Pyramiding Via Structure for Thermal Gradient Management
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Solution Overview
Problem
Abrupt thermal gradients caused by high currents in back-end of line (BEOL) devices, particularly in vias made of highly resistive materials like tungsten, lead to reliability issues such as sudden structure breakdown, delamination, and cracking due to stress from uneven temperature spikes.
Innovation Solution
A pyramiding via structure with a larger surface area and cross-sectional area is created, allowing for easier dissipation of thermal energy from Joule heating, reducing current density and generating a gradual temperature gradient by connecting multiple via plugs of large surface area to a single via plug or a single via plug with a larger surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high currents pass through highly resistive materials in vias, then electrical connection is achieved, but abrupt temperature spikes occur causing reliability problems
Solution Approach 1:
The via structure is segmented into multiple via sets (first via set, second via set) with different cross-sectional areas, creating a pyramiding configuration. This segmentation allows the heat generation and dissipation to be distributed across multiple regions with gradual area transitions, preventing abrupt temperature spikes while maintaining electrical connectivity through via plugs.
Solution Approach 2:
Different via sets are designed with different local qualities - specifically different cross-sectional areas. The first via set has a smaller cross-sectional area while the second via set has a larger cross-sectional area. This local variation in geometry creates a gradual temperature gradient from smaller to larger areas, allowing heat to dissipate more effectively in regions with larger cross-sections.
2Loss of energy
If via cross-sectional area is increased to reduce current density, then Joule heating is reduced, but device complexity increases
Solution Approach 1:
The via structure is divided into multiple via sets with progressively changing cross-sectional areas. This segmentation allows the total current path to be distributed across multiple regions, effectively reducing the current density in any single via set and thereby reducing Joule heating, while maintaining a manageable structural complexity through systematic progression.
Solution Approach 2:
The solution transitions from a single-dimension via structure to a multi-dimensional pyramiding configuration with via sets arranged in different layers or positions. By utilizing the vertical and spatial dimensions, the current path is extended and distributed across multiple via sets with varying cross-sectional areas, reducing Joule heating without requiring excessive complexity in any single plane.
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
The novel via structure eliminates the problems associated with abrupt temperature changes, enhancing reliability by preventing potential failure, delamination, and cracking under high currents, ensuring structural integrity.
Implementation Method 1
the thermal energy coming from the Joule heating caused by the high current
Implementation Method 2
Owing to a large surface area, the thermal energy coming from the Joule heating due to high current is dissipated more easily
Data Source
AI summary
A via structure includes at least a first via set and a second via set electrically connected to the first via set. There is at least one via in the first via set and at least one via in the second via set. The via in the first via set has a cross-sectional area which is larger than that of the via in the second via set.