Optical Alignment Marker Using Diffraction for Telecentric EUV Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical alignment systems in lithographic apparatuses, particularly those using extreme ultraviolet (EUV) radiation, suffer from inaccurate alignment measurements due to skewed and non-telecentric images formed by known markers when illuminated with off-axis monopoles, leading to unwanted positional shifts and overlay errors.
Innovation Solution
An optical alignment system that uses a marker configured to diffract an off-axis monopole into zeroth and first diffraction orders, filling more of the pupil's area and improving telecentricity, utilizing a reflective diffraction grating with specific pitch and duty cycle adjustments to enhance alignment accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If known markers are used with off-axis monopole illumination, then the alignment system can operate, but the images formed are severely skewed and non-telecentric causing unwanted positional shifts and measurement inaccuracy
Solution Approach 1:
The patent changes the geometric parameters of the marker by introducing a sub-resolution grating structure with specific pitch and duty cycle ratios. This transforms the marker from a simple reflective feature into a diffraction grating that redistributes the off-axis monopole illumination, converting the severely skewed image into a substantially telecentric image with reduced skew, thereby resolving the measurement inaccuracy caused by image distortion
Solution Approach 2:
The patent introduces a sub-resolution grating structure as an intermediary element between the off-axis monopole illumination and the image sensor. This grating acts as a mediator that diffracts the incident radiation, redistributing it to fill more of the pupil area and produce a telecentric image, thus eliminating the direct harmful effect of illumination skew on measurement accuracy
2Measurement precision
If the marker fills more of the pupil area through diffraction, then telecentricity is improved, but the device complexity increases due to the specific grating structure requirements
Solution Approach 1:
The patent specifies precise parameter ratios for the grating structure (pitch to feature size ratio between 5:1 and 20:1, duty cycle between 30% and 70%) to optimize the diffraction pattern. By carefully controlling these parameters, the marker achieves substantial telecentricity improvement while keeping the structure manufacturable, balancing performance enhancement with device complexity management
Solution Approach 2:
The patent employs a sub-resolution grating structure that can be integrated into existing lithographic equipment without requiring complete system redesign. The grating operates at a scale smaller than the resolution limit of the imaging system, making it an inexpensive add-on that provides significant measurement accuracy improvement without proportionally increasing device complexity
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
The system improves alignment measurement accuracy by reducing skew and enhancing telecentricity, ensuring precise alignment between patterning devices and substrates in EUV lithographic apparatuses.
Implementation Method 1
a marker configured to diffract the first off-axis monopole to form zeroth and first diffraction orders
Implementation Method 2
The marker of the present disclosure advantageously diffracts the off-axis monopole in order to fill more of a pupil of the projection system, thereby reducing a skew and increasing a telecentricity of the image formed by the marker
Data Source
AI summary
An optical alignment system including an illumination system configured to condition a radiation beam to form a first off-axis monopole, a marker configured to diffract the first off-axis monopole to form zeroth and first diffraction orders, a projection system configured to collect the zeroth and first diffraction orders and form an image of the marker, and a sensor apparatus configured to detect the image of the marker.