Lenslet Array Laser Illumination for High-Etendue Speckle Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional laser illumination sources for photolithographic inspection suffer from limited etendue and speckle generation due to coherence, leading to reduced image quality and false defect detection in microelectronic device manufacturing.
Innovation Solution
A light source system utilizing a multimode laser unit and optical system that splits the laser beam into incoherent beamlets using lenslet arrays and spatial filters to achieve high brightness and etendue, eliminating speckle formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a laser light source is used to provide high brightness illumination, then illumination intensity is improved, but etendue is limited and speckles are generated
Solution Approach 1:
The laser beam is divided into multiple beamlets using a lenslet array, where each lenslet creates a separate focused spot. This segmentation allows the light to be distributed across multiple spatial channels, effectively increasing the etendue while maintaining high brightness from the laser source.
Solution Approach 2:
A spatial filter mask with pinholes is introduced as an intermediary element between the lenslet array and the sample. This mask selects specific spatial frequencies and blocks others, enabling control over the illumination coherence and etendue while maintaining brightness.
2Illumination intensity
If a laser light source is used to provide high brightness illumination, then illumination intensity is improved, but speckles are generated due to coherence
Solution Approach 1:
By dividing the coherent laser beam into multiple independent beamlets through the lenslet array, the speckle patterns generated by each beamlet are spatially separated and do not interfere constructively, thereby reducing overall speckle visibility while maintaining brightness.
Solution Approach 2:
The system changes the spatial distribution parameters of the laser beam by using the lenslet array to create multiple focused spots at different positions. This parameter change in spatial distribution reduces coherence effects that cause speckles while preserving illumination intensity.
3Adaptability or versatility
If the beam is spread out using a diffuser to increase etendue, then etendue is improved, but speckles are generated due to coherence
Solution Approach 1:
Instead of using a diffuser that creates speckles through random scattering, the system segments the beam into discrete beamlets using a lenslet array. This controlled segmentation increases etendue through ordered spatial distribution rather than random scattering, avoiding speckle formation.
Solution Approach 2:
The harmful speckle-generating property of diffusers is extracted and replaced by the lenslet array system. The lenslet array achieves the same etendue increase through a different mechanism (ordered beam splitting) that does not produce speckles.
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 provides high-quality illumination with extended etendue, enhancing defect detection accuracy and reducing false alarms in aerial imaging and inspection of photolithographic masks and semiconductor wafers.
Implementation Method 1
a first lenslet array positioned in a path of the laser beam and configured to form an array of focused spots in a selected plane downstream of the first lenslet array
Implementation Method 2
a spatial filter mask carrying an array of pinholes positioned in the selected plane
Implementation Method 3
a second lenslet array having spatial arrangement of lenslets similar to the first lenslet array and positioned such that the spatial filter mask is in a back focal plane of the second lenslet array, thereby collimating laser light from the array of focused spots into a corresponding array of beamlets
Data Source
AI summary
A light source system is disclosed, the system comprises: a multimode laser unit; a first lenslet array positioned in a path of said laser beam and configured to form an array of focused spots in a selected plane downstream of said first lenslet array; a spatial filter mask carrying an array of pinholes positioned in said selected plane; a second lenslet array having spatial arrangement of lenslets similar to the first lenslet array and positioned such that said spatial filter mask is in a back focal plane of said second lenslet array, thereby collimating laser light from the array of focused spots into a corresponding array of beamlets; and a third lenslet array positioned downstream of said second lenslet array, configured for focusing said array of beamlets to form an output spot array at an exit pupil of said light source system.