L-Shaped SRAM Contact Plug for Line-End Bridging
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Solution Overview
Problem
In deep micro technology, long contact plugs are used to reduce contact sizes without increasing contact resistance, but they can lead to line-end shortening and bridging issues, which are exacerbated in future fin-type MOSFETs due to their narrow active regions, posing challenges for integrated circuit manufacturing.
Innovation Solution
The use of L-shaped contact plugs and data node jogs in SRAM cells, where the L-shaped contact plugs have one leg parallel to the gate electrodes and the other leg perpendicular, eliminating line-end facing issues by redirecting line ends to face gate electrodes, thereby reducing the likelihood of line-end shortening and bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If long contact plugs are used to reduce contact sizes, then gate density is improved and contact resistance is reduced, but line-end shortening and line-end bridging occur
Solution Approach 1:
The patent applies dimensionality change by transitioning from traditional straight contact plugs to L-shaped contact plugs. The L-shape introduces a second spatial dimension (vertical stacking) to the contact structure, allowing the contact to reach the active region while positioning line ends away from neighboring contacts. This geometric transformation in another dimension resolves the line-end bridging issue while maintaining the long contact plug benefits for gate density and contact resistance.
Solution Approach 2:
The L-shaped contact plug can be viewed as segmented into two perpendicular segments: a first segment extending in the gate pitch direction and a second segment extending in the gate lengthwise direction. This segmentation allows each segment to serve a specific function - the first segment provides the lateral reach while the second segment provides the vertical connection, and crucially, positions line ends away from neighboring contacts to prevent bridging.
2Reliability
If spacing between contact plugs is increased to reduce line-end shortening, then reliability is improved, but gate density decreases
Solution Approach 1:
By changing the contact plug geometry to L-shaped, the patent utilizes another spatial dimension to redirect line ends away from neighboring contacts. This allows maintaining tight spacing in the gate pitch direction while preventing line-end shortening through the perpendicular orientation of the second segment, thus resolving the contradiction between reliability and gate density.
3Reliability
If Optical Proximity Correction is made more aggressive to reduce line-end bridging, then reliability is improved, but manufacturing complexity increases
Solution Approach 1:
Instead of applying complex OPC processes to mitigate line-end bridging, the patent inverts the approach by designing the contact plug geometry itself to prevent bridging. The L-shape inherently positions line ends away from neighboring contacts, eliminating the need for aggressive OPC and reducing manufacturing complexity while maintaining reliability.
Data Source
AI summary
A Static Random Access Memory (SRAM) cell includes a first pull-up transistor and a second pull-up transistor, and a first pull-down transistor and a second pull-down transistor forming cross-latched inverters with the first pull-up transistor and the second pull-up transistor. A conductive feature includes a first leg having a first longitudinal direction, wherein the first leg interconnects a drain of the first pull-up transistor and a drain of the first pull-down transistor. The conductive feature further includes a second leg having a second extending direction. The first longitudinal direction and the second extending direction are un-perpendicular and un-parallel to each other. The second leg interconnects the drain of the first pull-up transistor and a gate of the second pull-up transistor.