Guard Ring Fringe Field Compensation for Wafer Edge Inspection
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Solution Overview
Problem
Current electron-optical inspection systems face challenges in accurately inspecting the edge region of semiconductor wafers due to fringe fields, which cause electron beam position errors, defocus, and astigmatism, leading to degraded defect location accuracy and image quality.
Innovation Solution
An electron-optical system with a guard ring device and a controller that adjusts its characteristics to compensate for fringe fields, using a look-up table to mitigate the effects of dipole and quadrupole fields, thereby improving electron beam imaging at the wafer edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If electron beam inspection is performed at the edge of wafer, then the inspection coverage is improved, but the image quality and defect location accuracy deteriorate due to fringe fields
Solution Approach 1:
A guard ring device is introduced as an intermediary component between the electron beam system and the wafer edge. The guard ring generates compensating electric fields that counteract the fringe fields, serving as a mediator to eliminate the harmful effects of fringe fields while enabling extended inspection coverage at the wafer edge
Solution Approach 2:
The system dynamically adjusts operational parameters including guard ring voltage, electron beam energy, and focus settings based on the position relative to the wafer edge. By changing these parameters adaptively, the system maintains optimal image quality and defect location accuracy across different inspection regions
2Area of stationary object
If electron beam inspection is performed at the edge of wafer, then the inspection coverage is improved, but the image quality deteriorates due to fringe field effects
Solution Approach 1:
The guard ring device acts as an intermediary that generates compensating electric fields to counteract fringe field effects. This mediator structure protects the electron beam from fringe field disturbances, maintaining image quality at the wafer edge while extending inspection coverage
Solution Approach 2:
The system applies preliminary compensating electric fields through the guard ring before the electron beam encounters fringe field effects. By preemptively counteracting the fringe fields, the system prevents image quality degradation before it occurs during edge inspection
3Measurement precision
If guard ring device is added to compensate for fringe fields, then the defect location accuracy is improved, but the device complexity increases
Solution Approach 1:
The guard ring device serves multiple functions simultaneously: it generates compensating electric fields, provides electrical shielding, and acts as a reference electrode for positioning. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving improved defect location accuracy
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
The system effectively reduces fringe field impacts, correcting beam position offset errors, defocus, and astigmatism, enhancing defect location accuracy and image quality at the wafer edge.
Implementation Method 1
a guard ring device disposed between the edge of the sample and the sample position reference device to compensate for one or more fringe fields
Data Source
AI summary
An electron-optical system for inspecting or reviewing an edge portion of a sample includes an electron beam source configured to generate one or more electron beams, a sample stage configured to secure the sample and an electron-optical column including a set of electron-optical elements configured to direct at least a portion of the one or more electron beams onto an edge portion of the sample. The system also includes a sample position reference device disposed about the sample and a guard ring device disposed between the edge of the sample and the sample position reference device to compensate for one or more fringe fields. One or more characteristics of the guard ring device are adjustable. The system also includes a detector assembly configured to detect electrons emanating from the surface of the sample.