Copper Interconnect Alloy Caps for Electromigration Resistance
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Solution Overview
Problem
The existing methods for metal cap integration in interconnect structures face challenges such as selectivity issues during metal cap deposition, leading to potential metal residues and leakage, which can affect the reliability and performance of the interconnects.
Innovation Solution
A method involving the deposition of a metal cap layer comprising titanium, ruthenium, or cobalt on copper interconnects, followed by thermal annealing to form copper alloy caps, and subsequent selective removal of the non-alloyed cap layer, ensuring good adhesion and electromigration resistance without residual metal on the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal cap layer is deposited on copper interconnects to prevent electromigration, then electromigration resistance is improved, but metal residues and leakage may occur due to selectivity issues during deposition
Solution Approach 1:
The patent applies local alloying to create a copper alloy cap layer at the interface between the metal cap layer and copper interconnect, while keeping the upper portion of the cap layer as pure metal. This local differentiation in composition (alloyed at interface, pure above) provides both strong adhesion and electromigration resistance without the selectivity issues of complete alloying.
Solution Approach 2:
The patent changes the compositional parameter of the cap layer by forming a copper alloy through thermal annealing, then controls the alloying extent to create a gradient structure. The alloying process is terminated at a specific point (forming a residual pure metal portion) to optimize both adhesion and prevent residue formation, representing a controlled parameter change approach.
2Strength
If thermal annealing is used to form copper alloy caps for good adhesion, then interface adhesion is improved, but residual non-alloyed cap layer must be removed selectively
Solution Approach 1:
The patent creates a local quality difference between the alloyed interface portion and the residual pure metal portion. The alloyed region provides strong adhesion to copper, while the residual pure metal portion maintains etch selectivity for easy removal, achieving both strong bonding and manufacturing ease through spatial differentiation.
Solution Approach 2:
The patent performs preliminary alloying through controlled thermal annealing to create the copper alloy cap layer before final deposition completion. This preliminary action establishes strong adhesion at the interface early in the process, while leaving the upper portion unalloyed for subsequent selective removal, optimizing both adhesion strength and ease of manufacture.
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 provides residue-less interconnect metallization with improved copper/metal interface adhesion and electromigration resistance, maintaining compatibility with existing metal deposition processes.
Implementation Method 1
A metal cap layer is deposited on the structure
Implementation Method 2
deposition of one or more dielectric layers and one or more cap layers
Implementation Method 3
subjecting the structure to thermal annealing to form metal alloy caps comprising copper and at least one of titanium, ruthenium and cobalt at the interfaces
Implementation Method 4
form metal alloy caps comprising copper and at least one of titanium, ruthenium and cobalt at the interfaces from the interconnects and a portion of the cap layer
Data Source
AI summary
A middle-of-line interconnect structure including copper interconnects and integral copper alloy caps provides effective electromigration resistance. A metal cap layer is deposited on the top surfaces of the interconnects. A post-deposition anneal causes formation of the copper alloy caps from the interconnects and the metal cap layer. Selective removal of unalloyed metal cap layer material provides an interconnect structure free of metal residue on the dielectric material layer separating the interconnects.