Marking pattern in forming staircase structure of three-dimensional memory device

Abstract

A device area and a marking area neighboring the device area over a dielectric stack are determined. The dielectric stack includes insulating material layers and sacrificial material layers arranged alternatingly over a substrate. The device area and the marking area are patterned using a same etching process to form a marking pattern having a central marking structure in a marking area and a staircase pattern in the device area. The marking pattern and the staircase pattern have a same thickness equal to a thickness of at least one insulating material layer and one sacrificial material layer, and the central marking structure divides the marking area into a first marking sub-area farther from the device area and a second marking sub-area closer to the device area. A first pattern density of the first marking sub-area is greater than or equal to a second pattern density of the second marking sub-area. A photoresist layer is formed to cover the staircase pattern and expose the marking pattern, and the photoresist layer is trimmed to expose a portion of the dielectric stack along a horizontal direction. An etching process is performed to maintain the marking pattern and remove the exposed portion of the dielectric stack and form a staircase.