Lithography Substrate Defect Detection via Reflected Radiation Intensity
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Solution Overview
Problem
Current substrate height sensors in lithographic apparatuses fail to detect defects on substrates, particularly at the edges, which can lead to further damage and contamination due to immersion liquid contact during the exposure process.
Innovation Solution
A method and apparatus that use a sensor to scan the substrate with a radiation beam, measuring the intensity of reflected radiation across a scan range to determine variations and detect defects, with a controller controlling the sensor's position to identify any defects present.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sensor is used to measure substrate height, then substrate positioning accuracy is improved, but defect detection capability deteriorates
Solution Approach 1:
The sensor system is designed to perform multiple functions: measuring substrate height for positioning accuracy while simultaneously detecting defects through reflected radiation intensity analysis. The same sensor that measures focus and height also scans for defects by detecting variations in reflected radiation intensity across the substrate surface.
Solution Approach 2:
Reflected radiation intensity serves as an intermediary parameter that provides information about substrate defects. Instead of directly detecting defects, the system measures the intensity of radiation reflected from the substrate surface, where variations in intensity indicate the presence of defects, thereby enabling indirect defect detection.
2Productivity
If substrate edges are not inspected, then measurement speed is maintained, but contamination risk increases
Solution Approach 1:
The system performs preliminary inspection of the entire substrate surface including edges before the lithography process. By scanning the substrate with radiation and analyzing reflected intensity variations in advance, defects at edges are detected before they can cause contamination during immersion exposure, allowing for preventive action.
Solution Approach 2:
The system continuously monitors reflected radiation intensity during the scanning process and provides feedback about defect presence. When variations in intensity indicate defects, the system can trigger alerts or reject the substrate, creating a feedback loop that prevents defective substrates from proceeding to exposure and causing contamination.
3Manufacturing precision
If immersion liquid is used, then numerical aperture is increased, but defect spread and contamination increase
Solution Approach 1:
The system performs defect detection before immersion liquid contact by scanning the substrate with radiation and analyzing reflected intensity. This preliminary inspection identifies defects that could spread through the immersion liquid, allowing for preventive rejection of affected substrates before contamination occurs during exposure.
Solution Approach 2:
The system uses the reflected radiation intensity from the substrate surface as a beneficial diagnostic signal. The same radiation that could potentially cause heating or damage is instead utilized to detect defects through intensity variations, converting a potential harmful effect into a useful detection mechanism.
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
Effectively detects defects on substrates by analyzing intensity variations, preventing further damage and contamination, and ensuring accurate substrate positioning within the focus of the optical projection system.
Implementation Method 1
measuring the fraction of the intensity of the radiation reflected from different substrate areas along the scan range
Data Source
AI summary
Method of determining defects in a substrate, the method comprising: scanning a scan range of the substrate with a sensor, the sensor projecting a beam of radiation on the substrate; measuring the fraction of the intensity of the radiation reflected from different substrate areas along the scan range; determining the variations of the measured fraction across the scan range; determining from the variations whether any defects are present in the substrate.