Autofocus Error Reduction via Light Segmentation
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Solution Overview
Problem
Autofocus errors in high-resolution lithography tools due to thin-film effects and pattern-dependent phase changes in the substrate, leading to inaccurate substrate height measurements and focus adjustments.
Innovation Solution
An autofocus system with a patterned optical element that separates regular and divergent AF light, using spatial filters and additional photodetectors to detect and correct for errors by identifying regions with significant divergent light, which indicates potential autofocus errors, allowing for alternative focus approaches based on substrate structure data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional autofocus devices are used to rapidly adjust substrate focus, then throughput is improved, but autofocus errors occur due to thin-film effects and pattern-dependent phase changes
Solution Approach 1:
The autofocus light is segmented into regular reflected light and divergent light components using spatial filters. The regular light path provides standard autofocus measurement, while the divergent light path detects thin-film effects and pattern-dependent phase changes. This segmentation allows simultaneous acquisition of both throughput-critical focus data and error-detection data without compromising measurement speed.
Solution Approach 2:
An intermediary detection system using additional photodetectors and spatial filters is introduced to detect the presence and magnitude of autofocus errors caused by thin-film effects. This intermediary system does not replace the conventional autofocus device but works alongside it to identify when autofocus errors are present, enabling selective correction only when needed.
2Measurement precision
If autofocus light reflects from patterned thin films, then autofocus measurements are obtained, but AF errors arise due to Goos-Hanchen effect and pattern-dependent phase changes
Solution Approach 1:
The system implements feedback by using additional photodetectors to detect divergent light that indicates the presence of autofocus errors. When divergent light is detected, the system feeds back this error information and applies corrective adjustments to the substrate positioning or autofocus calculations, thereby compensating for the harmful effects of thin-film interference and pattern-dependent phase changes.
Solution Approach 2:
The divergent light that was previously considered a harmful artifact causing autofocus errors is converted into a useful diagnostic signal. By detecting the characteristics of this divergent light through additional photodetectors and spatial filters, the system identifies the presence and magnitude of thin-film effects, then uses this information to correct the autofocus measurement, thereby transforming the harmful effect into a beneficial error-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
The system effectively identifies and compensates for autofocus errors, improving the accuracy of substrate positioning and focus adjustments in lithography tools by distinguishing between regular and divergent AF light, thereby reducing the impact of thin-film and pattern-dependent effects.
Implementation Method 1
The patterned optical element divides the received AF light into a selected first part that propagates to the system photodetector and a separate second part that is detected by the at least one additional photodetector
Implementation Method 2
The sending unit includes a first spatial filter. The receiving unit that includes a system photodetector and at least one additional photodetector
Implementation Method 3
The receiving unit receives AF light propagating from the substrate. The receiving unit comprises a patterned optical element that receives AF light from the substrate
Data Source
AI summary
In a lithography tool used in fabricating microelectronic devices, autofocus (AF) systems provide automatic image focusing before making exposures. To reduce production of erroneous results based on interaction of a beam of AF light with certain regions on lithographic substrates, a subject AF device has a sending unit and a receiving unit. The sending unit directs an AF light beam to the substrate, and the receiving unit receives AF light reflected from the substrate. The receiving unit has a system photodetector and a patterned optical element that receives AF light from the substrate and transmits a selected diffraction order(s) of said light. The system photodetector senses light of the selected diffraction order of reflected AF light while at least one additional photodetector detects divergent reflected AF light. Substrate areas exhibiting unusual amounts of divergent light may indicate a focus-error condition. The AF systems can be configured as fringe-projection or slit-projection AF systems.