Charged Particle Beam Focal Position Control via Electrostatic and Magnetic Fields
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Solution Overview
Problem
Charged particle beam apparatuses, such as scanning electron microscopes, face long processing times due to magnetic hysteresis issues in the objective lens, which affect image quality and throughput, especially with increasing acceleration voltages and complex semiconductor structures.
Innovation Solution
A charged particle beam apparatus that includes an excitation control unit for the electronic lens, an electrostatic field control unit, a focal position height estimation unit, and a control unit to determine necessary adjustments in the excitation of the electronic lens based on sample surface height comparisons, allowing for efficient focal position control using both magnetic and electrostatic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If magnetic field control is used for focal position adjustment, then the control range is wide, but the processing time increases due to magnetic hysteresis removal operations
Solution Approach 1:
The patent divides the focal position control into two segments: electrostatic field control for fine adjustments within a narrow range (avoiding hysteresis issues), and magnetic field control for large adjustments when necessary. This segmentation allows the system to optimize between speed and range by selecting the appropriate control method based on the required adjustment magnitude.
Solution Approach 2:
The patent dynamically switches between electrostatic and magnetic field control modes based on the required focal position adjustment. The system determines whether electrostatic control alone is sufficient or if magnetic field assistance is needed, thereby adaptively optimizing the processing time while maintaining the required control range.
2Measurement precision
If acceleration voltage is increased to observe complex semiconductor structures, then the observation capability improves, but the magnetic field requirement increases leading to longer hysteresis removal time
Solution Approach 1:
The patent applies partial magnetic field control by using electrostatic fields for the majority of focal adjustments and resorting to magnetic field control only when the required adjustment exceeds the electrostatic range. This partial use of magnetic control significantly reduces the frequency of hysteresis removal operations while maintaining the ability to handle high acceleration voltage requirements for complex semiconductor observation.
3Loss of time
If electrostatic field control is used exclusively for focal position, then the processing time is reduced, but the control range becomes too narrow
Solution Approach 1:
The patent introduces a control unit that acts as an intermediary, intelligently selecting between electrostatic and magnetic field control methods. The control unit evaluates the required focal adjustment and determines whether electrostatic control suffices or if magnetic field assistance is needed, thereby extending the effective control range beyond what electrostatic fields alone can provide while maintaining fast processing speeds.
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 reduces processing time by optimizing focal position control, improving throughput, and minimizing the impact of magnetic hysteresis, thereby enhancing the productivity of semiconductor inspection processes.
Implementation Method 1
an electrostatic field control unit that controls the focal position by changing a control value of an electrostatic field
Implementation Method 2
The objective lens is configured with an excitation coil and a surrounding magnetic body
Implementation Method 3
the magnetic field formed in the objective lens is not always proportional to the control current given to the excitation coil, but has a magnetic hysteresis that depends on the history of the excitation change
Data Source
AI summary
There is provided a charged particle beam apparatus that can reduce the processing time. A charged particle beam apparatus includes: an excitation control unit that controls a focal position by changing a control value of excitation of an electronic lens; an electrostatic field control unit that controls the focal position by changing a control value of an electrostatic field; a focal position height estimation unit that estimates a height of the focal position from the control value of the excitation of the electronic lens; and a control unit that controls the excitation control unit and the electrostatic field control unit. The control unit compares the height of the focal position estimated by the focal position height estimation unit with a height of a sample surface of a sample to be observed, and according to a result of comparison, determines whether it is necessary to change the control value of the excitation of the electronic lens before observing the sample.