Dr. Yanli Meng Profile

Dr. Yanli Meng

Associate Professor at Northeast Normal Univ

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Publications (3)

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Proceedings Article | 4 September 2018 Paper

Evaluate thin film surface roughness accurately by a simple x-ray reflectivity distribution method and first-order perturbation theory

Yanli Meng, Mi Lu

Proceedings Volume 10750, 107500L (2018) https://doi.org/10.1117/12.2319470

KEYWORDS: Thin films, X-rays, Surface roughness, Scattering, Aluminum, Atomic force microscopy, Spatial frequencies, Atomic layer deposition, Reflectivity

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The application of X-ray reflectivity (XRR) and X-ray scattering (XRS) technique for studying thin film surfaces is discussed. A simple method to evaluate thin film mass density accurately from the XRR distribution has been given, named XRR-DE method. According to the measured mass density, optical constant of thin film could be calculated, which is very important for evaluating the surface roughness of thin film from XRS distribution. The first-order perturbation theory (FOPT), one of the XRS methods, is extensively validated for smooth surfaces and can extract power spectral density (PSD) function of the surface roughness directly and uniquely from measured scattering distribution. The conditions of applicability of FOPT have also been discussed. While the three Al₂O₃ thin films were deposited by Atomic layer deposition (ALD), Au thin film was evaporated by electron beam coating. The density of the Al₂O₃ thin films evaluated by XRR-DE method is 3.25g/cm³, 3.227 g/cm³, and 3.224 g/cm³. The density difference is less than 1%, and the results are in good agreement with the reported data. However, as an amorphous film, its density is much smaller than that of the sapphire single crystal (3.965g/cm³). The density of Au film evaluated by XRR-DE method is 17.05g/cm³. The scattering indicatrix for different thin films were measured, and one-dimensional PSD functions and effective RMS roughness were calculated by FOPT, which coincide well with the measurements of atomic force microscopy (AFM). The results demonstrated that FOPT is valid for measuring the surface roughness of thin films. Specifically, calculating optical constants from the experimentally measured mass densities by XRR-DE of the studied thin films could improve the measurement accuracy.

Proceedings Article | 29 September 2009 Paper

Assessment of surface roughness by use of soft x-ray scattering

Yan-li Meng, Yong-gang Wang, Shu-yan Chen, Bo Chen

Proceedings Volume 7451, 745116 (2009) https://doi.org/10.1117/12.826000

KEYWORDS: Scattering, X-rays, Surface roughness, Laser scattering, Reflectometry, Light scattering, Electromagnetic scattering theory, Silicon, Zerodur, X-ray optics

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A soft x-ray reflectometer with laser produced plasma source has been designed, which can work from wavelength 8nm to 30 nm and has high performance. Using the soft x-ray reflectometer above, the scattering light distribution of silicon and zerodur mirrors which have super-smooth surfaces could be measured at different incidence angle and different wavelength. The measurement when the incidence angle is 2 degree and the wavelength is 11nm has been given in this paper. A surface scattering theory of soft x-ray grazing incidence optics based on linear system theory and an inverse scattering mathematical model is introduced. The vector scattering theory of soft x-ray scattering also is stated in detail. The scattering data are analyzed by both the methods above respectively to give information about the surface profiles. On the other hand, both the two samples are measured by WYKO surface profiler, and the surface roughness of the silicon and zerodur mirror is 1.3 nm and 1.5nm respectively. The calculated results are in quantitative agreement with those measured by WYKO surface profiler, which indicates that soft x-ray scattering is a very useful tool for the evaluation of highly polished surfaces. But there still some difference among the results of different theory and WYKO, and the possible reasons of such difference have been discussed in detail.

Proceedings Article | 9 September 2009 Paper

Comparative study of x-ray scattering by first-order perturbation theory and generalized Harvey-Shack theory

Yong-gang Wang, Yan-li Meng, Wen-sheng Ma, Bin Chen, Bo Chen

Proceedings Volume 7448, 744810 (2009) https://doi.org/10.1117/12.824550

KEYWORDS: Scattering, X-rays, Atomic force microscopy, Laser scattering, Silicon, Semiconducting wafers, Light scattering, Spatial frequencies, X-ray optics, Surface roughness

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Application of the x-ray scattering (XRS) technique for studying super-smooth surfaces such as Si wafers is discussed. The XRS method is demonstrated to enable quantitative evaluation of power spectrum density (PSD) functions and effective roughness of super-smooth surfaces. Within the calculation of PSD functions, comparative study between first-order vector perturbation theory (FOPT) and generalized Harvey-shack theory (H-S) is performed. First-order perturbation theory which is widely accepted and has been extensively validated even for large scattered and incident angles for "smooth" surfaces considers the scattering amplitude as a power series in the roughness height; its scattering diagram is related to the statistical parameters of surface roughness (PSD functions) in a very simple way (linear). Therefore, PSD functions can be uniquely and directly extracted from the measured data. However, generalized Harvey-shack theory considers that scattering behavior is characterized by a surface transfer function which relates the scattering behavior to the surface topography. With the grazing incident angle less than critical value about 0.22 degree, three Si wafers with rms roughness of 0.29nm, 0.46nm and 0.67nm are inspected by XRS (λ=0.154nm) method. The calculated values are all in a good agreement with the results obtained from Atomic force microscope (AFM). However, the difference resulting from the limits of applicability of the theories used in XRS data processing appears and be analyzed. Both of the theories are not only used for optical surface characterization, but also can allow accurate predictions of image degradation due to scattering effects in grazing X-ray telescopes. The experimental schemes are also analyzed.

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