Interferometric Overlay Tool with Variable Phase Delay
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing overlay metrology systems face challenges in accurately measuring the alignment of device-scale features due to differences in size, orientation, and density between overlay targets and device features, leading to mismatches between measured and actual overlay errors.
Innovation Solution
An interferometric overlay tool with a variable phase delay and spectroscopic detector is used to generate interferometric phase data, allowing for simultaneous measurement of multiple optical path differences and wavelengths, which is then used to determine overlay errors in grating-over-grating structures associated with lithographic exposure fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If overlay measurements are performed on dedicated overlay targets with features designed for sensitive measurements, then measurement precision is improved, but manufacturing precision deteriorates due to mismatch between target features and device features
Solution Approach 1:
The patent creates a virtual copy of the device features by using the same optical model (RCWA) to simulate both the diffraction pattern of actual device features and the measurement signal from overlay targets. This virtual copy allows the measurement system to account for the specific geometry, pitch, and configuration of device features, thereby eliminating the mismatch error between target and device features while maintaining high measurement sensitivity
Solution Approach 2:
The patent changes the parameters used in overlay measurement by incorporating device-specific parameters (pitch, feature geometry, layer configuration) into the optical model. By adjusting the model parameters to match actual device features rather than using generic target parameters, the system achieves both high measurement precision and manufacturing precision
2Manufacturing precision
If feature size is decreased and feature density is increased to achieve device-scale fabrication, then manufacturing precision is improved, but measurement precision deteriorates because features become unresolvable at optical wavelengths
Solution Approach 1:
The patent replaces direct optical imaging (mechanical/optical detection) with computational diffraction analysis. Instead of attempting to directly image unresolvable device-scale features, the system uses the RCWA model to compute expected diffraction patterns and compares these with actual measurements, enabling precise characterization of features below the optical resolution limit
Solution Approach 2:
The patent transitions from spatial domain measurement (direct imaging) to frequency domain analysis (diffraction pattern analysis). By measuring the diffraction pattern in the frequency domain and using RCWA to relate it to feature geometry, the system can characterize sub-wavelength features that cannot be resolved in the spatial domain
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 enables accurate and efficient overlay metrology by directly measuring device-relevant features, reducing errors associated with target-device mismatches and improving the precision of overlay measurements.
Implementation Method 1
one or more beam combiners to combine the measurement beam and the reference beam as an interference beam
Implementation Method 2
one or more illumination optics to illuminate a grating-over-grating structure with the probe beam
Implementation Method 3
a variable phase delay configured to vary an optical path difference (OPD) between the probe path and the reference path
Implementation Method 4
one or more dispersive elements to spectrally disperse the interference beam along a dispersion direction orthogonal to the expansion direction
Data Source
AI summary
An interferometric overlay tool may include an interferometer and a controller. The interferometer may include one or more beamsplitters to split illumination including one or more wavelengths into a probe beam along a probe path and a reference beam along a reference path, one or more illumination optics to illuminate a grating-over-grating structure with the probe beam, one or more collection optics to collect a measurement beam from the grating-over-grating structure, one or more beam combiners to combine the measurement beam and the reference beam as an interference beam, and a variable phase delay configured to vary an optical path difference (OPD) in the interferometer. The controller may receive one or more interference signals representative of interferometric phase data associated with a plurality of OPD values and the one or more wavelengths from a detector and determine an overlay error of the grating-over-grating structure based on the interferometric phase data.