原子力显微镜中微悬臂梁/探针横向力的标定

利用微加工制造的微悬臂梁／探针尖已经广泛应用在微观表面性质测试和微纳米尺度加工等领域，成为微纳米研究领域中不可缺少的重要工具．为了能够定量研究原子力显微镜中探针与表面的相互作用力，需要对微悬臂梁／探针的力学性能进行表征．本文简要地论述了原子力显微镜中微悬臂梁的形变光反射原理和探针与表面的接触刚度理论．阐明了微悬臂梁横向力标定的重要性．综述了目前几种微悬臂梁／探针横向力的标定方法、简单的推倒过程和特点、     

用于扫描刻蚀加工的微小等离子体反应器的设计和实验

提出了一种新的基于并行探针的扫描等离子体刻蚀加工方法,设计并研制了其中的核心器件--微小等离子体反应器,测量了该器件的伏安特性曲线,分析了其电学性能随工作气压和器件尺寸的变化规律,以及器件损坏的机制.实验结果表明,当放电气体为SF6,工作气压在2 000～6 000 Pa之间变化时,该器件能产生较为稳定的微等离子体,放电电压在390～445 V之间,功率密度在10～150 W/cm^2之间,从而为进一步将其应用到扫描硅刻蚀加工提供可能.     

ICP刻蚀4H-SiC栅槽工艺研究

为避免金属掩膜易引起的微掩膜,本文采用SiO2介质作为掩膜,SF6/O2/Ar作为刻蚀气体,利用感应耦合等离子体刻蚀(ICP)技术对4H-SiC trench MOSFET栅槽刻蚀工艺进行了研究。本文详细研究了ICP刻蚀的不同工艺参数对刻蚀速率、刻蚀选择比以及刻蚀形貌的影响。实验结果表明:SiC刻蚀速率随着ICP功率和RF偏压功率的增大而增加;随着气体压强的增大刻蚀选择比降低;而随着氧气含量的提高,不仅刻蚀选择比增大,而且能够有效地消除微沟槽效应。刻蚀栅槽形貌和表面粗糙度分别通过扫描电子显微镜和原子力显微镜进行表征,获得了优化的栅槽结构,RMS表面粗糙度0.4nm。     

基于MEMS技术集成硅微棱镜耦合和微流道的近红外表面等离子体谐振芯片

为促进表面等离子体谐振（surface plasmon resonance, SPR）测试技术在片上的实现,提出硅基近红外SPR芯片,由硅微棱镜、金属膜和聚合物微流体通道组成．利用有掩膜和无掩膜各向异性湿法腐蚀加工出底角为25．24。的单微硅棱镜阵列,用有掩膜各向异性湿法腐蚀加工出底角为54．74。的双微硅棱镜阵列,利用聚合物的复制注塑技术加工得到微流体通道．在波长1550nm时进行仿真与实验测试,实验测得以空气、水和乙醇为测试介质的SPR角分别为16．75°、22．58°和22．72°,这些值比以玻璃棱镜加工SPR传感器测得的SPR角要小很多．通过实验表明,近红外SPR芯片可以实现表面等离子体谐振传感器微型化,进而推动微全分析系统的实现,降低其成本并提高其性能．     

硅应力非均匀氧化影响因素及其在纳米孔制作中的应用

在微等离子体无掩模加工研究中,单晶硅在分布应力作用下的非均匀氧化现象决定了采用各向同性刻蚀得到氧化硅空心针尖纳米孔的可行性和可靠性.以V型槽为对象,研究了单晶硅在槽尖端的非均匀氧化现象.利用高温下氧化硅的黏弹性特性,建立了硅在几何约束导致的分布应力作用下的热氧化模型.该模型表明,应力通过抑制氧元素在氧化硅层中的扩散和氧化反应速率来抑制氧化进行,从而非均匀的应力分布造成了非均匀的氧化层厚度.实验证明,硅在应力作用和几何约束下的热氧化,当氧化层厚度仅为160 nm时,不同温度下的厚度非均匀性基本一致,为72%左右;而当氧化厚度增长为1.1μm时,低温与高温下的厚度非均匀性差距显著增大,分别为42%和100%.分析表明,氧化层厚度非均匀性是应力生成与应力释放过程的综合作用结果,受到氧化温度和氧化时间两个可控因素的共同影响.在此基础上,利用硅在950℃下10 h的应力非均匀氧化及后续稀释氢氟酸的各向同性刻蚀成功制作出空心针尖阵列尖端直径为50 nm~200 nm的纳米孔.     

碳氟感应耦合等离子体的SiO2介质刻蚀的研究

使用感应耦合等离子体技术,通过改变源气体流量比R(R=[C4F8]/{[C4F8] [Ar]})、射频源功率、自偏压等条件进行了SiO2介质刻蚀实验研究。碳氟等离子体的特征由朗谬探针和发射光谱技术来表征。结果表明,SiO2的刻蚀速率随放电源功率和射频自偏压的增大而单调上升,与R的关系则存在R=8%处的刻蚀速率峰值。C2基团的发射谱线强度随R的变化类似于SiO2刻蚀速率对R的依赖关系,对此给出了解释。在此基础上,对SiO2介质光栅进行了刻蚀。结果显示,在较大的R及自偏压等条件下,刻蚀后的槽形呈轻微的锥形图案,同时光刻胶掩膜图形出现分叉。结合扫描电镜技术对此进行了分析,认为光刻胶表面与侧面的能量传递和聚合物再沉积是导致出现上述现象的原因。     

基于移动LIGA工艺的微针阵列的设计与制作

提出了一种聚甲基丙烯酸甲酯（PMMA）微针阵列的微细加工工艺,即移动X光光刻在光刻胶上得到与LIGA掩模板图形相似的曝光能量分布图,再利用显影技术获得了其断面形状与LIGA掩模板图形相似的PMMA微针阵列结构．为了解决空心微针阵列的加工问题,通过对准曝光实现空心孔的微细加工．用此纳米加工技术获得了高度为350～700μm、针锋尖锐度为1μm的PMMA的微针阵列．该阵列面积约为1cm^2,微针数约为900根,实验结果表明,利用这种新方法可以非常方便地加工出高质量的实心微针、空心微针和带流体沟道的分又微针等各种微针．该微针阵列可与微泵、微通道等集成为一体,实现无痛化注射或无痛化采血。     

基于AFM氮化硅探针刻蚀方法制作聚碳酸酯纳米光栅

基于原子力显微镜(AFM)探针的纳米机械刻蚀技术以其成本低、分辨率高的优势被广泛应用于各种纳米元器件的制造中.为了得到最优的光栅结构,首先通过单次刻蚀实验定量分析了刻蚀方向、加载力和刻蚀速率等3个主要加工参数对所得纳米沟槽形貌和尺寸的影响,给出了普通氮化硅探针对聚碳酸酯(PC)的加工特性及加工效率.然后通过改变沟槽间距(100~500 nm)得到了不同周期的纳米光栅结构,并确定了这种探针与样品的组合对间距的要求及最佳加工参数:沿垂直于微悬臂长轴向右刻蚀,加载力2.3μN,刻蚀速率2.6μm/s.最后利用该技术对实验室已有原子光刻技术所得周期为213 nm的一维Cr原子光栅结构进行了复制加工,得到了均匀的213 nm一维光栅,证明这种基于AFM探针的纳米机械刻蚀技术可被广泛应用于纳米加工.     

用于微放电器的聚酰亚胺绝缘层的工艺和性能研究

研究了一种应用于微放电器的聚酰亚胺绝缘材料的工艺及性能。分析了聚酰亚胺制备过程中亚胺化程度以及图形化过程中反应离子刻蚀功率、气体流量、气体成分、清洗等因素对于薄膜质量、刻蚀速率和残留物的影响,设计了用于测定聚酰亚胺介电常数和击穿强度的电路。实验表明,当聚酰亚胺热环化采用阶梯升温方式,反应离子刻蚀功率为60 W、O2流量为60 cm3/min(标准状态)、加入5%SF6或10%CHF3时,可保证较好的薄膜质量且获得较高的刻蚀速率。实验测得聚酰亚胺相对介电常数为2.8,介电击穿强度为125 V/μm,使用该聚酰亚胺作为绝缘层而制备的微放电器可在10 kPa SF6中稳定放电。     

SiO_2空心纳米微球的合成

为了改善聚合物粒子与SiO2粒子之间的亲和力及SiO2粒子在聚合物粒子表面的吸附,首先使用共单体4-乙烯基吡啶(4VP)功能化苯乙烯(PS)粒子,合成了聚(苯乙烯-共-4-乙烯基吡啶)(P(St-4VP))粒子。然后在NH4OH/乙醇介质中,将溶胶-凝胶法生成的SiO2粒子包覆在P(St-4VP)粒子表面,聚合物核被溶解得到SiO2空心纳米微球。随着P(St-4VP)粒子中共单体4VP含量以及正硅酸乙酯(TEOS)用量增加,SiO2空心纳米微球的壳层厚度增加,且壳层表面变得粗糙。随着PVP用量增加,SiO2空心纳米微球的平均尺寸下降,其壳层从松散粗糙变得致密光滑。NH4OH用量增加对SiO2空心纳米微球尺寸和形态的影响不大。     

基于硅与非硅复合方法的异平面空心微针制作

为了解决制备空心微针工艺复杂且成本高的问题,本文提出了采用湿法刻蚀、光刻和电镀结合的方法制备低成本空心金属微针.首先采用湿法刻蚀硅,得到280μm深的倒四棱锥锥坑;然后在锥坑上甩200μm厚的负胶SU-8填充锥坑,并通过曝光显影负胶形成微针的形貌;最后在曝光显影后的负胶上电镀50μm厚的镍得到所需形状的空心金属微针.用此方法制备的空心微针高度为350μm、壁厚为50μm,其针尖形状为三棱锥和四棱锥.通过有限元仿真分析微针强度与微针结构尺寸的关系.用此方法加工出的微针具有锥形尖,改善了刺入皮肤的效果.     

Combined scanning electrochemical-atomic force microscopy

A combined scanning electrochemical microscope (SECM)-atomic force microscope (AFM) is described. The instrument permits the first simultaneous topographical and electrochemical measurements at surfaces, under fluid, with high spatial resolution. Simple probe tips suitable for SECM-AFM, have been fabricated by coating flattened and etched Pt microwires with insulating, electrophoretically deposited paint. The flattened portion of the probe provides a flexible cantilever (force sensor), while the coating insulates the probe such that only the tip end (electrode) is exposed to the solution. The SECM-AFM technique is illustrated with simultaneous electrochemical-probe deflection approach curves, simultaneous topographical and electrochemical imaging studies of track-etched polycarbonate ultrafiltration membranes, and etching studies of crystal surfaces.     

Fabrication of SiO2 Microcantilever Using Isotropic Etching With ICP

This paper reports a new design and microfabrication process for high sensing guard-armed silicon dioxide (SiO₂ ) microcantilever sensor, which can be widely used in chemical, environmental and biomedical applications. One sensor platform consists of two SiO₂ cantilever beams as the sensing and reference elements, two connecting wings, and three guard arms. The guard arms prevent damage to the cantilever beam from collision. To efficiently release the SiO₂ cantilevers from the silicon substrate, an isotropic etch method using inductively coupled plasma (ICP) was developed. The isotropic etching with ICP system provides an advantage in good profile control and high etching rate than wet isotropic etching or conventional RIE (reactive ion etching); however, it has not been gained many attentions. In this work, the effects of chamber pressure, plasma source power, substrate power, SF₆ flow rate relating with Si etching rate, undercutting rate, and isotropic ratio were investigated and discussed. The optimum isotropic etching process achieved a 9.1 mum/min etch rate, 70% isotropic ratio, and 92% etching uniformity. The SiO₂ cantilever sensor was fabricated and the cantilever beam was successfully released using a patterned photoresist layer as an etching mask. This plasma isotropic etching release processing can be also applied to release other SiO₂ or metal suspended MEMS structures, such as bridges and membranes, with a fast etch rate and reasonable isotropic ratio.     

The origin of wing tilt for uncoalesced GaN grown on maskless grooved sapphire fabricated by wet chemical etching

In this paper, wing tilt was detected by high resolution X-ray rocking curve for uncoalesced GaN epilayer grown on maskless periodically grooved sapphire fabricated by wet chemical etching. Stress distribution was characterized by the frequency shift in micro-Raman spectroscopy measurement. It shows inhomogeneous stress distribution between the mesa and wing region, which is in agreement with the finite-element analysis simulations. Meanwhile, the wing tilt calculated by finite-element analysis agrees well with the rocking curve result. The results show that the different relaxation of stress causes inhomogeneous displacements between the mesa and wing region is the main reason of wing tilt formation.     

Bulk wave membrane quartz resonators fabricated by a hollow cathode RF plasma etching technique

A hollow cathode maskless plasma etching method for fabrication of thin quartz membranes is presented. A special geometric arrangement of electrodes and substrates allows the complete plasma structure (plasma sheath, bulk plasma) to be transferred to the substrate area during the etching process. The process has successfully been used in preparing thin quartz membranes with plane-convex and plane-parallel shape, and thicknesses of less than 5 mum. Vibration modes in these thin quartz membranes are calculated using the method of equivalent resonant radius. The membranes are used for realization of bulk acoustic wave resonators at fundamental frequencies above 60 MHz. Good agreement between theoretical and experimental characteristics is achieved.     

基于电化学腐蚀法的钨探针制备装置研究

基于电化学腐蚀法制备钨探针的原理,设计了一套钨探针制备装置,并对钨探针制备参数进行了研究。装置的实验部分用于调整探针与电解槽的相对位置和运动参数,控制部分用于监测、控制并记录电化学反应的状态。与传统腐蚀探针相比,该装置通过控制电路控制探针腐蚀过程中运动参数,获得了形状可控的大长径比探针;同时通过精确控制腐蚀反应时间,可制备针尖曲率半径范围为5~20 nm的探针。     

Error in dynamic spring constant calibration of atomic force microscope probes due to nonuniform cantilevers

Many common atomic force microscope (AFM) spring constant calibration methods regard the AFM probe as a uniform cantilever, neglecting the tip mass and any nonuniformity in the thickness of the probe along its length. This work quantifies the error in the spring constant estimated by the Sader and thermal calibration methods due to nonuniformity in the thickness of the cantilever and the influence of the mass loading effect of the probe tip. Formulae are presented that can be used to compute the uncertainty in cantilever calibration for an arbitrary thickness nonuniformity, or to correct the calibration methods if the thickness nonuniformity is known. The results show that both methods are quite sensitive to nonuniformity. When the first dynamic mode is used in the calibration, the error in the spring constant estimated by either method is between - 4% and 9% for a cantilever whose thickness increases or decreases linearly by 30% along its length. The errors are several times larger if the second or higher dynamic modes are used. To illustrate the proposed methods, a commercial AFM probe that has significant nonuniformity is considered and the error in calibrating this probe is quantified and discussed. For this particular probe, variations in the thickness of the probe over the last 15% of its length are found to significantly reduce the accuracy of the calibration when the thermal method is used, since that method is sensitive to changes in the shape of the eigenmode of the probe near its free end.     

Synthesis and electroplating of high resolution insulated carbon nanotube scanning probes for imaging in liquid solutions

High resolution and isolated scanning probe microscopy (SPM) is in demand for continued development of energy storage and conversion systems involving chemical reactions at the nanoscale as well as an improved understanding of biological systems. Carbon nanotubes (CNTs) have large aspect ratios and, if leveraged properly, can be used to develop high resolution SPM probes. Isolation of SPM probes can be achieved by depositing a dielectric film and selectively etching at the apex of the probe. In this paper the fabrication of a high resolution and isolated SPM tip is demonstrated using electron beam induced etching of a dielectric film deposited onto an SPM tip with an attached CNT at the apex.