CS Industry Awards 2012 Metrology, Test and Measurement Award Award
Candela 8620 substrate and epitaxy (epi) wafer inspection system
Introduced to the market in January 2011, the Candela 8620 substrate and epitaxy (epi) wafer inspection system is designed for the inspection needs of the light- emitting diode (LED) industry to capture a wide variety of mission-critical substrate and epitaxial defects. For LED device manufacturers the Candela offers automated defect inspection for LED materials such as gallium nitride, sapphire, and silicon carbide—enabling enhanced quality control of both opaque and transparent substrates, faster time-to-root cause, and improved Metal Organic Chemical Vapor Deposition (MOCVD) reactor uptime and yield.
With its proprietary optical design and detection technology, the Candela 8620 LED substrate and epi wafer inspection system detects and classifies sub-micron defects that are not
consistently identified by current inspection methods— thereby enabling for the first time a production line monitor for these yield- limiting defects. As LED manufacturers transition production to larger wafer sizes and introduce new patterned sapphire substrate (PSS) processes, there is significant economic impact of resulting process-induced defects.
The 8620 can detect a wide variety of yield impacting defects such as substrate scratches and polishing residues, PSS etch pattern defects, GaN crescents,
hexagon defects, showerhead droplets, micropits and micro cracks. The automated defect classification capability allows customers to filter out nuisance defects and quickly zero in on mission- critical defects of interest. As a result, LED manufacturers are equipped to conduct rapid root cause analysis to speed process development, quickly fine-tune production processes to optimize yields and minimize process excursions, and achieve higher revenues per wafer.
Core to KLA-Tencor’s Candela series is providing critical analysis capabilities. Using an innovative proprietary design of optical technology, the Candela systems can detect and classify a wide range of user-defined defects of interest known to impact LED device performance and yield.
One of the most wide- spread and problematic yield-impacting defects plaguing the LED industry today is GaN-epi micropits. As LEDs make their way into higher-end applications such as LCD backlighting, automotive, and general lighting, field reliability and LED performance longevity are of critical importance. GaN epi microcracks can be extremely problematic to LED makers as these defects cannot be screened at final wafer test or final probe test and only later result in field failures and expensive recalls. Micropits typically
range in diameter from 0.1µm to 2µm and can occur in extremely high densities. Micropit excursions are frequent, difficult to detect, and result in significant yield
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www.compoundsemiconductor.net April / May 2012
impacts. It is estimated that minor excursions of micropits result in an additional 5-8 percent yield loss while major excursions cause yield losses in excess of 20-30 percent. Conventional methodologies employ AFM or SEM inspection to monitor for micropits but such techniques sample only a tiny fraction of the surface and are not production-worthy process control solutions. Candela 8620 technology has closed the gap on detection and classification of micropit defects and allows for full wafer inspection coverage at production-grade throughputs.
In use at a number of customer sites serving the emerging HBLED markets, the Candela system is a product of more than three decades of KLA-Tencor’s expertise in semiconductor process control.
© 2012 Angel Business Communications. Permission required.
Richard Stevenson, Editor, comments: “For years and years, LED chipmakers have had to use wafer inspection tools designed for silicon wafers. But thankfully these days are now over, due to Candela's introduction of tools focused on scrutinizing LED wafers, such as the 8620 inspection system”
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