Focus Metrology Targets Using Aerial Image Transformations
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current focus and dose metrology methods in lithographic printing tools face significant errors due to ambiguity in focus measurements and process variations, leading to inaccuracies in focus and dose measurements, particularly in the Focus Exposure Matrix (FEM) wafer, which affects subsequent measurements and production processes.
Innovation Solution
The method involves positioning multiple focus targets in each wafer field, transforming focus measurements into a single set of results using aerial images-based transformations, allowing for improved calibration and accuracy in focus and dose measurements by sharing information between targets with the same pitch, and designing targets that maintain printability and sensitivity across varying production conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional focus and dose metrology methods are used on FEM wafers, then measurements can be obtained, but significant errors and ambiguities occur due to focus position ambiguity and process variations
Solution Approach 1:
The patent combines multiple measurement signals from different targets (Dense cell and ISO cell) into a unified measurement approach. By merging the focus-insensitive Dense cell signal with the focus-sensitive ISO cell signal, the method eliminates focus position ambiguity while maintaining measurement accuracy, directly resolving the technical contradiction between measurement precision and reliability
Solution Approach 2:
The Dense cell serves as an intermediary element that provides a focus-insensitive reference signal. This intermediary measurement allows the system to de-correlate focus effects from dose effects, enabling accurate focus and dose measurements even when focus position is ambiguous, thus improving both precision and reliability
2Measurement precision
If multiple targets with different pitch and asymmetry are used to de-correlate focus and dose, then measurement accuracy improves, but device complexity and resource requirements increase
Solution Approach 1:
The patent designs metrology targets that serve multiple functions simultaneously. The Dense cell and ISO cell are integrated into a single metrology target structure, allowing both focus measurement and dose measurement to be performed using the same physical target, thereby reducing device complexity while maintaining measurement precision
Solution Approach 2:
The metrology target is segmented into distinct functional cells (Dense cell and ISO cell) with specific characteristics. Each segment serves a particular measurement purpose, but together they provide comprehensive focus and dose measurement capabilities, reducing the need for multiple separate complex targets
Data Source
AI summary
Focus metrology methods and modules are provided, which use aerial-images-based transformations to share measurement information derived from multiple targets and/or to design additional targets to specified compliant targets, which enable simple adjustment of focus targets to changing production conditions. Methods comprise positioning two or more focus targets in each wafer field, conducting focus measurements of the targets, transforming the focus measurements into a single set of results for each field, using a transformation between the targets that is based on the aerial images thereof, and deriving focus results from the single sets of results; and possibly designing the focus targets from specified targets using aerial image parameters of the specified targets.