SEM Control Electrodes Neutralize Charge-Up
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In semiconductor manufacturing, low-voltage scanning electron microscopes (LVSEM) face challenges in achieving high spatial resolution and throughput due to charge-up issues on insulative sample surfaces, which result in image distortion and reduced detection of secondary electrons.
Innovation Solution
The implementation of a scanning electron microscope design with a magnetic objective lens and control electrodes that generate electrostatic extraction and reflection fields during line-scanning and beam-retracing periods, respectively, to neutralize positive charges and maintain charge balance on the sample surface, thereby eliminating charge-up within a frame cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-voltage electron beam is used to reduce radiation damage on the sample surface, then the sample damage is reduced, but charge-up occurs on the insulative sample surface resulting in image distortion and reduced secondary electron detection
Solution Approach 1:
The patent applies preliminary anti-action by generating negative charges during beam retrace periods to counteract the positive charge-up that occurs during the imaging scanning periods. The control electrode generates an electrostatic reflection field during retrace to reflect secondary electrons back to the sample, neutralizing positive charges before they cause significant image distortion. This preemptive charge neutralization allows the use of low-voltage beams on insulative samples without suffering from charge-up effects.
2Productivity
If the primary electron beam current is increased to improve throughput, then the inspection speed is improved, but more positive charges are built up on the sample surface that cannot dissipate quickly during a frame cycle
Solution Approach 1:
The patent implements periodic action by alternating between imaging scanning periods (where positive charges are generated) and beam retrace periods (where negative charges are generated to neutralize the positive charges). During each retrace period, the control electrode switches to generate an electrostatic reflection field that reflects secondary electrons back to the sample surface, creating a periodic charge neutralization cycle. This allows higher beam currents to be used during imaging while the periodic retrace neutralization prevents charge accumulation.
3Measurement precision
If the dwell time and probe current of the primary electron beam are increased to improve signal detection, then the secondary electron detection is improved, but the charge-up on the sample surface increases
Solution Approach 1:
The patent applies feedback by using the beam retrace periods to sense and counteract the charge-up condition that develops during imaging. The control electrode dynamically adjusts the electrostatic field during retrace based on the charge accumulation that occurred during the preceding imaging period. This feedback mechanism allows optimization of dwell time and probe current for improved secondary electron detection while automatically compensating for the resulting charge-up through the retrace neutralization process.
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 allows for high-resolution imaging with a large field of view and high throughput by effectively eliminating charge-up, ensuring non-destructive defect inspection and critical dimension measurement in semiconductor manufacturing.
Implementation Method 1
During each period of line-scanning within a frame cycle of imaging scanning, the voltage is set at a first value so as to generate an electrostatic extraction field on the surface
Implementation Method 2
During each period of beam-retracing within the frame cycle of imaging scanning, the voltage is set at a second value so as to generate an electrostatic reflection field above the sample
Implementation Method 3
a magnetic objective lens, a control electrode between said magnetic objective lens and a surface of a sample to be observed
Implementation Method 4
the incident electron beam (typically called as primary electron beam) of the SEM interacts with the materials of the sample surface and consequently builds a radiation damage and a charge-up
Data Source
AI summary
The present invention provides means and corresponding embodiments to control charge-up in an electron beam apparatus, which can eliminate the positive charges soon after being generated on the sample surface within a frame cycle of imaging scanning. The means are to let some or all of secondary electrons emitted from the sample surface return back to neutralize positive charges built up thereon so as to reach a charge balance within a limited time period. The embodiments use control electrodes to generate retarding fields to reflect some of secondary electrons with low kinetic energies back to the sample surface.