Rhombic Reverse Fill Pattern for IC Metal Density and Current Crowding
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Solution Overview
Problem
Integrated circuits face challenges in meeting stringent local metal density requirements without exacerbating issues like IR drop and electromigration, which can lead to operational failures due to current crowding and physical damage to conductors.
Innovation Solution
A rhombic reverse fill pattern is designed and implemented in metal layers of integrated circuits, where slots are formed in a substantially rhombic shape to ensure even current distribution, preventing current crowding and allowing for more stringent metal density targets to be met without increasing conductor width or adding extra metal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rectangular slots are used in reverse fill pattern, then metal density targets can be achieved, but current crowding occurs leading to IR drop and electromigration problems
Solution Approach 1:
The patent transforms the traditional rectangular slot geometry into a rhombic (diamond-shaped) slot geometry. This asymmetric shape change fundamentally alters the current flow distribution pattern, preventing current crowding at slot corners while maintaining effective metal density control. The rhombic slots are oriented with diagonals parallel and perpendicular to the runner direction, creating symmetric current distribution relative to the runner axis.
Solution Approach 2:
The patent modifies geometric parameters of the slots including shape (from rectangular to rhombic), size, and spacing. By changing the slot shape to rhombic and optimizing dimensions such as slot diagonal lengths and spacing distances, the invention achieves both metal density targets and uniform current distribution. The slot dimensions are specifically tuned to prevent current crowding while meeting density requirements.
2Reliability
If conductor width is increased to prevent IR drop and electromigration, then reliability improves, but chip area increases
Solution Approach 1:
The patent applies local quality modification by introducing rhombic slots strategically positioned within the metal runner. Instead of uniformly increasing conductor width across the entire chip, the invention locally modifies the metal distribution by creating rhombic voids that prevent current crowding. This allows maintaining narrow conductor widths while ensuring reliable current distribution through the slot geometry that promotes uniform current density.
3Manufacturing precision
If slot-to-slot spacing is reduced to meet metal density targets, then metal density control improves, but current crowding worsens
Solution Approach 1:
The transition from rectangular to rhombic slot geometry fundamentally changes how spacing affects current distribution. The rhombic shape with diagonals oriented parallel and perpendicular to the runner creates a current flow pattern that remains uniform even at reduced spacings. The asymmetric diamond shape distributes current more evenly around each slot compared to rectangular slots, allowing tighter spacing without current crowding.
Data Source
AI summary
A reverse fill pattern is used in an integrated circuit (IC) that comprises a metal layer having slots formed therein in the shape of rhombuses. The distribution of rhombic slots ensures that electrical current is evenly distributed in the conductor, even at the edge regions of the conductor. This even distribution of rhombic slots ensures that electrical current is evenly distributed at least in the central region, and in most if not all cases, across the entire region of the conductor including the edge regions. Thus, the reverse fill pattern prevents current crowding. By preventing current crowding, more stringent metal distribution targets can be met without creating or exacerbating problems associated with IR drop and EM, and without having to add any extra metal to avoid such problems.