Wafer Inspection Optics for Separate Reflected and Scattered Light Paths
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Solution Overview
Problem
Conventional wafer inspection devices face challenges in accurately detecting defects due to the loss of valid information when blocking reflected light to isolate high-order scattered light signals, leading to reduced sensitivity and difficulty in identifying defect locations.
Innovation Solution
A wafer inspection device that simultaneously captures images from reflected and scattered light signals without blocking light, using separate image sensors and optical elements to enhance contrast and sensitivity in defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a blocking film is inserted to isolate high-order scattered light signals, then the defect signal is enhanced, but the background image becomes blurred and defect location identification becomes difficult
Solution Approach 1:
The patent divides the detection of reflected light and scattered light into separate channels using a beam splitter and separate image sensors. This segmentation allows each channel to be optimized independently - the scattered light channel for defect detection and the reflected light channel for background image preservation - thereby resolving the contradiction between enhancing defect signals and preserving background information.
Solution Approach 2:
The patent extracts scattered light signals containing defect information from the total light signal using a spatial filter that selectively transmits high-order scattered light while blocking low-order reflected light. This extraction isolates the defect signal without completely blocking the optical path, allowing subsequent processing to enhance defect detection while preserving necessary background context.
2Measurement precision
If low-order optical order is blocked to reduce background signal, then the signal-to-noise ratio is improved, but the background image becomes blurred making wafer pattern shape difficult to discern
Solution Approach 1:
The patent segments the optical detection into separate channels for reflected light and scattered light. The reflected light channel preserves low-order optical information for wafer pattern imaging, while the scattered light channel focuses on high-order information for defect detection. This segmentation resolves the contradiction by allowing both low SNR background images and high SNR defect images to coexist in their respective channels.
Solution Approach 2:
The patent introduces a beam splitter as an intermediary optical element that divides the incoming light into separate reflected light and scattered light paths. This intermediary allows the system to simultaneously process both low-order reflected light (for pattern imaging) and high-order scattered light (for defect detection) without mutual interference, resolving the information loss contradiction.
3Measurement precision
If a blocking film is inserted into the light receiving unit to isolate scattered light, then defect signal detection is enhanced, but valid information from the blocked region is lost
Solution Approach 1:
The patent segments the light detection into separate channels using spatial filtering and a beam splitter. The scattered light channel uses a spatial filter to isolate high-order scattered light for defect detection, while the reflected light channel captures low-order reflected light for pattern imaging. This segmentation ensures that each channel captures its specific valid information without blocking the other, eliminating information loss.
Solution Approach 2:
The patent transitions from a single-dimensional detection approach (single image sensor) to a multi-dimensional approach by separating reflected light and scattered light into different spatial channels. This dimensional separation allows the system to capture different types of valid information (pattern information from reflected light, defect information from scattered light) simultaneously without mutual blocking, thereby preserving all valid information.
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
The device improves defect detection sensitivity by collecting and focusing reflected and scattered light onto separate focal points, minimizing optical components, and efficiently achieving optimal inspection conditions without replacing parts.
Implementation Method 1
an objective lens for focusing light passing through the illumination optical system onto an inspection region
Implementation Method 2
receiving reflected light and scattered light from the inspection region
Implementation Method 3
Illuminating the inspection region 1 may generate reflected light disposed at a low angle in a low order and scattered light disposed at a high angle in a high order
Implementation Method 4
a signal separator disposed at the rear of the aperture stop, guiding reflected light along a first path, and guiding scattered light along a second path different from the first path
Data Source
AI summary
A wafer inspection device includes a light source, an illumination optical system disposed on a propagation path of light emitted from the light source, an objective lens for focusing light passing through the illumination optical system onto an inspection region, a light-receiving optical system for receiving reflected light and scattered light from the inspection region by using the objective lens, and a detection unit for detecting a reflected light signal and a scattered light signal. The light-receiving optical system includes an aperture stop for transmitting reflected light and scattered light passing through the objective lens, and a signal separator disposed at the rear of the aperture stop that guides reflected light along a first path, and that guides scattered light along a second path different from the first path.