Sidewall Nitridation for Floating Gate Integrity
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Solution Overview
Problem
As semiconductor devices evolve to increase storage capacity and reduce size, traditional fabrication processes lead to issues like floating gate pull-back and bowing, resulting in decreased memory performance and yield due to parasitic capacitances and charge trap regions, which existing encapsulation methods fail to adequately address.
Innovation Solution
The use of a nitridation process to form a thin encapsulating film, such as silicon oxynitride, along the sidewalls of charge storage material during the fabrication of NAND memory arrays, which protects the floating gate from etching damage and reduces pull-back and bowing, thereby maintaining channel width and reducing charge trap sites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional etching processes are used to form isolation trenches, then manufacturing simplicity is maintained, but floating gate pull-back and bowing occur resulting in decreased manufacturing precision
Solution Approach 1:
The patent applies preliminary action by forming the encapsulating film on the floating gate sidewalls before the isolation trench etching process. This pre-protection step prevents etchant attack on the floating gate sidewalls, eliminating pull-back and bowing effects without complicating the overall fabrication sequence.
Solution Approach 2:
The encapsulating film acts as an intermediary protective layer between the floating gate and the etchant. This film barrier prevents direct contact between the etching chemistry and the floating gate sidewalls, thereby preserving sidewall integrity while allowing the etching process to proceed.
2Manufacturing precision
If encapsulating films are formed to protect floating gate sidewalls, then manufacturing precision is improved, but process complexity and time increase
Solution Approach 1:
The patent merges the encapsulating film formation step with the existing tunnel dielectric layer deposition process. By combining these two functions into a single deposition sequence, the process adds minimal time while achieving both protection and dielectric layer formation simultaneously.
Solution Approach 2:
The encapsulating film is implemented as a thin film structure that provides sufficient protection against etchant attack while minimizing added thickness and process time. The thin film approach achieves the necessary protection without significantly extending the fabrication cycle.
3Reliability
If floating gate sidewalls are exposed during etching, then etching access is improved, but charge trap regions form decreasing device reliability
Solution Approach 1:
The encapsulating film serves as an intermediary protective barrier during the etching process. It allows the etchant to access and etch the tunnel dielectric and substrate effectively while preventing the etchant from attacking the floating gate sidewalls, thus avoiding charge trap region formation.
Solution Approach 2:
The patent applies preliminary anti-action by pre-forming the encapsulating film to counteract the potential harmful effect of etchant attack on the floating gate sidewalls. This preventive measure eliminates the formation of charge trap regions before they can occur during the etching process.
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 enhances memory performance by minimizing pull-back and bowing, increasing yield, and reducing failures associated with sidewall etching, while maintaining channel width and preventing charge trap regions, thus improving the reliability and endurance of non-volatile memory devices.
Implementation Method 1
forming an encapsulating layer along the sidewalls of the strips of charge storage material using a nitridation process
Implementation Method 2
forming an encapsulating layer along the sidewalls of the strips of charge storage material using a nitridation process
Data Source
AI summary
Semiconductor devices are provided with encapsulating films for protection of sidewall features during fabrication processes, such as etching to form isolation regions. In a non-volatile flash memory, for example, a trench isolation process is divided into segments to incorporate an encapsulating film along the sidewalls of charge storage material. A pattern is formed over the layer stack followed by etching the charge storage material to form strips elongated in the column direction across the substrate, with a layer of tunnel dielectric material therebetween. Before etching the substrate, an encapsulating film is formed along the sidewalls of the strips of charge storage material. The encapsulating film can protect the sidewalls of the charge storage material during subsequent cleaning, oxidation and etch processes. In another example, the encapsulating film is simultaneously formed while etching to form strips of charge storage material and the isolation trenches.