Heterodyning Optical Phase Metrology for Diffraction Overlay
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Solution Overview
Problem
Conventional image-based and diffraction-based overlay metrology techniques face challenges such as limited flexibility, wavelength and numerical aperture scaling issues, and design cost constraints, which affect the accuracy and throughput of overlay error measurements in semiconductor manufacturing.
Innovation Solution
The use of spatially structured light generated by an optical modulator, projected onto a multilayered periodic sample, and detected by sensors to estimate overlay errors through phase and intensity changes, allowing for more sensitive and flexible measurements by mixing the periodicity of the structured light with the sample's periodicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional image-based overlay metrology is used, then overlay error can be measured, but the method lacks flexibility and reliability with arbitrary overlay targets or device structures
Solution Approach 1:
The patent changes the fundamental measurement parameter from image intensity (conventional IBO) to diffraction phase. By measuring the phase of diffracted light rather than analyzing images of target features, the method achieves both high reliability and broad adaptability to different target structures and device geometries without requiring specialized target designs
Solution Approach 2:
The patent replaces the mechanical/image-processing-based measurement system with an optical diffraction-based system. Instead of capturing and analyzing images through complex algorithms, the system uses optical heterodyning to directly measure phase shifts in diffracted light, eliminating the need for image processing and improving both reliability and versatility
2Measurement precision
If conventional diffraction-based overlay measurements are used, then overlay error can be measured, but the method suffers from wavelength and numerical aperture scaling issues
Solution Approach 1:
The patent introduces an optical modulator as an intermediary element that imposes a known spatial frequency pattern on the incident light. This intermediary allows the system to measure overlay errors independently of wavelength and numerical aperture scaling by using the modulator's fixed spatial frequency as a reference, thereby eliminating the scaling issues that plague conventional DBO methods
Solution Approach 2:
The patent employs periodic modulation of the incident light through an optical modulator with a fixed spatial frequency. This periodic action creates a reference pattern that interferes with the diffracted light from the sample, enabling phase measurement that is invariant to wavelength and numerical aperture changes, thus resolving the scaling constraints
3Measurement precision
If spatially structured light with optical modulator is used, then measurement sensitivity and flexibility are enhanced, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical target structures and image processing systems with a relatively simple optical modulator that generates structured light. The optical modulator is a compact, programmable device that can be controlled via software, reducing mechanical complexity while enhancing measurement sensitivity through phase detection of the structured light pattern
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 enhances measurement sensitivity and flexibility, enabling more accurate overlay error detection while reducing design costs and avoiding the limitations of conventional methods, such as wavelength scaling and numerical aperture constraints.
Implementation Method 1
generating spatially structured light from a light source by projecting light emitted from the light source through an optical modulator
Implementation Method 2
detecting diffracted spatially structured light from the multilayered periodic sample
Implementation Method 3
detecting diffracted spatially structured light from the multilayered periodic sample at one or more of a plurality of sensors
Implementation Method 4
a synchronization module configured to apply lock-in amplification of light detected at one or more of the plurality of sensors with respect to a reference signal
Implementation Method 5
an analysis module configured to compute a phase difference between the reference signal and the diffracted spatially structured light detected at the one or more of the plurality of sensors
Data Source
AI summary
Methods and systems are provided for diffraction-based overlay (DBO) metrology of a multilayered sample. In one example, a method may include generating spatially structured light via a light source and an optical modulator, transmitting the spatially structured light onto the multilayered sample, detecting diffracted spatially structured light at one or more of a plurality of sensors, and estimating an overlay error of the multilayered sample based on the diffracted spatially structured light detected at the one or more of the plurality of sensors.