Tap Cell Isolation Layout for CMOS Latch-Up Prevention
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Solution Overview
Problem
Conventional latch-up prevention structures in CMOS ICs, such as guard rings and tap cells, occupy significant real estate on IC chips and are not entirely satisfactory in preventing latch-up due to the need for isolation structures that displace functional devices and introduce layout-dependent effects.
Innovation Solution
The use of fin-cut dielectric features formed after source/drain and metal gate structures to isolate tap cells from standard cells, eliminating the need for OD breaks and allowing for smaller isolation structures, along with interlocking well shapes to minimize area usage and improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional isolation structures are used to isolate tap cells from standard cells, then latch-up prevention is achieved, but the area occupied by isolation structures increases and displaces functional devices
Solution Approach 1:
The patent extracts the isolation function from traditional extensive isolation structures and concentrates it into targeted fin-cut dielectric features placed only at critical interfaces between tap cells and standard cells. This selective placement maintains latch-up prevention while minimizing the area occupied by isolation structures, allowing more space for functional devices.
Solution Approach 2:
The patent applies isolation structures with local quality by using fin-cut dielectric features specifically at the boundaries between tap cells and standard cells, rather than providing uniform isolation across the entire chip. This localized approach provides effective latch-up prevention exactly where needed while reducing overall isolation structure area.
2Reliability
If conventional isolation structures with OD breaks are used, then tap cells are isolated from standard cells, but layout-dependent effects are introduced and area is increased
Solution Approach 1:
The patent removes the need for OD breaks by using fin-cut dielectric features that provide isolation without requiring discontinuities in the active region. This extraction of the isolation function from OD breaks eliminates the associated layout-dependent effects and simplifies the overall device structure.
Solution Approach 2:
The patent changes the isolation mechanism from OD breaks (which require specific layout parameters and create discontinuities) to fin-cut dielectric features (which provide isolation through physical separation). This parameter change eliminates layout-dependent effects while maintaining effective cell isolation.
3Reliability
If tap cells are placed among standard cells for latch-up prevention, then latch-up is prevented, but the real estate for functional devices is reduced
Solution Approach 1:
The patent extracts the isolation function into compact fin-cut dielectric features, which reduces the space required for each tap cell. This allows tap cells to be placed among standard cells with minimal impact on functional device density, maintaining both latch-up prevention and high productivity.
Solution Approach 2:
The patent applies minimal isolation structures only where necessary between tap cells and standard cells, rather than providing extensive isolation that would consume significant area. This localized isolation approach maintains functional device density while ensuring latch-up prevention.
Data Source
AI summary
Semiconductor structures and methods are provided. A semiconductor structure according to an embodiment includes a first cell disposed over a first well doped with a first-type dopant, a second cell disposed over the first well, and a tap cell disposed over the first well. The tap cell is sandwiched between the first cell and the second cell. The first cell includes a first plurality of transistors and the second cell includes a second plurality of transistors.