What is a Spin Rinse Dryer?The job of a spin rinse dryer is to rinse and dry batches of silicon wafers in a cassette. The wafers are usually loaded into a stainless steel drum or chamber then rotated while injecting DI (de-ionised water) to rinse off any particle that might be left over from a previous process step such as etching.
Drying of the wafers usually is by rotating the wafers at around 10,000rpm while injecting heated nitrogen in to the bowl. Static electricity builds up while drying which could help particles adhere to the surface or even damage some delicate devices, this can be reduced by static eliminator assemblies.
Design Criteria - What Size Bowl?Normally wafer cassettes fit into a stainless steel rotor that has been balanced to spin smoothly during the speed ramping and maximum velocity stages of any recipe. Bowl size is the easiest option to discuss as bowls can normally handle several different wafer sizes with a rotor change or a liner that fits into an oversized rotor.
Design Criteria - How many Bowls?This depends on your required production throughput and flexibility needs. Dryers can be configured to be "Stand Alone" tools with independent bowls or can be incorporated into a wet bench. Future expansion is often considered and to save costs a frame maybe supplied with only one of the bowl positions occupied.
Design Criteria - Clean DesignDesigning to be clean from the outset means only stainless steel (highly or mirror polished) or non particle shedding materials should ever come into contact with the water or the dry nitrogen to be used in the system.
The system relies on a motor to rotate the wafers, so brushless ones should be utilised, and if possible the use of a non contact labyrinth seal is a simple way to ensure friction and wear are removed from the proximity of the wafers. One of the signs that the particles have been removed is that purity of the DI on the drain side of the process chamber. The rinse to resistivity options will continue to process the wafers until the resistance of the water in the drain reaches a certain ohmic value (usually 16-18Mohm)
Some other considerations...
- Contactless Nitrogen Seal
- Rinse to Resistivity Option
- AntiStatic Options
- Mirror Polished Stainless Steel
- Multi Step Processing
- Anti-Vibration Balancing
- Cutomised Rotors and Holders