Overlay Measurement via Lateral Shearing Interference
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Solution Overview
Problem
Current overlay measurement technologies, particularly diffraction-based overlay (DBO) methods, face challenges in accurately determining the specific value of overlay offset due to difficulties in measuring asymmetry of light intensity, especially with rough substrate backgrounds and deformation during chemical mechanical planarization processes.
Innovation Solution
An overlay measurement apparatus and method that utilizes lateral shearing interference to determine the existence and exact value of overlay offset by illuminating and measuring the reflections from overlay markers on a wafer, generating interference fringes to calculate offsets relative to the optical axis, allowing for precise determination of overlay offsets without requiring wafer movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffraction-based overlay (DBO) technology is used to measure overlay offset, then the measurement can determine the existence of overlay offset, but it is difficult to obtain the specific value of the overlay offset
Solution Approach 1:
The patent introduces an optical field distribution detection system as an intermediary between the DBO measurement and the final overlay offset value determination. This intermediary captures the complete optical field distribution information, which then serves as the basis for calculating the specific overlay offset value through image processing and analysis
Solution Approach 2:
The patent replaces the traditional direct mechanical measurement approach with an optical field distribution-based measurement system. By using optical field distribution characteristics and image processing algorithms, the system can determine the specific overlay offset value without relying on direct physical measurement methods
2Measurement precision
If image-based overlay (IBO) technology is used, then overlay measurement can be performed, but the measurement is easily affected by substrate defects such as rough background and marker deformation
Solution Approach 1:
The patent replaces the image-based overlay measurement system with a diffraction-based optical field distribution measurement system. This substitution eliminates the sensitivity to substrate surface conditions by using diffraction patterns rather than direct imaging, thereby improving measurement reliability
Solution Approach 2:
The patent changes the measurement parameter from direct image intensity (IBO) to optical field distribution characteristics (DBO). By measuring the distribution of light intensity in the diffraction pattern rather than the image intensity of the marker itself, the system becomes insensitive to substrate surface defects and marker deformation
3Measurement precision
If conventional overlay measurement methods are used, then overlay offset can be detected, but wafer movement during measurement introduces errors
Solution Approach 1:
The patent performs preliminary alignment by using the optical field distribution characteristics to determine the optical axis position before conducting the overlay measurement. This preliminary action establishes a stable reference frame that compensates for any wafer movement during the measurement process
Solution Approach 2:
The patent implements a feedback mechanism where the optical field distribution information is continuously analyzed to detect and compensate for wafer movement. The system uses the measured optical field characteristics to adjust and correct the measurement results, ensuring accuracy even when wafer position changes during measurement
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 enhances the accuracy of overlay measurement by minimizing errors caused by wafer movement and improves the precision of overlay offset determination, effectively addressing the limitations of existing DBO technologies.
Implementation Method 1
an illuminating unit configured to generate illuminating light to illuminate a first overlay marker formed on a wafer to generate reflected light
Implementation Method 2
a first measuring unit configured to receive the reflected light from the first overlay marker to cause the reflected light to laterally shift and shear to generate interference light
Data Source
AI summary
The present disclosure provides apparatus and methods for overlay measurement. An exemplary overlay measurement apparatus includes an illuminating unit configured to generate illuminating light to illuminate a first overlay marker formed on a wafer to generate reflected light; and a first measuring unit configured to receive the reflected light from the first overlay marker to cause the reflected light to laterally shift and shear to generate interference light, to receive the interference light to form a first image, and to determine existence of an overlay offset and an exact value of the overlay offset, according to the first image.