Direct Copper-Dielectric Bonding via Self-Aligned Diffusion Barriers
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Solution Overview
Problem
Existing methods for direct copper-copper bonding in microelectronic and nanoelectronic devices often require ultra-high vacuum, high temperatures, or specific atmospheres, and can result in copper diffusion into dielectric materials, causing leakage currents and other issues.
Innovation Solution
A method involving surface polishing to achieve low roughness, followed by the formation of self-aligned diffusion barriers on copper areas using cobalt or nickel alloys, allowing direct bonding at ambient temperature and atmospheric pressure, with optional heat treatment to reinforce bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct copper-copper bonding is performed without diffusion barriers, then bonding simplicity is improved, but copper diffusion into dielectric materials occurs causing leakage currents
Solution Approach 1:
Diffusion barriers are deposited on copper surfaces before bonding occurs. This preliminary action prevents copper diffusion into dielectric materials during the bonding process, eliminating leakage currents while maintaining bonding simplicity.
Solution Approach 2:
A diffusion barrier layer acts as an intermediary between copper and dielectric materials. This intermediary prevents direct contact and diffusion between copper and dielectric, eliminating harmful leakage currents while allowing the bonding process to proceed simply.
2Ease of manufacture
If conventional surface preparation methods are used, then bonding process is simplified, but surface roughness is high preventing effective direct bonding
Solution Approach 1:
Surfaces are polished to achieve very low roughness (less than 1 nm RMS) before bonding. This preliminary surface preparation ensures that when surfaces are brought into contact, they achieve effective direct bonding without requiring complex bonding processes.
3Object-generated harmful factors
If diffusion barriers are deposited to prevent copper diffusion, then copper diffusion is prevented, but bonding complexity increases
Solution Approach 1:
The diffusion barriers are deposited directly on the copper surfaces, and the copper portions themselves serve as the bonding surfaces. The system is designed so that the diffusion barrier and bonding interface are integrated, eliminating the need for separate complex processes.
Solution Approach 2:
The surface roughness parameter is controlled to be less than 1 nm RMS, and the diffusion barrier thickness is optimized to be at most equal to the depth of polishing depressions. These parameter changes enable effective bonding while preventing copper diffusion, without increasing process complexity.
4Reliability
If existing bonding methods are used, then bonding can be achieved, but harsh environmental conditions (ultra-high vacuum, high temperature, specific atmosphere) are required
Solution Approach 1:
Surfaces are polished to very low roughness and diffusion barriers are deposited before bonding. This preliminary preparation enables bonding to occur under mild conditions (ambient temperature and atmospheric pressure), eliminating the need for ultra-high vacuum, high temperature, or specific atmosphere requirements.
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 method effectively prevents copper diffusion into dielectric materials, ensuring reliable electrical conduction while avoiding the need for harsh environmental conditions, thus enhancing the stability and performance of microelectronic and nanoelectronic devices.
Implementation Method 1
the surfaces to be assembled are polished so as to achieve a very low roughness
Implementation Method 2
the surfaces having been activated by means of an argon plasma
Implementation Method 3
the copper areas an electrically conductive self-aligned diffusion barrier
Implementation Method 4
A heat treatment which takes place during or after contacting makes it possible in this case to reinforce the bonding energy
Data Source
Figure 1A~2B
Figure 3A~4
AI summary
Process for direct bonding a first (I) and a second (II) element, each element being provided with a surface comprising copper portions (6, 106) separated by a dielectric material (4, 104), said process comprising: A) a step of polishing said surfaces so that the surfaces to be joined can be direct bonded; B) a step of selectively forming a second diffusion barrier (10, 110) on the copper portions (6, 106) of the first and second elements, the surface of the second diffusion barrier of the first and second elements being flush with said surface to within less than 5 nanometres; and C) a step of bringing the two surfaces into contact with each other so that the copper portions (6, 106) of one surface at least partially cover the copper portions (106, 6) of the other surface, and so that the surfaces are direct bonded.