Metrology Method Using Reference Phase Profiles for Complex-Valued Field Determination
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Solution Overview
Problem
Current metrology methods for phase retrieval in lithographic processes are time-consuming and inefficient, particularly due to the need for sequential measurements at multiple focus levels, which slows down measurement speed and reduces throughput.
Innovation Solution
The method involves obtaining a reference phase profile from nominally identical reference targets and using this profile to determine the complex-valued field for subsequent measurements, allowing for 'phase transplant' and reducing the need for iterative phase retrieval on each individual target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential measurements at multiple focus levels are performed for phase retrieval, then measurement precision is improved, but acquisition time increases and throughput decreases
Solution Approach 1:
The patent performs phase retrieval measurements on reference targets in advance to pre-calculate and store reference phase profiles. These pre-calculated reference profiles are then used during production measurements to determine complex-valued fields without performing iterative phase retrieval on each production target, thereby reducing acquisition time while maintaining measurement precision.
Solution Approach 2:
The patent creates a copy of the phase information by measuring reference targets and storing their phase profiles. During production, instead of performing time-consuming iterative phase retrieval on each target, the system uses the stored reference phase profiles as templates to quickly determine the complex-valued fields of production targets, effectively copying the phase retrieval process to reduce measurement time.
2Measurement precision
If iterative phase retrieval is performed on each individual target, then measurement precision is improved, but acquisition time increases
Solution Approach 1:
The patent performs the computationally intensive phase retrieval process in advance on reference targets that are nominally identical to production targets. The reference phase profiles are pre-calculated and stored, eliminating the need to perform iterative phase retrieval on each production target during actual measurement, thus reducing acquisition time while preserving measurement precision.
Solution Approach 2:
The patent introduces reference targets as intermediaries between the measurement system and production targets. By measuring reference targets and storing their phase profiles, the system creates an intermediary database that can be queried during production measurements, avoiding the need to perform time-consuming iterative phase retrieval on each production target while maintaining the required measurement precision.
Data Source
AI summary
Disclosed is a method of measuring a structure, and associated metrology device and computer program. The method comprises obtaining an amplitude profile of scattered radiation relating to a measurement of a first structure on a first substrate and obtaining a reference phase profile relating to a reference measurement of at least one reference structure on a reference substrate. The at least one reference structure is not the same structure as said first structure but is nominally identical in terms of at least a plurality of key parameters. The method further comprises determining a complex-valued field to describe the first structure from the amplitude profile and reference phase profile.