Flash Memory Bit Line Capacitance Reduction via ALD Barrier Oxide
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Solution Overview
Problem
In the fabrication of 70 nm-grade NAND flash devices, the oxidization of tungsten hard mask films and the use of nitride films as wet barriers lead to increased bit line capacitance, reducing bit line speed due to higher dielectric constants.
Innovation Solution
The method involves forming barrier oxide films on the lateral faces of trenches using atomic layer deposition (ALD) to prevent oxidization of tungsten hard mask films and reduce bit line capacitance, replacing nitride films with oxide films as wet barriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nitride film is used as the wet barrier to prevent oxidization of the tungsten hard mask film, then the oxidization problem is solved, but the bit line capacitance increases and bit line speed is reduced
Solution Approach 1:
The invention changes the material parameter from nitride film to oxide film for the wet barrier layer, and changes the deposition method parameter from conventional CVD to atomic layer deposition (ALD). This dual parameter change achieves both oxidation prevention and reduced capacitance, resolving the contradiction between reliability and speed.
2Speed
If an oxide film by LPCVD method is used as the wet barrier, then bit line capacitance is reduced, but the tungsten hard mask film is oxidized
Solution Approach 1:
The invention introduces atomic layer deposition (ALD) as an intermediary deposition method that enables precise control of oxide film formation. ALD acts as a mediator between the oxide film material and the tungsten hard mask film, allowing the oxide film to prevent capacitance issues while ALD's controlled deposition process prevents unwanted oxidation of the tungsten film.
3Ease of manufacture
If the oxide film is lost due to the cleaning process, then manufacturing simplicity is maintained, but the wet barrier function is compromised
Solution Approach 1:
The invention changes the deposition method parameter from conventional CVD to atomic layer deposition (ALD). ALD's superior film quality and adhesion properties enable the oxide film to withstand the cleaning process without loss, maintaining both manufacturing simplicity and wet barrier function simultaneously.
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 prevents tungsten hard mask film oxidization and reduces bit line capacitance, enhancing bit line speed by using oxide films with lower dielectric constants compared to nitride films.
Implementation Method 1
forming barrier oxide films on lateral faces of the trenches by an atomic layer deposition (ALD) method
Data Source
AI summary
A method of fabricating flash memory devices includes the steps of forming a stop nitride film and an oxide film on a semiconductor substrate having a predetermined structure formed therein, forming trenches in the oxide film and the stop nitride film, forming barrier oxide films on lateral faces of the trenches by an atomic layer deposition method, and forming bit lines within the trenches.