Laser Wavelength Modulation Using Pre-Positioned Piezo Control
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Solution Overview
Problem
Existing lithographic systems face challenges in rapidly changing the wavelength of deep ultraviolet light sources due to long settling times, limiting the ability to achieve precise and repeatable etching and deposition in 3D NAND lithography, particularly in 3D NAND fabrication where multi-layered stack heights increase the difficulty in achieving consistent etch and deposition results.
Innovation Solution
The use of a piezoelectric actuator in a line narrowing module, combined with optimal control waveforms computed using methods like quadratic programming, dynamic programming, model inversion feedforward control, and iterative learning control, allows for rapid transition between different wavelengths by pre-positioning the actuator and utilizing a pre-populated look-up-table or FPGA to minimize settling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional wavelength control system with feedback and feed-forward compensators is used, then wavelength stability is improved, but the settling time increases to about 100 ms, which exceeds the time between pulses
Solution Approach 1:
The patent pre-calculates and stores optimal actuator waveforms in a look-up table before wavelength changes are needed. When a wavelength change is commanded, the pre-computed waveform is immediately applied without real-time calculation delay, enabling rapid wavelength switching while maintaining stability.
Solution Approach 2:
The patent replaces traditional feedback control mechanisms with a feed-forward approach using pre-computed optimal waveforms. This substitution eliminates the need for real-time feedback adjustment during wavelength transitions, significantly reducing settling time while maintaining wavelength accuracy.
2Adaptability or versatility
If the target wavelength set point is changed between pulses to achieve wavelength modulation, then adaptability is improved, but the conventional control system cannot provide desired wavelength tracking performance due to excessive settling time
Solution Approach 1:
The system pre-computes optimal actuator waveforms for various wavelength transitions and stores them in a look-up table. When wavelength modulation is needed, the appropriate pre-computed waveform is selected and applied immediately, enabling precise wavelength tracking between pulses without exceeding settling time constraints.
Solution Approach 2:
The patent implements dynamic wavelength control by computing optimal waveforms that account for the specific transition requirements. The system adapts the actuator waveform dynamically based on the desired wavelength change, enabling precise tracking performance for different wavelength modulation scenarios.
3Manufacturing precision
If more than one exposure pass is made over a wafer using different laser wavelengths, then depth of focus is improved for 3D NAND lithography, but productivity decreases due to multiple passes
Solution Approach 1:
The patent enables rapid switching between different laser wavelengths by implementing precise actuator control with pre-computed waveforms. This allows the system to change operational parameters (wavelength) quickly between pulses, maintaining depth of focus requirements while minimizing the impact on overall productivity through efficient wavelength modulation.
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 enables rapid wavelength modulation between pulses, achieving stable and precise laser radiation with minimal error, facilitating consistent etching and deposition in complex 3D structures with high-aspect-ratio features.
Implementation Method 1
The use of a piezoelectric actuator in a line narrowing module
Data Source
AI summary
Apparatus for and method of controlling a laser system capable of generating bursts of pulses of laser radiation having multiple alternate wavelengths in which an element controlling the wavelength is pre-positioned between bursts to be between its position for generating one wavelength and its position for generating another wavelength. Also disclosed is a system that determines an optimal control waveform for the element to move between positions using quadratic programming, dynamic programing, inversion feed forward control, or iterative learning control. A data storage device such as a pre-populated lookup table or a field programmable gate array may be used to store at least one optimal control parameter for each of a plurality of repetition rates.