Optical Inspector for GaN Wafer Surface Defect Detection
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Solution Overview
Problem
Detecting defects in transparent or opaque wafers, particularly in GaN layers on sapphire substrates, is challenging due to the difficulty in separating scattered light from the top and bottom surfaces, which affects light extraction efficiency and LED performance.
Innovation Solution
A surface optical inspector system that uses a time-varying beam reflector, telecentric scan lens, and detectors to distinguish between specular reflection and near specular scattered radiation, allowing for the separation of top and bottom surface scattered light without the need for a pinhole, utilizing a rotating polygon, bi-cell photodiode, and photomultiplier tube detectors to analyze radiation and determine defect presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pinhole and beam block are used to separate top and bottom surface scattered light, then the scattered light separation is achieved, but the device complexity increases and measurement precision is compromised
Solution Approach 1:
The patent segments the scattered light collection into two distinct optical paths: one for top surface scattered light and one for bottom surface scattered light. By using separate collection lenses and detectors for each surface, the system achieves precise scattered light separation without requiring complex pinhole arrangements or beam blocks, thus resolving the contradiction between measurement precision and device complexity.
2Ease of manufacture
If oblique or normal laser inspection is used, then the inspection method is simple, but the ability to separate top and bottom surface scattered light is insufficient
Solution Approach 1:
The patent applies local quality by configuring the optical system with different collection angles for top and bottom surface inspection. The top surface collection lens and bottom surface collection lens are positioned and oriented differently to selectively collect scattered light from specific surfaces, enabling precise surface-specific inspection while maintaining overall system simplicity.
3Measurement precision
If multiple detectors are used to measure different radiation types, then the defect detection accuracy improves, but the device complexity increases
Solution Approach 1:
The patent implements multi-functionality by designing a detector system where each detector serves multiple purposes. The first detector simultaneously measures specular reflection and top surface scattered light, while the second detector measures bottom surface scattered light. This universal approach enables comprehensive defect detection across different radiation types without requiring separate specialized detectors for each measurement, thus reducing overall system complexity while maintaining high detection accuracy.
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 detection of defects on wafer surfaces, improving light extraction efficiency and reducing the risk of defective LED production by effectively separating and analyzing scattered radiation from both surfaces, thus enhancing the quality control of wafer inspection processes.
Implementation Method 1
a time varying beam reflector, a radiating source that irradiates a first position on the time varying beam reflector with source radiation
Implementation Method 2
a telecentric scan lens that directs the source radiation from the time varying beam reflector onto a sample
Implementation Method 3
a first detector that receives a first portion of the reflected radiation from the separating minor, and a second detector that receives a second portion of the reflected radiation
Data Source
AI summary
An optical inspector includes a radiating source, a time varying beam reflector, a telecentric scan lens, a first and second lens, a field stop, and a detector. The radiating source irradiates a first position of on the time varying beam reflector with a source beam. The time varying beam reflector directs the source beam to the telecentric scan lens, which in turn directs the source beam to a sample. The first lens focuses scattered radiation from the sample to generate multiple scan lines at a first focal plane. The field stop is positioned at the first focal plane to block one or more scan lines at the first focal plane. The scan line not blocked by the field stop propagates to the second lens. The second lens de-scans the scan line and generates a point of scattered radiation at a second focal plane where the detector input is located.