TSV Dummy Structure for Thermal Stress Relief
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Solution Overview
Problem
Interface failure between through-silicon via (TSV) and interconnect pads, particularly due to thermal stress caused by temperature coefficient differences, leads to delamination issues in 3D integrated circuits.
Innovation Solution
Incorporating dummy structures around the vertical conductive post to improve adhesion between the top pad and interconnect pad, enhancing thermal tolerance and reliability by distributing stress evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper TSV is connected to aluminum interconnect pad, then electrical connection is achieved, but thermal stress causes delamination due to temperature coefficient difference
Solution Approach 1:
A dummy structure is introduced as an intermediary element between the copper TSV and aluminum interconnect pad. This dummy structure serves as a stress buffer that mediates the thermal expansion mismatch between the two dissimilar metals, preventing direct stress transmission that would cause delamination at the Cu-Al interface.
Solution Approach 2:
The dummy structure modifies the thermal and mechanical parameters of the interface region. By introducing a material or structure with intermediate thermal expansion properties, the abrupt parameter change between copper and aluminum is smoothed, reducing thermal stress concentration during temperature cycling.
2Reliability
If dummy structures are added around vertical conductive post, then adhesion and thermal tolerance are improved, but device complexity increases
Solution Approach 1:
The dummy structure is segmented into discrete elements positioned around the vertical conductive post rather than forming a continuous layer. This segmentation provides the necessary stress distribution function while minimizing the total material volume and structural complexity compared to a full dummy interconnect layer.
Solution Approach 2:
The dummy structure is applied locally only where thermal stress concentration occurs at the TSV-pad interface, rather than throughout the entire device. This localized application provides targeted stress relief exactly where needed while avoiding unnecessary complexity in other regions of the device.
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 TSV structure with dummy structures significantly increases temperature tolerance and maintains performance for over 2000 hours under stress, compared to conventional structures which fail within a day.
Implementation Method 1
Interface failure between TSV and interconnect pad is problematic. For example, copper TSV connected to an aluminum interconnect pad suffers high thermal stress because of temperature coefficient difference and the large thickness of copper.
Data Source
AI summary
A method of forming a through silicon via (TSV) structure includes forming an interconnect pad over a substrate. An under layer is formed over the interconnect pad. A vertical conductive post is formed at least partially through the substrate. At least one dummy structure is formed at least partially through the under layer. A top pad is formed over the dummy structure and the vertical conductive post. The top pad covers a wider area than a cross section of the vertical conductive post. The interconnect pad is electrically connected to the top pad. The dummy structure connects the top pad and the under layer thereby fastening the top pad and the interconnect pad.