Nanosheet MOSFET Dual Work Function Metal Formation
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Solution Overview
Problem
Current methods for forming dual work function metals in nanosheet MOSFETs face challenges due to work function metal pinch-off between sheets, leading to long etch times and potential damage to protected devices.
Innovation Solution
A method involving the use of a plug underneath the masking layer to protect the first work function metal while processing the second side, allowing for the removal of the first work function metal and subsequent deposition of a second work function metal on both sides, thereby avoiding pinch-off issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to remove work function metal between nanosheets, then the work function metal can be removed, but the etch time becomes excessively long and the protected devices may be damaged
Solution Approach 1:
A sacrificial plug material is introduced as an intermediary element between the mask and the first work function metal. This plug serves as a protective mediator that prevents etchant from reaching and damaging the first work function metal during the removal of the second work function metal, thereby enabling selective removal without excessive etch time or damage to protected devices
Solution Approach 2:
The work function metal removal process is segmented into two distinct stages: first removing the second work function metal while the first is protected by the plug, then removing the first work function metal after the plug is removed. This segmentation allows each etching operation to be optimized independently, reducing total etch time and preventing damage
2Reliability
If conventional masking methods are used to protect one side during dual work function metal formation, then one side can be protected, but work function metal pinch-off occurs between sheets leading to long etch times
Solution Approach 1:
The sacrificial plug acts as an intermediary protective structure that eliminates the need for extended masking during etching. By providing physical separation and protection, it enables rapid selective removal of the second work function metal without causing pinch-off between nanosheets, thereby maintaining both device integrity and fabrication efficiency
Solution Approach 2:
The sacrificial plug is formed in advance before the dual work function metal deposition and etching processes. This preliminary action prepares the structure for selective etching, preventing pinch-off issues before they occur and enabling faster, more reliable fabrication
Data Source
AI summary
A technique relates to a semiconductor device. A first work function metal is in first stack and second stacks, each having nanowires separated by the first work function metal. A mask is on the first stack such that the first work function metal in the first stack is protected while the first work function metal in the second stack is exposed. The mask is undercut by removing a portion of first work function metal in first stack, leaving a gap. A plug is formed in the gap underneath the mask so as to protect the first work function metal in first stack. First work function metal in the second stack is removed, thereby removing the first work function metal from in between the nanowires of the second stack. The mask and plug are removed from first stack. A second work function metal is formed on first and second stacks.