NAND Flash Memory Cell Metal Diffusion Barrier
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Solution Overview
Problem
The planar floating gate cell structure in NAND flash memory experiences reliability degradation due to metal diffusion into the inter-poly and tunnel insulating films, leading to degradation of insulating properties and memory cell reliability.
Innovation Solution
Incorporating an interlayer film containing a metal, such as a silicide layer, between the first and second insulating films in the memory cell structure to prevent metal diffusion into the high dielectric constant insulating film, thereby improving the trap level and charge retention characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal layer is formed directly on the floating gate with an inter-poly insulating film, then the memory capability is improved, but metal diffusion occurs into the insulating films causing reliability degradation
Solution Approach 1:
A barrier layer is introduced as an intermediary component between the metal layer and the inter-poly insulating film. This barrier layer prevents metal atoms from diffusing into the insulating film while allowing the memory cell to maintain its improved memory capability. The barrier layer acts as a mediator that blocks the harmful metal diffusion pathway without interfering with the functional metal-insulator interface.
Solution Approach 2:
The original direct contact structure between metal and insulating film is segmented by inserting a barrier layer. This segmentation divides the interface into two separate interfaces: metal-barrier and barrier-insulator. This structural segmentation effectively isolates the metal from the insulating film, preventing metal diffusion while preserving the functional requirements of the memory cell.
2Reliability
If the metal layer is formed on the floating gate, then the insulating properties should be maintained, but metal diffusion degrades the insulating properties
Solution Approach 1:
The barrier layer serves as a protective intermediary that prevents metal atoms from penetrating into and contaminating the inter-poly insulating film. By blocking the diffusion pathway, the barrier layer preserves the original composition and insulating properties of the insulating film, ensuring long-term reliability of the memory cell.
Solution Approach 2:
The barrier layer is positioned in advance between the metal and insulating film to preemptively block metal diffusion. This prior protective measure prevents metal contamination before it can occur, thereby maintaining the stability and insulating properties of the insulating film throughout device operation.
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 solution effectively prevents metal diffusion, enhancing the reliability and performance of the memory cell by reducing trap levels and improving leak current and charge retention in the high dielectric constant insulating film.
Implementation Method 1
Incorporating an interlayer film containing a metal, such as a silicide layer, between the first and second insulating films in the memory cell structure to prevent metal diffusion into the high dielectric constant insulating film
Data Source
AI summary
A nonvolatile semiconductor memory includes an electrically data rewritable or erasable memory cell. The memory cell includes a tunnel insulating film provided on a semiconductor substrate; a floating gate provided on the tunnel insulating film; a first insulating film provided on the floating gate; an interlayer film containing a metal provided on the first insulating film; a second insulating film provided on the interlayer film; a high dielectric constant insulating film provided on the second insulating film; and a gate electrode provided on the high dielectric constant insulating film.