EUVL Field Stop Positioning for Throughput and Precision
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Solution Overview
Problem
Conventional EUVL exposure apparatuses suffer from low throughput due to a large number of reflections in the optical path and difficulty in positioning a field stop near the reflective mask, which affects product yield and light transmission efficiency.
Innovation Solution
The exposure apparatus incorporates a field stop with a scanning window between the projection optical system and the substrate, allowing for adjustable exposure region width and reduced reflections by using reflective optical members and a pellicle to prevent foreign object shadows, while maintaining optical conjugation with the mask and substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an image-formation catoptric optical system is provided between the mask and the field stop to position the field stop optically conjugated with the mask, then the field stop can define the stationary exposure region, but the number of reflections in the optical path increases, causing light loss and reduced throughput
Solution Approach 1:
The patent removes the image-formation catoptric optical system from between the mask and field stop, extracting the source of excessive reflections. The field stop is repositioned to be physically adjacent to the mask, eliminating multiple reflection surfaces while maintaining exposure region definition capability through direct geometric positioning rather than optical conjugation.
Solution Approach 2:
Instead of positioning the field stop optically conjugated with the mask through a complex catoptric system (indirect positioning), the patent inverts the approach by placing the field stop in direct physical proximity to the mask (direct positioning). This reverses the conventional design logic and eliminates the need for intermediate optical components.
2Productivity
If the field stop is positioned in the vicinity of the reflective mask to reduce reflections, then light loss is minimized and throughput improves, but it becomes difficult to position the field stop while maintaining optical conjugation with the substrate
Solution Approach 1:
The patent replaces the complex optical conjugation mechanism (catoptric optical system) with a simplified mechanical positioning approach. The field stop is positioned adjacent to the mask using direct geometric relationships, where the exposure region width is defined by the physical dimensions of the field stop opening rather than by optical path geometry. This mechanical substitution eliminates the need for maintaining precise optical conjugation between distant components.
3Manufacturing precision
If the wavelength of exposure light is shortened to achieve finer circuit patterns, then resolution improves, but the number of available materials with sufficient transmittance decreases, requiring the use of reflective optical members only
Solution Approach 1:
The patent changes the operating wavelength parameter to EUV range (10-20 nm), which enables finer circuit pattern resolution. This parameter change necessitates a complete system redesign using only reflective optical members, as no materials exist with sufficient transmittance at these wavelengths. The invention adapts to this constraint by optimizing the reflective optical path and eliminating components that would exacerbate light loss.
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 configuration enhances product yield and throughput by minimizing reflections and ensuring accurate pattern transfer with reduced light loss, allowing for finer circuit patterns and improved EUV light transmission.
Implementation Method 1
When a foreign object is attached to the surface of a reticle of an exposure apparatus, all of the patterns transferred with the use of the reticle have a shadow of the foreign object.
Implementation Method 2
Since an EUVL exposure apparatus uses not a transmissive mask but a reflective mask, the illumination light needs to enter the mask (or reticle) at an angle
Implementation Method 3
a projection optical system used in an EUVL exposure apparatus comprises only reflective optical members
Data Source
AI summary
An exposure apparatus including a field stop is provided. The exposure apparatus includes an illumination optical system that guides light from a light source to a pattern forming section, a projection optical system that projects, onto an exposed surface, a pattern image formed by the pattern forming section with light from the illumination optical system, a driving section that moves, in a scanning direction, a substrate arranged on the exposed surface, and a block section that is disposed between the projection optical system and the exposed surface, where the block section has a scanning window that determines a width, in the scanning direction, of an exposure region exposed to light projected by the projection optical system.