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industry  MOCVD tools


Costs relating to the packaged LED can be sub-divided into those associated with substrates, wafer processing, phosphors, packaging and last but not least, epitaxy. This growth process is not the largest contributor to the overall cost; however, in 2010 epitaxy still accounted for one-fifth of the LED costs.


Given the strong track record in cost reduction that stretches back more than a decade, it is widely expected that the packaged LED will get far, far cheaper. For example, the Department of Energy predicts that prices will fall by more than 90 percent in the next ten years. But if that is to happen, costs associated with epitaxy must also fall tenfold (see Figure 1).


Slashing epitaxial cost by another order of magnitude within a decade is a tall order. To uncover the solutions to make this possible, it makes sense to begin by understanding how previous cost improvements were realised.


During the first 15 years of LED manufacture, the biggest drivers behind reductions in epitaxial costs were increases in MOCVD tool throughout and productivity. At Aixtron, which is the world’s largest manufacturer of MOCVD systems, we have led the way, launching new production platforms offering much larger wafer throughput than their predecessors every three-to-four years. For example, this progression has occurred in our Close Couple Showerhead (CCS) range of reactors. This began with a 3 x 2-inch R&D platform that was launched in 1996; a far more recent model, the Crius II,


can accommodate either 55 x 2-inch or 13 x 4-inch wafers. This large capacity makes the tool a popular choice for today’s LED manufacturers that are looking to expand capacity.


The bad news is that it is not possible to simply extrapolate historical cost and productivity improvements into the future. That’s because many factors influence the running cost of an MOCVD tool: Wafer capacity, growth rates, uptime, degree of automation, reproducibility and yield. Although all of these have already been used by MOCVD manufacturers to improve productivity, further gains will be possible by optimising many of these factors simultaneously.


This is a long-term goal, and it is not reflected in the activities of the LED industry, which has experienced rapid growth over the last two years and delivered a tremendous hike in the performance of LED products. This acceleration, along with the tail wind it has created, has led us to embark upon a quest to uncover the fastest, most effective solution for cost reduction.


We began by making a detailed analysis of the total cost of ownership (TCO), carried out with a home-built model that we have refined over many years. This model – which has been validated by our customers, who are impressed with its accuracy at predicting costs – calculates throughput and accounts for the reactor type, its wafer capacity, growth times, non-growth times and uptime. Also included in this model are realistic LED structures and processes, plus typical yield figures.


This model considers a wide variety of costs: depreciation; chemicals, including carrier gases, metal organics and ammonia; consumables, such as those related to hardware, and also spare parts; labour costs for operators and supervisors; and fab costs, for both the cleanroom and the facility. This model distinguishes between costs governed by the reactor chamber, which is considered to be the core part of the MOCVD system – these are depreciation, chemicals and consumables – and those that are related to the MOCVD platform, which are not directly related to the reactor and include fab and labour costs.


The key finding of this TCO analysis is that reactor-related costs account for more than 90 percent of overall costs (see Figure 2). In other words, attempts to significantly cut costs under the current circumstances must focus on the reactor design. Although changes to the MOCVD platform or periphery can deliver savings, the potential for driving down costs is far smaller.


44 www.compoundsemiconductor.net October 2011


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