Floating Stage Position Control Against Rotational Vibration
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Solution Overview
Problem
Conventional stack-type stage apparatuses experience increased residual vibration of the floating stage due to rotational vibration of the lower table, which hampers positional accuracy and throughput in semiconductor manufacturing and inspection processes.
Innovation Solution
A stage apparatus configuration that includes a base, a movable first table, a floating second table, position measuring devices for both tables, and a computer system that performs filter processing to remove rotational vibration frequency components from measurement values, allowing precise control and reduced residual vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the floating stage is driven by a drive mechanism with excellent controllability in six-axial directions, then the positional accuracy is improved, but the drive reaction force applied at a height position different from the center of gravity generates rotational moment causing rotational vibration
Solution Approach 1:
A reaction force generation mechanism is introduced as an intermediary component between the drive mechanism and the floating stage. This mechanism generates reaction forces to cancel the rotational moment produced by the drive reaction force, thereby preventing rotational vibration of the lower table while maintaining the benefits of six-axial drive controllability
Solution Approach 2:
The reaction force generation mechanism proactively generates counteracting forces before the rotational vibration can fully develop. By anticipating the rotational moment from the drive reaction force and applying an equal and opposite reaction force, the system prevents the harmful vibration from occurring in the first place
2Ease of operation
If tracking control is performed using position signal from linear scale, then the floating stage position control is achieved, but the rotational vibration of lower table is superimposed on measurement signal increasing residual vibration
Solution Approach 1:
A vibration cancellation mechanism acts as an intermediary between the position measurement system and the control system. It processes the position signal to remove vibration components before the control action is executed, preventing the amplification of rotational vibration through feedback control
Solution Approach 2:
The system uses feedback from position measurement to detect rotational vibration components, then adjusts the reaction force generation accordingly. The feedback loop continuously monitors and compensates for vibration, reducing residual vibration while maintaining accurate tracking control
3Device complexity
If the lower table is guided by a linear guide, then the structural simplicity is maintained, but the rotational vibration affects the measurement accuracy of the floating stage position
Solution Approach 1:
The reaction force generation mechanism serves as a mediator that isolates the measurement system from the mechanical vibrations of the lower table. By actively canceling rotational moments at the source, it protects the precision measurement of the floating stage position without requiring changes to the simple linear guide structure
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 effectively reduces residual vibration of the floating stage, enhancing positional accuracy and improving throughput by actively controlling the stage's movement based on filtered position data, thereby addressing the limitations of conventional systems.
Implementation Method 1
a linear motor that generates a thrust in a driving direction (Y direction) of the stage
Implementation Method 2
a floating portion includes a permanent magnet and an electromagnet, and a floating force in a z direction is obtained by using the linear motor for the driving direction
Data Source
AI summary
Provided is a stage apparatus including: a first table that is movable on a base; a second table that is movable in a state of floating above the first table and includes a first portion and a second portion below the first portion; a first position measuring device that measures a position of the first portion of the second table; a second position measuring device that measures a position of the second portion of the second table; and a computer that controls a motor that drives the second table. The computer drives the second table based on information on the position of the first portion measured by the first position measuring device and information on the position of the second portion measured by the second position measuring device.