LED Sapphire Etch System, a new technology developed for the etching of PSS or Patterned Sapphire Substrate wafers, is getting more and more popular today. This is a wet process solution that is more effective than the dry process as this can increase the light extraction and efficiency in high brightness LEDs. This technology is considered an advantage most especially to the semiconductor industry because it can lower the manufacturing costs but can produce better throughput. Indeed, this is an important development that makes the LEDs price competitive with fluorescent lighting.
Why wet process system is better?
More and more LED manufacturers switch from dry to wet process - and the use of PSS becomes more important - as it gives the following results:
- Decreased manufacturing costs
- An average light output power is up to 37% larger on PSS than a standard sapphire wafer
- Reduced dislocation density in the GaN (gallium nitride) layerv
- Enhanced LEE (light extraction efficiency) from the LED chip
Traditional dry etching on PSS
The use of traditional etching on Patterned Sapphire Substrate produces highly efficient, very bright light but the throughput is slow. Also, the scalability is impacted as wafer size increases. Traditionally, there is a need of more dry etch tools to keep throughput up as wafer size increases.
How the wet etch process works?
1. A silicon dioxide mask is patterned using PECVD ( plasma enhanced chemical vapor deposition)
2. Wafers coated with GaN or InGaN (indium gallium nitride) are submerged in the etch tank with a mixture of etching and buffering agents.
3. A lithography step exposes the desired pattern to etch
4. For sapphire etch, it is carried out at temperatures between 260C and 300C - an ultra high temperature that etches the wafers exponentially more quickly than standard 150-180C and thus, speeds throughput.
Wet process system evaluation and future development
Evaluations were done for wet process system and the assessment confirmed a significant improvement in light extraction and efficiency in the substrates. They also suggest that even if there is a need of polishing works on the wafers after the etching to increase efficiencies, still substantial cost saving is achieved.
Presently, engineers are working in order to make this wet process even better. In particular, they are improving the dome shapes created on the wafers with the help of CMP or chemical-mechanical polishing process. They are also working on non-cone shape, as part of this effort.
