【作者】 金如龙；

【导师】 孙洪波； 衣茂斌；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2012， 博士

【摘要】 集成电路的高速发展给集成电路芯片检测技术带来了巨大的挑战。电光探测作为一种电场探测的光学手段，由于其高响应速率(达到THz)、高空间分辨率和电场无侵扰等特性，引起人们的广泛关注。电光探测的机理是电介质材料的电光效应，即折射率在外加电场的作用下发生变化。电光探测通常把一小块电光晶体或极化聚合物附着在导光的石英锥或光纤的端面，然后把电光材料送到集成电路测量点的发散场中，发散场引起电光材料的折射率变化，从而通过干涉或检偏等方法把折射率变化测量出来，然后就可以推算出集成电路内部的电压信号。然而，电压定标困难和低的电压灵敏度始终是电光探测技术实用化的障碍。本论文的主要研究内容是围绕这两方面展开的。电压定标是电光探测的一个技术瓶颈，即很难通过测量到的电光信号的幅值来确定集成电路内部节点或传输线上的电压绝对值。原因主要有两个：芯片测量点的发散场分布与电路的布局布线有关；由于集成电路表面形貌的起伏、电光探头的不平整性和电光探头定位精度等原因，使得电光材料与被测量点之间不可避免地存在空气隙，而且空气隙厚度是不可控的。为了分析电压定标的具体问题，我们用有限差分法对集成电路表面的电场分布进行模拟。计算结果得知，电光材料厚度要小于或等于测量点与邻近互连线的间距，才能有效消除布线布局的影响；由于发散场分布在电路表面几微米处，只要有亚微米量级的空气隙对集成电路的定标造成巨大影响。针对空气隙问题，我们创新地提出参考电压法，即在电光材料的上表面引入已知的标准信号，用已知信号为被测信号定标。实验上，我们制作了以GaAs晶体为场敏感材料的电光探头，又设计了共面波导来模拟不同的集成电路。实验结果表明参考电压法的定标误差小于6%，基本满足集成电路检测要求。另一项研究内容是提高电光探测的电压灵敏度。传统电光晶体的电光系数很低，通常只有几pm/V，而且具有较大的介电常数，把集成电路发散场的大部分都屏蔽在空气隙内，因而造成电光转化效率很低。为了提高电压灵敏度，本论文提出了三种方法：1、利用电光材料的声学共振现象；2、利用极性液体分子的取向极化效应；3、利用聚合物稳定的手性液晶的巨大电光系数。首先，利用声学共振的方法提高电压灵敏度。本论文中，在理论上阐明电光材料是一定具备逆压电效应，而且通常情况下逆压电效应要比电光效应弱。然而，在外电场频率接近电光材料的压电共振频率时，逆压电效应的强烈形变可以辅助增强电光探测的电压灵敏度。实验上，通过GaAs电光探头的频率响应特性的测量，展示了逆压电共振现象并且在共振峰附近可以提高电压灵敏度两个量级以上。为了进一步证实共振效应，我们在电光探头上加不同重量的金属环，实验结果发现共振频率随外加重量增加而向低频移动，符合压电振子模型的理论。另外，ZnO多晶薄膜被引入到压电共振提高电压灵敏度的电光探测中。虽然ZnO薄膜电光系数很小，但是具有高的逆压电系数。实验上，采用磁控溅射的方法外延生长ZnO薄膜。经过生长条件摸索，在溅射功率为100W、基片温度为250℃和氩氧比为2：1的条件下，ZnO有较好的C轴取向和薄膜质量。同样，利用ZnO电光探头也测量到逆压电增强的频率曲线。因此在实际集成电路检测中，可以制作特定共振频率的电光探头用于故障诊断。其次，利用极性液体的取向极化来提高电光探测的电压灵敏度。液体的本质特性起到两个作用：一是由于液体的流动性解决了固体电光探测与被测点之间不可避免存在空气隙的问题；二是较大的电光系数可以进一步提高电压灵敏度，因为理论上极性液体的分子取向极化率要比无机晶体的离子位移极化或极化聚合物的电子位移极化大几个数量级。在实验上，我们设计了测量液体电光系数的光学系统，并测量了多种极性液体的电光系数。测量得到极性液体二甲基甲酰胺(DMF)的电光系数较大，达到250pm/V左右。此外，液态膜的电光探测结构使得被测电路和电光材料为一个整体，解决了困扰固体探头的探头定位问题。实验结果显示液态膜电光探测的电压灵敏度达到毫伏量级，在同一电学系统中至少比GaAs电光探头提高两个量级。另外，我们实验发现液态膜具有一阶电光效应的特性，而一阶电光效应只存在于没有反演对称中心的材料中。通过锁相放大器分频放大的方法把一阶和二阶电光调制信号分开，并分析出这两个信号的起源。实验发现液态膜的一阶和二阶电光效应都具有大的电光系数和低的响应频率等特点。根据这种电光效应的特性，我们提出液态膜一阶电光效应的物理模型：在电场的诱导下极性分子发生取向性的集聚，从而破坏了液体原有的各向同性。我们用红外吸收谱分析极性液体内在微观结构在电场作用下的变化。实验上，在脉冲电场的作用下，液体的吸收谱下降，并且这种变化能维持较长一段时间，从而证实了我们提出的物理模型。第三，利用聚合物稳定的手性液晶的巨大电光系数来提高电光探测的电压灵敏度。根据氟化液晶的低驱动电压、低粘度系数等优点，我们选择混合氟化液晶WTK83100和有较大折射率差的液晶单体5CB作为液晶主体材料。在不同的手性掺杂剂浓度下，制备出液晶聚合物并测量其电光系数。综合考虑液晶聚合物的稳定性和透明性等问题，实验上优化选择的手性液晶的螺距是1.2μm左右，其电光系数达到了7.2×10-9m/V2。我们把这种液晶聚合物用于电光探测，探头结构和液态膜类似，并实现了对短路和断路故障电路的测量。用Labview自动化软件控制对10μm线宽的叉指电极进行二维扫描电压定标探测，实验结果符合实际电压分布，且测量空间分辨率达到了1.25μm。更多还原

【Abstract】 The fast-growing integrated-circuit （IC） industry brings great challenges into chipdetection. Electrooptical detection is now being considered as a powerful andattractive option for high precision local electric field measurement, primarily due toits unique merits like large intrinsic bandwidths （DC to THz）, noninvasiveness andhigh spatial resolution. The core component of an electrooptical probe is a tiny pieceof electrooptical film consisting either of polymers or semiconductor crystals, affixedto the tip of a tapered waveguide or a fiber. If the optical performance of the film, e.g.,refractive index or birefringence, is affected by external electric field, the probe isfeasibly implemented as a proximity electric field sensor, functioning when it isbrought to the immediate surface of an integrated circuit （IC）. Waveform of theelectric signal at a particular site of the IC is thus attainable by measuring the phasemodulation of a laser beam traveling through the film on the probe. This makes theelectrooptical detection a promising tool for IC fault diagnosis and designimprovement.Nevertheless, a drawback of electro-optical detection that is hindering itspractical use is the inherent difficulty in calibrating the voltage magnitude. Althoughsome proposals try to overcome the complexity, they are not applicable to theelectrooptical detection using an external probe. It is difficult to correctly determinethe value of the applied voltage because of the emanating field divergence from an ICcircuit line and the uncertainty of the physical contact between the probe tip and thecircuit. The former, associated with the IC layout, local routing, line width andspacing, is caused by interruption of neighbored nodes or lines. The latter is inevitablein different runs of each voltage measurement process since no appropriate and finedistance monitoring or feedback mechanism has been found for such system. Atip-grounded waveguide micro-sensor was proposed to overcome the difficulty of quantitative voltage calibration in electrooptical detection for integrated circuits test.On this basis, we optimized the thickness of the electrooptical material of the sensorto eliminate the influence of the circuit layout on the measured signals by fringe fieldsimulation. The improved sensor in return made it possible to calibrate the voltagewith known reference electric signals quantitatively. This method circumvented theuncertainty of the probe conditions of each measurement point. Finally, a calibrationaccuracy of better than6%was obtained, which satisfied broad applications inintegrated circuit industry.Another essential drawback of electro-optical detection is low voltage sensitivity,primarily due to （i） the electrooptical coefficients γijof crystals are generally small, atthe order of several pm/V;（ii） the emanating field from circuits are subject tosignificant decay by the air gap between the electrooptical probe and the circuit undertest because of the nature of the non-contact detection mode and the existence of thepassivation layer of the circuit surface. In this dissertation，we has made threeproposals to increasing voltage sensitivity:（i） acoustic resonant effect of inorganiccrystals;（ii） molecular orientation effect of polar liquids;（iii） the large Kerr effect ofpolymer-stable liquid crystals.First, we solve the voltage sensitivity problem with the help of the acoustic （e.g.,piezoelectric and electrostrictive） effect, a common property of almost all dielectrics.In contrast to the general electro-optic effect, the light phase modulation induced bythe acoustic effect is two orders of magnitude stronger at its resonant frequency, as weobserved in a GaAs thin film probe. Furthermore, this novel method shows a highlyreproducible linearity between the detected signals and the input voltages, whichfacilitates the voltage calibration. Beside, we introduced ZnO films of highpiezoelectricity to the electro-optical detection. ZnO thin films were epitaxiallydeposited on the tip of a tapered waveguide using a radio frequency magnetronsputtering method. Although the electro-optical coefficient was evaluated as only0.2pm/V, ZnO films exhibits high sensitivity in electro-optical detection due to thepizeo-rensonance. Second, efforts have therefore been devoted to exploration of novel electroopticalmaterials. Electrooptical polymer, due to the γijas high as of the order of hundreds ofpm/V has shown a promising prospect to enhance the sensitivity. However, problemsassociated with the polymer film are low abrasive resistance and weak adhesion to theglass cone, so that the probe is difficult to endure high-speed, multi-point, large areadetection as an atomic force microscopic tip does. In addition, the air gap between theelectrooptical probe and the measurement point still can’t be eliminated. In thisdissertation, we propose a novel electro-optical probe mechanism, which useliquid-state polar molecules as the sensing film, which is coated onto the circuitsurface, instead of being affixed to the scanning tip end. An electro-optical probeconfiguration with polar molecule liquids as the sensing film was designed forelectro-optical detetion. This scheme has not only eliminated the air gap, but also usedmolecular orientation as a response to the electric field excitation, leading to asensitivity of0.1mV/√Hz. This method exhibited voltage sensitivity enhancement oftwo orders of magnitude larger than the normal method using a GaAs probe in thesame measurement system. Based on the mechanism of orientation polarization, theelectro-optic coefficient was measured to be250pm/V by Teng-Man method atmodulation field of100Hz. This technology will be promising in applications oflow-frequency field detection. We present an anomalous electro-optic effect in polarliquid films: liquids, usually considered to be isotropic, possess the linearelectro-optic effect that occurs only in materials lacking inversion symmetry. Due tothe observed large effect in the low-frequency range and slow response speed, thisstrange effect was thought to come from the field-induced orientation of large mass.Therefore, we brought forward a physical model that contributed to the interpretationof this phenomenon: field-induced pre-oriented, short-range orderly dipole clusters inliquid films break the macroscopic symmetry and results in this asymmetric effect.Finally, combined with spectral analysis, the formation of clusters induced by anelectric pulse was proved.Third, polymer-stabilized liquid crystals （PSLC） with experimentally observed large electro-optic effect are introduced to the electro-optical detection to improve thevoltage sensitivity. The Kerr constant of materials prepared in this study reached ashigh as7.2×10^-9 m/V², increasing the sensitivity by1000times than the conventionalelectro-optical materials. The noncontact detection configuration, using the laser beamas a probe, enables quick2-demension scanning measurements. This detection meansoffers several advantages including the following:（1） it uses the focused laser beamas a probe, which overcomes the complexity of the precision positioning ofconventional external probes;（2） due to the fluidity of PSLC materials before curing,field sensing materials could closely contact with the circuit surface,（3） an ITO layeris introduced to screen all the fringing electric field of the given circuit in the PSLCmaterial so as to further enhance the voltage sensitivity.更多还原