Formation of two-dimensional periodic nanostructures on fused quartz,polyimide, and polycrystalline diamond by pulsed four-wave interference laser modification

Atomic force microscopy is used to examine the topography of submicron periodic structures formed on the surfaces of synthetic polycrystalline diamond and polyimide films. The films are deposited on fused quartz substrates by four-wave interference modification using a pulsed 308-nm UV XeCl excimer laser. It is demonstrated that a two-dimensional periodic relief with a submicron period can be formed on the diamond surface directly by laser evaporation in the absence of a photoresist. Depending on the exposure, two mechanisms of polyimide film modification are observed. At exposures less than 100 mJ/cm², the relief is formed due to swelling at the positions of interference maxima. At exposures greater than 100 mJ/cm², holes are formed in the films. A periodic relief on the fused quartz surface is formed by using a UV photoresist exposed to pulsed interference laser radiation and subsequent Ar ion etching.     

Etching of silicon in fluoride solutions

The development and status of what is commonly called the Gerischer mechanism of silicon etching in fluoride solutions is reviewed. The two most widely used and studied wet etchants of silicon are F^? and OH^?. Their mechanisms of atom removal share many things in common; in particular, chemical passivation by a hydrogen-terminated surface plays an important role in both. Crucially, however, their initiation steps are different, and this leads to important differences in the structures of the materials produced by the etchants. The initiation of etching by F^? is electrochemical in nature, responding to the electronic structure of the Si, and is, therefore, a self-limiting reaction that can produce nanocrystalline porous silicon. Hydroxide etching destroys porous silicon because its initiation step is a catalytic chemical reaction and not a self-limiting process. A number of unanswered questions regarding the dynamics of fluoride etching are highlighted.     

Laser etching of fused silica using an adsorbed toluene layer

A new method for laser etching of transparent materials with a low etch rate and a very good surface quality is demonstrated. It is based on the pulsed UV-laser backside irradiation of a transparent material that is covered with an adsorbed toluene layer. This layer absorbs the laser radiation causing the etching of the solid. The threshold fluence for etching of fused silica amounts to 0.7 J/cm². The constant etch rate of about 1.3 nm/pulse that has been observed in a fluence interval from 2 to 5 J/cm² is evidence of a saturated process. The limited thickness of the adsorbed layer causes the low etch rates and the rate saturation. The etched surface structures have well defined edges and low surface roughness values of down to 0.4 nm rms. PACS 81.65.Cf; 81.05.Kf; 79.20.Ds; 61.80.Ba; 42.55.Lt     

感应耦合等离子体刻蚀在聚合物光波导制作中的应用

提出了利用感应耦合等离子体(ICP)刻蚀技术提高聚合物光波导器件性能的方法,介绍了ICP刻蚀技术的原理和优点。选取聚甲基丙烯酸甲酯-甲基丙烯酸环氧丙酯(P(MMA-GMA))作为波导材料,采用氧气作为刻蚀气体,研究了ICP参数变化对刻蚀效果的影响。介绍了倒脊形光波导的制备过程,采用改变单一工艺参数的方法,分析了刻蚀效果随时间、功率、压强、气体流量等参数的变化,对参数优化后刻蚀得到的凹槽和平板结构进行了表征。实验结果表明:在天线射频功率为300 W,偏置射频功率为30 W,气体压强为0.5 Pa,氧气流速为50 cm³/min的条件下,可获得侧壁陡直、底面平整的P(MMA-GMA)凹槽结构。     

Defect profiles in graded band-gap layers of <Emphasis Type="Italic">P</Emphasis>-HgCdTe heteroepitaxial structures under ion-beam etching

The results of investigations into spatial distribution of donors in p-HgCdTe graded band-gap layers with various composition profiles in the near-surface layer upon ion-beam etching are reported. It is found that the depth of the resulting n⁺-layer is weakly dependent on the conditions of ion-beam etching and composition of material of the surface and is about 0.5–1 μm. The electron density in the n⁺-layer on the surface is observed to increase with time of beam etching. It is shown that the conditions of ion-beam etching and the composition of the near-surface region significantly affect only the depth of the foregoing layer with low electron density. Analysis of experimental data shows that the process of ion-bean etching in p-HgCdTe heteroepitaxial structures with a composition gradient in the near-surface region is different from etching in HgCdTe homogeneous epitaxial structures and crystals. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 51–56, September, 2008.     

Ar ion milling of InSb for manufacturing single electron devices

Ar⁺ ion milling of InSb for manufacturing single electron devices was studied. It is shown that pyramidal structures (porous) are created on the (1 1 1) surface of InSb wafers by anisotropic etching. Also it was shown the axis of the pyramidal structure is a function of the angle of the Ar⁺ incident beam and does not depend on the energy of the beam. EDX measurement results show In_xO_y and Sb_xO_y were not created on the surface after milling process. FTIR measurement results show that the surface reflection was decreased and less than 0.3 V flat band voltage was seen in capacitance voltage measurement results. SEM images show that the etching has approximately vertical profile. Therefore the Ar⁺ milling technique can be used as a dry etching technique for manufacturing mesa and/or porous structures of InSb. Since the surface is porous and of near-pyramidal morphology, one can simulate the surface by a set of needles each of which is a nanometer-size capacitance (i.e. single electron device). We showed, the threshold voltage of this single electron device is 0.3 V approximately, and therefore it can be used for studying single-electron or Coulomb blockade effects.     

Laser fabrication of periodic microstructures from silver nanoparticles in polymer films

The fabrication of photoand thermostable periodic structures from silver nanoparticles in polymer plates (cross-linked oligourethanemethacrylate impregnated with silver precursors Ag(hfac) and Ag(fod) dissolved in the supercritical carbon dioxide) is studied. The process is based on the local (depending on the irradiated spot size) photochemical decomposition of the silver precursors in the polymer matrix that initiates the atomic aggregation and creation of silver nanoparticles with the plasmon resonance in absorption in the spectral range 420–430 nm. The third-harmonic radiation of a Nd:YAG laser (355 nm) and the Kr⁺-laser (521 nm) radiation are employed for the recording of periodic structures with submillimeter and micron resolutions. The photosensitivity of the polymer matrices impregnated with the silver precursors to the UV and visible radiation is discussed.     

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)     

亚微米尺寸元件的离子束刻蚀制作

采用软光刻技术中的微接触印刷(μCP)技术、表面诱导的水蒸气冷凝、表面诱导的去湿行为,在金基底上制作出了亚微米的环状周期结构聚合物掩膜.通过对离子束刻蚀过程中各个参量对刻蚀元件的表面光洁度、轮廓保真度和线宽分辨的影响分析,结合掩膜的实际情况选择出了合适的离子束入射角、离子能量、束流密度和刻蚀时间等参量.依照这些参量刻蚀出了高质量的亚微米尺寸环状周期结构元件.通过对刻蚀出的元件的检测发现,刻出的元件表面光洁度、轮廓保真度和侧壁陡峭度都非常好.     

类桑拿法制备的周期性结构Mo金属催化电极及其在电解水制氢中的应用

采用类桑拿法制备了聚苯乙烯微球模板, 结合双层Mo金属结构, 获得了具有周期性结构的Mo金属催化电极. 通控制氧气对聚苯乙烯球的刻蚀时间, 可有效调制Mo金属催化电极的横、纵向尺寸, 从而获得不同的衬底比表面积. 通过原子力显微镜表面形貌测试、电化学线性扫描、塔菲尔测试以及阻抗谱分析表明: 增大刻蚀时间可有效提高Mo金属催化电极的表面粗糙度和比表面积, 进而降低电荷传输电阻和塔菲尔斜率, 促进催化电极/电解液界面处析氢反应的进行. 采用类桑拿法和双层Mo金属结构制备周期性结构的方法简单, 可大面积化, 同时低温磁控溅射法制备的Mo金属催化电极成本低廉, 温度兼容多种太阳电池器件, 具有形成高效一体化光水解制氢器件的潜力.     

Chemically assisted femtosecond laser machining for applications in LiNbO3 and LiTaO3

We introduce and optimize a fabrication procedure that employs both femtosecond laser machining and hydrofluoric acid etching for cutting holes or voids in slabs of lithium niobate and lithium tantalate. The fabricated structures have 3 μm lateral resolution, a lateral extent of at least several millimeters, and cut depths of up to 100 μm. Excellent surface quality is achieved by initially protecting the optical surface with a sacrificial silicon dioxide layer that is later removed during chemical etching. To optimize cut quality and machining speed, we explored various laser-machining parameters, including laser polarization, repetition rate, pulse duration, pulse energy, exposure time, and focusing, as well as scanning, protective coating, and etching procedures. The resulting structures significantly broaden the capabilities of terahertz polaritonics, in which lithium niobate and lithium tantalate are used for terahertz wave generation, imaging, and control. The approach should be applicable to a wide range of materials that are difficult to process by conventional methods.     

X-ray spectroscopic examination of thin HfO<Subscript>2</Subscript> films ALD- and MOCVD-grown on the Si(100) surface

HfO₂ films 5 nm thick grown on Si(100) substrates by the methods of MOCVD hydride epitaxy and atomic layer deposition (ALD) are studied using X-ray photoelectron spectroscopy combined with Ar⁺ ion etching and X-ray reflectometry. It is found that (i) the ALD-grown HfO₂ films are amorphous, while the MOCVD-grown films show signs of a crystal structure; (ii) the surface of the ALD-grown films is more prone to contamination and/or is more reactive; and (iii) the amount of interfacial silicon dioxide in the case of the MOCVD-grown film is greater than in the case of the films synthesized by ALD. It is also shown that the argon ion etching of the HfO₂ film results in the formation of a metallic hafnium layer at the interface. This indicates that HfO₂ can be used not only as a gate dielectric but also as a material suitable for fabricating nanodimensional conductors by direct decomposition.     

Effects of halogenated organic solvents on laser-induced backside wet etching of fused silica

Laser-induced backside wet etching of fused silica using a solution of pyrene dissolved in halogenated and non-halogenated solvents is presented. A significant influence of the solvent used on the etch rate and the etched surface appearance was ascertained. The etching of uniform and smooth surfaces with rates of ∼0.1 nm/pulse for laser fluences below 500 mJ/cm² is observed only for halogenated solvents. Furthermore, reduced threshold fluences, only small incubation effects, and a constant etch rate in dependence on the pulse number were found. The experimental data suggest an additional etch process at low laser fluences characterized by the very low etch rate and the smooth etching observed only with halogen-containing solvents. The generation of halogen radicals/compounds close to the heated surface due to the decomposition of the solvent causing the attack of the surface seems the most probable mechanism. PACS 81.65.Cf; 81.05.Kf; 79.20.Ds; 61.80.Ba; 42.55.Lt; 68.45.Da     

Using IR laser radiation for backside etching of fused silica

Laser-induced backside etching of fused silica with gallium as highly absorbing liquid is demonstrated using pulsed infrared laser radiation. The influences of the laser fluence, the pulse number, and the pulse length on the etch rate and the etched surface topography were studied and the results are compared with these of excimer laser etching. The high reflectivity of the fused silica-gallium interface at IR wavelengths results in the measured high threshold fluences for etching of about 3 J/cm² and 7 J/cm² for 18 ns and 73 ns pulses, respectively. For both pulse lengths the etch rate rises almost linearly with laser fluence and reaches a value of 350 and 300 nm/pulse at a laser fluence of about 12 and 28 J/cm², respectively. The etching process is almost free from incubation processes because etching with the first laser pulse and a constant etch rate were observed. The etched surfaces are well-defined with clear edges and a Gaussian-curved, smooth bottom. A roughness of about 1.5 nm rms was measured by AFM at an etch depth of 0.95 μm. The normalization of the etch rates with respect to the reflectivity and the pulse length results in similar etch rates and threshold fluence for the different pulse widths and wavelengths. It is concluded that etching is a thermal process including the laser heating, the materials melting, and the materials etching by mechanical forces. The backside etching of fused silica with IR-Nd:YAG laser can be a promising approach for the industrial usage of the backside etching of a wide range of materials. PACS 81.65.C; 81.05.J; 79.20.D; 61.80.B; 42.55.L     

BRILLOUIN LIGHT-SCATTERING INVESTIGATION OF ELASTIC ANOMALY FROM SUPERLATTICES

In this paper we report some new experimental results concerning the elastic properties of periodic and quasiperiodic superlattices studied by means of Brillouin spectroscopy. The observation of both bulk and surface acoustic phonons as well as the fitting using effective medium approximation on the phonon spectrum enables us to extract accurately some rele-vant effective elastic constants in both structures. We have verified that the elastic anomaly which occurs in the periodic structures is also present in quasiperiodic ones. These results imply that the interaction mechanism of Fermi electrons with reduced Brillouin zone bound-ary is not responsible for the observed elastic anomalies, The comparative study of these superlattices proves that the elastic anomaly is relevant directly to interfacial effects.     

纳米压印多孔硅模板的研究

纳米压印模板通常采用极紫外光刻、聚焦离子束光刻和电子束光刻等传统光刻技术制备,成本较高.寻找一种简单、低成本的纳米压印模板制备方法以提升纳米压印光刻技术的应用成为研究的重点与难点.本文以多孔氧化铝为母模板,采用纳米压印光刻技术对纳米多孔硅模板的制备进行了研究.在硅基表面成功制备出纳米多孔阵列结构,孔间距为350—560 nm,孔径在170—480 nm,孔深为200 nm.在激发波长为514 nm时,拉曼光谱的测试结果表明,相对于单面抛光的硅片,纳米多孔结构的硅模板拉曼光强有了约12倍左右的提升,对提升硅基光电器件的应用具有重要的意义.最后,利用多孔硅模板作为纳米压印母模板,通过热压印技术,成功制备出了聚合物纳米柱软模板.     

Antireflection microstructures fabricated upon fluorine-doped SiO(2) films

Two-dimensional periodic structures were fabricated upon a fluorine-doped SiO(2) film in which the fluorine content changed gradually in the direction of film thickness. The films were deposited by plasma-enhanced chemical-vapor deposition. The film was periodically patterned into a 1-mum period and an ~1-mum -groove depth by inductive coupled plasma reactive-ion etching followed by chemical etching in a diluted HF solution. A surface reflectance of 0.7% was attained at 1.85-mum wavelength, a value that is one fifth as large as the 3.5% Fresnel reflection of a SiO(2) substrate with a flat surface.     

Periodic patterning of silicon by direct nanosecond laser interference ablation

The production of periodic structures in silicon wafers by four-beam is presented. Because laser interference ablation is a single-step and cost-effective process, there is a great technological interest in the fabrication of these structures for their use as antireflection surfaces. Three different laser fluences are used to modify the silicon surface (0.8 J cm⁻², 1.3 J cm⁻², 2.0 J cm⁻²) creating bumps in the rim of the irradiated area. Laser induced periodic surface structures (LIPSS), in particular micro and nano-ripples, are also observed. Measurements of the reflectivity show a decrease in the reflectance for the samples processed with a laser fluence of 2.0 J cm⁻², probably caused by the appearance of the nano-ripples in the structured area, while bumps start to deteriorate.     

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.     

Electrochemical impedance spectroscopy analysis of porous silicon prepared by photo-electrochemical etching: current density effect

Electrical impedance characteristics of porous silicon nanostructures (PSiNs) in frequency function were studied. PSiNs were prepared through photo-electrochemical etching method at various current densities (15–40 mA/cm²) and constant etching time. The atomic force microscope images of PSiNs show that pore diameter and roughness increase when current density increases to 35 mA/cm². The surface roughness subsequently decreases because of continuous etching of pillars, and a second etching process occurs. Photoluminescence spectra show blue and red shift with increasing applied current density that is attributed to PSiNs size. Variations of electrical resistance and capacitance values of PSiNs were measured using electrochemical impedance spectroscopy analysis. These results indicate that PSiNs prepared at 20 mA/cm² current density have uniform porous structures with a large number of pillars. Furthermore, this PSiNs structure influences large values of charge transfer resistance and double layer capacitance, indicating potential application in sensors.