Photon Counting Sensor for Semiconductor Wafer Inspection
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Solution Overview
Problem
Existing inspection devices face challenges in accurately detecting very small foreign materials on semiconductor wafers due to dark noises from sensors and variations in light multiplication factors across pixel areas, leading to difficulties in counting photons and detecting small defects.
Innovation Solution
The implementation of a photon counting sensor system with M current-voltage conversion sections, a voltage application section, and a detection signal generation section, which includes a photon counting sensor with N pixels, where M<N, to enhance response speed and uniformity of light multiplication factors, allowing for accurate detection of small foreign materials by applying reference voltages and converting output currents into detection signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a photon counting sensor is used to detect scattered light from foreign materials, then the detection capability for small foreign materials is improved, but dark noises from the sensor make up a large percentage of the detection signal, making it difficult to detect very small foreign materials
Solution Approach 1:
The sensor output is divided into multiple pixel areas, and the detection is performed by integrating signals from multiple pixels. This segmentation approach allows the system to distinguish between localized dark noise in individual pixels and actual scattered light signals from foreign materials, thereby improving the signal-to-noise ratio for small defect detection.
Solution Approach 2:
Multiple pixel signals are combined and integrated to form the final detection signal. By merging signals from multiple pixels, the system achieves better statistical accuracy and reduces the impact of random dark noise, enabling detection of very small foreign materials that would be obscured by sensor noise in a single-pixel system.
2Area of stationary object
If photo-detecting elements are allocated among several areas with several hundreds or more pixels, then the detection coverage is improved, but the multiplication factors of the photo-detecting elements differ depending on their locations, causing variations in output currents and preventing accurate photon counting
Solution Approach 1:
The patent applies different correction factors or calibration parameters to different pixel areas based on their individual characteristics. By recognizing that each pixel area has unique multiplication factor characteristics, the system performs localized calibration and correction, ensuring that photons counted from any pixel area can be accurately converted to absolute photon numbers despite variations in local sensor response.
Solution Approach 2:
The system adjusts and calibrates the multiplication factors for different pixel areas by changing operational parameters such as bias voltage or applying software-based correction factors. This parameter adjustment ensures uniformity across the sensor array, allowing accurate photon counting regardless of the pixel area where the light incident occurs.
3Speed
If a laser light source makes pulsed oscillation, then the temporal resolution is improved, but if the response speed of the photon counting sensor is not sufficient, signal components detected decrease, making it difficult to detect very small foreign materials
Solution Approach 1:
The system performs preliminary calibration and characterization of the sensor's temporal response before actual measurement. By understanding the sensor's response characteristics in advance, the system can optimize the laser pulse timing and integration window to maximize signal capture while minimizing loss due to insufficient response speed, thereby maintaining both temporal resolution and detection sensitivity.
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 configuration enables accurate detection of very small foreign materials by improving the photon counting sensor's response speed and uniformity of light multiplication factors, thereby enhancing the detection accuracy of small defects on semiconductor wafers.
Implementation Method 1
a laser beam is irradiated to a surface of a specimen and scattered light from the surface of the specimen is detected
Implementation Method 2
a photon counting sensor which outputs M output signals from photo-detecting elements of N pixels
Data Source
AI summary
A detection circuit for accurately detecting a very small foreign material and an inspection/measurement device using the same are provided. The inspection/measurement device includes: an irradiation section that irradiates a laser beam to a surface of a specimen; and a detection section that detects scattered light from the surface of the specimen and generates a detection signal. The detection section includes: a photon counting sensor that outputs M output signals from photo-detecting elements of N pixels (M and N are natural numbers, and M<N); M current-voltage conversion sections that execute current-voltage conversion on the output signals of the photon counting sensor respectively; a voltage application section that applies reference voltages to the current-voltage conversion sections; and a detection signal generation section that generates a detection signal on the basis of the outputs of the current-voltage conversion sections.