Imaging Ellipsometry for Accurate Wafer Overlay Error Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing spectroscopic ellipsometry methods for measuring alignment errors in semiconductor processes inaccurately represent overlay errors in die regions due to noise from polarization distortion and fail to accurately measure asymmetry in large-area measurements.
Innovation Solution
An imaging ellipsometer using elliptically polarized light technology measures alignment errors by calculating polarization transmittance through specific angle combinations of a polarizer and analyzer, generating a Mueller matrix to evaluate asymmetry, and minimizing optical system interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large-area measurement method is used to shorten measurement time, then productivity is improved, but measurement precision deteriorates due to noise from polarization distortion
Solution Approach 1:
The measurement process is segmented into two distinct phases: first measuring a reference wafer to obtain polarization transmittance characteristics, then measuring the target wafer using the obtained reference data to eliminate polarization distortion effects. This segmentation allows large-area measurement while maintaining precision by removing optical system noise through differential measurement.
Solution Approach 2:
The measurement system uses feedback by incorporating the reference wafer measurement results into the target wafer measurement process. The polarization transmittance obtained from the reference wafer serves as feedback to correct and eliminate polarization distortion effects during target wafer measurement, thereby maintaining measurement accuracy in large-area measurements.
2Device complexity
If overlay key measurement in scribe lane region is performed, then device complexity is reduced, but measurement precision deteriorates as it does not represent actual die region overlay error
Solution Approach 1:
A reference wafer serves as an intermediary element between the measurement system and the target wafer. By first measuring the reference wafer to characterize the optical system's polarization transmittance, the system creates a reference framework that enables accurate measurement of the target wafer's die region structures, thereby improving overlay error representation without significantly increasing device complexity.
3Measurement precision
If polarization transmittance calculation using reference wafer is performed, then measurement precision is improved by removing optical system noise, but device complexity increases
Solution Approach 1:
The measurement system performs self-characterization by using the reference wafer to automatically determine the polarization transmittance of the optical system. This self-service approach eliminates the need for separate calibration equipment or complex manual characterization procedures, thereby improving measurement precision while minimizing the increase in device complexity.
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
Accurately measures alignment errors by removing optical system noise, enabling precise evaluation of asymmetry in semiconductor wafer structures.
Implementation Method 1
a polarizer on an optical path of incident light on the sample surface, the polarizer being rotatable by a first angle to adjust a polarization direction of the incident light
Implementation Method 2
an analyzer on an optical path of light reflected from the sample surface, the analyzer being rotatable by a second angle to adjust a polarization direction of the reflected light
Implementation Method 3
spectroscopic ellipsometry analysis technology is a technology that irradiates polarized light onto a sample and measures a change in a polarization state of reflected light
Data Source
AI summary
In a method of measuring an alignment error, light is incident on a surface of a reference wafer having a known polarization transmittance at the surface. An image signal is obtained from the reference wafer at a set of angles including a first combination of values of a polarizer angle and an analyzer angle. Polarization transmittance of optical equipment including a polarizer and an analyzer is calculated from the image signal of the reference wafer. Light is incident on a surface of a measurement target wafer having a structure on the surface thereof. An image signal is obtained from the measurement wafer at a set of angles including a second combination of values of the polarizer angle and the analyzer angle. At least a portion of Mueller matrix is generated from the image signal of the measurement wafer.