Photo-Defined Through-Substrate Vias for Low-Loss Mixed-Signal Substrates
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Solution Overview
Problem
Existing mixed-signal substrates face challenges with increased via length leading to RF losses and high production costs, particularly in large-area silicon interposers, due to high resistivity silicon and thermal expansion mismatches, while previous photo-defined through substrate vias lack customizability and are restricted to specific fabrication processes.
Innovation Solution
The development of mixed-signal substrates with photo-defined through substrate vias and deep-trench decoupling capacitors, featuring varying via arrangements, dimensions, and functions, using photodefineable polymers and metallic fillers, allowing for customizable and low-loss via structures, including coaxial and optical vias, and high-density decoupling capacitors, fabricated using etching and electroplating techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If substrate thickness is increased to minimize warpage and improve mechanical stability, then mechanical stability is improved, but via length increases leading to increased via capacitance and RF losses
Solution Approach 1:
The patent changes the dielectric parameter by replacing conventional silicon dioxide with photodefineable polymer materials having lower dielectric constants (approximately 3.0-3.5 vs. 3.9 for SiO2). This parameter change reduces via capacitance and RF losses while maintaining the required substrate thickness for mechanical stability in large-area interposers
Solution Approach 2:
The patent employs composite material structures by combining photodefineable polymer liners with metallic fillers (copper, aluminum, or tungsten) in the via structures. This composite approach provides both mechanical support for the thick substrate and low-loss electrical performance through the polymer material
2Loss of energy
If high-resistivity silicon is used to combat increased via capacitance and RF losses, then RF losses are reduced, but production cost increases
Solution Approach 1:
The patent changes the material parameter from high-resistivity silicon to photodefineable polymer materials that can be deposited and patterned using standard semiconductor fabrication processes, achieving low RF losses without the high cost of high-resistivity silicon
Solution Approach 2:
The patent uses cost-effective photodefineable polymer materials that can be processed through standard fabrication techniques, replacing expensive high-resistivity silicon while achieving the desired electrical performance through alternative mechanisms
3Reliability
If conventional through-substrate vias are used in thick substrates, then via connectivity is achieved, but via capacitance and RF losses increase
Solution Approach 1:
The patent changes the dielectric parameter surrounding the via by using photodefineable polymer materials with lower dielectric constants, which directly reduces via capacitance while maintaining via connectivity through proper metallization
Solution Approach 2:
The photodefineable polymer acts as an intermediary material between the metallic via filler and the surrounding substrate, providing both mechanical support and low-capacitance electrical isolation that reduces RF losses
4Reliability
If copper metallization is used in through-substrate vias, then electrical conductivity is improved, but thermal expansion mismatch with silicon increases via stresses
Solution Approach 1:
The photodefineable polymer liner serves as a stress-absorbing intermediary between the copper metallization and the silicon substrate, accommodating thermal expansion mismatches during temperature cycling while maintaining via integrity and electrical connectivity
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 approach reduces RF losses and production costs by enabling customizable via arrangements and high-density decoupling capacitors, improving electrical performance and mechanical stability in mixed-signal substrates, while minimizing dependence on expensive high-resistivity silicon and specific fabrication processes.
Implementation Method 1
a photodefineable polymer within at least a portion of each trench, the photodefineable polymer defining one or more channels within each of the plurality of trenches
Data Source
AI summary
Disclosed are a variety of mixed-signal substrates comprising a plurality of photo-defined through substrate vias and methods of making the same. In an embodiment, a mixed-signal substrate can comprise a plurality of trenches embedded in a substrate, a photodefineable polymer within at least a portion of each trench, the photodefineable polymer defining one or more channels within each of the plurality of trenches, and a conductive material filling at least a portion of the one or more channels within the photodefineable polymer to form one or more through substrate vias. The photo-defined through substrate vias can comprise a variety of arrangements, numbers of vias, shapes, and dimensions across a single substrate.