Optical Inspector for Wafer 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 separate detectors to distinguish between specular reflection and near specular scattered radiation, allowing for effective detection of defects by processing radiation types and determining total reflectivity, surface slope, and scattered radiation intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a normal or oblique laser with a beam block and pinhole is 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 divides the detection of scattered light into two separate detection paths: one for top surface scattered light and one for bottom surface scattered light. By using two detectors positioned at different angles, the system segments the measurement process to avoid the complexity of pinhole-based separation while maintaining measurement precision.
Solution Approach 2:
The patent introduces an intermediary optical element (a mirror or beam splitter) that redirects the scattered light from different surfaces to separate detectors. This intermediary approach eliminates the need for direct pinhole separation and reduces device complexity while preserving the ability to distinguish between top and bottom surface scattered light.
2Measurement precision
If multiple detectors are used to measure different portions of reflected radiation, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent designs the optical system with components that serve multiple functions: the same optical path handles both top and bottom surface scattered light detection, and the detectors are positioned to simultaneously capture different angular distributions of reflected radiation. This multi-functionality reduces the need for additional separate systems while maintaining measurement precision.
3Device complexity
If scattered light from top and bottom surfaces is not separated, then device complexity is reduced, but measurement precision deteriorates due to inability to distinguish defect sources
Solution Approach 1:
The patent employs a dynamic detection approach where detectors are positioned to capture scattered light at different angles that correspond to different surface depths. By analyzing the angular distribution of scattered light dynamically, the system can distinguish between top and bottom surface defects without requiring complex mechanical separation mechanisms.
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 without the need for pinholes, improving light extraction efficiency and reducing resource waste by identifying defective areas before further processing.
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 separating mirror that receives reflected radiation from the sample, a first detector that receives a first portion of the reflected radiation from the separating mirror
Data Source
AI summary
An optical inspector includes a radiating source, a time varying beam reflector, a telecentric scan lens, a separating mirror, and a first and second detector. The radiating source is configured to irradiate a first position 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 telecentric scan lens directs specular reflection and near specular scattered radiation to the time varying beam reflector. The specular reflection is directed by the separating mirror to the first detector. The near specular scattered radiation is not reflected by the separating mirror and propagates to the second detector. In response, the optical inspector determines the total reflectivity, the surface slope, or the near specular scattered radiation intensity of the sample.