Alignment Optical System Using Polarization Control
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Solution Overview
Problem
Current alignment systems in lithographic apparatuses face challenges in achieving accurate alignment measurements due to radiation beam absorption and heating in fold mirrors, leading to reduced diffraction efficiency and wavefront errors.
Innovation Solution
An optical system comprising first and second optical elements that change the polarization state of a radiation beam, with the second optical element providing total internal reflection to minimize absorption and heating, ensuring accurate alignment measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fold mirrors with metallic layers are used to direct the radiation beam onto alignment marks, then the alignment system can perform alignment measurements, but the radiation beam is absorbed causing reduced diffraction efficiency and reduced diffraction signal intensity
Solution Approach 1:
The patent extracts and removes the metallic layer from the fold mirror, converting it from a metallic mirror to a non-metallic mirror (such as a dielectric mirror). This extraction eliminates the harmful absorption effect of the metallic layer on the radiation beam while preserving the mirror's primary function of directing the beam onto the alignment marks.
Solution Approach 2:
The patent introduces a non-metallic mirror as an intermediary element to replace the metallic mirror. This intermediary element (non-metallic mirror) performs the same beam directing function but without the harmful absorption characteristics, thereby mediating between the need for beam direction and the need to minimize energy loss.
2Ease of operation
If fold mirrors with metallic layers are used to direct the radiation beam, then the alignment system can operate, but the fold mirrors become heated causing wavefront errors in the reflected radiation beam
Solution Approach 1:
The patent extracts and removes the metallic layer that causes heating, replacing it with a non-metallic mirror material. This extraction eliminates the source of heat generation while maintaining the operational functionality of the alignment system.
Solution Approach 2:
The patent replaces the durable but harmful metallic mirror with a non-metallic mirror that, while potentially having different durability characteristics, eliminates the heating problem. The focus shifts from long-term durability to immediate operational integrity by using materials that do not absorb and heat the radiation beam.
3Ease of operation
If metallic layer fold mirrors are used, then the alignment system can direct beams, but diffraction signal intensity from alignment marks is reduced
Solution Approach 1:
The patent extracts the metallic layer that causes absorption and replaces it with a non-metallic mirror. This extraction preserves the beam direction capability while eliminating the absorption that reduces diffraction signal intensity, thereby improving the illumination intensity at the alignment marks.
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
The solution enhances the accuracy of alignment measurements by maintaining radiation intensity and preventing wavefront errors, thereby improving the precision of substrate alignment in lithographic processes.
Implementation Method 1
The first optical element may be configured to change a first beam having a first polarization state into a second beam having a second polarization state
Implementation Method 2
The second optical element may be configured to provide total internal reflection of the second beam and to convert the second beam into a third beam having a third polarization state
Data Source
AI summary
An optical system for improving alignment measurement accuracy is discussed. The optical system includes first and second optical elements. The first optical element may be configured to change a first beam having a first polarization state into a second beam having a second polarization state. The second optical element may be configured to provide total internal reflection of the second beam and to change the second beam into a third beam having a third polarization state. The first, second, and third polarization states may be different from each other.