Illumination System Attenuation for Microlithography
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Solution Overview
Problem
Microlithographic projection exposure systems face challenges in maintaining precise and stable illumination angle distributions due to inaccuracies in the alignment of micromirrors, leading to unfavorable effects on imaging quality.
Innovation Solution
An illumination system with an attenuation unit that reduces light intensity by more than 50% from defective beam deviating elements, using methods such as varying tilt angles, reducing reflectivity, or applying light-absorbing coatings, to prevent misguided light from reaching the pupil surface, ensuring stable illumination angle distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If micromirrors are used to variably illuminate the system pupil plane, then illumination angle distribution can be controlled, but alignment inaccuracies cause light spots to displace in the pupil plane, degrading imaging quality
Solution Approach 1:
A second micromirror array is introduced as an intermediary component between the first micromirror array and the pupil plane. This second array acts as a corrective mediator that receives light from the first array and redirects it to compensate for alignment inaccuracies, thereby maintaining imaging quality while preserving the variable illumination control capability.
Solution Approach 2:
The system performs preliminary alignment calibration by directing light from the first micromirror array through the second array to a detector before actual imaging occurs. This preliminary action allows the system to measure and compensate for alignment errors in advance, ensuring that light spots remain correctly positioned in the pupil plane during subsequent imaging operations.
2Measurement precision
If defective beam deviating elements direct light onto incorrect locations in the pupil surface, then illumination accuracy deteriorates, but completely blocking such light requires additional attenuation components
Solution Approach 1:
The second micromirror array serves multiple functions simultaneously: it corrects alignment errors from the first array, compensates for defective elements by redirecting their light to appropriate locations, and provides variable illumination control. This multi-functionality eliminates the need for separate attenuation components, maintaining precision while avoiding additional complexity.
Solution Approach 2:
Light from defective beam deviating elements that would normally cause errors is converted into a useful resource. By using the second micromirror array, this previously harmful light is redirected to compensate for other illumination deficiencies or to provide additional illumination angles, transforming the defect into a beneficial contribution to the overall illumination distribution.
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 effectively improves illumination angle distributions in the mask plane by mitigating the impact of defective micromirrors, maintaining imaging quality and precision over time.
Implementation Method 1
This reduction can be complete, i.e. no such light at all reaches the pupil plane. This may be achieved, for example, by absorbing this light or by directing this light to a region outside the usable pupil surface where it is absorbed.
Data Source
AI summary
An illumination system of a microlithographic projection exposure apparatus comprises a pupil surface and an arrangement of individually drivable beam deviating elements. Each beam deviating element is configured to direct light impinging thereon onto different positions on the pupil surface in response to a control signal applied to the beam deviating element. According to the disclosure an attenuation unit is provided which is configured to reduce the intensity of light, which is directed by any arbitrary beam deviating element (onto the pupil surface, by more than 50%. This makes it possible to reduce the intensity of light in the pupil surface that has been reflected by defective beam deviating elements.