用于MEMS的叠层光刻胶牺牲层技术

研究了用于制备悬空结构的叠层光刻胶牺牲层工艺.讨论了工艺中常遇到的烘胶汽泡、龟裂、起皱、刻蚀电镀种子层时产生的絮状物和悬空结构释放时的粘附等问题,并提出了相应的解决办法.借助于分层刻蚀法和逐步替换法,用叠层光刻胶作牺牲层并利用湿法释放技术,制备得到了长1400 μm、厚6 μm、宽40 μm、悬空高为10 μm的完好的悬臂梁结构.     

基于MgF2波导的谐振型乐甫波器件特性研究

在浅体声波(SSBW)器件上采用真空热蒸发法制备MgF2波导层,研究了器件的频率、插损、质量灵敏度随波导层厚度变化的特性.当波导层厚度约为2.48 μm时,器件的插损最小(-23.93 dB);当波导层厚度约为6.5 μm时,器件获得了最大质量灵敏度416.7 cm2·g-1.并分析了不同沉积速率对薄膜质量的影响.实验结果表明:要制备高质量的薄膜必须采用低的薄膜沉积速率,MgF2薄膜可作为乐甫波器件的波导层材料.     

全金属微电极阵列细胞电融合芯片的研制

研制了以硅为基底、金属铜(Cu)材料作为微电极的细胞电融合芯片.在500 μm厚的硅基底上应用离子刻蚀技术,刻蚀出与所需得到的微电极相同形状的槽,然后高温下使硅片表层形成二氧化硅绝缘层,在刻蚀槽的底部形成种子层(Ta/Cu材料),通过电镀在槽中形成金属微电极,应用湿法刻蚀去除表层硅,得到纯金属微电极.铜金属微电极其导电率高,减小了电压衰减,使细胞电融合芯片中电场分布一致性好.该方法利用刻蚀的硅模具和电镀工艺解决了lift-off制造的金属微电极较薄的难题,分别采用热氧化和等离子增强化学气相淀积(PECVD)工艺制作的二氧化硅薄膜也增强了芯片抗腐蚀能力.在利用黄瓜叶肉细胞的细胞排队和融合实验中,实验效果比现有硅微阵列芯片要好.     

闭环电流检测模块中Z轴TMR传感器的研制

阐述了灵敏方向垂直于芯片表面的Z轴TMR传感器的设计方法,并通过溅射镀膜及刻蚀工艺,在芯片表面电镀厚度、宽度、间距分别为为10 μm、10 μm、15 μm的NiFe聚磁层,研制出了Z轴灵敏的TMR传感器.通过实际测试,该方法制备的传感器在电源电压为5 V时,灵敏度达到了5 mV/Oe,证明了该设计方法的正确性.利用所研制的Z轴TMR传感器,构建了闭环电流检测模块,电流测量范围为0~100 A,测量误差小于0.3%.     

一种用于硅通孔的阻挡层和种子层一体化制备工艺研究

介绍了一种硅通孔中阻挡层和种子层制备的新型工艺方法。利用磁控溅射的方法在SiO2上沉积1μm的Ti膜。表层的Ti膜湿法氧化后作为种子层,底层Ti膜作为阻挡层。填充材料选择Cu,利用电镀的方法填充。利用热退火的方法来测试Cu的扩散性能,即Ti膜的阻挡特性,热退火试验选择350,400,450℃三种不同的温度。XPS结果表明:在400℃及以下温度阻挡层成功阻挡了Cu的扩散。目前已在硅通孔中初步实现此种结构并完成通孔中Cu的填充。     

薄膜线条宽度对坡莫合金AMR性能的影响

利用半导体标准工艺,在8英寸工艺平台上,通过光刻和剥离工艺制备出不同线条宽度的坡莫合金材料Ta(5 nm)/NiFe(12 nm)/Ta(2 nm),然后再进行表面钝化、电极引出和TO-94封装以后进行测试.测试结果表明:在常温条件下,不同薄膜线宽对材料AMR值影响不大,而对薄膜材料的饱和磁感应强度影响巨大.当线宽从1...     

全叉指电极d33模式压电悬臂梁俘能器研究

为了克服表面叉指电极d33模式微机电系统(MEMS)悬臂梁振动俘能器中存在的压电材料极化不完全、存在弯曲电场等问题,提出了一种电极贯穿于整个压电层的全d33模式MEMS悬臂梁振动俘能器.根据机电耦合模型,分析了电极尺寸与材料厚度对压电俘能器输出功率的影响.优化结果表明:当硅基底厚度为20μm、电极宽度1μm时,电极间距最优范围为25～75 μm,PZT材料最优厚度为7μm,归一化后得到功率密度为34.5mWcm-3gn-2.通过在表面叉指电极d33模式俘能器的基础上增加电镀电极工艺,设计了不锈钢基底的全d33模式MEMS俘能器的工艺流程,完成了部分单元工艺.     

MEMS制造中精确测量薄膜厚度的方法研究与比较

精确测量各种功能薄膜的厚度在微机电系统（ MEMS）制造加工过程中有非常重要的意义。利用接触式表面轮廓仪、光谱椭偏仪、电感测微仪、扫描电镜、原子力显微镜和工具显微镜分别测量了10 nm～100μm各种薄膜的厚度。比较了不同测量仪器的测量范围、分辨率和对样品的适用性,分析了薄膜厚度测量过程中误差产生的机理。实验结果表明：当存在膜层台阶时,10 nm～100μm的膜厚测量均可采用接触式表面轮廓仪,对于硬度较高的膜层可采用电感测微仪,对于厚度小于0.5μm的膜层可采用原子力显微镜;对于可观察样品侧面、厚度大于0.7μm的膜层可采用扫描电镜,工具显微镜适用于μm级膜层,对于厚度大于20μm的膜层不宜采用光谱椭偏仪。     

粘接层对PVDF换能器性能影响研究

环氧树脂作为聚偏氟乙烯(PVDF)膜与背衬之间的粘接层将会影响换能器的性能.采用52 μm厚的PVDF压电薄膜制作换能器,以EPO-TEK 301环氧树脂和铜分别作为粘接材料和背衬.通过阻抗分析仪和脉冲回波测试得到PVDF薄膜和换能器的压电性能,并与KLM等效模型的仿真结果进行比较,实验结果与仿真结果基本一致.研究结果表明:随着粘接层厚度的增加,换能器的灵敏度和中心频率将会降低,因此,在PVDF换能器设计制作过程中需合理控制粘接层的厚度.     

LiNbO3棱镜耦合双金属薄膜表面等离子共振传感器

高折射率铌酸锂(LiNbO3)(2.202)为棱镜耦合激发的角度调制型表面等离子共振传感器,利用反射率公式优化单层银膜、金膜和双层银/金膜传感器薄膜的厚度,分别计算了优化厚度的传感器在检测样品折射率为1.330时的共振角、灵敏度、峰值半宽度(FWHM)和品质因数(FOM),理论计算表明:双层金属薄膜,随着金膜厚度的增加,传感器灵敏度增加,但峰值半宽度增加,品质因数下降.综合考虑,选择银/金(41/5)优化组合,传感器品质因数为优化的单层金膜(47 nm)传感器品质因数的2倍以上,另外,与常用的BK7玻璃棱镜耦合相比,LiNbO3棱镜耦合具有较大的样品动态检测范围.优化厚度的传感器实验检测糖水浓度表明:糖水浓度与共振角为线性比例关系.     

Self-Assembly Based on Chromium/Copper Bilayers

In this paper, we detail a strategy to self-assemble microstructures using chromium/copper (Cr/Cu) bilayers. Self-assembly was primarily driven by the intrinsic residual stresses of Cr within these films; in addition, the degree of bending could be controlled by changing the Cu film thickness and by introducing a third layer with either a flexible polymer or a rigid metal. We correlate the observed curvature of patterned self-assembled microstructures with those predicted by a published multilayer model. In the model, measured stress values (measured on the unpatterned films using a substrate curvature method) were utilized. We also investigated the role of two different sacrificial layers: 1) silicon and 2) water-soluble polyvinyl alcohol. Finally, a Taguchi design of experiments was performed to investigate the importance of the different layers in contributing to the stress–thickness product (the critical parameter that controls the curvature of the self-assembled microstructures) of the multilayers. This paper facilitates a deeper understanding of multilayer thin-film-based self-assembly and provides a framework to assemble complex microstructures, including tetherless self-actuating devices. $hfill$[2008-0308]      

Fabrication of symmetrical meandering NiFe/Cu/NiFe film sensors and study of the effects of field direction and film thickness on giant magnetoimpedance

Sandwich NiFe/Cu/NiFe film sensors with symmetrical meandering structure are fabricated by Micro-Electro-Mechanical-System (MEMS) technology, the longitudinal, transverse, and perpendicular giant magnetoimpedance (GMI) effect have been investigated comprehensively. The correlation between film thickness and GMI effect are analyzed thoroughly. The experimental results show that the alternating current (AC) frequency of maximum GMI ratio decreases gradually with the increasing of magnetic layer thickness, but the conducting layer exhibits an opposite tendency. The NiFe and Cu layer both show a GMI ratio tendency from increasing to decreasing along with the increase of film thickness. It is observed the longitudinal, transverse and perpendicular GMI effect share a common characteristic: the AC frequency of maximum GMI ratio increases with the increase of external field intensity. However, there is a notable difference between them, it is demonstrated that the higher GMI ratio and sensitivity can be obtained in the longitudinal direction. The longitudinal GMI ratio reaches the peak value 191.2 % at f _AC = 6.5 MHz under H _L = 17 Oe in six turns sample with the Cu and NiFe thickness of 6 and 7 μm, respectively.     

Magnetic microstructure analysis of sputter deposited permalloy thin films on a spin-on polyimide substrate

We have performed magneto-optical measurements of sputter deposited permalloy (NiFe 81/19) thin films on a polyimide based spin-on substrate and a silicon oxide substrate. Experiments were performed by means of the magneto-optic Kerr effect in order to complement the findings concerning soft magnetic behaviour on the macroscopic scale presented previously (Rittinger et al., Impact of different polyimide-based substrates on the soft magnetic properties of NiFe thin films, SPIE Microtechnologies. International Society for Optics and Photonics, Bellingham, pp 95171R, 2015) with new insights into the magnetic domain structures of such samples. First, magnetization curves (R–H-, B–H-curves) are compared with corresponding magneto-optical hystereses. Second, by taking into consideration the results of the magnetic microstructure analysis, further aspects of the interactions between the substrate and the functional thin film are revealed in form of analogies between observations on the microscopic scale and variations of macroscopic magnetization curves of analysed samples. Furthermore, the shape and detailed spatial arrangement of domains and their boundaries are determined for the investigated samples, supplying further information on the properties and state of stress of the thin films. Doing so, we aim to provide precise and reliable anisotropic magnetoresistive (AMR) sensors on flexible polymer substrates in the future.     

Process Temperature–Dependent Mechanical Properties of Polysilicon Measured Using a Novel Tensile Test Structure

A new test structure was developed to measure three major unknown mechanical parameters of deposited thin films, i.e., fracture strength, Young's modulus, and residual stress. The structure was designed to have plural specimens of a deposited thin film bridging the gap of the silicon substrate and enables the easy and efficient tensile testing of the film. It was used to measure those parameters of various polysilicon films. Polysilicon is commonly used as a structural material of microelectromechanical systems (MEMS) after being deposited at a temperature below 600 degC and annealed at a temperature around 1000 degC to remove the residual stress. On the other hand, polysilicon can be also deposited at a temperature higher than 600 degC. The three parameters of polysilicon films depend on process temperature and were evaluated using the new test structure. Concerning the strength, films deposited at 560 degC had the highest strength when annealed at 850 degC. Films deposited at 625 degC and annealed at 1050 degC were weaker than those deposited at 560 degC and annealed at 1050 degC. Young's modulus was found to behave in a similar way. The trend of the residual stress was the same as already reported, but its local evaluation was possible in combination with the tensile strength determination     

Effects of microstructure on the mechanical properties of copper films for high aspect ratio structures

In this study the mechanical behavior and fracture properties of copper films used in high aspect ratio features of modern microelectronic devices are examined for three different electroplating conditions and yield stresses. Characteristic microstructure of the films is defined using atomic force microscopy and orientation imaging microscopy. Nanoindentation, utilizing continuous stiffness, was used to determine the hardnesses of the copper films, 750–1500 nm in thickness. Nanoindentation and stressed overlayers were then used to induce film delamination to determine the adhesion of the protective tungsten film on copper on a SiO₂ substrate. The dimensions of these delaminations were used in mechanics based models to calculate the interfacial fracture toughness of the interface. Results have shown that as the grain size decreases from 1.9 to 1.1 m the interfacial fracture toughness decreases from 2.6 to 1.4 J/m².The authors wish to thank AMD, Inc for providing the copper samples and the United States Department of Energy and Sandia National Laboratories for funding through the PECASE program (DFB and MJC) under contract DE-AC04–94AL85000.     

Microbridge testing on symmetrical trilayer films

In this paper, we extended the microbridge testing method to characterize the mechanical properties of symmetrical trilayer thin films. Theoretically, we analyzed the deformation of a trilayer microbridge sample with a deformable boundary condition and derived load-deflection formulas in closed-form. The slope of a load-deflection curve under small deformation gives the relationship between the bending stiffness and the residual force of a trilayer microbridge. Taking this relationship, we were able to assess simultaneously the Young's modulus of two kinds of materials composing the symmetrical trilayer film and the thickness-averaged residual stress of the film. Experimentally, we fabricated symmetrical trilayer microbridge samples of SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2/ on 4-inch p-type (100) silicon wafers and conducted the microbridge tests with a load and displacement sensing nanoindenter system equipped with a microwedge indenter. The experimental results verified the proposed microbridge testing method. The thickness-averaged residual stress of the 1.1-/spl mu/m trilayer thin films was determined to be 8.8 MPa, while the Young's modulus of the 0.3-/spl mu/m silicon oxide layers and the Young's modulus of the 0.5-/spl mu/m silicon nitride layer were evaluated to be 31 GPa and 294 GPa, respectively.     

Calibration of residual stress difference of MetalMUMPs silicon nitride films

The metal multi-user MEMS processes (MetalMUMPs) provide one nickel film, two silicon nitride films and one polysilicon film for constructing various nickel MEMS devices. The two silicon nitride films are either bonded together as a bi-layered structure or they sandwich the polysilicon film to form a tri-layered structure to support nickel structures. The residual stress difference of the two silicon nitride films causes undesired deformations of suspended MetalMUMPs devices. In this paper, the residual stress difference of the two MetalMUMPs silicon nitride thin films is calibrated and the result is 169 MPa. The Young’s modulus of the MetalMUMPs nitride films is also measured, which is 209 GPa.     

A new technique for producing large-area as-deposited zero-stressLPCVD polysilicon films: the MultiPoly process

Polysilicon films deposited by low-pressure chemical vapor deposition (LPCVD) exhibit tensile or compressive residual stresses, depending on the deposition temperature. Polysilicon films composed of alternating tensile and compressive layers can display any overall stress value between those of the individual layers, including a state of zero overall residual stress, depending on the relative thickness of each layer. The residual stress gradient can be similarly controlled by the layer thicknesses and distribution. This has been demonstrated with a ten-layer near-zero stress (<10 MPa), near-zero stress gradient (⩽0.2 MPa/μm) polysilicon film, containing flat cantilever beams whose length-thickness ratios exceed 150. Using multilayer deposition to control the stresses and stress gradients of polysilicon films is termed the MultiPoly process     

Pressure nonlinearity of micromachined piezoresistive pressure sensors with thin diaphragms under high residual stresses

Thermal residual stress plays a significant role in the performance of microelectromechanical system (MEMS) pressure sensor devices. For example, the voltage span and pressure nonlinearity (PNL) on the voltage output of a pressure sensing element can be significantly affected by the residual stresses of passivation films on the silicon diaphragm. The objective of this study is to resolve a pressure nonlinearity problem in terms of silicon nitride residual stress and diaphragm thickness in order to meet the PNL design criteria within ±3% at 25 °C. The curvatures of wafers were measured and the film residual stresses were calculated. Finite element analyses (FEA) were conducted and correlated with the PNL experimental tests. To build a design window for optimization, a central composite design (CCD) method was utilized to significantly reduce the number of FEA runs. It is concluded that the residual stress of PECVD silicon nitride needs to be optimized and controlled in order to reduce the pressure nonlinearity.     

一种用于测试坡莫合金薄膜机械性能的拉伸模型

坡莫合金(Ni80Fe20)薄膜是微机电系统常用的磁性材料之一.介绍了一种用于测试其机械性能的单轴拉伸试验模型.此模型的特点是微小试件两端固定、且与加载机构集成在基片上,从而可减少操作工作量、提高对准精度.整个机构以微细加工方法制成:坡莫合金拉伸试件以光刻和电镀技术成型,其余的加载机构以湿法蚀刻制成.实验表明:使用此机构可以简单且高精度地对薄膜试件进行拉伸试验,获得多项力学性能参数,从而为MEMS器件设计和分析提供可靠的理论基础.