Calling it a milestone towards fabricating low-cost GaN power devices for high-efficiency/high-power systems beyond the limits of silicon, IMEC and Aixtron have grown high-quality, uniform AlGaN/GaN heterostructures on 200-mm wafers. This is the first time crack-free AlGaN/GaN structures have been deposited onto 200-mm Si(111) wafers, according to the companies.
They said the deposition showed excellent morphology and uniformity. The AlGaN and GaN layers were grown in Aixtron’s application laboratory on the 300-mm CRIUS metal-organic chemical-vapor-phase epitaxy (MOVPE) reactor. The 200-mm wafers were custom-made by MEMC Electronic Materials Inc. using the Czochralski growth (CZ) method. CZ wafers are ideally suited for switching applications with large breakdown voltages. For such devices, the performance is independent of the resistivity of the Si substrate.
“The demonstration of GaN growth on 200-mm Si wafers is an important step towards processing GaN devices on large Si wafers,” said Marianne Germain, manager of IMEC’s Efficient Power program. “There is a strong demand for GaN-based solid-state switching devices in the field of power conversion. However, bringing GaN devices to a level acceptable for most applications requires a drastic reduction in the cost of this technology. And that is only possible by processing on large-diameter Si wafers. 150 mm, and then 200 mm are the minimum wafer sizes we need to fully leverage today’s silicon processing capabilities.”
The bow of the resulting wafers is still quite large, in the range of 100 µm. But IMEC said it believes that an optimized buffer can reduce this bow drastically, enabling further processing. “We aim to further develop the growth process and to qualify the wafers to be compatible with Si-CMOS process,” noted Germain.