Specular Reflection Blocking in Semiconductor Inspection
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Solution Overview
Problem
Current Fourier filtering techniques for semiconductor inspection systems face limitations such as high power densities, noise from wafer roughness, and limited numerical aperture, which affect the ability to block specular reflection and suppress modulation from periodic features, leading to reduced image resolution and sensitivity in defect detection.
Innovation Solution
The implementation of an inspection system using spatially incoherent light with a predetermined pattern, combined with optical elements like parallel slits and blocking bars, to block specular reflection and diffracted light from periodic features, thereby enhancing the signal-to-noise ratio and image resolution by suppressing modulation in the image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Fourier filtering techniques are used to block specular reflection, then modulation from periodic features is suppressed, but power density increases and noise from wafer roughness occurs
Solution Approach 1:
The patent segments the illumination into multiple discrete angular components using an annular aperture divided into sectors. Each sector illuminates the specimen at a different angle, and the reflected lights are imaged at different positions in the image plane. This segmentation allows selective blocking of specular reflection while maintaining illumination of scattered light from defects, thereby suppressing modulation from periodic features without increasing power density or generating noise from wafer roughness.
Solution Approach 2:
The patent applies different optical treatments to different regions of the illumination and imaging paths. The annular aperture is divided into sectors with different angular orientations, and the image plane contains specific regions where specular reflection is blocked while scattered light from defects is allowed to pass. This local differentiation enables selective suppression of harmful reflections while preserving useful defect signals.
2Measurement precision
If numerical aperture is increased to improve image resolution, then defect detection sensitivity improves, but modulation from periodic features increases
Solution Approach 1:
The patent uses an annular aperture segmented into multiple angular sectors, each contributing to image resolution while illuminating at different angles. The periodic features, being oriented in specific directions, reflect light at predictable angles that can be blocked by positioning opaque elements at corresponding locations in the image plane. This segmented approach maintains high numerical aperture for resolution while selectively suppressing modulation from periodic structures.
3Illumination intensity
If laser light source is used to provide sufficient brightness at short wavelengths, then signal-to-noise ratio improves, but speckle noise is generated
Solution Approach 1:
The patent segments the laser illumination into multiple angular sectors using the annular aperture. Each sector provides a coherent beam that illuminates the specimen at a different angle. The scattered light from defects, being incoherent across the different illumination angles, combines to reduce speckle noise while maintaining high brightness. The segmented approach preserves the intensity benefits of laser illumination while mitigating speckle through angular diversity.
4Illumination intensity
If coherent light is used to illuminate the specimen, then brightness is sufficient, but ringing artifacts appear in images
Solution Approach 1:
The patent divides the coherent laser illumination into multiple angular sectors. The periodic features in the specimen produce reflected light at specific angles corresponding to their orientation. By placing opaque elements in the image plane at positions corresponding to these reflection angles, the patent blocks the coherent reflected light that would create ringing artifacts, while allowing incoherent scattered light from defects to pass through to the detector.
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 approach effectively blocks specular reflection and suppresses modulation, improving the sensitivity of defect detection and image resolution, especially for patterned wafers, by allowing only scattered light from non-periodic features to be imaged, thus increasing the signal-to-noise ratio and capturing defects more effectively.
Implementation Method 1
block light reflected from the periodic features
Implementation Method 2
block at least some light diffracted from the periodic features
Implementation Method 3
illuminate the specimen with a predetermined pattern of spatially incoherent light
Data Source
AI summary
Systems and methods for blocking specular reflection and suppressing modulation from periodic features on a specimen are provided. One inspection system configured to block specular reflection and suppress modulation in an image of a specimen includes an illumination subsystem configured to illuminate the specimen with a predetermined pattern of spatially incoherent light. The system also includes an optical element configured to block light reflected from periodic features formed on the specimen and at least some light diffracted from the periodic features. The system further includes a detector configured to detect light that passes through the optical element and to generate an image of the specimen in response to the detected light. The optical element blocks specular reflection and at least partially suppresses modulation in the image due to the periodic features. The system also includes a processor configured to detect defects on the specimen using the image.