In a 40nm BSI CIS DBI module, the interconnect structure requires precise planarization and reliable hybrid bonding interfaces (Engineering Practice).The progression from ILD 6-5 down to 6-1 represents a sequential breakdown of a complex multi-layer stack, where ILD 6-4 specifically targets a distinct intermediate dielectric or hard mask layer within this architecture A1.By following the initial ILD 6-5 open, the ILD 6-4 etch transfers the critical dimension deeper into the interconnect stack A1