Air Gaps and Graded Nitride Caps in Flash Memory
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Solution Overview
Problem
As flash memory devices shrink in size to meet the trend of lightness and compactness, increasing integration density leads to coupling interference and reduced durability and reliability due to increased coupling interference between memory cells.
Innovation Solution
The solution involves forming a memory device with a substrate, word-line structures, cap structures made of nitride with decreasing nitrogen concentration, and air gaps between them, which enhances program speed and endurance by maximizing the air gap ratio and reducing coupling interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the integration density of the flash memory is increased to achieve lightness and compact size, then the device size is reduced, but the coupling interference between memory cells increases
Solution Approach 1:
The patent introduces air gaps that physically segment and isolate adjacent word-line structures, dividing the continuous conductive paths into separated segments. This segmentation reduces the electromagnetic coupling between neighboring memory cells while maintaining high integration density, directly resolving the contradiction between small device size and reduced coupling interference.
Solution Approach 2:
The air gaps act as intermediary elements between adjacent word-line structures, providing electrical isolation and reducing parasitic capacitance. These intermediary air gaps serve as insulating barriers that prevent direct electromagnetic coupling, allowing high-density integration without excessive interference.
2Quantity of substance
If the critical dimension is shrunk to increase integration density, then more memory cells can be packed, but the manufacturing process becomes more challenging
Solution Approach 1:
Instead of further reducing the lateral dimensions of word-line structures, the patent introduces air gaps in the vertical dimension and uses multi-layer cap structures with varying nitrogen concentrations. This dimensional approach allows increased integration density through better spatial arrangement rather than continuous scaling, easing manufacturing challenges associated with ultra-fine lithography.
Solution Approach 2:
The patent employs composite cap structures with multiple layers of nitride materials having different nitrogen concentrations. This composite material approach provides graded electrical properties that facilitate controlled charge trapping and tunneling, enabling high-density storage while maintaining manufacturability through established deposition and annealing processes.
3Reliability
If the air gap ratio between word-line structures is increased to reduce coupling interference, then reliability improves, but the device volume increases
Solution Approach 1:
The patent implements air gaps selectively at specific locations where coupling interference is most problematic, rather than uniformly throughout the entire device. The cap structures with graded nitrogen concentrations are positioned locally to enhance program speed and endurance where needed, maintaining high reliability without requiring uniform increases in device volume.
Solution Approach 2:
The patent embeds multiple cap layers with different nitrogen concentrations within each other, creating a nested structure. The first cap layer with higher nitrogen concentration is nested within the second cap layer with lower nitrogen concentration. This nested configuration maximizes the functional benefit of air gaps for reducing coupling interference while minimizing the overall volume occupied by the isolation structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach increases the reliability of the memory device by improving program speed and endurance while minimizing parasitic capacitance and RC delay, thereby enhancing overall performance.
Implementation Method 1
performing a nitridation treatment to nitride the upper portion of the nitride layer into a first cap layer
Implementation Method 2
performing an oxidation process to oxidize a thinned lower portion of the nitride layer to an oxide layer
Data Source
AI summary
Provided is a memory device including a substrate, a plurality of word-line structures, a plurality of cap structures, and a plurality of air gaps. The word-line structures are disposed on the substrate. The cap structures are respectively disposed on the word-line structures. A material of the cap structures includes a nitride. The nitride has a nitrogen concentration decreasing along a direction near to a corresponding word-line structure toward far away from the corresponding word-line structure. The air gaps are respectively disposed between the word-line structures. The air gaps are in direct contact with the word-line structures. A method of forming a memory device is also provided.