From Event: SPIE Optical Engineering + Applications, 2016
Patterned sapphire substrates (PSS) wafers are used in LED manufacturing to enhance the luminous conversion of LED
chips. The most critical characteristics in PSS wafers are height, width, pitch and shape of the pattern. The common way
to measure these characteristics is by using surface electron microscope (SEM). White light interferometry is capable to
measure dimension with nanometer accuracy and it is suitable for measuring the characteristics of PSS wafers. One of
the difficulties in measuring PSS wafers is the aspect ratio and density of the features. The high aspect ratio combined
with dense pattern spacing diffracts incoming lights and reduces the accuracy of the white light interferometry
measurement. In this paper, a method to improve the capability of white light interferometry for measuring PSS wafers
by choosing the appropriate wavelength and microscope objective with high numerical aperture. The technique is proven
to be effective for reducing the batwing effect in edges of the feature and improves measurement accuracy for PSS
wafers with circular features of 1.95 um in height and diameters, and 700 nm spacing between the features. Repeatability
of the measurement is up to 5 nm for height measurement and 20 nm for pitch measurement.
Abraham Mario Tapilouw, Yi-Wei Chang, Long-Yo Yu, and Hau-Wei Wang, "Reduction of batwing effect in white light interferometry for measurement of patterned sapphire substrates (PSS) wafer," Proc. SPIE 9960, Interferometry XVIII, 996006 (Presented at SPIE Optical Engineering + Applications: August 30, 2016; Published: 28 August 2016); https://doi.org/10.1117/12.2236874.
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