3D Non-Volatile Memory Pad Region Alignment via Stepwise Etching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for manufacturing 3-D non-volatile memory devices face challenges with misalignment and increased error probability in forming pad regions and contact plugs, leading to bridged neighboring word lines and disconnected circuits due to difficulties in uniformly shortening the photoresist pattern, which results in increased cell area and potential damage to the highest word line.
Innovation Solution
The method involves alternately stacking interlayer dielectric and conductive layers over a substrate, forming a stepwise pattern by gradually increasing the width of pad regions in each etching process, ensuring that the width of a pad region on a higher word line is greater than that of a lower word line, thereby maintaining alignment margin and preventing excessive cell area expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the photoresist pattern width is uniformly shortened in repeated etching processes, then the pad region width can be adjusted, but the mask pattern may be completely removed and the highest word line may be damaged
Solution Approach 1:
The patent divides the pad region formation into multiple stages with different etching depths. Each etching process targets a specific depth range, creating pad regions at different levels without completely removing the mask pattern. This segmented approach allows precise width control while preserving mask integrity.
Solution Approach 2:
The patent applies different etching depths to different regions of the mask pattern. The mask pattern is designed with varying thickness or material composition at different locations, allowing selective etching that creates wider pad regions at higher levels while maintaining mask protection at critical areas.
2Manufacturing precision
If the photoresist pattern is completely removed to form pad regions, then the etching can reach the desired depth, but misalignment between pad regions and contact plugs increases
Solution Approach 1:
The patent performs preliminary etching to create pad regions before complete mask removal. The mask pattern is strategically designed to remain as an alignment reference during subsequent contact plug formation, ensuring precise alignment while achieving the required etching depth for pad regions.
Solution Approach 2:
The mask pattern serves as an intermediary element that facilitates both pad region formation and alignment reference. By designing the mask with appropriate thickness and material properties, it enables deep etching while maintaining its structural integrity as an alignment guide for subsequent processing steps.
3Reliability
If the cell area is increased to secure alignment margin, then misalignment probability decreases, but the overall device area becomes excessive
Solution Approach 1:
The patent transitions from planar pad regions to three-dimensional stacked pad regions at different heights. This vertical dimensionality allows multiple pad regions to be formed within a smaller footprint area, providing sufficient alignment margin without increasing the overall cell area excessively.
Solution Approach 2:
The patent nests pad regions at different vertical levels within the same horizontal footprint. The mask pattern creates a hierarchical structure where pad regions are nested one above another, maximizing the use of vertical space to provide alignment margins without expanding the lateral cell area.
Data Source
AI summary
A non-volatile memory device according to an aspect of the present disclosure includes a substrate, a plurality of word lines stacked over the substrate and having a stepwise pattern, wherein the plurality of word lines each have a pad region, and a plurality of contact plugs coupled to the respective pad regions of the word lines, wherein a width of a pad region of a first one of the plurality of word lines is greater than a width of a pad region of a second word line lower than the first word line.