EUV Mirror Substrate Deformation for Aberration Correction
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Solution Overview
Problem
EUV projection objectives face manufacturing-related aberrations due to material and form errors in mirrors, which existing correction methods often reduce reflectivity and worsen light intensity uniformity.
Innovation Solution
A method that involves measuring and reprocessing the uncoated mirror supports to produce surface deformations before applying the reflective coating, allowing for aberration correction without altering the reflectivity of the coating, using either measuring light of a different wavelength for EUV objectives or the same projection light for catadioptric objectives, and replacing or reassembling mirrors as necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the surface of coated mirrors is reprocessed to correct manufacturing aberrations, then imaging properties are improved, but reflectivity decreases and light intensity uniformity deteriorates
Solution Approach 1:
The patent applies surface deformation to the mirror support before the reflective coating is applied. This preliminary action allows aberration correction to be built into the substrate itself, so that when the coating is applied afterward, it conforms to the pre-corrected surface geometry. This eliminates the need for post-coating reprocessing that would damage the reflective surface.
Solution Approach 2:
The patent separates the aberration correction function from the reflective coating by applying the surface deformation to the mirror support substrate independently before coating. This segmentation allows the correction of manufacturing aberrations without interfering with the integrity and reflectivity of the coating layer.
2Manufacturing precision
If local material is removed or applied to correct aberrations, then wavefront errors are reduced, but uniformity of light intensity distribution deteriorates
Solution Approach 1:
The patent applies localized surface deformations to specific regions of the mirror support where aberrations are present, while maintaining the original surface quality in other regions. This localized correction approach reduces wavefront errors without creating the non-uniformities that would result from adding or removing material from the coating itself.
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 approach effectively reduces manufacturing-related aberrations in EUV projection objectives without significantly changing the reflectivity, improving imaging properties by correcting wavefront errors and maintaining light intensity uniformity.
Implementation Method 1
Since the mirror support for the projection light is almost 100% absorbent and therefore does not reflect any projection light, a reflective coating with a reflectivity in the order of approximately 60% to 70%, is applied on the surface that is exposed to the projection light
Implementation Method 2
defining a surface deformation on the mirror support of the at least one mirror such that an improvement of the at least one image property can be achieved; producing the surface deformation defined in step e) on the surface of the mirror support
Implementation Method 3
a reflective coating with a reflectivity in the order of approximately 60% to 70%, is applied on the surface that is exposed to the projection light
Data Source
AI summary
A method of manufacturing a projection objective (22) of a microlithographic projection exposure apparatus (10). The projection objective (22) comprises at least one mirror (M1 to M6) that each have a mirror support (241 to 246) and a reflective coating (26) applied thereon. First imaging aberrations of a pre-assembled projection objective are measured. Before the coating (26) is applied, the mirror supports (241 to 246) are provided with a desired surface deformation (34). If the mirrors (M1 to M6) are not reflective for projection light without the coating (26), measuring light is used that has another wavelength. Alternatively, two identical mirror supports (246) may be provided. One support having a reflective coating is part of the pre-assembled projection objective whose imaging aberrations are measured. The other support is provided with surface deformations before coating and mounting the support into the objective.