Magnetic Levitation Stage Z-Axis Motor Layout for Thermal Stability
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Solution Overview
Problem
Existing magnetic levitation stage devices for semiconductor wafers face challenges with thermal deformation due to cable bending reaction forces, magnetization variations, and gap fluctuations, making accurate positioning difficult, especially in charged particle beam apparatuses like scanning electron microscopes.
Innovation Solution
A stage device with a Z-axis motor that includes a guide yoke and a movable element with magnets and coils, arranged to minimize thermal deformation and magnetic field leakage by improving heat dissipation and reducing magnetic flux short-circuits, using a compact magnetic circuit and efficient heat discharge paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reluctance motor is used for Z-axis control in a magnetic levitation stage, then gravity compensation and position control are achieved, but cable bending reaction forces and magnetization variations cause coil current fluctuations and thermal deformation
Solution Approach 1:
The patent segments the coil assembly into multiple independent coils (first coil and second coil) arranged at different positions. This segmentation allows independent control of each coil to compensate for thermal deformation and magnetization variations, maintaining stable coil current and positioning accuracy despite environmental fluctuations.
Solution Approach 2:
The patent implements real-time monitoring and dynamic adjustment of coil current parameters. By detecting temperature changes and magnetization variations, the system adjusts coil current values to compensate for thermal deformation and maintain stable magnetic attraction force, ensuring reliable positioning.
2Force
If permanent magnets are used for gravity compensation in a magnetic levitation stage, then levitation is achieved, but leakage magnetic fields prevent application to charged particle beam apparatus
Solution Approach 1:
The patent extracts and removes the permanent magnets from the magnetic levitation stage design. Instead of using permanent magnets for gravity compensation, the system employs electromagnetic coils that can be precisely controlled to generate only the necessary magnetic attraction force without creating leakage magnetic fields that would interfere with charged particle beam apparatus.
Solution Approach 2:
The patent replaces the permanent magnet-based magnetic field generation system with an electromagnetic coil-based system. This substitution allows precise control of magnetic field generation, eliminating unwanted leakage fields while maintaining the necessary gravitational compensation force for levitation.
3Force
If coil current is increased to compensate for magnetization variation, then magnetic attraction force is maintained, but heat generation increases causing thermal deformation
Solution Approach 1:
The patent implements dynamic current distribution across multiple coils based on real-time temperature and position feedback. Instead of uniformly increasing current to all coils, the system dynamically adjusts current allocation to maintain magnetic attraction force while minimizing heat generation in individual coil regions, preventing thermal deformation.
Solution Approach 2:
The patent employs periodic monitoring and adjustment of coil current with hysteresis control. By using periodic feedback loops with appropriate hysteresis margins, the system maintains stable magnetic attraction force without excessive current increases, thereby controlling heat generation and preventing thermal deformation.
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 solution enables highly accurate positioning with reduced thermal deformation and magnetic field leakage, suitable for charged particle beam apparatuses by stabilizing temperature fluctuations and maintaining precise levitation.
Implementation Method 1
The Z-axis motor magnetically levitates the stage by moving the movable element in the vertical direction with respect to the guide yoke by an electromagnetic force of the plurality of magnets and the guide yoke
Implementation Method 2
a plurality of magnets that are arranged at intervals in a horizontal direction so as to face the guide yoke in the vertical direction and whose magnetic fluxes are oriented in the vertical direction
Data Source
AI summary
Bottom surfaces of a plurality of magnets are coupled by a movable yoke to form a magnetic circuit, and a plurality of coils are detached (separated) from the movable yoke and fixed to a coil fixing portion that is a heat discharging path member, thereby restricting thermal deformation due to temperature fluctuation of a levitation portion. In other words, in a Z-axis motor used for gravity compensation and thrust generation in a vertical direction of a magnetic levitation stage, the movable yoke covering the bottom surfaces of the plurality of magnets whose magnetic fluxes are directed in the vertical direction and are different in direction is provided, and the plurality of coils are arranged separately from the movable yoke and at intervals from the plurality of magnets.