SONOS Etching Residual Nitride Fence Removal
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Solution Overview
Problem
During the fabrication of silicon-oxide-nitride-oxide-silicon (SONOS) structures in non-volatile static random access memory, unwanted residual material layers (redundant fences) form on the sidewalls of shallow trench isolation structures, altering the surface profile and reducing the effective area of active regions, which can lead to decreased device performance and increased risk of damage during additional etching processes.
Innovation Solution
A method involving the formation of a complex hard mask comprising a nitride layer and oxide layers, where the nitride layer is selectively etched using a phosphoric acid solution to remove redundant fences, allowing for precise control of layout patterns and minimizing damage to other material layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching processes are used to form SONOS structure, then the fabrication process can be completed, but unwanted residual material layers (redundant fences) form on the sidewalls of STI structures, reducing the effective area of active regions
Solution Approach 1:
The patent segments the etching process into multiple selective steps: first etching the oxide layer to form the ONO structure, then separately removing the redundant fence using phosphoric acid. This segmentation allows independent optimization of each step to avoid the harmful effect of redundant fence formation while maintaining manufacturing precision.
Solution Approach 2:
The patent introduces phosphoric acid as an intermediary substance to selectively remove the redundant fence without affecting other structures. The phosphoric acid acts as a mediator that targets specifically the nitride-based redundant fence material, enabling precise removal of the harmful element while preserving the active region geometry.
2Object-generated harmful factors
If additional etching processes are prolonged or added to remove the redundant fence, then the redundant fence can be eliminated, but other material layers or components on the wafer surface may be seriously damaged
Solution Approach 1:
The patent changes the chemical parameters of the etching process by using phosphoric acid with specific concentration and temperature conditions to achieve selective removal of the redundant fence. This parameter change enables the etching to be highly selective to the nitride-based redundant fence material while being gentle to other material layers, thus eliminating the harmful effect without causing damage to other components.
Solution Approach 2:
Phosphoric acid serves as a selective intermediary that targets only the redundant fence material for removal. Its chemical properties allow it to dissolve nitride-based materials selectively while leaving oxide layers, metal layers, and other sensitive components intact, thereby removing the harmful redundant fence without compromising the reliability of other material layers.
3Productivity
If the redundant fence is not removed, then the fabrication process can be completed quickly, but the surface profile of the STI structure is altered and the width of the STI structure increases
Solution Approach 1:
The patent segments the fabrication process to include a dedicated step for removing the redundant fence using phosphoric acid. This segmentation ensures that the surface profile and STI structure width are corrected to their intended dimensions, maintaining shape accuracy while the overall process remains efficient through the selectivity of the removal method.
Solution Approach 2:
The phosphoric acid treatment allows the redundant fence to be removed in a self-selective manner, where the chemistry automatically targets only the excess nitride material on the STI sidewalls. This self-service mechanism corrects the surface profile and width without requiring complex additional processing, thereby maintaining productivity while achieving the desired shape.
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 removes redundant fences, improving the performance and accuracy of active devices by maintaining the integrity of the SONOS structure and reducing the risk of damage to other layers, while allowing for precise control of the active region area and width.
Implementation Method 1
uses a phosphoric acid solution to remove the portion of the nitride layer covering the insulating structure
Data Source
AI summary
An exemplary method of patterning oxide layer and removing residual nitride includes steps of forming a first oxide layer, a nitride layer, a second oxide layer and a complex hard mask on a substrate in turn. The first oxide layer covers an insulating structure. The second oxide layer, the complex hard mask and the nitride layer are etched by utilizing a patterned photoresist as an etching mask, so as to expose the first oxide layer. In addition, the part of the nitride layer covering the insulating structure can be further removed. Accordingly, the present invention can effectively control layout patterns of material layers and doped regions and thereby can improve the performance of a narrow width device.