Zigzagged Dummy Metal Edges for Thermal Stress Relief
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Solution Overview
Problem
In the formation of integrated circuits, long straight edges of dummy metal pads can lead to cracking during thermal cycles due to uniform contraction or expansion, causing stress that results in cracks at the interface with dielectric materials.
Innovation Solution
The edges of dummy metal pads are redesigned with a zigzag pattern, where sections are shorter than a threshold length (approximately 400 μm) and extend in different directions, reducing the stress vector and likelihood of cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If long straight edges are used for dummy metal pads, then the manufacturing process is simple, but cracking occurs during thermal cycles due to uniform stress
Solution Approach 1:
The dummy metal pad is segmented into multiple sections by introducing zigzagged edges with alternating protrusions and recesses. This segmentation divides the continuous stress path into discrete segments, preventing uniform stress accumulation along long straight edges during thermal cycles, thereby reducing cracking while maintaining manufacturing simplicity
Solution Approach 2:
The dummy metal pad transitions from symmetric straight edges to asymmetric zigzagged edges with alternating protrusions and recesses. This asymmetry creates non-uniform stress distribution that prevents stress concentration at any single location, improving reliability during thermal expansion and contraction while keeping the manufacturing process straightforward
2Reliability
If zigzagged edges with sections shorter than threshold length are used, then cracking is reduced during thermal cycles, but the manufacturing precision requirements increase
Solution Approach 1:
The edge geometry parameters are changed from straight lines to zigzagged patterns with specific section lengths below a threshold (e.g., 400 μm). This parameter change disrupts uniform stress distribution, improving reliability during thermal cycles. The precision requirement increases but remains manageable through standard fabrication processes
3Reliability
If long straight edges are used, then the stress vector is concentrated, but if zigzagged edges are used, then the stress vector is distributed and cracking is reduced
Solution Approach 1:
The straight edges are replaced with curved zigzagged edges featuring alternating protrusions and recesses. This curvature introduces stress distribution along the edge path, preventing stress concentration and reducing cracking during thermal cycles. The added geometric complexity is minimal and does not significantly increase device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design discontinues the stress on the metal pads, reducing the occurrence of cracks along the edges during thermal cycles, ensuring the reliability of the dielectric and metal interfaces.
Implementation Method 1
long straight edges of dummy metal pads can lead to cracking during thermal cycles due to uniform contraction or expansion
Implementation Method 2
long straight edges of dummy metal pads can lead to cracking during thermal cycles due to uniform contraction or expansion
Data Source
AI summary
A structure includes a metal pad, a passivation layer having a portion covering edge portions of the metal pad, and a dummy metal plate over the passivation layer. The dummy metal plate has a plurality of through-openings therein. The dummy metal plate has a zigzagged edge. A dielectric layer has a first portion overlying the dummy metal plate, second portions filling the first plurality of through-openings, and a third portion contacting the first zigzagged edge.