In this paper, we propose a method to get more accurate metrology data using the tilt-axis on a transmission electron microscope (TEM) to compensate for microscopic tilt-axis changes that occur during focused ion beam (FIB) sample preparation processing. This method was developed using V-NAND plan-view samples which require channel hole measurements for each layer to support process monitoring. To test this method, we obtained the same image by progressively tilting the alpha and beta axes one degree in the positive and negative direction using a V-NAND planar sample. The strongest contrast edge was found by contrast profile analysis of each edge of the V-NAND channel using automated software. Through this method, we were able to optimize the sample position and automate the process to capture high quality images to accurately measure V-NAND channel holes. The details are discussed in this paper.

This paper describes the development and implementation of a TEM-based measurement procedure and shows how it is used to determine the verticality or etching angle of channel holes in V-NAND flash with more than 200 layers of memory cells. Despite the high aspect ratio of the region of interest, the method can resolve offsets down to a few nm. Such precision is critical, as the paper explains, because the radius and thus electrical characteristics of each memory cell is determined by the etching angle.