Angularly Resolved Intensity Sensor for EUV Optical Imaging
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Solution Overview
Problem
Conventional methods for determining wavefront aberration and pupil-resolved transmission behavior in optical imaging systems, particularly in microlithography, suffer from insufficient reproducibility and accuracy, especially when dealing with EUV radiation.
Innovation Solution
An apparatus and method that includes an illumination system directing electromagnetic radiation onto an object plane, a utilization detector to capture radiation after it has traveled through the optical system, and an intensity sensor to record an angularly resolved intensity distribution, allowing for high-resolution incidence-angle-resolved measurements. This setup enables accurate correction of interferograms and accounts for the actual intensity distribution in apodization measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional shearing interferometry methods are used for wavefront measurements, then the measurement process is simple and straightforward, but the reproducibility and absolute accuracy are insufficient
Solution Approach 1:
The measurement process is divided into two independent parts: (1) measuring the angularly resolved intensity distribution using a separate intensity sensor, and (2) using this distribution to correct the wavefront measurement from the utilization detector. This segmentation allows each part to be optimized independently, improving overall accuracy without requiring a complete redesign of the entire measurement system.
Solution Approach 2:
The angularly resolved intensity distribution is measured in advance and stored for later use. This preliminary measurement is then applied to correct subsequent wavefront measurements, eliminating the need to repeatedly measure the illumination profile and improving both accuracy and efficiency of the measurement process.
2Measurement precision
If conventional methods are used for determining pupil-resolved transmission behavior, then the measurement setup is straightforward, but the accuracy is insufficient
Solution Approach 1:
The angularly resolved intensity distribution is measured once in advance and reused for multiple pupil-resolved transmission measurements. This preliminary measurement captures the illumination profile that can be applied to correct subsequent measurements, reducing the need for repeated high-energy radiation exposure while maintaining measurement accuracy.
Solution Approach 2:
The measured angularly resolved intensity distribution is fed back into the evaluation process to correct the pupil-resolved transmission measurements. This feedback mechanism allows the system to compensate for illumination non-uniformities and improve measurement accuracy without requiring additional radiation energy or complex hardware modifications.
3Measurement precision
If an intensity sensor is added to record angularly resolved intensity distribution, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The intensity sensor is designed to be a simple detector that records angularly resolved intensity distribution, which can then be used to correct multiple different measurement types (wavefront measurements, pupil-resolved transmission measurements). This multi-functional approach allows a single additional component to improve various measurement processes without proportionally increasing overall system complexity.
Solution Approach 2:
The angularly resolved intensity distribution acts as an intermediary quantity that mediates between the illumination system and the utilization detector. By measuring this intermediate parameter separately with a simple intensity sensor, the system can correct the main measurement without requiring direct modification of the complex interferometric or imaging measurement paths.
4Measurement precision
If the entire angular range is measured with high resolution, then complete characterization of the optical system is achieved, but measurement time increases
Solution Approach 1:
The angularly resolved intensity distribution over the entire angular range is measured once in advance and stored for reuse. This preliminary comprehensive measurement captures all necessary angular information that can then be applied to correct multiple subsequent measurements, eliminating the need to repeatedly scan the full angular range and significantly reducing total measurement time.
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 provides improved accuracy and reproducibility in determining wavefront aberration and pupil-resolved transmission behavior, enabling precise characterization of optical imaging systems, particularly in EUV applications.
Implementation Method 1
an illumination system (20) configured to direct electromagnetic radiation (18), generated by a radiation source (16), onto an object plane (22) of the imaging system (12), in particular to focus it onto the object plane (22)
Implementation Method 2
an output coupling device (46) arranged in the utilized beam path (45) and configured to couple sensor radiation out of the utilized beam path (45) with the result that the coupled-out sensor radiation extends along a sensor beam path (49) that differs from the utilized beam path (45)
Implementation Method 3
an intensity sensor (50) arranged in the sensor beam path (49) to record an angularly resolved intensity distribution at least at one point in the object plane (22) of the optical imaging system (12), which intensity distribution reproduces the intensity of the electromagnetic radiation (18) in dependence on the angle of incidence with respect to the object plane (22)
Data Source
AI summary
An apparatus (10) determining an optical property of an imaging system (12) includes an illumination system (20) directing electromagnetic radiation (18) onto an object plane (22) of the imaging system, a utilization detector (42) determining the optical property, an output coupling device (46), and an intensity sensor (50). The detector captures the radiation after it has traveled along a utilized beam path (45) extending to the utilization detector. The output coupling device couples sensor radiation (48) out of the utilized beam path and into a sensor beam path (49) that differs from the utilized beam path. The intensity sensor records an angularly resolved intensity distribution present at least at one point in the object plane of the optical imaging system, which intensity distribution reproduces the intensity of the electromagnetic radiation in dependence on the angle of incidence with respect to the object plane.