26 May 2011

Imec processes first power devices on 200mm CMOS-compatible GaN-on-Si

Nanoelectronics R&D center Imec of Leuven, Belgium and its partners in its GaN industrial affiliation program (IIAP) have produced device-quality wafers with gallium nitride/aluminium gallium nitride (GaN/AlGaN) layers on 200mm silicon wafers.

Picture: Power devices on 200mm CMOS-compatible GaN-on-Si wafer.

With these wafers, functional GaN metal-insulator-semiconductor high-electron-mobility transistor (MISHEMTs) were processed using standard CMOS tools. The processes that were used are compatible with the strict contamination rules in a standard CMOS processing line (e.g. no use of gold), says Imec, which adds that these first GaN devices on 200mm wafers are a key milestone on the path to cost-effective production of power devices in high-productivity 200mm fabs.

Imec recently produced 200mm GaN-on-Si wafers with crack-free surfaces and a bow of less than 50µm. The wafers were made using an advanced MOCVD system from the semiconductor industry’s largest equipment maker Applied Materials Inc of Santa Clara, CA, USA. The ability to use 200mm wafers is a key milestone, says Imec, because it brings processing within reach of regular high-productivity 200mm fabs, allowing an important cost reduction compared with processing smaller wafers on dedicated processing lines.

A second prerequisite for cost-effective processing (next to the wafer size) is that power devices can be fabricated with processes that are compatible with standard CMOS processes and tools, says Imec. The research institute proved this by processing its GaN-on-Si wafers using standard CMOS tools, yielding functional GaN MISHEMTs. All equipment was verified for its capability to handle the wafers, and required only minimal adjustments in software and hardware.

Conventionally, gold is used for ohmic contacts and gate structures in power devices, but it makes GaN processing incompatible with conventional CMOS processing. To overcome this, Imec based the ohmic contact formation on a gold-free metallization system, and modified the Schottky gate to a gate-dielectric-based gold-free metal-insulator-semiconductor (MIS) structure. The introduction of this MISHEMT structure had the added advantage of reducing the high leakage current of conventional HEMTs, adds Imec.

Tags: Imec MOCVD GaN Applied Materials

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