Grazing Incidence Mirror Pair for EUV Light Throughput
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Solution Overview
Problem
Current projection optical units face challenges in achieving a well-corrected imageable field with high imaging light throughput, particularly at grazing incidence angles, which affects the efficiency and quality of imaging in projection exposure apparatuses.
Innovation Solution
The use of a projection optical unit with multiple mirrors, including pairs for grazing incidence, where at least two mirrors are arranged directly behind each other with angles of incidence greater than 60°, along with reflective coatings like ruthenium and molybdenum, to enhance light reflectivity and correct image aberrations, ensuring uniform light throughput across the field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If mirrors with grazing incidence angles greater than 60° are used, then imaging light throughput is improved, but image aberration correction becomes more difficult
Solution Approach 1:
The projection optical unit is divided into multiple mirror elements (at least two mirrors) arranged in sequence, each contributing to both light throughput and aberration correction. By segmenting the optical function across multiple grazing incidence mirrors, the system achieves high light throughput while distributing the aberration correction task across several optical surfaces.
Solution Approach 2:
Each mirror in the grazing incidence pair is designed with specific local optical properties and surface figures tailored to its position in the beam path. The mirrors have different orientations and surface characteristics optimized for their respective locations, enabling simultaneous achievement of high reflectivity and aberration correction at each local position.
2Loss of energy
If multiple mirrors are arranged directly behind one another, then light reflectivity is improved through grazing incidence, but system complexity increases
Solution Approach 1:
Multiple mirror functions are merged into a compact arrangement where at least two mirrors are positioned directly behind one another in the beam path. This merging approach achieves high cumulative reflectivity through grazing incidence while maintaining a relatively compact optical system layout.
Solution Approach 2:
The mirrors are arranged in a sequence along the beam path with different orientations, utilizing angular and spatial dimensions to achieve high reflectivity. By changing the dimensional arrangement from a single mirror to multiple mirrors at different angles, the system optimizes light throughput without proportionally increasing system footprint.
3Loss of energy
If reflective coatings like ruthenium and molybdenum are applied, then light reflectivity is improved, but manufacturing complexity increases
Solution Approach 1:
The mirrors are coated with composite reflective layers comprising ruthenium and/or molybdenum materials. These composite coatings provide enhanced reflectivity for EUV radiation while being applied as integrated layers on the mirror surfaces, combining multiple material properties in a single coating structure.
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 enables high imaging light throughput and image correction, reducing light loss and exposure duration, thereby increasing wafer throughput in projection exposure apparatuses while maintaining high structure resolution.
Implementation Method 1
At least two of the mirrors are embodied as mirrors arranged directly behind one another in the beam path of the imaging light for grazing incidence with an angle of incidence of the imaging light which is greater than 60°
Implementation Method 2
Ruthenium and/or molybdenum can be used as coating materials for these coatings. The mirrors for grazing incidence can have a reflectivity which lies in the range between 75 and 95% and which, in particular, can be at least 80%
Data Source
AI summary
A projection optical unit images an object field in an image field. The projection optical unit includes a plurality of mirrors guides imaging light from the object field to the image field. At least two of the mirrors are arranged directly behind one another in the beam path of the imaging light for grazing incidence with an angle of incidence of the imaging light which is greater than 60°. This results in an imaging optical unit that can exhibit a well-corrected imageable field with, at the same time, a high imaging light throughput.