Straight Narrow Fin CMOS Structure via Selective Oxidation
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Solution Overview
Problem
Semiconductor devices, particularly FinFET CMOS devices at the 20 nm technology node and beyond, face challenges in forming narrow and straight fin profiles due to high aspect ratios, leading to fin bending and tapered profiles, with existing methods failing to create desired straight fin profiles at narrow widths.
Innovation Solution
The method involves forming silicon fins separated by shallow trench isolation regions, recessing these regions, and using a nitride layer and organic planarization layer to expose and remove portions, followed by oxidation to thin the fin upper portions while protecting lower portions, allowing for the formation of a metal gate, resulting in straight and narrow fins in the channel region and wider fins in source/drain regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fins are made narrower to increase device density, then device density is improved, but fin bending occurs due to high aspect ratio
Solution Approach 1:
The fin structure is segmented into different width regions: narrower width in the channel region (improving density) and wider width in the source/drain regions (improving stability). This segmentation allows each region to have optimized dimensions for its specific function while maintaining overall structural integrity.
Solution Approach 2:
Different portions of the fin structure are given different local properties: the channel region fins are made narrow for high density, while the source/drain region fins are made wider for structural support. The nitride layer is also applied selectively to protect specific regions during processing.
2Manufacturing precision
If fins are made taller to increase channel length control, then device performance is improved, but fin bending increases due to higher aspect ratio
Solution Approach 1:
The fin structure is divided into channel region fins and source/drain region fins with different widths. The taller fins in the channel region are stabilized by the wider fins in the source/drain regions, allowing height increase for better channel control while preventing bending through the wider base structure.
Solution Approach 2:
The wider source/drain region fins act as counterweights or support structures that balance the high aspect ratio of the taller channel region fins, preventing them from bending while maintaining the desired channel length control.
3Ease of manufacture
If current fin shaping process is used, then manufacturing simplicity is maintained, but fins have undesirably tapered profile
Solution Approach 1:
A nitride layer is deposited conformally over the fin structure before the final shaping process. This preliminary layer serves as a protective and guiding structure that enables subsequent selective removal to create straight fin profiles with narrow widths, achieving the desired shape while maintaining reasonable manufacturing complexity.
4Length of moving object
If fin width is reduced to 20 nm or below, then device scaling is achieved, but fin bending becomes more susceptible
Solution Approach 1:
The fin structure is segmented such that the channel region fins have the target narrow width (20 nm or below) for scaling, while the source/drain region fins are made wider to provide structural support. This segmentation allows aggressive scaling in the channel while maintaining stability through the wider support regions.
Solution Approach 2:
The fin width is optimized locally for each region: narrow width (20 nm or below) in the channel region for scaling and performance, and wider width in the source/drain regions for structural stability. This local optimization allows achieving both scaling goals and structural integrity.
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 approach effectively prevents fin bending and achieves the desired straight and narrow fin profiles in the channel region while maintaining wider profiles under the gate spacer and source/drain regions, enhancing the structural integrity and performance of semiconductor devices.
Implementation Method 1
oxidizing exposed portions of the Si fins; and removing the oxidized Si
Data Source
AI summary
A method of forming straight and narrow fins in the channel region and the resulting device are provided. Embodiments include forming Si fins separated by STI regions; recessing the STI regions to reveal the Si fins; forming a nitride layer over the STI regions and the Si fins; forming an OPL over the nitride layer between the Si fins; recessing the OPL to expose portions of the nitride layer over the Si fins; removing exposed portions of the nitride layer; removing the OPL; forming an oxide layer over exposed portions of the Si fins; forming a dummy gate over the nitride layer and the oxide layer perpendicular to the Si fins and surrounded by an ILD; removing the dummy gate and the oxide layer forming a cavity; thinning the Si fins in the cavity; and forming a RMG in the cavity.