Excimer Laser Wavelength Modulation for Variable Repetition Rates
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Solution Overview
Problem
Lithographic systems face challenges in maintaining wavelength stability and depth of focus during the transition from 2D to 3D NAND architecture, particularly due to variations in repetition rates across a wafer, which can lead to production halts and wafer scrap due to incorrect dose control optimization.
Innovation Solution
A laser system with a trigger circuit and wavelength control device that adjusts waveforms based on repetition rates, using a comparator and field programmable gate array to determine optimal parameters for burst pulses, allowing for dynamic waveform adjustments and transition management between different repetition rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single wavelength is used for lithography, then the system operates in single-color mode with stable wavelength control, but the depth of focus is limited and cannot meet the requirements for 3D NAND fabrication
Solution Approach 1:
The system dynamically switches between different wavelengths (193nm and 248nm) based on the required depth of focus for different target portions of the substrate. The wavelength control device adjusts the excimer laser operation mode in real-time, transitioning from static single-wavelength operation to dynamic multi-wavelength operation to meet varying manufacturing precision requirements across the substrate.
Solution Approach 2:
The invention changes the wavelength parameter of the excimer laser to optimize depth of focus. By switching between 193nm and 248nm wavelengths, the system adjusts the optical parameters to achieve the required depth of focus for different fabrication stages, particularly for high-aspect-ratio features in 3D NAND where greater depth of focus is critical.
2Productivity
If the repetition rate varies across the wafer to optimize dose control, then productivity is improved, but wavelength stability deteriorates leading to production halts and wafer scrap
Solution Approach 1:
The system employs feedback control where the wavelength control device continuously monitors and adjusts the excimer laser wavelength based on the actual repetition rate. This closed-loop control compensates for wavelength drift caused by repetition rate variations, maintaining wavelength stability within acceptable tolerances even when optimizing dose control across different wafer regions.
Solution Approach 2:
The wavelength control device pre-adjusts the wavelength compensation parameters based on the expected repetition rate changes across different target portions. By anticipating the repetition rate variations and pre-configuring the wavelength adjustment profile, the system prevents wavelength instability before it occurs, avoiding production halts and wafer scrap.
3Manufacturing precision
If multi-layered stack heights increase for 3D NAND, then the manufacturing complexity increases, but the requirement for consistent etch and deposition results becomes more difficult to achieve
Solution Approach 1:
The lithography process is segmented into multiple exposure passes, each targeting specific depth ranges within the multi-layered stack. The system divides the complex 3D structure fabrication into manageable layers, applying appropriate wavelengths (193nm or 248nm) to different depth zones, thereby achieving consistent etch and deposition results across the entire high-aspect-ratio structure.
Solution Approach 2:
The excimer laser system is designed with multi-functionality to perform both 193nm and 248nm lithography using the same hardware platform. This universal capability allows the system to handle diverse fabrication requirements across different layers of the 3D NAND stack, maintaining manufacturing precision while managing device complexity through a consolidated approach.
4Adaptability or versatility
If wavelength switching is implemented for depth of focus optimization, then the adaptability for different target portions is improved, but the system complexity increases with additional control mechanisms
Solution Approach 1:
A wavelength control device acts as an intermediary between the excimer laser and the control system. This intermediary component simplifies the overall system architecture by consolidating the wavelength switching functionality into a dedicated module, reducing the complexity of the main control system while maintaining the required adaptability for wavelength selection based on target portion requirements.
Data Source
AI summary
Apparatus for and methods of controlling wavelength in a system for producing laser radiation at more than one wavelength (color) in which one or more actuators control wavelength in response to being supplied with a waveform. The characteristics of the waveform, and/or of a controller for controlling the waveform, are determined based on a current repetition rate of the laser. A current repetition rate is determined and if it is new then a new waveform is commanded. Also disclosed is a system in which a correction depending on repetition rate is applied to an ILC algorithm determining a wavelength.