Flash Memory U-Shaped Dielectric Layer Fabrication
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Solution Overview
Problem
The fabrication of flash memory devices often encounters issues such as encroachment in the oxide-nitride-oxide (ONO) stack and tunnel oxide layer, which affects the operation and performance of the device, necessitating an improvement in the architecture and process to enhance endurance.
Innovation Solution
A method involving the formation of a U-shaped dielectric layer between the floating gate and substrate, achieved by selectively removing parts of the electrode layers and ONO stack without exposing the tunnel oxide layer, followed by a re-oxidation process to create a U-shaped dielectric structure, which includes a horizontal portion with a tunnel oxide layer and two vertical portions, with the spacer's bottom aligned with the tips of the vertical portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication process is used, then flash memory can be manufactured, but encroachment in ONO stack and tunnel oxide layer occurs affecting device performance
Solution Approach 1:
A U-shaped dielectric layer is formed in advance between the floating gate and substrate before completing the ONO stack fabrication. This preliminary structure prevents encroachment of the ONO stack and tunnel oxide layer by providing a protective barrier, thereby maintaining manufacturing precision while ensuring device performance
Solution Approach 2:
The U-shaped dielectric layer acts as an intermediary structure between the floating gate and substrate. This intermediate layer prevents direct contact and potential encroachment between the ONO stack and tunnel oxide layer, resolving the conflict between maintaining precise layer integrity and achieving reliable device operation
2Ease of manufacture
If tunnel oxide layer is exposed during fabrication, then electrode layers can be removed, but device endurance deteriorates
Solution Approach 1:
The U-shaped dielectric layer is formed preliminarily to cover and protect the tunnel oxide layer before any electrode layer removal operations. This allows complete removal of electrode layers without exposing the tunnel oxide layer, thereby maintaining device endurance while facilitating ease of manufacture
Solution Approach 2:
The U-shaped dielectric layer serves as a protective cushion formed beforehand to prevent direct exposure of the tunnel oxide layer during subsequent fabrication steps. This cushioning structure enables aggressive electrode layer removal while preserving the tunnel oxide layer integrity, thus maintaining device endurance
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 maintains stable electron transmission and better coupling during writing and erasing operations, improving the endurance and performance of the flash memory device by preventing tunnel oxide layer exposure and optimizing the ONO stack profile.
Implementation Method 1
a re-oxidation process to create a U-shaped dielectric structure
Data Source
AI summary
A method for fabricating memory device is disclosed. The method includes the steps of: providing a substrate having a tunnel oxide layer on the substrate, a first electrode layer on the tunnel oxide layer, an oxide-nitride-oxide (ONO) stack on the first electrode layer, and a second electrode layer on the ONO stack, and then removing part of the second electrode layer, part of the ONO stack, and part of the first electrode layer so that the tunnel oxide layer is not exposed.