Wavelength-Dependent Spatial Filter for Metrology Sensor Alignment
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Solution Overview
Problem
Current metrology sensors face challenges in achieving accurate position measurement on substrates due to low wafer quality and surface scattering issues, particularly when opaque layers are present, which limits dynamic range and requires larger zero-order stops that can compromise alignment accuracy and sensor size constraints.
Innovation Solution
A metrology sensor system employing a wavelength-dependent spatial filter that blocks zero diffraction order radiation based on wavelength, with adjustable obscuration size and polarization filtering to separate signal and noise radiation, allowing for improved measurement accuracy in both coarse and fine positioning phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the zero-order stop size is increased to block more scattered light, then wafer alignment performance improves, but the sensor module volume increases and may block desired first-order diffraction orders
Solution Approach 1:
The patent employs a movable zero-order stop that can be dynamically adjusted in size and position. This allows the stop to be enlarged only when and where needed to block scattered light, rather than being permanently large. The dynamic adjustment mechanism enables the stop to adapt its dimensions to match the specific measurement requirements, thus improving alignment performance temporarily without permanently increasing sensor module volume.
Solution Approach 2:
The invention applies local quality by making the zero-order stop movable and adjustable only in the specific region where scattered light blocking is needed. Rather than uniformly increasing the size of the entire sensor module, the stop can be locally enlarged at the precise location and time when scattering compensation is required, leaving other parts of the sensor module compact and maintaining small overall volume.
2Measurement precision
If the zero-order stop size is increased to block more scattered light, then wafer alignment performance improves, but alignment accuracy may be compromised due to blocking of first-order diffraction orders
Solution Approach 1:
The movable zero-order stop can be dynamically adjusted to change its size and position during operation. This allows the system to temporarily enlarge the stop to block scattered light when measuring wafer alignment, then retract or reposition it to avoid blocking the first-order diffraction orders that carry the alignment signal, thus maintaining alignment accuracy.
Solution Approach 2:
The system employs periodic adjustment of the zero-order stop, alternating between an expanded state for blocking scattered light and a retracted state for allowing alignment signals to pass. This periodic action ensures that at any given moment, the stop configuration is optimized for the current measurement phase, preventing continuous blocking of alignment-critical diffraction orders.
3Measurement precision
If a larger zero-order stop is used to block scattered light, then dynamic range improves, but the sensor design becomes more complex and constrained by thermal and vibrational factors
Solution Approach 1:
The movable zero-order stop design allows the system to achieve a large stop size only when needed for blocking scattered light, rather than permanently incorporating a large stop structure. This dynamic approach improves dynamic range temporarily without permanently increasing device complexity, as the stop can be retracted or repositioned when its full size is not required.
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
Enhances measurement accuracy and reduces noise interference, enabling precise alignment even through opaque layers by effectively filtering out unwanted radiation, thus improving wafer quality and alignment reproducibility.
Implementation Method 1
radiation in the 'zeroth diffraction order' (e.g., radiation that is scattered from the edges of the spot mirror, from surface roughness (random scattering), from target edges, etc.
Implementation Method 2
a wavelength dependent spatial filter for spatially filtering said scattered radiation, said wavelength dependent spatial filter having a spatial profile dependent on the wavelength of said scattered radiation
Implementation Method 3
an optical collection system configured to collect scattered radiation, following scattering of said illumination radiation by said metrology mark
Implementation Method 4
adjustable obscuration size and polarization filtering to separate signal and noise radiation
Data Source
AI summary
Disclosed is a metrology sensor apparatus comprising: an illumination system operable to illuminate a metrology mark in on a substrate with illumination radiation; an optical collection system configured to collect scattered radiation, following scattering of the illumination radiation by the metrology mark; and a wavelength dependent spatial filter for spatially filtering the scattered radiation, the wavelength dependent spatial filter having a spatial profile dependent on the wavelength of the scattered radiation. The wavelength dependent spatial filter may comprise a dichroic filter operable to substantially transmit scattered radiation within a first wavelength range and substantially block scattered radiation within a second wavelength range and at least one second filter operable to substantially block scattered radiation at least within the first wavelength range and the second wavelength range.