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Knowledge Base:
Wet benches, Chemical Process & Process Baths

What is a wet bench?

“Wet Bench” “WetDecks” “Wet Process” “Process Baths” or “Sinks” are terms used in semiconductor manufacturing to describe the machine or machines used to sequentially process a batch of wafers (or single wafers) through a variety of chemical steps.

Typical processes can be cleaning, etching, or even electroplating - each carried out in a dedicated process bath containing chemicals dependent on the substrate material being processed.

Common chemicals used are HF, Hydrofluoric Acid, H2SO4 Sulphuric Acid, H2O2 Hydrogen Peroxide or Piranha ( H2SO4 + H2O2 mix). Most rinsing is carried out with DI, (De-ionised Water). Proprietary solvents are also used.

Sequential processing in a wet bench

Benches and baths need to be made from suitable materials depending on the chemistry to be used and often involve polypropylene, PVDF, Stainless Steel.)

Wafers or batches of wafers are then sequenced through the wet processes with each stage being monitored and timed depending on the required result.

Handling of wafers or batches of wafers can be fully automatic, semi-automatic or manual. Most wet benches are designed and configured to a customer requirements and while there are “standard systems” most need to be custom made.

Defining a wet bench can be quite difficult so we provide on-site meetings for design and work with you every step of the way.

Need a Wet Bench?

Some key factors for buying a wet bench...

Process – what are you trying to achieve in the line – this will determine the material the tool need to be made from.

Floor Space and facilities - what is the tool footprint and where will it fit in term of - what drains are required and how are chemicals to be handled

Note: some of these benches can be large so ensure you can get the tools in and out of the cleanroom along corridors or in elevators!

Safety – many of the materials are dangerous, corrosive and even explosive so consider fire safety as well as chemical safety.

Handling and Automation – robots can add complexity and cost but can help with process repeatability as we well as safety. Automatic chemical dispense for spiking (topping up the active chemical component) and chemical replenishment can also help, not only in reducing chemical costs but also combatting any safety issues.

Recirculation - Overflow - Quick Dump - SRD – DI water use is normally expensive to produce so a variety of cleaning and rinsing methods can be adopted to suit the needs of the process. Each variant has pros and cons so it's important to get it right to reduce wasted resources.

Batch v Single Wafer

As wafers get larger, and devices and geometries get smaller, greater process control is required to improve the uniformity of the process. While agitation of wafers or chemicals in a bath can help uniformity chemical reaction speed determines things like etch rate, active chemical depletion – getting chemical to the right place in the right quantities consistently has led to the development of single wafer wet processing often using a spinning mchansimto ensure uniformity of chemical reaction

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