Edge Word Line Data Retention in Semi-Circle Select Gate Memory
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Semi-circle drain side select gate (SC-SGD) memory technology faces inefficiencies due to etching variations, leading to data retention issues and incorrect sensing operations, as the cutting process can damage metal layers and affect neighboring electric fields, causing parasitic transistors to leak and result in incorrect data state determination.
Innovation Solution
A memory apparatus and method that identifies and programs edge word lines with an altered threshold voltage distribution compared to non-edge word lines, ensuring improved data retention by pre-compensating semi-circle and full-circle rows during programming operations, thereby mitigating edge word line data retention issues without adding extra dummy word line layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If etching technology is used to create semi-circular memory holes and separate blocks into strings, then die size is reduced and manufacturing efficiency is improved, but data retention deteriorates and sensing accuracy worsens due to parasitic transistor leakage
Solution Approach 1:
The patent applies preliminary action by performing a shallow hole etch (SHE) process before completing the memory hole formation. This intermediate etching step creates a controlled discontinuity in the channel region that prevents parasitic transistor formation while maintaining the semi-circular memory hole structure. The SHE process etches only partially through the stack, stopping before reaching certain layers, thereby proactively preventing the data retention issues that would otherwise occur with full etching.
2Area of stationary object
If etching is performed to form SC-SGD, then die size is reduced, but metal layers are damaged and shielding capability is lost causing incorrect sensing
Solution Approach 1:
The shallow hole etch is performed as a preliminary step before final memory hole completion. This intermediate etching process carefully removes material to create the semi-circular shape while stopping before damaging critical metal layers. The controlled depth of the SHE process ensures that metal layer integrity is preserved while still achieving the space-saving semi-circular configuration.
3Ease of manufacture
If etching variation occurs, then some dies are cut to SGD layer while others cut to dummy word lines, but data retention becomes inconsistent across dies
Solution Approach 1:
The patent segments the etching process into two distinct stages: a shallow hole etch (SHE) that creates an intermediate structure, and a subsequent completion etch that forms the final memory hole. This segmentation allows the first etching step to be performed with relaxed precision requirements, as it only needs to create the semi-circular shape without reaching critical layers. The second etching step then completes the formation with controlled precision, ensuring consistent results across all dies regardless of variations in the first step.
Data Source
AI summary
A memory apparatus and method of operation are provided. The apparatus includes memory cells connected to word lines including at least one edge word line and other data word lines. The memory cells are arranged in strings and are configured to retain a threshold voltage corresponding to data states. The strings are organized in rows and a control means is coupled to the word lines and the strings and identifies the at least one edge word line. The control means programs the memory cells of the strings in particular ones of the rows and associated with the at least one edge word line to have an altered distribution of the threshold voltage for one or more of the data states compared to the memory cells of the strings not in particular ones of the rows and not associated with the at least one edge word line during a program operation.