Spectrally resolved white-light interferometry for 3D inspection of a thin-film layer structure

Abstract

We describe an improved scheme of spectrally resolved white-light interferometry, which provides 3D visual inspection of a thin-film layer structure with nanometer level resolutions. Compared to the authors' previous method [Appl. Phys. Lett.91, 091903 (2007)APPLAB0003-695110.1063/1.2776015], 3D tomographic information of thin films can be obtained by decoupling the film thickness and top surface profile, which is embodied by inducing spectral carrier frequency to the reference arm and applying a low-pass filter to the interferogram instead of two troublesome measurement steps of activating and deactivating a mechanical shutter. We test and verify our proposed method by measuring a patterned thin-film layer structure as well as standard specimens of thin films with various thicknesses.

Measurement of thin film interfacial surface roughness by coherence scanning interferometry

“…Some methods treat the interference signals in the time domain [6][7][8] when each thin film has a thickness in a certain range (տ1.5 lm), while others make use of the spectral phase or amplitude of the signals in the frequency domain to allow measurement in the thin film range (Շ1.5 lm). [9][10][11][12][13][14] The use of the CSI-methods for thin film thickness measurements based on time domain analysis is limited to film thickness (տ1.5 lm). This is because as the surfaces of the film assembly get closer, the peaks in the interference signal overlap more in the time domain.…”

On-line surface inspection using cylindrical lens–based spectral domain low-coherence interferometry

“…There has been considerable interest in SD-LCI since it was first proposed by Schwider and Zhou [14], for the purpose of retaining the unambiguous measurement advantage while eliminating mechanical scanning. Furthermore, the development of computers and spectrometers has allowed for SD-LCI for many applications, such as measuring the differential index of refraction, the distance and displacement, the thickness of the thin film, and the profile [15,16]. However, in all these existing SD-LCI techniques, spherical lenses such as micro-objectives were utilized to establish the interferometric objective, which gives only a small measuring range.…”

Absolute distance measurement method without a non-measurable range and directional ambiguity based on the spectral-domain interferometer using the optical comb of the femtosecond pulse laser

“…Spectral-domain interferometers (SDIs) have been utilized widely for 3D surface profile measurements because they can offer high measurement precision and speed without phase ambiguity. [1][2][3][4][5][6][7][8][9][10] For the practical realization of SDIs, incoherent wide-spectral light sources such as white-light lamps, light-emitting diodes, and superluminescent diodes have generally been used to produce spectrally resolved interference fringes. However, due to the short coherence length caused by their wide bandwidths, the working range of conventional SDIs is limited up to several mm.…”