Low-cost, low-defect, 2" GaN epi-ready substrates processed with E-Grinding

Gallium nitride substrates are the key material for achieving high-end, energy-efficient semiconductor devices such as light emitting diodes (LEDs), laser diodes, power transistors and RF transistors. Significant effort has been exerted to develop cost-effective near-equilibrium ammonothermal (NEAT) growth of bulk GaN crystals; however, due to extreme hardness and chemical stability, a low-cost wafering process for bulk GaN crystals has not been fully established yet. During this DOE SBIR Phase I and Phase II project, SixPoint has met milestones to achieve a low-cost wafering process with incorporation of a novel grinding process called E-Grinding. We have achieved atomically smooth 2" GaN substrates with minimum amount of residual subsurface damage. In addition, incorporation of E-Grinding led to a 45% reduction of total processing time. The developed wafering process provided a high-quality GaN surface suitable for successive device fabrication. Through the ARPA-E SWITCHES program, we have demonstrated 1200 V p-n diodes fabricated on NEAT GaN substrates. However, while commercializing the NEAT GaN substrates, we have recognized three remaining problems which are impeding wide customer acceptance. In this Phase IIB project, we will solve 1) crystal lattice and physical bowing of GaN substrates, 2) large variation of miscut angle, and 3) residual nano-scale particle contaminants on the surface. Through reduction of oxygen concentration in NEAT GaN growth, we will reduce lattice mismatch which causes crystal lattice bowing. In addition, we will examine mechanical stress at each step in the wafering process to minimize the physical bow. To control miscut angle accurately, we will improve both the slicing and grinding processes through development of new adjustable stages. A new method for cleaning CMP-ed GaN surfaces will be established through surface analysis of GaN with residual particles. Chemical etching as well as physical removal methods will be employed to achieve particle-free GaN surfaces. The successful development of low-cost, low-defect 2" epi-ready GaN substrates will increase customer acceptance of SixPoint’s GaN substrates and consquently accelerate development of various in-demand GaN-based devices for making society more energy-efficient and IoT-connected.