An Improved Dimensional Measurement Method of Staircase Patterns With Higher Precision in 3D NAND

Abstract

3D NAND is a great architectural innovation in the field of flash memory. The staircase for control gate is a unique and important process in the manufacturing of 3D NAND. The staircase is employed to form the electrical connection between the control gate and contact. The current method used to measure the dimension of staircase patterns is, however, not precise enough for the development of state-of-the-art 3D NAND. In this circumstance, an accurate measurement of dimension for as-formed staircase patterns is of great importance and technical interest. In this paper, an improved measurement method is proposed to meet the requirement for higher precision. By taking the overlay into account, a calculation formula for measuring the dimensional error of as-formed staircase is derived for the first time. Two kinds of anchor design (convex SS0 and concave SS0) are put forward to perform dedicated experiments. Achieved results show that the measurement error of as-formed staircase using this improved method is improved from 31.6 nm for normal measurement method to 14.1 nm. The dimensional uniformity of as-formed staircase is therefore improved significantly which in turn leads to well controlled word line leakage. Furthermore, in advanced staircase structure of stair divided scheme (SDS), the convex SS0 shows an advantage in cost compared to the concave SS0.INDEX TERMS 3D NAND, staircase, large dimension measurement, high precision.

Review of Semiconductor Flash Memory Devices for Material and Process Issues

“…Fortunately, several types of the two-directional-staircase-forming method have been developed, where staircases are made not only in the direction along a WLy but also in the direction perpendicular to the WL. [97,98] By using this method, both the lithography cost and WLy contact area could be remarkably reduced.…”