Polarization modulation imaging ellipsometry for thin film thickness measurement

A polarization modulation (PM) imaging ellipsometer is proposed and setup in order to measure precisely the thickness of thin film. Five images are collected sequentially by CCD camera with respect to five pre-determined azimuth angles of a quarter wave plate (QWP) during measurement. Then two-dimensional (2-D) distributions of the ellipsometric parameters ψ and Δ over the full dynamic range are obtained. Conceptually, PM imaging ellipsometer integrates the features of phase shift interferometry with conventional photometric ellipsometry by rotating the QWP sequentially to produce polarization modulation that is able to measure the thickness of a thin film in two dimensions precisely and quickly. The basic principle of PM imaging ellipsometer is derived wherein features such as common path configuration, full dynamic range of measurement, and insensitive to non-uniform response of the CCD are analyzed. The experimental results verify the ability and performance of PM imaging ellipsometer on 2-D thin film thickness, while the errors regarding the ellipsometric parameters measurements are discussed.     

基于激光外差干涉术的薄膜厚度测量方法

针对光学薄膜厚度测量困难问题，提出了一种基于激光外差干涉术的薄膜厚度测量方法。采用经典迈克尔逊干涉光路，利用外差干涉原理将薄膜厚度差转换为光程差，以精密位移平台为扫描机构实现薄膜厚度的逐行扫描测量。测量系统在恒温实验条件下20 min内的漂移不超过8 nm，测量结果平均差小于1 nm，通过与椭圆偏振仪的测量结果比较，测量差值为12.97 nm，表明了该方法的可行性。     

A modulated ellipsometer for studying thin film optical properties and surface dynamics

A modulated ellipsometer has been constructed for the study of the optical properties of thin films deposited and maintained in a variety of controlled environments. The ellipsometric technique involves a photoelastic device which modulates the state of polarization of the light beam. Quantities related to the ellipsometric parameters ψ and Δ are extracted simultaneously by synchronous detection of reflected light intensities in two different frequency channels. Signal processing is completed by an on-line computer which samples data at a repetition rate of approximately one data set per second. Once the optical system is aligned, all elements remain rigidly in place; hence, the precision and stability are high. In terms of ψ and Δ, the precision is of the order of 0.001° and stability over one hour is of the order of 0.01°. Various systematic uncertainties limit the absolute accuracy of the measured optical constants to a few percent for high reflectivity materials. Because of its speed, precision, and stability, this ellipsometer is suited both to comparison measurements of samples prepared under different conditions and to time-lapse measurements of a single film in order to observe annealing, gas adsorption, or surface corrosion in process. Preliminary experimental results are presented.     

Thickness dependent optical properties of titanium oxide thin films

TiO₂ thin films of different thickness were prepared by the Electron Beam Evaporation (EBE) method on crystal silicon. A variable angle spectroscopic ellipsometer (VASE) was used to determine the optical constants and thickness of the investigated films in the spectral range from 300 to 800 nm at incident angles of 60°, 70°, and 75°, respectively. The whole spectra have been fitted by Forouhi–Bloomer (FB) model, whose best-fit parameters reveal that both electron lifetime and band gap of TiO₂ thin film have positive correlation to the film thickness. The refractive indices of TiO₂ thin film increase monotonically with an increase in film thickness in the investigated spectral range. The refractive index spectra of TiO₂ thin films have maxima at around 320 nm and the maxima exhibit a marginally blue-shift from 327.9 to 310.0 nm with an increase in film thickness. The evolution of structural disorder in the TiO₂ thin film growth can be used to explain these phenomena.     

Dual-frequency paired polarization phase shifting ellipsometer

A novel dual-frequency paired polarization phase shifting ellipsometer (DPPSE) is proposed and experimentally demonstrated. It combines the features of the phase shifting interferometer and common-path polarized heterodyne interferometric ellipsometer where the ellipsometric parameters (EP) of a specimen are measured accurately. The experimental results verify that DPPSE is capable of determining the full dynamic range of EP. In addition, the properties of dual-frequency paired linearly polarized laser beam in DPPSE perform in common phase noise rejection mode. It is insensitive to environmental disturbance and laser frequency noise. The capability of DPPSE to perform higher accuracy EP measurement than conventional ellipsometer is verified according to error analysis.     

双层光学薄膜参数的多入射角椭偏分析方法

本文讨论了多入射角椭偏测量中光学参数的误差因子以及最佳测量条件的选取.指出,当薄膜较厚时,多入射角椭偏测量可以精确确定膜系的光学常数和几何厚度,并用二例实测结果加以证实.本文的方法也适用于分析多层光学薄膜.     

纳米厚度薄膜外差椭偏测量技术的研究

结合激光外差干涉法和透射式椭偏测量原理,研究了一种快速、高精度测量纳米厚度薄膜光学参数的方法。计算并分析了复灵敏度因子随薄膜参数和入射角度的变化规律、椭偏参数的选择及容许测量误差。两个声光调制器产生20kHz的拍频,采用简单的直接比相方法即可获得优于0.1°的相位分辨率,而且测量系统中没有使用任何波片和运动部件,抗干扰能力强且测量过程完全自动化,适用于工业现场在线连续测量。实验数据和理论分析表明,此方法可以达到亚纳米级测量精度。     

一种最小化薄膜光学参数表征偏差的椭偏测量系统误差处理技术

基于对椭偏测量数据中难以消除的系统误差的作用机理分析,提出了一种新型的薄膜光学参数表征误差处理技术。建议选取薄膜椭偏角关于折射率和几何厚度的一阶偏导数,对大部分测量入射角满足符号相反或只有其中一个为零的条件的波段,剔除偏导数对全部测量入射角满足符号相同或同时为零的条件的奇点波长附近波段,作为反演表征用的椭偏测量数据采集区域,以最小化椭偏测量系统误差引起的薄膜光学参数反演表征值相对真实值的偏差大小。其本质是通过一阶偏导数筛选测量数据,来最小化椭偏测量系统误差对薄膜光学参数表征的误差传递作用。通过数值模拟实验,对比研究了该技术对不同测量入射角范围的适用性及实施技巧,以可复现的数值实验数据和合理的理论解释支持和验证了这种误差处理技术的可靠性,为薄膜在线表征和镀膜监控提供了一定的参考价值。     

光谱型椭偏仪对各向异性液晶层的测量

探讨了利用普通光谱型椭偏仪对各向异性液晶层进行综合性测量的可行性. 并利用法国Jobin Yvon公司的UVISEL SPME(Spectroscopic Phase Modulated Ellipsometer)光谱型椭偏仪测量了光学各向异性液晶层的折射率n_o和n_e及液晶层厚d，进一步利用椭偏仪在透射方式下测量了平行排列液晶层的光延迟特性Δnd，二者取得了很好的一致性，说明利用光谱型椭偏仪可以实现对光学单轴性液晶层及其他材料的测量，测厚精度为纳米量级. 关键词： 光谱型椭偏仪 各向异性 折射率 相位延迟     

Copper phthalocyanine film studied with spectroscopic ellipsometry

The ellipsometric spectra of vacuum sublimed copper phthalocyanine (CuPc) thin film on single-crystal silicon were studied on a new type of scanning ellipsometer with the analyser and polarizer rotate synchronously. The electronic structure of the spectra is discussed.     

椭偏光谱测量中椭偏参数的灵敏度分析

在对椭圆偏振测量的基本原理进行了简单介绍和推导后,讨论了椭圆偏振测量中椭偏参数关于薄膜参数的灵敏度以及入射角对椭偏参数的影响,并进行了具体的仿真分析,得到如下结论：椭偏参数Delta对薄膜光学常数和薄膜厚度变化的灵敏度明显高于椭偏参数Psi。在椭偏数据处理中,椭偏参数Delta的测量精度直接影响薄膜光学常数和薄膜厚度的拟合精度。为了提高椭偏参数Delta的测量精度,可以选择入射角在膺布儒斯特角附近。所得结论对高精度椭偏测量具有指导意义。     

多功能椭偏测厚仪

研究成功一台变入射角反射式消光法多功能智能椭偏测厚仪。实验表明 :仪器的测厚准确度为± 0 1nm ;椭偏参数Ψ和Δ的测量重复性精度分别为± 0 1°和± 0 3° ,适用于纳米级薄膜厚度和折射率的测量     

酞菁钴薄膜的折射率及吸收特性

通过真空镀法在单晶硅片上制备了酞菁钴薄膜，在波长扫描和入射角可变全自动椭圆偏振光谱仪上研究了ＣｏＰｃ薄膜的椭偏光谱并分析了其电子结构。     

System for measuring optical admittance of a thin film stack

A new method based on the polarization interferometer structure has been applied to measure the optical admittance, the refractive index and thickness of a thin film. The structure is a vibration insensitive optical system. There is one Twyman-Green interferometer part to induce a phase difference and one Fizeau interferometer part to induce the interference in the system. The intensities coming from four different polarizers were measured at the same time to prevent mechanical vibration influence. Using the polarization interferometer, the optical admittance, the refractive index and thickness of a single layer of Ta₂O₅ thin film has been measured. The measurement results were compared with the results obtained by ellipsometer. The results meet reasonable values in both refractive index and thickness.     

酞菁铜薄膜的折射率及吸收特性

通过真空镀膜法在单晶硅制备了酞菁铜薄膜，在波长扫描和入射角可变全自动椭圆偏振光谱仪上研究了ＣｕＰｃ薄膜的椭偏光谱并分析了其电子结构。     

A spectroscopic ellipsometer using rotating polarizer and analyzer at a speed ratio 1:1 and a compensator

Ellipsometers have been widely used in thin film characterization. They have shown a high degree of accuracy. We here propose theoretically a rotating polarizer and analyzer ellipsometer at a speed ratio 1:1 with a fixed compensator placed just after the rotating polarizer. Our calculations of the optical properties of c-Si and SiO \(_{2}\) reveal a substantial decrease in the percent error due to the fixed compensator. The uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are presented in details.     

In situ study of the Si-H bond in a-Si:H ultrathin films

A preliminary in situ analysis of the growth mechanisms and vibrational properties of plasma deposited amorphous silicon (a-Si:H) ultrathin films (d_f<200 Å) is presented. The hydrogen incorporation, as a function of the film thickness and the influence of the nature of the substrate on the early stage of the growth are studied by a new infrared phase modulated ellipsometer (IRPME). The Si-H bond (near 1990 cm^-1) is evidenced for the first time on films as thin as 5 Å. This new ellipsometer offers extremely high resolution thanks to a very small noise (0.02° in ψ and Δ).     

制备工艺条件对SiO2薄膜非均质特性的影响

薄膜材料的生长过程随镀膜机尺寸的增大而呈现新的规律,为制备膜层均匀性好、材料均质的大尺寸光学元件,分别在不同离子源能量、沉积压强、基板加热温度及基板转速条件下,采用离子辅助电子束蒸发方法制备了不同单层SiO2薄膜样品;利用分光光度计及椭偏仪分别对样品的透过率及椭偏参数进行测量,并对测量结果进行拟合得到不同样品的折射率及非均质特性。实验结果表明,工件架转速是使大尺寸SiO2薄膜材料产生非均质特性的主要影响因素,离子源能量、基板温度、沉积压强通过影响材料生长过程对材料的非均质特性产生调控;对于大尺寸薄膜光学元件,工件架转速存在限制的条件下,优化其他工艺参数可以获得均质SiO2薄膜材料,该结果对于制备具有优良性能的大尺寸薄膜光学元件具有借鉴意义。     

Ellipsometry of precision optical surfaces and mirror coatings

The possibility of testing a surface damaged layer and the cleaning quality of precision optical surfaces using the monochromatic ellipsometry method is discussed. The results of ellipsometric measurements of the thickness homogeneity of nanofilms deposited by the ion-beam sputtering method are analyzed. The results of calculations of the film thicknesses and parameters of surface layers performed by solving an inverse ellipsometric problem are presented. The results of measurements of the thickness of thin films by the profilometric and ellipsometric methods are compared.     

A high precision,polychromatic, automatic ellipsometer

The design and performance of a versatile, high precision, automatic ellipsometer, which follows rapid changes in surface properties, scans through the entire visible spectrum and through angles of incidence between 50° and 89°, is described. The state of polarization of the light beam is phase and amplitude modulated by means of two Faraday modulators working at a single frequency but in quadrature. Out-of-balance error signals are electronically processed and applied to a servodrive system which rotates the polarizing elements to the null positions. The angular positions of the prisms are measured by means of moiré fringe-counting systems which have digital displays reading to 0.001° over a range of 360°. The absolute accuracy of measurement of Δ and ψ, once all effects of intrinsic component imperfections and misalignments have been minimised, is better than ±0.013° in ψ and ±0.014° in Δ. The ellipsometer has been shown to work satisfactorily for a wide range of surface problems and in particular for surfaces with reflectivities as low as 0.001. The mechanical construction of the ellipsometer allows simultaneous movement of the two optical arms in opposite directions hence allowing a change in angle of incidence to be effected without any sample realignment. The ellipsometer has been designed with a sufficiently large sample space to allow the inclusion of bulky environmental chambers such as cryostats or vacuum systems and may be used to examine either vertical or horizontal surfaces.