GaN Wafer Substrate CTE Mismatch Mitigation
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Solution Overview
Problem
The manufacturing of solid-state lighting devices faces challenges due to differences in coefficients of thermal expansion (CTE) among device elements, leading to cracking and delamination, particularly for wafers over 102 mm in diameter, which complicates the production of high-yield devices with improved performance, reliability, and reduced manufacturing costs and time.
Innovation Solution
A method for growing gallium nitride (GaN) on a substrate with a support substrate having a CTE matching that of GaN, using a seed material and intermediate structure to form a crystal-oriented material, which is then annealed and etched to enhance crystallinity, allowing for epitaxial growth of GaN without the need for bonding preformed silicon- or gallium-nitride-containing substrates, thereby reducing dislocation densities and improving GaN quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire substrates are used for growing GaN wafers, then GaN growth is enabled, but cracking and delamination occur due to CTE mismatch between sapphire and GaN
Solution Approach 1:
The patent introduces an intermediate structure comprising a seed material layer and a crystal-oriented material layer between the sapphire substrate and the GaN layer. This intermediate structure acts as a mediator that gradually transitions the thermal expansion properties from sapphire to GaN, reducing the abrupt CTE mismatch that causes cracking and delamination. The seed material layer (e.g., AlN) and crystal-oriented material layer (e.g., silicon with (111) orientation) create a stepped transition zone that accommodates the thermal stress differential.
Solution Approach 2:
The patent changes the physical and chemical parameters of the intermediate layers through controlled deposition and annealing processes. The seed material layer is deposited with specific thickness and composition parameters, followed by annealing at controlled temperatures to enhance crystallinity. The crystal-oriented material layer is deposited with controlled orientation parameters to match the GaN crystal structure. These parameter changes optimize the intermediate structure's ability to bridge the CTE gap between sapphire and GaN.
2Productivity
If large-diameter wafers (over 102 mm) are manufactured, then production capacity increases, but manufacturing yield decreases due to CTE-related defects
Solution Approach 1:
The intermediate structure serves as a mediator that enables large-diameter wafer manufacturing by distributing thermal stress across the expanded wafer area. The seed material layer and crystal-oriented material layer create a stress-management architecture that prevents the propagation of cracks and delamination across large wafer surfaces, thereby maintaining high manufacturing yields even as wafer diameter increases to 102 mm and beyond.
Solution Approach 2:
The patent segments the GaN growth process into multiple controlled stages with distinct intermediate layers. Rather than attempting to grow GaN directly on large sapphire substrates in a single step, the process is divided into sequential deposition and annealing steps that create a graded transition structure. This segmentation allows each layer to be optimized independently for stress management, enabling scalable production of large-diameter wafers with maintained yield.
3Device complexity
If conventional direct growth methods are used, then process simplicity is maintained, but dislocation densities remain high reducing GaN quality
Solution Approach 1:
The patent applies preliminary actions by depositing and annealing the seed material layer and crystal-oriented material layer before initiating GaN growth. The seed material layer (e.g., AlN) is deposited first and annealed to establish a crystalline foundation. Then the crystal-oriented material layer (e.g., silicon) is deposited and annealed to further enhance crystal orientation. These preliminary actions prepare the substrate surface with optimized crystallographic properties before GaN deposition, thereby reducing dislocation densities and improving GaN quality without significantly increasing overall process complexity.
Solution Approach 2:
The patent replaces the simple mechanical deposition process with a more sophisticated sequence involving chemical vapor deposition followed by thermal annealing. Instead of directly depositing GaN onto sapphire, the process substitutes intermediate chemical deposition steps (forming AlN and silicon layers) combined with thermal treatment. This substitution of mechanical deposition with chemical-thermal processes enables better crystal orientation and reduced dislocation densities in the final GaN layer.
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 enables the production of high-quality GaN films with reduced dislocation densities, facilitating the manufacture of large-diameter wafers without the need for high bonding forces, improving throughput and enabling the use of existing equipment for large-scale LED production.
Implementation Method 1
The at least partially crystal-oriented material can be annealed
Implementation Method 2
an epitaxially-grown gallium nitride (GaN) material
Data Source
Figure 1A~1B
Figure 2~3
Figure 4A
AI summary
Gallium nitride wafer substrate for solid state lighting devices, and associated systems and methods. A method for making an SSL device substrate in accordance with one embodiment of the disclosure includes forming multiple crystals carried by a support member, with the crystals having an orientation selected to facilitate formation of gallium nitride. The method can further include forming a volume of gallium nitride carried by the crystals, with the selected orientation of the crystals at least partially controlling a crystal orientation of the gallium nitride, and without bonding the gallium nitride, as a unit, to the support member. In other embodiments, the number of crystals can be increased by a process that includes annealing a region in which the crystals are present, etching the region to remove crystals having an orientation other than the selected orientation, and/or growing the crystals having the selected orientation.