T-Shaped STI Widened Cap for Flash Memory Alignment
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Solution Overview
Problem
The alignment accuracy tolerance of floating gate wing fabrication in flash memory cells is challenging due to the stringent requirements in 90 nm manufacturing processes, where conventional methods struggle to maintain the necessary precision below 30 nm.
Innovation Solution
A novel method involving the formation of a T-shaped shallow trench isolation (STI) structure with a widened cap layer, which increases the process window during floating gate wing fabrication by allowing for greater alignment accuracy tolerance through the use of a substrate with a conductive layer and insulating structure, where the cap layer is wider than the bottom, embedded in the conductive layer and substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional floating gate fabrication methods are used, then manufacturing simplicity is maintained, but alignment accuracy tolerance deteriorates (cannot achieve below 30 nm precision)
Solution Approach 1:
The patent divides the floating gate fabrication process into multiple stages: forming the first conductive layer with initial pattern, depositing the second conductive layer, and performing selective etching to create the floating gate wing structure. This segmentation allows each step to be optimized independently, achieving below 30 nm alignment accuracy while maintaining manageable process complexity.
Solution Approach 2:
The patent performs preliminary actions by first forming the first conductive layer and first mask layer with precise patterns before depositing the second conductive layer. The shallow trench isolation structure is also prepared in advance with specific dielectric layers. These preliminary structures serve as alignment references that guide subsequent fabrication steps, ensuring the required alignment accuracy tolerance is achieved.
2Productivity
If floating gate wing is formed to increase gate coupling ratio, then programming and erasing speed is improved, but alignment precision requirement becomes more stringent (below 30 nm)
Solution Approach 1:
The patent introduces a shallow trench isolation structure with specific dielectric layers as an intermediary element between the floating gate and surrounding structures. This isolation structure acts as a mediator that defines precise boundaries and alignment references, enabling the floating gate wing to achieve the necessary sub-30 nm alignment accuracy while maintaining the enhanced gate coupling ratio for faster programming and erasing operations.
Solution Approach 2:
The patent changes critical parameters including the width and depth of the shallow trench isolation, the thickness of dielectric layers, and the pattern dimensions of conductive layers. By optimizing these parameters, the patent achieves both high gate coupling ratio (for speed) and precise alignment (below 30 nm tolerance), resolving the contradiction between productivity and manufacturing precision.
3Adaptability or versatility
If shallow trench isolation with widened cap layer is formed, then process window is increased, but fabrication process complexity increases
Solution Approach 1:
The patent employs asymmetric design in the shallow trench isolation structure by creating a widened cap layer that extends beyond the trench boundaries. This asymmetric structure provides increased process window and tolerance for alignment variations. The asymmetric isolation structure serves as a robust reference framework that simplifies subsequent symmetric pattern formation, effectively managing overall fabrication complexity while enhancing adaptability.
Solution Approach 2:
The widened cap layer of the shallow trench isolation structure serves as a beforehand cushioning element that compensates for potential alignment errors and process variations in subsequent fabrication steps. By providing this extra margin of tolerance in advance, the patent increases the process window and makes the overall fabrication process more robust, while the standardized isolation structure keeps the added complexity manageable.
Data Source
AI summary
A method of fabricating a flash memory and an isolating structure applied to a flash memory is provided. The feature of the method lies in a T-shaped shallow trench isolation (STI). The T-shaped STI has a widened cap covering on a substrate and a tapered bottom embedded in the substrate. The widened cap of the T-shaped STI can provide a high process widow when fabricating the floating gate wings, and the product yield will thereby be increased.