INDUSTRY MOCVD
Left: The UR26K can accommodate ten 6-inch wafers or six 8-inch wafers
Developers and manufacturers of all of these devices are working with different types of substrate for chip production. Sapphire is the most common platform for the LED, but savings are promised by switching to large area silicon substrates that enable chip processing in under-utilised, depreciated silicon fabs. Silicon substrates are also popular within the III-N power electronics industry, but in both this sector and in that of the LED, if native, low-cost substrate were available, they would be widely used. In fact, a small proportion of the world’s LEDs are already being manufactured on GaN, while some groups pioneering ultraviolet LEDs are using AlN substrates for device development.
However, regardless of the substrate employed for making their nitride-based devices, engineers are searching for excellence from their MOCVD tools in three areas: control of the gas-phase reaction for high aluminium concentration and high growth rate; control of carbon doping, from low to high doping densities; and deposition of high-quality layers at high growth rates.
At Taiyo Nippon Sanso of Tokyo, Japan, we satisfy all these requirements with a portfolio of MOCVD reactors featuring a ‘horizontal three-layer’ design and growth at atmospheric pressure. Our smaller tools have an enviable reputation with the R&D community, and our large-scale production machines share the same design philosophy, making it easy to transfer recipes from one type of machine to the other.
Although many know of us through our supply of industrial gases – this activity dates back to the founding of our company in 1910 – we have a strong track record in MOCVD, with efforts commencing in 1983. We initially launched systems for the growth of materials based on the InP and GaAs families of materials. However, by the late 1980s, we started to develop our range of GaN MOCVD systems. They now meet the needs of every customer, from those wanting to carry out research on a single-wafer 2-inch system, to those requiring a large-scale machine for volume production that is capable of accommodating up to six 8-inch wafers or ten 6-inch wafers (see Table 1).
THE III-N CHIP generates billions of dollars every year, with revenues continuing to grow. Sales in this sector are currently dominated by InGaN-based LEDs, which are backlighting many screens and driving a revolution in LED lighting. But other significant markets are emerging: ultraviolet LEDs, which are attractive replacements for mercury lamps, thanks to superior robustness, longer lifetime and portability; and power electronics based on GaN that offers a step up in efficiency compared to silicon incumbents.
The majority of GaN MOCVD reactors employ either a vertical or a horizontal gas flow. Our reactors adopt the latter approach, with precursors supplied from a nozzle upstream of the substrate holder, which is a part of the machine that is also referred to as the susceptor. Materials are consumed along the direction of gas flow, so rotation of the wafers is required to ensure a uniform thickness of film growth. In a single-wafer tool the wafer is rotated about its centre. Meanwhile, in multi-wafer reactor, planetary motion is used, with accurate control resulting from a carefully chosen gear and ball bearing system. One distinctive feature of our reactors is their three-layered gas ejection nozzle. Materials are injected into the reactor via high flow speeds through this nozzle, to enable good control of organometallics and ammonia, and ultimately the deposition of high-quality GaN, AlN, and AlGaN at high growth rates.
March 2014
www.compoundsemiconductor.net 39
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