Transmission Image Sensor Slit Pattern for High NA Lithography
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Solution Overview
Problem
Current transmission image sensors in lithographic apparatuses face challenges in achieving high sensitivity, particularly in high NA systems, which limits their ability to accurately measure overlay errors and optical performance for creating devices with higher component densities.
Innovation Solution
A device and method for transmission image sensing that includes a projection system forming an aerial image with a numerical aperture larger than 1, using a slit pattern with features corresponding to the aerial image, where the smallest feature dimension of the slit pattern is less than 0.85 times the wavelength of the detection radiation multiplied by the numerical aperture, allowing for improved detection of radiation transmitted by the slit pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional transmission image sensor is used in high NA systems, then the system can achieve high numerical aperture for imaging smaller patterns, but the sensor sensitivity is insufficient to accurately measure overlay errors and optical performance
Solution Approach 1:
The patent changes the geometric parameters of the slit pattern features, specifically making the smallest feature dimension less than 0.85 times the wavelength divided by numerical aperture. This parameter optimization enables the sensor to resolve fine aerial image details in high NA systems, directly improving measurement precision while maintaining reliability
Solution Approach 2:
The sensor uses a slit pattern that divides the aerial image into discrete features corresponding to different image regions. This segmentation allows independent measurement of different parts of the aerial image, improving the ability to detect overlay errors and optical performance parameters with high sensitivity
2Ease of manufacture
If the slit pattern features are made larger, then the sensor structure is easier to manufacture, but the sensitivity to detect fine aerial image details decreases
Solution Approach 1:
The patent establishes an optimized parameter range for slit pattern features: the smallest dimension is less than 0.85λ/NA but not so small as to be unmanufacturable. This parameter optimization balances fabrication feasibility with the need to resolve fine aerial image details, achieving both ease of manufacture and high measurement precision
3Productivity
If the numerical aperture is increased to image smaller patterns, then device component density increases, but the overlay error budget becomes more difficult to achieve
Solution Approach 1:
The optimized transmission image sensor provides high-precision measurement feedback on aerial image position and optical performance. This feedback enables real-time detection of overlay errors and optical aberrations in high NA systems, allowing corrective actions to maintain manufacturing precision even as component density increases
Solution Approach 2:
The patent replaces conventional mechanical alignment methods with optical-based transmission image sensing. By using light interaction through the slit pattern to detect aerial image characteristics, the system achieves superior measurement precision compared to mechanical approaches, enabling accurate overlay control in high NA immersion lithography
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 enhances the sensitivity and accuracy of transmission image sensing, reducing overlay errors and improving optical performance, especially in immersion lithographic apparatuses, with demonstrated performance increases of up to 30% in immersion lithography systems.
Implementation Method 1
a projection system arranged to form, at an image side of the projection system, an aerial image of an object mark, the image side having a numerical aperture larger than 1
Implementation Method 2
the detector further being arranged to detect detection radiation transmitted by the slit pattern
Data Source
AI summary
A device for transmission image sensing for sensing an aerial image in a lithographic exposure apparatus comprises a projection system arranged to form, at an image side of the projection system, an aerial image of an object mark. The device further comprises a detector comprising a slit pattern having features corresponding to at least a part of the aerial image. The slit pattern is arranged to be exposed to the aerial image. The detector is further being arranged to detect detection radiation transmitted by the slit pattern; wherein d<0.85 λ/NA, where d represents the dimension of the smallest feature of the slit pattern, λ represents the intended wavelength of the detection radiation, and NA, which is larger than 1, represents the numerical aperture of the image side.