FinFET Fin Removal via Isotropic Etching to Reduce Air Gaps
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Solution Overview
Problem
In the fabrication of FinFET semiconductor devices, the RX cut process often results in the formation of air gaps due to incomplete filling of recesses by dielectric layers, leading to defects such as shorts, which are difficult to avoid with anisotropic etching methods due to alignment issues and small pitch of fins.
Innovation Solution
A method involving forming fins with cap and liner layers, followed by an anisotropic etch to expose sidewalls, and then an isotropic etch to remove fins, reducing the height and aspect ratio of recesses, thereby minimizing air gaps and encapsulating them within dielectric layers, which reduces defect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If anisotropic etching is used to remove fins, then alignment precision can be maintained, but air gaps form due to incomplete dielectric filling of deep recesses
Solution Approach 1:
Instead of using anisotropic etching that etches vertically downward and creates deep recesses, the patent employs isotropic etching that etches laterally from the exposed top surface. This inverted etching direction allows dielectric material to fill the recesses completely during subsequent deposition, eliminating air gaps while maintaining alignment precision through careful mask design.
Solution Approach 2:
The patent changes the etching parameters by switching from anisotropic to isotropic etching conditions. This parameter change transforms the etching behavior from vertical preferential etching to uniform lateral etching, enabling complete dielectric filling and eliminating the air gap defect while preserving manufacturing precision through controlled mask patterns.
2Manufacturing precision
If isotropic etching is used to remove fins, then alignment problems are avoided, but deep recesses are created that lead to air gap formation
Solution Approach 1:
The patent applies preliminary action by forming a cap layer on the fins before etching. This cap layer serves as a stop layer during isotropic etching, preventing excessive etching depth and controlling the recess depth. The preliminary placement of this protective layer ensures that while isotropic etching is used to avoid alignment problems, the recess depth is controlled to minimize air gap formation.
Solution Approach 2:
The cap layer acts as an intermediary element between the fin structure and the etching process. It mediates the etching depth by providing a controlled termination point, allowing isotropic etching to proceed without creating excessively deep recesses that would lead to air gaps, while still achieving the alignment accuracy benefits of isotropic etching.
3Reliability
If dielectric material is deposited to fill recesses, then isolation is improved, but air gaps remain due to incomplete filling
Solution Approach 1:
The patent inverts the etching approach from anisotropic to isotropic, which fundamentally changes the recess geometry. Isotropic etching creates shallower, wider recesses that can be completely filled by dielectric material deposited from the top, achieving both improved isolation quality and complete filling without air gaps.
Solution Approach 2:
By changing the etching mode from anisotropic to isotropic, the patent alters the recess geometry parameters. This parameter change creates a more favorable recess profile with reduced depth and increased width, enabling complete dielectric filling and eliminating air gaps while maintaining high isolation quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process flow significantly reduces the formation of air gaps and associated defects, enhancing the reliability of FinFET semiconductor devices by ensuring better isolation and reducing the likelihood of shorts during subsequent processing steps.
Implementation Method 1
An anisotropic etch process is performed to remove a portion of the cap layer, the liner layer, and the dielectric material exposed by the opening
Implementation Method 2
An isotropic etch process is used to avoid alignment problems associated with anisotropic etch processes given the small pitch of the fins
Data Source
AI summary
A method includes forming a plurality of fins above a substrate, forming at least one dielectric material above and between the plurality of fins, and forming a mask layer above the dielectric material. The mask layer has an opening defined therein. At least one etching process is performed to remove a portion of the at least one dielectric material exposed by the opening so as to expose a top surface portion and sidewall surface portions of at least one fin in the plurality of fins. The at least one dielectric material remains above the substrate adjacent the at least one fin. An etching process is performed to remove the at least one fin.