IMEC, AIXTRON Grow Uniform AlGaN/GaN Heterostructures on 200mm Wafers

IMEC, Europe’s leading independent research center in the field of nanoelectronics, and AIXTRON, the world leader in metal-organic chemical-vapor deposition (MOCVD) equipment, have demonstrated the growth of high-quality and uniform AlGaN/GaN heterostructures on 200mm silicon wafers. This demonstration is a milestone towards fabricating low-cost GaN power devices for high-efficiency / high-power systems beyond the silicon limits.

Thickness uniformity map of a 1um GaN layer deposited on 200mm Si(111) using an AlN/AlGaN buffer. The average thickness measured in-situ is 1008nm (s = 0.5%) for the full wafer excluding a 5mm edge.IMEC and AIXTRON deposited, for the first time ever, crack-free AlGaN/GaN structures onto 200mm Si(111) wafers. The layers show good crystalline quality as measured by high-resolution x-ray diffraction (HR-XRD). Excellent morphology and uniformity were obtained as well. The high-quality AlGaN and GaN layers were grown in AIXTRON’s application laboratory on the 300mm CRIUS metal-organic chemical-vapor-phase epitaxy (MOVPE) reactor.

“The demonstration of GaN growth on 200mm Si wafers is an important step towards 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. 150mm, and then 200mm 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 100µm; but IMEC believes that an optimized buffer can reduce this bow drastically, enabling further processing. Marianne Germain: “We aim to further develop the growth process and to qualify the wafers to be compatible with Si-CMOS process.”

Gallium nitride (GaN) has outstanding capabilities for power, low-noise, high-frequency, high-temperature operations, even in harsh environment (radiation); it considerably extends the application field of solid-state devices. Due to the lack of commercially available GaN substrates, GaN heterostructures are nowadays grown mainly on sapphire and silicon carbide (SiC). Si is a very attractive alternative, being much cheaper than sapphire and SiC. Other benefits include the acceptable thermal conductivity of Si (half of that of SiC) and its availability in large quantities and large wafer sizes. But until now, Si wafers with (111) surface orientation were only available with a diameter up to 150mm. The 200mm 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.

Process details
For the AlGaN/GaN heterostructures, a standard layer stack, that had already been successfully demonstrated on 100 and 150mm 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 20nm thin AlGaN (26% Al) layer and capped with a 2nm 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 200mm wafers (5mm EE).

AIXTRON AG is a leading provider of deposition equipment to the semiconductor industry. The Company’s technology solutions are used by a diverse range of customers worldwide to build advanced components for electronic and opto-electronic applications based on compound, silicon, or organic semiconductor materials and more recently carbon nanostructures. Such components are used in display technology, signal and lighting technology, fiber communication networks, wireless and cell telephony applications, optical and electronic data storage, computer technology as well as a wide range of other high-tech applications. Founded in 1983, the Company is headquartered in Aachen, Germany.

About IMEC
IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. Its research focuses on the next generations of chips and systems, and on the enabling technologies for ambient intelligence. IMEC’s research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network of companies, universities and research institutes worldwide position IMEC as a key partner for shaping technologies for future systems. IMEC vzw is headquartered in Leuven, Belgium, has a sister company in the Netherlands, IMEC-NL, concentrating on wireless autonomous transducer solutions, and has representatives in the US, China, Japan and Taiwan. Its staff of more than 1600 people includes more than 500 industrial residents and guest researchers. In 2007, its revenue (P&L) amounted to EUR 244.5 million.