Micro LED Epitaxial Surface Flattening for Accurate PL Inspection
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Solution Overview
Problem
The miniaturization of light-emitting diodes (LEDs) renders traditional probe card testing inadequate, and existing non-contact inspection methods like photoluminescence are affected by the patterned surface of micro LEDs, limiting their application due to light scattering.
Innovation Solution
A semiconductor structure is formed with a patterned substrate, an epitaxial structure, and a filling structure that converts the patterned surface into a flat surface, reducing light scattering and enhancing inspection accuracy using photoluminescence methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If photoluminescence inspection method is used for micro LED testing, then non-contact inspection is achieved, but light scattering from the patterned surface interferes with measurement accuracy
Solution Approach 1:
A filling structure (intermediary material) is introduced between the patterned surface and the inspection system. This filling structure has a refractive index matched to the semiconductor material, serving as an optical intermediary that eliminates air gaps and prevents light scattering, thereby enabling accurate photoluminescence inspection without contact
Solution Approach 2:
The refractive index parameter of the inspection interface is changed by filling the patterned surface with material having a refractive index close to the semiconductor material (e.g., epoxy resin with refractive index 1.5-1.7 matching GaN materials). This parameter change transforms the optical properties of the interface, eliminating scattering and enabling precise measurement
2Measurement precision
If traditional probe card testing is used for LED testing, then contact-based electrical testing is achieved, but the probe card size is too large for miniaturized micro LEDs
Solution Approach 1:
The mechanical contact-based probe card testing system is replaced with a non-contact photoluminescence inspection system. This substitution eliminates the size constraint of physical probe cards, allowing inspection of miniaturized micro LEDs through optical excitation and emission detection without mechanical contact
3Stability of the object's composition
If the patterned surface of the epitaxial structure is directly inspected, then the original surface structure is maintained, but light scattering occurs and interferes with measurement
Solution Approach 1:
The filling structure acts as an intermediary that preserves the underlying patterned surface structure while eliminating its harmful optical effects. The filler material fills the patterns without removing or altering the original semiconductor surface structure, maintaining compositional integrity while preventing light scattering during inspection
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
The method allows for accurate and efficient inspection of micro LEDs by minimizing light scattering, enabling faster and more precise testing of micro LEDs without physical contact.
Implementation Method 1
the patterned surface of the LED can scatter light and interfere the measurement
Implementation Method 2
non-contact inspection methods, such as photoluminescence (PL), have gradually been used in the testing process of micro LEDs
Data Source
AI summary
The present application discloses a method of forming a semiconductor structure. The method of forming the semiconductor structure includes the following steps. A substrate is provided. An epitaxial structure with a patterned surface is formed on the substrate. The substrate is removed to expose the patterned surface of the epitaxial structure. A filling structure is formed over the patterned surface to form a flat surface. A singulation process is performed on the epitaxial structure to form a plurality of light emitting structures.