3D NAND Staircase Etch Stop Structure for Uniform Via Etching
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Solution Overview
Problem
3D NAND devices exhibit etch variations in the nitride etch stop layer and subsequent oxide layers, leading to overetch and underetch at different regions of the staircase structure, affecting contact via formation.
Innovation Solution
A method and apparatus to mitigate etch variations by adjusting the etch process to maintain consistent etch stop layer thickness across the staircase structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single nitride etch stop layer is used in 3D NAND devices, then the device structure is simple, but etch variations occur causing overetch at top regions and underetch at bottom regions of the staircase structure
Solution Approach 1:
The patent divides the single nitride etch stop layer into multiple segmented nitride layers separated by oxide layers. This segmentation allows each nitride layer to serve as an independent etch stop, preventing through-etching to underlying layers while maintaining overall etch control. The segmented structure resolves the contradiction by improving thickness uniformity (manufacturing precision) without significantly increasing device complexity.
Solution Approach 2:
The patent applies preliminary patterning and selective removal of specific nitride layers before final via formation. By pre-configuring the etch stop layer structure and selectively removing certain nitride layers in specific regions, the process achieves uniform etch stopping across the staircase structure while maintaining structural simplicity.
2Manufacturing precision
If the nitride etch stop layer thickness is increased to prevent underetch at bottom regions, then etch control improves, but overetch occurs at top regions of the staircase structure
Solution Approach 1:
By segmenting the nitride etch stop layer into multiple thinner layers separated by oxide spacers, the patent prevents both overetch and underetch. Each segmented nitride layer acts as an independent etch barrier, ensuring consistent etch stopping across the entire staircase structure without generating harmful overetch or underetch variations.
Solution Approach 2:
The oxide layers inserted between nitride layers serve as intermediaries that control etch progression. These intermediary oxide spacers prevent direct through-etching to underlying layers while allowing controlled etching of the nitride layers themselves, thereby eliminating harmful etch variations.
3Manufacturing precision
If a complex multi-layer etch stop structure is used to eliminate etch variations, then manufacturing precision improves, but device complexity increases
Solution Approach 1:
The patent implements a segmented etch stop structure where nitride layers are divided into multiple sections separated by oxide layers. This segmentation achieves consistent thickness control (improving manufacturing precision) while maintaining a relatively simple overall structure that can be integrated into existing 3D NAND fabrication processes without significantly increasing device complexity.
Data Source
AI summary
An apparatus, a method and a system. The apparatus comprises a memory array including word lines defining a staircase structure, and a staircase etch stop layer including: a sandwich etch stop layer disposed on a top region the staircase and including a first etch stop layer and a third etch stop layer of a first material, and a second etch stop layer sandwiched between the first etch stop layer and the third etch stop layer and made of a second material having etch properties different from the first material; a precut etch stop layer disposed at a region of the staircase structure below the top region and including the second etch stop layer and the third etch stop layer and not the first etch stop layer; and contact structures extending through a dielectric layer and the staircase etch stop layer and landing on the word lines at the staircase structure.