Wafer Alignment Sensor Optics Using Glass Plates for Off-Axis Beams
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Solution Overview
Problem
Current alignment sensors in lithographic apparatuses use a single measurement illumination spot, limiting the number of measurable alignment marks due to throughput considerations, and grating-based off-axis illumination systems are cumbersome and require significant space.
Innovation Solution
The use of glass plates to create pairs of off-axis illumination beams, allowing for better control and space savings within the optical system, with each glass plate having spot mirrors to reflect or partially reflect and transmit illumination beams, and an aperture plate to block unwanted radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single measurement illumination spot is used, then the alignment system is simple, but the number of measurable alignment marks is limited due to throughput considerations
Solution Approach 1:
The illumination system is segmented into multiple independent illumination spots (first illumination spot and second illumination spot) that can simultaneously illuminate different alignment marks. This segmentation allows parallel measurement of multiple alignment marks, increasing throughput without requiring a completely complex reconfiguration of the illumination system.
2Measurement precision
If grating-based off-axis illumination is used, then finer pitch alignment marks can be detected, but the system becomes cumbersome and requires significant space
Solution Approach 1:
The invention extracts the off-axis illumination function from the complex grating-based system and implements it using simpler optical elements (mirrors and beamsplitters) arranged in a compact configuration. The off-axis illumination capability is taken out of the bulky grating structure and reconstructed using smaller, more manageable optical components that achieve the same measurement precision with reduced footprint.
Solution Approach 2:
Instead of using a grating that disperses light into multiple angles, the invention uses mirrors and beamsplitters to create multiple discrete off-axis illumination beams that replicate the functional effect of grating-based illumination. This copying approach replaces the distributed grating structure with a set of discrete optical elements that achieve the same measurement capability in a more compact form factor.
3Productivity
If multiple illumination spots are used to increase throughput, then more alignment marks can be measured simultaneously, but the optical system becomes more complex
Solution Approach 1:
Multiple illumination spots are merged into a single optical path that branches into parallel measurement channels. The first illumination spot and second illumination spot are combined through beamsplitters and mirrors to simultaneously illuminate multiple alignment marks on the substrate, enabling parallel measurement while maintaining a unified and manageable optical architecture rather than requiring separate independent systems.
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 increases the process window for detecting finer pitch alignment marks and reduces the optical system's footprint, enabling more efficient alignment measurements with improved control over off-axis illumination.
Implementation Method 1
Each glass plate has a plurality of spot mirrors that can reflect or partially reflect and transmit an illumination beam from the illumination source
Implementation Method 2
The glass plates reflect and refract the illumination beam to create pairs of off-axis illumination beams
Implementation Method 3
a transmissive optic with at least one reflective mirror configured to reflect radiation received from the glass plates
Implementation Method 4
an objective configured to focus light from the transmissive optic towards an object to be illuminated
Data Source
AI summary
A novel approach for an alignment system by using glass plates to create off-axis illumination beams is described. A pair of glass plates is inserted into an alignment system to create a pair of off-axis illumination beams. The off-axis illumination beams pass through an aperture stop. A transmissive optic with a plurality of fully reflective mirrors reflects the beams toward the objective. Thereafter, the objective focuses the beams onto the alignment mark on the substrate. The diffracted beam is then detected and analyzed to determine alignment of the substrate. The compact nature of the glass plate alignment system significantly reduces the optical system footprint.