Schwarzschild Objective Prism Beam Division
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Solution Overview
Problem
Existing UV optical projection systems using Schwarzschild objectives suffer from energy transfer losses due to the 'dark zone' created by light entering close to the axis, which are costly and difficult to mitigate with cylindrical lenses and beam homogenizing elements.
Innovation Solution
Incorporating a prism with multiple facets that divides the radiation beam into convergent portions, ensuring all radiation intersects on an annular zone of the first mirror, minimizing losses by reflecting onto the second mirror outside the dark zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cylindrical lenses and beam homogenizing elements are used to distribute illumination light evenly across the photomask, then the dark zone effect is minimized, but the system becomes costly and difficult to implement
Solution Approach 1:
The beam is divided into multiple segments using a beam-splitting element (such as a beam splitter cube or dichroic mirror) that separates the incoming illumination beam into several distinct beams. These segmented beams are then directed along different paths to illuminate different regions of the photomask, effectively covering the dark zone area without requiring complex homogenizing optics.
Solution Approach 2:
The invention introduces a spatial dimension solution by using multiple beam paths at different angles or positions to illuminate the photomask. Instead of trying to homogenize the beam in the same dimension, the system uses multiple beams from different directions to collectively cover the entire mask area including the dark zone, transforming a one-dimensional homogenization problem into a multi-dimensional illumination approach.
2Loss of energy
If a Schwarzschild objective is used for projection, then UV light absorption is minimized, but a dark zone is created on the secondary mirror causing energy transfer losses
Solution Approach 1:
The illumination beam is segmented into multiple separate beams that are directed to different regions of the photomask. By dividing the single beam into multiple beams, the system ensures that no single beam passes through the dark zone area, thereby eliminating the energy loss associated with the dark zone while maintaining the benefits of the Schwarzschild objective's UV transmission characteristics.
Solution Approach 2:
A beam splitter or dichroic mirror is introduced as an intermediary element that redirects portions of the illumination beam along alternative paths. This intermediary device enables the light to bypass the dark zone region on the secondary mirror while still achieving uniform illumination across the photomask, effectively mediating between the Schwarzschild objective's optical path and the need to avoid the dark zone.
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 achieves high illumination intensity on the mask while minimizing radiation losses, providing a cost-effective and simpler solution compared to prior systems, with the prism also acting as a beam homogenizer for uniform illumination.
Implementation Method 1
The facets are configured and arranged such that the beam is divided thereby into a plurality of beam-portions
Implementation Method 2
The beam portions incident in the annular zone are reflected onto the second mirror
Implementation Method 3
reflected by the second mirror to a focus in the substrate location
Data Source
AI summary
An optical system for projecting an image of a photomask on a substrate, using a Schwarzschild objective includes an excimer laser, beam shaping optics for shaping a laser beam from the laser and a beam-dividing prism. The beam-dividing prism has a dividing-face including four facets inclined at an angle to each other. The four facets divide the shaped beam into four beam-portions propagating at an angle to the system axis. The beam-portions overlap at the photomask and mutually diverge into the entrance aperture in the concave mirror of the Schwarzschild objective such that all of the light in the beam portions is incident on the convex mirror of the objective in an annular zone outside of the central obscuration zone of the convex mirror. This essentially eliminates transfer losses normally caused by this obscuration zone.