Self-Aligned Buried Power Rail Cap for Gate Formation Protection
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Solution Overview
Problem
Buried power rails in semiconductor devices are prone to physical exposure and breakdown during further device processing, leading to undesirable results such as gate structure failure and increased design and manufacturing costs.
Innovation Solution
A buried power rail is implemented with a dielectric liner on its lower sidewall and bottom surface, and a self-aligned dielectric cap on its upper sidewall and top surface, which can be removed after the functional gate structure is formed, allowing for the creation of a via to buried power rail contact structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If buried power rails are embedded in shallow trench isolation structure, then power supply function is provided, but physical exposure and breakdown occur during further processing
Solution Approach 1:
The isolation structure is segmented into two distinct dielectric layers: a first dielectric layer filling the shallow trench isolation structure, and a second dielectric layer formed over the first dielectric layer. This segmentation allows each layer to serve specific protective functions, with the second layer specifically protecting the buried power rail during gate formation while the first layer provides the isolation function.
Solution Approach 2:
The second dielectric layer is formed preliminarily before the functional gate structure fabrication process. This preliminary action ensures that the buried power rail is protected in advance during subsequent processing steps, preventing physical exposure and breakdown before they can occur.
2Ease of operation
If shallow trench isolation structure is recessed, then access to buried power rail is improved, but physical exposure and breakdown occur
Solution Approach 1:
The second dielectric layer is formed preliminarily over the buried power rail before any recessing operations are performed. This ensures that even when the shallow trench isolation structure is recessed to improve access, the buried power rail remains protected by the overlying second dielectric layer, preventing physical exposure and breakdown.
Solution Approach 2:
The second dielectric layer acts as a cushioning protective layer formed beforehand over the buried power rail. This beforehand cushioning prevents direct exposure and potential damage during recessing and subsequent processing, while still allowing controlled access when needed.
3Reliability
If dielectric cap is present during functional gate structure fabrication, then breakdown is prevented, but additional processing steps are required
Solution Approach 1:
The second dielectric layer is formed preliminarily before gate structure fabrication, serving as a protective cap during the process. After gate formation is complete, the second dielectric layer is selectively removed to expose the buried power rail for contact formation. This preliminary protective action prevents breakdown while the subsequent removal step restores fabrication efficiency.
Solution Approach 2:
The second dielectric layer serves as a temporary protective structure that is discarded after serving its protective function during gate formation. Its selective removal recovers access to the buried power rail, allowing the process to continue efficiently without permanent structural complications.
Data Source
AI summary
A buried power rail is provided in a non-active device region. The buried power rail includes a dielectric liner located on a lower portion of a sidewall and a bottommost surface of the buried power rail. A dielectric cap is located on an upper portion of the sidewall of the buried power rail as well as on a topmost surface of the buried power rail. The dielectric cap is present during the fabrication of a functional gate structure and thus the problems associated with prior art buried power rails are circumvented. The dielectric cap can be removed after the functional gate structure has been formed and a via to buried power rail (VBPR) contact structure can be formed in contact with the buried power rail. In some applications, and after a gate cut process, a gate cut dielectric structure can be formed in contact with the dielectric cap.