Charged Particle Beam Axis Adjustment via Thermal Drift Prediction
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Solution Overview
Problem
High-precision charged particle beam devices face accuracy deterioration due to thermal deformation of lenses caused by changes in excitation current, leading to shifts in the optical axis and fluctuating measurement values, especially in CD-SEM and DR-SEM with multiple lenses, where optimal axis adjustment intervals may vary and frequent adjustments can delay measurement processes.
Innovation Solution
A charged particle beam device and method that utilize a computer system to determine control amounts for axis adjustment based on changes in lens and deflector intensities, using calculation formulas or tables to relate intensity changes to control amounts, thereby stabilizing the beam state under changing observation conditions without increasing measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If axis adjustment is performed frequently to maintain measurement precision, then optical axis stability is improved, but measurement time increases
Solution Approach 1:
The system performs preliminary axis adjustment based on predicted thermal deformation before measurement begins. By calculating the expected thermal drift from lens excitation current changes and pre-adjusting the optical axis, the system eliminates the need for frequent adjustments during measurement, thus maintaining precision without increasing measurement time
Solution Approach 2:
The system implements feedback control by continuously monitoring lens excitation current changes and using this information to dynamically adjust the optical axis. The control unit receives feedback on thermal deformation trends and automatically compensates for axis shifts, maintaining measurement precision while minimizing adjustment frequency
2Stability of the object's composition
If axis adjustment is performed at fixed time intervals to stabilize optical axis, then optical axis stability is improved, but measurement efficiency decreases
Solution Approach 1:
The system transitions from static fixed-interval adjustment to dynamic condition-based adjustment. The control unit dynamically determines when adjustment is needed by monitoring real-time changes in lens excitation current and thermal deformation predictions, performing adjustments only when actual thermal conditions warrant them, thus maintaining optical axis stability without following a rigid time schedule
Solution Approach 2:
The system changes the control parameter from fixed time intervals to variable parameters based on thermal deformation predictions. By using lens excitation current changes and predicted thermal deformation as triggering conditions for adjustment, the system adapts the adjustment timing to actual thermal conditions, improving both optical axis stability and measurement efficiency
3Device complexity
If thermal deformation of lens is allowed to occur naturally with excitation current changes, then device complexity is reduced, but optical axis stability deteriorates
Solution Approach 1:
The control unit acts as an intermediary between lens excitation current changes and optical axis position. It receives information about excitation current changes, calculates predicted thermal deformation, and automatically adjusts the optical axis accordingly, serving as a mediator that compensates for thermal effects without requiring complex mechanical modifications to the lens system
Solution Approach 2:
The system replaces complex mechanical thermal compensation mechanisms with a computational approach. Instead of using mechanical structures to physically compensate for thermal expansion, the system uses calculation formulas to predict thermal deformation and electronically controls the optical axis position, substituting mechanical complexity with computational processing
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
Enables precise observation and inspection under varying conditions while preventing time delays in measurement points by accurately adjusting the optical axis, reducing thermal deformation influences and optimizing axis adjustments.
Implementation Method 1
a lens configured to focus a charged particle beam emitted from a charged particle source
Implementation Method 2
a deflector configured to deflect the charged particle beam or to deflect a charged particle obtained by irradiating a sample with the charged particle beam
Data Source
AI summary
Provided are a charged particle beam device and a charged particle beam adjustment method capable of observing or inspecting a change in observation conditions in a more appropriate beam state while preventing an increase in a time required for each measurement point. The charged particle beam device includes a condenser lens 3 and an objective lens 14 configured to focus an electron beam 4 emitted from an electron source 2, a primary beam scanning deflector 5 or a secondary electron deflector 15, an adjusting element 13 configured to adjust an axis of the electron beam 4, and a control device 9 configured to supply a signal representing a control amount to the adjusting element 13 for control. The control device 9 is configured to determine the control amount by using a change amount of an intensity of the condenser lens 3, the objective lens 14, the primary beam scanning deflector 5, or the secondary electron deflector 15, and a calculation formula or a table showing a relation between the change amount of the intensity and the control amount.