DRAM Bit Line Trench Structure for Parasitic Capacitance Control
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Solution Overview
Problem
Conventional DRAM cell designs face issues with short channel effects and increased parasitic capacitance due to shrinking device sizes, leading to unexpected connections between word lines and bit lines, which affect the reliability and efficiency of semiconductor memory devices.
Innovation Solution
A semiconductor structure with a substrate having active and isolation areas, where bit lines are formed within the active areas with a conductive structure and insulating layer, and additional bit lines are aligned with isolation areas to prevent unexpected electrical connections, using a sacrificial layer to ensure precise alignment and avoid conductive material residual risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If device size is reduced to increase density, then storage density is improved, but parasitic capacitance increases and unexpected connections occur
Solution Approach 1:
The substrate is divided into distinct active areas and isolation areas, with bit lines precisely confined to active areas through controlled trench formation. This segmentation prevents unwanted electrical connections between adjacent bit lines while maintaining high density through optimized spacing.
Solution Approach 2:
Different regions of the substrate are assigned different functions: active areas contain bit lines for data transmission, while isolation areas provide electrical separation. The bit lines have varying widths (first width at top level, second width at bottom level) to optimize both connectivity and isolation properties in different spatial locations.
2Quantity of substance
If channel length is reduced to increase density, then storage density is improved, but short channel effects such as DIBL increase
Solution Approach 1:
The bit line structure transitions from a simple planar configuration to a multi-dimensional structure with trenches extending into the substrate. This vertical dimension provides better electrostatic control over the channel region, suppressing short channel effects like DIBL while maintaining reduced channel length for high density.
Solution Approach 2:
The bit line structure is nested within the active area, with the conductive bit line material contained within trenches that are themselves defined within the active region boundaries. This nested configuration provides multiple layers of confinement that improve electrostatic control and reduce short channel effects.
3Ease of operation
If bit line etching is performed to form connections, then connectivity is improved, but conductive material residual risk increases causing unexpected connections
Solution Approach 1:
The problematic conductive material residues are completely removed by forming trenches that extend through the bit line formation region and into the substrate. This extraction of material eliminates the source of residual contamination that could cause unexpected connections, while the trench structure itself provides the necessary connectivity pathways.
Solution Approach 2:
The trenches are formed in advance before bit line material deposition, creating pre-defined pathways that confine the conductive material. This preliminary action ensures that bit line material can only deposit within the intended trench regions, preventing residual material from forming in isolation areas and causing unexpected connections.
Data Source
AI summary
A semiconductor structure includes a substrate and a bit line. The substrate has a plurality of active areas and isolation areas. Each isolation area is located between immediately-adjacent two of the active areas to isolate the active areas from each other. The first bit line is formed on a first active area of the active areas. A bottom portion of the first bit line extends within the first active area. The extending bottom portion is surrounded by the first active area.