Cross-Coupled Gate Contact Structures for SRAM Area Optimization
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Solution Overview
Problem
The formation of gate contact structures and cross-coupled contact structures in modern integrated circuits is challenging due to the need for precise positioning to avoid electrical shorts and area penalties, particularly in SRAM circuits where gate-to-source/drain contacts are required, and existing methods restrict the placement of gate contacts above the active region to prevent shorts.
Innovation Solution
A novel method involving the formation of gate-to-source/drain (GSD) and CB gate contact openings in insulating material, followed by recess etching to create recessed contact structures, allowing for conductive coupling between gate electrodes and source/drain regions while maintaining the necessary spacing to prevent electrical shorts, enabling the placement of CB gate contacts above the active region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the CB gate contact is positioned above the isolation region to avoid electrical shorts, then electrical short prevention is improved, but chip area utilization deteriorates due to area penalty
Solution Approach 1:
The patent transitions from a two-dimensional planar contact structure to a three-dimensional vertically-stacked contact structure. Multiple contact structures (first contact structure contacting source/drain, second contact structure contacting gate, third contact structure providing cross-coupling) are arranged vertically above the active region, allowing electrical connections to be established without requiring lateral spacing that would consume chip area.
Solution Approach 2:
The patent implements a nested arrangement where multiple contact structures are positioned vertically one above another. The first contact structure contacts the source/drain region, the second contact structure contacts the gate electrode, and the third contact structure provides cross-coupling between them, with all three contacts vertically aligned or closely spaced above the active region, similar to nested dolls occupying the same footprint.
2Adaptability or versatility
If cross-coupled contact structures are formed to enable gate-to-source/drain connectivity, then circuit functionality is improved, but manufacturing complexity increases
Solution Approach 1:
The patent forms all three contact structures (first contact to source/drain, second contact to gate, third contact for cross-coupling) during the same fabrication process step, before subsequent metallization layers are deposited. This preliminary formation of multiple contacts in one go simplifies the overall manufacturing process compared to forming them separately in different steps.
Solution Approach 2:
The contact structures serve multiple functions: the first contact structure provides source/drain connection, the second contact structure provides gate connection, and the third contact structure enables cross-coupling between gate and source/drain. This multi-functionality is achieved within a unified contact formation process, reducing the need for separate specialized process steps.
Data Source
AI summary
One integrated circuit (IC) product disclosed herein includes a first conductive source/drain contact structure of a first transistor and an insulating source/drain cap positioned above at least a portion of an upper surface of the first conductive source/drain contact structure. In one example, the product also includes a gate-to-source/drain (GSD) contact structure that is conductively coupled to the first conductive source/drain contact structure and a first gate structure of a second transistor, wherein an upper surface of the GSD contact structure is positioned at a first level that is at a level above the upper surface of the first conductive source/drain contact structure, and a CB gate contact structure that is conductively coupled to a second gate structure of a third transistor, wherein an upper surface of the CB gate contact structure is positioned at a level that is above the first level.