Wet Processing

Wet processing refers to any process where the wafer encounters liquids used to clean or modify the wafer surface. The processes range from removing photoresist and particulate contamination to wet etch or material removal. Wafers can also be scrubbed to remove particles using a high-pressure spray or a brush. Additionally, megasonics can be used for particle removal. Wafers can be wet-processed in a batch, i.e., dipped simultaneously in a bath or tank; or one at a time, i.e., in a single-wafer configuration.

As noted above, the two primary types of wet process equipment are batch, where multiple wafers are placed in a cassette and dipped in a bath or a tank of chemicals all at once, and single-wafer, where the chemicals are placed directly on the surface of each wafer, individually, in succession. In a batch process, the wafers may pass through a series of baths using chemistries such as SP1 SPM, SC1, and SC2, and then rinsed and dried; in the most advanced processes, wafers are dried using hot isopropyl alcohol or SCCO2 in single-wafer processing, the entire process, from cleaning through drying, can take place in one chamber.

To select the right wet processing equipment, you need to consider the desired outcome, as well as what technology your wafer contains. For example, if you have a deep trench or a gate-all-around (GAA) feature, you need to be certain that the chemicals can successfully clean the bottom of the trench this would involve ACM research SAPS solution and for the all around GAA structure. This could mean using a megasonic solution, such as ACM Research’s TEBO system, to effectively remove the contamination on that feature. If you are cleaning a relatively planar surface, you might consider a batch process that can effectively strip photoresist and provide SC1 and SC2 cleans. For a backside process, you might consider a tool that is capable of etching the backside of the wafer while leaving the front side untouched. 

Wet processing equipment is required to clean the wafer surface both before most oxidation/annealing steps, deposition processes, and lithography steps and after every etch and dry ash process to remove any residual photoresist, particulate or metal contamination that may remain on the wafer. In addition, wet processes are used to remove sacrificial layers, such as oxides and nitrides, that are used in wafer manufacturing.

Wet processes are designed to remove both particulate contamination and chemical contamination that could either cause a short or alter the electrical characteristics of a transistor. By having an effective cleaning tool that can remove all of the contaminants and deliver a clean, dry wafer to the next process step, you ensure optimized yield for that process, as well as for the fab’s entire chip yield.