Group III Nitride Semiconductor Buffer Layer Dislocation Reduction
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Solution Overview
Problem
The existing methods for reducing dislocation density in group III nitride semiconductor crystals grown on sapphire substrates are limited by high dislocation densities, which lead to decreased light emission efficiency, increased leak currents, and reduced operating life in devices such as LEDs and electronic elements, and the separation process is inefficient and costly due to issues like incomplete peeling and cracking.
Innovation Solution
A manufacturing method involving the deposition of a metal nitride layer on an AlN template or single crystal substrate, followed by a heating nitridation process to form a metal nitride buffer layer with triangular-pyramid or triangular-trapezoid microcrystals, allowing for chemical etching to separate the substrate and reduce dislocation density, and optimizing the Cr film thickness and nitridation conditions to improve crystallinity and etching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a group III nitride semiconductor layer is grown on a sapphire substrate, then the manufacturing cost is reduced and substrate availability is improved, but the dislocation density increases to about 10^9 to 10^10/cm^2
Solution Approach 1:
An AlN buffer layer is introduced as an intermediary between the sapphire substrate and the group III nitride semiconductor layer. This buffer layer acts as a mediator that reduces lattice mismatch and thermal expansion coefficient differences, thereby significantly reducing dislocation density while still allowing the use of cost-effective sapphire substrates.
Solution Approach 2:
The invention changes the buffer layer material composition parameter from conventional materials to AlN (aluminum nitride), which has lattice constants and thermal expansion coefficients closer to group III nitride semiconductors. This parameter change in buffer layer composition effectively reduces dislocation density while maintaining manufacturing feasibility.
2Reliability
If dislocation density is reduced to improve device reliability and light emission efficiency, then device performance is improved, but the manufacturing process complexity and cost increase
Solution Approach 1:
The AlN buffer layer serves as an intermediary that simplifies the overall manufacturing process by providing a single, effective solution to reduce dislocation density. This approach avoids more complex methods such as heterogeneous epitaxial lateral overgrowth (ELO) or pseudo-substrate techniques, thereby reducing manufacturing process complexity while improving device reliability.
3Temperature
If a laser lift-off method is used to separate the crystal layer from the sapphire substrate, then heat conductivity is improved, but the separation process time increases and cracking occurs
Solution Approach 1:
A separation layer is formed preliminarily during the epitaxial growth process, before the laser lift-off step. This pre-formed separation layer facilitates easier and faster separation, reducing the laser processing time and preventing cracking by providing a predetermined weak interface for separation.
Solution Approach 2:
The separation layer acts as an intermediary interface between the crystal layer and sapphire substrate, enabling clean separation. This intermediary layer prevents direct laser-sapphire interaction that causes cracking and reduces the energy required for separation, thereby reducing process time.
4Manufacturing precision
If the thickness of the AlN buffer layer is increased to reduce dislocation density, then crystal quality is improved, but the separation efficiency decreases and processing time increases
Solution Approach 1:
The buffer layer structure is designed with local quality variation, consisting of a first AlN buffer layer for dislocation reduction and a second AlN buffer layer (separation layer) optimized for separation. This local differentiation allows the first layer to be thicker for crystal quality while the second layer remains thin for efficient separation.
Solution Approach 2:
The buffer layer is segmented into two distinct functional layers: a first AlN buffer layer primarily for reducing dislocation density and improving crystal quality, and a second AlN buffer layer (separation layer) specifically designed for efficient separation. This segmentation allows optimization of each layer's thickness for its specific function.
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
This method significantly reduces dislocation density and processing time for producing high-quality group III nitride semiconductor substrates and elements, enhancing light emission efficiency and extending device life while improving the efficiency and cost-effectiveness of the separation process.
Implementation Method 1
forming a metal nitride layer having a plurality of substantially triangular-pyramid-shaped or triangular-trapezoid-shaped microcrystals by performing a heating nitridation process on the metal layer under a mixed gas atmosphere of ammonia
Implementation Method 2
dissolving and removing the metal nitride layer using a chemical etching and separating the template substrate or the AlN single crystal substrate from the group III nitride layer
Data Source
AI summary
A manufacturing method of a group III nitride semiconductor includes the steps of: depositing a metal layer on an AlN template substrate or an AlN single crystal substrate formed by depositing an AlN single crystal layer with a thickness of not less than 0.1 μm nor more than 10 μm on a substrate made of either one of sapphire, SiC, and Si; forming a metal nitride layer having a plurality of substantially triangular-pyramid-shaped or triangular-trapezoid-shaped microcrystals by performing a heating nitridation process on the metal layer under a mixed gas atmosphere of ammonia; and depositing a group III nitride semiconductor layer on the metal nitride layer.