BEOL Noble Metal Interconnect Reflow for Easier CMP Removal
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Solution Overview
Problem
Conventional BEOL interconnect structures using noble metals face challenges with macro-to-macro and center-to-edge variations due to the slow polishing rate of noble metal layers, making it difficult to remove the overburden portion effectively.
Innovation Solution
A surface diffusion dominated reflow anneal is used to reduce the thickness of the noble metal layer outside the via/line opening, and a lesser noble metal layer is deposited on top before polishing, with a second metal layer that is easier to remove, thereby reducing or eliminating the polishing burden.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a noble metal layer is deposited in a combined via/line opening, then the electrical conductivity and reliability are improved, but the polishing rate decreases making overburden removal difficult
Solution Approach 1:
The noble metal layer is segmented into two distinct parts: a first noble metal layer deposited within the combined via/line opening providing electrical conductivity, and a second noble metal layer deposited outside the opening serving as a sacrificial overburden. This segmentation allows the first layer to maintain reliability while the second layer facilitates easier removal during polishing processes.
Solution Approach 2:
The second noble metal layer acts as an intermediary sacrificial layer that simplifies the removal process. During chemical mechanical polishing (CMP), this outer layer is removed more easily than the inner functional layer, serving as a mediator that protects the underlying noble metal while enabling efficient overburden removal.
2Manufacturing precision
If a noble metal layer is used in combined via/line opening, then the manufacturing precision is improved, but macro-to-macro and center-to-edge variation increase
Solution Approach 1:
The patent applies local quality by giving different regions of the noble metal structure different functions and properties. The first noble metal layer within the opening maintains precise dimensional control for electrical connectivity, while the second noble metal layer outside the opening provides a uniform sacrificial thickness that compensates for polishing variations, thereby reducing macro-to-macro and center-to-edge variations.
Solution Approach 2:
The patent changes the thickness parameter of the noble metal layer as a function of position. The second noble metal layer is deposited with a controlled thickness outside the opening that is optimized for removal during polishing, while the first layer inside the opening maintains the precise thickness required for electrical performance. This parameter variation compensates for polishing non-uniformity.
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 minimizes macro-to-macro and center-to-edge variations, enhancing the efficiency of the polishing process and improving the uniformity of the BEOL interconnect structures.
Implementation Method 1
A surface diffusion dominated reflow anneal is used to reduce the thickness of a noble metal layer outside the combined via/line opening
Data Source
AI summary
Back-end-of-the line (BEOL) interconnect structures are provided in which an alternative metal such as, for example, a noble metal, is present in a combined via/line opening that is formed in an interconnect dielectric material layer. A surface diffusion dominated reflow anneal is used to reduce the thickness of a noble metal layer outside the combined via/line opening thus reducing or eliminating the burden of polishing the noble metal layer. In some embodiments and after performing the anneal, a lesser noble metal layer can be formed atop the noble metal layer prior to polishing. The use of the lesser noble metal layer may further reduce the burden of polishing the noble metal layer.