Laser Beam Conditioning via Temporal Differentiation for Speckle Reduction
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Solution Overview
Problem
Highly coherent laser beams used in IC fabrication inspection cause speckle noise, leading to ineffective inspection processes due to the noisy and distorted images produced on rough surfaces.
Innovation Solution
The use of plane and corner cube reflectors, along with right-angle reflectors, to temporally differentiate electromagnetic beam subsections, reducing spatial coherence and generating a grid of temporally differentiated sub-beams to minimize speckle noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a highly coherent laser beam is used for inspection, then the beam provides strong illumination and directionality, but it causes speckle noise and image distortion when illuminating rough surfaces
Solution Approach 1:
The patent segments the coherent laser beam into multiple incoherent sub-beams by introducing random path length variations through mirrors positioned at different distances from the beam splitter. This segmentation transforms the single coherent beam into multiple statistically independent coherent subsets that combine to form an incoherent composite beam, thereby reducing speckle noise while maintaining illumination intensity.
Solution Approach 2:
The patent merges multiple coherent sub-beams with different random path lengths into a single composite beam. By combining these sub-beams after they have traversed different optical paths, the patent creates an incoherent beam that retains the illumination benefits of laser while eliminating the harmful speckle effects through statistical averaging of the interference patterns.
2Object-affected harmful factors
If multiple mirrors at different distances are introduced to reduce speckle, then spatial coherence is reduced and speckle noise decreases, but the device complexity increases
Solution Approach 1:
The patent introduces a beam splitter as an intermediary device that divides the incoming coherent beam into multiple paths. This intermediary component, along with positioners and mirrors, creates a controlled complexity that achieves speckle reduction through a systematic and adjustable optical configuration, making the complexity manageable and tunable.
Solution Approach 2:
The patent employs dynamically adjustable mirrors mounted on positioners that can independently vary the path lengths of different beam subsets. This dynamic capability allows real-time optimization of the incoherence level and speckle reduction, transforming a static complex system into a flexible, adaptable system that can be tuned for different inspection requirements.
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 solution effectively reduces speckle noise in inspection images, enhancing the effectiveness of the inspection process by ensuring even contributions from all parts of the beam, thereby improving image clarity and inspection accuracy.
Implementation Method 1
a first set of reflectors spaced along a first axis of the electromagnetic beam such that each reflector in the first set reflects a subsection of the electromagnetic beam
Data Source
AI summary
Methods and apparatus relating to electromagnetic beam (e.g., laser beam) conditioning are described. In an embodiment, electromagnetic beam conditioning may be performed utilizing reflectors to temporally differentiate electromagnetic beam subsections and sub-beams resulting in reduced spatial coherence of the beam. Other embodiments are also described.