Diffraction Sensor Layout for Lithography Aberration Mapping
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Solution Overview
Problem
Lithographic apparatuses face challenges in accurately determining optical aberrations and alignment due to projection system imperfections, which affect the precision of pattern projection on substrates.
Innovation Solution
A measurement system utilizing a sensor apparatus with patterned regions that form diffraction beams, allowing interference patterns to be formed on a radiation detector, and a method involving shearing directions to determine aberration maps by analyzing phases of oscillating signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple patterned regions with different pitches are used in the sensor apparatus, then the amount of data collected in a single measurement is increased, but the device complexity increases
Solution Approach 1:
The sensor apparatus is divided into multiple patterned regions (first, second, third, and fourth patterned regions) with different pitches. Each region generates diffraction beams at different angles, allowing simultaneous measurement of aberrations across multiple spatial frequencies. This segmentation enables comprehensive aberration characterization in a single measurement without requiring multiple separate measurements or complex scanning procedures.
2Loss of information
If the pitches of adjacent patterned regions are made different, then signals from adjacent regions can be distinguished without spatial separation, but the difficulty of detecting and measuring increases
Solution Approach 1:
Different pitches of the patterned regions act as different 'optical colors' or spatial frequency signatures. Each pitch generates diffraction beams at characteristic angles according to the grating equation. By assigning different pitches to different patterned regions, the system can distinguish signals from each region based on the angular position and spatial frequency of the resulting interference patterns, similar to how different wavelengths of light can be distinguished.
3Productivity
If interference patterns from adjacent patterned regions are allowed to overlap, then the amount of information per measurement increases, but the measurement precision may be affected by pattern complexity
Solution Approach 1:
The overlapping interference patterns are segmented by their spatial frequency content. Each patterned region with a specific pitch produces interference patterns at characteristic spatial frequencies. By analyzing the spectrum of spatial frequencies in the combined interference pattern, the system can separate and analyze contributions from each patterned region independently, maintaining measurement precision while achieving high productivity through simultaneous 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
Enhances data collection efficiency and accuracy in measuring optical aberrations and alignment, enabling better control over projection system performance.
Implementation Method 1
the sensor apparatus comprising a patterned region arranged to receive a radiation beam and to form a plurality of diffraction beams, the diffraction beams being separated in a shearing direction
Implementation Method 2
the patterned region is arranged such that at least some of the diffraction beams form interference patterns on the radiation detector
Data Source
AI summary
A measurement system (11), the measurement system comprising: a sensor apparatus (22); an illumination system (IL1) arranged to illuminate the sensor apparatus with radiation, the sensor apparatus comprising a patterned region arranged to receive a radiation beam and to form a plurality of diffraction beams, the diffraction beams being separated in a shearing direction; the sensor apparatus comprising a radiation detector (24); wherein the patterned region is arranged such that at least some of the diffraction beams form interference patterns on the radiation detector; wherein the sensor apparatus comprises a plurality of patterned regions (19a-19c, 20a, 20b), and wherein pitches of the patterned regions are different in adjacent patterned regions.