Nanotwinned Copper Direct Bonding Contacts for Low-Temperature Joints
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Solution Overview
Problem
Current direct bonding techniques face challenges in forming reliable copper-to-copper joints at low temperatures, particularly when using nanotwinned copper (NTC) as a contact material, due to difficulties in retaining its columnar microstructure in deep copper damascene trenches, which affects copper diffusivity and void formation.
Innovation Solution
The use of a two-layer direct bonding contact structure, where a bulk portion is filled with polycrystalline or fine-grain copper and a cap portion is made of nanotwinned copper, with the NTC being deposited only in a recess less than 300 nanometers deep to preserve its columnar structure and faster copper diffusivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If nanotwinned copper is used in deep copper damascene trenches for direct bonding, then copper diffusivity is improved, but the columnar microstructure cannot be retained
Solution Approach 1:
The copper contact structure is segmented into two distinct portions: a bulk portion filled with polycrystalline or fine-grain copper providing mechanical stability, and a cap portion made of nanotwinned copper deposited in a shallow recess (<300nm deep) providing fast copper diffusivity. This segmentation allows each portion to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the copper contact are assigned different microstructural qualities: the bulk portion uses polycrystalline or fine-grain copper for structural integrity, while the cap portion uses nanotwinned copper with columnar microstructure for enhanced copper diffusivity. This local differentiation resolves the contradiction by providing both properties in appropriate locations.
2Temperature
If direct bonding is performed at low temperatures to reduce thermal budget, then thermal damage is reduced, but reliable copper-to-copper joint formation becomes difficult
Solution Approach 1:
The invention changes the microstructural parameters of the copper contact material by introducing nanotwinned copper with specific twin boundary spacing and columnar grain structure. This parameter change enables reliable copper-to-copper bonding at low temperatures (≤200°C) by providing fast copper diffusivity through the twin boundaries, which facilitates interdiffusion and joint formation without requiring high thermal energy.
3Speed
If nanotwinned copper is deposited in deep trenches, then copper diffusivity is enhanced, but void formation increases
Solution Approach 1:
The copper contact is segmented into a bulk portion that provides mechanical support and a shallow cap portion (<300nm deep) containing the nanotwinned copper. This segmentation confines the NTC to a depth where columnar microstructure can be maintained, preventing void formation while still providing the diffusivity enhancement benefits in the critical bonding region.
Solution Approach 2:
The cap portion is specifically designed with local nanotwinned copper quality to enhance diffusivity at the bonding interface, while the bulk portion uses conventional copper structure. This local quality differentiation ensures fast diffusivity where needed without the void formation problems associated with deep NTC deposition.
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 enables the formation of reliable copper-to-copper joints at temperatures of or below 200°C, maintaining the advantages of low thermal budget bonding and reducing void formation, thus enhancing the adaptability of NTC in direct bonding interconnects.
Implementation Method 1
faster copper diffusivity
Implementation Method 2
direct bonding
Data Source
AI summary
Disclosed herein are microelectronic assemblies with direct bonding using nanotwinned copper (NTC). An example microelectronic assembly may include a first microelectronic component and a second microelectronic component coupled to the first microelectronic component by a direct bonding (DB) region, wherein the DB region includes a DB contact comprising a first portion and a second portion having different microstructures. The first portion is between the first microelectronic component and the second portion. The second portion is between the first portion and the second microelectronic component. In some implementations, the first portion has non-columnar microstructure, and the second portion has columnar microstructure. In some implementations, less than about 40% of grains of the first portion have ac <111> orientation, and at least about 50% of grains of the second portion have the <111> orientation. In some embodiments, the first portion includes PCC or FGC, and the second portion includes NTC.