Nanotwinned Copper Bonding Surfaces for Low-Temperature Joining
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Solution Overview
Problem
Current direct copper-copper bonding methods require high thermal budgets and ultra-high vacuum conditions, leading to void formation and reliability issues, and are not universally applicable in IC fabrication contexts.
Innovation Solution
Forming copper features with nanotwinned structures and using electroplanarization to achieve direct copper-copper bonding at low temperatures and moderate pressures, eliminating the need for chemical mechanical polishing (CMP) by electrochemically removing excess copper to ensure smooth and uniform bonding surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high thermal budget and ultra-high vacuum conditions are used for direct copper-copper bonding, then bonding strength is improved, but void formation increases and reliability deteriorates
Solution Approach 1:
The patent changes the bonding parameters from high temperature (thermal budget) and ultra-high vacuum to low temperature and atmospheric pressure conditions. This is achieved by modifying the surface properties of copper features through electroplanarization and nanotwinning, which enable cold welding at temperatures below 250°C without requiring vacuum conditions, thereby eliminating void formation while maintaining bonding strength
Solution Approach 2:
The patent replaces the thermal-mechanical bonding system (high temperature and pressure) with an electrochemical-preparation system. By using electroplanarization to create atomically smooth surfaces and nanotwinned structures to enhance surface energy, the bonding process substitutes thermal activation with surface preparation, enabling reliable bonding at low temperatures without vacuum equipment
2Ease of manufacture
If conventional electroplating is used to form copper features, then manufacturing simplicity is improved, but surface uniformity deteriorates
Solution Approach 1:
The patent applies preliminary electroplanarization treatment to copper features before bonding to remove surface irregularities, oxides, and contaminants. This pre-treatment step creates atomically smooth surfaces that are essential for achieving uniform cold welds, addressing the surface uniformity problem while maintaining the simplicity of electroplating as the base manufacturing method
Solution Approach 2:
The patent creates a composite structure by combining electroplated copper with nanotwinned copper surface layers. The bulk copper provides electrical conductivity and mechanical strength, while the nanotwinned surface layer (formed through controlled electroplating with specific additives and parameters) provides enhanced surface uniformity and bonding capability, combining the advantages of both conventional plating and advanced surface engineering
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
Enables direct copper-copper bonding with reduced voids, improved uniformity, and enhanced electrical conductivity, mechanical strength, and thermal stability, suitable for advanced packaging applications.
Implementation Method 1
forming a plurality of first copper features on a first substrate, each of the plurality of first copper features having nanotwinned copper structures
Implementation Method 2
contacting a surface of the substrate with an electroplating solution, and applying a first current to the first substrate when the first substrate is contacted with the electroplating solution to deposit the plurality of first copper features
Implementation Method 3
electroplanarizing the plurality of first copper features by electrochemically removing a portion of exposed copper from the first copper features
Implementation Method 4
anodically biasing the first substrate and contacting the plurality of first copper features with an electrolyte
Implementation Method 5
the first current includes a pulsed current waveform that alternates between a constant current and no current
Data Source
AI summary
Direct copper-copper bonding at low temperatures is achieved by electroplating copper features on a substrate followed by electroplanarizing the copper features. The copper features are electroplated on the substrate under conditions so that nanotwinned copper structures are formed. Electroplanarizing the copper features is performed by anodically biasing the substrate and contacting the copper features with an electrolyte so that copper is electrochemically removed. Such electrochemical removal is performed in a manner so that roughness is reduced in the copper features and substantial coplanarity is achieved among the copper features. Copper features having nanotwinned copper structures, reduced roughness, and better coplanarity enable direct copper-copper bonding at low temperatures.