Angular-Resolved Spectroscopic Lithography Characterization
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Solution Overview
Problem
Current methods for determining overlay error in lithographic processes are limited by sensor asymmetry, which can be time-consuming to correct, either through substrate rotation or the use of multiple reference targets, impacting throughput.
Innovation Solution
A method involving the projection of radiation beams with different polarizations or wavelengths onto targets with predetermined biases to measure asymmetry, allowing for the calculation of overlay error with reduced sensor asymmetry influence, using a radiation projector, detector, and processor to analyze the reflected radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If substrate rotation is used to reduce sensor asymmetry, then measurement accuracy is improved, but throughput is reduced due to time loss
Solution Approach 1:
The patent replaces the mechanical substrate rotation system with an optical/electronic solution. Instead of physically rotating the substrate to change the sensor's angular position, the system uses a rotating sensor assembly that can be quickly repositioned between measurements. This substitution eliminates the time-consuming substrate rotation while maintaining the ability to reduce sensor asymmetry effects through angular variation.
Solution Approach 2:
The patent implements a dynamic sensor assembly that can rotate or reposition itself rapidly between measurements. This dynamic capability allows the sensor to change its angular orientation relative to the substrate without requiring the substrate itself to be rotated, thereby maintaining measurement accuracy while minimizing throughput impact.
2Measurement precision
If multiple reference targets are used to reduce sensor asymmetry, then measurement accuracy is improved, but substrate space and measurement time are increased
Solution Approach 1:
The patent changes the measurement parameters by using a single reference target with multiple known overlay values rather than multiple separate reference targets. The system measures the same physical target at different angular positions, using the known overlay parameters to calculate sensor asymmetry. This approach reduces the time and space requirements while maintaining measurement accuracy.
3Area of stationary object
If a single reference target is used, then substrate space is saved, but sensor asymmetry cannot be effectively reduced
Solution Approach 1:
The patent introduces a new dimension to the measurement process by varying the angular position of the sensor relative to the single reference target. Instead of using multiple targets along the substrate surface, the system uses angular variation as an additional degree of freedom. This allows sensor asymmetry to be reduced while occupying minimal substrate space.
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 effectively reduces the impact of sensor asymmetry on overlay error measurement, improving accuracy and throughput by using multiple signal measurements to isolate and correct for asymmetry.
Implementation Method 1
a beam is reflected off the surface of the substrate, for example at an alignment target, and an image is created on, for example, a camera of the reflected beam
Implementation Method 2
projecting a first beam of radiation onto a first target of the substrate... the first and second beams have different polarizations, or different wavelengths, or both
Data Source
AI summary
An inspection system is arranged to measure an overlay error by projecting a plurality of radiation beams, differing in wavelength and/or polarization, onto two targets. A first radiation beam is projected onto a first target and the reflected radiation A1+ is detected. The first target comprises two gratings having a bias +d with respect to each other. The first radiation beam is also projected on to a second target, which comprises two gratings having a bias −d with respect to each other, and the reflected radiation A1− is detected. A second radiation beam, having a different wavelength and/or polarization from the first radiation beam, is projected onto the first target and reflected radiation A2+ is detected and projected onto the second target and reflected radiation A2− is detected. Detected radiations A1+, A1−, A2+, and A2− is used to determine the overlay error.