀特性;由此制备的多晶硅片反射率从25.7%下降到了23.9%,表面出现变形的金字塔、三角形等,且不同晶面的金字塔和三角形的大小和倾斜角度不同。最后根据杨氏理论,从界面张力的角度解释了含氟表面活性剂对制绒的影响机理。     

Fabrication of silicon dioxide submicron channels without nanolithography for single biomolecule detection

We successfully fabricated nanochannel arrays with silicon dioxide (SiO(2)) surfaces for single biomolecule detection. The SiO(2) nanochannel fabrication is based on the combination of anisotropic etching by potassium hydroxide (KOH) solution, local oxidation of silicon (LOCOS) and plasma etching of silicon. This fabrication technique is easily controllable and is a simple and practical solution for low-cost and high-throughput fabrication of nanofluidic channels. Thus, this technique enables the generation of nanochannels with various nanoscale dimensions without using nanolithography.     

Fabrication of high aspect ratio silicon micro-tips for field emission devices

The evolution of higher order {221} and {331} crystal planes during corner undercutting in the anisotropic etching of (100) silicon is discussed, and the occurrence of highly vertical (72.5°) {311} planes unique to KOH etches are demonstrated. Using a combined etching technique, very high aspect ratio micro-tips are formed and their distinct advantages for vacuum microelectronics and field-emission devices (FED) are described. This revised version was published online in November 2006 with corrections to the Cover Date.     

Catalytic synthesis of ZnO nanorods on patterned silicon wafer—An optimum material for gas sensor

ZnO nanorods have been synthesized over etch-patterned Si (110) wafer using annealed silver thin film as growth catalyst. The growth of ZnO nanorods were performed by a two-step process. Initially, the deposition of Zn thin film was done on the annealed silver catalyst film over etch-patterned Si (110) substrate by thermal evaporation, and then annealed at 800°C in air. The etching of the patterned Si (110) wafers was carried out by 50% aqueous KOH solution. The samples were investigated by optical microscopy, scanning electron microscopy, X-ray diffraction, Raman spectroscopy and room temperature photoluminescence spectroscopy. ‘V’ shaped grooves with no undercut were formed after etching due to the anisotropic nature of the KOH etchant. The etch-patterned wafer was used to provide larger surface area for ZnO growth by forming ‘V’-grooves. This ZnO film may be predicted as a very good material for gas sensor.     

Silicon template fabrication for imprint lithography with a very smooth side wall profile

A new fabrication process of silicon template for nanoimprint lithography is developed. A very fine and high aspect Si lines are fabricated by the combination of plasma process for Si deep etching and anisotropic wet etching by potassium hydroxide solution (KOH treatment). Improved switching process, which consists of sequentially alternating etching and deposition steps, is used as the Si deep etching. The side wall profile of the Si lines can be controlled by the deposition step time. Line pattern with vertical side wall is fabricated. The line width and height are 0.2 µm and 2.9 µm, respectively. By the KOH treatment the side wall corrugation can be reduced and the line width also decreases. Very fine line of 45 nm width at the line top with the pattern height of 3.0 µm can be fabricated by use of the line width shrink by the KOH treatment.     

Lapping assisted dissolved wafer process of silicon for MEMS structures

Dissolved wafer process (DWP) is being extensively used to fabricate complex micro-electro-mechanical system (MEMS) structures. Etching non-uniformity, increased surface roughness and duration of DWP is often influence MEMS devices yields. This paper presents a modified DWP involving lapping and polishing followed by chemical etching of silicon to release MEMS based structure. The lapping experiments are performed using silicon-carbide (SiC) and alumina (Al₂O₃) abrasive. The polishing of the silicon samples is also done. The lapped and polished surfaces are compared with etched silicon surfaces in KOH and EDP solutions. The lapping-polishing process is found to be 2.5 (Al₂O₃)–3 (SiC) times faster than a standard etching processes based on KOH and EDP solutions. The average roughness (R_a) of the lapped–polished silicon surfaces are found to be 19.2 and 32.9 nm corresponding to SiC and Al₂O₃ abrasive respectively. The R_a value of EDP and KOH etched silicon surfaces are found to be 16.2 and 238.3 nm respectively. Based on the lapping—polishing results, SiC based lapping followed by polishing of silicon surface can be used as an alternate of etching of silicon during DWP. In this paper, a two-step DWP, involving lapping-polishing followed by EDP chemical etching of silicon, is used to fabricate suspended comb-type microaccelerometer structure.     

Effect of nonionic surfactants on the solubilization of alachlor

The ability of nonionic surfactants to solubilize the pesticide alachlor was studied. Two homologue series, octylphenol ethoxylates (Triton X-114, Triton X-100 and Triton X-102) and ethoxylated decyl alcohols (Neodol 91-5E, Neodol 91-6E and Neodol 91-8E) were used at concentrations 3 critical micelle concentration (CMC) and 6 CMC. The rate of solubilization of a sufficient quantity of alachlor (for saturation) in aqueous solution containing the micelles of nonionic surfactant was recorded. The experimental data were fitted to a first-order kinetic model. The rate constant, saturation concentration and enhancement factor were estimated for each surfactant system. The effect of surfactant structure, CMC concentration, pesticide structure and its physicochemical properties on the effectiveness of solubilization was determined. In terms of solubilization capability, the nonionic surfactants of each homologue series can be ranked as follows: Neodol 91-8E>Neodol 91-6E>Neodol 91-5E and Triton X-102>Triton X-100>Triton X-114. The more hydrophilic Neodol series was proved more efficient in alachlor solubilization than Triton series. The enhancement factor values ranged from 1.064 to 1.995 at 3 CMC and 1.320 to 2.919 at 6 CMC. The results will be used mainly for micellar-enhanced ultrafiltration since the extent of solubilization is a critical factor.     

Evaporation and decomposition of Triton X-100 under various gases and temperatures

The thermal behaviour of Triton X-100 (surfactant in PTFE dispersion) under various gases was studied with differential scanning calorimetry (DSC) and IR spectrophotometry below 350° C. In nitrogen or argon gas, Triton X-100 evaporated without decomposition. However, in air or oxygen containing gas, thermal oxidation occurred, where a strong _co band appeared in IR spectra. Oxygen increased the evaporation rate of Triton X-100 remarkably. The heat of vaporization was about 16 kcal mol^–1 which is independent of the oxygen concentration. The evaporation mechanism is discussed briefly.     

Characterization of stain etched p-type silicon in aqueous HF solutions containing HNO3 or KMnO4

Stain etching of p-type silicon in hydrofluoric acid solutions containing nitric acid or potassium permanganate as an oxidizing agent has been examined. The effects of etching time, oxidizing agent and HF concentrations on the electrochemical behavior of etched silicon surfaces have been investigated by electrochemical impedance spectroscopy (EIS). An electrical equivalent circuit was used for fitting the impedance data. The morphology and the chemical composition of the etched Si surface were studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques, respectively. A porous silicon layer was formed on Si etched in HF solutions containing HNO₃, while etching in HF solutions containing KMnO₄ led to the formation of a porous layer and simultaneous deposition of K₂SiF₆ inside the pores. The thickness of K₂SiF₆ layer increases with increasing the KMnO₄ concentration and decreases as the concentration of HF increases.     

Endotaxial silicide nanowires: A review

We review the topic of self-assembled endotaxial silicide nanowires on silicon. Crystallographic orientation, lattice mismatch and average dimensions are discussed for a variety of systems including Ti, Mn, Fe, Co, Ni, Pt and several rare earths on Si(100), Si(111) and Si(110) surfaces. In situ observations of growth dynamics support a constant-shape growth model, in which length, width and thickness all change in proportion as the nanowire grows, with thermally activated, facet-dependent rates.     

Surfactant-dependent macrophage response to polypyrrole-based coatings electrodeposited on Ti6Al7Nb alloy

In this study, polypyrrole (PPy) films were successfully synthesized on Ti6Al7Nb alloy by potentiostatic polymerization in the presence of poly(sodium 4-styrenesulfonate) (NaPSS), t-octylphenoxy polyethoxyethanol (Triton X-100) and N-dodecyl-β-D-maltoside (DM) surfactants. Atomic force microscopy (AFM) analysis of the PPy/surfactant composite films revealed a granular structure characterized by a lower surface roughness than un-modified PPy films. The results demonstrated that addition of surfactants, namely Triton X-100 and DM, can improve electrochemical film stability and corrosion resistance. Further, Triton X-100 enhanced the adhesive strength of PPy films to the substrate. The surfactant type also showed a great influence on the surface wettability, the highest hydrophilic character being observed in the case of PPy/PSS film. Few studies have been devoted to the elucidation of inflammatory cell response to PPy-based materials. Therefore, RAW 264.7 macrophages were cultured on PPy-surfactant films to determine whether they elicit a differential cell behavior in terms of cell adhesion, proliferation, cellular morphology and cytokine secretion. Our results highlight the dependence of macrophage response on the surfactants used in the pyrrole polymerization process and suggest that the immune response to biomaterials coated with PPy films might be controlled by the choice of surfactant molecules.     

Influence of Triton X-100 on growth of Pseudomonas putida No. 69-3, an n-heptanol-tolerant variant of an organic solvent-sensitive bacterium, Pseudomonas putida No. 69

 When Pseudomonas putida No. 69-3 cells, changed as an organic solvent-resistant variant from an organic solvent-sensitive parent, Pseudomonas putida No. 69, were cultivated with 0.01% surfactants, Triton X-100 provided the highest cell growth in the presence of 10% n-heptanol. When strain No. 69-3 was cultivated in a medium containing 10% n-heptanol and various concentrations of Triton X-100, 0.01% Triton X-100 gave the most improved cell growth. Hydrophobicity of the cell membrane did not change in the presence or absence of Triton X-100. However, when strain No. 69-3 was cultivated in a medium containing 0.01% Triton X-100 or without Triton X-100 and the culture broth was centrifuged at 500×g, the decrease in optical density of the supernatant was smaller when the cells were cultivated in a medium containing 0.01% Triton X-100 than when cultivated without Triton X-100. This result suggests that Triton X-100 decreased the degree of aggregation and improved growth. Received: 15 May 1998 / Accepted: 30 September 1998     

Nanoindentation of laser micromachined 3C-SiC thin film micro-cantilevers

Single crystalline thin films of 3C-SiC with a thickness of 1.7 ± 0.2 μm were deposited on Si (100) substrate using atmospheric chemical vapor deposition technique. A Q-switched Nd:YAG laser in the fundamental wavelength with a pulse duration of 100 ns and average power of 1 W was then used to pattern 50 μm wide and 150 μm long cantilever beams in direct-writing mode. Following laser patterning, wet chemical etching using KOH anisotropic etchant was carried out to remove the underlying Si and form free-standing 3C-SiC cantilever beams. The cantilevers were subjected to nanoindentation test to obtain deflection versus load curves. The average Young’s modulus and fracture strength were determined to be 423 GPa and 1.5 GPa respectively which are comparable to those obtained by the reactive ion etching. Laser patterning thus offers nearly identical properties as that of ion etching with the added benefit of much higher etch rates.     

Plasma-surface interactions for advanced plasma etching processes in nanoscale ULSI device fabrication: A numerical and experimental study

Plasma-surface interactions in Cl- and Br-based plasmas have been studied for advanced front-end-of-line (FEOL) etching processes in nanoscale ULSI device fabrication. A Monte Carlo-based atomic-scale cellular model (ASCeM) was developed to simulate the feature profile evolution on nanometer scale during Si etching in Cl₂ and Cl₂/O₂ plasmas, including surface oxidation, inhibitor deposition, and ion reflection and penetration on surfaces. A classical molecular dynamics (MD) simulation for Si/Br and Si/HBr as well as Si/Cl systems was also developed, along with an improved Stillinger-Weber interatomic potential model for Si/halogen interactions, to clarify surface reaction kinetics on atomic scale during Si etching in Cl₂ and HBr plasmas. The numerical results revealed the origin of profile or surface anomalies such as microtrench, roughness, and residue, and also etching fundamentals such as etch yield, product stoichiometry, and atomistic surface structures. Moreover, the etching of high-k dielectric and metal electrode materials, such as HfO₂ and TaN, was investigated in BCl₃- and Cl₂-containing plasmas with and without rf biasing, to gain an understanding of the etch mechanisms and to achieve anisotropic and selective etching of metal/high-k gate stacks.     

Hierarchical silicon etched structures for controlled hydrophobicity/superhydrophobicity

Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surfaces generated by KOH anisotropic etching. Results demonstrated that by altering the surface hydrophobicity, the apparent contact angle changed in accord with the Wenzel equation for surface structures with inclined side walls. Hierarchical structures were also constructed from Si pyramids where nanostructures were added by Au-assisted electroless HF/H2O2 etching. Surface hydrophobicity and superhydrophobicity were achieved by surface modification with a variety of silanes. Stability of the Cassie state of superhydrophobicity is described with respect to the Laplace pressure as indicated by the water droplet meniscus in contact with the hierarchical structures. The contact angle hysteresis observed is also discussed with respect to water/substrate adhesion.     

Anisotropic etching of silicon crystals in KOH solution

The anisotropic etching behaviour of various crystalline silicon plates in an aqueous KOH solution was studied. Variations of the etch rate with the angle of cut related to singly-rotated plates have been determined and orientation effects in the out-of-roundness profiles related to various {h k 0} sections have been analysed in terms of crystal symmetry. In addition, changes in the surface texture with crystal orientation were systematically investigated. All the experimental results furnished evidence for a dissolution process governed by the crystal orientation. A procedure has been proposed to derive the dissolution slowness surface from experiments starting from a tensorial representation of the anisotropic etching.     

Pristine semiconducting [110] silicon nanowires

We report results of ab initio calculations on silicon nanowires oriented along the [110] direction and show for the first time that these pristine silicon nanowires are indirect band gap semiconductors. The nanowires have bulk Si core and are bounded by two (100) and two (110) planes in lateral directions. The (100) planes are atomically reconstructed with dimerization in a manner similar to the (100) surface of bulk Si but the dimer arrays are perpendicular to each other on the two (100) planes. An interesting consequence of surface reconstruction is the possibility of polytypism in thicker nanowires. We discuss its effects on the electronic structure. These findings could have important implications for the use of silicon nanowires in nanoscale devices as experimentally [110] nanowires have been found to grow preferentially in the small diameter range.     

Characterization of nanoporous silicon layer to reduce the optical losses of crystalline silicon solar cells

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si AR layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layers were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The structure of porous Si layers was investigated using SEM. The formation of a nanoporous Si layer on the textured silicon wafer result in a reflectance lower than 5% in the wavelength region from 500 to 900 nm. Such a surface modification allows improving the Si solar cell characteristics. An efficiency of 13.4% is achieved on a monocrystalline silicon solar cell using the electrochemical technique.     

Anisotropic characteristics and morphological control of silicon nanowires fabricated by metal-assisted chemical etching

Low-cost fabrication methods enabling the morphological control of silicon nanowires are of great importance in many device application fields. A top-down fabrication method, metal-assisted chemical etching, is proved to be a feasible solution. In this paper, some novel approaches based on metal-assisted chemical etching, alkaline solution etching, and electrochemical anodic etching are presented for fabricating micro- and nano-structures, which reveal the anisotropic characteristics of metal-assisted chemical etching in silicon. A new model is proposed to explain the motility behavior of Ag particles in metal-assisted chemical etching of silicon. It is shown that Ag particle forms a self-electrophoresis unit and migrates into Si substrate along [100] direction independently. Diameter and length control of silicon nanowires are achieved by varying Ag deposition and etching durations of metal-assisted chemical etching, respectively, which provide a facilitation to achieve high-aspect-ratio silicon nanowires at room temperature in a short period. These results show a potential simple method to microstructure silicon for devices application, such as solar cells and sensors.