Dual-Stop Optical Filter for Lithography Alignment Noise Reduction
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Solution Overview
Problem
Current lithographic processes face challenges in achieving accurate position measurements due to noise in the radiation signal and detection of radiation that does not carry alignment information, leading to errors in overlay control as feature sizes decrease.
Innovation Solution
A measurement apparatus is developed that includes an optical system with a first stop to block zero-order radiation and allow non-zero order radiation to pass, and a second stop to further block any remaining zero-order radiation, ensuring only non-zero order radiation reaches the detector for accurate alignment measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If radiation detection is performed without filtering zero-order radiation, then the signal intensity is higher, but measurement precision deteriorates due to noise and detection of radiation that does not carry alignment information
Solution Approach 1:
The patent extracts and removes the harmful zero-order radiation component from the radiation signal using a spatial filter (stop) positioned in the optical path. This allows the detector to receive only the useful non-zero order radiation that carries alignment information, thereby eliminating noise while maintaining sufficient signal intensity for accurate measurements
Solution Approach 2:
The spatial filter (stop) acts as an intermediary element between the periodic structure and the detector. It selectively transmits non-zero order radiation while blocking zero-order radiation, serving as a mediator that separates useful signal from noise without requiring complex processing at the detector
2Measurement precision
If zero-order radiation is blocked using a single stop, then noise is reduced, but some zero-order radiation may still pass through, requiring additional filtering
Solution Approach 1:
The patent divides the noise filtering function into multiple segments by using two separate stops positioned at different locations in the optical path. The first stop provides primary filtering while the second stop provides secondary filtering, ensuring complete elimination of zero-order radiation through cumulative blocking rather than relying on a single complex filter
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 solution significantly reduces noise and improves the accuracy of position measurements, enhancing the precision of overlay control in lithographic processes by eliminating unnecessary radiation signals that contribute to measurement errors.
Implementation Method 1
radiation redirected by the periodic structure
Implementation Method 2
a first stop to block zero order radiation from the periodic structure and allow non-zero order radiation to pass
Implementation Method 3
a second stop to block zero order radiation passing the first stop and to allow the non-zero order radiation to pass
Implementation Method 4
a radiation detector, downstream of the optical system, to receive the non-zero order radiation
Data Source
AI summary
A measurement apparatus including an optical system to provide illumination radiation into a spot on a periodic structure and to receive radiation redirected by the periodic structure, the optical system including a first stop to block zero order radiation from the periodic structure and allow non-zero order radiation to pass, and a second stop to block zero order radiation passing the first stop and to allow the non-zero order radiation to pass, and a radiation detector, downstream of the optical system, to receive the non-zero order radiation.