Interconnect Structure with Segmented Liner and Metal Cap
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Solution Overview
Problem
Conventional interconnect formation in semiconductor ICs faces challenges with liner layer damage during middle-of-line (MOL) or back-end-of-line (BEOL) processes, leading to decreased yields and misalignment issues between vias and metal lines.
Innovation Solution
The proposed solution involves forming an interconnect structure with a conformal liner layer and a metal cap layer, both made of different metals, which collectively encapsulate the bulk metal. This structure includes a method where a metal line or plug is formed with a conformal liner layer, and a metal cap is deposited on exposed surfaces, followed by the formation of a self-aligned via aligned to the etch stop layer, ensuring robustness and alignment even in cases of misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional interconnect structure with a single liner layer is used, then the manufacturing process is simple, but the liner layer is damaged during MOL or BEOL processes leading to decreased yields
Solution Approach 1:
The single liner layer is segmented into two distinct liner layers: a first liner layer in contact with the bulk metal and a second liner layer above it. This segmentation allows each layer to perform specific functions - the first liner layer provides adhesion and protection while the second liner layer facilitates subsequent processing steps, thereby preventing liner layer damage during MOL or BEOL processes and improving yield without excessive complexity
Solution Approach 2:
The interconnect structure uses composite materials by combining two different liner layer materials with distinct properties. The first liner layer material is selected for adhesion and protection characteristics, while the second liner layer material is chosen for compatibility with subsequent processing. This composite approach enhances overall reliability and yield by addressing multiple functional requirements simultaneously
2Reliability
If the via is misaligned with the underlying metal line, then the manufacturing process is more flexible, but the connection surface area is reduced leading to increased resistance
Solution Approach 1:
The via opening is formed to extend through the interlayer dielectric to a depth that exposes the etch stop layer before the metal line is fully encountered. This preliminary action ensures that even if misalignment occurs, the via will still make contact with the metal line at the etch stop layer interface, maintaining connection quality without requiring precise alignment
Solution Approach 2:
The etch stop layer serves as an intermediary element between the interlayer dielectric and the metal line. By forming the via to expose the etch stop layer, the structure creates a reliable contact point that mediates the connection, ensuring that misalignment does not result in loss of electrical contact or increased resistance
3Ease of manufacture
If the liner layer is exposed and removed during processing, then subsequent steps can be performed, but the liner layer integrity is compromised leading to yield loss
Solution Approach 1:
The liner layer is segmented into two distinct layers that can be differentially processed. The first liner layer remains protected and intact to maintain adhesion and structural integrity, while the second liner layer can be selectively removed or modified to enable subsequent processing steps. This segmentation allows processing to proceed without compromising overall liner layer integrity
Solution Approach 2:
Different regions of the liner layer structure are given different qualities and functions. The first liner layer near the metal line maintains full integrity for adhesion and protection, while the second liner layer at the top surface is made more accessible to processing chemicals. This local quality differentiation enables manufacturing steps to be performed while preserving the critical adhesion interface
Data Source
AI summary
Interconnect structures and methods for forming the interconnect structures generally include forming a bulk metal encapsulated in first and second interlayer dielectrics, a liner layer about a lower surface of the bulk metal and a metal cap layer about an upper surface of the bulk metal. The liner layer is in the first interlayer dielectric and the metal cap layer is in the second interlayer dielectric, wherein liner layer and the metal cap layer are different metals.