Selective Noble Metal Deposition on Copper Interconnects
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Solution Overview
Problem
Current methods for forming copper interconnects in semiconductor devices face challenges such as leakage current, electromigration, and adhesion issues due to copper diffusion into dielectric layers, leading to reliability failures and increased effective k-values of interlevel dielectrics, which are not effectively addressed by conventional capping layers like SiN.
Innovation Solution
A method involving the selective formation of a noble metal layer on copper surfaces using vapor phase compounds, either through selective CVD or ALD, where a replacement reaction replaces copper atoms with noble metal atoms, enhancing the reliability of copper interconnects by forming a conductive layer that inhibits copper migration and improves adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional CVD dielectric capping layer (SiN) is used on copper interconnects, then copper diffusion into dielectric is prevented, but the effective k-value of interlevel dielectric increases and adhesion strength is insufficient
Solution Approach 1:
The patent applies selective deposition to create different material compositions at different locations: a noble metal layer is deposited only on copper surfaces where adhesion and diffusion prevention are critical, while dielectric regions maintain their original low-k properties. This local differentiation resolves the contradiction by providing enhanced protection where needed without globally increasing the effective k-value.
Solution Approach 2:
The invention creates a composite structure by depositing a noble metal layer (such as ruthenium, rhodium, or iridium) over the copper interconnect surface. This composite copper-noble metal structure combines the electrical conductivity of copper with the adhesion strength and diffusion barrier properties of the noble metal, while the selective deposition ensures the underlying dielectric's low-k properties are preserved.
2Ease of manufacture
If copper atoms are allowed to migrate along the Cu-dielectric interface, then process simplicity is maintained, but electromigration and stress-induced voiding occur leading to interconnect failure
Solution Approach 1:
The patent performs preliminary protection by depositing the noble metal layer on the copper surface before final interconnect formation and testing. This pre-established protective layer prevents electromigration and stress-induced voiding from occurring in the first place, rather than attempting to repair failures after they occur. The selective deposition ensures this protection is applied only where copper surfaces exist.
3Reliability
If a thicker diffusion barrier layer is formed by PVD, then copper diffusion is better prevented, but via or trench volume for copper is reduced and conductivity decreases
Solution Approach 1:
The patent extracts the diffusion barrier function from the bulk diffusion barrier layer and relocates it to the copper surface through the noble metal layer. This separation allows the diffusion barrier functionality to be maintained at the copper-dielectric interface where it is most needed, while minimizing the volume occupied by barrier materials and maximizing the copper fill volume in vias and trenches.
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 significantly enhances the reliability of copper interconnects by preventing electromigration and stress-induced migration, while maintaining conductivity and reducing the effective k-value of interlevel dielectrics, thus improving the overall performance and longevity of semiconductor devices.
Implementation Method 1
A method involving the selective formation of a noble metal layer on copper surfaces using vapor phase compounds, either through selective CVD or ALD
Implementation Method 2
A method involving the selective formation of a noble metal layer on copper surfaces using vapor phase compounds, either through selective CVD or ALD
Implementation Method 3
where a replacement reaction replaces copper atoms with noble metal atoms
Data Source
AI summary
A method for enhancing the reliability of copper interconnects and/or contacts, such as the bottom of vias exposing top surfaces of buried copper, or at the top of copper lines just after CMP. The method comprises contacting the exposed copper surface with a vapor phase compound of a noble metal and selectively forming a layer of the noble metal on the exposed copper surface, either by a copper replacement reaction or selective deposition (e.g., ALD or CVD) of the noble metal.