Hybrid Copper RDL Structure for Electromigration-Resistant IC Packaging
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Solution Overview
Problem
The challenge in advanced 2.5D/3D IC packaging is the limited usage of nanotwinned copper in manufacturing due to difficulties in via-filling and the formation of voids, which exacerbates electromigration and thermal migration issues in fine-pitch redistribution layers (RDLs) with high current densities.
Innovation Solution
A hybrid copper structure combining fine grains and nanotwinned copper is developed, with a weight ratio of 30:70, to enhance structural stability and resistance to surface corrosion, formed by electroplating a solution containing CuSO4·5H2O, H2SO4, HCl, and additives, which reduces oxidation rates and improves electromigration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nanotwinned copper is used in RDL structures, then electromigration resistance is improved, but manufacturing difficulty increases due to via-filling challenges and void formation
Solution Approach 1:
The patent employs a composite copper structure combining nanotwinned copper regions and coarse-grained copper regions within the same RDL. The nanotwinned copper (with twin boundaries spaced 50-500 nm apart) provides superior electromigration resistance, while the coarse-grained copper facilitates easier manufacturing and via-filling. This composite approach allows the structure to benefit from both the high reliability of nanotwinned copper and the manufacturing ease of conventional copper structures.
2Stability of the object's composition
If nanotwinned copper structure is formed, then structural stability is improved, but manufacturing complexity increases due to special electrolyte requirements
Solution Approach 1:
The patent applies local quality by creating distinct regions with different grain structures within the copper RDL. The nanotwinned copper regions (50-500 nm twin spacing) provide enhanced structural stability and electromigration resistance, while coarse-grained regions provide manufacturing flexibility. This localized differentiation allows each region to optimize its properties for its specific function without requiring the entire structure to meet the most stringent manufacturing requirements.
3Area of moving object
If RDL dimension is reduced below 10 μm, then device density is improved, but current density increases leading to enhanced electromigration
Solution Approach 1:
The patent changes the microstructural parameters of the copper RDL by introducing nanotwins with specific spacing (50-500 nm) and controlling the volume fraction of nanotwinned regions (30-70%). This parameter optimization allows the RDL to maintain low electromigration sensitivity even at reduced dimensions below 10 μm, as the nanotwin boundaries act as barriers to dislocation motion and atomic diffusion, thereby compensating for the increased current density in narrower conductors.
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 hybrid copper structure significantly increases electromigration lifetime by at least 50% at high current densities, with a maximum increase of 190% at 4×106 A/cm2, and maintains structural integrity even after extended post-plating resting periods, addressing the limitations of nanotwinned copper in real manufacturing processes.
Implementation Method 1
formed by electroplating a solution containing CuSO4·5H2O, H2SO4, HCl, and additives
Implementation Method 2
enhance structural stability and resistance to surface corrosion, formed by electroplating a solution containing CuSO4·5H2O, H2SO4, HCl, and additives, which reduces oxidation rates
Implementation Method 3
the diffusion rate of copper atoms could be significantly reduced by ten times when copper atoms pass through triple junctions of twin boundaries and grain boundaries
Data Source
AI summary
The present invention introduces a composite copper (Cu) structure that combines fine grains and nanotwins, providing structural stability and effective resistance to surface damage even after extended periods. This offers a promising solution for achieving finer Redistribution Layer (RDL) in advanced packaging technologies, with a longer electromigration lifetime compared to regular coarse-grain lines.