Nanotwin Copper Bonding Surfaces for Low-Temperature Interconnects
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Solution Overview
Problem
Conventional electrochemical deposition methods for semiconductor processing face challenges in achieving uniform metal layer deposition on non-planar features, leading to defects such as voids and non-uniform thicknesses, particularly with polycrystalline copper, which requires high bonding temperatures and pressures, and has poor oxidation resistance.
Innovation Solution
The method involves electroplating nanotwin copper (NTCu) with a significant percentage of grains oriented in the same direction, followed by polishing to reduce surface roughness and forming a barrier layer to prevent phase conversion, and optionally adding a second metal layer for enhanced low-temperature, low-pressure bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional electrochemical deposition is used to deposit metal on non-planar features, then the deposition process can be performed, but the deposited material exhibits non-uniform thickness and voids
Solution Approach 1:
The patent applies pulse plating parameters (varying current density over time) and modifies electrolyte composition to achieve uniform metal deposition on non-planar features. These parameter changes enable controlled deposition that fills voids and eliminates thickness variations, directly resolving the contradiction between manufacturing precision and reliability.
2Reliability
If polycrystalline copper is used for metallization, then electrical connections can be formed, but high bonding temperatures and pressures are required
Solution Approach 1:
The patent changes the crystal structure parameter of copper from polycrystalline to nanotwin structure. This fundamental material parameter change enables bonding at lower temperatures and pressures while maintaining or improving bonding quality, resolving the contradiction between reliability and temperature requirements.
3Reliability
If polycrystalline copper is used for metallization, then electrical connections can be formed, but oxidation resistance is poor
Solution Approach 1:
The patent changes the crystal structure parameter from polycrystalline to nanotwin structure, which fundamentally alters the material's oxidation resistance properties. The nanotwin structure provides enhanced stability against oxidation while maintaining electrical connectivity, resolving the contradiction between reliability and compositional stability.
4Productivity
If electroplating is performed on non-planar features with patterned substrates, then metal connections can be formed, but variations in deposition rate occur across different points
Solution Approach 1:
The patent employs dynamic pulse plating parameters that adjust current density over time during deposition. This dynamic approach compensates for geometric variations in non-planar features, maintaining both high productivity and uniform deposition precision across all surface points.
Solution Approach 2:
The patent modifies electrolyte composition and deposition parameters to achieve consistent deposition rates across non-planar surfaces. These parameter changes ensure uniform metal layer formation while maintaining efficient deposition productivity.
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 results in metal contact surfaces with improved bonding properties, reduced oxidation, and lower bonding temperatures and pressures, while maintaining high NTCu content and low surface roughness, addressing the limitations of polycrystalline copper in high-interconnect-density integrated circuits.
Implementation Method 1
Electroplating is performed in an electroplating chamber with the target side of the wafer in a bath of liquid electrolyte, and with electrical contacts on a contact ring touching a conductive layer, such as a seed layer, on a substrate material. Electrical current is passed through the electrolyte and the conductive layer from a power supply. Metal ions in the electrolyte plate out onto the substrate material, creating a metal layer on the substrate material.
Implementation Method 2
the metal material is polished with chemical mechanical polishing
Implementation Method 3
the metal material is polished with electropolishing
Implementation Method 4
the polishing of the exposed surface of the metal material is performed in an oxygen-free environment, and where the polishing removes one or more metal oxides from the exposed surface of the metal material
Data Source
AI summary
Exemplary methods of electroplating a metal with a nanotwin crystal structure are described. The methods may include plating a metal material into at least one opening on a patterned substrate, where at least a portion of the metal material is characterized by a nanotwin crystal structure. The methods may further include polishing an exposed surface of the metal material in the opening to reduce an average surface roughness of the exposed surface to less than or about 1 nm. The polished exposed surface may include at least a portion of the metal material characterized by the nanotwin crystal structure. In additional examples, the nanotwin-phased metal may be nanotwin-phased copper.