电化学腐蚀多孔硅表面形貌的结构特性

多孔硅作为微电子机械系统中重要的热绝缘层和牺牲层材料，其表面形貌结构特性是影响多孔硅上薄膜器件性能的重要因素，为此，利用双槽电化学腐蚀方法制备了多孔硅薄膜，并通过原子力显微镜和场发射扫描电子显微镜对制备多孔硅的表面形貌和孔径大小分布进行了观察．结果发现：腐蚀初期，在硅表面会有大量的硅柱形成，硅柱的直径、高度、分布密度与电流密度成正比关系；硅柱在进一步腐蚀过程中会消失，多孔硅的表面粗糙度随着腐蚀的进行，先减小再增大，最后达到稳定值0．52nm；多孔硅孔径大小分布区间随腐蚀时间增加变窄．     

硅基含能材料爆炸性能研究

采用电化学双槽腐蚀法在P型单晶硅片表面生长多孔硅膜。通过扫描电镜（SEM）、能量色谱（EDS）对多孔硅结构参数以及多孔硅含能材料性能进行了分析,同时进行了爆炸性能测试。结果表明：采用电化学腐蚀法可以制备出20nm左右孔径的多孔硅膜;通过原位装药技术形成的多孔硅含能材料在开放空间以及热能、机械撞击、电能、激光能量刺激下发生猛烈爆炸作用。     

多孔硅的制备及其吸杂处理对电学性能的影响

多孔硅吸杂是减少晶体硅中杂质和缺陷,提高太阳能电池转换效率的有效方法。采用电化学腐蚀方法在单晶硅片上制备多孔硅,通过观察多孔硅的形貌、结构及单晶硅片的电阻率变化,研究不同电流密度制备的多孔硅对吸杂效果的影响,并从多孔硅的结构出发探究多孔硅吸杂的机理。结果表明,随电流密度增加,孔隙率明显增加,多孔硅在电流密度为100mA/cm2时,孔隙率最大;电流密度越大,多孔硅伴随所产生的弹性机械应力增加,晶格常数相应增加,这两个因素都有利于缺陷和金属杂质在多孔硅层-基底界面处迁移和富集,导致单晶硅吸杂后电阻率增大。     

电偶腐蚀法制备多孔硅的研究EI

用电偶腐蚀法制备多孔硅,主要研究了铂电极的优化制备工艺以及腐蚀条件对多孔硅厚度的影响,并且结合SEM,AFM等测试手段对所制备的多孔硅的表面形貌进行了分析。实验发现,在相同的腐蚀条件下,多孔硅的厚度随铂电极的厚度以及铂电极与腐蚀硅片的面积比的增大而增大。     

采用原电池法制备纳米多孔硅

利用原电池法在硅片表面制备了纳米多孔硅层；用扫描电镜SEM和原子力显微镜AFM观察了多孔硅表面形貌：原电池法与电化学法得到的多孔硅孔径均在10～20nm范围．研究结果表明：铂膜电极厚度的增大以及铂膜电极与暴露硅片面积比的增大，会导致多孔硅层的厚度增大．热学模拟结果表明：以纳米多孔硅作为绝热层可获得与悬浮结构相同的效果．     

纳米多孔硅的电化学制备及性能研究

纳米多孔硅是一种潜在的化学和生物传感材料,本文采用电化学腐蚀法制备纳米多孔硅。采用SEM技术分析多孔硅的表面形貌,研究了腐蚀条件对多孔硅的孔隙率、厚度、I-V特性的影响。结果表明,多孔硅的孔隙率随着腐蚀电流密度和腐蚀时间的增加而呈线性增大趋势;其厚度随着腐蚀电流密度的增加而近似呈线性增大趋势,随腐蚀时间的成倍增加而显著增大;其I-V特性表现出非整流的欧姆接触。     

MEMS中多孔硅绝热技术

主要介绍了多孔硅的制备方法(化学法、电化学法及原电池法等)、多孔硅导热系数测试的几种常用手段(温度传感器法、显微拉曼散射法及光声法等)、导热系数的理论模型及影响因素．此外,采用不同方法制备了多孔硅样品,分析了其表面形貌并用显微拉曼光谱法测定了导热系数．结果发现,化学法制备的多孔硅孔径尺寸大于微米量级,而利用大孔硅电化学和原电池法得到的样品孔径尺寸小(约20nm),属于介孔硅．由于腐蚀条件的不同,多孔硅的孔隙率和厚度也不同,多孔硅的导热系数随孔隙率和厚度的增大而迅速减小．     

一种氮氧化物气体传感器元件的制备方法

申请（专利）号：201210400849.9公开（公告）日：2013．03．27申请（专利权）人：天津大学 摘要：本发明公开了一种氮氧化物气体传感器元件的制备方法,步骤为：（1）对n型单面抛光的单晶硅片进行清洗;（2）采用双槽电化学腐蚀法在硅片的抛光表面制备孔径尺寸在50～200nm的硅基孔洞有序多孔硅,腐蚀液为6％一8％的氢氟酸水溶液,施加的腐蚀电流密度为115～135mA／cm2,腐蚀时间为5—25min;（3）再将多孔硅置于超高真空对靶磁控溅射设备的真空室,制备基于硅基孔洞有序多孔硅的氮氧化物气体传感器元件。本发明的制备方法简单,灵活可调,工艺条件较少,易于控制;提供了一种可在室温及极低浓度（0．1×10-6）下具有高灵敏度、高选择性、快速响应／恢复特性、重复性好的氮氧化物气体传感器元件。     

用脉冲电化学法在低HF浓度下制备多孔硅的研究

用脉冲电化学阳极氧化的方法在5％的低HF浓度下获得多孔硅。多孔硅的形成和脉冲电场的施加、去除过程中与电解液－硅半导体体系中物理化学过程的变化有关。在施加电场的间隙，由于Si／电解液界面处HF的补充，SiO2的溶解增强，使得在低HF浓度下Si的溶解速率比其氧化速率高，从而导致多孔硅的形成。同时，在高电场作用下，由于产生了高浓度的空穴，使得氧化层变厚，导致在低HF浓度或大电流密度下多孔硅的平均孔径增大。     

阳极氧化电流密度和时间对多孔硅形貌和电子发射特性的影响

为了应用于场发射显示器,采用电化学阳极氧化,快速热氧化和磁控溅射等方法制备出了金属/多孔硅/硅基底/金属结构的多孔硅电子发射体,并运用扫描电子显微镜观察了多孔硅的微观形貌,结果发现多孔硅的孔径随着电化学阳极氧化电流密度的增加而增加,多孔硅层的厚度随着阳极氧化电流密度和时间乘积的增加而增加。在真空系统中测量了多孔硅的电子发射特性,电子发射的阈值电压Vth随着多孔硅层厚度的增加而增加;最大的发射效率η为7.5‰,此效率出现在孔径6~16 nm,多孔硅层厚度为11.06μm的样品中,对应的器件电压Vps为30V。     

Morphology of porous silicon structures formed by anodization of heavily and lightly doped silicon

By computer simulation the growing process of porous silicon under p⁻-Si and p⁺-Si anodization in HF solution is studied. The model of electrochemical etching of p⁺-Si includes the relief selective mechanism, which allows one to establish the relationship between anodization conditions (current density, HF concentration, temperature and doping level) and the topological characteristics of porous silicon (PS). The simulation of p⁻-Si dissolution is based on the model of diffusion limited aggregation (DLA), taking into account the thermal generation of holes and the quantum confinement effect. The various morphology of simulated PS structures exhibits a close resemblance to that of experimental ones formed in p⁺-Si and p⁻-Si wafers. For simulated p⁻-Si-based PS layers the porosity profiles and fractal dimension are calculated. It is shown that PS in p⁻-Si is multifractal with fractal dimension varying monotonously from 0.1 to 3 with size increase.     

Low mechanical pressure during electrochemical etching: induced modification in optical and structural properties of n-type porous silicon

In this study, n-type porous silicon (PS) layers are formed in the dark with the assistance of a low mechanical pressure during electrochemical etching process. Pressure-induced stress/strain modifies the resistivity of the silicon substrate to enhance the etching process. Under the same equivalent etching condition, pressure-assisted etching can yield PS layer with stronger room temperature photoluminescence intensity than the layer formed by ordinary electrochemical etching. The porosity of pressure-assisted etched PS layers is found to be much higher than that of ordinary etched layer. Fourier transformation infrared absorption spectroscopy and grazing incidence X-ray diffraction measurements and analysis show that application of the pressure during electrochemical etching promotes the degree of oxidation and reduces the crystallites size of the PS layer. The effect of the pressure during etching process on the surface topography of PS is revealed by scanning electron microscopy imaging.     

Surface and optical characterization of the porous silicon textured surface

In the present studies, the structural and optical properties of the electrochemically etched PS layers are presented. The formation conditions under constant anodization current density was varied to get a variety of PS samples to analyze the structural and optical characteristics of the porous silicon layers and, then to correlate the resultant surface morphology with the etching process. The low-porosity PS layers thus formed on the silicon substrate have a refractive index value (n_ps = 1.9), which is an intermediate value between bulk silicon substrate (n_Si = 3.4) and air (n_air = 1.0). The results of diffused reflectance, surface morphology by atomic force microscopy (AFM), and Raman scattering measurements show that the resultant surface morphology of the PS layers consist of irregular and randomly distributed nanocrystalline Si structures. The reduction in reflection of the low porosity porous silicon layers is due to light scattering and light trapping of the incoming light by total randomization of the incoming light within the PS structure. The Fourier transform infrared (FTIR) measurements on the PS layer on Si substrate show that PS surface is characterized by chemical species like Si—H and Si—O etc., co-existing on the surface. The presence of hydrogen-related species on the PS layer can provide to some extent a surface passivation effect.     

Demonstration of the formation of porous silicon films with superior mechanical properties,morphology and stability

Highly stable and mechanically strong thick porous silicon (PS) films have been obtained on textured silicon substrates. Porous silicon formed on textured substrates exhibits higher porosity, better mechanical strength, non-fractured surface morphology and lower stress compared to porous silicon formed on polished silicon substrates at the same current density, time of anodization and method of drying. The improved properties are attributed to the formation of localized highly porous macroscopic plastic regions.     

多孔硅的微结构及其冷阴极的电子发射特性研究

采用电化学腐蚀法在n型单晶Si基底上制备多孔硅(PS)膜,利用场发射扫描电子显微镜(FE-SEM)分析其微结构特征,研究了硅基底材料、腐蚀电流密度和腐蚀时间等制备条件和工艺参数对PS微结构的影响。实验结果表明,轻掺杂n型Si基底上形成的PS膜(n--PS)中的孔较深且孔径较大,而重掺杂n型Si基底上的PS膜(n+-PS)中的孔分布较为密集,而且呈多分枝结构;腐蚀电流密度相同时,PS的膜厚和腐蚀时间成正比,而在较高的腐蚀电流密度下制备得到的PS膜在结构上更为疏松。制作了基于n+型硅基底的PS阴极,此阴极的阈值电压约为14 V,高于该电压后发射电流随着二极管电压提高而呈指数性增加趋势,而且发射电流对环境气压不敏感,即使在0.1 Pa的低真空中也没有明显的衰减。     

Porous silicon nanowires fabricated by electrochemical and laser-induced etching

Electrochemical and laser-induced etching processes were simultaneously used to synthesize the nanowires structure of porous silicon (PS). Surface morphology and structural properties of nanostructured silicon were characterized by using scanning electron microscopy (SEM) and atomic forces microscopy (AFM) images. Nanowires with dimensions of few nanometers were formed on the whole etched surface. The optical properties of silicon nanostructures were studied. Raman spectra were shifted and broadened relatively to 519.9 cm⁻¹ of PS prepared by electrochemical etching, and shifted to 517.2 cm⁻¹ for laser-induced etching process and to 508.9 cm⁻¹ for electrochemical and laser etching simultaneously. Blue shift luminescence was observed at 649.6 nm for PS produced by electrochemical etching, and at 629.5 nm for laser-induced etching. PS produced a blue shift at 626.5 nm using both etching procedures simultaneously. X-Ray diffraction (XRD) was used to investigate the crystallites size of the PS as well as to provide an estimate of the degree of crystallinty of the etched sample.     

Application of nanoporous silicon for a metal-semiconductor-metal visible light photodetector

In this paper we present a study on the application of nanoporous silicon to an optoelectronic device called a nanoporous silicon metal-semiconductor-metal (MSM) visible light photodetector. This device was fabricated on a nanoporous silicon layer which was formed by electrochemical etching of a silicon wafer in a hydrofluoric acid solution under various anodization conditions such as the resistivity of the silicon wafer, current density, concentration of the hydrofluoric acid solution and anodization time. The structure of this device has two square Al/nanoporous silicon Schottky-barrier junctions on the silicon substrate and the electrode spacing is 500 microm. The experiment will study photoresponse and the response time of a nanoporous silicon MSM photodetector which was fabricated on the various porosity of a nanoporous silicon layer. It is found that when devices are fabricated on a higher porosity nanoporous silicon layer, the photoresponse of the device will expand toward the short-wavelength and the bandwidth of the spectrum response will cover visible light. In addition, it is found that the response time of the device decreases.     

适用于微型燃料电池扩散层的多孔硅的可控制备工艺研究

多孔硅以其多孔结构及大的表面体积比等特点被认为是可在基于MEMS技术的微型燃料电池中代替碳 纸、碳布作为扩散层的材料. 本文考虑传统碳纸、碳布作为扩散层的要求, 并结合多孔硅材料的特点, 选用n<100>(0.04～0.15 Ω·cm)单晶硅进行了多孔硅制备工艺的研究; 考察了腐蚀液的浓度、电流密度和氧化处理时间对多孔硅的孔隙率、孔深度及氧化速率 的影响, 实现了多孔硅的可控制备. 孔隙率为40%、孔径为350～700nm、厚度为60μm的多孔硅膜电极经循环伏安测定, 在0.5mol/L H₂SO₄溶液中, 表现出与碳纸相近的电活性, 显示了潜在的应用价值.     

永冲电化学腐蚀制备n型多孔硅及其发光性能

采用脉冲电化学腐蚀法,以n型单晶硅为衬底制备多孔硅（n—PS）,通过扫描电镜（SEM）、室温500—700nm范围内荧光光谱,系统研究腐蚀时间、占空比和脉冲频率对n-PS的结构形貌和可见光区室温光致发光特性（PL）的影响,结果表明,相比直流电化学腐蚀方法,脉冲腐蚀能获得孔径分布均匀且发光强度更高的多孔硅;随腐蚀时间、占空比和脉冲频率等腐蚀条件的变化,其发光峰位及发光强度均有明显改变;当等效腐蚀时间为30min、占空比为0．5、脉冲频率为10Hz时,制备的n—PS的PL强度较高,发光性能较好。