SEM Overlay Metrology Scan Direction Alignment
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Solution Overview
Problem
Scanning electron microscopy (SEM) overlay metrology systems face challenges with edge blurring due to large e-beam spot diameter and interaction volume, leading to reduced precision and accuracy in overlay measurements.
Innovation Solution
The method involves scanning the electron beam in a direction substantially aligned with or parallel to the feature placement or patterning of overlay target structures, minimizing edge blurring by primarily affecting non-essential edges, thus reducing errors in overlay determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scanning electron microscopy is used with standard scanning directions, then high resolution imaging is achieved, but edge blurring occurs due to electron collection at scanned edge regions
Solution Approach 1:
The patent inverts the conventional scanning approach by scanning parallel to the pattern lines instead of perpendicular to them. This reversal of the scanning direction relative to the pattern orientation causes the electron beam to travel along the edges rather than across them, significantly reducing edge blurring artifacts while maintaining high resolution imaging capability
Solution Approach 2:
The patent introduces asymmetry in the scanning configuration by aligning the scan direction with the pattern line direction rather than using the conventional perpendicular arrangement. This asymmetric scanning approach creates different interaction geometries between the electron beam and pattern edges, reducing the harmful edge blurring effect that occurs with symmetric perpendicular scanning
2Measurement precision
If frame averaging and sophisticated edge detection algorithms are used to reduce edge blurring error, then measurement accuracy improves, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-aligning the scan direction parallel to the pattern lines before the actual measurement process. This preparatory configuration prevents edge blurring from occurring in the first place, eliminating the need for subsequent complex post-processing algorithms and frame averaging operations to correct the artifact
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
This approach enhances the precision and accuracy of SEM overlay metrology by minimizing edge blurring, improving tool matching and tolerance of tool-induced shifts, and reducing nuisance signals from electron collection at edges.
Implementation Method 1
scanning an electron beam across a surface of the sample
Implementation Method 2
detecting electrons from a scanned portion of the surface of the sample including the first set of linear pattern elements
Data Source
AI summary
The present disclosure is directed to a method of performing SEM overlay metrology with scan direction substantially aligned with or parallel to feature placement or patterning of overlay target structures. By scanning target structures in the same or similar direction to the feature placement, blurring at the edges of interest is avoided and a line-to-line or edge-to-edge offset between pattern elements is less susceptible to error from blurring at scanned edges of interest. For example, at least two linear pattern elements corresponding to at least two sample layers may be scanned along or parallel to the direction of feature placement (i.e., along or parallel to long edges of the pattern elements).