Shallow and deep dry etching of silicon using ICP cryogenic reactive ion etching process

We achieved to etch nanostructures as well as structures with high aspect ratios in silicon using an inductively coupled plasma cryogenic deep reactive ion etching process. We etched cantilevers, submicron diameter pillars, membranes and deep structures in silicon with etch rates between 13 nm/min and 4 μm/min. These structures find applications as templates for metal organic vapour phase epitaxial growth of GaN-based nanostructures for optoelectronic devices or they are the basic constituents of a nanoparticle balance in the subnanogram range and of a thermoelectric generator.     

Microfabrication of high-temperature silicon devices using waferbonding and deep reactive ion etching

As part of an effort to develop a micro gas turbine engine capable of providing 10-50 W of electrical power in a package less than one cubic centimeter in volume, we report the fabrication and testing of the first hydrogen combustor micromachined from silicon. Measuring 0.066 cm ³ in volume, and complete with a fuel manifold and set of fuel injector holes, the fabrication of the device was largely enabled by the use of deep reactive ion etching (DRIE) and aligned silicon wafer bonding. The 150-W microcombustor has a power density in excess of 2000 MW/m³ and has been successfully demonstrated to provide turbine inlet temperatures up to 1800 K. After 15 h of experimental tests, the combustor maintained its mechanical integrity and did not exhibit any visible damage. Combined with the results of a materials oxidation study, these tests are used to demonstrate the satisfactory performance of silicon in the harsh oxidizing environment of a combustion chamber     

Application of deep reactive ion etching for silicon angular rate sensor

 A new silicon resonant angular rate sensor by deep reactive ion etching was developed. The sensor consists of a glass-silicon-glass structure. To have a sensor of high Q factor, a one-side suspended tuning fork structure was adopted. The silicon resonator structure which has high aspect ratio was machined by reactive ion etching. The etching gas of the RIE was SR₆ and etching rate was 0.8 μm/min. The resonator is driven electromagnetically and the torsional vibration caused by the Coriolis force is detected capacitively. The test device showed a sensitivity of 6 fFsec./deg. and had an output to the angular rate in a range from −360 deg./sec to 240 deg/sec. Received: 30 October 1995/Accepted: 20 May 1996     

Application of deep reactive ion etching for silicon angular rate sensor

A new silicon resonant angular rate sensor by deep reactive ion etching was developed. The sensor consists of a glass-silicon-glass structure. To have a sensor of high Q factor, a one-side suspended tuning fork structure was adopted. The silicon resonator structure which has high aspect ratio was machined by reactive ion etching. The etching gas of the RIE was SR₆ and etching rate was 0.8 μm/min. The resonator is driven electromagnetically and the torsional vibration caused by the Coriolis force is detected capacitively. The test device showed a sensitivity of 6 fFsec./deg. and had an output to the angular rate in a range from −360 deg./sec to 240 deg/sec.     

Study of silicon backside damage in deep reactive ion etching for bonded silicon–glass structures

 For devices of bonded silicon and glass structures fabricated by deep reactive ion etching (DRIE), it is important to avoid damage at the silicon sidewall and backside during through-wafer etching in order to ensure reliability of devices. The silicon damage caused by charge accumulation at the glass surface is inhibited by means of an electrically conducting layer patterned onto the glass and connected with the silicon. In this study, indium tin oxide films were applied in order to identify the positions of silicon damage in the structural layout without destruction of samples. From the results, we report that there exists silicon damage caused by charge accumulation at the silicon islands divided by DRIE and we present important rules for mask layout when utilizing this method. Received: 10 August 2001/Accepted: 24 September 2001 This paper was presented at the Fourth International Workshop on high Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

An advanced reactive ion etching process for very high aspect-ratio sub-micron wide trenches in silicon

This paper reports on a practical modification of the two-step time-multiplexed plasma etching recipe (also known as the Bosch process) to achieve high aspect-ratio sub-micron wide trenches in silicon. Mixed argon and oxygen plasma depassivation steps are introduced in between the passivation and etching phases to promote the anisotropic removal of the passivation layer at the base of the trench. Argon does not chemically react with polymers and silicon and removes the passivation layer only by physical sputtering. Therefore, it results in a highly anisotropic polymer etching process. This recipe can be easily integrated on conventional ICP equipment and the scalloping on the trench sidewall can potentially be reduced in size to less than 50 nm. To clean up all the passivation residues, a short oxygen plasma step is also added at the end of the cycle that effectively improves the uniformity of the etching profile over various opening sizes. Excellent anisotropy of the inserted argon depassivation step facilitates narrow trenches down to 130 nm wide and gap aspect-ratios as high as 40:1, extending the application of deep reactive ion etching (DRIE) processes into a new broad regime.     

Vertical mirrors fabricated by deep reactive ion etching forfiber-optic switching applications

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. The mirror height is 75 μm, covering the fiber core of a single-mode fiber when the latter is placed into a groove of equal depth and etched simultaneously with the mirror. To obtain a uniform etch depth, etching is stopped on a buried oxide layer. Using the buried oxide as a sacrificial layer allows to fabricate mirrors with suspension and actuation structures as well as fiber-alignment grooves in one and the same processing step. A minimal mirror thickness of 2.3 μm was achieved, resulting in an aspect ratio higher than 30. The verticality was better than 89.3°. In the upper part of the mirror a surface roughness below 40 nm rms was obtained. At a wavelength of 1300 nm the reflectivity of the aluminum-coated mirrors was measured to be higher than 76%. Using a reactive ion etched mirror we have fabricated an optical fiber switch with electrostatic actuation. The coupling loss in the bar state of two packaged prototypes was between 0.6 and 1.7 dB and between 1.4 and 3.4 dB in the cross state. The switching time is below 0.2 ms     

High-aspect-ratio nanoporous membranes made by reactive ion etching and e-beam and interference lithography

Nanoporous membranes engineered to mimic natural filtration systems can be used in “smart” implantable drug delivery systems, hemodialysis membranes, bio-artificial organs, and other novel nano-enabled medical devices. Conventional membranes exhibit several limitations, including broad pore size distributions and low pore densities. To overcome these problems, lithographic approaches were used to develop porous silicon, silicon nitride, ultrananocrystalline diamond (UNCD), and polymer film membranes. Here we report processing of high porosity, high-aspect-ratio membranes by two techniques: UNCD fabricated by reactive ion etching after e-beam lithography and epoxy fabricated by interference lithography.     

Fabrication of silicon microstructure for cell separation using ultrashort laser ablation

Many decades have seen the exploration of a novel methodology for developing microstructure in Microfluidic devices. Despite many methodologies, femtosecond laser technique has been a rising method in the conspicuous way of developing microstructures through direct write method which provides an ease of fabrication. For fabrication precise microstructure in semiconductor devices such as silicon, the femtosecond laser is preferred. An array of micro-holes has been created in monocrystalline silicon (100) using femtosecond laser ablation with multiple pulses. An investigation is carried out for obtaining the minimum diameter holes by varying the power for multiple pulses. The fabricated microhole array find its application in cancer cell separation from human blood.

     

Evaluation of Young’s modulus of imprinted hydrogen silsesquioxane pillar after residual layer removal by reactive ion etching

Nanoimprint lithography has two basic steps. The first is the imprint step in which a mold with nanostructures on its surface is pressed into a resin film on a substrate, followed by removal of the mold. The second step is the residual layer removal by a reactive ion etching (RIE). There is no report whether the properties of the imprinted structure after RIE change or not. In this work, the authors evaluated the Young’s modulus of the imprinted pillar after residual layer removal by RIE. In this experiment, hydrogen silsesquioxane (HSQ), a type of spin-on-glass, was used as an imprint material. The residual layer was etched by RIE using CHF₃ gas. The Young’s modulus of imprinted pillar after RIE was measured via cantilever method. The Young’s modulus of HSQ pillar after RIE was twice as much as that of HSQ pillar before RIE. From the Fourier transform infrared measurement, it was founds the chemical structure of HSQ was changed by forming network structure due to heating by RIE plasma energy. These results indicate that the mechanical property of imprinted structure was changed in the residual layer removal step by using RIE.     

Semitransparent monocrystalline solar cells manufactured by laser cutting and anisotropic etching

This paper presents two possible technologies used to manufacture semitransparent monocrystalline building integrated solar cells: laser cutting and anisotropic etching. Nd:YAG 1,064 nm laser cut sidewalls are rough and contain molten residues, resulting in shunts across the through-holes confirmed by I–V characteristic measurement and reverse bias measurement results. Tetramethylammonium hydroxide etched edges are uniform with smooth sidewalls. Carrier lifetime and Kelvin probe measurements reveal the flaws occurring in the two technologies.     

CO2激光直写结合湿法刻蚀加工玻璃基微流控芯片

玻璃是制作微流控芯片的重要材料,其加工工艺主要基于光刻后湿法腐蚀,对设备和实验室要求较高.本文提出以普通指甲油和指甲油/金/铬为牺牲层,利用CO2激光烧蚀开窗口,辅以湿法腐蚀加工玻璃基微流控芯片的方法,并考察了激光加工参数,腐蚀液组成,牺牲层等因素对芯片质量的影响.该方法简便易行,不需要光刻的昂贵设备和繁杂步骤.     

硅KOH腐蚀<100>晶向凸角补偿技术及应用

在(100)硅上制作边沿<100>晶向的长方形掩模,用KOH各向异性腐蚀液腐蚀可制得竖直微镜,这种微镜存在凸角削角问题.研究了边沿<100>晶向掩模的凸角补偿技术,提出了2种凸角补偿图形,并应用于竖直微镜制作.实验表明:"工" 形补偿可获得方正的反射面;"Y"形补偿的微镜,反射面呈底角为75.96°的梯形.经补偿后的微镜,可提高光开关切换光束效率.讨论了(100)硅的<100>晶向掩模凸角补偿技术应用于微机械加速度计质量块制作的可能性.     

3D Optical microstructure fabrication and its bonding to micro IR detector using elastomeric polymer

This paper describes polidimethylsiloxane(PDMS) based bonding for assembly of microstructure device, an UV lithography applications for fabricating a 3-dimensional (3D) feed-horn-shaped structure mold array, and obtaining parallel light by using a mirror-reflected parallel-beam illuminator (MRPBI) system. A 3D feed-horn-shaped micro-electro-mechanical systems (MEMS) antenna has some attractive features for array applications, which can be used to improve microbolometer performance and to enhance the optical efficiency for thin film transistor-liquid crystal display (TFT-LCD) and other display devices but currently, MEMS technology has faced many difficulties in the fabrication of a 3D feed-horn-shaped MEMS antenna array itself. The purpose of this paper is to propose a new fabrication method to realize a 3D feed-horn-shaped MEMS antenna array by using a mirror-reflected parallel-beam illuminator (MRPBI) System with a very slowly rotated, inclined x-y-z stage. With a conventional UV lithography apparatus, it is very difficult to fabricate high-aspect-ratio structures (HARS) because a typical UV lithography apparatus cannot produce perfectly parallel light. From a theoretical analysis, a columnar illuminator over 6 m in height is required to achieve parallel light, but generally a laboratory height is not 6 m. Also, a novel method of lithography was tried to make a 3D structure array by exposing a planar wafer to the generated parallel light and rotating an inclined x-y-z stage at an ultra-slow rate. An optimization of the 3D structure array can be achieved by simulating a 3D feed-horn MEMS antenna. The feasibility of fabricating both a 3D feed horn MEMS antenna and assembly of detector with 3D feed-horn MEMS antenna was demonstrated. As a result, it seems possible to use a 3D feed-horn-shaped MEMS antenna to improve microbolometer performance and to fabricate several optical microstructure applications.The authors wish to acknowledge that this paper is the result of research accomplished with the financial support of the Intelligent Microsystems Center, Seoul, Korea, which is carrying out one of the 21st centurys New Frontier R&D Projects sponsored by the Korea Ministry of Science & Technology.     

Study of black silicon obtained by cryogenic plasma etching: approach to achieve the hot spot of a thermoelectric energy harvester

In this paper, we study the enhanced absorption properties of micro/nano structured silicon surface under incident electromagnetic illumination and its capacity to convert light into heat. We simulate the optical reflectance of three-dimensional micro/nano silicon cones of different dimensions and under different electric field incident angles (θ _i ). According to the favorable simulation results, we fabricate black silicon with conical microstructures that exhibits excellent anti-reflectivity behavior. Plasma etching under cryogenic temperatures is used for this purpose in an inductively coupled plasma-reactive ion etching reactor. The reflectance of the black silicon is measured to be approximately 1?% in the optical wavelength range, by using an integrating sphere coupled to a calibrated spectrometer. Furthermore, a device integrating a resistance temperature detector in a black silicon area is developed in order to investigate its efficiency as a photo-thermal converter.     

Simulation of tree and its swaying with wind generated by L-system

This paper constructs a tree model by using the 3D stochastic and L system with brackets. Adjusting the range of the parameters, the present method ensures a favorable randomness and reflects the reality and the real time. Based on a simple mechanical model, the simulation of the phenomenon of wind swaying trees satisfies visual effects well.     

Risk bound of transfer learning using parametric feature mapping and its application to sparse coding

Machine Learning - In this study, we consider a transfer-learning problem using the parameter transfer approach, in which a suitable parameter of feature mapping is learned through one task and...