EUV Lithography Grating Structure for Dose Measurement
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Solution Overview
Problem
Current lithographic apparatuses face challenges in accurately measuring the dose of EUV radiation delivered to a substrate and determining the focal plane position, especially as feature sizes decrease, requiring innovative methods to ensure precise pattern transfer and alignment.
Innovation Solution
A lithographic apparatus with a grating structure comprising alternating first and second reflective portions, where the second reflective portions have a lower reflectivity than the first but still greater than zero, allowing for measurable EUV radiation effects on the substrate, enabling dose measurement by imaging the grating into resist and determining the focal plane by analyzing the center of gravity of the imaged pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reflectivity of the second reflective portions is reduced to enable measurement, then the measurability of EUV radiation dose improves, but the signal strength decreases
Solution Approach 1:
The grating structure implements local quality by creating alternating reflective portions with different reflectivities (first portions with higher reflectivity and second portions with lower but non-zero reflectivity). This spatial variation in reflectivity across the grating structure enables differential measurement signals while maintaining sufficient overall signal strength for detection.
Solution Approach 2:
The invention applies parameter changes by carefully controlling the reflectivity parameter of the second reflective portions to be lower than the first portions but greater than zero. This specific parameter range optimization allows the grating to produce measurable interference patterns while maintaining adequate signal strength for EUV radiation detection.
2Length of moving object
If the feature size is reduced to enable miniaturization, then the IC device size decreases, but the measurement precision of focal plane position deteriorates
Solution Approach 1:
The grating structure serves as an intermediary element between the projection system and the substrate. By projecting this known grating pattern onto the substrate and analyzing the resulting image, the system obtains indirect measurement information about focal plane position and EUV radiation dose, enabling precise measurements even with reduced feature sizes.
Solution Approach 2:
The invention replaces direct mechanical measurement methods with optical measurement using the grating structure. By using optical interference and diffraction effects from the projected grating pattern, the system achieves precise focal plane positioning and dose measurement without relying on mechanical reference structures, thereby maintaining measurement precision despite feature size reduction.
3Measurement precision
If the reflectivity difference between first and second reflective portions is increased to improve measurement contrast, then the measurement signal improves, but the manufacturing complexity increases
Solution Approach 1:
The invention optimizes the reflectivity parameter difference between first and second reflective portions to achieve sufficient measurement contrast while maintaining manufacturability. By carefully selecting reflectivity values that provide adequate signal differentiation without requiring extreme values, the design balances measurement performance with fabrication feasibility.
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 precise measurement of the EUV radiation dose and focal plane determination, enhancing the accuracy of pattern transfer and alignment in lithographic processes, particularly beneficial for miniaturization efforts in IC manufacturing.
Implementation Method 1
the second reflective portions having a reflectivity which is less than the reflectivity of at least part of the first reflective portions and which is greater than zero
Data Source
AI summary
A lithographic apparatus comprising a support structure constructed to support a patterning device, the patterning device being capable of imparting an EUV radiation beam with a grating in its cross-section to form a patterned EUV radiation beam, and a projection system configured to project the patterned EUV radiation beam onto a target portion of the substrate, wherein the support structure is provided with a grating comprising a series of first reflective portions which alternates with a series of second reflective portions, the second reflective portions having a reflectivity which is less than the reflectivity of at least part of the first reflective portions and which is greater than zero.