Scattering Structure for Pupil Filling in Projection Exposure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing microlithographic projection exposure apparatuses face challenges in achieving optimal pupil filling and accurate measurement of imaging aberrations due to suboptimal angular distribution of illumination rays, leading to incomplete illumination of the projection lens pupil and potential measurement errors.
Innovation Solution
Incorporating a scattering structure within the illumination system that deflects measurement illumination rays by less than 15°, ensuring a diffuse radiation pattern that improves pupil filling and allows for robust measurement without affecting exposure operations, and utilizing a facet mirror with adjustable mirror elements to switch between exposure and measurement modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a coherence mask is used to split illumination radiation into individual rays for wavefront measurement, then measurement of imaging aberration is enabled, but the angular distribution of rays may not optimally fill the pupil of the projection lens
Solution Approach 1:
A scattering structure is introduced as an intermediary element between the coherence mask and the projection lens. This scattering structure modifies the angular distribution of the illumination rays, causing them to intersect the pupil plane at closely meshed points that optimally fill the entire pupil area. The scattering structure acts as a mediator that transforms the ray distribution without requiring changes to the coherence mask or projection lens design.
2Measurement precision
If the measurement beam path uses a complex interferometric setup, then wavefront measurement is achieved, but the complexity of the measurement system increases
Solution Approach 1:
The projection lens is designed to serve dual functions: it acts as both the imaging optical system for exposure operations and the test object for wavefront measurement. The same projection lens used in manufacturing also performs the measurement function, eliminating the need for separate test optics and reducing overall system complexity. The illumination system is similarly configured to serve both exposure and measurement purposes.
3Area of stationary object
If individual rays are deflected at large angles to fill the pupil, then pupil filling is improved, but the rectilinear beam path between scattering structure and mask plane is compromised
Solution Approach 1:
The scattering structure is designed to deflect illumination rays by small angles (less than 15°, preferably less than 10° or 8°). This parameter constraint on the deflection angle ensures that the measurement beam path remains substantially rectilinear between the scattering structure and the mask plane, while still achieving sufficient angular distribution to optimally fill the projection lens pupil. The small angle parameter maintains geometric simplicity while achieving the desired pupil filling.
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 and completeness of imaging aberration measurements by ensuring closer-meshed intersection points within the pupil plane, improving illumination of the entire pupil area, and increasing measurement robustness without increasing complexity.
Implementation Method 1
a scattering structure arranged on the illumination side with respect to the mask plane and outside the exposure illumination beam path. The measurement illumination beam path extends via the scattering structure
Data Source
AI summary
A microlithographic projection exposure apparatus (10) includes a projection lens (26) that images an object field (22) arranged in a mask plane (24) onto a substrate (28) during exposure operation of the projection exposure apparatus, and an illumination system (16) that has: an exposure illumination beam path (44) for radiating illumination radiation (14) onto the object field on the illumination side with respect to the mask plane, a measurement illumination beam path (48) for irradiating a measurement structure (54) arranged in the mask plane with the illumination radiation, and a scattering structure (50) arranged on the illumination side with respect to the mask plane and outside the exposure illumination beam path. The measurement illumination beam path extends via the scattering structure and runs rectilinearly between the scattering structure and the mask plane.