Fast-Response MFC Pulsing for Uniform TiN Work Function Deposition
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Solution Overview
Problem
Conventional mass flow controllers (MFCs) have response delays that exceed 0.25 seconds, leading to non-uniformity in titanium nitride film deposition, particularly affecting the nitrogen ratio across the substrate surface, which in turn causes variations in threshold voltage (Vt) of transistors.
Innovation Solution
Employing a fast response mass flow controller with ON and OFF response delays of less than 0.25 seconds at flow rates between 5 sccm to 100 sccm to pulse the process gas between a poison and metallic regime, ensuring precise control during titanium nitride film deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mass flow controllers are used with response delays greater than 0.25 seconds, then the device complexity is reduced and ease of operation is maintained, but the manufacturing precision of titanium nitride film deposition deteriorates due to non-uniform nitrogen ratio across substrate surface
Solution Approach 1:
The patent changes the temporal parameter of the mass flow controller by switching from conventional MFCs with response delays >0.25s to fast response MFCs with response delays ≤0.25s. This parameter change enables precise pulsing of nitrogen flow to achieve uniform nitrogen ratio (0.95-1.05) across the substrate surface, directly resolving the manufacturing precision issue.
2Manufacturing precision
If fast response mass flow controllers with response delay less than or equal to 0.25 seconds are used, then the manufacturing precision of titanium nitride film deposition is improved, but the device complexity increases
Solution Approach 1:
The patent implements a feedback control mechanism where the fast response MFC continuously monitors and adjusts nitrogen flow rates based on real-time process conditions. The controller receives feedback about the actual nitrogen ratio in the deposited film and dynamically adjusts the pulsing parameters to maintain the target ratio of 0.95-1.05, ensuring uniform threshold voltage across the substrate.
3Manufacturing precision
If pulsed flow process is implemented to improve nitrogen ratio uniformity, then the manufacturing precision is improved, but the response delay of conventional MFC becomes a substantial portion of the pulse width causing mis-match with programmed pulsing pattern
Solution Approach 1:
The patent applies preliminary action by pre-configuring the fast response MFC with pulsing parameters before the deposition process begins. The controller is programmed with the exact pulse widths and flow rates needed to achieve the desired nitrogen ratio, and its fast response capability ensures these pre-planned actions are executed without significant delay, maintaining synchronization between the programmed pulsing pattern and actual gas delivery.
4Quantity of substance
If nitrogen flow rate is increased to improve film composition, then the concentration of nitrogen in film is improved, but the uniformity across substrate surface deteriorates due to conventional MFC response delay
Solution Approach 1:
The patent employs periodic action through pulsed nitrogen flow delivery, where the fast response MFC delivers nitrogen in controlled pulses during the deposition process. This periodic supply of nitrogen, combined with the fast response capability, ensures uniform distribution of nitrogen atoms across the substrate surface, achieving both adequate nitrogen content and center-to-edge uniformity with atomic ratio variation of only 0.95-1.05.
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 enhances the uniformity of the nitrogen-to-titanium atomic ratio, reducing center-to-edge non-uniformity and stabilizing the plasma, thereby improving the consistency of threshold voltage (Vt) across the substrate.
Implementation Method 1
The process gas is energized to create a plasma in the inner volume to cause titanium atoms to eject from the sputtering target toward the substrate surface
Implementation Method 2
Titanium nitride films are frequently deposited using physical vapor deposition (PVD)
Data Source
AI summary
Methods for forming work function layers (e.g., titanium nitride work function layers) for transistors are described. The methods energizing a process gas disposed in an inner volume of a processing chamber to create a plasma, and pulsing the process gas between a poison regime and a metallic regime using a fast response mass flow controller to deposit the work function layer on the substrate surface.