Focal Position Determination for Substrate Edge Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current coordinate measuring machines face challenges in achieving high measurement repeatability and accuracy, particularly in determining the focal position of edges on a substrate, which affects structure width measurements and overlay evaluations.
Innovation Solution
The method involves acquiring multiple images of a structure with a detector during movement in the Z-coordinate direction, determining intensity profiles and contrast values to find the optimal focus position, using an analytic function to fit measurement points and determine the Z-position for optimal focus, and calculating the position of edges within measurement windows to establish a functional relationship between edge positions and Z-positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple images are acquired during Z-coordinate movement to determine focal position, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The method performs preliminary actions by acquiring multiple images at different Z-positions and calculating contrast values in advance. The contrast maximum method pre-determines the focal position by evaluating contrast at multiple positions before final measurement, allowing subsequent measurements to use this pre-established reference point, thus reducing total measurement time while maintaining accuracy.
2Reliability
If contrast maximum method is used to determine focal position, then measurement repeatability is improved, but device complexity increases
Solution Approach 1:
The system uses self-service by automatically calculating contrast values from the acquired images and determining the focal position at the contrast maximum point without requiring manual intervention or complex external equipment. The evaluation unit autonomously processes the images, computes contrast metrics, and identifies the optimal focal position, simplifying the overall system architecture while ensuring repeatable measurements.
3Measurement precision
If analytic function fitting is applied to determine Z-position, then measurement accuracy is improved, but computational complexity increases
Solution Approach 1:
The method applies parameter changes by using analytic function fitting to transform discrete contrast maximum measurements into a continuous mathematical model. By fitting a function to the measured data points and extracting parameters such as peak position and curvature, the system achieves high precision in determining the focal position while maintaining manageable computational complexity through efficient curve fitting algorithms.
Data Source
AI summary
A method for determining the focal position of at least two edges of structures (31) on a substrate (30) is disclosed. During the movement of a measurement objective (21) in the Z-coordinate direction, a plurality of images of the at least one structure (31) is acquired with at least one measurement window (45) of a detector. An intensity profile of the structure (31) is determined for each image.