Critical dimension measurement of transparent film layers by multispectral imaging

Abstract

An optical microscopy system as a non-destructive method for measuring critical dimension (CD) is widely used for its stability and fastness. In case of transparent thin film measurement, it is hard to recognize the pattern under white light illumination due to its transparency and reflectance characteristics. In this paper, the optical measurement system using multispectral imaging for CD measurement of transparent thin film is introduced. The measurement system utilizes an Acousto-Optic Tunable Filter (AOTF) to illuminate the specimen with various monochromatic lights. The relationship between spectral reflectance and CD measurement are deduced from series of measurement experiments with two kinds of Indium Tin Oxide (ITO) patterned samples. When the difference of spectral reflectance between substrate and thin film layers is large enough to yield a large image intensity difference, the thin film layer can be distinguished from substrate, and it is possible to measure the CD of transparent thin films. This paper analyzes CD measurement of transparent thin film with reflectance theory and shows that the CD measurement of transparent thin film can be performed successfully with the proposed system within a certain wavelength range filtered by AOTF.

Improvement of spectral resolution in spectroscopic imaging reflectometer using rotating-type filter and tunable aperture

“…New approaches by many research groups have been developed to measure the spatially resolved thickness and refractive index of thin film by analyzing self-interference using a spectroscopic imaging reflectometer [8][9][10][11][12][13]. In a spectroscopic imaging reflectometer, to obtain a stack of multispectral…”

Fast Analysis of Film Thickness in Spectroscopic Reflectometry using Direct Phase Extraction

“…The measurement of volumetric thickness using a CCD camera as a spectrum detector has been studied recently [5][6][7][8][9][10][11][12]. It is often called imaging spectroscopic reflectometry (ISR) when the volumetric thickness is measured by SR theory [8,9].…”