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One of the most challenging steps for the 3D flash memory device fabrication is the etching process of the high aspect ratio (HAR) holes/trenches, which is becoming more difficult as the number of the stacked layers increases. A measurement technique which features both non-destructivity and high accuracy is a must to assure high accuracy of the process control to realize the wafer-wide uniform HAR etching.
T-SAXS (transmission small angle X-ray scattering) is the measurement technique utilizing transmission X-rays. As presented in Fig. 1, it constructs the high precision HAR structural images based on the multiple X-ray elastic scattering images (SAXS images), which are obtained by the X-ray irradiation at different angles of incidence. We reported the studies of the T-SAXS applicability to the HAR structures of the future generation 3D flash memories, employing the X-rays elastic scattering simulations. We confirmed that T-SAXS is capable of inspecting the future generations 3D flash memory structures which are constructed in even higher aspect ratios as the measurement error of less than 1 % on the HAR hole structures of the depth of 30 μm is secured.
This technique was presented at the SPIE AL (society of photo-optical instrumentation engineers advanced lithography) and the 41st nano-testing symposium.
This article is based on the quotes from the refs  and , and edited accordingly.
 Kaori Sasaki, Takaki Hashimoto, Yenting Kuo, Hiroshi Tsukada, and Hiroyuki Tanizaki "Measurability analysis of the HAR structure in 3D memory by T-SAXS simulation",
Proc. SPIE 11611, Metrology, Inspection, and Process Control for Semiconductor Manufacturing XXXV, 116110U (22 February 2021) © 2021 Society of Photo Optical Instrumentation Engineers (SPIE).
 Kaori Sasaki, Takaki Hashimoto, Yenting Kuo, Hiroshi Tsukada, and Hiroyuki Tanizaki "Measurability analysis of the HAR structure in 3D memory by T-SAXS simulation", The 41st Annual NANO Testing Symposium, Metrology and Inspection, (2) (25 October 2021) © 2021 The institute of NANO Testing (INANOT).