Patterned Sapphire Epitaxial Template for Low-Defect AlN Overgrowth
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Solution Overview
Problem
Conventional methods for growing an ELO-AlN layer on a sapphire substrate require high temperatures above 1,300°C, leading to rapid heater wear and instability in the manufacturing process, and result in a rough surface, while also increasing manufacturing costs due to complex processing and low throughput.
Innovation Solution
A method involving C axis orientation control to grow an initial-stage AlN layer oriented in the C+ axis direction on the sapphire substrate's protrusion tops, followed by lateral overgrowth to cover recesses, achieving a fine and flat surface at temperatures below 1,300°C, thereby reducing threading dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high temperature growth above 1,300°C is used to grow ELO-AlN layer on sapphire substrate, then the layer can be formed, but the heater wears rapidly and manufacturing stability deteriorates
Solution Approach 1:
The patent changes the growth temperature parameter from above 1,300°C to below 1,300°C (specifically 1,000-1,200°C), which resolves the heater wear and stability issues while maintaining acceptable surface quality through the ELO growth method on grooved substrates
Solution Approach 2:
The patent segments the growth process into two stages: first forming grooves on the sapphire substrate to create isolated growth regions, then growing AlN layers that laterally overgrow to cover the grooves. This segmentation allows lower temperature growth while achieving good surface quality
2Manufacturing precision
If high temperature growth above 1,300°C is used, then AlN layer can be grown, but the surface becomes rough
Solution Approach 1:
By segmenting the substrate into grooved regions that isolate lateral overgrowth, the patent enables smooth surface formation at lower temperatures where atomic diffusion is more controlled, avoiding the rough surfaces that occur at higher temperatures
3Manufacturing precision
If conventional processing with etching steps is used, then template quality is improved, but manufacturing complexity increases and throughput decreases
Solution Approach 1:
The patent merges the template formation and AlN layer growth into a single continuous epitaxial process. The grooved substrate structure is formed, then AlN layers are grown in situ that laterally overgrow to cover the grooves, eliminating the need for separate etching steps and achieving both high quality and high throughput
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 approach allows for the stable growth of an AlN layer with a reduced threading dislocation density and a fine surface at lower temperatures, improving the crystal quality of GaN nitride semiconductor layers without increasing manufacturing costs, resulting in superior semiconductor device properties.
Implementation Method 1
an AlN layer is grown so as to cover over the recesses by a lateral overgrowth method
Implementation Method 2
epitaxially growing an initial-stage AlN layer that is oriented in the c+ axis direction
Data Source
Figure 1A~1D
Figure 2A~2B
Figure 3A~3B
AI summary
A surface of a sapphire (0001) substrate is processed to form recesses and protrusions so that protrusion tops are flat and a given plane-view pattern is provided. An initial-stage AlN layer is grown on the surface of the sapphire (0001) substrate having recesses and protrusions by performing a C+ orientation control so that a C+ oriented AlN layer is grown on flat surfaces of the protrusion tops, excluding edges, in such a thickness that the recesses are not completely filled and the openings of the recesses are not closed. An AlxGayN(0001) layer (1 ≥ x > 0, x + y = 1) is epitaxially grown on the initial-stage AlN layer by a lateral overgrowth method. The recesses are covered with the AlxGayN(0001) layer laterally overgrown from above the protrusion tops. Thus, an template for epitaxial growth having a fine and flat surface and a reduced threading dislocation density is produced.