Defocused Optical Contrast for Semiconductor Defect Inspection
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Solution Overview
Problem
Standard bright-field and dark-field imaging techniques struggle to detect defects with small topography variations or local stress affecting the refractive index, as these defects do not exhibit contrast differences, making them difficult to visualize in semiconductor inspection.
Innovation Solution
A method and system that utilize spatially coherent and collimated radiation with a small aperture stop in the optical path to enhance contrast by creating constructive or destructive interference patterns, allowing for the detection of phase shifts indicative of defects, which can be integrated into existing bright-field or dark-field microscopy systems with minimal modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard bright-field or dark-field imaging is used, then the imaging system is simple and easy to operate, but defects with small topography variations or local stress are not detected due to lack of contrast
Solution Approach 1:
The patent changes the optical parameters by introducing a defocus amount and using spatially coherent radiation to create interference patterns. By adjusting the defocus amount to a specific value, the system enhances contrast for defects with small topography variations or local stress, enabling detection without requiring complex additional optical elements beyond what is already present in standard microscopy systems.
2Measurement precision
If phase contrast imaging methods such as DIC are used, then contrast of defects is enhanced, but special optical elements must be inserted in the optical illumination and imaging path
Solution Approach 1:
The patent makes the defocus amount a variable parameter that can be adjusted to achieve different imaging modes. By setting the defocus amount to a first value, the system performs standard imaging; by setting it to a second value, it performs contrast-enhanced imaging for detecting defects with small topography variations. This multi-functionality eliminates the need for separate specialized optical elements while achieving phase contrast-like effects.
Solution Approach 2:
The system uses parameter changes by adjusting the defocus amount and the size of the aperture stop to transform a standard imaging system into one capable of detecting phase shifts. This approach avoids inserting special optical elements by instead modifying operational parameters of existing components.
3Measurement precision
If a small aperture is used to create interference patterns, then contrast enhancement is achieved, but the aperture size must be precisely controlled as a fraction of the aperture stop size
Solution Approach 1:
The patent defines the aperture size as a specific fraction (e.g., 1/10 to 1/25) of the aperture stop size, creating a controllable parameter that balances contrast enhancement with ease of implementation. This fractional relationship provides a practical manufacturing guideline that achieves the necessary precision without requiring extremely tight tolerances.
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
Enables the visualization of defects like bubbles, scratches, and stress defects by improving contrast in 2D optical imaging, effectively differentiating between flat and rough semiconductor surfaces, and analyzing surface haze with enhanced sensitivity.
Implementation Method 1
The sensed radiation may include interference patterns formed between radiation reflected from different points of the area
Data Source
AI summary
An inspection system and a method for inspection an object. The method may include acquiring a defocused image of an area of an object, and processing the defocused image of the area to find a phase shift between optical paths associated with certain proximate points of the area. The phase shift may be indicative of a defect. The acquiring of the defocused image may include illuminating the area with a radiation beam that may be spatially coherent and collimated when impinging on the area. The illuminating may include passing the radiation beam through an aperture that may be defined by an aperture stop that may be positioned within an aperture stop plane. The size of the aperture may be a fraction of a size of the aperture stop.