Level Sensor Topography Fusion for Lithography Focus Control
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Solution Overview
Problem
Current methods for measuring surface topography of patterned substrates in lithographic processes are either slow and destructive or provide low resolution, making it difficult to accurately predict defects and maintain focus control in lithographic processes.
Innovation Solution
A method and apparatus that combine measured topography data with intra-die topology knowledge to derive higher resolution topography data, using a level sensor system and high-resolution metrology devices like electron beam metrology, and referencing measurements to reduce process dependency and improve focus control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If specialist metrology tools such as interferometric optical surface profilers are used to measure surface topography, then measurement precision is improved, but measurement speed deteriorates and the measurement becomes highly process dependent
Solution Approach 1:
The patent replaces mechanical contact-based measurement systems with optical measurement systems. Specifically, it uses optical diffraction patterns and light interference principles to measure surface topography without physical contact, thereby eliminating mechanical limitations and achieving both high precision and fast measurement speeds.
Solution Approach 2:
The patent changes the measurement parameters by using optical wavelength-scale measurements instead of mechanical probe measurements. By analyzing diffraction pattern parameters (intensity distributions, phase information) and optical path differences, the system achieves high-resolution topography measurement at the speed of light rather than mechanical scanning speeds.
2Reliability
If a metal layer is applied to the substrate before measurement to remove process dependency, then measurement reliability is improved, but the substrate is destroyed
Solution Approach 1:
The patent creates an optical copy or representation of the surface topography through diffraction patterns rather than physically altering the substrate. The measured optical parameters (diffraction intensities, phases) serve as copies of the actual surface geometry, allowing repeated non-destructive measurements without applying metal layers or other consumable coatings.
Solution Approach 2:
The substrate's own optical properties (refractive index, surface geometry) are utilized for measurement without requiring external coatings or preparations. The surface itself serves as the measurement target and reference, eliminating the need for metal layer application and subsequent substrate destruction.
3Productivity
If low resolution topography data is used, then measurement speed is improved, but defect prediction accuracy deteriorates
Solution Approach 1:
The patent utilizes optical wave interference and diffraction phenomena (analogous to vibration principles) where the wavelength of light provides inherent high-resolution sampling of the surface. The oscillating nature of light waves enables precise measurement of surface height variations at the nanometer scale, achieving both speed and precision simultaneously.
Solution Approach 2:
The patent transitions from direct spatial domain measurement to frequency domain analysis by examining diffraction patterns. The diffraction order and angular distribution provide additional dimensional information about surface features, enabling high-resolution topography reconstruction from optically measured parameters that would otherwise require much finer spatial sampling.
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
Enables faster, non-destructive, high-resolution topography measurements that improve defect prediction and focus control, reducing the risk of out-of-focus features and enhancing overall lithographic process accuracy.
Implementation Method 1
a first measurement system operable to measure topographical variation across a substrate on which one or more patterns have been applied
Implementation Method 2
a processor system operable to combine the measured topography data with knowledge relating to intra-die topology to obtain derived topography data having a resolution greater than that of the first measurement system
Data Source
AI summary
A method of determining topographical variation across a substrate on which one or more patterns have been applied. The method includes obtaining measured topography data representing a topographical variation across a substrate on which one or more patterns have been applied by a lithographic process; and combining the measured topography data with knowledge relating to intra-die topology to obtain derived topography data having a resolution greater than the resolution of the measured topography data. Also disclosed is a corresponding level sensor apparatus and lithographic apparatus having such a level sensor apparatus, and a more general method of determining variation of a physical parameter from first measurement data of variation of the physical parameter across the substrate and intra-die measurement data of higher resolution than the first measurement data and combining these.