Roughened Reflective Marker for EUV Lithography Pupil Filling
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Solution Overview
Problem
Current patterning devices in lithographic apparatuses face challenges in effectively measuring properties like aberrations and alignment due to limited angular spread of radiation, which affects the accuracy of measurements and the ability to fill the projection system's pupil, especially when using EUV radiation.
Innovation Solution
A patterning device with a reflective marker featuring a combination of reflective and absorbing regions, where the reflective regions have a roughened surface with a root mean squared roughness of about an eighth of the given wavelength or more, diffusing radiation and increasing its angular spread, and the absorbing regions are configured to reduce manufacturing steps and costs by being disposed on an absorbing layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a smooth reflective surface is used in the marker, then specular reflection is strong, but the angular spread of radiation is limited and the pupil of the projection system is not sufficiently filled
Solution Approach 1:
The reflective surface roughness parameter is changed to have a root mean squared roughness of about an eighth of the given wavelength or more. This parameter change transforms the smooth surface into a roughened surface that diffuses radiation, increasing the angular spread and filling the projection system's pupil while maintaining measurement precision through controlled diffusion characteristics
2Illumination intensity
If a roughened reflective surface with RMS roughness of about an eighth of the wavelength or more is used, then the angular spread of radiation is increased and the pupil is filled, but specular reflection is reduced
Solution Approach 1:
The roughened surface converts the potentially harmful specular reflection into beneficial diffuse radiation. By controlling the RMS roughness to be about an eighth of the wavelength or more, the surface transforms concentrated specular reflection into controlled diffuse radiation that fills the pupil and increases angular spread, while the absorbing regions simultaneously manage residual specular reflection to improve signal-to-noise ratio
3Reliability
If the absorbing regions are implemented as separate structures, then the marker functionality is complete, but the manufacturing complexity and cost increase
Solution Approach 1:
The absorbing regions are merged with the absorbing layer that is already present on the patterning device. By integrating the marker's absorbing regions with the existing absorbing layer structure, the patent eliminates separate manufacturing steps for creating absorbing regions, reduces overall manufacturing complexity, and lowers costs while maintaining complete marker functionality through the combination of reflective and absorbing regions
Data Source
AI summary
A patterning device comprising a reflective marker, wherein the marker comprises: a plurality of reflective regions configured to preferentially reflect radiation having a given wavelength; and a plurality of absorbing regions configured to preferentially absorb radiation having the given wavelength; wherein the absorbing and reflective regions are arranged to form a patterned radiation beam reflected from the marker when illuminated with radiation, and wherein the reflective regions comprise a roughened reflective surface, the roughened reflective surface being configured to diffuse radiation reflected from the reflective regions, and wherein the roughened reflective surface has a root mean squared roughness of about an eighth of the given wavelength or more.