This specific ashing and strip/clean step occurs immediately after the N-Well ion implantation and before the next photolithography step for the photocathode P4.During the preceding high-energy N-Well implant, the photoresist mask undergoes severe physical and chemical changes, forming a carbonized, highly cross-linked crust known as high-dose ion-implanted photoresist (HDI-PR) P2.The purpose of this step is to completely remove this degraded photoresist and any metallic or organic contaminants