Floating Gate Lateral Protrusion Stabilizes Stack During Megasonic Cleaning
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Solution Overview
Problem
The manufacturing method of nonvolatile flash memories results in a lateral notch in the gate oxide layer, causing the stacked structure of the floating gate and control gate to be unsupported, leading to potential collapse during megasonic cleaning processes.
Innovation Solution
A method involving the formation of a first sidewall insulating film on the control gate, selective removal of the floating gate conducting film, introduction of nitrogen into the exposed gate insulating film, and subsequent removal of the sidewall insulating film to create a lateral protrusion, which stabilizes the floating gate and allows for the formation of an erase gate that prevents collapse during cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the floating gate is patterned using the spacer oxide layer as a mask, then the floating gate can be formed with precise dimensions, but the gate oxide layer below the floating gate erodes laterally causing a notch that destabilizes the stacked structure
Solution Approach 1:
The patent applies preliminary action by forming a protective oxide layer on the gate oxide layer before the floating gate patterning process. This protective layer prevents lateral erosion of the gate oxide layer during etching, while still allowing precise patterning of the floating gate to occur. The protective oxide is formed in advance and removed after serving its protective function.
Solution Approach 2:
The patent introduces an intermediary protective oxide layer that acts as a mediator between the etching process and the gate oxide layer. This intermediary layer absorbs the harmful lateral erosion effect during floating gate patterning, protecting the underlying gate oxide layer while allowing the patterning process to proceed with high precision.
2Ease of manufacture
If megasonic cleaning is applied to remove dirt and dust, then cleaning effectiveness is improved, but the unstable stacked structure of floating gate and control gate collapses
Solution Approach 1:
The patent applies beforehand cushioning by strengthening the gate oxide layer with a protective oxide layer prior to the megasonic cleaning process. This protective layer acts as a cushion that prevents the stacked structure from collapsing during the intense megasonic cleaning, allowing effective cleaning to occur without compromising structural integrity.
3Productivity
If the spacer oxide layer is removed after floating gate patterning, then the floating gate structure is completed, but the exposed gate oxide layer erodes and creates lateral notches
Solution Approach 1:
The patent forms a protective oxide layer in advance before the spacer oxide layer is removed. This preliminary protective action ensures that when the spacer oxide is removed and the gate oxide layer becomes exposed, the protective layer is already in place to prevent lateral erosion, maintaining dimensional accuracy throughout the manufacturing 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
Prevents the collapse of the floating gate and control gate stack structure during megasonic cleaning, reducing lateral notches and enhancing the stability of the gate stack structure, thereby improving the manufacturing process and device reliability.
Implementation Method 1
A first nitrogen introduced portion is formed by introducing nitrogen into the exposed portion of the gate insulating film
Data Source
AI summary
An insulating film made of the same material as that of a gate insulating film is formed so as to cover one sidewall of a control gate on a conducting film for floating gate. By selectively removing the conducting film for floating gate with the insulating film as a mask, a floating gate is formed from the conducting film for floating gate, and a portion of the gate insulating film is exposed at the floating gate. A nitrogen introduced portion is formed by introducing nitrogen into the exposed portion of the gate insulating film. Then, the insulating film is removed to expose an upper surface of a lateral protrusion of the floating gate. An erase gate is formed so as to face the upper surface and a side surface of the lateral protrusion.