Continuous Active Areas in Standard Cells for IC Layout
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Solution Overview
Problem
Conventional integrated circuits face issues with the last gate on active areas due to undesirable epitaxial growth, undercutting, and material leftovers, leading to performance and yield problems, which existing solutions attempt to address by using dummy gates or minimizing the last gate, but these methods consume significant IC space.
Innovation Solution
The integration of continuous active areas in integrated circuits, where standard cells have parallel active areas extending from boundary to boundary, with gate strips isolated by interconnects directly tied to ground or power rails, eliminating the need for vias or additional wires, thus minimizing the presence of last gates and conserving IC space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional standard cell layouts with bounded active areas are used, then manufacturing processes can be simplified, but the last gate on the active area exhibits performance problems including contact problems, yield problems, and variability problems
Solution Approach 1:
The active area is segmented to extend continuously across standard cell boundaries, dividing the problem of the 'last gate' by eliminating the endpoint where such problems occur. Multiple active areas from adjacent cells align to form a continuous structure, so that gates at cell interfaces are no longer terminal gates but intermediate gates within a larger continuous active region.
Solution Approach 2:
Adjacent standard cells are merged in terms of their active areas, which extend beyond individual cell boundaries to form a continuous active region. This merging eliminates the discrete endpoints that cause last-gate problems, as the active area becomes a continuous structure spanning multiple cells rather than being confined within individual cell boundaries.
2Reliability
If dummy gates are added at the end of active areas to avoid last gate problems, then transistor performance improves, but a significant amount of IC area is consumed
Solution Approach 1:
Instead of adding dummy gates at the end of active areas to mitigate last-gate problems, the invention inverts the approach by extending the active area continuously across cell boundaries. This eliminates the need for dummy gates entirely, as there are no more 'last gates' in the traditional sense - every gate is now an intermediate gate within a continuous active region spanning multiple cells.
3Reliability
If continuous active areas extending across standard cell boundaries are used, then last gates are minimized or eliminated, but gates on each side of the interface between standard cells must be isolated requiring additional IC space
Solution Approach 1:
The isolation of gates at cell interfaces is merged with the existing interconnect structure. Rather than adding separate isolation elements, the interconnect lines that already exist in the standard cell design are utilized to provide both electrical connection and gate isolation functions simultaneously, eliminating the need for additional isolation structures.
Solution Approach 2:
The interconnect structure is given multiple functions: it provides electrical connection between gates and power/ground rails, and simultaneously serves as the isolation mechanism for gates at cell interfaces. This multi-functionality eliminates the need for dedicated isolation structures, avoiding additional IC area consumption.
Data Source
AI summary
Integrated circuits and methods for fabricating integrated circuits are provided. In an embodiment, an integrated circuit includes a standard cell having a first boundary, a second boundary opposite the first boundary, a third boundary interconnecting the first and second boundaries, and a fourth boundary opposite the third boundary and interconnecting the first and second boundaries. The standard cell further includes parallel active areas extending from the first boundary to the second boundary. Also, the standard cell has parallel gate strips extending from the third boundary to the fourth boundary and over the active areas. A cut mask overlies the gate strips. An interconnect is positioned overlying the cut mask and forms an electrical connection with a selected gate strip.