Angular-Resolved Spectroscopy for Overlay Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current scatterometry techniques for overlay measurement are limited in detecting small pitch gratings due to the requirement of capturing +1 and −1 orders, which restricts the minimum grating pitch that can be measured, hindering the ability to reduce wafer space and improve measurement precision.
Innovation Solution
An inspection apparatus and method using a high numerical aperture lens to measure an angle-resolved spectrum in the pupil plane, where anti-symmetric components of the spectrum are generated by subtracting the reflected spectrum and its mirror image, allowing for the determination of overlay errors from small pitch gratings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scatterometry techniques are used to measure overlay, then measurement capability is available, but the minimum grating pitch that can be measured is restricted due to the requirement of capturing +1 and -1 diffraction orders
Solution Approach 1:
The patent applies asymmetry by measuring only the +1 diffraction order instead of requiring both +1 and -1 orders. By detecting the asymmetry in the scattered light intensity between opposite sides of the specular reflection, the system can determine overlay without needing to capture symmetric diffraction orders, thus enabling measurement of smaller pitch gratings
Solution Approach 2:
The patent extracts only the necessary information for overlay measurement by isolating the +1 diffraction order and using the asymmetry in its intensity distribution. This extraction approach eliminates the requirement to capture and process both +1 and -1 orders, reducing the minimum pitch constraint while maintaining measurement capability
2Area of stationary object
If smaller pitch gratings are used to reduce wafer space, then wafer space efficiency improves, but conventional scatterometry cannot detect them due to the +1 and -1 order capture requirement
Solution Approach 1:
By measuring the asymmetry in the +1 diffraction order intensity rather than requiring symmetric +1 and -1 orders, the system can detect smaller pitch gratings that would otherwise be invisible to conventional scatterometry, enabling reduced wafer space usage
Solution Approach 2:
The patent changes the measurement parameter from requiring both +1 and -1 diffraction orders to measuring only the +1 order with asymmetry analysis. This parameter change enables detection of smaller pitch gratings, allowing reduced wafer space while maintaining detectability
3Productivity
If in-line measurement techniques are used, then productivity improves by simultaneous production and measurement, but the ability to detect and quantify apparatus errors is limited
Solution Approach 1:
The patent uses a specialized target structure with known geometric relationships as an intermediary between the lithographic apparatus and the measurement system. This target enables the extraction of apparatus error information from routine production exposures, maintaining both productivity and error detection capability
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 the measurement of overlay errors in small pitch gratings, reducing wafer space requirements and improving measurement precision by effectively capturing detailed information about grating structures that were previously inaccessible.
Implementation Method 1
a high numerical aperture lens to collect radiation scattered by a target on the substrate
Implementation Method 2
measuring, in the pupil plane of a high numerical aperture lens, a reflected spectrum of a target on a substrate
Data Source
AI summary
An apparatus and method to determine overlay of a target on a substrate (6) by measuring, in the pupil plane (40) of a high numerical aperture len (L1), an angle-resolved spectrum as a result of radiation being reflected off the substrate. The overlay is determined from the anti-symmetric component of the spectrum, which is formed by subtracting the measured spectrum and a mirror image of the measured spectrum. The measured spectrum may contain only zeroth order reflected radiation from the target.