28nm Planar Flow

Device Context and Integration Logic

AA Pad Oxidation is positioned at the beginning of the AA module within the STI flow to establish a thin, high-quality silicon dioxide layer between the silicon substrate and the subsequent pad nitride film, serving as a mechanical and chemical buffer during later isolation patterning and etching steps [A1].This oxide mitigates stress transfer from the nitride hardmask into the silicon by accommodating lattice and thermal expansion mismatch, which is cri…

• [High] Excessive STI-Induced Stress Transfer: If the pad oxide does not adequately buffer nitride and trench-fill stresses, residual compressive or tensile stress can propagate into the silicon active region, modifying carrier mobility and threshold voltage via piezoresistive and deformation-potential mechanisms, leading to layout-dependent variability [P2][P4].