28nm Planar Flow

Device Context & Integration

The Deep N-Well Photo step defines the lateral geometry of the deep n-type well by selectively opening photoresist windows that will later permit high-energy n-type implantation, thereby establishing electrically isolated substrate regions required for mixed-signal, RF, and noise-sensitive devices in a 28nm planar CMOS flow [T1]. This lithography step is intentionally placed after STI formation and post-CMP surface conditioning so that the resist pattern aligns …

• [High] Overlay Misalignment to STI: If the deep n-well photo pattern is laterally misaligned relative to STI edges, the resulting pn-junction curvature becomes non-uniform, leading to localized electric-field enhancement and degraded isolation efficiency due to altered depletion region geometry [P1][A2].