LEDs industry
nothing of automobile lights versus cell phone displays, all requiring different tradeoffs of complexity and costs. So LED makers tend to put together their own systems of source-measure units, probers, spectrometers and custom software, or have a local systems integrator do so. To make it even more complex, companies are also going to larger devices, or to multiple-device die cut from the original wafer, which require higher voltages or currents and shorter pulses for testing.
“We have to remain flexible to all these different ways of doing things because there are no established methods for test yet,” says Cejer. “But the relentless price pressures will drive the industry towards efficiency, and if we put our heads together maybe we can do it efficiently.”
Going forward, one solution might be finding enough correlation to characterize optical quality from only electrical tests, at least in some applications where the trade-offs were acceptable. Metrology and test are also easier for LED makers to talk about with suppliers. There is no advantage in not being able to measure things, so no one loses if a company works with a supplier to develop technology to test things that can’t be tested now.
Materials, substrates, automation and metrology are usually the first areas to standardize as an industry matures, says Semilab’s Chris Moore, noting the accelerating speed with which some other sectors have moved up to consistent volume manufacture. The solar industry, which also differentiates on process IP, was skeptical of manufacturing standards only a few years ago. However, it has now embraced standards with amazing rapidity, compared to the slow and painful process of the IC and LCD sectors before. Now two years in to starting standards discussions, there are some 400 photovoltaic industry experts working to facilitate efficient volume manufacture. This team is starting by coming to a consensus on the best measurement methodology for purity and setting benchmarks to define PV grade materials, and agreeing on carrier and equipment interfaces to facilitate automation. First agreement on defining consistent characteristics of solar grade silicon was reached in only three meetings over one year. They’ve reached consensus on 12 standards so far, with another 6 expected to be published by the end of the year, and more than a dozen more under development.
Automation Though small wafers, cheap labor and long batch processes have limited the need for automation so far, the LED industry is transitioning to more and more automation as it moves to larger wafers and higher volumes. Robotic wafer handling, automated glove boxes, interbay automation, mini-environments and standardized carriers such as SMIFS are all technologies that will become pervasive in LED fabs of the future, argues Clint Haris, Senior Vice President of the Systems Solution group at Brooks Automation. He points out that LED makers are starting to look towards automation to improve yields and traceability. “The industry is rapidly evolving from manual
operation to fully automated factories,” he says, noting that the LED industry has seen change in the last five years that took 40 years in the semiconductor industry. “Things are moving so quickly, standards need to focus on the leading edge, 6-inch wafers, 6-inch cassettes, and some sort of wafer or carrier-level identification for traceability as the basics to enable automation.”
“Automation always increases yield,” points out Quinn, noting that Veeco has found that when its experienced technicians instead of its interns load the tools, yields are improved by as much as 50 percent. Automation also may enable a faster ramp to volume than finding or developing all the qualified operators and engineers to run all the new epi reactors now out in the field. Though HB LED manufacturing is unlikely to move to the expensive full automated materials handling required for the heavy cassettes of 300 mm semiconductor wafers, it is likely to move towards the semiconductor automation of the 200 mm generation of the 1990s.
Automating data collection, analysis and even correction will also be key to getting more die into the bins that bring high margins, notes Applied Materials’ Phil Walker, global product manager for automation products. “We need to get the data out of the tool and metrology, and linked to the right wafer to be able improve bin yields,” he says, pointing to the potential for tracking the parameters of the production process, mining the data for the root cause of defects, and making needed adjustments to the tool as soon as possible.
“We also need the software to compare tools and tune them to match those that provide the best performance,” he added. “The first step to unlocking hidden performance is collecting the data and understanding it.”
HB LEDs production is fast transitioning to larger wafer diameters, moving to mass adoption of 4-inch (actually 100 mm) wafers next year, and to 6-inch (150 mm) within a few years, as the better use of reactor carrier real estate and reduced edge losses can increase throughput by as much as 30 percent, and allow use of the other semiconductor equipment available at 6-inch. Source: Yole Développement Sapphire Market 2010 Q4 Update
November / December 2010
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