Lithography Illuminator Parabolic Beam Homogenization
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Solution Overview
Problem
Lithographic scatterometers face challenges in ensuring the homogeneity of the incident radiation beam, leading to inconsistencies in measured substrate properties due to beam inhomogeneities, which can be misinterpreted as substrate surface errors.
Innovation Solution
A system is developed that includes a radiation source and an optical system configured to render a parabolic distribution to the radiation beam, ensuring its homogeneity before reflection from the substrate, using components like a xenon arc lamp and a parabolic reflective exterior, fly's eye integrator, and telecentric lens to achieve spatial and angular homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If optical systems such as lenses are used to focus the radiation beam, then the beam can be directed onto the substrate, but the beam homogeneity is compromised because the output direction depends on the input direction which may not be homogenized
Solution Approach 1:
The illumination system is divided into separate functional modules: a beam conditioning section that homogenizes the radiation beam using integrating elements, and a focusing section that directs the homogenized beam onto the substrate. This segmentation ensures that beam homogeneity is established before focusing occurs, eliminating the trade-off between focusing capability and homogeneity.
Solution Approach 2:
An integrating element (such as an integrating rod or diffuser) is introduced as an intermediary component between the radiation source and the substrate. This intermediary homogenizes the beam by scattering and redistributing the radiation, ensuring uniform intensity distribution while allowing subsequent focusing optics to maintain beam directionality without compromising homogeneity.
2Measurement precision
If the radiation beam properties are measured to ensure homogeneity, then measurement accuracy improves, but the measurement process interferes with the beam itself
Solution Approach 1:
Instead of measuring the primary radiation beam directly, the system uses a separate reference beam or creates an optical copy of the beam properties through non-intrusive sensing. This allows measurement of beam homogeneity and other properties without the measurement apparatus interfering with or absorbing the actual measurement beam, thus maintaining both precision and avoiding interference.
3Measurement precision
If beam homogeneity is ensured through multiple optical components, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
Multiple optical functions (beam homogenization, focusing, and measurement) are merged into a single integrated optical path. The system uses a unified illumination and detection module where the same optical components serve multiple purposes, reducing the total number of separate elements while maintaining measurement precision through careful optical design.
Solution Approach 2:
The optical components are designed to perform multiple functions simultaneously. For example, the objective lens both focuses the beam onto the substrate and collects the reflected or scattered radiation for measurement. This multi-functionality reduces device complexity while maintaining the precision required for accurate substrate property measurement.
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 results in a more accurate measurement of substrate properties by eliminating beam inhomogeneities, reducing errors, and enhancing the homogeneity of the radiation beam, thereby improving the reliability of metrology measurements in lithographic processes.
Implementation Method 1
a radiation source configured to produce a radiation beam; a detector configured to detect the radiation beam once it has reflected from a surface to be measured
Implementation Method 2
an optical system configured to render a parabolic distribution to the radiation beam
Implementation Method 3
In scatterometry, misalignments and overlay errors of properties of a substrate are determined by the reflected spectra of a radiation beam having been reflected from the substrate in question
Data Source
AI summary
An illuminator configured to create a radiation beam for the metrology of a substrate surface includes an arc lamp, a parabolic reflector (150), a double cone (160) and a fly's eye integrator (110) in order to create a homogenized beam with a parabolic distribution.