ONO Film Structure for Flash Memory Cell Integration
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Solution Overview
Problem
Existing nonvolatile flash memory technologies face challenges in high integration and miniaturization due to electron interference and inefficient data erasing methods, particularly with the punch-through phenomenon and excessive erasing issues when reducing channel length.
Innovation Solution
A semiconductor device with a specific ONO film structure, including a tunnel oxide film, a nitride trap layer, and a top oxide film, where the oxide film thickness between bit lines is optimized to be larger than the sum of the tunnel and top oxide film thicknesses but smaller than the ONO film thickness, allowing for effective electron removal using the Fowler-Nordheim tunnel effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the channel length is reduced to achieve high integration and miniaturization, then the memory cell size is reduced, but electron interference between charge storage areas increases and data reading becomes difficult
Solution Approach 1:
The charge storage layer is divided into two separate charge storage areas (first and second charge storage areas) along the channel length direction. This segmentation allows electrons to be stored in distinct regions, reducing interference between stored electrons and enabling clear data reading even with reduced channel length
Solution Approach 2:
The trap layer is configured with different thicknesses in different regions: a first thickness in the first charge storage area, a greater second thickness in a middle region between bit lines, and a third thickness in the second charge storage area. This local variation in trap layer thickness optimizes electron storage and prevents interference while maintaining data reading capability
2Ease of manufacture
If data erasing is performed using the hot hole effect, then electrons can be removed from the trap layer, but a punch-through phenomenon occurs when channel length is reduced, making current uncontrollable
Solution Approach 1:
The invention extracts and eliminates the problematic middle region trap layer configuration that causes punch-through phenomenon. By carefully controlling the trap layer thickness in the middle region and using alternative erasing methods, the punch-through issue is avoided while maintaining data erasing capability
Solution Approach 2:
The invention changes the erasing mechanism from hot hole effect to Fowler-Nordheim tunnel effect, and adjusts the trap layer thickness parameters in different regions. These parameter changes enable effective data erasing without causing punch-through phenomenon in miniaturized devices
3Ease of manufacture
If data erasing is performed using the Fowler-Nordheim tunnel effect, then electrons can be removed from charge storage areas, but apparent excessive erasing occurs in the middle of the trap layer between bit lines
Solution Approach 1:
The trap layer is designed with spatially varying thickness: thinner in charge storage areas and thicker in the middle region between bit lines. This local quality variation prevents excessive erasing in the middle region while maintaining effective electron removal from actual charge storage areas during Fowler-Nordheim tunneling
Solution Approach 2:
The middle region trap layer acts as an intermediary barrier that prevents direct Fowler-Nordheim tunneling between bit lines. The increased thickness in this region blocks the tunneling path, preventing apparent excessive erasing while still allowing proper erasing function in the charge storage areas
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 configuration enhances data reading distinctness, prevents excessive erasing, and enables high integration and miniaturization of memory cells while allowing efficient data erasing using the F-N tunnel effect.
Implementation Method 1
electrons can be removed from a charge storage layer by the F-N tunnel effect
Implementation Method 2
injecting electrons into the trap layer 16 using the hot electron effect
Implementation Method 3
removing electrons from the trap layer 16 using the hot hole effect
Data Source
AI summary
A semiconductor device includes bit lines provided in a semiconductor substrate; an ONO film that is provided along the surface of the semiconductor substrate and is made of a tunnel oxide film, a trap layer, and a top oxide film; and an oxide film that is provided on the surface of the semiconductor substrate in the middle between the bit lines and contacts the side face of the ONO film, in which the film thickness of the oxide film is larger than the sum of the thicknesses of the tunnel oxide film and the top oxide film, and smaller than the thickness of the ONO film.