Fin Isolation Structure Using Oxide-Nitride Split to Cut Body Leakage
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Solution Overview
Problem
In advanced semiconductor fabrication, the CPODE structure formed with silicon nitride-based material induces negative charges in fins and substrates, leading to body leakage current between adjacent transistors, even when they are in the off state.
Innovation Solution
A semiconductor structure is manufactured with an isolation structure that includes a lower portion made of silicon oxide and an upper portion of silicon nitride, preventing negative charge induction in fins and substrates, thereby mitigating body leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CPODE structure made of silicon nitride-based material is used to electrically isolate adjacent transistors, then electrical isolation is achieved, but negative charges are induced in the fin and substrate, causing body leakage current
Solution Approach 1:
The isolation structure is divided into two distinct portions: a first portion extending from the CPODE structure to the fin top surface, and a second portion filling the trench between fins. This segmentation allows each portion to serve specific functions - the first portion provides electrical isolation while the second portion prevents charge induction, thereby resolving the contradiction between achieving isolation and avoiding leakage current.
Solution Approach 2:
Different materials are used in different regions of the isolation structure. The first portion uses silicon nitride-based material for effective electrical isolation, while the second portion uses silicon oxide-based material that does not induce negative charges. This local differentiation of material properties allows the structure to simultaneously achieve isolation without generating harmful leakage currents.
2Reliability
If silicon nitride-based material is used for the entire isolation structure, then electrical isolation between transistors is achieved, but negative charge induction occurs throughout the structure
Solution Approach 1:
The isolation structure employs different materials in different regions: silicon nitride in the first portion for isolation and silicon oxide in the second portion to avoid charge induction. This local quality differentiation resolves the contradiction by ensuring that only the necessary portion for isolation uses silicon nitride, while the trench-filling portion uses charge-neutral material.
Solution Approach 2:
The isolation structure is segmented into two functional portions with different material compositions. The first portion (silicon nitride) handles the isolation function, while the second portion (silicon oxide) handles the charge prevention function, thereby eliminating the harmful effect of widespread charge induction while maintaining isolation effectiveness.
Data Source
AI summary
A method for manufacturing a semiconductor structure includes: forming a fin structure on a substrate; forming two trench isolations on the substrate; forming dummy structures over the fin structure and the two trench isolations so that the fin structure has exposed portions which are exposed from the dummy structures, each of the dummy structures including a dummy gate; forming source/drain portions respectively in the exposed portions of the fin structure; forming a trench which penetrates through the dummy gate of a selected one of the dummy structures and through the fin structure to terminate at the substrate; and forming an isolation structure in the trench, the isolation structure including an upper portion and a lower portion which extends from the upper portion into the substrate, the upper portion and the lower portion being made of different materials, an atomic percentage of nitrogen in the lower portion being less than 1%.