FinFET Gate Air Gaps for Wider Process Windows and Isolation
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Solution Overview
Problem
Conventional FinFET device fabrication methods face challenges such as small process windows in the gate-replacement process, leading to leakage and line-end bridging issues due to incomplete removal of dummy gates, which affects device performance and yield.
Innovation Solution
A 'pull back' process is performed during the gate replacement process to widen the opening and create air gaps between adjacent gate structures, reducing the risk of line-end bridging and improving electrical isolation by using lateral etching to remove remnants of the dummy gate layer and forming air gaps in the dielectric material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional gate-replacement process is used, then device fabrication can proceed, but small process windows lead to leakage and line-end bridging issues
Solution Approach 1:
The gate replacement process is segmented into multiple distinct steps: forming mandrels with spaced-apart sidewalls, depositing dielectric material in the spaces, and performing selective removal. This segmentation allows each step to be optimized independently, enlarging the overall process window and reducing defects like line-end bridging and leakage.
Solution Approach 2:
The patent performs preliminary actions by forming mandrels and depositing dielectric material before final gate formation. The dielectric material is deposited in the spaces between mandrels while they are still in place, ensuring precise positioning and preventing defects that would occur if these steps were performed later.
2Reliability
If dummy gates are not completely removed, then line-end bridging occurs, but more aggressive removal increases process complexity
Solution Approach 1:
The patent introduces mandrels as intermediary structures that define the spaces where dielectric material will be deposited. These mandrels act as temporary placeholders that guide the dielectric deposition process, ensuring complete and precise removal of dummy gates without requiring overly aggressive processes that would increase complexity.
Solution Approach 2:
The patent replaces mechanical/chemical etching processes with a dielectric deposition and removal approach. Instead of using complex etching processes to remove dummy gates, dielectric material is deposited in defined spaces and then selectively removed, simplifying the overall process while improving reliability.
3Reliability
If air gaps are not formed, then electrical isolation between adjacent gate structures is insufficient, but forming air gaps requires additional process steps
Solution Approach 1:
The patent merges the air gap formation process with the existing dielectric material deposition step. The same dielectric material deposition process that defines the spaces between mandrels also creates the air gaps when the dielectric is selectively removed, eliminating the need for separate air gap formation steps and reducing overall process complexity.
Solution Approach 2:
The mandrels are discarded after serving their purpose of defining spaces for dielectric deposition. Their removal creates the air gaps, and the process is designed so that the mandrels are temporary structures meant to be removed after fulfilling their positioning function, simplifying the overall fabrication process.
Data Source
AI summary
A semiconductor device includes a first gate structure disposed over a substrate. The first gate structure extends in a first direction. A second gate structure is disposed over the substrate. The second gate structure extends in the first direction. A dielectric material is disposed between the first gate structure and the second gate structure. An air gap is disposed within the dielectric material.