MicroTech Systems, Inc. Engineering Wet Process Solutions

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LEDs on Patterned Sapphire Substrates

In the ongoing quest to make LEDs more efficient, LED chip manufacturers have developed patterned sapphire substrates (PSS). In fact, most high-brightness LEDs are made using PSS.

PSS helps extract more light from LEDs. A lot of light bounces back into the LED when using a polished sapphire substrate. Researchers discovered that patterning the surface of the substrate by etching nano-scale patterns helps more light, in the form of photons, escape, improving the light generated or extracted by the LED. It is reported that patterning can improve the extraction of light by as much as 30%.

LED chip manufacturers originally developed PSS. The patterns are quite proprietary and helped the LED chip companies differentiate themselves. Today, the sapphire industry has joined in and sapphire wafer manufacturers have begun to put patterns on sapphire wafers in partnership with the LED chip manufacturers. The patterning work is concentrated with smaller wafers in the 2 to 4-inch diameter range, but manufacturers of large diameter wafers are beginning to develop PSS for larger wafers.

Most patterning is based on a proprietary design from the LED chip manufacturer. The patterns can vary from cones, pyramids and flat tops and can be organized in hexagonal or trigonal patterns. Some basic design rules based on height and height/pitch ratio have emerged, but so far, no standards exist. Currently the most popular pattern is a cone shape, but these patterns change frequently.
However, the sapphire substrate is very hard, chemically resistant, and is therefore very difficult to process. To form fine structures on the substrate, plasma dry etching is somewhat effective, but it is accompanied by several problems such as a low etching rate and poor etch mask selectivity.

MicroTech has developed a WET etching process for sapphire substrates and has supplied various LED manufacturers with this system.

For more details about MicroTech’s proprietary HTSE-1000 Sapphire Etch System for sapphire removal in LED processing, click here.

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