Off-Axis Pupil Illumination for Reduced-Pitch Mark Position Measurement
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Solution Overview
Problem
Current lithographic apparatuses face challenges in accurately measuring the positions of marks on substrates with reduced pitch grating lines, which is essential for precise device feature placement as product features become smaller, while maintaining compatibility with existing marks and infrastructure without compromising throughput.
Innovation Solution
A position measurement method and apparatus using off-axis illumination with a self-referencing interferometer, where radiation from source regions confined to the peripheral portion of the objective lens's pupil is used to form a spot on the mark, allowing for accurate detection of position variations and calculation of mark positions, compatible with both reduced and conventional pitch marks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pitch of grating lines in alignment marks is reduced to improve position measurement accuracy, then measurement precision improves, but device complexity increases and existing infrastructure becomes incompatible
Solution Approach 1:
The patent changes the illumination parameters by using off-axis illumination at specific angles (e.g., 45 degrees) instead of normal incidence. This parameter change enables the measurement of reduced pitch marks (down to 1 μm) without requiring complex new sensor instruments, as the oblique illumination creates sufficient optical path differences for interferometric detection while maintaining compatibility with existing mark designs
Solution Approach 2:
The patent segments the illumination into multiple discrete sources at different angular positions relative to the optical axis. This segmentation allows the system to measure different spatial frequencies of the grating lines, enabling accurate position measurement of reduced pitch marks while using existing detector designs that can process the segmented interference patterns
2Manufacturing precision
If the pitch of grating lines is reduced to measure smaller features, then manufacturing precision improves, but compatibility with existing marks and infrastructure deteriorates
Solution Approach 1:
The patent creates a universal measurement method that works with both conventional pitch marks and reduced pitch marks using the same sensor instrument. The off-axis interferometric technique is adaptable to various mark designs and pitch sizes, allowing existing infrastructure to measure both old and new mark types without requiring separate specialized instruments for each mark type
3Measurement precision
If new sensors are developed to measure reduced pitch marks, then measurement precision improves, but processing requirements increase and throughput may be compromised
Solution Approach 1:
The patent replaces complex mechanical measurement systems with an optical interferometric system that uses light interference patterns to measure position. This substitution enables high-precision measurement of reduced pitch marks through optical processing rather than mechanical scanning, maintaining high throughput by using non-contact optical detection that can operate at the speeds required for production 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
Enables accurate position measurement of marks with a wide range of pitches from 1 μm to 20 μm without altering existing detector designs, improving measurement sensitivity and reducing the impact of mark deformation, while maintaining compatibility with existing systems and infrastructure.
Implementation Method 1
illuminating the mark with a spot of radiation via an objective lens
Implementation Method 2
receiving radiation diffracted by the mark via the same objective lens
Implementation Method 3
processing the diffracted radiation in a self-referencing interferometer; detecting variations in an intensity of radiation output by the interferometer
Data Source
AI summary
An apparatus (AS) measures positions of marks (202) on a lithographic substrate (W). An illumination arrangement (940, 962, 964) provides off-axis radiation from at least first and second regions. The first and second source regions are diametrically opposite one another with respect to an optical axis (O) and are limited in angular extent. The regions may be small spots selected according to a direction of periodicity of a mark being measured, or larger segments. Radiation at a selected pair of source regions can be generated by supplying radiation at a single source feed position to a self-referencing interferometer. A modified half wave plate is positioned downstream of the interferometer, which can be used in the position measuring apparatus. The modified half wave plate has its fast axis in one part arranged at 45° to the fast axis in another part diametrically opposite.