Black Silicon Method Research Articles

마이크로/나노 구조를 갖는 초발수성 표면의 제작 및 분사 액적의 충돌 특성 연구

In this study, we fabricated the superhydrophobic and super-water-repellent surface with the micro/nano scale structures using simple conventional silicon wet-etching technique and the black silicon method by deep reactive ion etching. These fabrication methods are simple but very effective. Also we reported the droplet impact experimental results on the micro/nano-scaled surface. There are two representative impact behaviors as “rebound” and “fragmentation”. We found the transition Weber number between “rebound” and “fragmentation” statements, experimentally. Additionally, we concerned about the dimensionless spreading diameters for our super-water-repellent surface. The novel characterization method was introduced for analysis including the “fragmentation” region. As a result, our super-water-repellent surface with the micro/nano-scaled structures shows the different impact behaviors compared with a reference smooth surface, by some meaningful experiments.

Black silicon method XI: oxygen pulses in SF6 plasma

A detailed study is performed to understand and show the potential of high-speed, deep reactive ion etching (DRIE) of silicon using oxygen inhibitor pulses as a replacement for hydro-fluorocarbons (HFCs). This process might be considered the ‘holy grail’ in DRIE as the environmental restrictions for the use of HFCs are becoming increasingly stronger. When compared to the usual cryogenic mixed oxygen DRIE and with respect to profile control, the proposed cryogenic pulsed oxygen DRIE is virtually independent of silicon loading, mask material and trench width, and it is less prone to the formation of black silicon (BS). Some indication is found that one of the major causes for the formation of BS is the existence of dust inside the plasma. Dust is created when oxygen and silicon tetra fluoride (SiF4 being the reaction product of silicon etching) coincide inside the plasma glow. This occurs in mixed oxygen plasma; the silica dust falls onto the wafer where it starts to form BS when directional etching is requested. Dust particles can also form when strong polymerizing gases are fed into the plasma. This is the case for the Bosch process using HFC pulses forming carbonic dust. The particles, and consequently the BS, are observed to be limited when the SiF4 and O2 gases are time separated, which forms the basis of the proposed pulsed oxygen DRIE. Another advantage of pulsed oxygen DRIE with respect to Bosch processing is that the protective skin of the sidewall during etching—a kind of native oxide—is believed to be self-terminating. This makes the process insensitive to profile variations caused by parameter fluctuations. It is found that inhibiting oxygen pulses give excellent results with respect to profile control at cryogenic temperatures (between −120 and −80 °C) and can still compete with HFC pulses up to intermediate low temperatures (between −80 and −40 °C). When selecting the proper DRIE conditions, the oxygen pulsed mode performs with excellent profile verticality and selectivity while keeping the silicon clean. It also shows a high etch rate up to 25 µm min−1 (<1% Si load of a 100 mm wafer). When the temperature is raised further (between −40 and 0 °C), the strength of the oxygen sidewall protection progressively fails and more oxygen with more bias is needed to keep sufficient profile directionality. The use of stronger oxide-forming agents is suggested in order to enable good performance at the more convenient, higher temperature, low bias conditions.

Fabricating high-aspect-ratio sub-diffraction-limit structures on silicon with two-photon photopolymerization and reactive ion etching

We fabricated sub-micrometer objects with feature sizes about one third of the exposure wavelength using two-photon photopolymerization in an epoxy-based photoresist SU-8 . Owing to the high mechanical strength of this photoresist, an aspect ratio as high as nine was achieved with a 200–300 nm lateral dimension. A simple equation was used to estimate the feature size from the laser parameters such as spot size, exposure time, pulse width, pulse repetition rate, and the material properties including the two-photon absorption coefficient and the exposure threshold dose. Patterns in SU-8 were transferred onto silicon using reactive ion etching, preserving both the feature size and aspect ratio. Vertical sidewalls of the transferred patterns were achieved using the black silicon method.

Guidelines for etching silicon MEMS structures using fluorine high-density plasmas at cryogenic temperatures

This paper presents guidelines for the deep reactive ion etching (DRIE) of silicon MEMS structures, employing SF/sub 6//O/sub 2/-based high-density plasmas at cryogenic temperatures. Procedures of how to tune the equipment for optimal results with respect to etch rate and profile control are described. Profile control is a delicate balance between the respective etching and deposition rates of a SiO/sub x/F/sub y/ passivation layer on the sidewalls and bottom of an etched structure in relation to the silicon removal rate from unpassivated areas. Any parameter that affects the relative rates of these processes has an effect on profile control. The deposition of the SiO/sub x/F/sub y/ layer is mainly determined by the oxygen content in the SF/sub 6/ gas flow and the electrode temperature. Removal of the SiO/sub x/F/sub y/ layer is mainly determined by the kinetic energy (self-bias) of ions in the SF/sub 6//O/sub 2/ plasma. Diagrams for profile control are given as a function of parameter settings, employing the previously published black silicon method. Parameter settings for high rate silicon bulk etching, and the etching of micro needles and micro moulds are discussed, which demonstrate the usefulness of the diagrams for optimal design of etched features. Furthermore, it is demonstrated that in order to use the oxygen flow as a control parameter for cryogenic DRIE, it is necessary to avoid or at least restrict the presence of fused silica as a dome material, because this material may release oxygen due to corrosion during operation of the plasma source. When inert dome materials like alumina are used, etching recipes can be defined for a broad variety of microstructures in the cryogenic temperature regime. Recipes with relatively low oxygen content (1-10% of the total gas volume) and ions with low kinetic energy can now be applied to observe a low lateral etch rate beneath the mask, and a high selectivity (more than 500) of silicon etching with respect to polymers and oxide mask materials is obtained. Crystallographic preference etching of silicon is observed at low wafer temperature (-120/spl deg/C). This effect is enhanced by increasing the process pressure above 10 mtorr or for low ion energies (below 20 eV).

The black silicon method. VIII. A study of the performance of etching silicon using SF6/O2-based chemistry with cryogenical wafer cooling and a high density ICP source

This paper presents a study of the performance of current trends in high speed, highly controllable anisotropic plasma etching of silicon for its use in micro- and nano-engineering. Optimisation rules for tuning the equipment are formulated to enable maximum results with respect to etch rate, etch selectivity, and profile control (e.g. anisotropy). The optimisation process uses the black silicon method to allow for an easy to use design-of-experiment method. After optimisation, etch rates of silicon up to 15μm/min were obtained at a relatively high pressure (4Pa=30mTorr and ICP power (2kW), while keeping the anisotropy high. At the same time, the erosion rates of thermal silicon dioxide and ordinary photoresist (Shipley S1805) were around 7nm/min (i.e. selectivities up to 2000). Increasing the pressure to 20Pa, the selectivity increased to 10,000, although bottling became more pronounced. The high etch rate and high selectivity are especially important in the case of micro-engineering, where wafer through etching with the help of plasmas become a standard in the near future. In the case of nano-engineering, however, profile control is the main concern. To prevent undercut in such cases, in particular, bottling due to a broad ion angular distribution, the pressure should be sufficiently low. The best results were found at pressures below 0.2Pa=1.5mTorr and at a low ICP power of 350W to prevent a too strong mask erosion caused by the low pressure. The silicon etch rate decreased to 1μm/min and the erosion rate of the oxide and resist were both approximately 20nm/min, giving a selectivity of 50. Reproducibility (wafer-to-wafer) and uniformity were also output factors of prime concern. Surprisingly enough, for two different equipment manufacturers the results were almost identical when using the same parameter setting. This indicates that the SF6/O2-based chemistry was optimised rather than the equipment itself.

A lateral symmetrically bistable buckled beam

We have micromachined a lateral symmetrically bistable buckled beam for snap-in holding structures by oxidizing released beams micromachined on thick silicon-on-insulator wafers. The wafers were prepared by bonding and chemical mechanical polishing, and the structures were fabricated by deep silicon reactive ion etching using the black silicon method, subsequently released and thermally oxidized. The bistability was monitored in situ in a scanning electron microscope using a micromanipulator. Guidelines for designing beams of an expected performance are given and arguments for considering beams that are not `fairly slender' have been found.

The black silicon method: a universal method for determining the parameter setting of a fluorine-based reactive ion etcher in deep silicon trench etching with profile control

Very deep trenches (up to 200 mu m) with high aspect ratios (up to 10) in silicon and polymers are etched using a fluorine-based plasma (SF6/O2/CHF3). Isotropic, positively and negatively (i.e. reverse) tapered as well as fully vertical walls with smooth surfaces are achieved by controlling the plasma chemistry. A convenient way to find the processing conditions needed for a vertical wall is described: the black silicon method. This new procedure is checked for three different reactive ion etchers (RIE), two parallel-plate reactors and a hexode. The influence of the RF power, pressure and gas mixture on the profile will be shown. Scanning electron microscope (SEM) photos are included to demonstrate the black silicon method, the influence of the gases on the profile, and the use of this method in fabricating microelectromechanical systems (MEMS).

The black silicon method II:The effect of mask material and loading on the reactive ion etching of deep silicon trenches

Very deep trenches in Si with smooth controllable profiles are etched using a fluorine-based Reactive Ion Etcher(RIE). The effect of various mask materials and loading on the profile is examined using the Black Silicon Method. It is found that most metal layers have an almost infinite selectivity. When the aspect ratio of the trenches is beyond five, RIE lag is found to be an important effect. Evidence is found that this effect is caused by the bowing of incoming ions by the electrical field.

側方こう合位の歯牙接触要素と筋活動との関連性に関する研究 第２報 筋活動について

Electromyographic (EMG) activity was measured in the masseter muscle (Mm), anterior temporalis (Ta) and posterior temporalis muscle (Tp) during maximal voluntary clenching (MVC) and recording occlusal contacts by black silicon method (RBS) on 12 normal subjects with sound dentitions. Intercuspal position (IP), lateral position which was horizontally apart 1 mm from IP (LP-1) and canine's edge to edge lateral position (LP-E) were fabricated using LED mandibular tracking device; MVC was performed at IP and LP-E on all subjects; and RBS was at IP, LP-1 and LP-E on 9 subjects.Total muscle activity during RBS was about 10% of that during MVC at both IP and LP, but individual variation of EMG pattern exists. Ta and Tp showed significantly greater activity on the working side than the balancing side, while Mm showed no clear difference between the sides during both MVC and RBS at LP. The working side Ta showed significantly less activity during RBS than MVC at LP and was greatly affected by the clenching level, but while the balancing side Tp remained unchanged, activity was hardly affected.