Nitrided Tungsten Via Adhesion in NAND Flash Memory
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Solution Overview
Problem
In NAND flash memory manufacturing, there is a need for a reliable process to form vias and horizontal metal lines to prevent chemical penetration during etching or cleaning, which can lead to unsatisfactory memory operation due to poor adhesion and resistance characteristics.
Innovation Solution
A method involving a nitridation step to form tungsten nitride on tungsten vias and silicon oxynitride on silicon oxide layers, followed by the deposition of a second silicon oxide layer and a wet clean step, ensuring that the tungsten via remains isolated from direct exposure to chemical etches, thereby enhancing adhesion and preventing chemical penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nitridation step is performed to form tungsten nitride on tungsten vias, then adhesion between metal lines and vias is improved, but process complexity increases
Solution Approach 1:
The nitridation step is performed in advance, before trench etching and metal line deposition, to pre-form the tungsten nitride adhesion layer on the tungsten via surface. This preliminary action ensures that when subsequent processing steps occur, the adhesion layer is already in place to prevent chemical penetration and ensure strong bonding between the metal line and via, thereby resolving the adhesion problem without requiring additional steps later in the process.
2Manufacturing precision
If chemical etching is used to form trenches, then manufacturing precision is improved, but chemical penetration at interfaces occurs leading to poor adhesion
Solution Approach 1:
A silicon oxynitride layer is introduced as an intermediary barrier between the silicon oxide and the etching environment. This intermediate layer has resistance to the chemical etchants used, preventing them from penetrating to the tungsten via interface. The silicon oxynitride layer is formed by nitridation of the silicon oxide layer, creating a protective barrier that maintains trench formation precision while preventing chemical penetration and adhesion degradation.
3Manufacturing precision
If wet clean steps are performed to remove residues, then manufacturing precision is improved, but direct exposure of tungsten via to chemicals causes penetration and adhesion loss
Solution Approach 1:
The silicon oxynitride layer serves as a protective intermediary during wet clean steps. This layer is resistant to the wet cleaning chemicals, preventing them from reaching and damaging the tungsten via surface or penetrating to the via-interface. The intermediary layer allows thorough cleaning of the structure while maintaining the integrity and adhesion properties of the tungsten via, thereby resolving the contradiction between cleanliness and adhesion preservation.
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 process improves the adhesion between metal lines and vias, reducing chemical penetration and ensuring reliable electrical contact, leading to better memory performance and reduced risk of current leakage.
Implementation Method 1
performing a nitridation step that forms a tungsten nitride layer on an exposed top surface of the tungsten via
Implementation Method 2
forming silicon oxynitride on exposed surfaces of the silicon oxide layer
Data Source
AI summary
A nitridation step applied to a tungsten via in a first silicon oxide layer forms a tungsten nitride layer on an exposed top surface of the tungsten via. Subsequently, a second silicon oxide layer is formed over the first silicon oxide layer and the tungsten via. Subsequently, an opening is formed through the second silicon oxide layer to expose at least part of the silicon nitride layer. Subsequently, a wet clean step is performed.