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industry  sapphire substrates


The processed Al2


O3


produced in-house is fed into


custom-built, proprietary furnaces, named ES2-XLG3.0. We make these furnaces for less than half the cost of merchant furnaces. These growth tools, which have all been recently upgraded, are installed in our facilities in Batavia, Franklin Park and Bensenville, Illinois, where we maintain tight control over this valuable intellectual property.


Our customized furnaces are equipped with automation for monitoring all the vital functions and crystal growth rates. This is the key to greater yield consistency. Our proprietary ES2 crystal growth methodology is automated, requiring operator intervention only at pre-set points during the growth process. Thanks to this, it requires less operator intervention than competing methods – with our approach, the operator must be present for less than 10 percent of total cycle time. The primary role of the technician is to initiate crystal growth.


Crystal Growth


Leading MOCVD tool makers,such as Aixtron,offer multi- wafer reactors with a variety of configurations. Loading the reactors with 6-inch wafers, rather than 2-inch wafers,leads to more efficient use of gases and pre-cursors. Credit: Aixtron


provides better control of product quality and delivery schedules. Vertical integration is also central to our ability to grow larger and larger sapphire and be the first firm to market with large- diameter sapphire wafers. To date, we have shipped more than 400,000 6-inch wafers.


One of the great strengths of our vertically integrated approach is that we have the materials on hand to meet our customers’ expectations. Production begins with the processing of powdered Al2


to yield purified, ‘densified’ material, which is then fed into the furnace to produce a large sapphire crystal or boule. Recently, we started a transition to on-premise processing of Al2


O3 O3 .


Processing our material in-house gives us greater control of our raw material supply, reduces our costs and enables us to ensure the quality of our starting materials for making sapphire crystals. If we were not able to do this, we would have to rely on commercially purchased crackle, which can be highly expensive and subject to an unreliable, fluctuating supply. Even high purity crackle can be plagued with impurities from transition metals such as silicon, chromium and titanium, resulting in lower quality sapphire boules. For example, the addition of small amounts of titanium can lead to a pink boule – titanium and chromium give the red sapphires found in nature their ‘ruby’ red colour.


54 www.compoundsemiconductor.net March 2013


During the last 11 years, we have refined our ES2 growth process that is based on the Kyropoulos method (see box “Building on the Kyropoulos method” for details of this growth technology). Our now-perfected methodology involves a top-seeded approach that allows a clear, contaminant-free sapphire crystal to grow unconstrained. Thanks to this, growth is stress-free and defect densities are incredibly low. We employ a master seed crystal, made from one of our own high-quality boules, over and over again to produce consistently high-quality material.


Additional advantages stemming from our furnace design and growth process include: A low thermal gradient; in-situ annealing; minimal bubble formation, due to no crystal rotation; and continual monitoring of the entire growth process, which is possible with a weight sensor. Thanks to this impressive set of attributes, it is possible to routinely yield material with very little stress and a low dislocation density, which is of the order of 10-100 defects cm-2


. This is far lower than that found in sapphire formed by either the Czochralski method or the heat exchanger method, which both yield defect densities of 1000-10,000 cm-2


. High crystal


quality with a high yield is even possible when scaling the growth of bulk crystal. The mass of our boules has steadily increased from 30 kg to 85 kg and then to 200 kg.


Finishing steps


Processing our crystals into substrates involves high-precision core drilling, wafer slicing, surface lapping, large diameter polishing and wafer cleaning. We have strong intellectual property in


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