Belgium’s microelectronics research center IMEC and Germany’s metal-organic chemical-vapor deposition (MOCVD) equipment developer AIXTRON have jointly demonstrated the growth of high-quality and uniform AlGaN/GaN heterostructures on 200 mm silicon wafers. This demonstration is a milestone toward fabricating low-cost GaN power devices for high-efficiency/high-power systems beyond the silicon limits, said the partners. In fact, for the first time, the two have deposited crack-free AlGaN/GaN structures onto 200 mm Si(111) wafers. The layers show good crystalline quality as measured by high-resolution x-ray diffraction (HR-XRD), stated IMEC.

Excellent morphology and uniformity were obtained as well. The high-quality AlGaN and GaN layers were grown in AIXTRON's application laboratory on the 200 mm CRIUS metal-organic chemical-vapor-phase epitaxy (MOVPE) reactor.

"The demonstration of GaN growth on 200 mm Si wafers is an important step toward processing GaN devices on large Si wafers," said Marianne Germain, program 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. “To fully leverage today's silicon processing capabilities, we need 150 mm, and then 200 mm wafer sizes," said Germain. "The bow of the resulting wafers is still quite large, in the range of 100µm; but IMEC 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," she said.

For the AlGaN/GaN heterostructures, a standard layer stack that had already been successfully demonstrated on 100 and 150 mm Si(111) substrates was used. First an AlN layer was deposited onto the Si substrate, followed by an AlGaN buffer, which provides compressive stress in the 1 micron thick GaN top layer. The stack was finished with a 20 nm thin AlGaN (26% Al) layer and capped with a 2 nm GaN layer. From in-situ measurements, researchers from IMEC were able to extract the thickness uniformity of the different layers, which show a standard deviation well below 1% over the full 200 mm wafers (5 mm EE).

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