Determination of film thickness and surface profile using reflectometry and spectrally resolved phase shifting interferometry

Abstract

Surface profiling and film thickness measurement play an important role for inspection in semi conductor industry. White light source had been used as scanning white light interferometry and spectrally resolved white light interferometry for determining surface and film thickness profile. These techniques however failed for thinner film. Recently, reflectometry and spectrally resolved white light interferometry was combined for the same. This technique used Fourier Transform for the calculation of phase in spectral domain with the use of Linnik interferometer. In this method a large amount of carrier offset (carrier fringes) is required to be effective. This carrier fringes in spectrally resolved white light interferometry was achieved by increasing the optical path difference between the test and the reference surface. But, Linnik interferometer cause defocusing problem to create these carrier fringes. We propose in this paper to combine reflectometry and spectrally resolved phase shifting interferometry for measurement of surface and film thickness profile with the use of Michelson objective. Michelson objective will be convenient to implement as compared to the Linnik type and the use of phase shifting interferometry does not necessarily need large number of fringes in the spectral domain.

Tear film measurement by optical reflectometry technique

“…The reflected light measured by the spectrometer, namely wavelength dependent reflectance RðλÞ, is then processed by the software program. By curve fitting, the film thicknesses of different layers of the tear film can be extracted based on the theory of multilayer optical reflection [23][24][25] in white light reflectometry.…”

“…The mathematical framework of the reflectometry method [23][24][25] can be described as follows. For a single film as shown in Fig.…”

“…(8) for a multilayer film, curve fitting computation by the nonlinear least-squares numerical method 24 to determine the film thicknesses can be performed. The system first predicts a group of film thicknesses d 1 ; d 2 ; : : : ; d k to initiate the reflectance calculation.…”

“…For a single layer film thickness determination, the same curve fitting computation process described above is performed by using theoretical reflectance Eq. (1) and a single thickness variable d. In general, the film thickness measurement by optical reflectometry technique with nonlinear least-squares curve fitting method 24 as conceptually described above has been maturely developed.…”

Thickness and Surface Measurement of Transparent Thin-Film Layers using White Light Scanning Interferometry Combined with Reflectometry

“…And it has the limitation of spectral resolution, which is most important in calculating thickness. To compensate for the ambiguity in spectral analysis, reflectometry and Thickness and Surface Measurement of Transparent Thin-Film Layers using … -Taeyong Jo et al spectrally resolved white light interferometry were combined [5,6]. But this method was too sensitive to the detection of the peak signal.…”