Microlithography Illumination System Using Pulsed Light and Deflection
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Solution Overview
Problem
In microlithographic projection exposure apparatuses, existing illumination systems face challenges in uniformly illuminating large target surfaces using arrays of digitally switchable optical elements, often resulting in gaps between images due to the high number of micromirrors or optical elements, which can lead to undesirable light distribution patterns.
Innovation Solution
An illumination system with a light source generating a sequence of pulses and an array of digitally switchable optical elements, combined with an adjustable light-deflection optical unit that changes deflection angles between pulses, allowing for successive build-up of intensity distribution on the target surface, enabling seamless illumination of large areas by non-overlapping or entangling light patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large number of micromirrors or optical elements are used to illuminate large target surfaces, then the coverage area is improved, but gaps appear between the images of the elements resulting in non-uniform light distribution
Solution Approach 1:
The patent applies periodic action by using a pulsed light source that emits light in periodic pulses. Between successive pulses, the deflection angles of the light-deflection optical unit are changed to adjust the positioning of optical elements. This allows the system to build up intensity distribution progressively over multiple pulses, ensuring uniform coverage of large target surfaces without gaps between element images.
2Area of stationary object
If the number of micromirrors is increased to cover larger areas, then the device complexity increases, but this leads to gaps between elements that cannot be tolerated
Solution Approach 1:
The patent applies dynamics by making the light-deflection optical unit adjustable between different deflection angles. This dynamic capability allows the same optical element to be positioned at different locations during successive light pulses, effectively increasing the illuminated area without requiring a proportional increase in the number of physical elements. The system adapts its configuration dynamically to cover larger areas with fewer elements.
3Device complexity
If optical elements are spaced far apart to simplify the array structure, then the device complexity is reduced, but large gaps appear between the images of the optical elements on the target surface
Solution Approach 1:
The patent applies dimensionality change by introducing the time dimension through periodic pulsing. Instead of trying to achieve continuous coverage in space with densely packed elements, the system uses temporal separation to deliver light from the same element at different positions during different pulses. This transforms a spatial problem into a spatio-temporal solution, allowing elements to be spaced farther apart while still achieving complete coverage through sequential positioning.
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 approach allows for uniform and efficient illumination of large target surfaces with precise control over light distribution, tolerating gaps between optical elements and enabling the generation of complex intensity patterns, ensuring complete coverage and high resolution.
Implementation Method 1
a light source (LS), in particular a laser, which is operated in a pulsed manner
Implementation Method 2
An adjustable light-deflection optical unit is arranged in the light path between the array and the target surface. The light deflection optical unit is configured to deflect incident light with different deflection angles
Data Source
AI summary
An illumination system of a microlithographic projection exposure apparatus includes a light source operated in a pulsed manner and a DMD (digital mirror device) or another array of optical elements, which are digitally switchable between two switching positions.