There are varying levels of wet bench automation mainly tied to safety, process, and budget.
· Manual Wet Benches An operator moves wafers from one process bath to another
· Semi Automated Wet Benches A robot moves wafers from one bath to another, but the wafer drying is done in a separate tool.
· Fully Automated Wet Benches The Wet Bench has an integrated dryer and all moves are by robotics, including the transfer of wafers from FAB cassette to process carrier.
It is somewhat inconvenient when wafers sit in a process cassette or carrier during wet processing. These carriers negatively impact cleaning and drying efficiencies because of their added mass, wafer contact, and all the carriers crevices and pours. If a wet bench could talk, it might say, Do I really have to clean and dry a pound of Teflon with every run? For these reasons, the world's leading suppliers have migrated from cassette style wet benches to cassetteless wet benches.
Cassetteless processing offers better throughput because you're not cleaning and drying an added mass of plastic in every run. And, you don't have to purchase Mass Transfer Units or Teflon process carriers. But most important, the cleaning, etching, and drying results on the wafer are best in a cassetteless system.
On the downside, cassetteless wet benches are complicated and very few suppliers offer this level of automation. Process baths need to be specially outfitted to support the wafers. Robotics and handlers must be precision manufactured, and as such, the overall wet bench cost is more expensive.
All sophisticated FABs simply must run cassetteless to get the required results. Cassetteless wet bench manufacturers lead the industry and enjoy the greatest market share.