Analysis of P-Doped Polycrystalline Silicon Missing of W-Polycide Gate for 2X nm NAND Flash

Abstract

We studied the control-gate (CG-Poly) missing behavior after post in-situ steam generation (ISSG) re-oxidation for W-polycide gate of 2X nm NAND Flash and attempted to determine the possible mechanism. On the other hand, various effective countermeasures were also been proposed. We found that Si atoms diffuse upward on WSi2.3 films, driven out of the underlying doped polycrystalline silicon film during steam radical oxidation process based on energy dispersive X-ray (EDX) analysis. A 2.5 nm remaining of SiN at least on sidewall before oxidation results in CG-Poly missing free and WSix deformation improvement simultaneously. A selective oxidation such as water vapor generator (WVG) and rapid thermal oxidation (RTO) can achieve the same efficient performance. Additionally, less intrinsic tensile stress of WSix film employment also shows immunity against CG-Poly missing. Satisfactory sidewall barrier utilization for ISSG oxidation, diverse thermal oxidation selection, and even by WSix film property modifying might avoid poly-Si missing occurrence and reduce the WSix film deformation extent for the narrower dimension of 2X nm and beyond.