industry LEDs
Getting the Crius II XL up and running has gone very well. “[It] was delivered, installed and commissioned on time,” reveals Dennington. Since then, engineers at this site, supported by technical staff from Aixtron, have employed a step-by-step approach to developing the 6-inch GaN-on-silicon growth process, which began with GaN deposition on 2-inch sapphire. The quality of the material produced with this process met the expectations of the Aixtron staff, who use this as a benchmark for installation. 6-inch sapphire then replaced the 2-inch substrates, prior to the introduction of the Cambridge recipe and standard silicon wafers with thicknesses of either 750 µm or 1 mm.
One of the features of the Thomas Swan reactor installed in Humphreys’ group is its comprehensive suite of in-situ monitoring tools: It has a Laytec instrument for determining wafer bow from measurements of light reflectance off of the epiwafer’s surface, and it is equipped with an Aixtron Argus instrument for determining temperature profiles. Both tools are fitted on the Crius XL II to monitor growth processes within the reactor.
The acquisition of CamGaN did not give Plessey a finished product: It just received a process capable of repeatedly growing, on silicon, flat nitride epiwafers with active regions producing internal quantum efficiencies of 80-85 percent. The engineers at Plymouth have taken this as a basis for producing a range of LEDs.
“We’ve been able to produce lateral LEDs for some time – there’s no challenge in that – and we are now focusing on the vertical LED,” explains Dennington. Light extraction in this class of LED is enhanced through the introduction of mirror layers and a roughening of the chip’s surface.
Modifications to the 6-inch line to equip it for LED manufacture have been relatively minor, and include the addition of a wafer bonder and an X-ray diffraction tool for scrutinizing epilayer crystal quality. Operating at three growth runs per day, with seven 6-inch wafers per load, the line is capable of churning out 2 million 1 mm by 1 mm LEDs every week. And this capacity is set to increase, because Plessey’s business plan includes the installation of three more MOCVD tools. “With the efficiency of running four machines together, we don’t think we just have to multiply 2 million die by four,” claims Dennington. “We have modelled that we can get up to 10 million die per week from four reactors.”
Silicon absorbs the light produced by the LED,so it is removed with a process that begins with bonding the epiwafer to a carrier wafer
Once the die are made, they are sent off-site for packaging, as either single die or chip-board products. “We have an external partner,” explains Dennington, “which is one the traditional IC assembly houses that wants to move into this area.”
It is also possible that Plessey will team up with a strategic partner that will make GaN-on-silicon LEDs overseas. “This is partly likely because of capacity,” explains Dennington, “but as we are more
Operating at three growth runs per day, with seven 6-inch wafers per load, the line is capable of churning out 2 million 1 mm by 1 mm LEDs every week. And this capacity is set to increase, because Plessey’s business plan includes the installation of three more MOCVD tools.“With the efficiency of
running four machine together,we don’t think we just have to multiply 2 million die buy four,we have modelled that we can get up to 10 million die per week from four reactors,” says Plessey COO, Barry Dennington.
January / February 2013
www.compoundsemiconductor.net 31
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