Ashing is a common cleaning process in semiconductor manufacturing, primarily aimed at removing residual photoresist from the wafer surface. This process relies on the reactive properties of plasma, typically using oxygen plasma to “burn” the organic photoresist into gaseous CO and CO₂, thereby thoroughly cleaning the surface. This method is known as “dry cleaning,” in contrast to the liquid solvent-based dissolution process used in wet cleaning.
Throughout the chip fabrication process, photoresist serves as a temporary masking material that must be completely removed once its purpose is fulfilled. Any residue left behind can severely impact subsequent steps, particularly before deposition, etching, or ion implantation. The significance of ashing lies in its ability to efficiently and selectively remove photoresist while avoiding damage to other structures on the wafer.
Although it may resemble etching, ashing is fundamentally different in that it does not aim to transfer patterns or thin materials—it solely restores a clean, uncontaminated surface. This treatment has a direct impact on chip yield, especially in advanced processes, where even the smallest residue can become a defect source.
Within the cleanroom logic, ashing is a “step back” technology—it does not build, but rather clears the way, resetting each stage to the cleanest, most pristine state. For this reason, it is often overshadowed by primary processes such as lithography, etching, and deposition, yet remains indispensable.
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