Wafer Positioning Rotor With Feedback Height Compensation
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Solution Overview
Problem
Existing wafer inspection systems face challenges in accurately positioning wafers for high-speed, high-throughput defect detection, particularly in unpatterned wafers, due to issues like tilt and thickness variations, which affect the precision of optical inspection methods.
Innovation Solution
A positioning device with a rotor and stator configuration using air bearings, combined with rotary and linear actuators, allows for high-speed rotational and axial movements, compensated by decoupled actuators and encoders, ensuring precise positioning and compensation for tilt and thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wafer is rotated at high speeds to increase inspection throughput, then productivity is improved, but positioning precision deteriorates due to tilt and thickness variations
Solution Approach 1:
The patent employs feedback control by continuously measuring the actual position of the wafer surface using encoders on both the rotation axis and height axis, comparing it with the target position, and dynamically adjusting the height actuator to compensate for deviations caused by tilt and thickness variations during high-speed rotation
Solution Approach 2:
The system transitions from static positioning to dynamic positioning by implementing real-time control during rotation. The height actuator dynamically adjusts the wafer position at high speeds (up to 100 Hz) to maintain optimal focus, enabling high-speed inspection without sacrificing precision
2Measurement precision
If the focal zone of the light beam is reduced to improve inspection precision, then measurement precision is improved, but the tolerance for positioning errors decreases
Solution Approach 1:
The feedback control system continuously monitors the actual wafer surface position and dynamically adjusts the height actuator to maintain the wafer surface within the narrow focal zone of the focused light beam, enabling the use of tight focal zones without compromising reliability
3Measurement precision
If decoupled actuators are used to compensate for tilt and thickness variations, then positioning precision is improved, but device complexity increases
Solution Approach 1:
The positioning system is segmented into independent rotational and height adjustment functions. The rotation actuator handles rotational positioning while the height actuator handles axial positioning, allowing each actuator to be optimized for its specific function and simplifying the control strategy through functional decomposition
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
Enables accurate and high-speed wafer inspection at up to 100 Hz rotation, effectively compensating for tilt and thickness variations, enhancing defect detection precision and throughput.
Implementation Method 1
the rotor (2) is engaged with the stator (3) by a bearing (4) which is configured to allow rotational movement of the rotor (2) around the rotor axis (A) and axial movement along the rotor axis
Data Source
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AI summary
The present invention concerns a positioning device (1) for inspection of wafers and chips, comprising a rotor (2) and a stator (3), the rotor comprising a rotor axis (A) defining a height direction, whereby the rotor (2) is engaged with the stator by a bearing (4) which is configured to allow rotational movement of the rotor (2) around the rotor axis and axial movement along the rotor axis, whereby the device (1) comprises a rotary (RT) actuator (5A, 5B) configured to induce a rotational movement on the rotor, whereby the rotary actuator (5A, 5B)) comprises a static actuator component (5A) attached to the stator, and a mobile actuator component (5B) attached to the rotor and configured to interact with the static actuator component to induce an rotational movement of the rotor with respect to the stator, whereby the device (1) comprises a linear height actuator (6A, 6B) provided along the rotor axis and configured to induce a linear movement on the rotor in the height direction, whereby the linear height actuator (6A, 6B) comprises a static linear component (6A) attached to the stator and a mobile linear component (6B) attached to the rotor and configured to interact with the static linear component to induce an axial movement of the rotor with respect to the stator, whereby the device comprises an RT position measurement component (9) configured for obtaining an angular position of the rotor with respect to the stator and a Z position measurement component (10) configured for obtaining a height position of the rotor with respect to the stator, whereby the device comprises a processor configured for: - receiving a measured height value of the height position obtained by the Z position measurement component; - compare the measured height value with a predefined target height value, and - steer the linear height actuator to compensate for differences between the measured height value and the target height value, thereby steering the height position of the rotor.