7nm FinFET

Device Context and Integration Logic

The SiN hardmask deposition in the STI module is introduced immediately after pad oxide growth to create a chemically and mechanically robust masking layer that defines active regions during subsequent trench etch and isolation formation, while protecting the silicon surface from plasma and wet-chemical damage [A1].The pad oxide beneath the nitride acts as a stress-relief and interface-protection layer, while the SiN hardmask provides high etch selectivi…

• [High] Hardmask Erosion During STI Etch: Insufficient film density or incomplete Si–N network formation leads to accelerated chemical and physical erosion in fluorine-based plasma etches, reducing effective masking capability and causing critical dimension loss, consistent with the etch-resistance dependence on bonding structure described in [P1].