Commutation Offset Determination for Magnetic Levitation Stages

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Solution Overview

Problem

In semiconductor processing, determining the commutation offset for movers in exposure apparatuses is critical for precise positioning, but existing methods lack accuracy, leading to inefficiencies and reduced force generation, especially with errors in calculated versus real offsets.

Innovation Solution

A method involving closed-loop control of the mover assembly to determine commutation offsets by imparting a disturbance and evaluating forces, using a compensation map to improve positioning accuracy and efficiency, applicable to both planar and linear motor arrangements like magnetic levitation stages.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the commutation offset is calculated using conventional methods, then the positioning can be maintained, but the force generation is reduced and positioning accuracy deteriorates due to errors between calculated and real offsets

Engineering Contradiction:

Improvecommutation offset accuracyVSAvoidmover force generation efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent applies feedback by measuring the actual forces generated by the mover in response to applied voltages and using these measurements to iteratively adjust the commutation offset values. The system continuously refines the offset by comparing expected forces (based on sinusoidal models) with actual measured forces, thereby improving both measurement precision and force generation efficiency through closed-loop optimization

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs self-calibration by automatically determining its own commutation offset values without requiring external intervention or complex alignment procedures. The mover assembly itself generates the test forces and measurements needed to calculate the correct offset values, enabling the system to self-optimize its performance

Inventive Principle:

Principle #25Self-service

2Manufacturing precision

If the commutation offset error is three percent, then the system operates with acceptable positioning, but the force generated is only ninety-eight percent of maximum possible

Engineering Contradiction:

Improvepositioning accuracyVSAvoidmover force output

Core Design Contradiction:

Manufacturing precisionVSPower

Solution Approach 1:

The patent systematically varies the commutation offset parameters to find the optimal values that maximize force generation. By treating the commutation offset as a tunable parameter and using measurement data to identify the precise value that aligns with the actual magnetic pole positions, the system recovers both positioning accuracy and full force output capability

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the commutation offset error increases to seven percent, then positioning remains functional, but force generation drops to approximately ninety percent of maximum

Engineering Contradiction:

Improveoperational stabilityVSAvoidmover force output

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The patent replaces mechanical alignment methods with an electrical/measurement-based approach to determine commutation offset. Instead of relying on mechanical positioning or visual alignment, the system uses voltage application and force measurement to electronically identify the correct offset values, achieving higher precision and full power output

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 allows for precise and efficient positioning of stages, enhancing the manufacturing of high-density semiconductor wafers by accurately determining commutation offsets, thereby optimizing force generation and reducing errors.

Implementation Method 1

each of the movers includes a coil array that interacts with a magnet assembly

Methodology Applied

Scientific EffectElectromagnetic force: Lorentz Force

Implementation Method 2

The measurement system constantly monitors the position of the reticle and the wafer

Methodology Applied

Scientific EffectInterferometry: Interference

Data Source

PatentUS9465305B2Method for determining a commutation offset and for determining a compensation map for a stage

Publication Date: 2016.10.11 NIKON CORP

AI summary

A method for determining a commutation offset for a mover (250A) of a mover assembly (220C) that moves and positions a stage (220A) relative to a stage base (220B) includes controlling the mover assembly (220C) in a closed loop fashion to maintain the position of the stage (220A) along a first axis and along a second axis with the stage (220A) levitated above the stage base (220B). The method also includes the steps of (i) directing current to a coil array (240) of the mover assembly (220C) so that the mover assembly (220C) imparts a disturbance on the stage (220A); and (ii) evaluating one or more forces generated by the mover assembly (220C) as a result of the disturbance on the stage (220A) created by the mover (250A). Further, a method for generating a compensation map (1402) includes sequentially directing a plurality of excitation signals to the control of the mover assembly (220C) and determining the control commands that result from the plurality of excitation signals.