Via-First Self-Aligned Interconnect Layout for Leakage Control
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Solution Overview
Problem
The formation of interconnect structures, particularly with via-first and trench-first processes, faces challenges in maintaining CD uniformity and overlay control, leading to issues like via-to-trench space window limitations, leakage between metal lines, and residue of bottom anti-reflective coating in via holes, especially when pitches are smaller than 40 nm.
Innovation Solution
A via-first process is employed where a via pattern is formed in a first hard mask, followed by a trench pattern in a second hard mask, allowing the via hole to be defined by both masks, resulting in self-aligned metal vias to overlying metal lines, which maintains distance between metal lines and vias, controlling leakage and eliminating bridging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If via-first process is used to form via patterns before trench patterns, then via pattern formation is simplified, but overlay shift between trench patterns and via patterns causes leakage between metal lines
Solution Approach 1:
The via pattern itself serves as the definition for the trench pattern position. The trench pattern is formed to be directly overlying the via pattern, using the via pattern's own geometry to determine the trench location, thereby eliminating the need for separate overlay alignment processes and preventing leakage.
Solution Approach 2:
The via pattern is formed first and serves as a pre-established reference structure. The trench pattern is then formed based on this pre-existing via pattern, ensuring that the trench is correctly positioned relative to the via before metal line formation occurs.
2Manufacturing precision
If trench-first process is used to form trench patterns before via patterns, then metal line spacing is controlled, but via-formation process window is limited due to surface topography
Solution Approach 1:
Instead of forming trenches first and then vias, the process inverts the sequence by forming vias first and then trenches. This inversion eliminates the surface topography problems caused by pre-formed trenches, as the via pattern (which has smaller depth variations) serves as the reference for subsequent trench formation.
3Length of moving object
If via sizes are reduced to maintain pitch scaling, then optical effects limit further reduction, but CD uniformity is strongly impacted by stochastic effects
Solution Approach 1:
The via pattern serves as the self-aligned reference for trench formation, eliminating the need for separate overlay alignment processes. This self-service approach ensures that the critical dimensions are determined by the via pattern geometry itself rather than by overlay precision, thereby maintaining CD uniformity even as via sizes are reduced for pitch scaling.
Data Source
AI summary
A structure includes a dielectric layer, and a metal line in the dielectric layer. The metal line has a first straight edge and a second straight edge extending in a lengthwise direction of the metal line. The first straight edge and the second straight edge are parallel to each other. A via is underlying and joined to the metal line. The via has a third straight edge underlying and vertically aligned to the first straight edge, and a first curved edge and a second curved edge connecting to opposite ends of the third straight edge.