基于频率调制与分振幅解调的广义光谱椭偏技术

提出了一种基于频率调制与分振幅解调的广义光谱椭仪方案,与现有时间调制型与时频混合调制型广义光谱椭偏技术相比,其不含运动部件与电控元件,可实现被测样品全部16个Mueller矩阵元素光谱的实时测量。与现有频率调制型广义光谱椭偏技术相比,其测量结果的光谱分辨率更高且降低了通道串扰产生的概率。

基于弹光调制的椭偏测量驱动电路系统设计

随着椭偏测量技术的发展,对椭偏测量速度、测量范围有了更高的要求。针对传统的双旋转补偿器测量方法受限于机械限制,调制频率低的问题。采用弹光调制技术,利用调制器的快轴旋转取代传统的旋转补偿器,设计了一种基于LC谐振放大的双驱动电路,利用现场可编程门阵列(FPGA)实现对弹光调制器(PEM)的高速驱动控制。根据弹光调制驱动控制要求对电路设计思路和方法进行了详细分析。通过仿真和实验结果表明,所设计的电路系统输出频率能稳定控制在60 kHz,幅值能达到430 VPP以上,满足PEM快轴高速稳定驱动的需求。

广义椭偏仪双补偿器任意比例旋转控制系统

针对目前广义椭偏仪双旋转补偿器控制旋转比例单一的问题,提出一套基于STM32单片机与步进电机的广义椭偏仪双补偿器任意比例旋转控制系统。该系统采用STM32F1单片机进行编程控制两个步进电机旋转的基础速度、速度比、旋转光学周期数,并通过LabVIEW软件进行编程,获得与之配套的上位机控制系统,完成双补偿器的任意比例旋转控制。通过搭建的广义椭偏实验系统采集双补偿器不同转速比下对空气样本测量的图像,并将其中转速比为5∶3的数据采集结果与理论空气样本波形进行归一化处理。结果显示,实际空气穆勒矩阵与理论穆勒矩阵元素的最大误差为0.014,平均误差为0.004 3,验证了该系统具有较高的可靠性与测量精度。

宽光谱穆勒矩阵椭偏技术的拓展应用

为了解决现有光谱穆勒矩阵椭偏检测仪的测量功能固定、不能根据实验需求满足更多物理量测量的问题,提出了结合多物理场光学仿真与宽光谱穆勒矩阵椭偏测量数据,以实现更多参数测量的新方案。以膜厚测量为实例,通过比较硅基底上不同厚度、不同入射角下,二氧化硅薄膜仿真值与椭偏仪实验测量值所得穆勒矩阵的匹配度,得到均方误差值相对最小时的二氧化硅薄膜厚度值。结果表明,所得膜厚结果与实际值符合得较好。该研究验证了光谱穆勒矩阵椭偏测量与仿真模拟相结合方法的可行性和有效性。

薄膜多参数测量系统设计及实验

设计薄膜多参数测量系统,对薄膜在制备后膜厚、厚度分布及薄膜残余应力等表征薄膜制备效果的参数同时进行测量,减少测量误差。通过分析椭偏测量、光谱测量和激光测量技术,设计薄膜多参数测量系统,并搭建测量系统。为验证该系统,通过RC2和设计系统对不同厚度的SiO_(2)薄膜和Ta_(2)O_(5)薄膜进行测量对比实验,表明设计系统对不同薄膜厚度的测量偏差均小于0.3 nm,厚度分布测量偏差值小于0.06%;通过ZYGO激光干涉仪和设计系统对不同直径的薄膜进行对比测试实验,表明该系统的测量偏差在±1°以内。测量系统能够满足薄膜制备后对不同参数同时测量的测量需求,简化了测量过程。

非晶氧化铝薄膜结构及其不同色散模型光谱椭偏对比研究

针对非晶态氧化铝纳米薄膜材料性能预测难度较大的问题,本文提出一种基于光谱椭偏技术的不同色散模型对比分析方法,用于测算纳米薄膜的结构和光电特性。通过建立Tauc-Lorentz和Forouhi-Bloomer色散模型,系统地研究了原子层沉积技术制备的氧化铝薄膜的物相结构、微观形貌和光电特性。结果表明,该薄膜具有无定型结构,表面光滑无裂纹。不同模型获得的结构参数及光电常数并不一致,Forouhi-Bloomer模型得到薄膜厚度与扫描电子显微镜测量的结果更接近,而Tauc-Lorentz模型的粗糙度更符合原子力显微镜测试结果。Tauc-Lorentz模型提取的带隙结果与Tauc法外推出的禁带宽度均保持在3 eV左右。根据分析发现,结构参数的差异主要是由于模型间数学处理方式和参数描述差异导致的,光电参数的不同主要源于模型推导过程中假设条件和收敛特性的差异。

超高速快轴旋转圆形弹光调制技术研究

针对目前广义椭偏测量速度受限问题,提出利用对称性更优的圆形弹光调制器代替机械旋转补偿器实现超高速测量。对弹光调制器内部受力进行理论研究,得到纯行波模式调制条件并利用COMSOL仿真验证。仿真结果表明,当弹光调制器处于纯行波调制模式时可视为一种快轴方向高速旋转的相位调制器。通过建立阻尼弦振动模型分析不同快轴方向下弹光晶体表面振动位移分布,提出一种弹光调制器在纯行波调制模式下的中心支撑方式用于实验。实验结果表明弹光调制器的快轴以f/2的角速率做圆周运动。同时验证了中心支撑方式可确保弹光调制器谐振后所受阻力均匀且最小,达到最佳支撑效果。研究结果可用于后续广义椭偏测量及各类高速偏振调制领域。

Optical simulation of external quantum efficiency spectra of CuIn_(1-x)Ga_xSe_2 solar cells from spectroscopic ellipsometry inputs

Applications of in-situ and ex-situ spectroscopic ellipsometry （SE） are presented for the development of parametric expressions that define the real and imaginary parts （ε1, ε2） of the complex dielectric function spectra of thin film solar cell components. These spectra can then be utilized to analyze the structure of complete thin film solar cells. Optical and structural/compositional models of complete solar cells developed through least squares regression analysis of the SE data acquired for the complete cells enable simulations of external quantum efficiency （EQE） without the need for variable parameters. Such simulations can be compared directly with EQE measurements. From these comparisons, it becomes possible to understand in detail the origins of optical and electronic gains and losses in thin film photovoltaics （PC） technologies and, as a result, the underlying performance limitations. In fact, optical losses that occur when above-bandgap photons are not absorbed in the active layers can be distinguished from electronic losses when electron-hole pairs generated in the active layers are not collected. This overall methodology has been applied to copper indium-gallium diselenide （Culn1-xGaxSe2; CIGS） solar cells, a key commercialized thin film PV technology. CIGS solar cells with both standard thickness （〉2 μm） and thin （〈1 μm） absorber layers are studied by applying SE to obtain inputs for EQE simulations and enabling comparisons of simulated and measured EQE spectra. SE data analysis is challenging for CIGS material components and solar cells because of the need to develop an appropriate （ε1, ε2） database for the CIGS alloys and to extract absorber layer Ga profiles for accurate structural/compositional models. For cells with standard thickness absorbers, excellent agreement is found between the simulated and measured EQE, the latter under the assumption of 100% collection from the active layers, which include the CIGS bulk and CIGS/CdS heterojunction interface layers. For cells with thin absorbers, however, an observed difference between the simulated and measured EQE can be attributed to losses via carrier recombination within a- 0.15 μm thickness of CIGS adjacent to the Mo back contact. By introducing a carrier collection probability profile into the simulation, much closer agreement is obtained between the simulated and measured EQE. In addition to the single spot capability demonstrated in this study, ex-situ SE can be applied as well to generate high resolution maps of thin film multilayer structure, component layer properties and their profiles, as well as short-circuit current density predictions. Such mapping is possible due to the high measurement speed of 〈1 s per （ , 4） spectra achievable by the multichannel ellipsometer.

Mixed polarization in determining the film thickness of a silicon sphere by spectroscopic ellipsometry

The effect of a spherical shape on the measurement result of spectroscopic ellipsometry （SE） is analyzed, and a method to eliminate this effect is proposed. Based on the simulation result of the SE measurement on a silicon sphere by ray tracking, we find that the sphere makes the parallel incident beam of the SE be divergent after reflection, and the measurement error of the SE caused by this phenomenon is explained by the mixed polarization theory. By settling an aperture in front of the detector of the SE, we can almost eliminate the error. For the silicon sphere with a diameter of 94 mm used in the Avogadro project, the thickness error of the oxide layer caused by the spherical shape can be reduced from 0.73 nm to 0.04 nm by using the proposed method. The principle of the method and the results of the experimental verification are presented.

Optical study of Ba(Mn_xTi_(1-x)O_3) thin films by spectroscopic ellipsometry

Stoichiometric Ba（MnxTi（1-x）O3） （BMT） thin films with various values of x were deposited on Si（111） substrates by the sol-gel technique. The influence of Mn content on the optical properties was studied by spectroscopic ellipsometry （SE） in the UV–Vis–NIR region. By fitting the measured ellipsometric parameter （Ψ and Δ） with a four-phase model （air/BMT＋voids/BMT/Si（111））, the key optical constants of the thin films have been obtained. It was found that the refractive index n and the extinction coefficient k increase with increasing Mn content due to the increase in the packing density. Furthermore, a strong dependence of the optical band gap Eg on Mn/Ti ratios in the deposited films was observed, and it was inferred that the energy level of conduction bands decreases with increasing Mn content.

ELLIPSOMETRY MEASUREMENT ON ANISOTROPIC FILM AND CRYSTAL

In this paper, a method of light intensity mode ellipsometry for optical constant measurement on anisotropic films and crystals is studied. Softwares for this method have also been developed Based on the theories and correspond softwares, experiments are carried out carefully for anisotropic film and bulk samples with optical axis parallel to their surface as well as optical axis perpendicular to the surface. Moreover, the discrepancy between measured data and calculated results are also analyzed. The measurement system developed in this paper is powerful to measure optical parameter of anisotropic film and bulk samples.

Applying ellipsometry to studying the effect of two kinds of rare earth metal salts on anodizing aluminum alloy

The effects of rare earth metal salts (REMs), cerium(IV) salt and lanthanum (III) salt, on the property of anodized coating of LD10 aluminum alloy are studied by corrosion tests including neutral salt spray test and copper accelerated acetic acid immersion test, polarization curves measurement, energy dispersion analyzer of X-Ray(EDAX) analysis, and in situ ellipsometry. The results show that the addition of either of the two REMs in anodizing solution hardly changes the composition of an anodized coating, while increases the thickness of barrier part and reduces the porosity of porous part, which contributed to the improvement of the corrosion resistance of the anodized coating. The results also demonstrate that the effect of cerium salt was better than that of lanthanum salt.

Error Corrected Sub-Monolayer Ellipsometry for Measurement of Biomolecular Interactions

Already in 1946 Alexandre Rothen from the Rockefeller Institute for Medical Research, New York published the use of ellipsometry for the measurement of antigen-antibody interactions. And he found some effects that could not be explained by the assumption that the interaction of the molecules is only of chemical nature. 55 years later we started research on antibody-antigen interaction and found similar results. To make sure that these measurements are not produced by measurement artifacts, each component of our measurement technique is error analyzed and error corrected if necessary. With such type of error corrected instrumentation we found, that there must be an interaction between antigens and antibodies that is based on longitudinal electromagnetic waves, which are able to work through thin 7 nm membranes. A similar interaction is found for the virus-antigen interaction. Our measurement results are in contrast to the assumption that the antigen-antibody and antigen-virus interaction is only of chemical nature.

Rotating polarizer, compensator, and analyzer ellipsometry

In this paper we propose theoretically a set of ellipsometric configurations using a rotating polarizer, compensator, and analyzer at a speed ratio of N1ω：N2ω：N3ω. Different ellipsometric configurations can be obtained by giving different integral values to N1, N2, and N3. All configurations are applied to bulk c-Si and GaAs to calculate the real and imaginary parts of the refractive index of the samples. The accuracies of all ellipsometric configurations are investigated in the presence of a hypothetical noise and with small misalignments of the optical elements. Moreover, the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are studied. The comparison among different configurations reveals that the rotating compensator–analyzer configuration corresponds to the minimum error in the calculated optical parameters.

Identification of Optical Transitions by Spectroscopic Ellipsometry (SE) on CuIn₃Se₅Bulk Compounds

Bulk materials were synthesized by the Bridgman technique using the elements Cu, In and Se. These samples were characterized by Energy Dispersive Spectrometry (EDS) to determine the elemental composition, as well as by X-ray diffraction for structure, hot point probe method for type of conductivity, Optical response (Photoconductivity) and Photoluminescence (PL) to determine the band gap value and Spectroscopic Ellipsometry to find energy levels above the gap in the band scheme at room-temperature. They show a nearly perfect stoechiometry and present a p-type conductivity. CuIn3Se5 either has a Stannite structure, an Ordered Defect Chalcopyrite structure (ODC), or an Ordered Vacancy Chalcopyrite structure (OVC). The gap energy obtained for the different samples was 1.23 eV. Energy levels above the gap in the band scheme were determinate by measuring the dielectric function at room temperature for energies lying between 1.5 and 5.5 eV. Many transitions were observed above the gap for different samples. Spectroscopic Ellipsometry gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum.

Terahertz Bessel Beam Applied to Thickness Measurement of Ellipsometry Methods

This paper introduces a Terahertz (THz) ellipsometer thickness measurement method based on Bessel beams. The ellipsometry method is used to measure the thickness of film in the THz band. And the thickness of film could be measured in the range of hundreds of microns which the measurement of film thickness by ellipsometer is usually only a few hundred nm in visible light. In addition, the photon energy of the THz-wave is very low and has little damage to the film. The THz Bessel beam has the characteristics of self-healing and diffraction-free. It can make the film thickness measurement within the diffraction-free distance, which is conducive to the flexibility of the ellipsometer system. We use a multi-frequency method to measure film with two-dimensional finite different time domain (FDTD) to numerical simulation analysis of light intensity successfully.

Spectroscopic Ellipsometry Study of the Dielectric Function of Cu(In_1–xGa_x)₃Se₅Bulk Compounds: Identification of Optical Transitions

Using Spectroscopic Ellipsometry (SE), the optical properties of Cu(In1−xGax)3Se5 bulk compounds, grown by the Bridgman method, were analyzed by varying x composition (0 ≤ x ≤ 1). Energy levels above the gap in the band scheme were determined by measuring the complex dielectric function ?at room-temperature for energies between 1.5 and 5.5 eV using a variable angle of incidence ellipsometer. The transitions values E1, E2 and E3 were observed above the gap for different samples of Cu(In1−xGax)3Se5 alloy. When a gallium atom replaces an indium atom, one assumes globally that the levels related to selenium and copper are unchanged. Conversely, the levels corresponding to the conduction band are shifted towards higher energies. Thus, the gap increases as the composition of gallium increases. Spectroscopic Ellipsometry (SE) gave evidence for the interpretation of the choice of gap values which were compatible with that obtained from solar spectrum. Several other characterization methods like Energy Dispersive Spectrometry (EDS), hot point probe method, X-ray diffraction, Photoluminescence (PL), Optical response (Photoconductivity) were presented in this paper. The Cu(In1−xGax)3Se5 have an Ordered Vacancy Chalcopyrite-type structure with lattice constants varying as a function of the x composition. The band gap energy of Cu(In1−xGax)3Se5 compounds is found to vary from 1.23 eV to 1.85 eV as a function of x.

Characterization of Nanorod Structure Using Spectroscopic Ellipsometry

We investigate the resonance modes of gold nanorods on an Indium tin oxide (ITO) coated glass substrate using spectroscopic ellipsometry. The unit cell of the structure investigated is composed of two gold nanorods with differing lengths. In such a structure, we can excite the bright resoance and the dark resonance modes. Numerical simulation of the gold nanorod on substrate was performed with the bright resonance mode at 825.0 nm and the dark resonance mode at 1107.1 nm respectively. Using spectroscopic ellipsometry we optically characterize the fabricated gold nanostructure, with the bright resonance mode at 700.0 nm and the dark resonance mode at 1350.0 nm respectively. The experimental results from ellipsometry show a good agreement with the results from simulation.

SnTe纳米薄膜的椭圆偏振光谱研究

SnTe纳米薄膜材料光学常数的准确获取,对于其在高性能光电器件设计和在光电子领域的潜在应用具有重要的意义。然而,目前仍然很少有关于获取其纳米薄膜光学常数方法的相关研究报道。采用磁控溅射法以SnTe单靶为靶材,在石英衬底上制备了SnTe纳米薄膜;在未加衬底温度和未进行退火处理的条件下,通过制备工艺参数优化,即得到晶化的、组分可控的面心立方结构SnTe纳米薄膜。采用椭圆偏振光谱法,建立不同的拟合模型结构,利用SE数据库中的SnTe材料数据列表和Tauc-Laurents模型对所制备的SnTe纳米薄膜材料的膜厚、组成及折射率、消光系数等光学常数进行了研究。结果显示,具有该厚度的SnTe纳米薄膜材料在可见光波段具有较高的折射率、在可见到近红外具有较宽的光谱吸收。

基于光谱干涉椭偏法的薄膜厚度测量

薄膜厚度的测量在芯片制造和集成电路等领域中发挥着重要作用。椭偏法具备高测量精度的优点,利用宽谱测量方式可得到全光谱的椭偏参数,实现纳米级薄膜的厚度测量。为解决半导体领域常见的透明硅基底上薄膜厚度测量的问题并消除硅层的叠加信号,本文通过偏振分离式光谱干涉椭偏系统,搭建马赫曾德实验光路,实现了近红外波段硅基底上膜厚的测量,以100 nm厚度的二氧化硅薄膜为样品,实现了纳米级的测量精度。本文所提出的测量方法适用于透明或非透明基底的薄膜厚度测量,避免了检测过程的矫正步骤或光源更换,可应用于化学气相沉积、分子束外延等薄膜制备工艺和技术的成品的高精度检测。