Photon Counting Defect Inspection with Nonlinearity Correction
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Solution Overview
Problem
Conventional defect inspection methods for semiconductor substrates face challenges in detecting infinitesimal defects with dimensions less than 10 nanometers due to weak scattered light signals being buried in noise, leading to thermal damage and reduced inspection speed, and struggle with nonlinear signal detection and sensitivity loss in photon counting methods.
Innovation Solution
A defect inspection device with a detection optical system using a combination of photon counting detectors with few pixels for small background scattered light and many pixels for large background scattered light, along with analog detectors, and a nonlinearity correction mechanism to enhance defect detection sensitivity and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If illumination power is raised to detect infinitesimal defects, then defect detection sensitivity is improved, but thermal damage to the sample increases
Solution Approach 1:
The patent applies periodic action by using pulsed illumination instead of continuous illumination. The illumination light is radiated in pulses with a duty cycle of 10% or less, allowing the sample to cool down between pulses. This periodic illumination maintains defect detection sensitivity while reducing thermal damage accumulation, directly resolving the contradiction between detection sensitivity and thermal damage.
Solution Approach 2:
The patent maintains continuous useful action through high-speed scanning that continuously moves the illumination spot across the sample surface. This ensures that even with pulsed illumination, every point on the sample receives sufficient illumination over time to detect defects, while no single point is exposed to excessive thermal energy, thus maintaining detection sensitivity without causing thermal damage.
2Object-affected harmful factors
If scanning velocity is reduced to minimize thermal damage, then thermal damage is decreased, but inspection speed and productivity deteriorate
Solution Approach 1:
By using pulsed illumination with periodic action, the patent allows for faster scanning velocities because the sample is not continuously exposed to thermal energy. The periodic nature of illumination provides thermal recovery time, enabling high-speed scanning without accumulating excessive heat, thus resolving the contradiction between minimizing thermal damage and maintaining inspection speed.
3Measurement precision
If detector gain is increased to detect weak scattered light, then defect detection sensitivity is improved, but dark current noise increases
Solution Approach 1:
The patent uses periodic pulsed illumination synchronized with the detector integration period. By setting the illumination duty cycle to 10% or less and synchronizing the detector to integrate only during illumination pulses, the system achieves high defect detection sensitivity while minimizing dark current noise accumulation, as the detector is actively measuring only during brief illumination windows rather than continuously accumulating dark current.
4Measurement precision
If photon counting method is used to detect weak light signals, then measurement precision is improved, but nonlinearity in signal detection occurs
Solution Approach 1:
The patent applies parameter changes by adjusting the illumination duty cycle to 10% or less and synchronizing the detector integration period with the illumination pulses. This parameter optimization ensures that the photon counting detector operates in a linear response regime, maintaining both high measurement precision and signal linearity by preventing detector saturation and ensuring proportional response to incident photon flux.
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 detection of both small defects generating weak light and deformed defects, while minimizing thermal damage and improving inspection speed and sensitivity by correcting nonlinearity in signal detection.
Implementation Method 1
illumination light is converged to dimensions of several tens of microns and radiated to the surface. Then, scattered light from the defect is converged and detected
Implementation Method 2
a photon counting detector configured to comprise a plurality of pixels
Data Source
AI summary
In defect scanning carried out in a process of manufacturing a semiconductor or the like, a light detection optical system comprising a plurality of photosensors is used for detecting scattered light reflected from a sample. The photosensors used for detecting the quantity of weak background scattered light include a photon counting type photosensor having few pixels whereas the photosensors used for detecting the quantity of strong background scattered light include a photon counting type photosensor having many pixels or an analog photosensor. In addition, nonlinearity caused by the use of the photon counting type photosensor as nonlinearity of detection strength of defect scattered light is corrected in order to correct a detection signal of the defect scattered light.