Solid Immersion Lens Inspection System Angular Compliance
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Solution Overview
Problem
Conventional Solid Immersion Lens (SIL) systems face instability and imaging degradation due to surface irregularities, lack of angular compliance, and excessive force, leading to aberrations and non-repeatable image acquisition, particularly in high-resolution sub-micron structure inspection.
Innovation Solution
The system employs a housing with flexures and an anti-contamination ring to provide controlled angular compliance and thermal isolation, allowing the SIL to rotate freely and maintain optimal contact with the DUT, while flexures ensure minimal force and prevent damage, and an anti-contamination ring prevents contamination and maintains the SIL's orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the SIL lens is rigidly fixed to constrain five degrees of motion, then alignment stability is improved, but angular compliance deteriorates causing imaging degradation due to surface irregularities
Solution Approach 1:
The patent transitions from a rigid fixed mounting to a dynamic compliant mounting system that allows the SIL lens to adjust its angle relative to the DUT surface. The compliant mounting enables real-time adaptation to surface irregularities while maintaining optical coupling, resolving the contradiction between stability and adaptability.
Solution Approach 2:
The patent changes the mechanical parameters of the mounting system by introducing compliance elements that allow angular adjustment. This enables the system to optimize the contact angle between SIL and DUT dynamically, improving both alignment stability and angular compliance simultaneously.
2Ease of operation
If downward gravity-fed spring loaded housing is used to hold SIL, then lens positioning is simplified, but excessive force is applied causing stress and potential damage to DUT
Solution Approach 1:
The patent replaces the gravity-fed spring loaded mechanical system with an active force control system. This substitution allows precise regulation of the contact force between SIL and DUT, maintaining ease of positioning while eliminating excessive stress through electronic control and feedback mechanisms.
3Temperature
If the SIL lens is allowed to float and settle by gravity, then thermal contact is improved, but lateral position repeatability deteriorates due to surface irregularities
Solution Approach 1:
The patent introduces feedback control mechanisms that monitor and adjust the SIL position and orientation in real-time. This feedback system maintains consistent thermal contact while compensating for lateral position variations caused by surface irregularities, achieving both thermal coupling and positional repeatability.
4Reliability
If coil-over spring design with preload is used, then SIL holder stability is improved, but backlash occurs between sliding elements causing SIL wobble and non-repeatable lateral displacements
Solution Approach 1:
The patent replaces the mechanical coil-over spring system with an active force control mechanism. This substitution eliminates backlash and mechanical play while maintaining holder stability, achieving both stability and lateral position repeatability through electronic control rather than mechanical precision.
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 design achieves high-resolution imaging with improved repeatability and reduced thermal impact, enabling precise control of the SIL's position and temperature, thus enhancing the ability to inspect small features and stitch images into a mosaic array without damaging the DUT.
Implementation Method 1
Since the optical numerical aperture is based on the index of refraction of the medium between the objective and sample and the collection angle of the objective, the highest numerical aperture (NA) achievable by an air lens is unity. When this SIL lens is used in conjunction with a corresponding backing objective it will yield an image with both an increased magnification and numerical aperture (NA). As stated above, this increase is brought about by the simple increase in index of refraction of the SIL material versus that of air.
Data Source
AI summary
An inspection system including a lens. In one instance, the lens is a solid immersion lens. The inspection system includes a component or components for providing a self aligning solid immersion lens arrangement in order to allow at most a small distance between the solid immersion lens and a device under test and components or components for constraining a force exerted on the device under test. The inspection system may include a “purge” port, or a thermal isolation configuration or an anti-contamination component. The inspection system may include software and hardware to prevent crashing of the lens. The inspection system may also include a method for ensuring that various objective lenses can be replaced while maintaining the intended spacing between lenses.