Precise thickness measurement and comparison of step-shaped microfluidic channel mold using optical interferometry

摘要

Optical interferometry is one of the suitable methods which can be used to measure the physical thicknesses of microscalestructures because this approach can measure optical path differences accurately with a non-contact method. In thispaper, on the basis of the simultaneous measurement of the physical thickness and refractive index of an opticallytransparent plane-parallel plate, a spectral-domain interferometer capable of measuring the physical thickness andrefractive index of separate layers in a step-shaped structure with two layers was proposed and realized. For a feasibilitytest, a microfluidic channel mold with two layers was selected as a sample. For verification of the measured thickness ina double-layered region, a contact-type surface profilometer equipped with laser interferometers on the x-y-z axes wasused for a thickness comparison. However, it is never simple to compare measured thicknesses due to positioning errorsand the different measuring sizes of each method. For these reasons, the corresponding thickness value was defined as anoffset between height values at center points of the single-layered and double-layered region in a specific area of 5 mm ×5 mm. For an accurate determination of the offset, the slopes of the surface profile were removed. The assumption thatthe surface profile of the bottom layer in the double-layered region is very flat was applied to calculate the thicknessfrom the measured surface profile, and this assumption was checked as to whether it is acceptable or not in this study. Inconclusion, the physical thicknesses according to a surface profilometer and by the proposed method were determined tobe 106.332 μm and 106.304 μm, respectively, in good agreement within the respective uncertainty values.