Projection Optical System Rear Mirror Support
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Solution Overview
Problem
The existing projection optical systems for exposure apparatuses face challenges in maintaining imaging performance when the light beam path is widened due to increased incident angles or mask illumination areas, leading to light beam blockage by supporting members, which results in distorted patterns and non-uniform line widths on substrates.
Innovation Solution
A projection optical system design featuring a polygonal optical member with a through hole and a supporting member that extends through the hole to support the convex mirror, allowing the light beam to pass without obstruction, even when the beam area is widened, without increasing the system size, and includes adjustable components to maintain high natural frequencies and reduce vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the area of the mask to be illuminated is widened or the incident angle of the light is increased, then the resolution or throughput is improved, but the light beam overlaps the supporting member which blocks or reflects the light beam
Solution Approach 1:
The supporting member is extracted from the optical path by providing a through-hole through which the light beam passes. The supporting member is positioned at the rear surface of the convex mirror rather than extending into the optical path, eliminating the blockage while maintaining structural support.
2Reliability
If the size of the projection optical system is increased to avoid light beam blockage, then the light beam can pass without obstruction, but the manufacturing costs and installation space increase
Solution Approach 1:
The supporting member is repositioned from a configuration that extends into the optical path (x-y plane) to one that supports the mirror from the rear surface (z-direction). This dimensional change allows the light beam to pass through the optical path unobstructed while the supporting member maintains its structural function behind the convex mirror.
3Adaptability or versatility
If the sizes of the polygonal optical member and convex mirror are increased, then the light beam path can be widened, but the weights increase and the eigenvalues (natural frequencies) are lowered
Solution Approach 1:
The supporting member is extracted from the optical path configuration and repositioned to support the convex mirror from its rear surface. This allows the convex mirror and polygonal optical member to be sized appropriately for the required beam area without the constraint of needing larger supporting structures that would extend into the optical path.
4Adaptability or versatility
If the eigenvalues of the polygonal optical member and convex mirror are lowered, then the sizes can be increased for wider beam area, but the amplitude of vibration due to disturbance becomes large
Solution Approach 1:
The support structure is repositioned to the rear surface of the convex mirror, changing from a lateral support configuration to a rear-surface support configuration. This allows the optical components to be optimized for wider beam area while the support structure, positioned in a different spatial dimension, does not interfere with the optical path and can be designed to minimize vibrations.
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 design ensures favorable imaging performance by preventing light beam blockage and allowing higher incident angles, reducing pattern distortion and non-uniformity, while maintaining system size and improving dynamic stiffness and temperature control.
Implementation Method 1
Light emitted from the illumination optical system IL in the −z direction is transmitted through the mask 18 and is redirected in the +y direction by the first reflecting surface 1a of the polygonal optical member 1
Implementation Method 2
The light redirected by the first reflecting surface 1a of the polygonal optical member 1 is reflected by the first concave reflecting surface 17a
Implementation Method 3
the convex mirror 2, the second concave reflecting surface 17b, and the second reflecting surface 1b in that order and falls onto the substrate 14
Data Source
AI summary
There is provided a projection optical system that projects an image of an object onto an image plane. The projection optical system includes an imaging optical system including a first concave mirror, a convex mirror, and a second concave mirror; an optical member having a first reflecting surface and a second reflecting surface each redirecting an optical path; and a supporting member that supports the convex mirror. The first reflecting surface, the first concave mirror, the convex mirror, the second concave mirror, and the second reflecting surface are provided in that order in a direction of travel of light from an object plane. The optical member has a through hole having an opening on a side facing the convex mirror. The supporting member extends through the through hole and from the opening to the convex mirror.