MicroTech Systems has developed a wet process station for etching patterned sapphire substrate (PSS) wafers, which are used to increase light extraction and efficiency in high-brightness LEDs. The wet station’s improvement of manufacturing throughput could make LEDs cost-competitive with fluorescent lighting.

As LED manufacturers try to decrease costs, PSS becomes more important, the company said, and that LEDs produced on substrates using this wet process increase overall efficiency: Switching from the dry to the wet process reduces capital and manufacturing costs and improves scalability and throughput.

The average light output power is reported to be up to 37% greater on a PSS than on a standard sapphire wafer. PSS wafers reduce the dislocation density in the GaN layer and enhance the light extraction efficiency from the LED chip.

In MicroTech’s wet-etch process, GaN- or InGaN-coated wafers are submerged in the etch tank with a mixture of etching and buffering agents. Before submersion, a silicon dioxide mask is patterned using plasma-enhanced chemical vapor deposition. A lithography step exposes the desired pattern to etch. The sapphire etch process takes place between 260 and 300 °C. This ultrahigh temperature etches the wafers exponentially more quickly than the standard 150 to 180 °C process, speeding throughput.

The company said that independent customer evaluations show a significant improvement in light extraction and efficiency in the substrates and considerable cost savings, even if polishing work is performed on the wafers after etch to increase efficiencies.

Traditional dry-etching on PSS produces highly efficient, very bright light, but throughput is slow, and scalability is affected as wafer sizes increase. Typically, more dry-etch tools are needed to keep throughput up as wafer size increases.

For more information, visit: www.microtechprocess.com