RESEARCH REVIEW SiC-on-silicon edges
closer to LEDs Will a new buffer material for GaN tempt LED manufacturers away from sapphire and onto silicon?
MORE THAN A DECADE AGO, researchers from Australia-based Queensland Micro and Nanotechnology Facility (QMF) of Griffith University were depositing silicon carbide on silicon as part of a venture capital funded programme to develop novel non-volatile memory cells. Come the global financial crisis, funding waned and the project was shelved. The process, however, was not.
In 2011, the QMF researchers joined forces with micro-device equipment manufacturer, SPTS Technologies, to develop a production reactor targeted at producing SiC-coated silicon wafers for GaN for LEDs. As Alan Iacopi, QMF director of operations, explains: “Silicon carbide makes a great buffer layer for GaN, but we knew that if the industry was going to take us seriously, we needed a production vehicle to commercialize the technology.”
And, today, this is what they have. Sited at QMF, the team’s vertical reactor – dubbed EpiFlx – is designed for high temperature vacuum processing of large batches of wafers sized from 50 mm to 300 mm.
Right now, the team is finalising the baseline SiC-on-silicon growth processes on the reactor to produce a cost-effective buffer material. Will this at last enable LED manufacturers to switch from sapphire to silicon substrates? Iacopi and the rest of the team thinks so.
“Since March of this year we’ve been transferring our process from the original research reactor to the EpiFlx and the initial uniformities are very encouraging,” says Iacopi. “We’ve already achieved SiC film thickness uniformities of around 1 percent on 300 mm wafers from the EpiFlx and are now characterising the processes on smaller wafers.”
At the same time, SPTS and QMF have been working with industry partners to
validate the technology within the LED and Power GaN-on-silicon markets. Structures fabricated on silicon are already showing promising results and as SPTS chief executive, Bill Johnson, says: “These manufacturers feel that a SiC buffer layer offers a real value proposition and like the ability to have a batch tool capable of supporting multiple GaN MOCVD reactors.”
Both Iacopi and Johnson agree that there is no demand for 300 mm wafers right now, but as Johnson says: “We wanted to say, ‘look, here’s a 300 mm wafer with industry-leading uniformity’. It clearly shows the industry that a very uniform buffer layer can be epitaxially grown on smaller wafer sizes.”
Today, LED manufacturers are migrating from 100 mm to 150 mm sapphire substrates to boost chip yields per wafer, but the partners are looking to enter the market with 200 mm wafers.
“The leading LED manufacturers are now interested in 150 mm substrates and we believe that by the time we are ready with our technology, 150 mm sapphire substrates will have a usable cost structure. So 200 mm would be a logical insertion point,” says Johnson.
Initial estimates suggest the team’s SiC-on-silicon coating process, in volume production, will add no more than $35 to the cost of a silicon wafer.
This, without a doubt, would draw LED manufacturers away from large sapphire substrates, costing hundreds of dollars, but what about competition from, say, Azzurro, Translucent and Kyma? The team reckons its technology offers greater appeal than commercially- available templates.
Johnson asserts EpiFlx-produced wafers would be much cheaper than templates with exotic layers produced via more expensive deposition processes while
The EpiFlx reactor will extend the epitaxial growth process, pioneered at QMF, to commercial scale production of SiC coated silicon wafers
Iacopi believes his team offers a more flexible proposition.
As he highlights, many makers of buffer materials claim templates are good for LED manufacturers to ‘play with’, but is this the case?
“LED manufacturers can’t ‘tune’ these and will not be in control of their manufacturing process; they also can’t control how much they pay for those wafers,” he says. “With an EpiFlx system, manufacturers will get a baseline process and you can imagine them tuning this for their own applications to develop a competitive advantage.”
So as the SPTS-QMF team continues to fine-tune its process, where next for the partners? “By early next year customers will be engaged in beta tests with us,” says Johnson. “This is not years away, it’s quarters away. And from a performance and cost-of-ownership point of view, EpiFlx will be far and away the clear winner.”
July 2013
www.compoundsemiconductor.net 23
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179