Zhi Tao

Anti-reflectance investigation of a micro-nano hybrid structure fabricated by dry/wet etching methods

Black silicon fabrication and manipulation have been well reported by institutes around the world and are quite useful for solar absorption and photovoltaic conversion. In this study, silicon micro-nano hybrid structures were fabricated, and the morphologies of the hybrid structures were analyzed. This paper studied nanostructures formed on tips, pits and a flat surface using a dry etching method and a wet etching method. In terms of nanostructure morphology, nanostructures etched by the wet etching method (13u2009μm) were taller than those etched by the dry etching method (1u2009μm), but the wet etched morphology was less organized. After the nanostructures were grown, six samples with nano sturctures and three samples with micro sturctures were measured by a photometer for reflectivity testing. The nine samples were compared and analyzed using the integral of reflectivity and solar emissivity at the earth’s surface. The results show that the nanostructures grown on a tip surface using the wet etching method had the minimum reflectivity in the wavelength range of 300u2009nm–1100u2009nm, in consideration of the forbidden energy gap of silicon.

Effects of deep reactive ion etching parameters on etching rate and surface morphology in extremely deep silicon etch process with high aspect ratio

This study empirically investigates the influences of several parameters on surface morphology and etch rate in a high-aspect-ratio silicon etching process. Two function formulas were obtained, revealing the relationship between the controlled parameters and the etching results. All the experiments were conducted on an inductively coupled plasma system, using a Bosch process. The tested trenches’ width ranged from 15 to 1500u2009µm and their depth ranged from 50 to 500u2009µm, which covers nearly all the typical sizes of micromechanical devices in practical applications. The controlled parameters are etching chamber pressure, bias power, and gas flow rate. The parameters of surface morphology include sidewall angle, surface roughness, and sidewall condition. We tested how the controlled parameters can influence the surface morphology and etch rate and formulated assumptions to explain those relationships. Meanwhile, we utilized linear regression to obtain experiential function formulas of the relationships among etch depth, structure width, etching time, and passivation time, with a correlation coefficient higher than 0.99. Using these formulas, 12-µm-wide and 377-µm-deep (aspect ratio 31.4) trenches with sidewall angles of 89° were achieved. Additionally, this experience was applied as a critical structure in a gas turbine structure system.

Anti-Reflectance Optimization of Secondary Nanostructured Black Silicon Grown on Micro-Structured Arrays

Owing to its extremely low light absorption, black silicon has been widely investigated and reported in recent years, and simultaneously applied to various disciplines. Black silicon is, in general, fabricated on flat surfaces based on the silicon substrate. However, with three normal fabrication methods—plasma dry etching, metal-assisted wet etching, and femtosecond laser pulse etching—black silicon cannot perform easily due to its lowest absorption and thus some studies remained in the laboratory stage. This paper puts forward a novel secondary nanostructured black silicon, which uses the dry-wet hybrid fabrication method to achieve secondary nanostructures. In consideration of the influence of the structure’s size, this paper fabricated different sizes of secondary nanostructured black silicon and compared their absorptions with each other. A total of 0.5% reflectance and 98% absorption efficiency of the pit sample were achieved with a diameter of 117.1 μm and a depth of 72.6 μm. In addition, the variation tendency of the absorption efficiency is not solely monotone increasing or monotone decreasing, but firstly increasing and then decreasing. By using a statistical image processing method, nanostructures with diameters between 20 and 30 nm are the majority and nanostructures with a diameter between 10 and 40 nm account for 81% of the diameters.

Fabrication and Optimization of High Aspect Ratio Through-Silicon-Vias Electroplating for 3D Inductor

In this study, the filling process of high aspect ratio through-silicon-vias (TSVs) under dense conditions using the electroplating method was efficiently achieved and optimized. Pulsed power was used as the experimental power source and the electroplating solution was prepared with various additive concentrations. Designed control variable experiments were conducted to determine the optimized method. In the control variable experiments, the relationship of multiple experimental variables, including current density (0.25–2 A/dm2), additive concentration (0.5–2 mL/L), and different shapes of TSVs (circle, oral, and square), were systematically analyzed. Considering the electroplating speed and quality, the influence of different factors on experimental results and the optimized parameters were determined. The results showed that increasing current density improved the electroplating speed but decreased the quality. Additives worked well, whereas their concentrations were controlled within a suitable range. The TSV shape also influenced the electroplating result. When the current density was 1.5 A/dm2 and the additive concentration was 1 mL/L, the TSV filling was relatively better. With the optimized parameters, 500-μm-deep TSVs with a high aspect ratio of 10:1 were fully filled in 20 h, and the via density reached 70/mm2. Finally, optimized parameters were adopted, and the electroplating of 1000-μm-deep TSVs with a diameter of 100 μm was completed in 45 h, which is the deepest and smallest through which a three-dimensional inductor has ever been successfully fabricated.

Optimization and limit of a tilt manipulation stage based on the electrowetting-on-dielectric principle

This work designed a new tilt manipulation stage based on the electrowetting-on-dielectric (EWOD) principle as the actuating mechanism and investigated the performance of that stage. The stage was fabricated using a universal MEMS (Micro-Electro-Mechanical System) fabrication method. In the previously demonstrated form of this device, the tilt stage consisted of a top plate that functions as a mirror, a bottom plate that was designed for changing the shape of water droplets, and supporters that were fixed between the top and bottom plate. That device was actuated by a voltage applied to the bottom plate, resulting in a static electric force actuating the shape change in the droplets by moving the top plate in the vertical direction. Previous experimental results indicated that that device can tilt at up to ±1.8°, with a resolution of 7 μm in displacement and 0.05° in angle. By selecting the best combination of the dielectric layer, the tilt angle was maximized. The new device, fabricated using a common an...

Packaging and testing of high speed rotor for MEMS gas turbine engines

A micro rotor with high rotation speed is of vital importance for MEMS gas turbine engine to achieve its higher power density and transfer energy with high efficiency. In this investigation, a micro silicon rotor, which is fabricated by one-time multi-depth silicon etching method and supported by a 3-wafers bearing system, is completed to reach high rotation speed. To ensure wafer bonding quality, a non-destructive method based on analyzing infrared images through multilayer wafers is proposed and practiced. After the rotor and its bearing system are packaged successfully, a platform which consists of the rotor, the 3-wafers bearing system, air supply and control systems is established for testing and optimizing performance of the high speed micro rotor. The platforms control scheme is closed-loop and is based on the principle of stiffness changing, in which the stiffness of the bearing system is varied by adjusting inlet pressure based on the rotation speed.

The Control Method of Surface Morphology and Etch Rates for Silicon Etch Process With Extremely Deep and High Aspect Ratio

The manufacture method based on the silicon etching process is one of the most important methods to fabricate micro mechanical structure, e.g. micro-engine. In the processing, the high aspect ratio silicon etch process (HARSE process) is very important to improve the efficiency of structure. At the same time, the surface morphology should be controlled exactly to keep the performance of structure.In this paper, the feasibilities of controlling the surface morphology and Si etch rates were experimentally investigated. In the experiments, the width of structure changes from 15um to 1500um and the depth changes from 50um to 500um. The parameters of surface morphology including sidewall angle, surface roughness, and so on were measured and compared. The influence mechanisms of etching parameters were analyzed.The etching process were completed in a surface technology system (STS) multiplex advanced silicon etcher inductively coupled plasma (ICP) system with SF6/O2 plasma as etching plasma and C4F8 as passivation plasma. In the experiments, the etching experiments were conducted in a low pressure (5–50mTorr), high density, inductively coupled plasma etching reactor (ICP) with a planar coil. The Si etches rates and sidewall angle were investigated as a function of chamber pressure, cathode RF-power, and gas flow.The results indicated that the increasing of total etching time results in an acceleration in etch rate as well as the decrease in sidewall angle (the top width of trench is narrow than the bottom width). Meanwhile, the total passivation time has an opposite effect in the influence of etch rate and sidewall angle. All the experiments indicate that the quick shift between etch and passivation period leads to a smoother surface. An interesting phenomenon were discovered that the etch rate will not change with the changing of width parameter in most of the high aspect ratio silicon etch recipes when the width-depth ratio is upper than 0.34. An experiential function formula were fitted based on four parameters, including width and depth of the structure, and total etching and passivation time.Copyright

One-Time Multi-Depth Silicon Etching Method Based on SiO2Masking Layer

In order to improve the possibility of successful bonding and performance of structures, the new method for multi-depth silicon etching is required. This paper aims to design and create a new method for one-time multi-depth silicon etching in manufacturing complex structures based on SiO2 masking layer. The core idea of this method is that: Firstly, all patterns are transferred into photo resist through photo etching; Then etch pattern will be transferred in the SiO2 masking layer by multi-time shallow etching with different time etching control; Finally, patterns will be transferred to the silicon wafer with uniform ratio based on the measured etching selectivity of SiO2-Si with one time.In the experiments, the process is completed in the silicon wafer with SiO2 masking layer whose thickness is elaborately designed. Firstly, the etching rate of SiO2 and the etching selectivity of SiO2-Si were measured accurately. Secondly, the shallow structure based on the designed structure, the etching rate of SiO2 and the etching selectivity of SiO2-Si is etched on the SiO2masking layer. The second step forms different thickness version of SiO2 masking layer. At last, the SiO2 masking layer is etched until final structure and consequently different depth of groove accomplish due to various thickness of SiO2 etched by previous step.The experimental results indicated that the new methods has at least three advantages compared to traditional method: That is faster efficiency, higher cleanness and more complex structure. Fast work efficiency owes to only SF6 etching rather than two gases of SF6 and C4F8 to reduce half of time. Also high cleanness comes from being not exposed to air and researchers directly. The largest benefit of new method may be that can create more complex structure for higher required machine design and for higher mechanical function. It is because that normal etching method could only build few different depth of grooves due to multi-process limitation and contrary to normal one, new method can create more different depth of groove. And more different depth of groove means that more complex structure can be designed.Copyright