Compact SRAM Structure Using Backside Connections Without Tap Cells
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Solution Overview
Problem
Existing SRAM structures require tap cells in the edge region to prevent latch-up issues, which increase the geometry size and reduce functional density.
Innovation Solution
The SRAM structure eliminates tap cells by connecting source/drain features to supply voltages via backside connections, reducing the need for edge region tap cells and allowing for a more compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If tap cells are included in the edge region to prevent latch-up issues, then reliability is improved, but the geometry size increases
Solution Approach 1:
The patent moves the connection path from the planar (2D) edge region to the vertical (3D) dimension by implementing backside connections through substrate through-holes. This allows the source/drain features to be connected to supply voltages via conductive paths that traverse through the substrate thickness, effectively removing the need for lateral tap cell structures and reducing the planar geometry size while maintaining latch-up prevention functionality.
Solution Approach 2:
The patent introduces intermediary structures including substrate through-holes filled with conductive material and intermediate conductive layers that facilitate the connection between source/drain features and supply voltages through the substrate. These intermediary elements enable the backside connection architecture, allowing voltage supply without requiring traditional edge-region tap cells.
2Reliability
If tap cells are included in the edge region to prevent latch-up issues, then reliability is improved, but functional density decreases
Solution Approach 1:
By transitioning from lateral connections in the planar dimension to vertical connections through the substrate dimension, the patent eliminates the need for tap cells occupying edge region area. This frees up functional area for additional memory cells or circuitry, thereby increasing functional density while maintaining the essential latch-up prevention capability through the alternative backside connection path.
Solution Approach 2:
The intermediary conductive structures (through-holes and intermediate layers) enable voltage supply through the substrate without consuming functional area. This mediator approach allows the main functional region to be fully utilized for productive purposes while the latch-up prevention function is achieved through the intermediary backside connection infrastructure.
3Length of stationary object
If backside connections are used to eliminate tap cells, then geometry size is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent segments the connection architecture into distinct components: substrate through-holes, intermediate conductive layers, and final connection points. This segmentation allows each element to be formed using specialized processes optimized for that specific structure type, making the overall complex architecture manageable through modular fabrication steps rather than attempting to create the entire connection system in a single process.
Solution Approach 2:
The patent incorporates the formation of substrate through-holes and intermediate conductive layers as preliminary actions during the fabrication sequence, establishing the backside connection infrastructure before final device assembly. By preparing these connection pathways in advance, the patent simplifies subsequent steps and avoids the need for complex post-processing or retroactive modifications.
Data Source
AI summary
A static random-access memory (SRAM) structure and the manufacturing method thereof are disclosed. An exemplary SRAM structure includes a first source/drain (S/D) feature and a second S/D feature formed in an interlayer dielectric layer (ILD) of a bit cell region of the SRAM structure, a frontside via electrically connecting to the first S/D feature, and a first backside via electrically connecting to the second S/D feature. The first S/D feature and the second S/D feature are of a same type.