Illumination Optical Rod with Specification Element for Low-Loss Lithography
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Solution Overview
Problem
Illumination optical units for projection lithography face challenges in achieving low-loss illumination settings due to non-homogeneous illumination intensity and angle distributions, leading to inefficiencies and potential light blocking at correction stops.
Innovation Solution
An optical rod with a specification element that uses total internal reflection and diffractive/refractive elements to mix and homogenize illumination light, allowing for tailored intensity and angle distributions, and an axicon for additional shaping, along with a pupil correction stop for fine adjustments, enables effective illumination settings with minimal light loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional illumination optical units are used with standard homogenization, then the structure is simple, but light loss increases due to non-homogeneous illumination distribution and the need for correction stops
Solution Approach 1:
The illumination optical unit is segmented into distinct functional zones: the optical rod for light transmission and mixing, the specification element for angular distribution control, and the correction stop for intensity uniformity. This segmentation allows each component to perform its specific function efficiently, reducing overall light loss while maintaining manageable complexity through modular design.
Solution Approach 2:
The specification element acts as an intermediary component between the light source and the optical rod. It transforms the illumination angular distribution before light enters the rod, enabling better utilization of light for achieving the desired illumination setting without requiring excessive light blocking at downstream correction stops.
2Loss of energy
If the illumination intensity distribution is made homogeneous at the rod entrance, then light loss is reduced, but the ability to achieve specific illumination settings is compromised
Solution Approach 1:
The specification element creates locally differentiated illumination conditions at the rod entrance by controlling the angular distribution of light rays. Different regions of the rod entrance receive light with specific angular characteristics tailored to achieve the desired illumination setting, while maintaining overall efficiency by avoiding unnecessary light blocking.
Solution Approach 2:
The system dynamically adjusts illumination parameters (angular distribution and intensity distribution) at the rod entrance based on the required illumination setting. The specification element modifies the angular parameter of incoming light, while the correction stop adjusts the intensity parameter, enabling adaptation to different illumination requirements without excessive light loss.
3Manufacturing precision
If correction stops are used to achieve desired illumination distribution, then illumination setting precision is improved, but light loss increases
Solution Approach 1:
The specification element performs preliminary action by pre-shaping the angular distribution of illumination light before it enters the optical rod. This preliminary control reduces the burden on downstream correction stops, allowing them to make only fine adjustments rather than creating the entire illumination pattern, thereby minimizing light loss while maintaining precision.
4Loss of energy
If beam directions at rod entrance do not match desired illumination setting, then adaptability is reduced, but light loss can be minimized by blocking mismatched rays
Solution Approach 1:
The system converts potentially harmful mismatched beam directions into beneficial contributions. The specification element transforms incoming light with various angular distributions into the desired angular distribution for the illumination setting. Even light rays that initially appear mismatched are redirected and utilized effectively, turning what would be waste into useful illumination.
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 solution allows for precise control of illumination settings, reducing light loss and enabling the desired illumination distribution, even when initial beam directions do not match the desired setting, thereby improving the effectiveness of the illumination optical unit.
Implementation Method 1
The optical rod is designed in such a way that the illumination light is mixed and homogenized at lateral walls of the optical rod by multiple instances of total internal reflection
Implementation Method 2
The optical rod illumination specification element can have a diffractive embodiment or else a refractive/diffractive embodiment
Implementation Method 3
The optical rod illumination specification element can have a diffractive embodiment or else a refractive/diffractive embodiment
Implementation Method 4
An axicon in the illumination light beam path between the intensity specification element and the optical rod illumination specification element
Data Source
AI summary
An illumination optical unit for projection lithography serves to illuminate an object field along an illumination light beam path. The illumination optical unit includes an optical rod with end-side entrance and exit areas. The optical rod is designed in such a way that illumination light is mixed and homogenized at lateral walls of the optical rod by multiple instances of total internal reflection. An optical rod illumination specification element is disposed upstream of the optical rod in the illumination light beam path and serves to specify an illumination of the entrance area with a distribution, specified over the entrance area, of an illumination intensity and, simultaneously, an illumination angle distribution. The specified illumination intensity distribution deviates from a homogeneous distribution over the entrance area. This can result in an illumination optical unit including an optical rod, in which a specified illumination setting can be set with lower illumination light losses.