FIB Scan Pattern Modification for Time-of-Flight Error Compensation
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Solution Overview
Problem
Charged particle beam systems face precision issues due to time-of-flight errors, particularly at short dwell times and low landing energies, leading to patterning errors and misdirection of particles, which are problematic in applications like circuit edit and gas-assisted etching.
Innovation Solution
The implementation of digital filters, applied prior to digital-to-analog conversion, or the use of analog filters and signal amplifiers with lower bandwidth to compensate for time-of-flight errors, effectively reducing or eliminating over-shoot effects by altering the scan pattern and deflector signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the deflector is placed above the objective lens to minimize working distance, then the working distance is reduced, but the beam aberration increases due to deflection away from the lens center
Solution Approach 1:
The pre-lens two-stage deflector applies preliminary deflection actions before the beam enters the objective lens. The first stage deflects the beam to one side of the optical axis, and the second stage deflects it back to the other side, ensuring the beam passes through the center of the objective lens while achieving the desired deflection on the work piece.
Solution Approach 2:
The deflection function is segmented into two separate stages rather than using a single deflector. This segmentation allows the beam to be deflected in two steps, maintaining passage through the lens center while achieving the required positional deflection on the work piece.
2Productivity
If the beam dwell time is reduced for high-speed patterning, then the productivity increases, but time-of-flight errors cause patterning precision to deteriorate
Solution Approach 1:
The system pre-calculates and applies time-of-flight compensation to the deflection signals before the beam actually deflects. By anticipating the delay caused by finite particle velocity, the system adjusts the timing of voltage changes in the deflector stages to ensure accurate beam positioning even at short dwell times.
Solution Approach 2:
The system incorporates feedback mechanisms that account for the time-of-flight delay, adjusting the deflection signals based on the known transit time of particles through the deflector. This feedback loop ensures that the beam reaches the correct position despite the finite response time.
3Object-affected harmful factors
If the landing energy is reduced for gentle processing, then the damage to the work piece decreases, but the beam becomes more susceptible to time-of-flight errors
Solution Approach 1:
The time-of-flight compensation is applied in advance to the deflection signals, accounting for the longer transit time experienced by low-energy particles. This preliminary adjustment ensures that even though low-energy beams are more affected by TOF errors, the compensation pre-corrects for these delays.
Solution Approach 2:
The system dynamically adjusts the deflection signal parameters based on the landing energy of the beam. For lower energy beams, the system modifies the timing and magnitude of deflection voltages to compensate for the increased susceptibility to time-of-flight errors.
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 significantly improves the precision of particle delivery, reducing patterning errors and ensuring accurate processing of work pieces, even at short dwell times and low landing energies, by compensating for time-of-flight artifacts.
Implementation Method 1
correcting time-of-flight errors that occur with beams having short dwell times and/or low landing energy
Implementation Method 2
In focused ion beam systems, the deflection optics are typically electrostatic. Electrostatic deflectors for focused ion beams are typically octupoles
Implementation Method 3
The focusing optics focus the beam into a spot or a predefined shape on the surface of a sample. Focusing optics typically include a combination of condenser lenses and an objective lens. The lens can be electrostatic, magnetic, or various combinations of the two
Implementation Method 4
One type of aberration, referred to as 'beam interaction' occurs because the particles in the beam, all having the same electrical charge, repel each other
Data Source
AI summary
An improved method of directing a charged particle beam that compensates for the time required for the charged particles to traverse the system by altering one or more of the deflector signals. According to one embodiment of the invention, a digital filter is applied to the scan pattern prior to digital-to-analog (D/A) conversion in order to reduce or eliminate over-shoot effects that can result from TOF errors. In other embodiments, analog filters or the use of signal amplifiers with a lower bandwidth can also be used to compensate for TOF errors. By altering the scan pattern, over-shoot effects can be significantly reduced or eliminated.