Flash Device ONO Pattern Protection via Hard Mask Segmentation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for fabricating flash devices using hard masks often damage the oxide-nitride-oxide (ONO) pattern during the wet etching process, which degrades the device's capacity due to the thinner coating thickness of ArF photoresist patterns, making it difficult to form a stack gate thicker than the photoresist pattern.
Innovation Solution
A flash device is designed with an ONO pattern that projects farther out than the sides of the floating and control gates, and a manufacturing method involving specific etching conditions and a hard mask layer pattern to prevent damage during the wet etching process, ensuring the ONO pattern is not etched along with the control and floating gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a hard mask layer is formed under the ArF photoresist pattern to enable patterning, then the control gate can be formed with proper thickness, but the ONO pattern is damaged during subsequent wet etching processes
Solution Approach 1:
The patent segments the etching process into multiple stages: first etching the control gate using the hard mask pattern, then removing the hard mask, and finally etching the floating gate. This segmentation allows the ONO pattern to be partially protected during critical etching steps while still achieving the desired control gate thickness through the hard mask layer.
Solution Approach 2:
The hard mask layer is formed in advance on the control gate before the floating gate etching process. This preliminary action creates a protective barrier that prevents the ONO pattern from being damaged during the floating gate etching, while still allowing the control gate to be properly formed in earlier steps.
2Ease of manufacture
If the hard mask layer is removed after forming the control gate, then the floating gate can be etched, but the ONO pattern is damaged during the wet etching process
Solution Approach 1:
The hard mask layer is retained on the control gate after control gate formation as a preliminary protective measure. This preliminary action ensures that when the floating gate etching process is performed later, the ONO pattern is protected from damage, while still allowing easy access to etch the floating gate through the exposed regions.
Solution Approach 2:
The hard mask layer serves as an intermediary protective element between the etching process and the ONO pattern. It mediates the etching process by being present during control gate formation to ensure proper thickness, then remaining in place during floating gate etching to protect the ONO pattern from damage.
3Productivity
If the ONO pattern is damaged during wet etching, then the fabrication process can be completed, but the flash device capacity is largely degraded
Solution Approach 1:
The hard mask layer acts as an intermediary protective barrier during the floating gate etching process. It allows the etching to proceed efficiently to complete fabrication while protecting the ONO pattern from damage, thereby maintaining device capacity and preventing degradation.
Solution Approach 2:
The hard mask layer is maintained in place as a preliminary protective measure before the floating gate etching process. This preliminary action ensures that the ONO pattern is protected during the etching process, allowing fabrication to be completed without degrading device capacity.
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 effectively inhibits damage to the ONO pattern during fabrication, maintaining the integrity and capacity of the flash device by using etching selectivity and over etching processes to maintain the ONO pattern's structure.
Implementation Method 1
forming a floating gate by patterning the auxiliary floating polysilicon layer using an etching material with an etching selectivity such that the etching material does not etch the ONO film
Implementation Method 2
The hard mask pattern 8 is typically removed by performing a wet etching process, such as a vapor phase chromatography (VPC) process
Data Source
AI summary
A flash device and a manufacturing method thereof are provided. An ONO pattern can be formed on a floating gate, and a control gate can be formed on the ONO pattern. The ONO pattern can be formed with a portion that projects farther out than the sides of the floating gate and the control gate.