Rotating Diffuser Speckle Noise Reduction in Die-to-Die Inspection
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Solution Overview
Problem
Current inspection systems face challenges in reducing speckle noise from coherent illumination, which decreases sensitivity and makes it difficult to detect defects, especially as semiconductor device dimensions shrink, while also facing limitations in maintaining throughput and avoiding stress on rotational system components.
Innovation Solution
The system employs a rotating diffuser with a variable rotational rate and a reflective optical component to ensure identical speckle noise patterns across adjacent die, adjusting the rotational rate and illumination angle to align the diffuser position with the specimen, thereby eliminating speckle noise and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser light source is used to generate brighter light at shorter wavelengths, then resolution is improved, but speckle noise is introduced which decreases sensitivity
Solution Approach 1:
A rotating diffuser is introduced as an intermediary component between the laser light source and the specimen. The diffuser scatters the coherent laser light to reduce spatial coherence, thereby eliminating speckle noise while maintaining the brightness and short wavelength benefits for high-resolution inspection
Solution Approach 2:
The diffuser is made rotational rather than stationary. By rotating the diffuser during image acquisition, multiple speckle patterns are averaged, dynamically reducing the speckle noise effect while maintaining consistent illumination for high-resolution imaging
2Measurement precision
If the number of images averaged is increased to reduce noise, then sensitivity is improved, but inspection throughput is reduced
Solution Approach 1:
The system uses periodic rotation of the diffuser to generate multiple independent speckle patterns during a single inspection cycle. This periodic action allows noise reduction through averaging without requiring multiple separate inspections, thereby maintaining high throughput while improving sensitivity
3Object-affected harmful factors
If the rotational rate of the diffuser is increased to reduce speckle noise, then noise reduction is improved, but stress and vibrations on the rotational system increase
Solution Approach 1:
The system incorporates feedback control where the actual rotational position of the diffuser is monitored and used to adjust the integration time and triggering of image acquisition. This ensures that the required number of speckle patterns are captured regardless of minor variations in rotational speed, allowing operation at lower, less stressful rotational rates
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 minimizes speckle noise and enhances defect sensitivity without compromising inspection throughput, allowing for more accurate defect detection in semiconductor devices with smaller features.
Implementation Method 1
The diffuser is arranged within the illumination path between the coherent light source and the specimen for reducing the coherency of the light generated by the coherent light source
Implementation Method 2
The reflective optical component is arranged within the illumination path for directing light exiting the diffuser onto a surface of the specimen
Implementation Method 3
The lens is arranged within the illumination path for focusing the light, which is directed onto the surface of the specimen
Data Source
AI summary
Systems and methods are provided herein for eliminating speckle noise in die-to-die inspection systems. In one embodiment, an illumination system in accordance with the present invention may include a coherent light source, a diffuser, a first detector, a second detector and a controller. The diffuser may be coupled within an illumination path between the coherent light source and the specimen. In one embodiment, the diffuser may be a rotational diffuser having a variable rotational rate. The first detector may be coupled for detecting a desired position on the specimen. The second detector may be coupled for detecting a rotational position of the diffuser when the desired position on the specimen is detected. The controller may be coupled to: (i) the first and second detectors for determining a difference between the rotational position of the diffuser and the desired position on the specimen, and (ii) the diffuser for adjusting the rotational rate of the diffuser to eliminate the difference.