industry wide bandgap technologies
are on a much larger length scale than our nanocolumns. The way we like to phrase this is that our PVDNC process puts a nanostructure onto the microstructure of a patterned sapphire substrate.
We have strong IP covering our growth technology, which is based on forming nanocolumnar III-N layers by PVD. When NCSU researchers Gerald Cuomo and Mark Williams founded our company, they brought their PVD technology with them. NCSU then licensed key patents to us, and we have strengthened our IP with additional patents – together they cover several important aspects of growth technology and equipment design relating to AlN PVD.
For many years, we kept our PVDNC AlN template growth process under wraps. During that time, we learnt and refined how to use it to improve our HVPE process for growing GaN. As with MOCVD growth of LEDs, defect density falls and film uniformity increases when HVPE-grown GaN layers are formed on top of our AlN template. What’s more, with this approach we don’t have to perform a two-step buffer layer growth, making our process faster while simultaneously providing added IP protection for our HVPE GaN growth processes.
Marketing templates
When the market for sapphire substrates for LEDs took off around 2005, we decided to launch our PVD-grown AlN templates. This was our first addition to our bulk-GaN products, and it marked the beginning of our transition to a more diversified product portfolio. At the outset, LED manufacturers were very reluctant to evaluate our material. A stigma surrounded PVD growth for epitaxial growth applications, and it did not help matters that our AlN layer characteristics were markedly different from most of the MOCVD- grown AlN-on-sapphire materials being used in many of the commercial LED recipes. But persistence on our part paid off, and a handful of companies in Taiwan and the US gave them a try.
Initially, these templates did not work well for the chipmakers, because the AlN layer was too thick. So we devoted time and effort to optimizing the thickness of AlN and its growth conditions, working in partnerships with a few companies. Although each firm settled on a different optimal thickness, their preferred values were quite similar. That didn’t surprise us, but we were caught off- guard when we found that these LED makers had their best results using buffer layers that were far thinner than the ones we used in-house for our own trials. We quickly migrated to these thinner AlN buffers, and very positive reports followed from our customers.
We have subsequently mulled over possible explanations behind the benefit of employing a thinner AlN buffer. We cannot divulge many details regarding our conclusions, but we can reveal that the benefits are not limited to LEDs, and extend to any application involving MOCVD growth of a GaN buffer layer on top of the template. A great strength of the PVDNC process is its scalability. Until about two years ago, we carried out our growth on small- scale PVDNC equipment built in-house a decade ago. However, as our sales started to climb, we needed more capacity and a more robust platform, so we talked to commercial PVD tool
Kyma’s PVD growth systems
suppliers. Our conversations with them were not that helpful. None had ever built a PVD tool operating in the growth window that our process required, and after attempts at forming creative partnerships, we concluded that it would be best to go it alone. This has yielded significant success: Our homebuilt, higher- capacity tool may not be fully automated, but it has produced thousands of templates, and it has also enabled us to demonstrate growth of AlN on 12-inch silicon and on 10-inch sapphire. We are now in the process of further automating this tool, as well as actively developing plans for a larger platform.
PVD tools
As we worked hard to increase our AlN template sales, we found that many customers wanted to make these engineered substrates in-house. Often they asked us if we could supply them with PVD tools. Deciding if we would fulfil their wishes was very tricky, due to our heritage as a material company that employed proprietary growth tools and refined deposition technologies to give ourselves a competitive edge.
Could we allow all this knowledge to enter the market place? Our view was that we could. We believe that it is important for us to listen to the views of our customers and act in their interests, and we fully recognize that expansion into the equipment market is an excellent commercial opportunity for us. Process engineers that use our equipment discover that growth times are very short, thanks to a fairly fast growth process and the need for a relatively thin buffer of AlN to ensure optimal device performance.
We see PVDNC growth cycle times shrinking to below 20 minutes as we mature the equipment platform. Thanks to these short deposition times, the addition of AlN costs much less than the purchase of sapphire. Our first tool to market can be configured in many ways: 19 x 2-inch, 3 x 4-inch, or single wafer growth on substrates with diameters ranging from 6-inch to 12-inch. We are now working on a bigger tool, which we expect to support multiple 6-inch wafers and have the capacity to produce more
March 2013
www.compoundsemiconductor.net 63
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