Metrology Apparatus Overlay Measurement Thick Stacks
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Solution Overview
Problem
Current metrology apparatuses face challenges in accurately measuring overlay between layers in thick stacks due to unreliable intensity asymmetry and the need for large targets and separate acquisitions, which complicates the determination of interference patterns.
Innovation Solution
A method is proposed to computationally determine the interference electric field by separately determining the electric fields of radiation scattered by each structure and combining them, allowing for accurate overlay measurement even in thick stacks without direct interference measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If intensity asymmetry method is used for overlay determination, then measurement process is simple, but measurement reliability deteriorates for thick stacks
Solution Approach 1:
The patent introduces an intermediary computational process that simulates the scattering of radiation by individual structures and combines these simulations to determine overlay. This computational intermediary allows the system to achieve reliable overlay measurement for thick stacks without directly measuring interference patterns, thus resolving the contradiction between measurement simplicity and reliability.
2Reliability
If pupil plane image method is used for thick stacks, then overlay measurement becomes possible, but device complexity and measurement time increase due to large targets and separate acquisitions
Solution Approach 1:
The patent creates computational copies of the scattering processes for each structure in the stack. By simulating and combining these copied scattering events, the system can determine overlay from a single acquisition without requiring large physical targets or multiple separate measurements, thus reducing device complexity while maintaining measurement capability for thick stacks.
3Ease of operation
If direct interference measurement is performed, then overlay determination is straightforward, but measurement precision deteriorates for thick stacks due to lack of stable intensity regions
Solution Approach 1:
The patent replaces the physical/mechanical process of directly measuring interference patterns with a computational approach. By simulating radiation scattering and combining these simulations, the system determines overlay without relying on stable intensity regions in direct interference measurements, thereby maintaining precision for thick stacks while keeping the process simple.
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 precise overlay calculation by leveraging computational imaging techniques, providing stable and accurate results for thick stacks and other configurations where direct interference is difficult to measure.
Implementation Method 1
determining a first electric field relating to first radiation scattered by the first structure; determining a second electric field relating to second radiation scattered by the second structure
Implementation Method 2
computationally determining the interference of the first electric field and second electric field, to obtain a computationally determined interference electric field
Data Source
AI summary
Disclosed is a method for obtaining a computationally determined interference electric field describing scattering of radiation by a pair of structures comprising a first structure and a second structure on a substrate. The method comprises determining a first electric field relating to first radiation scattered by the first structure; determining a second electric field relating to second radiation scattered by the second structure; and computationally determining the interference of the first electric field and second electric field, to obtain a computationally determined interference electric field.