Group III Nitride Single Crystal Substrate Separation for Reduced Cracking

The patent introduces a buffer layer composed of AlN/GaN multilayer structure as an intermediary between the silicon substrate and the target AlN layer. This buffer layer acts as a mediator that gradually transitions the lattice constant and thermal expansion characteristics, reducing dislocation propagation while maintaining the simplicity of using silicon substrates. The buffer layer comprises multiple alternating layers of AlN and GaN with controlled thickness ratios to optimize the transition.

The patent employs a composite buffer layer structure combining AlN and GaN materials with different lattice constants and thermal expansion coefficients. This composite structure creates a gradient effect that mitigates the mismatch between the silicon substrate and the target AlN layer, reducing dislocation density while maintaining manufacturing simplicity.

The patent uses inexpensive silicon substrates as the base support, which are mass-produced and relatively low-cost, replacing the expensive sublimation-grown AlN substrates. The silicon substrates serve as a disposable base that can be easily replaced after use, significantly reducing the overall manufacturing cost while enabling large-diameter production through the availability of large silicon wafers.

The AlN/GaN buffer layer serves as an intermediary that enables the use of cheap silicon substrates to produce high-quality AlN layers with good crystallinity. This intermediary structure allows the benefits of inexpensive silicon substrates while achieving the crystallinity quality previously only obtainable through expensive sublimation methods.

The patent uses a silicon substrate as an intermediary base that is then coated with AlN/GaN buffer layers. This intermediary approach allows the use of large-diameter, low-cost silicon substrates while the buffer layers provide the necessary thermal expansion and lattice constant matching for GaN single crystal growth, effectively combining the advantages of both approaches.

The patent creates a composite structure combining silicon substrate with AlN/GaN buffer layers. This composite material structure provides the thermal expansion matching and lattice constant compatibility of AlN/GaN ceramics while using the large-diameter, low-cost silicon substrate base, thereby increasing substrate diameter and reducing cost.

The patent performs preliminary actions by pre-forming the AlN/GaN buffer layer structure on the silicon substrate before epitaxial growth. This preliminary preparation creates a ready-to-grow surface that reduces the time required for subsequent epitaxial processes and minimizes cracking during device fabrication by establishing a stable crystalline foundation in advance.

The patent optimizes parameters such as the thickness ratio of AlN and GaN layers in the buffer layer, the deposition temperature, and the growth rate during epitaxial growth. By carefully controlling these parameters, the patent achieves high single crystal quality while reducing the overall fabrication time and preventing cracking through optimized process conditions.