Self-Aligned Trap Layer Patterning for Flash Memory Scaling
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Solution Overview
Problem
The existing self-aligned semiconductor memory device fabrication processes face challenges in scaling due to the limitations imposed by the upwardly extending wings of the charge trapping layers, which restrict the close placement of memory cells, impacting memory capacity and cost-effectiveness.
Innovation Solution
A method involving the deposition of a non-conformal film over the charge trapping layer, followed by a dry or wet etch process to create a void and separate the trapping structures, allowing for closer placement of memory cells by forming a pinch-off or narrow channel region, and subsequent oxidation to isolate the trapping layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a self-aligned process with upwardly extending wings is used, then alignment precision is improved, but memory cell spacing increases reducing scalability
Solution Approach 1:
The patent segments the charge trapping layer into isolated regions between core cells by etching away the nitride material in the trenches. This segmentation removes the upwardly extending wings that previously occupied space, allowing memory cells to be placed closer together while maintaining self-alignment benefits.
Solution Approach 2:
The patent extracts the problematic upwardly extending wing structures from the charge trapping layer by selectively etching the nitride material in the trench regions. This removal eliminates the space occupation that limited scalability while preserving the self-aligned charge trapping functionality over the core cells.
2Productivity
If memory cells are placed closer together, then memory capacity increases, but short channel effect worsens
Solution Approach 1:
The patent addresses the short channel effect by modifying the vertical structure of the charge trapping layer. By removing the upwardly extending wings and creating a more confined vertical profile, the electric field distribution is improved, mitigating short channel effects even as cells are placed closer together horizontally to increase capacity.
3Stability of the object's composition
If a conformal film is used, then film uniformity is improved, but void formation is prevented reducing etch selectivity
Solution Approach 1:
The patent inverts the conventional approach by using a non-conformal film deposition process that intentionally creates voids in the trench regions. This inversion of the conformal deposition principle allows the film to be thinner or absent in specific areas, enabling selective etching of the nitride charge trapping layer in trenches while preserving it over core cells.
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 enables superior scalability by allowing core cells to be placed closer together, reducing the drain voltage and mitigating the short channel effect, thereby enhancing memory capacity and reducing costs.
Implementation Method 1
a non-conformal film is deposited over the charge trapping layer to form a thick film on top of the core source/drain region
Implementation Method 2
A dry or wet etch or a combination of dry and wet etch is performed on the non-conformal film and the thin oxide on the trapping layer
Implementation Method 3
A dry or wet etch or a combination of dry and wet etch is performed on the non-conformal film and the thin oxide on the trapping layer on the STI oxide
Implementation Method 4
subsequent oxidation to isolate the trapping layers
Data Source
AI summary
A method for fabricating a memory device with a self-aligned trap layer which is optimized for scaling is disclosed. In the present invention, a non-conformal film is deposited over the charge trapping layer to form a thick film on top of the core source/drain region and a pinch off and a void or a narrow channel at the top of the STI trench. An etch is performed on the non-conformal film to open pinch-off or widen the narrow channel in the non-conformal. The trapping layer is then completely or partially etched between the core cells. The non-conformal film is removed. And a top oxide is formed. The top oxide converts the remaining trap layer to oxide if the trapping layer is partially etched and thus isolate the trap layer.