Dummy Diffusion Guard Bands for STI Stress Control
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Solution Overview
Problem
Conventional integrated circuit designs fail to achieve uniform drive current performance across MOS devices due to variations in shallow trench isolation (STI) stress, which are influenced by irregular diffusion patterns and spacing, leading to unpredictable device performance and simulation inaccuracies.
Innovation Solution
A method involving the formation of guard bands conforming to active layer shapes with uniform spacings and the addition of dummy diffusion patterns outside these bands to control STI widths and reduce stress variations, ensuring consistent diffusion spacings and densities across the chip.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If dummy diffusion patterns are added to fill spacing variations, then diffusion density uniformity is improved, but STI stress variation is not adequately controlled
Solution Approach 1:
The dummy diffusion patterns are segmented into two distinct types: guard bands that conform to active layer shapes with uniform spacings, and fill patterns that occupy remaining spaces. This segmentation allows each type to serve a specific function - guard bands control STI stress by maintaining consistent spacing, while fill patterns achieve diffusion density uniformity without interfering with stress control.
Solution Approach 2:
Different regions of the chip receive different treatments: areas near active layers receive guard bands with specifically controlled uniform spacings to manage STI stress, while other areas receive fill patterns to achieve overall diffusion density uniformity. This local differentiation resolves the contradiction by addressing each region's specific requirements.
2Manufacturing precision
If conventional dummy patterns are placed randomly outside block layers, then manufacturing process uniformity is improved, but STI width control deteriorates
Solution Approach 1:
Guard bands are placed in preliminary positions with predetermined uniform spacings relative to active layers before final layout completion. This preliminary positioning ensures that STI widths will be consistent, while subsequent fill patterns are added to achieve CMP uniformity without disrupting the pre-established spacing relationships.
3Adaptability or versatility
If spacing between MOS devices is varied to accommodate layout, then layout flexibility is improved, but drive current uniformity deteriorates
Solution Approach 1:
The guard band structure introduces asymmetry by conforming to the specific shapes of active layers while maintaining uniform spacings. This asymmetric design allows the layout to adapt to different circuit configurations while the uniform spacing relationship ensures consistent STI stress and drive current characteristics across all devices.
Data Source
AI summary
A method of forming an integrated circuit structure on a chip includes extracting an active layer from a design of the integrated circuit structure, forming a guard band conforming to the shape of the active layer, the guard band surrounds the active layer, and the guard band is spaced from the active layer at a first spacing in the X-axis direction and at a second spacing in the Y-axis direction, removing any part of the guard band that violates design rules, removing convex corners of the guard band, and adding dummy diffusion patterns into the remaining space of the chip outside the guard band. The first and second spacing can be specified as the same spacings in a Spice model characterization of the integrated circuit structure. The dummy diffusion patterns with different granularities can be added so that the diffusion density is substantially uniform over the chip.