3D Memory Device Non-Uniform Pitch Void Prevention
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Solution Overview
Problem
Three-dimensional vertical NAND strings face electrical failures and structural instability due to void formation during the replacement of sacrificial material layers with electrically conductive layers, caused by non-conformity leading to non-uniform spacing in memory stack structures.
Innovation Solution
A three-dimensional memory device is designed with an alternating stack of insulating and sacrificial material layers over a substrate, where memory stack structures with a non-uniform pitch are formed, and sacrificial material layers are replaced with electrically conductive layers through backside trenches, arranged in a two-dimensional array to minimize void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If uniform pitch is used in memory stack structures, then manufacturing process is simpler, but void formation occurs during sacrificial material replacement leading to electrical failures
Solution Approach 1:
The patent applies asymmetry by implementing non-uniform pitch arrangement where memory stack structures have different spacing in different directions. Specifically, the pitch between adjacent memory stack structures is larger in the first direction (word line direction) compared to the second direction (bit line direction). This asymmetric spacing prevents void formation during sacrificial material replacement while maintaining electrical reliability.
2Reliability
If non-uniform pitch is used in memory stack structures, then void formation is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by forming the non-uniform pitch arrangement of memory stack structures before the sacrificial material replacement process. The alternating stack structure with predetermined non-uniform spacing is established in advance, ensuring that when sacrificial material is removed and replaced with conductive material, voids are minimized due to the pre-optimized spacing configuration.
3Manufacturing precision
If uniform spacing is maintained among memory stacks, then device symmetry is preserved, but conformality during material deposition becomes difficult leading to voids
Solution Approach 1:
The patent applies local quality by varying the pitch spacing locally in different regions and directions of the memory array. Instead of maintaining uniform spacing throughout, the pitch is optimized locally - larger spacing in the word line direction to prevent void formation during deposition, and smaller spacing in the bit line direction to maintain high density. This local variation in quality achieves both conformal deposition and structural stability.
Data Source
AI summary
An alternating stack of insulating layers and sacrificial material layers is formed over a substrate. Memory stack structures including a memory film and a vertical semiconductor channel are formed through the alternating stack in an array configuration. Backside trenches extending along a lengthwise direction are formed through the alternating stack. Backside recesses are formed by removing the sacrificial material layers. Filling of the backside recesses with electrically conductive layers can be performed without voids or with minimal voids by arranging the memory stack structures with a non-uniform pitch. The non-uniform pitch may be along the direction perpendicular to the lengthwise direction such that the nearest neighbor distance among the memory stack structures is at a minimum between the backside trenches. Alternatively or additionally, the pitch may be modulated along the lengthwise direction to provide wider spacing regions that extend perpendicular to the lengthwise direction.