Super Via Interconnect Structure for BEOL CD Control
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Solution Overview
Problem
In the fabrication of silicon-based devices, maintaining the critical dimensions of super via structures during BEOL processing is challenging, as additional etch time required for the bottom portion can degrade the top portion, leading to incorrect critical dimensions and issues like unwanted lateral recessing and transition challenges between BEOL and MOL layers.
Innovation Solution
The method involves forming a monolithic interconnect structure with a sacrificial placeholder via that maintains the critical dimensions of the bottom super via portion while allowing the top portion to be formed without degradation, using a patterned dielectric layer and sacrificial material to create a super via structure with controlled bottom and top portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If extended etch time is applied to the bottom super via portion, then alignment precision is improved, but lateral recessing occurs at the top portion
Solution Approach 1:
The via formation is divided into separate bottom and top portions with distinct etching and patterning steps. The bottom portion receives extended etch time for alignment precision, while the top portion is formed separately to maintain its shape and avoid lateral recessing.
Solution Approach 2:
The bottom portion is formed first with extended etch time to ensure proper alignment and critical dimensions. The top portion is then formed as a preliminary structure that is subsequently patterned and etched, preventing lateral recessing by controlling the etch parameters specifically for the top section.
2Adaptability or versatility
If super via structures are formed during BEOL processing, then interconnect functionality is improved, but transition challenges arise between BEOL and MOL layers
Solution Approach 1:
The super via structure is segmented into bottom and top portions that can be formed during different processing stages. This allows the via to span across the transition between MOL and BEOL layers, with each portion optimized for its specific processing conditions and material requirements.
Solution Approach 2:
The bottom portion of the super via is formed in advance during earlier processing steps, establishing a foundation that bridges the MOL and BEOL layers. Subsequent BEOL processing then completes the top portion, allowing the structure to accommodate transition challenges between different processing regimes.
Data Source
AI summary
Interconnect structures including super vias are formed during back-end-of-line processing using sacrificial placeholders to protect the bottom portions of the super vias while upper portions of the super vias are formed. The sacrificial placeholders are removed and replaced by metal conductors that fill the bottom and upper portions of the super vias.