Tilted Edge Wordline Implants for Flash Memory Erase Endurance
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Solution Overview
Problem
Erase cycling in flash memory devices leads to charge accumulation adjacent edge wordlines, making it difficult to completely erase memory cells and reducing the drain-source current, which affects the endurance and performance of the memory cell string.
Innovation Solution
The formation of tilted edge wordline implants, either using critical masks or without them, to supplement drain implants and mitigate charge accumulation, where the implants are projected at specific angles to target areas adjacent edge wordlines, thereby reducing the impact of charge accumulation and maintaining threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional drain implants are formed in the substrate, then the basic memory cell structure is established, but charge accumulates adjacent edge wordlines during erase cycling, making complete erasure difficult and reducing drain-source current
Solution Approach 1:
The patent applies preliminary action by forming edge wordline implants in advance, before erase cycling occurs. These implants are strategically positioned adjacent to edge wordlines to preemptively counteract the charge accumulation problem that would otherwise develop during subsequent erase cycles, ensuring complete erasure capability is maintained from the outset
Solution Approach 2:
The patent applies local quality by creating spatially non-uniform doping through tilted implants at specific angles (e.g., 30 degrees). The implants are localized to specific regions adjacent to edge wordlines rather than uniformly distributed, with varying dopant concentrations tailored to the local charge accumulation risk at different positions around the edge wordlines
2Manufacturing precision
If tilted edge wordline implants are formed to mitigate charge accumulation, then erasure completeness is improved, but the manufacturing process complexity increases due to additional implant steps and tilt angle requirements
Solution Approach 1:
The patent applies dimensionality change by transitioning from conventional vertical (90-degree) implants to tilted implants at oblique angles (e.g., 30 degrees). This angular dimension change allows the implant ions to reach regions adjacent to edge wordlines that are inaccessible to vertical implants, thereby improving erasure completeness without requiring additional implantation steps or complex mask patterns
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
The tilted edge wordline implants enhance the endurance of flash memory devices by ensuring complete erasure and reducing edge wordline degradation, improving the program-erase cycle performance beyond conventional memory cells.
Implementation Method 1
forming a first tilted implant in the substrate adjacent a first edge wordline to supplement the first drain implant (where the first tilted implant is provided at a tilt angle from a first direction)
Data Source
AI summary
A process for forming tilted edge wordline implants is disclosed. The process includes forming a first drain implant in a substrate, forming a first tilted implant in a substrate adjacent a first edge wordline to supplement said first drain implant where the first tilted implant is provided at a tilt angle from a first direction and forming a second tilted implant in the substrate adjacent a second edge wordline to supplement another first drain implant where the second tilted implant is provided at a tilt angle from a second direction. A second drain implant is formed in the substrate.