Illumination Optical System Cable Shadow Management
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Solution Overview
Problem
In photolithography, the shadows from light source unit members such as power supply cables and cooling nozzles affect the effective light source distribution, leading to uneven imaging performance, especially when projecting repetitive patterns, as they cause differences in line widths between the X and Y directions due to the directional transfer efficiency of diffracted light.
Innovation Solution
An illumination optical system with a polygonal cross-sectional internal reflection optical integrator and a power supply cable arrangement where the shadow of the cable is neither parallel nor perpendicular to the sides of the integrator's entrance surface, ensuring a symmetrical effective light source distribution by dispersing the shadow evenly across the X and Y axes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power supply cable and cooling nozzle are integrated and arranged in the optical path, then the loss of light amount is reduced, but the shadow of the integrated component falls on the exposure light causing adverse effects on the effective light source distribution and imaging performance
Solution Approach 1:
The power supply cable is arranged at an asymmetric angle of 45 degrees relative to the optical axis, rather than parallel or perpendicular to it. This asymmetric arrangement ensures that the shadow of the cable does not align with the periodic pattern directions, preventing directional differences in line width and maintaining uniform imaging performance across different pattern orientations
Solution Approach 2:
The problem is solved by introducing a rotational dimension - the cable is positioned at a specific angle (45 degrees) in the radial direction around the optical axis. This angular positioning in the third dimension (azimuthal angle) ensures that the shadow falls in a direction that does not coincide with the periodic pattern, thereby eliminating the adverse effect on effective light source distribution
2Illumination intensity
If the shadow of the power supply cable falls on the exposure light, then the effective light source distribution is affected, but this causes directional differences in line width and reduces imaging performance
Solution Approach 1:
The power supply cable is arranged at an asymmetric angle of 45 degrees relative to the optical axis, rather than parallel or perpendicular to it. This asymmetric arrangement ensures that the shadow of the cable does not align with the periodic pattern directions, preventing directional differences in line width and maintaining uniform imaging performance across different pattern orientations
Solution Approach 2:
The angular parameter of the cable arrangement is optimized to 45 degrees. By changing this specific parameter (arrangement angle), the shadow distribution on the effective light source is modified to achieve uniformity, ensuring that no particular direction experiences excessive shadowing that would cause line width variations
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 arrangement reduces the impact of shadows on imaging performance by achieving a more uniform effective light source distribution, minimizing intensity differences between the X and Y directions, thereby enhancing the imaging quality and productivity of the exposure apparatus.
Implementation Method 1
an internal reflection optical integrator which has a polygonal cross-sectional shape and is arranged on an optical path from the condensing mirror to the target illumination region
Implementation Method 2
a condensing mirror configured to condense the light emitted from the discharge lamp
Data Source
AI summary
Provided is an illumination optical system that illuminates a target illumination region by using light emitted from a discharge lamp. The system includes a condensing mirror that condenses the light from the discharge lamp, an optical integrator which has a polygonal cross-sectional shape and is arranged on an optical path from the condensing mirror to the target illumination region, an imaging optical system that forms an image on the target illumination region with respect to an exit end face of the optical integrator as an object plane, and a power supply cable connecting to an electrode of the discharge lamp across the optical path directed from the condensing mirror to the optical integrator. The cable is arranged so that a shadow of the cable is neither parallel nor perpendicular to each side of the polygon of an entrance surface of the optical integrator.