MicroTech has designed a wet process station for performing etching on patterned sapphire substrate (PSS) wafers utilized to improve light extraction efficiency of high-brightness LEDs.
The average light output power on a PSS wafer is 37% higher when compared to that of a standard sapphire wafer. The PSS wafer decreases the gallium nitride layer’s dislocation density and improves the LED chip’s light extraction efficiency. Hence, the demand for PSS wafers is ever-increasing among LED producers looking for reduction in production costs.
In the wet process station, wafers coated with indium gallium nitride or gallium nitride are immersed in the etch tank containing a mixture of buffering and etching agents. Before immersion, patterning of a silicon dioxide mask is done using plasma enhanced chemical vapor deposition. A desired pattern is exposed by a lithography process for etching. The etching process of sapphire occurs at ultra-high temperatures of the order of 260-300° C, enabling rapid etching of the wafers, which in turn results in high throughput and scalability.
Based on independent customer evaluations, the wet process station has drastically improved the light extraction and efficiency of the substrates, while significantly reducing production cost although polishing work is done on the wafers subsequent to the etching process for improving efficiency . Chemical mechanical polishing process is now being utilized to enhance the dome patterns formed on the wafers. Development work is also being carried out for non-cone shapes.