Lower Surface Mark Detection via Upper Surface Position Feedback
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for detecting alignment marks on the lower surface of a substrate, such as Si wafers, are inefficient due to the need for a large search range and high calculation errors, leading to low throughput and inaccurate alignment, especially when the substrate thickness varies.
Innovation Solution
A detection apparatus comprising a first detector that illuminates the mark from the upper surface to detect its image, a second detector that measures the upper surface position, and a processor that calculates the focus position based on this measurement, allowing the substrate stage to adjust and maintain the mark within an allowable focus range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a large search range is used to detect alignment marks on the lower surface, then detection coverage is improved, but measurement precision deteriorates due to high calculation errors
Solution Approach 1:
The system performs preliminary measurement of the upper surface position using a second detector before detecting the alignment mark on the lower surface. Based on this preliminary information and the known thickness, the focus position is calculated in advance, allowing the first detector to start searching from a pre-calculated position rather than a wide range, thus improving both coverage efficiency and precision
Solution Approach 2:
The upper surface position measurement acts as an intermediary step between the known substrate thickness and the lower surface mark detection. By measuring the upper surface and using it as a reference point, the system can accurately determine the lower surface position without needing to search a large range, resolving the contradiction between coverage and precision
2Measurement precision
If the focus position is not accurately determined, then detection accuracy deteriorates, but the search time increases when using a large search range
Solution Approach 1:
The system performs preliminary measurement of the upper surface position and calculates the expected focus position before the actual mark detection. This preliminary calculation eliminates the need for time-consuming wide-range searches while maintaining high detection accuracy, as the search starts from a pre-determined accurate position
Solution Approach 2:
The system uses feedback from the upper surface position measurement to adjust and determine the optimal focus position for detecting the lower surface mark. This feedback mechanism ensures accurate detection while minimizing search time by continuously refining the focus position based on measured data
3Adaptability or versatility
If substrate thickness varies, then alignment precision deteriorates, but maintaining a fixed focus position reduces detection accuracy
Solution Approach 1:
The system dynamically adjusts the focus position based on the measured upper surface position and the known substrate thickness. Rather than using a fixed focus position, the system calculates and adapts the focus position for each substrate, accommodating thickness variations while maintaining high alignment precision through real-time adjustment
Solution Approach 2:
The system changes the focus position parameter based on measured upper surface position and substrate thickness. By dynamically modifying this critical parameter rather than keeping it fixed, the system adapts to substrate variations and maintains consistent detection accuracy across different thickness conditions
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 enables quick and accurate detection of alignment marks on the lower surface, improving throughput and alignment precision by reducing the search range and calculation errors, even with varying substrate thickness.
Implementation Method 1
An Si substrate is transparent to infrared light (wavelength: 1,000 nm or more). Hence, a method of observing a mark on the lower surface from the upper surface side using a position detection system that uses infrared light as a light source has also been proposed.
Implementation Method 2
to measure a best focus position of an alignment mark, an image of the alignment mark is obtained while a wafer stage is driven in the optical axis direction of a position detection system, and a position with a maximum contrast is calculated.
Data Source
AI summary
A detection apparatus, which detects a mark formed on a lower surface of a target object, includes: a first detector which illuminates the mark from an upper surface side of the target object to detect an image of the illuminated mark; a second detector which detects an upper surface position of the target object; and a processor which obtains information indicating a focus position to focus on the mark in the first detector, based on the upper surface position detected by the second detector.