Wafer LED Inspection Using Absolute and Relative Fluorescence
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Solution Overview
Problem
Existing methods for determining the quality of light-emitting elements on a wafer based on photoluminescence luminance are inaccurate due to process unevenness, leading to difficulties in distinguishing defective products when the luminance distribution is gentle, and relative luminance is affected by dust or dark regions.
Innovation Solution
An inspection apparatus and method that calculates the relative luminance of a light-emitting element based on its fluorescence compared to surrounding elements, correcting for the influence of adjacent elements and edge effects, using a product of absolute and relative luminances to determine quality accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If quality determination is based on absolute luminance value, then measurement is simple, but accuracy deteriorates due to process unevenness causing gentle luminance distribution
Solution Approach 1:
The patent changes the parameter basis from absolute luminance to relative luminance (ratio of target element luminance to average surrounding element luminance). This transformation allows quality determination to remain accurate despite process unevenness affecting absolute values, as the relative comparison normalizes out systematic variations across the wafer surface.
Solution Approach 2:
The patent replaces the simple absolute luminance measurement approach with a relative luminance calculation system that incorporates surrounding element data. This substitution introduces computational processing (comparing target element with neighboring elements) to achieve higher measurement precision in the presence of process variations.
2Measurement precision
If quality determination is based on relative luminance, then process unevenness is compensated, but false non-defective determination occurs when dust or dark regions cover the light-emitting element group
Solution Approach 1:
The patent merges both absolute luminance and relative luminance into a composite determination criterion. By evaluating both metrics simultaneously, the system benefits from relative luminance's ability to compensate for process unevenness while using absolute luminance as a safeguard against false negatives caused by dust or dark regions that affect all elements uniformly.
Solution Approach 2:
The patent introduces a feedback mechanism where the absolute luminance value provides corrective information to the relative luminance assessment. When absolute luminance is extremely low (indicating dust coverage or dark regions), the system overrides the relative luminance result and correctly identifies the element as defective, preventing false non-defective determinations.
3Ease of manufacture
If only absolute luminance is used for determination, then calculation is simple, but gentle luminance distribution due to process unevenness makes accurate quality determination difficult
Solution Approach 1:
The patent transforms the determination parameter from absolute luminance to relative luminance, which is calculated as the ratio of the light-emitting element's luminance to the average luminance of surrounding elements. This parameter change compensates for process unevenness and gentle luminance distribution, improving measurement precision while maintaining reasonable computational simplicity.
4Measurement precision
If relative luminance is used to determine quality, then dust or dark region effects are normalized, but defective elements in dark regions are incorrectly identified as non-defective
Solution Approach 1:
The patent combines absolute luminance and relative luminance assessments into a unified quality determination system. The absolute luminance serves as a protective indicator that prevents dust and dark region interference from causing false non-defective identifications, while relative luminance handles normal process variations.
Solution Approach 2:
The system uses absolute luminance as a feedback check on relative luminance results. When absolute luminance falls below a threshold (indicating dust coverage or dark region contamination), the system overrides the relative luminance assessment and correctly flags the element as defective, thereby eliminating the harmful effect of dust and dark regions on measurement 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
Accurately determines the quality of light-emitting elements by considering both absolute and relative luminances, effectively identifying defective products even when covered in dust or dark regions, enhancing the precision of photoluminescence-based inspections.
Implementation Method 1
an excitation light source that generates excitation light to irradiate the object, an imaging unit that images fluorescence from the object
Implementation Method 2
a method for determining the quality of a light-emitting element group formed on a wafer, there has been a known method of observing the photoluminescence emitted by a light-emitting element
Data Source
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AI summary
An inspection apparatus is an inspection apparatus for inspecting a sample in which a plurality of light-emitting elements including a first light-emitting element and a second light-emitting element arranged around the first light-emitting element is formed, the inspection apparatus including an excitation light source that generates excitation light to irradiate the sample, a camera that images fluorescence from the sample, and a determining unit that calculates a relative luminance of fluorescence from the first light-emitting element based on the fluorescence from the first light-emitting element and fluorescence from the second light-emitting element imaged by the camera, and compares a calculated value based on an absolute luminance and the relative luminance of the fluorescence from the first light-emitting element with a predetermined threshold value, thereby determining a quality of the first light-emitting element.