Self-Aligned Shallow Trench Isolation for Vertical FinFETs
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Solution Overview
Problem
The challenge in forming vertical fin field effect transistors (finFETs) lies in aligning mask layers with existing semiconductor features, leading to dimensional variations and misplacement of trench isolation regions, which complicates the formation of smaller device components due to scaling issues.
Innovation Solution
A method involving the formation of a pinch-off layer on vertical fin segments, followed by a trench mask layer, allows for self-aligned shallow trench isolation by controlling the thickness of the pinch-off layer to determine the distance of isolation region trenches to adjacent fin segments, thereby reducing misalignment and dimensional variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional mask alignment methods are used, then the fabrication process is simpler, but dimensional variations and misplacement of trench isolation regions increase
Solution Approach 1:
A pinch-off layer is formed on the sidewalls of vertical fin segments before trench isolation formation. This preliminary layer serves as a self-aligned mask that defines the exact position where substrate removal should occur, eliminating the need for separate alignment steps and reducing dimensional variations in trench isolation regions.
Solution Approach 2:
The pinch-off layer automatically serves dual functions: it acts as both a structural element for fin formation and a self-aligned mask for trench isolation. The layer's thickness directly determines the trench depth and position, allowing the structure to define its own isolation regions without external alignment references, thereby reducing misplacement errors.
2Productivity
If device dimensions are decreased for scaling, then device density increases, but alignment difficulty and dimensional control become more challenging
Solution Approach 1:
The thickness of the pinch-off layer is precisely controlled through deposition parameters to directly define the trench isolation dimensions. By adjusting this single parameter, both the depth and lateral position of trenches are controlled, enabling accurate dimensional control even as device features are scaled down to increase device density.
Solution Approach 2:
The solution transitions from two-dimensional planar alignment to three-dimensional self-alignment using vertical sidewall structures. The pinch-off layer formed on vertical fin sidewalls creates a depth dimension that automatically defines trench positions, eliminating alignment errors that plague traditional planar methods at scaled dimensions.
3Manufacturing precision
If self-aligned pinch-off layer method is used, then trench isolation alignment precision improves, but process steps increase
Solution Approach 1:
The pinch-off layer performs multiple functions simultaneously: it serves as a mask for trench isolation formation, defines the lateral boundaries of isolation regions, and controls trench depth through its thickness. This multi-functionality consolidates what would otherwise require separate alignment and depth-control steps, offsetting the added deposition step with eliminated alignment operations.
Solution Approach 2:
The formation of trench isolation is merged with the fin structure definition process. The same pinch-off layer that defines fin dimensions also serves as the mask for isolation trenches, combining two previously separate processes into one integrated sequence, thereby reducing overall process complexity despite the additional layer deposition.
Data Source
AI summary
A method of forming a vertical fin field effect transistor (vertical finFET) with a self-aligned shallow trench isolation region, including forming a pinch-off layer on one or more vertical fin segments, wherein the pinch-off layer has a thickness on the sidewalls of the one or more vertical fin segments, forming a trench mask layer on predetermined portions of the pinch-off layer, removing portions of the pinch-off layer not covered by the trench mask layer, where the removed portions of the pinch-off layer exposes underlying portions of the substrate, and removing at least a portion of the substrate to form one or more isolation region trenches, where the distance of the sidewall of one of the one or more isolation region trenches to an adjacent vertical fin segment is determined by the thickness of the pinch-off layer.