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Rectangular Amplitude Mask-Based Auto-Focus Method with a Large Range and High Precision for a Micro-LED Wafer

Wenjun He¹, Yufeng Ma¹, Wenbo Wang¹

¹College of Opto-Electronic Engineering, Changchun University of Science and Technology, Changchun 130022, China.

Sensors (Basel, Switzerland)

|September 9, 2023

Summary

A novel auto-focus method uses a rectangular amplitude mask for Micro-LED wafer defect detection. This technique accurately measures defocus amount and direction, crucial for precise inspection systems.

Keywords:

Micro-LED auto-focus eccentric beam rectangular amplitude mask

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Area of Science:

Optics and Photonics
Semiconductor Manufacturing

Background:

Auto-focus technology is critical for Micro-LED wafer defect detection systems.
Accurate measurement of defocus amount and direction is essential for effective defect identification.

Purpose of the Study:

To propose a large-range, high-precision auto-focus method for Micro-LED wafer defect detection.
To address the challenge of accurately measuring defocus in Micro-LED wafer samples.

Main Methods:

A rectangular amplitude mask without a long edge is employed to modulate incident laser beams.
The modulation alters the reflected laser spot shape on the sensor based on wafer defocus.
Defocus amount and direction are simultaneously determined by analyzing the light spot shape.

Main Results:

The auto-focus system achieves a linear range of 480 μm with a 20× microscopy objective.
The measurement accuracy reaches 1 μm.
The method successfully obtains both defocus amount and direction concurrently.

Conclusions:

The proposed auto-focus method offers a large linear range and high accuracy.
Its compact structure makes it suitable for Micro-LED wafer defect detection equipment.
This technique enhances the capabilities of automated inspection in semiconductor manufacturing.