Rectangular Via Layout for Interconnect Yield
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Solution Overview
Problem
The use of redundant vias in integrated circuits can block a high number of adjacent routing tracks, impacting die yields, while minimal redundant vias may compromise the reliability of electrical connections due to misalignment during fabrication.
Innovation Solution
A rectangular via with a width equal to the interconnects and a length twice that, aligned along the long dimension of the upper interconnect, provides a robust electrical connection while minimizing the blocking of adjacent routing tracks, even with minor misalignment during fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If redundant vias are used to improve connection reliability, then the reliability of interlevel connections is improved, but a high number of adjacent routing tracks are blocked
Solution Approach 1:
The via structure transitions from a conventional square cross-section to a rectangular cross-section with dimensions 2:1 (length to width). This dimensional change allows the via to be elongated along one axis, providing greater alignment tolerance in the lateral direction while maintaining adequate contact area, thus reducing the need for redundant vias and freeing up routing tracks.
Solution Approach 2:
The via geometry parameters are changed from a square cross-section (equal width and length) to a rectangular cross-section where the length is twice the width. This parameter modification enables the via to accommodate misalignment more effectively, ensuring reliable connections with fewer vias required, thereby reducing routing track blockage.
2Productivity
If minimal numbers of redundant vias are used to reduce routing track blockage, then adjacent routing tracks are less blocked, but die yields are adversely impacted
Solution Approach 1:
By changing the via cross-section from square to rectangular (2:1 aspect ratio), the via gains extended length in one dimension, which provides increased tolerance for fabrication misalignment. This allows minimal via counts to achieve both routing flexibility and acceptable die yields by reducing the need for additional redundant vias.
Solution Approach 2:
The via structure employs asymmetric rectangular geometry rather than symmetric square geometry. The 2:1 aspect ratio creates an elongated shape that is more tolerant of misalignment in the wider dimension, enabling reliable connections with fewer vias and thus improving routing track availability without sacrificing die yield.
3Manufacturing precision
If conventional square vias are used, then fabrication alignment is critical, but misalignment during fabrication compromises connection reliability
Solution Approach 1:
The via cross-section changes from square to rectangular with a 2:1 aspect ratio. This dimensional transformation creates an elongated shape that provides greater margin for alignment errors in the lateral direction, as the longer dimension can accommodate misalignment while still maintaining adequate contact area with the interconnect, thus reducing the criticality of fabrication alignment precision.
Solution Approach 2:
The geometric parameters of the via are modified from equal width and length to a rectangular configuration where length is twice the width. This parameter change increases the via's tolerance to misalignment during fabrication, ensuring that connection reliability is maintained even when alignment precision is not perfect.
Data Source
AI summary
A rectangular via extending between interconnects in different metallization levels can have a planform with a width equal to the width of the interconnects and a length equal to twice the width and can be aligned along a long dimension with a length of the upper interconnect. In an integrated circuit layout, the planform can be centered over the width of the lower interconnect, allowing for misalignment during fabrication while maintaining a robust electrical connection. The bottom of the via may be aligned with an upper surface of the lower interconnect or may include portions below the lower interconnect's upper surface. Fewer adjacent routing tracks are blocked by use of the rectangular via than would be blocked using redundant square vias, while ensuring reliability of the electrical connection despite potential misalignment during fabrication.