Servo Control Slip Compensation for Lithography Positioning
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Solution Overview
Problem
Conventional servo control systems in lithographic apparatuses face challenges in accurately positioning objects due to slip between the movable support and the object, especially at high accelerations, leading to imaging errors such as focus and overlay errors.
Innovation Solution
A servo control system with a slip compensation device that measures the object's position relative to the movable support and adds a compensation signal to the error signal, allowing for precise positioning by accounting for slip between the object and the support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high accelerations are used to increase productivity, then throughput is improved, but slip between the patterning device and support occurs causing positioning errors
Solution Approach 1:
The patent implements a feedback mechanism where a sensor measures the actual position of the patterning device relative to the support during acceleration. This measured position is fed back to the control system, which calculates the slip amount and compensates for it by adjusting the setpoint position. This closed-loop feedback enables high acceleration movements while maintaining positioning accuracy through real-time correction of slip-induced errors.
Solution Approach 2:
The patent changes the control parameter from simply controlling the support position to controlling the pattern position by introducing a slip compensation term. The setpoint position is modified to account for measured slip: setpoint_position = support_position - slip_amount. This parameter transformation allows the system to maintain pattern positioning accuracy even when the support experiences acceleration-induced slip.
2Device complexity
If conventional servo control is used to simplify the system, then device complexity is reduced, but positioning accuracy deteriorates due to unaccounted slip
Solution Approach 1:
The patent adds a relatively simple feedback element - a position sensor and slip compensation calculation - to the conventional servo control system. This feedback mechanism directly measures the slip phenomenon and compensates for it, providing high positioning accuracy without requiring a complete redesign of the control system or additional complex mechanical structures.
3Loss of time
If acceleration is increased to reduce cycle time, then productivity is improved, but slip occurs causing imaging errors
Solution Approach 1:
The patent uses real-time feedback from a position sensor to detect and compensate for slip during high-acceleration movements. By continuously measuring the actual pattern position and adjusting the setpoint accordingly, the system maintains positioning accuracy even during rapid acceleration and deceleration phases, enabling short cycle times without sacrificing imaging quality.
Solution Approach 2:
The patent performs preliminary measurement of the slip characteristic during acceleration phases and uses this information to pre-calculate compensation values. The control system determines the slip amount based on measured acceleration and pre-established slip characteristics, allowing it to proactively adjust positioning before imaging occurs, thus preventing imaging errors rather than correcting them afterward.
Data Source
AI summary
A servo control system to control a position of an object supported by a movable support includes a first measurement system to measure a position of the movable support, a comparative device to provide an error signal based on the comparison between a measured movable support position and a desired movable support position, a controller unit to provide a control signal based on the error signal, and an actuator configured to actuate the movable support based on the control signal. The servo control system further includes a slip compensation device to compensate a slip between the object and the movable support, the slip compensation device including a second measurement system to measure an object position with respect to the movable support, and an addition device to add a slip compensation signal to the measured movable support position or the error signal based on the measured object position.