Multilayer thin-film inspection through measurements of reflection coefficients

Abstract

A vibration-insensitive interferometer is described to measure the thickness, refraction index and surface profile of thin-film stack at normal incidence. By satisfying the continuous boundary conditions of electric and magnetic fields at interfaces in a multilayer film stack, the reflection coefficient phase of the thin-film stack can be distinguished from the phase of spatial path difference, thus thickness and refraction index can be extracted. The experiment results showed that the measurement precision is significantly increased after the phase analysis was added into the reflectance analysis.

Simultaneous measurements of top surface and its underlying film surfaces in multilayer film structure

“…By combining the nonlinear part of the total phase and the absolute reflectance of the test specimen together, we can define a merit function as a function of each layer’s film thickness of the multilayer films as follows where Φ nl E and ℜ E are the measured non-linear phase and spectral reflectance, ψ nl T and ℜ T are the analytical models of the non-linear phase and spectral reflectance derived from the Fresnel’s equations for the multilayer 1 , 21 , 23 . The superscript ‘E’ and ‘T’ represents ‘experiment’ and ‘theory’, respectively.…”

“…Recently, in response to industrial needs, much research has been done on 3D inspection of complex thin-film structures using white-light interferometry 4 – 23 . These approaches allow simultaneous measurements of top surface and its underlying film surfaces with high precision, but their applications are only limited to measurement of a single layer film structure.…”

“…These approaches allow simultaneous measurements of top surface and its underlying film surfaces with high precision, but their applications are only limited to measurement of a single layer film structure. To further effort to expand into multilayer films, other research attempt 23 has been performed by utilizing both the phase and reflectance spectra of sample to measure individual film thickness of each layer in a stack with more improved precision. However, this technique selects only several phase and reflectance spectra with corresponding filters available with narrow bandpass regions and polarization components as phase shifters such as wave plates also inherently introduce the wavelength-dependent errors in the phase shift.…”

Spatially Multiplexed Micro-Spectrophotometry in Bright Field Mode for Thin Film Characterization

“…Optical techniques, such as imaging ellipsometry [ 6 , 7 , 8 ], white light interferometry [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ] and micro-spectrophotometry [ 17 , 18 , 19 , 20 , 21 , 22 ] are widely used experimental methods for thin film thickness characterization. These are nondestructive methods, they do not require any previous sample preparation and can easily achieve spatial lateral resolution in the micrometer range.…”

Amplified phase measurement of thin-film thickness by swept-source spectral interferometry

“…While in spectral interferometry, the dispersive detection offers it the capability of obtaining depth-resolved information without mechanical scanning. To determine thin-film thickness by spectral interferometry, approaches based on spectral reflectance [6,7], nonlinear spectral phase [5,8,9] and spectral domain optical coherence tomography [10] have been reported. Among these approaches, the nonlinear spectral phase method demonstrates a high sensitivity.…”