Deep trench etching in macroporous silicon

We present a method to create at the same time trenches and ordered macropore arrays during photo-electrochemical etching of n-type silicon. This novel method allows in situ separation of single devices with a submicrometer precision. It also enables new device structures in macroporous silicon in the areas of photonics, sensing and electronics. The limits of this new process are simulated using electrostatic models and are verified experimentally. PACS 82.45.Yz; 81.16.-c     

基于三维元胞模型的刻蚀工艺表面演化方法

为了更好地理解和认识刻蚀机理, 并为制造工艺提供优化指导, 采用三维元胞模型研究了刻蚀工艺的表面演化过程, 并着重探讨了离子对表面演化过程的影响.针对刻蚀离子入射角度的求解问题, 提出了一种降维分量拟合方法, 将一个三维曲面拟合问题转化为两个二维曲线拟合进行求解, 对入射点的表面法向量计算实现了快速求解, 与采用最小二乘多项式曲面拟合求解离子入射角度相比, 其计算精度和效率都有较大的提高; 对用于拟合计算的表面元胞的选取方法进行了改进, 提高了拟合的准确度.将这种方法应用到硅刻蚀工艺三维仿真中, 其模拟结果与相关实验结果对比, 验证了该方法对刻蚀工艺描述的有效性. 关键词： 刻蚀 三维元胞模型 表面演化算法 降维分量拟合     

Alumina nanotubes and nanowires from Al-based porous alumina membranes

Using ultrasonic vibrations, we have successfully fabricated alumina nanotubes and nanowires from Al-based porous alumina membranes, which are the products of bulk aluminium in oxalic acid via electrochemical etching. Fine configurations and structures of the alumina nanotubes and nanowires are clearly revealed following a series of atomic force microscope and transmission electron microscope observations. Their formation mechanisms are analyzed in detail by comparing different growth characteristics of Al-based alumina membranes with Si-based alumina membranes. Based on our experimental results, we have also pointed out that when using porous alumina templates to fabricate nanostructured materials, it is necessary to carefully distinguish the obtained products from the alumina nanotubes and nanowires. PACS 82.45.Qr; 81.07.De     

Estimation of the capabilities of maskless micropatterning by laser-induced chemical etching

A three-dimensional mathematical model of laser-induced chemical etching of polysilicon films in chlorine atmosphere is presented. The model takes into account both photochemical and thermochemical mechanisms. A numerical solution of a simple process model and consequences for spatial resolution limits of the mask-less laser-induced chemical etching are presented.     

Sub-nanometer precision modification of the optical properties of three-dimensional polymer-based photonic crystals

We present a convenient post-fabrication technique to precisely tune the optical properties of polymer-based three-dimensional photonic crystals with sub-nanometer precision. Conventional air-plasma etching is utilized to modify the filling fraction of direct laser written polymer photonic crystals beyond the wavelength-imposed limits. Tuning of the optical properties is monitored in transmission and reflection spectroscopy. A simple model for the etching process is proposed and found to be in good agreement with the experimental observations.     

基于压缩表示的离子刻蚀仿真三维表面演化方法

为了研究表面演化过程的机理, 提出了一种基于压缩表示的三维表面演化方法来模拟等离子体刻蚀工艺,并着重探讨了对离子刻蚀的仿真. 为了解决三维元胞自动机内存需求量大的问题, 该方法将二维数组和动态存储方式相结合, 既实现元胞信息的无损压缩存储, 又保持三维元胞间的空间相关性. 实验结果也表明该方法不仅节省了大量内存, 而且在高分辨率条件下查找离子初始碰撞的表面元胞效率较高, 满足高分辨率仿真的要求. 将该方法应用于实现刻蚀工艺三维表面仿真中, 模拟结果与实验结果对比验证了该方法的有效性. 关键词： 等离子体刻蚀 元胞自动机 表面演化方法 高分辨率仿真     

Fabrication of three-dimensional crystalline microstructures by selective ion implantation and chemical etching

We present a new fabrication technique to produce three-dimensional (3D) microstructures on crystalline substrate using selective ion implantation and chemical etching. Localized lattice-damage layers at the specified depth beneath the substrate surface are formed by selective ion implantation. After etching out the partial surface regions and the buried lattice-damage layers by chemical etching, the 3D crystalline microstructures are produced. This technique is demonstrated on LiNbO₃ crystal to produce undercutting and free-standing microstructures, including microwire, microring, and microdisk. The measurement results of micro-Raman spectra show that the used fabrication process does not affect the original crystalline structure. The features of this technique include smooth structure surface, large undercutting range, and auto-etching stop. By using multiple implantations or repeating the proposed process several times, versatile 3D crystalline microstructures can be produced.     

Electrochemical formation and properties of thin polyaniline films on Au(111) and p-Si(111)

The specific aspects of phase formation phenomena involved in electrodeposition of conducting polymer layers are critically discussed. The mechanism of formation and the properties of electrodeposited thin polyaniline (PANI) films on Au(111) and p-Si(111) are investigated by means of transient measurements, cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy (AFM). Experimental results show that the initial stages of PANI electrodeposition on Au(111) can be described by a model including progressive appearance and preferential 2D growth of polymer islands. The electropolymerization process on p-Si(111) substrates is preceded by anodic formation of an inhomogeneous thin SiO₂ layer giving rise to a progressive appearance and growth of 3D PANI islands. The electrochemical redox properties of electrodeposited PANI films on p-Si(111) are influenced strongly by the electronic band structure of silicon. PACS 81.10.Aj; 82.45.Wx; 82.45.Vp     

Three-dimensional structuring of sapphire by sequential He+ ion-beam implantation and wet chemical etching

We present a method for the selective two- and three-dimensional patterning of sapphire using light ion-beam implantation to generate severe lattice damage to depths exceeding 1 μm and subsequent selective wet chemical etching of the damaged regions by hot H₃PO₄. C-cut sapphire crystals were implanted through contact masks using ion fluences of 1×10¹⁶ to 5×10¹⁷ He⁺/cm² and energies up to 400 keV. The etching process is characterized by a high selectivity and a rate of approximately 19 nm/min. Whereas an implantation that produces a continuously damaged pathway results in complete etching from the surface, sole in-depth implantation using only high-energy ions leads to under-etching of the crystalline surface layer. By a combination of these processes we have fabricated three-dimensional structures such as channels and bridges in sapphire. Received: 14 October 2002 / Accepted: 15 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax +41-21/693-3701, E-mail: aurelian.crunteanustanescu@epfl.ch     

Direct fabrication of freely movable microplate inside photosensitive glass by femtosecond laser for lab-on-chip application

We demonstrate the fabrication of complicated three-dimensional (3D) microstructures embedded in a photosensitive glass by a high-order multiphoton process using a femtosecond (fs) laser. Direct writing of the fs laser followed by a post baking process and preferential etching in a dilute hydrofluoric (HF) acid solution results in a microplate that can freely move in hollow structures embedded in the glass. The fabricated structure functions as a microvalve that can control the flow direction of fluids in the microreactor. PACS 42.62.-b; 81.05.Kf; 82.50.Pt     

Electrode surface treatment and electrochemical impedance spectroscopy study on carbon/carbon supercapacitors

Power improvement in supercapacitors is mainly related to lowering the internal impedance. The real part of the impedance at a given frequency is called ESR (equivalent series resistance). Several contributions are included in the ESR: the electrolyte resistance (including the separator), the active material resistance (with both ionic and electronic parts) and the active material/current collector interface resistance. The first two contributions have been intensively described and studied by many authors. The first part of this paper is focused on the use of surface treatments as a way to decrease the active material/current collector impedance. Al current collector foils have been treated following a two-step procedure: electrochemical etching and sol-gel coating by a highly-covering, conducting carbonaceous material. It aims to increase the Al foil/active material surface contact leading to lower resistance. In a second part, carbon-carbon supercapacitor impedance is discussed in term of complex capacitance and complex power from electrochemical impedance spectroscopy data. This representation permits extraction of a relaxation time constant that provides important information on supercapacitor behaviour. The influence of carbon nanotubes addition on electrochemical performance of carbon/carbon supercapacitors has also been studied by electrochemical impedance spectroscopy. PACS 82.45.Yz; 81.16.-c     

The study of the solution concentration influencing on laser-induced electrochemical etching silicon

The laser electrochemical etching process, which combines the laser direct etching process and the electrochemical etching process, is a compound etching technique. In order to further understand the solution concentration influencing on the laser-induced electrochemical etching of silicon; a 248 nm excimer laser as a light source and KOH solution as an electrolyte were adopted in this study. The experiments of micromachining silicon by laser-induced electrochemical etching were carried out. On the basis of the experiments results, the solution concentration influencing on the etching rates in the process of laser electrochemical etching of silicon was researched. The reasons of the etching phenomena were analyzed in detail. The experimental results indicate that the solution concentration influencing on the etching process is mainly rooted in the absorption of different concentration solutions to laser. In general, less absorption and low solution concentration are good for the etching role in the process of laser electrochemical etching.     

Femtosecond laser-assisted etching of Pyrex glass with aqueous solution of KOH

A femtosecond laser-assisted etching technique was applied to Pyrex glass, a kind of borosilicate glass, to perform removal processing with three-dimensional arbitrarity in design and micrometer-order spatial resolution. An aqueous solution of potassium hydroxide (KOH) was adopted as a highly selective etchant. The rate and selectivity of etching were evaluated from in situ images, and fabrication of three-dimensional microchannels was demonstrated.     

The fabrication technique and electrical properties of a free-standing GaN nanowire

We fabricated a free-standing structure of a GaN nanowire by selectively etching Si₃N₄, previously grown on a SiO₂ substrate, for application to three-dimensional integrated circuits such as nanorelays and actuators. In the nanowire-deposition process we adopted electrophoresis and reactive ion etching techniques to achieve a well-aligned and free-standing nanowire. The electrical transport measurements were performed from room temperature down to liquid-nitrogen temperature. The current–voltage (I–V) characteristics showed a rectifying behavior in the whole temperature range. We analyze this property as a Schottky barrier formation between the nanowire and electrodes. PACS  61.46.+w; 73.22.-f; 73.40.Ei; 81.07.Bc; 81.16.Rf     

Characterization of MoO<Subscript>3</Subscript> nanobelt cathode for Li-battery applications

Molybdenum trioxide (MoO₃) and PPy_xMoO₃ (x=0.5 and 1) nanobelts were obtained by the simple hydrothermal process from MoO₃ sol. The morphology and structure of the samples were characterized using X-ray diffractometry (XRD), Fourier transformation infrared spectroscopy (FTIR), Raman spectra, SEM and AFM. The results show that the H atoms in polypyrrole are H-bonded with the O atoms in the Mo=O bonds of MoO₃ nanobelts. Using the electrolyte, we fabricated electrochemical cells with a configuration of Li/(LiPF₆+EC+DMC)/(MoO₃+acetyleneblack+PTFE) and studied discharge profiles. PACS 81.07.BC; 81.05.Je; 82.47.Aa; 82.45.Fk; 82.45.Gj     

Laser-induced etching of silicon

Conventional fabrication method of porous silicon is anodisation of single crystal silicon in hydrofluoric acid. In this report, we show that it is possible to fabricate porous silicon by laser-induced etching. An earlier report by us has demonstrated the dependence of porous silicon photoluminescence characteristic on the etching laser wavelength [1]. Here we used 780 nm line from a diode laser as the etching source, and the optimum etching conditions were obtained. A simple model was proposed to explain the etching process. Scanning Electron Microscope (SEM) images of the samples support the proposed process.     

Formation of three‐dimensional GaAs microstructures by combination of wet and metal‐assisted chemical etching

Previously, plasma‐enhanced dry etching has been used to generate three‐dimensional GaAs semiconductor structures, however, dry etching induces surface damages that degrade optical properties. Here, we demonstrate the fabrication method forming various types of GaAs microstructures through the combination etching process using the wet‐chemical solution. In this method, a gold (Au)‐pattern is employed as an etching mask to facilitate not only the typical wet etching but also the metal‐assisted chemical etching (MacEtch). High‐aspect‐ratio, tapered GaAs micropillars are produced by using [HF]:[H₂O₂]:[EtOH] as an etching solution, and their taper angle can be tuned by changing the molar ratio of the etching solution. In addition, GaAs microholes are formed when UV light is illuminated during the etching process. Since the wet etching process is free of the surface damage compared to the dry etching process, the GaAs microstructures demonstrated to be well formed here are promising for the applications of III–V optoelectronic devices such as solar cells, laser diodes, and photonic crystal devices. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The pore opening process and its influence on conductivity measurements of irradiated polymer films by application of the electrochemical etching method

The technique of the electrochemical etching of irradiated polymer films is an useful method to investigate structures of the track cores.

The transversale etching rate as a function of the radius, derived from the time-dependence of the radius of the etching pore, can be interpreted as a corresponding magnitude of the degree of the damage within the track core.

In the case of polymer films irradiated by a high track density, the influence of the time distribution of the breakthroughs (pore opening process) of the etching microchannels on the conductivity changes during the etching process is to be discussed. First represented results lead to statements about the statistical nature of the pore opening process.     

Femtosecond laser-assisted three-dimensional microfabrication in silica

We demonstrate direct three-dimensional (3-D) microfabrication inside a volume of silica glass. The whole fabrication process was carried out in two steps:(i) writing of the preprogrammed 3-D pattern inside silica glass by focused femtosecond (fs) laser pulses and (ii) etching of the written structure in a 5% aqueous solution of HF acid. This technique allows fabrication of 3-D channels as small as 10mum in diameter inside the volume with any angle of interconnection and a high aspect ratio (10mum -diameter channels in a 100mum -thick silica slab).     

结合实际刻蚀数据的离子刻蚀产额优化建模方法

刻蚀表面仿真是研究等离子体刻蚀工艺过程机理的重要手段.在刻蚀表面仿真方法中,刻蚀表面演化模型和离子刻蚀产额模型直接决定了刻蚀表面演化结果.但现有的刻蚀表面演化模型不够精确,且目前离子刻蚀产额模型主要来自分子动力学仿真和物理实验,而实际加工过程十分复杂,等效的离子刻蚀产额包含很多因素.针对这些问题,首先对当前的刻蚀表面演化模型进行改进,同时重新定义了离子刻蚀产额模型的优化目标,并利用实际刻蚀加工数据来优化离子刻蚀产额模型.为缩短优化模型所用时间,采用并行方法来加速优化过程.最后,将得到的离子刻蚀产额模型参数应用于采用元胞自动机法的刻蚀工艺实际仿真过程中.实验结果表明,该优化建模方法确实提高了仿真的精确度,同时优化过程所用时间也大大减少.