Photomask Laser Etch for EUV Lithography
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Solution Overview
Problem
Conventional techniques for creating black borders and pellicle anchor areas on photomasks using plasma etching are complex, time-consuming, and can damage the photomask due to the use of cleaning chemicals and result in rough sidewalls, leading to pattern overlap issues during EUV lithography.
Innovation Solution
A laser etch method employing a femtosecond laser with a lens of focal length between 30 mm and 110 mm is used to remove films from the black border and pellicle anchor areas without damaging the photomask, utilizing low power (about 100 mW or less) and short pulse duration (200-300 femtoseconds) to prevent heat transfer and achieve smooth sidewalls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If plasma etching is used to create black border and pellicle anchor areas, then films can be removed from the photomask, but the process becomes complex and time-consuming requiring multiple photoresist deposition and cleaning steps
Solution Approach 1:
The patent replaces the complex plasma etching process with a laser-based ablation process. The laser system directly removes films from the photomask without requiring photoresist deposition, plasma chamber processing, or multiple cleaning steps. This substitution of mechanical/chemical etching with optical ablation dramatically simplifies the process flow and reduces processing time while maintaining the ability to create precise black border and pellicle anchor areas.
Solution Approach 2:
The patent extracts and eliminates the intermediate photoresist steps from the film removal process. Instead of depositing photoresist, performing plasma etching, and then removing photoresist with chemicals, the laser system directly ablates the films. This extraction of unnecessary intermediate steps reduces both process complexity and time while achieving the same functional result of removing films from specific photomask areas.
2Ease of operation
If cleaning chemicals are used in the plasma etching process, then photoresist can be removed from the photomask, but the photomask becomes damaged
Solution Approach 1:
The patent replaces chemical cleaning processes with laser ablation. The laser directly removes films and photoresist through photothermal ablation without requiring harsh chemical solvents. This substitution eliminates the harmful interaction between cleaning chemicals and the photomask substrate, absorber layer, and other sensitive films, thereby preventing damage while achieving complete removal of organic materials.
Solution Approach 2:
The patent converts the potential harm of aggressive cleaning chemicals into a beneficial laser ablation process. The high energy density of the laser, which could potentially damage the photomask if misapplied, is instead used precisely to ablate only the intended films and photoresist. The short pulse duration and focused beam deliver energy selectively to the target materials, converting what could be harmful excessive energy into a controlled, beneficial removal process that leaves the photomask intact.
3Ease of manufacture
If conventional etching is used to create black borders, then films are removed from the photomask, but rough sidewalls are created causing pattern overlap during EUV lithography
Solution Approach 1:
The patent changes the fundamental parameters of the etching process by using laser ablation instead of plasma etching. The laser parameters (wavelength, pulse duration, energy density, scanning speed) are optimized to achieve smooth sidewalls. The short pulse duration (nanosecond or picosecond scale) and controlled energy delivery prevent the formation of rough surfaces and redeposition that occur in plasma etching, thereby achieving the dual goal of effective film removal and smooth sidewall formation that prevents pattern overlap.
Solution Approach 2:
The patent employs periodic laser pulsing to remove films in a controlled manner. The laser delivers energy in short, periodic pulses that allow for precise control of material removal. This periodic action prevents excessive heating and material redeposition that cause rough sidewalls, enabling smooth vertical profiles on the black border and pellicle anchor areas that maintain pattern fidelity during EUV lithography.
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
The laser etch method simplifies the processing of photomasks, reduces damage, and minimizes pattern overlap by creating precise black borders and pellicle anchor areas, enhancing the accuracy of EUV lithography without increasing the photomask's temperature.
Implementation Method 1
The photomask is etched with a femtosecond laser to remove at least a second layer disposed on the photomask from the black border
Implementation Method 2
a femtosecond laser source configured to emit a laser beam through the second volume to remove material from the photomask without damaging the photomask
Data Source
AI summary
Embodiments described herein relate to apparatus and methods for removing one or more films from a photomask to create a black border and one or more pellicle anchor areas thereon. A photomask substrate is exposed by removing the one or more films in the black border and pellicle anchor areas. The black border prevents a pattern on the photomask from overlapping a pattern on a substrate being processed. To create the black border and pellicle anchor areas, a laser beam is projected through a lens and focused on a surface of the films. The films are ablated by the laser beam without damaging the photomask substrate.