Wafer Inspection Detector Using Split Light APD Arrays
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Solution Overview
Problem
Current semiconductor wafer inspection systems face limitations in sensitivity and dynamic range due to detector noise, particularly with avalanche photodiodes operating in Geiger mode, which are blind for a period after triggering, restricting their utility in detecting defects on wafer surfaces effectively while avoiding thermal damage.
Innovation Solution
The system employs a combination of avalanche photodiodes operating in Geiger mode and other photodetectors, such as PIN photodiodes or CCDs, to enhance the dynamic range by directing light from each pixel to multiple detector arrays, optimizing sensitivity and resolution for detecting both low and high photon counts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If avalanche photodiodes operate in Geiger mode to achieve high sensitivity, then detection sensitivity is improved, but dynamic range is reduced due to quench time blindness
Solution Approach 1:
The detector array is segmented into multiple independent photodetector elements (e.g., APDs, PIN diodes, PMTs) that can operate in different modes simultaneously. Each detector type handles different photon count ranges, with APDs in Geiger mode for low photon counts and other detectors for higher photon counts, thereby extending the overall dynamic range while maintaining high sensitivity.
2Measurement precision
If illumination power is increased to overcome detector noise, then signal-to-noise ratio is improved, but thermal damage to the wafer surface occurs
Solution Approach 1:
The system changes the operational parameters of the photodetectors, specifically operating APDs in Geiger mode with gain values exceeding 10^5, which dramatically amplifies weak optical signals from single photons. This parameter change enables detection of extremely low light levels without requiring high illumination power, thereby improving signal-to-noise ratio while avoiding thermal damage to the wafer surface.
3Measurement precision
If Geiger mode APDs are used to detect single photons, then sensitivity is improved, but the quench time creates periods of blindness reducing operational efficiency
Solution Approach 1:
The system merges multiple detector types (APDs in Geiger mode, PIN diodes, PMTs) into a single integrated detector array. The APDs provide single-photon sensitivity while other detector types compensate during quench time, ensuring continuous operation without blindness periods. This combination maintains high sensitivity while restoring full operational efficiency across the entire detection bandwidth.
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 increases the sensitivity and dynamic range of the inspection system, allowing for more effective detection of defects on semiconductor wafers with reduced risk of thermal damage, while maintaining high throughput.
Implementation Method 1
Avalanche photodiodes (APDs) are small sensors that provide significant gain and require lower drive voltage than PMTs. In Geiger mode, the voltage across the APD is set at a value above the break-down voltage. Absorption of a single photon may give rise to a large pulse at the output
Implementation Method 2
Light collected from the wafer surface is directed to a detector, or an array of detectors, for conversion to electrical signals useful for storage and analysis
Data Source
AI summary
Methods and systems for enhancing the dynamic range of a high sensitivity inspection system are presented. The dynamic range of a high sensitivity inspection system is increased by directing a portion of the light collected from each pixel of the wafer inspection area toward an array of avalanche photodiodes (APDs) operating in Geiger mode and directing another portion of the light collected from each pixel of the wafer inspection area toward another array of photodetectors having a larger range. The array of APDs operating in Geiger mode is useful for inspection of surfaces that generate extremely low photon counts, while other photodetectors are useful for inspection of larger defects that generate larger numbers of scattered photons. In some embodiments, the detected optical field is split between two different detectors. In some other embodiments, a single detector includes both APDs operating in Geiger mode and other photodetectors having a larger range.