M – Metal-Organic Chemical Vapor Deposition (MOCVD)
MOCVD is a process used to grow an epitaxial layer of GaN. Pits often appear during the MOCVD process, correlated with the temperature gradients that result as the wafer bows from center to edge. Not all defects found at the post-epi inspection originate in the MOCVD process, however. Sometimes the fault lies with the sapphire substrate.
In looking at a defective wafer through an inspection tool, how do you determine which defects are killer defects that impact the yield or electrical performance, and which defects are simply a nuisance? Manufacturers need to detect killer defects at the earliest possible time in terms of the repetitive epitaxial-growth wafer-production runs in an MOCVD reactor.
Ideally, the manufacturer will optimize the MOCVD process over time to reduce killer defects, whereas a line without such monitoring can lead to what’s often called an excursion—or the shutdown and revamping of part of the manufacturing process. MOCVD is a popular method for the epitaxial growth of p andn layers with quantum well in between. The typical thickness of the p and n layers combined is around a few microns. It is important to have an inspection point before MOCVD because poor quality of the incoming substrate can potentially be the culprit of future electrical probe test failures downstream—such as failing forward voltage and reverse leakage current specifications.
Matrix LED Assemblies
Matrix LED assemblies are the basis of many systems found in production. Their emerging popularity is derived from their ability to get more lumens per watt from this configuration.
Matrix LED process steps include material preparation, pick-and-place, pulsed reflow, clean, wire bond, and test. LED matrix assembly is an extremely temperature-sensitive process that requires careful control during assembly. Palomar Technologies has been working with advanced LED designs for almost a decade, and was one of the first companies to process matrix LEDs – in modules containing anywhere from six to over 1,000 die.
N – Niche markets
The application of LED packaging and assembly covers a broad range of niche markets. Some include automotive lighting applications (indicators, spot utility, and headlamps), camera functions (display backlights and camera flashes), consumer products (LCD display backlight and projection systems), architectural uses (accent lighting for buildings and signs), laser or inkjet (LED printhead arrays), aircraft lighting, and powerful heaters in water purification systems.
Sources:
LEDs Magazine, “Improve LED manufacturing via in-line monitoring and SPC”, http://ledsmagazine.com/features/10/7/10.
Solid State Technology Journal: “The gleam of well-polished sapphire”, http://electroiq.com/blog/2013/01/the-gleam-of-well-polished-sapphire/.
Photo credit: http://optics.org/news/2/9/20.
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Janine Hueners
Marketing Specialist
Palomar Technologies, Inc.