Hai-Bin Zhao

Application of image spectrometer to in situ infrared broadband optical monitoring for thin film deposition

A path-folded infrared image spectrometer with five sub-gratings and five linear-array detectors was applied to a broadband optical monitoring (BOM) system for thin film deposition. Through in situ BOM, we can simultaneously acquire the thickness and refractive index of each layer in real time by fitting the measured spectra, and modify the deposition parameters during deposition process according to the fitting results. An effective data processing method was proposed and applied in the BOM process, and it shortened the data processing time and improved the monitoring efficiency greatly. For demonstration, a narrow band-pass filter (NBF) at 1540 nm with ~10 nm full width at half-maximum (FWHM) had been manufactured using the developed BOM system, and the results showed that this BOM method was satisfying for monitoring deposition of thin film devices.

Study of Positive and Negative Refraction of Visible Light at the Cu/Air Interface

Light transmission at the Cu/air interface was measured in the visible region for a series of wedge-shaped Cu film samples. It is found that light refraction at the Cu/air interface changes from negative in the Drude region, passing through zero at about Eg, to positive in the interband-transition region. Detailed discussion is given to exclude those mechanisms which have been arguably assigned as the cause of negative refraction at a metal/dielectric interface. Based on the spectra of the measured refractive index and modeled in the Drude region, the positive and negative refraction analyzed in this work are qualitatively in agreement with dispersion of the group refractive index, and may aid in understanding light transmission at the metal/dielectric interface as characterized by the law of refraction.

Random Noise Reduction with More Accurate Calibration for a Spectrometer Using a Two-Dimensional Array Detector

An efficient noise-reduction method with a more accurate wavelength calibration procedure is proposed for a spectrometer system to achieve a higher signal-to-noise ratio and spectral resolution. By using a two-dimensional (2D) array detector with an integrated grating composed of 10 sub-gratings, the system has a merit of high data acquisition speed to satisfy the condition in which in-situ spectral data analysis is critically required. The noise level has been effectively reduced down to approximately 25% of the previous level. The spectral curvature effect due to imperfection of the optical system is also analyzed and significantly reduced using the spectral calibration procedure to achieve higher resolution.

Study of the Correlation of Plasma Resonance and the Refractive Index to Dielectric Dispersion in the Complex Plane

Based on the dispersive feature of the dielectric function of noble metals and the wave vector conservation in physics, both the plasma effect and the complex refractive index, which are profoundly correlated to the complex dielectric function and permeability, have been studied and analyzed. The condition to induce a bulk or a surface plasma in the visible region will not be satisfied, and there will be one solution for the real and the imaginary parts of the refractive index, restricting it only to region I of the complex plane. The results given in this work will aid in understanding the properties of light transmission at the metal/dielectric interface as characterized by the law of refraction in nature.

Lateral shift effect on the spatial interference of light wave propagating in the single-layered dielectric film.

Under the oblique incidence condition, the multiple reflection of wave packets in a layered film structure will have a lateral shift increasing with the film thickness. In the analysis of the spatial interference with consideration of the lateral shift effect, a set of new analytic formulae to normalize the intensity of the s-and p-polarized wave packet was obtained to reduce the error of the ellipsometry parameters significantly as the optical path difference delta is close to mpi. The principle and method developed in this work also can be applied to other film structures in more general applications.