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Wet Processing

Wet chemical cleans typically involve “Wet Bench” Batch type tools. As the Semiconductor industry and the companion wafer level packaging industry evolves, more processing needs to be done on a single wafer basis to ensure a dynamic removal of unwanted material during spin processing. S-Cubed’s long familiarity with photolithographic spin processing has been adapted to this new application. 

Lift-Off

S-Cubed employs appropriate methods of lift-off processing depending on customer requirements.  One technique is to form a puddle on top of the wafer with hot NMP or DMSO (around 70° C) in order to “soak” the wafers to be “lifted off”. The treated wafers are then subjected to high pressure solvent spray or agitated with a megasonic nozzle, followed by an IPA rinse.  Our systems can also be set up as separate modules according to each step: soak agitated cassette, high-pressure/megasonic, and rinse.

Another method is more straightforward and can be done effectively in a simpler system and at a lower cost.  In this case we subject the substrate to a high pressure acetone spray and use a recycling system to recover the spent acetone so that the final acetone rinse is sourced from the recycled solvent. This process is both fast, effective, and safe since the system is inerted with nitrogen.

In both these methods, the entire process is carried out without operator involvement, eliminating problems caused by improper sequencing. Further, the entire tool does “double-duty”, thereby saving time, money, and footprint.

Photoresist Stripping

Another useful application of our wet processing tools is for rework purposes and etch/veil removal. The principal differences between the lift-off operation and photoresist stripping is the actual component on the wafer being removed. The photoresist stripping process often deals with stubborn, harder to remove components such as post-etch veils. One method S-Cubed has invented to target this is with a self-rotating round brush that can both scrub the wafer with direct contact, and can also operate while hydroplaning on the surface solvent with no direct contact. 

Key elements in our tools that allow this evolution in performance:

  1. Programmability.  Our tool enables multiple processes and chemistries to be used and allows the user to program the process parameters throughout the operation.
  2. Process uniformity.  The use of radial arms to dispense chemistries over the wafer permits control of the aerial residence time as the arm moves. We refer to this capability as Constant Aerial Timing or CAT. The arm moves quicker as the arm approaches the center of the wafer and slower as it approaches the edge. This is a feature unique to S-Cubed.
  3. Dry IN, Dry Out. The process is “dry in and dry out” as both sides of the wafer can be processed simultaneously. The final chuck based spin process separates the often incompatible fluids permitting recirculation as appropriate.

 

For more information on our unique abilities in photoresist stripping and rework,

please contact an S-Cubed Engineer today!

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