This specific Pre Litho Cleaning step occurs immediately after the deposition of the Upper Vertical Grid in the Light Shield (LS) Grid module of a 40nm BSI CIS (Engineering Practice).The Upper Vertical Grid typically consists of a Tungsten core and a TiN barrier, which will be patterned and etched in the subsequent steps (Engineering Practice).Unlike earlier Pre Litho Cleaning steps (such as steps #7 or #13) that prepare bare silicon or front-end dielectrics for patterning, this step is uniquely