Silicon wafers are etched after grinding/lapping to remove sub-surface damage caused in the mechanical processes. Typically, wafers that are 150mm and smaller are etched in a heated caustic solution. The caustic is typically potassium hydroxide (KOH) with a concentration ranging between ~24% to ~40%. Operating temperatures range from 80°C to 105°C.
Wafers etched in caustic exhibit no degradation of wafer geometry but have higher surface roughness with the creation of large faceted features. The converse is true for acid etched wafers. Manufacturers of larger diameter wafers typically use an acid etch, or a combination of caustic and acid etching, to achieve a smoother surface with an acceptable geometry, which can then be improved in double-sided polish.
Intersurface Dynamics has developed a patented chemical invention that makes it possible to achieve the best of each etching process, while eliminating the environmental aspect of acid etching. Please contact Intersurface Dynamics for further information.