Saddle-Shaped N+/N-/N+ Source Structure for DRAM Cell Isolation
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Solution Overview
Problem
Conventional DRAM configurations suffer from wordline-wordline (WL-WL) disturb failures due to changes in the operation state of adjacent cells, which affect the information stored in other cells, necessitating an improved semiconductor structure to reduce these disturbances.
Innovation Solution
A semiconductor structure featuring a semiconductor substrate with an active area divided into source and drain regions by trenches, containing a saddle-shaped N+/N−/N+ structure and trench gates made of titanium nitride and tungsten, with N+ extension regions overlapping the trench gates to suppress WL-WL disturb and reduce bitline-bitline coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional DRAM layout with perpendicular wordlines and shared source region is used, then high integration and miniaturization are achieved, but wordline-wordline disturb failures occur between adjacent cells
Solution Approach 1:
The shared source region is segmented into two separate source regions by introducing a saddle-shaped N+/N−/N+ structure. This segmentation electrically isolates adjacent memory cells, preventing wordline-wordline disturb while maintaining high integration. The saddle-shaped structure creates distinct potential wells that confine carriers within each cell's source region.
Solution Approach 2:
The saddle-shaped N+/N−/N+ structure introduces localized doping variations with different conductivity types (N+ and N−) in specific spatial positions. This local quality modification creates electrostatic potential barriers that selectively prevent carrier diffusion between adjacent cells while maintaining proper transistor operation within each cell.
2Productivity
If memory cell layout is miniaturized for high integration, then device density increases, but wordline-wordline disturb and bitline-bitline coupling increase
Solution Approach 1:
The saddle-shaped N+/N−/N+ structure segments the continuous source region into isolated pockets, preventing electrical interaction between adjacent cells. This segmentation maintains high integration density while eliminating crosstalk and disturb effects that increase with miniaturization.
Solution Approach 2:
The N− region in the saddle-shaped structure acts as an intermediary barrier between adjacent N+ source regions. This intermediate layer with different doping characteristics creates electrostatic potential barriers that block carrier diffusion and prevent harmful electrical coupling between miniaturized adjacent cells.
3Ease of manufacture
If adjacent cells share a common source doping region, then manufacturing is simplified, but information integrity between cells is compromised due to state changes affecting neighboring cells
Solution Approach 1:
The saddle-shaped N+/N−/N+ structure segments what would otherwise be a common source region into electrically isolated individual source regions. Although the doping process remains similar to conventional methods, the resulting structure prevents information loss by confining carriers within each cell's dedicated source region.
Solution Approach 2:
By introducing localized N− regions within the source area, the structure creates local electrostatic barriers that prevent carrier diffusion between cells. This local quality modification maintains manufacturing simplicity while ensuring information integrity through electrostatic confinement.
Data Source
AI summary
A semiconductor structure includes a semiconductor substrate, an active area in the semiconductor substrate, two trenches intersecting the active area to thereby divide the active area into a source region and two drain regions spaced apart from the source region, a saddle-shaped N+/N−/N+ structure in the source region of the active area; and two N+ drain doping regions in the two drain regions, respectively.