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Polishing - produces the final mirror surface most users require. It is a two step operation. A first polish produces what appears to the unaided eye to be a mirror surface. However, inspection of the surface using an intense light or laser inspection equipment shows a very fine surface roughness. A second polish, using a fine grit and soft pad, removes that roughness. Careful polishing equipment maintenance is necessary for the preservation of wafer flatness and parallelism. In particular very flat surfaces must be maintained on polisher platens and carriers. Lapping machines and devices have been procured for that purpose.
Lapping - improves the wafer quality by restoring wafer flatness and parallelism planarity as well as physically removing diffusion and coatings that are resistant to chemical removal. Double sided lapping removes equal amounts of silicon from both sides of the wafers and restores flatness and TTV. Single sided lapping removes coatings and silicon just from the front side of the wafer where most damage has occur during processing. The minimal removal of silicon allows multiple reclamations.
Etching - silicon wafers is used primarily after lapping and relieves stress and removes any coatings that might still be on the edges of the silicon. This process cleans the silicon and prepares it for polishing. This same etch is also used in the stripping process when necessary to remove some types of coatings.
Stripping - the chemical removal of coatings, patterns and other deposits on the silicon wafers, cuts customer costs and improves the finished quality. It follows an initial sorting of the wafers by type, orientation and thickness to eliminate the customer costs of processing wafers that won’t meet specifications. Depending on the deposits and customer requirements, some silicon wafers can go directly from stripping to polishing, possibly to cleaning, thereby eliminating the costs of lapping and etching and the attendant loss of material from the wafer. If the wafer history is unknown or known to have unwanted diffusions or has residual patterning, it is sent to lapping after stripping.
