3D Memory Staircase Formation via Mandrel Segmentation
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Solution Overview
Problem
Conventional methods for forming staircase structures in 3D memory devices face challenges such as low product throughput and high fabrication costs due to multi-cycle trim and etch processes, which are costly and difficult to control, especially as the number of staircases increases, leading to errors in etch rate control and mask patterning precision.
Innovation Solution
A method involving forming an alternating layer stack on a substrate, dividing it into staircase regions, using a hard mask layer, and applying multi-cycle trim and etch processes to pattern the photoresist layer, reducing the number of masks and cycles, and repeating the process to form staircases efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-cycle trim and etch processes are used to form staircase structure, then manufacturing precision can be achieved, but productivity decreases and fabrication cost increases
Solution Approach 1:
The patent applies preliminary action by forming a mandrel structure before the staircase regions, which serves as a pre-established template for subsequent material deposition. This preliminary structure enables controlled formation of staircase regions through targeted removal processes, achieving precise width and location control while reducing the number of iterative trim-etch cycles needed, thereby improving productivity
Solution Approach 2:
The patent segments the staircase formation process into distinct phases: forming the mandrel structure first, then creating staircase regions through selective material removal. This segmentation allows each phase to be optimized independently, with the mandrel providing a stable foundation that reduces the complexity of subsequent patterning steps, thus maintaining precision while enhancing throughput
2Manufacturing precision
If multi-cycle trim and etch processes are used to form staircase structure, then manufacturing precision can be achieved, but fabrication cost increases
Solution Approach 1:
By establishing the mandrel structure in advance, the patent reduces the number of expensive iterative trim-etch cycles required. The preliminary mandrel serves as a cost-effective template that guides subsequent material deposition and removal, achieving precise staircase formation with fewer process steps and lower overall fabrication costs
Solution Approach 2:
The mandrel structure acts as an intermediary element that simplifies the formation of staircase regions. This intermediate structure enables controlled material deposition and removal, serving as a cost-effective mediator that reduces the complexity and cost of direct staircase patterning while maintaining manufacturing precision
3Quantity of substance
If number of staircases increases, then memory density improves, but etch rate control errors increase
Solution Approach 1:
The patent segments the staircase formation into controlled phases using a mandrel structure. By dividing the process into mandrel formation followed by targeted material removal, it enables precise control over each staircase region even when multiple staircases are present, preventing error accumulation that would occur with traditional multi-cycle approaches
Solution Approach 2:
The mandrel structure serves as an intermediary that enables precise control of multiple staircase regions simultaneously. This intermediate template allows uniform material deposition and removal across all staircase regions, maintaining etch rate control precision regardless of the number of staircases, thus supporting higher memory density without sacrificing precision
4Quantity of substance
If number of staircases increases, then memory density improves, but mask patterning precision errors increase
Solution Approach 1:
The preliminary mandrel structure establishes a stable geometric reference before mask patterning is performed. This pre-formed template reduces the complexity of mask alignment and patterning, enabling precise definition of multiple staircase regions in a single or fewer patterning steps, thereby maintaining mask precision even as the number of staircases increases
Solution Approach 2:
The mandrel acts as an intermediary reference structure that simplifies mask patterning for multiple staircases. By providing a pre-defined geometric framework, it serves as a mediator that reduces alignment errors and patterning variability, enabling precise fabrication of high-density multi-staircase structures
Data Source
AI summary
Disclosed is a method for forming a staircase structure of 3D memory devices, comprising (i) forming a stack of layers on a substrate; (ii) removing a portion of the stack to form a lower region and a upper region; (iii) forming a mask to cover the lower region and the upper region of the stack; (iv) forming a first opening in the mask to expose a first portion of the stack in the lower region and a second opening in the mask to expose a second portion of the stack in the upper region; (v) forming a photoresist layer to cover the stack and the mask; (vi) using a same set of trim-etch processes to pattern the photoresist layer to form a set of staircases in the first opening and the second opening; (vii) removing the photoresist layer and the mask; and repeating (iii), (iv), (v), (vi) and (vii) sequentially.